tag:blogger.com,1999:blog-72742483851864710832024-03-13T19:54:42.229-07:00Chapter 1. Physiography of IndonesiaThis electronic publication is part of the Geology of Indonesia book, a modified and updated version of van Bemmelen 1949 book with the same title. This systematic approach is started in 2014, which aim to provide a new generation of this publication.Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-7274248385186471083.post-33215282629846342342014-08-09T09:35:00.002-07:002014-08-17T05:31:16.474-07:004.CIRCUM-AUSTRALIAN BELT<b>4.1.NEW GUINEA</b> (See fig. 21 on pI. 1)<br />
This is the second largest island of the world, after Greenland. It extends between 0° 19' and 10° 43' southern latitude and between 130° 45' and 150° 48' eastern longitude. The length is 2400 km 1) and the maximum width is 660 km. With the Fre&rik Hendrik Island (Kolepom) it has an area of 785,360 sq km, and, together with some small neighbouring islands, it measures 805,000 sq km. The area of the Netherlands territory is 394,000 sq km.<br />
Physiographically New Guinea can be divided into three parts:<br />
A.<span class="Apple-tab-span" style="white-space: pre;"> </span>The western peninsula or Vogelkop (Birds- head), connected by a narrow neck to the mainland (130°-135° E. long.).<br />
B.<span class="Apple-tab-span" style="white-space: pre;"> </span>The Mainland or Trunk (between 135 ° and 143~ E. long.).<br />
C.<span class="Apple-tab-span" style="white-space: pre;"> </span>The eastern part, including the tail (143t 0- 151 ° E. long.).<br />
North of New Guinea we find a part of the Pacific Ocean of about 4000 m depth bordered in the North by the Caroline Islands. Coral islands rising steeply from the Ocean floor (like Mapia, North of Manokwari), suggest that this part of the ocean represents a submerged continental block. This impression is strengthened by the occurrence of crystalline amphibole- and talc-schists in Japen (North of the Geelvink Bay) and in the Cyclops and Bougainville Mts along the North coast of New Guinea. as well as on Jap in the western and Truk in the eastern Carolines 1). This submerged continental block North of New Guinea has been considered as belonging to the borderland of "Melanesia" (the author 1933 e).<br />
To the South, the Sahul Shelf (Arafura Sea) and Strait Torres connects New Guinea with the Australian Continent.<br />
<br />
4.1.1.<span class="Apple-tab-span" style="white-space: pre;"> "BIRDHEAD" (</span>VOGELKOP in Dutch) AND "NECK"<br />
Parallel to the North coast of the Vogelkop a mountain range occurs, stretching West to East between Salawati and Manokwari. This range is divided into a northern and a southern one by a longitudinal depression. We find in this median depression the valleys and plains of Waren-Momi- Ransiki (9000 hectares). Dwons-Irai with the Anggi Lakes (3000 + 1000 hectares). Kasi-Kebar (some thousands of hectares), Warsamsom (3200 hectares) Sorong (300 hectares). described by KLEIN (1937).<br />
The northern range (III) 2) consists chiefly of neogene and quaternary volcanic rocks with the presumably active, or at any rate solfataric, Umsini volcano (FEUILLETAU DE BRUYN, 1937).<br />
Starting from the islands Batanta and Salawati in the West, it first forms a narrow low ridge along the northern margin of the Vogelkop between Sorong and Mega. Then it rises to the Tamrau Range (40 km broad, Mt Kwoka 3000 m). After an interruption by the plains of Wajori and Prafi, its east- ward continuation is found in the Arfak Mts near Manokwari (with a NW and SE trend; Umsini volcano 2.666 m). The farther extension is not clear. Possibly the trend changes (in the spur of Oransbari) into an eastward direction, and then it might be traced via the threshold of -640 m between the Geelvink Basin and the Pacific Ocean across Mios Noom and Japen. If this is correct, the Geelvink Basin (-1,627 m) might be conceived as the wide southeastern extension of the above mentioned median depression between the northern and the southern range of the Vogelkop.<br />
The southern range (IV) consists of strongly folded lower tertiary and pre-tertiary sediments. It has a more or less E-W trend (Mt Togwormeri, 2.680 m) and then curves southeastward to the Lina Mts (2,870 m). It can be traced farther south- ward in the isthmus between the Vogelkop and Bombarai, the islands Rumberpon, Mios Waar, Roon and the promontory with the Wondiwoi Mts (2,239 m). In the neck the general trend changes again to a southeast- and an eastward direction. The isthmus South of the Geelvink Bay shows an axial depression, marked by Lake J amur and the transverse valley of the Omba.<br />
The northern part of the Vogelkop is separated from the southern part (Bombarai) by the large but shallow Macc1uer Gulf. The latter has a typical submerged relief with a sedimentation which hardly can keep step with the subsidence. It is characterized by a shallow shelf carrying many islands, anastomosing gullies, and isolated hills.<br />
The Bombarai Peninsula is a promontory of the Neck of the Vogelkop. On the northwestern spur or Onin, the Fakfak Mts with typical Karst topography reach a height of 1,450 m, and on the southern spur the Kamawa Mts are 1,489 m high. These mountain ranges (VI) occupy an intermediate position between the Banda Outer Arc and the Neck of New Guinea. They possibly belong to a zone which might be traced from Misool via the Pisang Islands to the western margin of Bombarai, and from there, along the Islet of Adi and across the northeastward extension of the Aru Basin, to the Aru Islands. If so, this physiographic zone Misool-Bombarai-Aru skirts the foredeep of the Outer Banda Arc. being interrupted by an extension of the latter between Aru and Adi.<br />
<br />
4.1.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>MAINLAND OR TRUNK<br />
The main part of the island shows a number of parallel, WNW and ESE trending zones. We mentioned already the Cyclops Mts (1,950 m) and the Bougainville Mts (VII) which show a basement complex of crystalline schists. They possibly belong to the southern rim of a hypothetical, sub- merged continental block, which we might call "North Melanesia".<br />
Next follows a longitudinal zone of low land and hills, the Mamberamo-Bewani Depression, (VIlla), whith coincides partly with the northern coastal belt of the trunk. It stretches from the East coast of the Geelvink Bay along the Lakes of Rombebai and Sentani to the Finsch coast with Aitape. South of this Mamberamo-Bewari depression is a complex mountain range, called the Northern Divide Range (VIII).<br />
This Northern Divide Range (VIII) is generally described as the series of ranges and ridges between the Geelvink Bay in the West and the mouth of the Sepik River in the East. In this sense it starts in the West with the Dom, which reaches a height of 1,340 m. Eastward we first find the Van Rees Mts which are cut transversely by the Mamberamo River. Next follow the Gauttier Mts (over 1000 m high), Foja Mts, Karamoor Mts, and Bonggo Mts. South of the Cyclops Mts there is an axial depression. However, from the borderline between the Netherlands and Australian part the axis rises again to the Bewani Range (1,617 m), which joins on eastward to the Torricelli Mts and the Prince Alexander Mts (1,200 m). From Wewak the axis plunges eastward to Marienberg on the Sepik River, where the Northern Divide Range disappears beneath the alluvial plains of the lower Sepik and Ramu Rivers.<br />
Possibly there is a physiographical connection between the non-volcanic range in the Vogelkop (IV) and the Northern Divide Range of the Trunk (VIII). This connection might be traced around the southern border of the Geelvink Bay by way of the isthmus of the neck and the divide between the Waipoga and Rouffaer Rivers. If this conception is correct, it would mean a linking of the structural belt of IV + VIII with the central mountain ranges of the mainland of New Guinea in the area of the Charles Louis and Weyland Mts.<br />
On the physiographic map (fig. 21) we have pro- visionally drawn a connection between IV and VIII. This structural belt might be called the Northern Divide Range sensu largo. The Northern Divide Range sensu stricto on the mainland of New Guinea (VIII) is bordered to the South by a longitudinal median depression (IX). This depression finds its typical development in the wide basins of the Tariku or Rouffaer River and the Taritatu or Idenburg River, and that of the Sepik River.<br />
The former basin is the so-called Lake-Plain (Neth. "Meervlakte"). This name is not very ad- equate, because permanent lakes of any importance do not occur in this alluvial basin. Only isolated meanders of the large rivers in this plain, situated only 50 m above sealevel, are temporarily flooded in the rainy season. The name "Plain of the Idenburg River", proposed by W. C. KLEIN (Kol. Tijdschrift, 27, 669-675) is to be preferred.<br />
This longitudinal depression is bordered on the West by the divide between the Waipoga and the Rouffaer River. The find of pleistocene coral reefs in this area at an elevation of 500 m (see chapter II) suggest the possibillity that in lower quaternary time there was a marine connection between the Geelvink Bay and the Lake-Plain.<br />
The divide area between the Idenburg River and the Sepik River forms a threshold in this longitudinal depression. This area is still little known.<br />
The next zone is the main axis of the island, the complex system of the Central Mountain Range (X) on which are high plateaus (Wissel Lakes, Baliem Valley). In the Indonesian territory the highest part is called "Sneeuwgebergte" or Snow Mountain Range, because the highest summits reach into the climatic zone of perennial snow and ice (above 4300 m) 1).<br />
The name Snow Mountain Range might be applied to the whole complex of Central Ranges between the Neck (1350 E. long.) and the Star Mts (1400 E. long.). The Snow Mountain Range sensu largo (Xa) has a cross section of about 150 km.It starts in the West with the Charles Louis- and Weyland Mts (3,700 m), Eastward it follows the imposing Nassau Range, with the Idenburg (4,800 m) and Carstensz tops (Nggapulu 5,030 m), the latter being the highest summit of the Indian Archipelago. Further the Oranje Range, with the Wilhelmina top (4,750 m) and the Juliana top (4,700 m). Near the borderline with the Australian part we find the Star Mts (4,200 m).<br />
The highest summits of the Snow Mountain Range are situated at its southern side, forming sharp crests and fim basins.<br />
Northward the height of the ranges decreases step by step. The highest summits of these northern ranges are Mt Doorman (4,050 m) and Mt Angemuk (3,950 m). To the South, however, the Snow Mountains break off rather abruptly, forming precipitous es- carpments. The latter probably represent a system of longitudinal stepfaults, and they are locally accompanied by some young volcanic activity, (viz. in the area of Ok Biriem near the Australian border).<br />
The Leonard-Murray or Bosavi Mts (2,438 m) are situated on this fault system at the southern border of the central ranges in Papua. The young volcanic nature of Leonard-Murray Mt has been recognized from the air.<br />
Special mention deserves the course of the Baliem River. This river forms wide valleys in the mountainland between the Orange Range and the Angemuk, which are rather densiIy populated by Papuan tribes (Archbold Expedition in 1938-1939; ARCHBOLD, RAND, and BRASS, 1942). The river takes its rise north of the Wilhelmina top. It first makes a northward loop around Lake Hobbema (3,225 m), and then flows southeastward, breaking with a huge gorge through the Orange Range. It joins on to the Vriendschaps River 1), a righthand tributary of the Eilanden River. Beyond the borderline, in the Australian part, follows the Victor Emanuel Range. The width of the Central Ranges then increases to about 250 km in the cross section of Mt Champion (3,700 m) and Mt Hagen (3,812 m = 12,500 ft), containing the central plateaus of Benembi (or Benambe) and Purari (SPINKS, 1934 and 1936). Here also some young volcanic activity occurred.<br />
South of the Central Range of the Mainland extends the Digul-Fly depression (XI). This lowland plain has a width of 200-300 km. Only a small transitional zone of gently folded neogene, covered by enormous pleistocene fans of debris, separates it from the central mountain ranges.<br />
The Digul-Fly depression is still subsiding as is demonstrated by submerged woods, extensive swamps, lakes (Lake Murray), flood canals, etc. However, the extension of the swamps is not as large as was originally supposed. In literature it is often mentioned as the largest swamp of the world. This is not true, for the major part of this depression is situated well above the flood level of the rivers. The latter are often bordered along their lower courses by swampy belts. The main swamp extends between the lower courses of the Eilanden River and the Digul River, and it is bordered to the NE by the Wildeman River 2), a left hand tributary of the Eilanden River. Along the Wildeman River, and also along the Groote Moeras River ("Big Swamp River") which empties near Torpedo Islet, farther NW, extensive decayed forests were observed. The tops of the trees have fallen off and the naked stems stand amidst of the swamp vegetation. These trees belong to species which grow only on relatively dry ground and have died because of the flooding. Therefore, this area has recently subsided (ZWIERZYCKI, 1928, p. 256). This Digul-Fly depression between the Central Ranges and the Australian Continent is analogous to the Indus-Ganges depression between the Himalayan Ranges and the Indian continental block. The rim of the Australian continent (XII) is formed by a low ridge of some dozens of metres height, which can be traced from the Aru Islands by way of an ill-defined rise of the floor of the Sahul Shelf (less than 50 m deep) to the Island of Frederik Hendrik or Kolepom and the Merauke Ridge along the South coast of the Mainland. It ends in the ridge near Mabaduan (60 m) and Daru Island in the East (SPERLING, 1936). Perhaps this zone (XII) can be traced southward across Strait Torres to the Torres Peninsula of the Australian Continent. This so-called "Merauke Zone" represents the slightly warped margin of the continental frame of Australia.<br />
<br />
4.1.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>EASTERN PART, INCLUDING THE "TAIL"<br />
From 143.5o E. long. the general trendlines become NW and SE. This eastern part shows some features which differ from those of the Mainland. Several parallel zones can be distinguished: The volcanic belt off the North coast. The Ruk- or Rook Arc of SIEBERG (XIII) forms a chain of volcanic islets off the North coast. It starts North of Wewak (the eastern end of the Northern Divide Range on the Mainland) with Kairiru and continues eastward along Garnot, BlosseviIle, Lesson, Manam, Long, Lottin, Umboi or Rook, and Ritter. Its extension farther eastward is formed by the volcanoes on the northern side of New Britain.<br />
The Ranges along the Northeast coast. Along the northeastern coast of New Guinea, and opposite to this volcanic arc, we find the Adalbert, Finisterre, Hahl (3,962 m), and Rawlinson Ranges (XIVa). The two last mentioned ranges occupy the Huon Peninsula. This peninsula plunges eastward into the foredeep of New Britain. Orographically this group might be pictured as the eastern continuation of the Northern Divide Range on the Mainland (beyond the interruption by the deltas of the Sepik and the Ramu). Structurally they probably belong to the Rook-New Britain System, of whichXXXXXXBetween the NE-ranges and the central ones extends a depression zone (XV), marked by the lleys of the Ramu and the Markham. Eastward - zone passes into the Huon Gulf. The central Ranges. The Victor Emanuel Range forms a relatively narrow part of the central mountain system of New Guinea. From this range the headwaters of the Sepik flow northwestward and those of the Fly and Strickland Rivers southward. The orographic situation suggests that in this area the Snow Mountain System (Xa) finds its eastern end and that from here in a southeastward direction another complex mountain system might be distinguished (Xb).<br />
The latter has a NW -SE trend and joins on obliquely to the W-E or WNW-ESE trend of the central ranges of the mainland. In this eastern unit the highest summits no longer are at the southern side, as is the case in the Snow Mountain Range.<br />
The following ranges can be distinguished: Bismarck Range (Mt Wilhelm, 4,260 m), Kubor Mts (Mt Leahy, 4,350 m), Kratke Range, and South of Wau. These ranges join on to the central mountain range of the "Tail" of New Guinea, viz. the Owen Stanley Range (Mt Chapman, 3,470 m, Mt Edward, 4,030 m, Mt Victoria, 4,010 m). The width of the Central Range in the Tail is about 100 km.<br />
The axis of the Owen Stanley Range gradually descends and narrows in an ESE-direction, till it plunges below sealevel, forming the Louisiade Archipelago at its end.<br />
Another contrast between the central ranges of the western part of the trunk on the one side and those of the eastern part and tail of New Guinea on the other side is formed by the widespread terti ary and quaternary volcanism in the latter. The centres of volcanic activity are grouped around a central belt of plateaus and ranges, such as the Benembi-Purari Plateau in the eastern part of the trunk, and the Owen Stanley Range on the taiL It begins with Mt Hagen in the North. Along the southern side of the geanticlinal belt we find the volcanic complexes of Leonard Murray, Mt Favenc, Mt Yule, Astrolabe Range with Mt Sogeri and the Cloudy Mts, On the northern flank of the geanti- cline we can distinguish another row of volcanoes, such as Mt Lamington (1,787 m), Mt Trafalgar (1,549 m), Mt Victory (1,819 m), the Goropu Mts, Mt Dayman, The latter might be considered as a new physiographic element, viz. the volcanic zone of the d'Entrecasteaux Islands (XVI) 1). This volcanic belt runs parallel to the southeastern end of the taiL It forms the volcanic inner zone of an orogenic system while the non-volcanic outerzone, which is represented by the Tobriand Islands and Woodlark Islands, lies to the North of it (XVII).<br />
<br />
<b>4.2. THE SAHUL SHELF</b><br />
This extensive shelf-sea is the submerged platform of Australia. It forms the counterpart of the Sunda Shelf at the Asiatic side of the East Indies. Most of the islands situated on the Sahul Shelf are closely related with Australia and, therefore, they will not be treated in this book. However, the Aru Islands are an exception, because they are influenced by the youngest oro genetic processes in the Indian Archipelago.<br />
The Am Islands consist of four larger and many smaller islands (in total 85) with a total area of about 8000 sq km. The length of the group (NNE-SSW) measures 183 km and its width is 92 km. The islands emerge gradually from the shelf, which is only 20 m deep in this part. 30,km West of them, however, the seafloor drops abruptly to the 1000 m isobath and then descends rapidly into the Aru Basin, which has a depth of 3,650 m.<br />
The islands have a flat surface at some dozens of metres above sealevel (maximum 90 m), The most characteristic feature of this group is formed by the remarkably deep canal like straits, called "Sungi", separating, the islands. In Chapter V these Sungis will be discussed more in detaiL The East coast of the main islands shows a great fringing reef of 15-40 km width. At the West coast, fringing reefs are only locally present. The coast itself is partly an alluvial stretch, partly an abrasion coast.<br />
<br />
<b>4.3. CHRISTMAS ISLAND</b><br />
This island lies isolated in the eastern part of the Indian Ocean (10° 30' s.t«, 105° 40' E.long.; about 300 km from the South coast of Java; 364 m high; diameter 14t-19 krn: area 161 sq km).<br />
It has steep abrasion cliffs on all sides and forms the flat top of a submarine volcanic cone, rising steeply from a depth of 4500-5000 m.<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-P2ORpnYcK-E/U_CgMhElVMI/AAAAAAAA0f8/ZVvXrkCodgo/s1600/physiography-christmas-island-01.JPG" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-P2ORpnYcK-E/U_CgMhElVMI/AAAAAAAA0f8/ZVvXrkCodgo/s1600/physiography-christmas-island-01.JPG" height="199" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig.4.3.1. Christmas Island (source: <a href="http://www.appszoom.com/">appszoom</a>)</td></tr>
</tbody></table>
On account of its position, on an E and W trending submarine ridge, bordering the Java trough to the South, it forms a part of the structural pattern of the Indian Archipelago. Moreover, this islet and the Cocos Islands belong to a series of rises of the ocean floor which border the West Australian Basin (-6,459 m) to the Northwest. According to the author (1933 e), this rise of the ocean floor forms a part of the circum-Australian median ridge. Therefore, it is treated in this book under the heading of the circum-Australian System.<br />
<br />
<div>
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Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.com2tag:blogger.com,1999:blog-7274248385186471083.post-59075686377239442652014-08-09T09:34:00.003-07:002014-08-14T23:57:30.636-07:003.CIRCUM-SUNDA ARCHIPELAGOThe Sunda Shelf area is surrounded by a number of island groups, characterized by a very complicated relief of the sea bottom, such in contradistinction to the flat continental shelf. We will designate this garland of islands as the circum-Sunda Archi- pelago. It consists of heterogeneous elements, which will be outlined in the following pages.<br />
<br />
<b>3.1. THE SIN-COWE REEFS IN THE SOUTH CHINA SEA</b><br />
The southern part of the South China Sea belongs to the Sunda Shelf up to the connecting line between the most southern point of Cochin China and the border between Sarawak and British North Borneo. North of this line the depth increases abruptly to more than 1000 m (2000 to 4000 m), This, however, does not apply to a rather extensive platform of less than 1000 m depth, which occupies the eastern part of the South China Sea (West of Palawan). On this flat a great number of coral reefs are found, which group might be called the "Sin- Cowe Reefs" after an islet in their centre (VAN BEMMELEN, 1933 f, p. 894).<br />
Only a few soundings are available of this area, which is very dangerous for navigation. The chart by VAN RIEL (1934Y,'reproduced in the "Atlas van Tropisch Nederland" (1938, map 3), accepts a depth of the seafloor of about 1000-2000 m, from which the coral islands rise steeply to the surface. However, the interpretation given by the chart of the gravity expeditions at sea by VENING MEINESZ (1934) seems to be more probable, accepting that the mean depth of this part of the South China Sea is less than 1000 m. See the isobaths on fig. 78, plate 8.<br />
<br />
<b>3.2. THE PHILIPPINE ARCHIPELAGO</b> (See fig. 17, and fig. 18)<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-ucXKUYhFs4Q/U-u9Ud3VelI/AAAAAAAA0dU/7OOxwN7ke6o/s1600/physiography-philippines.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-ucXKUYhFs4Q/U-u9Ud3VelI/AAAAAAAA0dU/7OOxwN7ke6o/s1600/physiography-philippines.jpg" height="320" width="240" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 17. Relief map of the Philippine Archipelago</td></tr>
</tbody></table>
This group lies between 21 ° 8' and 4 ° 35' northern latitude, and between 116°55' and 124°37' eastern longitude. The total number of islands is 7,083; 466 of them have an area of more than 2 sq krn, and 2,441 have a proper .name. The rest is formed by small rocky islets emerging from the sea. FIG. 17. (Opposite to page 3.) Reproduction of the relief map of the Philippine Archipelago by. Coast- and Geodetic Survey. The total area amounts to 296,000 sq km, that is some what less than Great Britain (314,713 sq km). The principal islands with an area of more than 1000 sq km are:<br />
<br />
C.2.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>GENERAL OUTLINES<br />
The outline of this archipelago is roughly triangular with its apex in the North (Batan Islands) and its basis between Borneo and Palmas Island. It is bounded to the West by the China Basin, which attains a depth of over 5000 m, and to the East by the Philippine Basin of about 6000 m depth. The East coast of Samar and Mindanao is skirted by the narrow furrow of the Philippine Deep, which is the deepest trough of the world (the Emden Deep, -10,830 m).<br />
Broadly speaking the foundation structure of the Philippines is a raised part of the ocean floor, which begins South of Formosa (Taiwan), gradually rising and broadening via the Batan and Babuyan Islands to northern Luzon. The distance between the southernmost point of Taiwan and the northernmost island of the Philippines is only 145 km.<br />
South of the line from the Lingayen Gulf to Dingalan Bay, the framework of the Archipelago becomes suddenly much wider ramifying into a number of branches, which connect it with the Indonesian Archipelago.<br />
The island festoon of Lubang-Mindoro-Cala- mian-Palawan-Balabac joins on to the Kinabalu Range of North Borneo; the submarine Sulu ridge, which forms the pedestal of several islands, links the Zamboanga Peninsula of Mindanao with the Northeast peninsula of Borneo; finally, the Sangihe and Talaud ridges form the connecting links, respectively with Sulawesi and the Northern Moluccas. These ridges are separated by two large basins, the Sulu Basin (-5,580 m) and the Sulawesi Basin (-6,220 m).<br />
Where these ridges branch off from the Philippines the framework is broken into a number of blocks, separated by smaller basins, straits, isthmian narrowings or structural valleys. The islands are not always individual blocks; they are in places connected by submerged platforms, such as the Visayan Shelf in the Central Philippines.<br />
It is as if the top part of the great Philippine undation, where it becomes broader, breaks down into a number of blocks, until it is finally engulfed into the deep intervening basins of Sulu and Sulawesi.<br />
Analysing the Philippine framework more in detail these very characteristic and important physiographical trendlines will become apparent.<br />
<br />
3.2.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>LUZON<br />
Northern Luzon measures about 300 km from S to N and about 200 km from E to W. Within this area occur several structural units, namely a complex mountain range in the western part, the Cagayan Valley in the centre and the cordillera skirting the East coast.<br />
The western mountain complex can be divided into three ranges, viz. the Malaya Range, the Central Range and the Polis Range (respectively ± 1800 m, 1800-2400 m, and .1500-2100 m high). The highest summit is Mt Pulog (2,930 m) in the Central Range. The Cagayan Valley, drained by the Cagayan River (ca 300 km long), is a structural downwarp between the western and eastern cordilleras. The Polis Range gently slopes eastward, whilst the eastern cordillera is a block or strip which is highest along the East coast and slopes westward to this median downwarp. In the northern part of this Cagayan trough lies the young-quaternary Cagua volcano (1,159 m), which belongs to a volcanic zone which can be traced northward to the volcanoes of the eastern Babuyan and the Batan Islands.<br />
The Cagayan Valley rises gradually southward to the mountains of Adams or "Central Knot", which constitutes the southeastern part of the northern peninsula of Luzon. Here the transition to the plain of Central Luzon is affected by a steep morphological flexure, trending NW-SE. BAILY WILLIS (1937, p. 20) remarks that the profile of this southern termination of North Luzon is not one of an eroded fault scarp, but the one of a flexure. The summits of the mountains carry remnants of the tertiary mature land and the front has the same topographical character, though the surface bends down towards the plain. Only in the eastern section, from Dingalan Bay on the East coast to Bongabon, there is a distinct fault. Elsewhere, from Rizal to Damortis on the Lingayen Gulf, the front is a steep bend. The character of the mountain front is best explained by assuming that the bulging up of the mountains of northern Luzon and the subsidence of the Central plain are still in progress.<br />
South of this Lingayen-Dingalan flexure, the basement foundation of the Philippines widens considerably, increasing from ± 200 km to more than 500 km.<br />
Central Luzon. The western cordilleras of Central Luzon or Zambales Range are displaced some dozens of kolimetres to the West with respect to those of Northern Luzon 1). The Zambales Range is a tilted block with a high eastern edge and a more gradual westward slope. The eastern descent is probably a faultscarp. Its southern section is capped by a series of quaternary volcanoes, the youngest of which is the Mariveles volcano on the Bataan Peninsula.<br />
The Central Plain, extending from the Lingayen Gulf to Manila Bay, is a subsiding block, covered by more than 300 m of shallow water and alluvial delta deposits, as is attested by the logs of artesian wells (FAUSTINO, 1931).<br />
From this Central Plain rise several, deeply eroded, plio-pleistocene volcanoes, such as the Cabarnan Hills, Mt Balungao, Mt Amorong and Mt Bancay in its northern part, and the conspicuous Mt Arayat in its centre.<br />
The Central Plain is the southern continuation of the median Cagayan downwarp, though wider and more deeply depressed than the latter. It is bounded to the East by the eastern cordilleras. At the transition from the plain to the eastern mountains ALVIR (1929) mapped some longitudinal and transverse faults, which are partly very young, e.g. those bordering the Mariquina graben. Movements along these faults caused probably the destructive earth- quake of June 3, 1863.<br />
The eastern Coast Range stretches along the eastern side of the Central Plain for nearly 200 krn, extending from Laur, NE of Cabanatuan, to the head of the Bondoc Peninsula. It is from 40 to 50 km in width and has the cross section of a flat, dissected arch. On both sides the marginal slopes are steep rather than gentle, but the eastern is the steeper one and is most abrupt where it descends into the sea. The drainage pattern is that of rivers which grew upon a plain or mature land at relatively low altitude and were captured by vigorous, consequent streams as a result of uplift and uparching of the terrain (BAILEY WILLIS, 1937, p. 23-24).<br />
The median depression of Central Luzon extends utheastward from Manila Bay to Tayabas Bay. The intervening stretch is occupied by the southeastern volcanic district, with the active Taal volcano in the caldera of Lake Bombon, and the Gonzales, Maquiling, Malaraya, and Banahao volcanoes.<br />
This volcanic district is separated from the Eastern Cordilleras by the great lake of Laguna de Bay, which is perhaps a former extension of Manila Bay, separated from it by a slight arching up of the pleistocene tuff layers (Guadalupe Formation). This can-be clearly observed near Fort William Mc Kinley at the Pasig, which river maintained an antecedent course, draining the lake towards Manila Bay.<br />
The main physiographic trendlines of North and Central Luzon are the flariks of the Luzon undation, formed by the zones of the Eastern and Western Cordilleras, and its top part, occupied by a median depression (Cagayan Valley-Central Plain). This central depression zone will be called "Manila Zone". Besides being a young downwarp on the top of the undation, it is characterized by young volcanic activity.<br />
It will appear from the following analysis that the zones of the eastern and western cordilleras can be traced south- and southwestward to North Borneo, whilst the intervening Manila Zone ends in the Sulu trough.<br />
SE-Luzon or Camerines Peninsula represents a new structural element, separated from the Eastern Cordilleras by the Strait of Polillo and Ragay Gulf and attached to the main land by a narrow isthmian lirik. This southeastern peninsula of Luzon forms part of the eastern Philippine rim.<br />
Camerines Norte and Camerines Sur are connected with Polillo Island and Catanduanes Island by' a submerged platform, called the Polillo Shelf, which has a gradual slope into the oceanic depths. Along the inner, or southwestern side of this block another depression zone is found, separating it from the zone of the Eastern Cordilleras of the Luzon undation. This intervening depression might be called "Ragay Zone". Like the Manila Zone, it is characterized by young volcanic activity, such as Mt Labo in Camerines Norte and the NW-SE row of volcanoes: Isarog, Iriga, Malinao, Mayon, Pocdol, and Bulusan on the Bicol Peninsula.<br />
The Ragay Zone, or "Philippine Fault Zone" as it was called by BAILEY WILLIS (1937, p. 38-40), extends from the Ragay Gulf past Ticao Island, through the Island of Leyte, and into the intermontane depressions of Mindanao. It ends in the Sulawesi Basin as well as in the narrow trough between the Sangihe and Taland Islands. The Ragay Zone is bounded on the West by the Zone of the Eastern Cordilleras of the Luzon Arc and on the East by the "Samar-Diuata Zone", which forms the eastern rim of the Philippines. Thus we see that the main structural belts of the Philippine framework can already be distinguished in the island of Luzon. They belong either to the Luzon Arc, which is convex to the East, extending from Taiwan to Borneo, or to the Samar Arc along its eastern side, extending between Polillo Island in the North to Palmas (or Miangas) Island in the South.<br />
<br />
3.2.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>LUZON ARC<br />
The elements of the Luzon Arc can be traced from this island to North Borneo.<br />
The Zone of the Western Cordilleras, forming its West flank, passes via the Lubang Islands and Mindoro to the platform carrying the Calamian Islands, Cuyo Islands, Palawan and Balabac. The trend of the Zambales Range is NNW -SSE, whilst the Palawan block has a NNE-SSW direction. Mindoro forms the pivot of this change of direction. North and South of this island deep tranverse, trough- like channels are found, viz. the Verde Passage and the Mindoro Strait. These troughs occur at the bending points of the general trendlines, interrupting the physiographic connections. However, the geological analysis of the Philippine structure in chapter V makes it probable that Mindoro forms a link in the zone of Western Cordilleras.<br />
Mindoro is a high point in the structural arc. It is a great tilted block, the crest of which extends in a direction N 20° W from Mt Patrick to Mt Wood. From this crest line there is a long slope to the SW -coast and a short, steep slope toward the NE. At the base of the latter is a longitudinal valley in which the Aglubang and Rosanna rivers flow respectively NW and SE. It is, according to BAILEY WILLIS (1937, p. 29), obviously a structural feature and presumably a fault valley. In southern Mindoro an almost East-and-West trending fault was observed by ALVIR (1926), which marks the breakdown of this block to the Mindoro Strait. In rock character, in physiographical aspects, and in structural tilt this mountain bloc resembles the northern part of the Zambales Range. The northern part of Mindoro consists largely of volcanic flows from the Mt Halcon (2,587 m), Mt Calavite, and intermediate vents. These are all extinct, being presumably of plio-pleistocene age, and they might be considered as the continuation of the volcanic Mariveles chain along the inner side of the Zambales Range. This zone of extinct volcanoes can be traced to the Cuyo Islands situated on the eastern edge of the Palawan platform, which consists also of basalts and andesites.<br />
A younger, probably subrecent row of submarine volcanoes is found, according to BAILEY WILLIS (1937, p. 8), between CagayanSulu and the Cagayanes Islands, but this belongs to the young volcanic activity of the Manila Zone, to be discussed here after. However, it is possible that this Cagayan belt of volcanism, forming the southwestward extension of the volcanic belt of Mariveles-Halcon-Calavite- Cuyo, has structurally the same meaning as the latter. It is probably related with the fault system along the eastern and southeastern edge of the zone of Western Cordilleras, along which the latter broke down to the Manila Zone.<br />
The older formations and plutonic rocks of the basement complex occur in the western part of the zone of Western Cordilleras formed by the Zambales Range, Lubang Islands, Central and West Mindoro, Calamian, Palawan, and Balabac.<br />
Whilst the Zambales-Mindoro section rises from the more than 4000 m deep floor of the South China Sea, the Palawan platform is skirted by a rather narrow trench with a maximum depth of -2,890 m, which separates it from the platform of the Sin Cowe Reefs, discussed in a preceding paragraph.<br />
The Manila Zone of Luzon has been traced already to Tayabas Bay. Here the central part of the Philippines is reached with the Sibuyan Sea and the Visayan Sea. In this area the cross section of the Manila Zone increases from 75-100 km to 250- 300 km, whilst it assumes a much more complicated appearance. Instead of being a simple structural downwarp, it ramifies into a number of irregular channels and basins separated by raised blocks or partly submerged platforms. Between Mindoro and the Bondoc Peninsula of Luzon we find the Island of Marinduque, an elevated block, with a south- ward tilt. South of this island the Manila Zone splits into three or four branches.<br />
A western branch of the Manila depression runs in a southern direction, from Tayabas Bay along the channel between Mindoro and the Tablas Islands, and West of Panay, ending in the Sulu Basin. It is generally over 1000 m in depth and has a width of about 50 km. Next comes a relatively elevated, sinuous ridge, on which are the islands of Sibuyan and Tablas and the western range of Panay.<br />
The following branch of the Manila-depression zone comprises the basins of the Sibuyan Sea. The one between Sibuyan Island and Bondoc Peninsula is more than 2000 m deep and the other, extending between Sibuyan Island and Panay, has a depth of over 1000 m. This branch extends across the central plain of Panay, which is a rather simple, structural downwarp, filled by thousands of metres of miocene and younger sediments, comparable with the Cayan Valley in North Luzon. This branch of the Manila Zone also ends via the Panay Gulf in the Sulu Basin. East of it extends the Visayan platform, which carries the islands of Masbate, eastern Panay, Guimaras, Bantayan Islands and Negros.<br />
Negros consists of two distinct parts. The northern part is formed by elevated tertiary sediments, capped by a young volcanic range with the cones of Silay, Mandalagan, and Canlaon (2,465 m), The southern part of the island is formed by two volcanoes: Mt Malapantao and Mt Magaso or Cuernos de Negros (1,903 m). These cones stand on the edge of the Visayan block, where it breaks down into the Sulu trough.<br />
Masbate consists also of two distinct parts, viz. a NW-SE cordillera, at the northern end of which are found the NW -SE trending gold veins of the Aroroy district, and a NE-SW spur, pointing to eastern Panay. It is possible that only the latter belongs to the Visayan block in a stricter sense, whilst the NW-SE cordillera curves southward into the NNE-SSW trending narrow crustal slice of Cebu.<br />
Cebu is separated from the Visayan block (viz. Negros) by a very narrow trench of more than 500 m depth. The southern end of this graben is filled by the volcanic cone of the Cuernos de Negros, which masks its transition into the Sulu Basin.<br />
The easternmost branch of the Manila Zone follows the narrow channel between the Islands of Burias and Ticao on the NE and Masbate on the SW -side, then curves southward into the passage between Leyte and the northern part of Cebu, where it attains a depth of over 1000 m. It curves farther into a SSW-direction between Bohol and southern Cebu, passes along the young volcanic island of Siquijor, and ends, like the other branches of the Manila Zone, in the large Sulu trough.<br />
It appears that the Manila Zone has a very sinuous course. In northern Luzon it is slightly convex to the East, whilst in Central Luzon it is convex to the SW. It then forms a great bulge to the East, considerably wider and rarified into four branches, separated by relatively high block-slices. Finally, it assumes a SW-direction in the Sulu Basin, where the entire belt has been engulfed to considerable depth. Especially the southeastern part of this basin is a remarkable trough, 200-250 km broad and more than 500 km long, with steep sub- marine walls. This trough is deepest (more than 5000 m) at its NE side near Negros and Zamboanga. From there the floor shoals to about 3000 m at its southwestern end, where it rises again steeply towards the Bornean Shelf.<br />
The Sulu trough is bordered to the SE by the Zamboanga-Pangutarang ridge and to the NW by the Cagayan Sulu-Cagayan ridge, which carries probably some submarine volcanoes. The four branches of the Manila Zone all end in this trough.<br />
The NW part of the basin, between the Cagayan ridge and Palawan is probably not a separate trough. but its floor can be considered as the more or less gradual slope of the Palawan platform towards the edge of the Cagayan ridge, where it plunges down a depth of 2000 m to 4000 metres. Therefore, this NW part of the Sulu Basin might still be reckoned with the zone of Western Cordilleras, which forms the West flank of the Luzon Arc.<br />
The Zone of the Eastern Cordilleras forms the East flank of the Luzon Arc. The structural connections in the inner part of the Philippine Archipelago are difficult to unravel. The geological analysis indicates as a probable solution that the zone of the Eastern Cordilleras extends from the Bondoc Peninsula of Luzon along Burias and Ticao, and the eastern edge of Masbate to the northeastern peninsula of Leyte. It then curves south and south- westward via the Camotes Islands to Bohol.<br />
Between Bohol and Zamboanga it is interrupted by the Mindanao Sea of more than 1500 m depth, but it reappears in the NW-SE trending block of Zamboanga. The latter is connected by way of the Sulu Archipelago with the Darvel Bay area of North Borneo. The Sulu Archipelago consists of two parallel ridges; one stretching from Zamboanga to the peninsula North of Darvel Bay and carrying the coral reef islands of the Pangutarang group; the other extending from the Sibuguey Peninsula via Basilan, Jolo, Tawitawi to the peninsula South of Darvel Bay. The latter has a young volcanic nature and belongs to the young volcanic belts of the Ragay-Zone, to be discussed later. The shoals of both ridges are separated by an intervening, narrow depression of nearly 600 m depth. This double ridge is a repetition of the situation found at the NW side of the Sulu Trough. There, the Cagayan ridge forms a volcanic belt parallel with the non-volcanic Palawan ridge, in the same way as here the Jolo ridge is a volcanic belt parallel with the non-volcanic Pangutarang ridge. The Cagayan Sulu volcanoes stand on the edge of the Sulu Trough, and the Tawitawi-Basilan row of volcanoes is built upon the steep and straight slope which bounds the great Sulawesi Basin at its NW side. Both volcanic belts are probably related with fault zones along the en- gulfed blocks which form the floor of these basins. The only difference is that the distance between the Palawan ridge and the NW-side of the Sulu Trough is 150-200 km, whilst the two parallel ridges at the NW side of the Sulawesi Basin lie closely together.<br />
<br />
3.2.4.<span class="Apple-tab-span" style="white-space: pre;"> </span>SAMAR ARC<br />
East of the Luzon undation, outlined in the preceding paragraphs, a new element is welded to the framework of the Philippine Archipelago, causing a widening of its basement structure. We will call this element the Samar Arc. It is separated from the Luzon Arc by a depression zone, called "Ragay Zone".<br />
The Ragay Zone begins in Strait Polillo, crosses the isthmus of the Camerines Peninsula to the Ragay Gulf. BAILEY WILLIS (1937, p. 39) writes about this isthmian link as follows:<br />
"At the head of the Ragay Gulf, between the Bondoc Peninsula and Camerines Norte there is a strip about 16 kilometres wide that is cut from NW to SE apparently by several vertical faults. One skirts the NE coast of Caluag Bay; another defines the NE coast of Alabati Island; a third is inferred in Lopez Bay. All three extend across the isthmian strip to Ragay Gulf, as is indicated by river valleys, and reappear in the sharp-cut fault coast of that depression" .<br />
It extends farther southeastward along the NE- sides of Burias and Ticao to the Samar Sea and forms the sound between Biliran and Leyte at the head of Leyte Bay. Along the northeastern margin of this Ragay Zone, young quaternary volcanoes are found, which has been mentioned already in the description of SE-Luzon (Mayon volcano, etc.). This row extends southeastward into the young volcanic and solfataric Biliran Island and the central volcanic cordillera of Leyte with the Amandiung and Cabalian (see description by MUSPER & NEUMANN VAN PADANG, 1937; p. 76-77).<br />
In southern Leyte the Ragay Zone curves southward and becomes much wider in cross-section. Here begins a splitting up into several branches, divided by elevated blocks, like the ramification of the Manila Zone South of Tayabas Bay.<br />
A western branch skirts the Zone of Eastern Cordilleras between southern Leyte and Bohol, forming the western part of the Mindanao Sea between Camiguin and Siquyor and then narrows down into the Panguil Bay of Mindanao. It then crosses the isthmus of the Zamboanga Peninsula and ends in the Illana Bay, which is an extension of the Sulawesi Basin, having a depth of more than 2000 m. The northern portion of this branch is bordered on the East by the SW Peninsula of Leyte, and its southern portion by the raised blocks of Bukidnon and Lanao in Mindanao.<br />
The middle branch starts from the Mindanao Sea East of Camiguin and passes southward along the structural valleys of the Tagoloan and upper Pulangi to the wide, triangular basin of the Pulangi, Here it bifurcates into a western branch, ending in the Illana Bay near Cotabato, and a southeastern one, ending in Sarangani Bay. Thus both branches end also in the Sulawesi Basin. The intervening stretch is occupied by the elevated block of the Tiruray plateau, which rises as a horst between the Pulangi Basin and the Sulawesi Trough. It is concave to the NW and presents a convex front to the adjoining Sulawesi Basin (-6,220 m).<br />
This Pulangi Basin is a former sea arm, as is attested by widely distributed raised coral-reefs. It is skirted by two ranges of young quaternary volcanoes.<br />
The northwestern one is convex to the SE. It begins with the Catarman volcano on Camiguin Island. The eastern margin of the Bukidnon plateau is little known, but IcKES gave a topographical sketch of the divide area between the Tagoloan and the Pulangi rivers (reproduced by SMITH, 1924, p. 209) on the western side of which is distinguished the Katunlund, an extinct volcano of an estimated elevation of 6000-7000 feet. South of it follows the also problematical "Calayo" volcano (MUSPER & NEUMANN VAN PADANG, 1937, p. 80-81; MUSPER, 1939, p. 42-43). Here the volcano zone assumes definitely a westward trend across the active Ragay volcano and the extinct Makaturing Cone. This volcanic belt stands on the edge of the Bukidnon and Lanao plateaux, where they break down to the Pulangi trough.<br />
The other volcanic belt forms the eastern margin of this trough, with the cones of the Apo, Magolo, and Matutum (MUSPER & NEUMANN VAN PADANG, 1937, p. 81-82).<br />
This belt extends by way of the Sarangani Bay to the Balut on the Sarangani Islands, being linked by a submarine ridge to the active volcanoes of the Sangihe Islands and those of the Minahasa in North Sulawesi.<br />
The median Pulangi branch of the Ragay Zone is seperated by .a N-S range from the eastern branch. The latter is a structural downwarp, be- ginning in the deep trench East of the SW-penin- sula of Leyte; it passes along the eastern margin of the Mindanao Sea and then joins on to the NNW- SSE trending, structural valley of the Agusan River, where it traverses a low dividing ridge into the Tagum Valley, finally ending via the Davao Gulf into the Sangihe Trough.<br />
The group of raised blocks and intervening depressions in Central Mindanao bears a close resemblance in topography and geology to the group of islands in the Central Philippines which comprises Panay, Negros, Cebu, and some smaller islands. Both occupy a widened part of a median depression zone, respectively the Manila Zone and the Ragay Zone. Both consist of raised blocks alternating with intervening graben structures. Both are the site of young volcanic activity. And finally, both break down at their SE-side into basins of 5000-6000 m depth (respectively the Sulu- and the Sulawesi Basin).<br />
In lower-quaternary time Central Mindanao was still a group of islands separated by straits, and the sea regressed only in late quaternary time owing to a general uplift of this area.<br />
The Samar-Diuata Zone. The eastern units of the Philippine Archipelago, namely Camerines, Samar and the Diuata Range of East Mindanao, form an arc which is bordered by the Philippine Deep. The waters between them are generally shallow, considerably less than 200 metres deep as a rule. It descends abruptly from the marginal ranges, about 500-1000 m in height, into the adjoining trench, which is 8000-10000 m deep. This Samar-Diuata Zone forms a long and narrow platform with a sligthly convex face toward the East, and concave along the inner side. Its total length is 1.200 km, extending from Polillo Island, North of the Camerines, to the southern tip of Mindanao 1). Its width is rarely more than 75 km.<br />
This elevated eastern flank of the Samar Arc consists of two portions. The northern one is the Polillo block whichhas a WNW-ESE trend. Its elevated edge lies at its southern side, in Camerines Norte and Sur and Catanduanes, whilst its northern flank gradually slopes down to the ocean floor of more than 5000 m depth. The Philippine Deep terminates off its eastern side.<br />
The southern part or Samar-Diuata Zone (sensu stricto) is an almost straight block, extending from the northern margin of Samar to the southern point of the Eastern Cordilleras of Mindanao. The WNW- ESE trend of the Polillo block abruptly changes into the NNW -SSE trend of the Samar block. This change of direction occurs East of the Bicol Pen- insula, where Batan and some other small islands are found. Here the outer arc has been largely engulfed, so that a deep branch of the Philippine Deep penetrates into the Lagonoy Gulf. Such transverse trenches occur also in the zone of the Western Cordilleras, where its general direction changes from N-S to NE-SW, viz. the Verde Passage and the Strait of Mindoro, at both sides of Mindoro.<br />
The inner boundary of the Samar-Diuata block is a zone of faulting, along which the downwarp of the Ragay Zone has occurred. The Southwest coast of Samar Island is an obvious fault of vertical attitude, extending between and beyond Calbayog and Catbalogan. It strikes about NW-SE. The valley of the Ulut River trends NE from Maqueda Bay as a structural valley under a NW facing scarp from near Catbalogan to the NE coast, according to BAILEY WILLIS (1937, p. 36). This transverse fault through Samar meets the above mentioned fault along the SW coast approximately at a right angle.<br />
South of Samar the platform of the eastern rim is submerged for a distance, except for the Islands of Dinagat and Siargao. Continuing southward the platform rises and becomes the eastern mountain range of Mindanao, a composite upland. Its northeastern section, known as the Diuata Range, is the extension of the range of Dinagat Island. It is a tilted and deeply dissected tableland, with a crest near the W -side presenting a steep slope towards the West and descending with a longer, gentler grade to the drowned East coast.<br />
Lake Mainit is a depression in the western slope; it is probably a fault-trough and not a volcanic centre, according to MUSPER and NEUMANN VAN PADANG (1937, p. 79). The inner boundary of this block is an almost straight fault zone with a NNW-SSE trend, whilst the outer boundary is formed by a drowned coastline, as though it has been submerged by a tilt towards the adjoining Philippine Deep.<br />
At the southern end of the eastern cordilleras of Mindanao a long and narrow block can be distinguished which extends along the East coast of the Davao Gulf, being separated from the main block of the Eastern Cordilleras by a narrow structural valley. This block might be interpreted as a slice, which broke off from the main block. It continues southward via a narrow submarine ridge, carrying Palmas (or Miangas) Island, into the non-volcanic Talaud Ridge of the Northern Moluccas.<br />
<br />
3.2.5.<span class="Apple-tab-span" style="white-space: pre;"> </span>SUMMARY OF THE MAIN STRUCTURAL TRENDLINES<br />
The foregoing analysis shows that the seemingly chaotic distribution of the Philippine Islands can be grouped according to some general structural trend- lines. The basement structure of this group of islands consists of two crustal waves, the Luzon Arc, extending from Taiwan tot Borneo, and the Samar Arc, extending from Camerines to Sulawesi. The latter arc represents a branch of the former, splitting off in SE Luzon. The Luzon Arc consists of two distinct portions. The northern one extends from Taiwan to the transverse flexure of Lingayen- Dingalan, and the southern one from this line to North Borneo.<br />
The frame work of the Philippines is thus formed by both flanks of the Luzon Arc (viz. the zones of the Western- and Eastern Cordilleras) and a median downwarp on its top, called "Manila Zone". This Luzon Arc is separated from the Samar Arc by another zone of partial engulfment, called "Ragay Zone".<br />
The Manila Zone ends in the Sulu Trough and the Ragay Zone in the Sulawesi Basin. The ridges connecting the Luzon- and Samar Arcs with the Indonesian Archipelago are double ridges, consisting of a volcanic- and a non-volcanic belt.<br />
These are: 1) The non-volcanic Palawan ridge and the volcanic Cagayan Sulu ridge between the Sulu Trough and the South China Sea; 2) the non- volcanic Pangutarang ridge and the volcanic Jolo ridge 1) between the Sulu- and the Sulawesi Troughs, and finally 3) the non-volcanic Palmas-Talaud ridge and the volcanic Sarangani-Sangihe-Minahasa ridge between the Sulawesi Basin and the Philippine Deep.<br />
Thus the Philippines represent an instance of the transition of a single arc with volcanic activity on its crest (namely the northern part of the Luzon Arc), into systems of double-arcs, the outer ones being non-volcanic, whilst the inner ones have a volcanic nature.<br />
The volcanoes stand on the edges of deep basins, formed by the engulfment of the top parts of crustal waves.<br />
<br />
3.2.6.<span class="Apple-tab-span" style="white-space: pre;"> </span>ACTUAL SHORE LINES<br />
The outlines of the Philippine Archipelago are the result of considerable vertical movements, which continued up to the present time. The present appearance of the islands appears to be chiefly the result of tectonical movements, which blockfaulted and warped the crust, though the eustatic movements of the sealevel in glacial and post-glacial times too have largely influenced the actual shore lines.<br />
Extensive peneplains formed during and before the pleistocene glaciations, submerged after the melting of the ice caps. These submerged platforms now form the shelf-seas of Polillo, Palawan, Visa- yan, Leyte-Samar-East Mindanao, and Zamboango- Sulu, which are about 50 metres deep, according to FAUSTINO (1926).<br />
This eustatic rise of the sealevel caused the formation of barrier-reefs, atolls (in the Sulu Archipelago), and coral shoals.<br />
FAUSTINO (1931) somewhat modified the definition for coral-shoals or drowned coral reefs, given by NIERMEYER. According to FAUSTINO they do not rise above sealevel, they are surrounded by water and they are not connected with neighbouring reefs. The coral-shoals of the Philippines are situated on the above mentioned platforms.<br />
The eustatic rise of the sea level is also responsible for the drowned and deeply indented coastlines, in so far as these are not the result of tectonic subsidence and tilting of crustal blocks. Besides these relative subsidences there are also numerous indications for late quaternary uplift. FAUSTINO (1926 b) mentions the following instances:<br />
In the Batan group, North of Luzon, FERGUSON reported in Sabtan Island on its western side, at an elevation of about 7 metres, a raised beach, while on its eastern side the shore rises towards the centra of the island in a rather irregular series of marine terraces. The highest terrace occurs at an elevation of about 180 metres. At its southern end there is in Batan a series of terraces reaching a maximum elevation of about 275 m.<br />
In general, the whole western coast of Luzon is a shore line of emergence. Along the western coast of Ilocos Sur, Ilocos Norte, and La Union Province there are two or three well marked marine terraces, attaining an elevation of 75 to 90 metres in the coastal region South of the town of Vigan. On the peninsula which forms the western side of Lingayen Gulf there is found a well developed system of marine terraces. Along the western coast of Zambales, ridges of coralline limestone to an elevation of at least 100 metres are known. On the southern coast of Batangas at Malbrigo Point, fairly broadstepped terraces in regular succession rise to an elevation of 180 metres.<br />
Extensive marine terraces are found on Panay, Negros and Masbate. In the latter island the higher terraces attain an approximate elevation of about 200 metres. Along the northern coast of Mindanao several benches to a maximum elevation of 360 metres have been observed.<br />
MOODY suggested (in the Philippine J. of Sci., 25, 1924, 22) that the present island of Mindanao was divided into five islands in early pleistocene time and that successive uplifts were in the main responsible for the joining together of these islands and the formation of a much larger island area.<br />
These young nsmg movements of the islands have been certainly accompanied by subsidences of the crust in the intervening channels and basins. The combination of these vertical movements of the crust and the eustatic oscillations of the sea level have resulted in the formation of the present configuration of the archipelago.<br />
<br />
<b>3.3. SULAWESI</b> (See fig. 182)<br />
This island has an area of about 172,000 sq km, and together with surrounding islands it measures about 188,000 sq km, being the third in area of the Larger Sunda Islands. But for some narrow stretches of coastal lowland and intermontane plains, Sulawesi in entirely occupied by mountainland, being one of the most mountainous of the larger islands of the archipelago.<br />
Its typical outline, like a huge K, has long drawn the attention of geographers and geologists. The island consists of four narrow branches or arms, separated by deep gulfs and uniting in a central trunk. This outline has some resemblance to Halmaheira. The distribution of volcanic rocks of the Pacific suite in the western and northern parts of both islands, whilst basic and ultra-basic ophiolites are widely distributed in their eastern parts, causes also some geological analogy. Nevertheless, the geological analysis of both units in chapter V will show that this similarity is largely accidental, their orogenic evolution being entirely different.<br />
Sulawesi is surrounded by deep basins and troughs. Sulawesi and Borneo are separated by the Makassar Trough, which is about 2000-2500 m deep (max. depth 2,717 m). Between Sulawesi and the Philippine Islands we find the Sulawesi Basin, about 5000-5500 m deep (max. depth 6,220 m). Between North Sulawesi and the northern Moluccas extends the Moluccan Sea, which has depths up to more than 4000 m. Between South Sulawesi and the southern Moluccas stretches the North Banda Basin, about 4500-5500 m deep (max. depth 5,750 m). Finally, between South Sulawesi and the Lesser Sunda Islands we find the western part of the South Banda Basin (about -4,500 m) and the Flores Deep (max. -5,140 m). On the other hand the mountain ranges of Sulawesi reach altitudes of over 3000 m (max. Mt Rantemario in the Latimodjong Range with a height of 3,440 m).<br />
This shows that there is at present a considerable crustal relief in the Sulawesi area. with differences of altitude in adjoining areas amounting to 7000- 8000 m. In this respect the Sulawesi area shows some analogy to the Philippine Archipelago. Sulawesi is connected with the latter by the island festoon of Sangihe-Wawio-Sarangani.<br />
In the chapter on the geological evolution it will be shown that indeed the Sulawesi Oro gene can be considered as the southern end of the East-Asiatic island festoons, namely of the Samar Arc of the Philippines. Only in the southern parts of the South- and Southeast arms of Sulawesi occurs a convergence with elements of the Sunda Mountain System.<br />
<br />
3.3.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>NORTH ARM<br />
The North arm of Sulawesi has a sinuous outline. The eastern end, with a NE-SW trend, is the highly volcanic Minahasa area. This part joins on to the volcanic Sangihe Ridge which connects Sulawesi with Mindanao. The rise of the submarine Sangihe Ridge towards the Minahasa is probably accompanied by transverse faults, one along the Northeast coast. one from the Manado Bay to Kema (with the hotsprings of Airmadidi). and one from the Amurang Bay to Belang. The latter NW-SE fault forms the boundary between the young volcanic Minahasa area and the Gorontalo section of the North arm. Between this fault and the Ongkag Dumora River the main trend curves from NE-SW to E- W. In this transitional section still some isolated young volcanoes and solfataric action are found (Mt Lolombulan, Ambang Mts). The central part of the North arm has an East- to-West direction. Here the volcanism is entirely extinct. The width of this central or Gorontalo Section of the North arm ranges from 35 km in the middle to 110 km at its western end, where it is also highest (Mt Maling, 2.707 m).<br />
It then suddenly narrows down to 30 km between the Dondo Bay at the North coast and Tinombo at the South coast. Here the general trend sweeps round from E-W via NE-SW to N-S.<br />
The narrow isthmian stretch between Tinombo and Parigi is called the "Neck" of the North arm. This neck is about 20-40 km wide. It culminates in Mt Ogoamas (2,565 m) at its northern end, and in Mt Sidole (2,199 m) at its southern end.<br />
The Gorontalo section is traversed by a longitudinal median depression. This stretches between the mountain ranges of the North coast (U-Mountains with Mt Tentolomatinan, 2,207 m; T-Mountains, 1,960 m), and those of the South coast (W- Mountains, Dapi Mts, Southern Mts East of Gorontalo, culminating in Mt Nunuka, 1, 606 m).<br />
The median depression is formed by the valleys of the Paguat River, Randangan River, Pagujaman River, Lake Limboto, Bone River, Ongkag Dumoga River. We will call this longitudinal depression the "Limboto Zone".<br />
The Limboto Zone can also be traced into the Minahasa, where its presence is indicated by Lake Tondano at the West foot of the Lembean Range. However, if such a median depression is present in the Minahasa, it is largely masked by young volcanic cones.<br />
The North arm is separated from the East arm by the Gulf of Tomini or Gorontalo, which is about 100 km wide at its eastern end, broadening to 200 km in the West between Tomini and Poso. This gulf is a western extension of the Gorontalo Trough, which lies in front of the transitional part of the North arm between the Minahasa and the Gorontalo section (max. depth -4,180 m). The seafloor gradually shoals westward in the Gulf of Gorontalo, being less than 2000 m deep in its western part.<br />
Between this broad western part of the Gulf of Gorontalo and the Gorontalo Trough in the East a median submarine ridge is found, which carries the Togian or Schildpad Islands. This ridge is at present subsiding; atols and barrier reefs are being formed on its top (UMBGROVE, 1939).<br />
The higher central hills of these islands are presumably extinct volcanoes. Offside the Togian Ridge lies the active Una-Una volcano, rising steeply from the seafloor at -2000 m to about 500 m above sealevel.<br />
The Togian Ridge branches off from the Bualemo Peninsula of the East arm of Sulawesi, being separated from the latter by the Gulf of Poh.<br />
<br />
3.3.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>EAST ARM<br />
The East arm of Sulawesi has a ENE- WSW trend. Three parts can be distinguished. The Bualemo Peninsula at its eastern end (with the Balantak Mts 1,590 m) is separated from the central part by the isthmian narrowing between the Gulf of Poh and the Besama Bay. The central part of the East arm gradually increases in width from about 20 km in the East to 80 km in North Bunku. The central axis is formed by the Batui Mts with Mt Bulutumpu (2,400 m), which traverses this part diagonally with a NE-SW trend. The western part of the East arm stretches between the line Cape Api - Kolokolo Bay in the East and the line Lemoro - Tomori Bay in the West. Its width ranges from 75 to 100 km. It is a highly mountainous area. The highest summit lies in the Tokala Mts near the South coast (2,628); Mt Lumut in the North reaches an altitude of 2,280 m. This mountain-land is dissected by the complicated drainage system of the Bongka River, which rises on the Tokala Mts and empties near Bongka at the NE coast.<br />
<br />
3.3.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>BANGGAI ARCHWELAGO<br />
The Banggai Archipelago lies off the eastern part of the East arm, being separated from it by the Strait of Peleng (-920 m, 15-30 km wide). The largest island of this group is Peleng. Geologically this group belongs to a more stable crustal belt which extends eastward via the Sula Islands to the SW-part of the Vogelkop of New Guinea, forming a barrier between the Northern- and Southern Moluccas.<br />
<br />
3.3.4.<span class="Apple-tab-span" style="white-space: pre;"> </span>SOUTHEAST ARM<br />
The Southeast arm of Sulawesi is about 100 km wide between the Usu Bay and the Tomori Bay. This isthmus forms the connection with the central trunk of the island.<br />
In the Southeast arm also three parts can be distinguished. The northern part is situated between the Bight of Palopo (northern end of the Gulf of Bone) and the Gulf of Tolo or Tomaiki. It is occupied by the large peridotite massif of the Verbeek Mts (with Mt Salura, 1,102 m, as highest point). In its centre two graben are found, Lake Matano (surface 382 m above sea, depth 590 m) and Lake Towuti (surface 293 m above sealevel, depth 203 m).<br />
The central part of the Southeast arm is much wider (max. 170 km). In its western part the crystalline schists of the Mekongga or Mengkoka Range rise to an altitude of 2,790 m, whilst in its eastern part peridotites and mesozoic sediments are found. The boundary between both areas is formed by the Tangeasinua Range which has a NW-SE direction. It is highest at its NW-end (Mt Tangkeleboke, 1,782 m) and its axis gradually plunges southeastward to Kendari. The wide basin between this range and the Mekongga Range is drained by the Konaweha River, which flows through an extensive alluvial plain in its lower course, before it empties North of Kendari. The East coast of the central section is formed by another low, NW-SE trending, southeastward plunging range. This belt gradually submerges, forming a number of bights and islets. It can be traced farther southeastward in the submarine relief via the Salabangka Islands to Manui Island. The basin between the Tangeasinua Range and the eastern coast range is drained by the Lasolo River.<br />
The southern part of the Southeast arm is separated from the central part by an East-to-West depression, extending between Kendari and Kolaka and occupied by alluvial swampy plains. The southern section is occupied by an irregular hilly mountainland with more East-to- West trendlines, less than 1000 m high (Mt Mendoke, 981 m).<br />
<br />
3.3.5.<span class="Apple-tab-span" style="white-space: pre;"> </span>BUTON ARCHIPELAGO AND TUKANG BESI ISLANDS<br />
The Southeast arm of Sulawesi crumbles at its end >'into a number of islands, forming the Buton Archipelago.<br />
Buton (or Butung), Muna, Kabaena and Wowoni are the larger islands of this group. They are .separated from the Southeast arm by narrow straits.<br />
The islands form a rising anticlinorium, concave to the NW. The truncated neogene folds are locally capped by a carapace of pleistocene coral. reefs, which rise, for example, in South Buton WIth 14 terraces to an altitude of 703 m above the present sealevel (Mt Kontu).<br />
From this Buton Archipelago submerged crustal blocks radiate in eastern, southeastern, southern, and southwestern directions. From Wowoni a submarine ridge plunges eastward to the floor of the North Banda Basin. Then follows a deep of 5,100 m. Next come the block-slices of the Tukang Besi group, which point from central Buton to the SE. The physiography of this interesting island group has been discussed by ESCHER, MOLENGRAAFF, RUITEN, HET ZEL and KUENEN. We will postpone its treatment to Chapter V.<br />
The Buton trough stretches parallel with the Tukang Besi blocks, separating them from a more or less triangular block, carrying Hagedis Island (Batuata) and Kabia Island. The latter block has its apex off the southernmost point of Buton ann 1tS base s\61:ts tne western enu 0\ \ne 'i)O\l\'n Banda Basin. This area has a depth of about 2000 m. In Batuata raised young coral reefs occur to an altitude of 193 m above sealevel. From South- west Buton several ridges plunge southwestward via the small islands Kadatuang and Siumpa towards the Bone trough.<br />
The orogenic meaning of this peculiar radial arrangement of crustal slices (some of which are rising in the present time, whilst the intervening blocks are engulfed to depths of thousands of metres) will be discussed in Chapter V.<br />
<br />
3.3.6.<span class="Apple-tab-span" style="white-space: pre;"> </span>SOUTH ARM<br />
The South arm of Sulawesi is connected to the trunk along a NE-SW line from Palopo to the Gulf of Mandar. However, from a geological point of view, the southwestern part of the trunk with the Quarles Mts can better be discussed in relation with the South arm. So we consider the northern part of the South arm as the area comprised between the SE-NW line from Palopo to the mouth of the Karama River at the West coast of the trunk on the one side, and the Tempe depression on the other side. The latter extends along the SE-NW line from the mouth of the Tjenrana River via Lake Tempe to the mouth of the Sadang River.<br />
This northern part of the South arm is one of the most mountainous areas of Sulawesi.<br />
The promontory between Madjene and Mamuuju shows S-to-N trending ridges of tertiary strata WIth a capping of raised coral reefs near. Madjene. It is further more characterized by leucite-bearing volcanic rocks (Cape William). Farthher East, the granite massif of the Quarles Mts rises to an altitude of 3,107 m. The eastern part of the Quarles Mts, with Mt Kalando (2,963 m), consists largely of tertiary volcanic rocks of andesitic comp~sit~on, invaded by intrusions of diorites afold gran?dlOntes. The Karua massif (over 2,500 m high) at Its southeastern side is a centre of eruption of large dacito- liparitic tuff-flows which fill the valleys, being in their turn incised by deep canyons. The Quarles Mts are separated from the Latimodjong ~ange by the Sadang Valley. Large righthand tnbutanes from the Quarles Mts are the Masupu and the Mamaso.<br />
Between the Sadang Valley and the Gulf of Bone, the N-to-S trending Latimodjong Range rises to altitudes of over 3000 m (Mt Rante-Mario, 3,440 m; Mt Latimodjong ± 3,300 m).<br />
The northern part of the South arm is separated from its southern part by a notable NW-SE depress- ion. This depression has been a sea-strait until late in the geological history, as is attested by the presence cl young clays with recent marine shells around lake Tempe. The surface of this lake is situated 9 m above sea level and its depth is only 2 m. Northeast of it is Lake Sidenreng and North of it the small Crocodile Lake. These lakes are drained by the Tjenrana River.<br />
The southern part of the South arm of Sulawesi has a much smaller average elevation than the northern part. There can be distinguished a Western and an Eastern Divide Range with the intervening valley of the WaIanae River.<br />
The Western Divide Range rises to altitudes of over 1000 m (Peak of Maros ± 1,377 m, Tonrong Krambu + 1,660 m, Bulu Laposo ± 1,270 m), The Eastern Divide Range or Bone Range is only about 800 m high.<br />
Both ranges unite in the South in the Bontorilni Mts (± 800 m) with Mt BohongLangieng (;1: 1,973 m). The latter is a young-tertiary volcanic boss. This southern mountain complex, from which the WaIanae River flows northward, is dominated by the large volcanic cone of the Lompobatang or Peak of Bonthain (2,871 m), which still has a recognizable crater rim.<br />
Off the Makassar coast lies the Spermonde shelf with numerous coral reefs, and off the Watampone coast we find another shelf with coral reefs. These shelf -seas finally break down to the Makassar Trough in the West and the Bone Trough in the East.<br />
The belt of the Western Divide Range can be traced southwest and westward along the Postiljon and 'paternoster coral reefs to the Maria Reigersbergen reefs. The belt of the Eastern Divide or Bone Range extends southward and then eastward via Salajar (or Salayer), to Tanah Djampea and Kalao. Between these two diverging belts the Flores Basin is intercalated and has a triangular outline. It is over 5000 m deep at its base, formed by the E-to- W . trending Flores Deep. Northward it shoals to its apex, which lies at the South coast of the South arm of Sulawesi. The WaIanae Depression in the Southarm is presumably a northern extension of the Flores Basin, being separated from it by the capping massif of the Lompobatang volcano. In Chapter V the tectonic meaning of these physio- graphic trendlines will be discussed.<br />
<br />
3.3.7.<span class="Apple-tab-span" style="white-space: pre;"> </span>CENTRAL SULAWESI<br />
The four branches of Sulawesi unite in the central trunk. The central part has a wedgelike shape with its base at the West coast and pointing to the Tomori Bay and the Gulf of Tolo in the East.<br />
It is bounded to the NE by a NW -SE line from Dongala via Parigi and Lemoro to the Tomori Bay, which separates it from the North and East arm. To the SE it is limited by a SW-NE line from Madjene via Palopo to Dongi at the Tomori Bay. This line separated the trunk from the South and Southeast arms. We have pointed out already that the southwestern part of Central Sulawesi (with the Quarles Mts) might be considered as a part of the South arm.<br />
BROUWER (1930, 1934, 1941) distinguishes three structural belts with a N-to-S direction:<br />
1.<span class="Apple-tab-span" style="white-space: pre;"> </span>The western belt, which might be called "Palu Zone", lies between the West coast and BROUWER'S "Median line". The latter is a structural boundary extending from Masamba in the South to Malakosa at the Gulf of Tomini, along the West side of the Tawaelia depression or graben.<br />
2.<span class="Apple-tab-span" style="white-space: pre;"> </span>The central belt, which will be called "Poso Zone" in this discussion, stretches between the median line and a N to-S line from Lemoro at the Bight of Poso, via Peleru, to the Verbeek Mts of the Southeast arm.<br />
3.<span class="Apple-tab-span" style="white-space: pre;"> </span>The eastern belt is bounded by the lines Lemoro- Peleru, Lemoro-Tomori Bay, and the Verbeek Mts. This third area we will call the "Kolonodale Zone", after the place of this name at the Tomori Fay.<br />
In connection with the tectonical analysis in chapter V a slightly different grouping is preferred. From West to East the following physiographic units may be distinguished:<br />
1a. The western coastal belt and foothills of the Molengraaff Mts, consisting of folded tertiary strata (Mamudju - Doda embayment.)<br />
1b. The Molengraaff Range, which runs from Dongala in a SSE-direction to Masamba (highest summits Mt Waukara 3,122 m, Mt Kasenturu 2,855 m, Mt Kambuno 2,950 m).<br />
1c, The "Fossa Sarasina", a narrow graben along the East side of the Molengraaff Range, extending from the Palu Bay in the North in a SSE-direction to the intermontane plain of Leboni, where it meets the Median Line.<br />
1d. The X-Mountains with Mt Nokilalaki (3,311 m) between the Fossa Sarasina and the Median Line. North of Parigi these mountains join on to the neck of the North arm.<br />
2a. The Tawaelia depression or graben with the median fault along its western side, running N-S from Malakosa to Masamba.<br />
2b. The Fennema Range between the Tawaelia depression and the Poso depression.<br />
2c. The Poso depression, which is concave to the East, formed by the valley of the Poso River, Lake Poso (surface 510 m above sea, depth at least 440 m) and the valley of the Kodina River. The Takolekadju Mts (1,637 m) are a relatively high part of this structural depression.<br />
2d. The Kruyt Mts and the Wanaripalu Mts, East of the Poso depression, 1300-1400 m high. 2e. The Pompangeo Range, a structural culmination (Mt Kajoga 2,563 m) between Lemoro and Majumba.<br />
3a. The East foot of the Pompangeo Range is formed by a complex belt in which rocks of the Poso Zone (2) and the Kolonodale Zone (3) are tectonically mixed. This "Peleru subzone" extends between Lemoro and Peleru.<br />
3b. The Era depression, extending from the plain of Malino southward along the valley of the Ban River to Era, and from there to Kolaka (in Central Sulawesi). It is characterized by extensive outcrops of mesozoic sediments.<br />
3c. The hilly upland between the Era depression and the Tomori Bay, which comprises the Peleru- and Towi Mts, consisting largely of mesozoic sediments, and the peridotite and serpentine belt of the Makaleke- and Tiu Rivers to Mandowe.<br />
3d. The depression, separating the trunk from the East arm, formed by the valley of the Sumara River and the Tomori Bay.<br />
These structural elements can be grouped into larger units in the following way:<br />
<br />
<b>3.4. HALMAHERA AND BANDA ARC (MOLUCCAS or MALUKU)</b><br />
The name Moluccas was first used by the Portuguese for the Spice Islands between Sulawesi and New Guinea. To these islands belong Halmaheira, Ternate, Tidore, Obi, Sula, Ceram, Buru, Ambon, and Banda. The name will be used in this book in a wider sense, comprising the whole complex of island-groups and -festoons, bordered by the Philippines in the North, New Guinea in the East, Australia in the Southeast, the Lesser Sunda Islands in the Southwest and Sulawesi in the West.<br />
It is an area of considerable relief with alternating basins and ridges, in which the process of mountain-building is very active at present. The Northern Moluccas are partly connected with the East-Asiatic island festoons and partly with the Melanesian System, whilst the Southern Moluccas (or Banda Arcs) form a section of the Sunda Mountain System. As dividing barrier between the Northern and the Southern Moluccas we may consider the E-and-W trending ridge, which extends from the East arm of Sulawesi to the Vogelkop of New Guinea via the Banggai Archipelago, the Sula Islands, Gomumu (South of Obi) and Misool. The connection between the Sula Ridge and Misool is less pronounced. The axis plunges East of Mangola to the circa 2000 m deep threshold in the Strait of Lifamatola, which separates the Mangole Basin and the Buru Basin. It then rises again in a WoE trending ridge South of Obi major, which carries the Island of Gomumu. This narrow submarine ridge extends farther eastward, forming a barrier between the small basin South of Tobalai 1) (-2,080 m) and the eastern part of the Buru Basin. Finally it rises to the western edge of the shelf sea of New Guinea which carries the Island of Misool.<br />
In the physiographic description of New Guinea it will be pointed out that Misool occupies the western end of a ridge which skirts the foredeep of the Banda Arcs and then curves eastward into the Merauke Ridge. This threshold between the Northern and the Southern Moluccas forms in geo- tectonic sense the dividing barrier between the oro- genic systems around the western Pacific, and the Sunda Mountain System, which belongs to the Tethys geosyncline.<br />
Therefore, we will discuss separately the trendlines of the Northern- and Southern Moluccas.<br />
<br />
3.4.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>NORTHERN MOLUCCAS (See {jg. 19)<br />
The Northern Moluccas form the connecting link between the Philippines in the North, New Guinea in the East and Sulawesi in the West. They are composed of a complex of submarine ridges and platforms carrying island-festoons and island-groups, separated by comparatively small basins and troughs. The latter are generally 2000-4000 metres in depth, and the mean level of this area may be roughly estimated at -1,500 m. The Northern Moluccas have approximately a triangular outline. The comers of the triangle are connected with more extensive land areas (viz. Mindanao, New Guinea, and Sulawesi).<br />
Its sides are skirted by deep troughs, respectively, the Philippine Deep of 6000-9000 m depth along its NE-side, the Ceram Sea (-5,319 m) and the north- western Banda Basin (-5,800 m) along its southern side. and the Sulawesi Basin (-6.220 m) along its NW-side.<br />
It thus appears that the Northern Moluccas form a strongly warped part of the crust which stands on theaverage some thousands of metres above the surrounding downwarps.<br />
We will now consider the physiographic trendlines of this area more in detail.<br />
The submarine ridge. connecting the southern- most point of Mindanao with the Minahasa (North- arm of Sulawesi) carries the volcanic Sarangani Islands (belonging to the Philippines). the Kawio Islands (a number of small coral reefs), and the volcanic Sangihe Islands. It is, therefore, a volcanic island-festoon, called the Sangihe Ridge, which connects the volcanic Ragay Zone with the volcanic North arm of Sulawesi. Next comes a depressed belt, extending from the Davao Gulf of Mindanao southward via the Sangihe Trough (-3,800 m) and via a narrow trench of 2500-3000 m depth to the Gorontalo Basin (-4,180 m).<br />
The latter bends westward into the Gulf of Tomini, which separated the North- and the North- east arm of Sulawesi.<br />
The following unit is again a crustal upwarp, which has a rather complicated relief. The Samar- Diuata Zone of the Philippine Islands, forming the eastern cordilleras of Mindanao, plunges southward into the Sangihe Trough and disappears as a physiographic unit at about 5t 0 N, latitude. It is, however, connected by a narrow ridge, carrying Palmas or Miangas Island, with the platform of the Talaud and Nanusa Islands. This ridge forms a threshold between the Philippine Deep and the Sangihe Trough.<br />
The Samar-Diuata belt has a position "en echelon" with respect to the Talaud-Maju belt, outlined here under.<br />
The Talaud platform joins on to a 75 km broad crustal upwarp, which extends southward in the bottom configuration of the Moluccan Sea. This upwarp might be called the Maju Ridge, after the islet of Maju in its centre. It is composed of several parallel ridges, giving it the appearance of an anticlinorium.<br />
There are two axial depressions in it, one South of the Talaud Islands (between the Sangihe and the Morotai Basins), and the other near its southern end (between the Gorontalo and the Batjan Basins). The axial culmination lies in its middle part, between Manado and Ternate. The section through the Maju Ridge at this place is composed of the following units, from West to East: First the marginal trench, over 2500 m in depth, then a ridge of about 1200 metres below sealevel; this is separated by a trench of more than 2000 m depth from two interchanging ridges which carry the islets Maju or Mojau and Tifore or Tofure; next a trench, over 2500 m in depth, paralleled to the East by a sub- marine ridge of about 1500 m depth; finally, the sea floor plunges down to the Ternate Trough, which reaches a depth of 3200 m halfway between Maju and Ternate.<br />
These ridges plunge southward to an axial depression, which is more than 2000 m in depth. Southward the sea floor rises again to a culmination, little over 1500 m in depth.<br />
The Maju Ridge is terminated at its southern end by the E-W trending Mangole Basin (-3.510 m), which separates it from the Sula barrier. An indistinct threshold between the Mangole Basin and the Gorontalo Basin runs southwestward connecting the Maju Ridge with the East arm of Sulawesi. Another submarine threshold, between the Mangole Basin and the Batjan Basin, connects this ridge with the Obi group.<br />
The Snellius Ridge forms a problematical part of the Talaud-Maju Ridge. It is a crustal upwarp along the southern end of the Philippine Deep (-8,710 m), rising to 360 m below sealevel. The SneIIius Ridge is separated from the Talaud Islands by the Talaud Trough (3,410 m), and from Morotai and the northern peninsula of Halmaheira by the Morotai Basin (-3,890 m), This submarine SneIIius Ridge extends northwestward from the northern end of Morotai and disappears as a distinct feature of the seafloor off the Nanusa Islands.<br />
It looks like the reflected image of a similar rise of the sea floor, skirting this part of the Philippine Deep along its eastern side. As such it is a feature related with this Deep; the edges of the bordering crustal parts appear to be slightly turned up. The central culmination of the SneIIius Ridge is connected by a ridge of more than 2000 m depth with the Talaud-Maju Ridge. This connecting link is a distinct threshold between the Talaud and the Morotai Troughs. The central cuhnination of the SneIIius Ridge might, therefore, be considered also as a branch of the Talaud-Maju Ridge.<br />
The complex rise of the floor of the Moluccan Sea is bordered along its eastern side by a down- warp, extending from the Morotai Basin (-3,890 m), by way of the Ternate Trough (-3,450 m) to the Batjan Basin (-4,810 m). An eastward branch of the latter, 1000-2000 m in depth, separates Batjan from Obi.<br />
Next comes again a relatively high portion of the crust, carrying Halmaheira and the neighbouring is- lands. This northeastern part of the Moluccas, lying between the Moluccan Sea and the Carolinan Basin and joining on to the Vogelkop of New Guinea, will be called the Halmaheira group of islands. In its central part we find the Halmaheira Sea (-2,039 m).<br />
Halmaheira is the largest island of the Moluccas (about 18.000 sq km). The form of this island resembles that of Sulawesi, but on a reduced scale. Its diameters are about one third of those of Sulawesi and its surface is about one tenth. Like Sulawesi it has fplJr arms, forming a capital K. The interjacent bays are the Kau Bay, the Buli Bay, and the Weda Bay.<br />
The Kau Bay ends in a peculiar circular depression. some 500 m deep and 60 by 30 km in diameter. It is separated from the open sea by a broad threshold which exceeds nowhere 50 m in depth.<br />
Morotai, off the northern peninsula, is largely composed of neogene volcanic rocks. Active volcanoes are found on the northern peninsula of Halmaheira. The highest cone is the Gamkonora 0,653 m), which is also the highest summit of Halmaheira. The most active volcano is at present the Dukono 0,335 m) near Tobelo.<br />
This young volcanic chain is continued in the islets of the West coast of the main island: Hiri, Ternate, Tidore, Mare, Moti, Makian.<br />
Makian is the southernmost volcano of this belt which has had eruptions in historical time. But young volcanic rocks are also known in the zone which curves eastward via Batjan to Kofiau (Kajoa, GuraItji Islands, Waidoba, Taneti, Latalata, Kasiruta, Mendioli, Batjan, Woka, Salo Islands, with Djoronga, Kekik, Lawin, Pisang, Kofiau).<br />
This volcanic zone seems to extend farther east- ward via northern Salawati to the mountain range along the North coast of the Vogelkop, in which also young neogene and quaternary volcanic rocks are found (Tamrau Range and Arfak Range with Umsini volcano).<br />
Thus we see that the Halmaheira group is bordered at its western and southern side by a belt which contains young neogene-quaternary volcanic rocks. It is strongly convex to the West and South. Active volcanoes are only found in its middle part, from Tobelo to Makian. We will call this volcanic belt the Temate Zone.<br />
The Ternate Zone is separated from the inner part of the Halmaheira group by a discontinuous, depressed zone, consisting of the following elements: Kau Bay-Kau depression; Pajahe Bay; Patientie or<br />
Patinti Strait (-2.048 m); the strait between the southernmost point of Halmaheira and Damar; the southern end of the Halmaheira Basin (1300-1400 m deep); the strait between Jef Doif and Kofiau, ending either in the Sagewin Strait between Batanta and Salawati or in the Dampier Strait between Batanta and Waigeo.<br />
The islands of the central part of the Halmaheira group consist largely of a basement complex of basic and ultrabasic rocks, covered by marine tertiary strata, rich in detritus of igneous rocks. It is bordered to the Northeast by the southern end of the Philippine Deep, whilst it is limited to the West and South by the Ternate Zone.<br />
The largest land-units of the inner part of the Halmaheira group are the arms of Halmaheira East and South of the Kau cauldron, and further the islands of Gebe, Waigeo, and Batanta. The islands between Halmaheira and the Vogelkop of New Guinea are called the Radja Ampat group. Salawati belongs also to this group, but physiographically it forms a part of theVogelkop area, being situated, like Misool, on the Vogelkop Shelf, and separated from Batanta by the narrow (4 km wide), trough-like Sagewin Strait (over 200 m deep). This strait is presumably a young graben, comparable with a similar graben farther East, on the NW edge of the Vogelkop, which is occupied by the Valley of the Warsamson.<br />
The small Aju- and Asia Islands form a spur of the Halmaheira group which extends into the Carolinan Basin.<br />
The centre of the Halmaheira group is a broad downwarp, viz. the Halmaheira Basin, which reaches a depth of more than 2000 m. General structural picture of the Northern Moluccas.<br />
After this analysis of the physiographical trend- lines in the Northern Moluccas we will unite them again in a general picture.<br />
The Northern Moluccas are formed by two converging systems of ridges, one bordering the Sulawesi Basin, being convex to the East. and the other skirting the central part of the Halmaheira group, being convex to the West. We will call them respectively the Sangihe System and the Ternate System. The Sangihe System is composed of the following units:<br />
a.<span class="Apple-tab-span" style="white-space: pre;"> </span>Backdeep: Sulawesi Basin;<br />
b.<span class="Apple-tab-span" style="white-space: pre;"> </span>Volcanic inner arc: Sangihe Ridge;<br />
c.<span class="Apple-tab-span" style="white-space: pre;"> </span>Interdeep: Sangihe-Gorontalo Troughs;<br />
d.<span class="Apple-tab-span" style="white-space: pre;"> </span>Non-volcanic outer arc: Talaud-Maju Ridge.<br />
This system forms the connecting link between the Samar arc in the Philippines and the North and East arms of Sulawesi.<br />
The Temate System consists of the following elements:<br />
a.<span class="Apple-tab-span" style="white-space: pre;"> </span>Backdeep: general part of the Halmaheira group. only partially engulfed (Halmaheira Basin);<br />
b.<span class="Apple-tab-span" style="white-space: pre;"> </span>Volcanic inner arc: Ternate Zone;<br />
c.<span class="Apple-tab-span" style="white-space: pre;"> </span>Interdeep: Morotai-Ternate-Batjan Troughs;<br />
d.<span class="Apple-tab-span" style="white-space: pre;"> </span>Non-volcanic outer arc: Snellius-Maju-Obi Ridge.<br />
It appears that in the Maju Ridge of the Central Moluccan Sea both systems coincide, having a mutual outer arc. This is a fact of geotectonic importance. which will be amply dicussed in Chapter V.<br />
<br />
3.4.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>SOUTHERN MOLUCCAS OR BANDA ARCS (See fig. 20)<br />
The Central Banda Basin is skirted by two parallel arcs; the inner one is crowned by active volcanoes. Where as the outer one is free of young volcanism. This Banda area clearly represents a coherent. orogenic system. which has often been considered as an example of a mountain system in statu nascendi. 1) (See Chapter V B).<br />
The Banda Basin consists of a northern and a southern part. The first or"Northem Banda Basin" lies between Sulawesi and Buru, the second or "Southern Banda Basin" between Batu Tara (North of Lomblen) in the West and Manuk in the East. (See also the physiographic sketchmap of the Northern Banda Basin. fig. 187.)<br />
The Southern Banda Basin. in its turn. is divided (by the Api volcano) into a western and an eastern section. The latter is surrounded by the Banda Arcs and might be called "Central Banda Basin". We will start the physiographical description of the Southern Moluccas from this centre.<br />
The Central Banda Basin has a diameter of 400 km between Damar and Buru (SE-NW) and also between Api and Banda (SW-NE).<br />
In the northern part of the Central Banda Basin some complicated SW-NE swells are found. The Luymes and Siboga Ridges do not reach the sea- level; only some coral reefs of the Lucipara- and Schildpad Islands emerge. Between the Luymes Ridge and Buru a depth of 5.330 m is attained; the floor of its southern part is about 5000 m deep. with a maximum of -5,400 m West of Damar.<br />
In the western part of the Southern Banda Basin (see fig. 187) the Api Volcano (282 m) rises from a flat floor of about 4500 m depth. This western deep-sea platform ramifies west- and north- westward into a number of trenches. The main one parallels the inner arc from Alor westward. across a rise of -2,480 m North of Flores. to the Flores Deep (-5.130 m). The next branch curves. steadily decreasing in depth. into the Gulf of Bone between the South and Southeast arm of Sulawesi. A smaller one leads (across a rise to -3.850 m) to the Buton Trough (-4.180 m). Finally, a number of ill-defined. NW -SE trenches across the rise between the Tukang Besi Islands and the Luymes Ridge connect the western part of the Southern Banda Basin with the northern one.<br />
The Northern Banda Basin. like the central part has a diameter of about 400 km. Its maximum depth is -5.800 m.<br />
The Central Banda Basin is bordered on its southern. eastern and northern sides by the Banda Inner Arc. This arc consists of a number of ridges. which have an "en echelon" orientation according to the maps of the Snellius Expedition ").<br />
In the Southwest this inner arc is not the direct continuation of the inner row of the Lesser Sunda Islands. The axis of the latter geanticlinal elevation of the crust plunges from Wetar via Romang east- ward to the submarine ridge between Damar and Moa, finally ending in the Weber Deep. The volcanic inner arc of the Banda System has an "en echelon" position with respect to this belt. First comes the SW-NE trending Damar Ridge. crowned by the volcanoes of Damar (868 m), Teon (655 m), Nila (781 m), and Serua (641 m). This ridge plunges northward, and separated from it by a trench of more than 3000 m deep we find the S-N trending Manuk Ridge (Manuk, 285 m). The latter is separated in turn from the Banda Dome (Api, 656 m) by a depth of more than 4000 m. A southeastern spur of the Banda group plunges down into the Weber Trough. while a northwestern one curves westward. ending South of the Uliassers and Ambon. Thus we see that the inner arc consists of some ridges and dome-like culminations which have an "en echelon" arrangement. This interchanging position occurs in that part of the geanticline, where its general trend shows an intensive curvature; from an East-to-West trend in the inner arc of the Lesser Sunda Islands it sweeps round to the NE and N. and finally back to the NW and W. In Ambon the direction becomes even ENE to WSW. extending (by way of the submerged volcano(?) in the Manipa Basin) to Amblau.<br />
Between the Banda Inner- and Outer Arc an "interdeep" occurs, with a typical crescentic out- line bulging eastward, called Weber Deep (-7,440 m, max. width 150 km). It shoals northwestward finally passing into the rising axis of the ridge which carries the Uliassers and Ambon; and it becomes also shallower in a SW direction, joining on to the submarine ridge between Damar and Moa. The Weber Deep is separated from the Wetar Basin by this threshold of 1,480 m depth. The island of Kisar farther West is one of the very few islands occupying an intermediate position between the inner- and outer arc.<br />
The Banda Outer Arc is a geanticlinal uplift of the crust, 100-200 km broad, in which geosyn- clinal deposits have been elevated into mountain ranges with overthrust structures, but without active volcanism (such in contrast to the young volcanic composition of the islands of the inner arc).<br />
In Ceram the mean elevation above the fore- deep is about 5000 m and that above the inter- deep amounts to about 6500 m. In the eastern or Kai section these differences of mean altitude are respectively 4500 m and 7500 m. This is in rather close accordance with the elevation of the Ceram sector, notwithstanding the fact that the latter shows a mountain range up to 3000 m height, while the Kai group reaches only 800 m above sealevel.<br />
The southern section of the Banda Outer Arc forms the continuation of the outer arc of the Lesser Sunda Islands. It begins East of Timor with the narrow Leti-Sermata Ridge. Then follows the Babar culmination from which low spurs radiate in several directions. The northeastern one plunges down into the Weber Trough and the southwestern one into the Timor foredeep; some smaller ones point to the Wand NW, while a broad rise of the seafloor unites the Babar Dome with the Tanimbar group. The general trend of the latter is SW and NE, whereas that between Leti and Sermata is more Wand E. This curvature is marked by an "en echelon" arrangement of the ridges, which also characterizes the inner arc.<br />
The eastern sector of the Banda arcs comprises the Tanimbar-Kai (or Ewab) Islands. It has a steep inner slope to the Weber Trough. The width of the geanticline is 100 km in the Tanimbar group and increases to 200 km in the Kai Islands, narrowing again to 75 km in the SE-NW stretching submarine ridge which forms the link with Ceram. On the whole this eastern sector shows an eastward bulge like the crescentic Weber Deep. This broadening is accentuated by the presence of a rise of the seafloor (less than 1000 m deep) in the Aru foredeep, East of the Kai Group. .<br />
Along the crest of this broad geanticline a longitudinal depression occurs, the width of which increases with the cross section of the geanticlinal arch. In the Tanimbar Group the median depression measures some dozens of kilometres across, widening to about 100 km in the Kai Group (between the "Drie Gebroeders" and Nuhutjut), then narrowing again to the Masiwang-Bobot graben of East Ceram. The eastern section of the outer arc is divided into an inner and an outer zone by this belt of relative subsidence on its crest. The inner zone runs from Wuliaru (188 m) along Molu (274 m) to the "Drie Gebroeders" and Kur (423 m), and farther across Tiur or Tioor (376 m), Kasiui (362 m), Watubela, Manawoke, Pulu Pandjang, and Ceram Laut with Geser, to the southeastern spur of Ceram. This garland of islets skirts the interdeep along its eastern side. The outer zone can be traced from Selaru via Jamdena and Sofiani to Nuhutjut or Great Kai. Its connection with Northeast Ceram is less clear, because here this outer festoon is interrupted by a westward extension of the foredeep (viz. Aru Trough).<br />
The northern section of the Banda Outer Arc comprises the islands Ceram, Boano, Kellang, Manipa, and Buru.<br />
Seram is the largest island of the Banda Outer Arc (17,152 sq km, that is more than half of the size of the Netherlands; 340 km long, about 70 km broad; highest summit Binaja 3,055 m). The median depression of the Banda Outer Arc is represented by the Masiwang-Bobot Graben in East Ceram, which can probably be traced westward along the series of depressions: Teluti Bay - Kawa Valley - Ruatan Valley - EIQa- putih Bay - Tala Valley. The inner festoon of the eastern section continues in Ceram across the low mountains South of the Masiwang - Bobot Graben (723 m), the Y-Mountain-range, and the Z- or Wallace Range (1,260 m). The outer garland is representend in Ceram by the ESE to WNW trending X- Mountains (Binaja 3,055 m) and the ENE to WSW trending Lumute Mts 1,373 m).<br />
West of the Piru Bay the structural pattern of Ceram becomes more irregular. The Hoamoal Peninsula is bordered by more or less N-S directed faults.<br />
The islands of Boano, Kellang (Kelang) and Manipa form a NE-SW row between Ceram and Buru. On the southern tip of Hoamoal and on Kellang young volcanic rocks, like those of Ambon, are found. Most geographers and geologists trace the western end of this northern section of the Banda Outer Arc from Ceram via the islets of Kellang and Manipa to the large islands of Buru.<br />
Buru (9,599 sq km; 140 km long and 90 km broad; highest summit Kau Palatmada, 2,429 m).<br />
The physiographic structure of Buru is less clear than that of Ceram. Three mountain blocks can be distinguished, separated by structural valleys. The western massif with the Kau Palatmada is over 2000 m high. It is bordered to the East by the NNE-SSW depression of Nibe River - Lake Rana - Wala River. The central block rises to about 1000 m, being situated between the above mentioned structural valley and an ENE-WSW depression formed by the Kajeli Bay and the Apu Valley. The southeastern block is formed by the Walua Range, which has an ENE-WSW trend, reaching an altitude of 1,731 m in Mt Batakbual. This range is separated from the row of Manipa, Kelang and Boano by the northern part of the Manipa Basin.<br />
Buru forms a domelike elevation of the crust, which is surrounded by four compensative basins:<br />
a.<span class="Apple-tab-span" style="white-space: pre;"> </span>the Manipa Basin, Southeast of Buru, 4,360 m deep, with a cone shaped elevation in its centre, presumably a submerged or submarine volcano;<br />
b.<span class="Apple-tab-span" style="white-space: pre;"> </span>a basin between Buru and the Luymes Ridge, -5,330 m;<br />
c.<span class="Apple-tab-span" style="white-space: pre;"> </span>the northern Banda Basin, reaching a depth of 5,290 m West of Buru;<br />
d.<span class="Apple-tab-span" style="white-space: pre;"> </span>the Buru Basin, North of this island, with a maximum depth of 5,319 m.<br />
The northwestern corner of the island is connected by a distinct, though locally more than 3000 m deep, submarine ridge with Sanana of the Sula Islands. The southwestern corner is connected with the. Luymes Ridge by a more than 3000 m deep rise of the sea floor.<br />
Foredeep of the Banda Arcs. The Banda Outer Arc is skirted by a typical foredeep, which begins SE of the Tanimbar Islands with a narrow trough (30 km wide and 1,690 m deep), opening north card into the sickle-shaped Aru Trough (-3,680 m). Here the crescentic shape of the Weber Trough, convex to the East, is repeated in a still more pronounced form.<br />
At its concave western side a rise of the seafloor to -530 m (East of Kai) interrupts its regular outline, and also at its northern side the Kumawa promontory of the Vogelkop of New Guinea with Adi Island form an inward bulge in the outline of the Aru Trough.<br />
The foredeep of the NE- and N-sector of the Banda Outer Arc is formed by the Ceram Sea, a geosyncline of about 80 km width and more than 2000 m depth. Westward it joins on to the Buru Trough which has a depth of 5,319 m.<br />
<br />
3.5.LESSER SUNDA ISLANDS (See figures 187, 212, 214)<br />
These islands are situated on two geanticlinal belts, which form the westward extension of the Banda Arcs. The inner (i.e. northern) geanticline carries from East to West the islands Roma(ng), Wetar, Kambing, Alar (or Ombai), Pantar, Lomblen, Solor, Adonara, Flores, Rintja, Komodo, Sumbawa, Lombok, and Bali. The outer (i.e. southern) arc is formed by the islands Timor, Semau, Roti, Sawu (or Savu) Raidjua, and Dana. The geanticlinal ridge bifurcates in the Sawu area. One branch forms a spur, which plunges westward across Raidjua and Dana, pointing towards the submarine ridge in the trough South of Java; the other branch forms a connecting link with the inner arc across the island of Sumba. In this subchapter will be described successively the physiographical features of the Backdeep, the Inner Are, the Interdeep. the Outer Arc, and the Foredeep of the section of the Sunda Mountain System represented by the Lesser Sunda Islands.<br />
<br />
3.5.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>BACKDEEP<br />
East of Flores the back deep of the Lesser Sunda Islands is formed by the western part of the Southern Banda Basin, which has been described with the Southern Moluccas. North of Flores and Sumbawa extends the Flores Sea. This sea consists of three parts:<br />
a.<span class="Apple-tab-span" style="white-space: pre;"> </span>The NW Flores Sea is the broad and shallow platform which connects the South Arm of Sulawesi with the Sunda Shelf.<br />
b.<span class="Apple-tab-span" style="white-space: pre;"> </span>The Central Flores Basin has a triangular form, its apex lying South of the Lompobatang volcano, which masks its supposed connection with the Walanae Depression of the South arm of Sulawesi, while its base along the North coast of Flores forms its deepest part (-5,140 m).<br />
c.<span class="Apple-tab-span" style="white-space: pre;"> </span>The East Flores Sea comprises the ridges and interjacent troughs 1), which connect the South arm of Sulawesi with the submarine Batu Tara Ridge.<br />
North of Bali and Lombok the back deep is formed by the Bali Sea (about 100 km wide and about 1500 m deep). Westward its floor gradually rises, till it joins on to the shelf sea in the Strait of Madura (about 100 m deep).<br />
<br />
3.5.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>INNER ARC<br />
The Inner Arc of the Lesser Sunda Islands connects Java with the Banda Inner Arc, thus forming a sector of the long belt of fertile volcanic islands, which "winds around the equator like a girdle of emeralds" (a metaphor given by the author "Multatuli"). The Lesser Sunda Islands of the inner arc are all situated on a geanticlinal ridge, which has a width of about 100 km in its western end, gradually diminishing eastward (especially from E Flores) to about 40 km.<br />
The straits between the islands are shallow in the western part, becoming deeper eastward.<br />
Bali is separated from Java by the narrow Strait Bali, which originated, according to Hindu records, in 280 A. D. (STUTTERHEIM, 1922, pag. 22, Note 1). In this island the zones, distinguished in Java, can be retraced. The northern and largest part of the island consists of quaternary and active volcanoes, representing the continuation of the young volcanic complexes in the Solo Zone of Java. The fertile plain of Denpasar, extending on the southern foot of these volcanoes, belongs to the Blitar Subzone of Java. This plain is connected by an isthmian narrowing with the tertiary limestone hills of the "Tafelhoek" (213 m), which are comparable with those of the Blambangan Peninsula of Java (Southern Mountains). The same can be said of the islet of Nusa Penida (529 m) between Bali and Lombok.<br />
Lombok. The general structure of the island is similar to that of Bali: in the North a volcanic zone with the active Rindjani (Solo Zone); then the lowland plain of Mataram (Blitar Subzone); in the South, the "Southern Mountains" with tertiary limestones and volcanic breccias (Maredje, 716 m).<br />
Sumbawa. The physiographical trendlines of Java, which could also be traced through Bali and Lombok, are no longer present on this island.<br />
A typical feature is the Saleh Bay which divides the island in a western and an eastern part. The bay is separated from the sea by the Island of Mojo (600 m) which gives it the character of an intermontane depression on the crest of the geanticline.<br />
The northern side of the island is crowned by some young volcanoes. The Ngenges, Tambora and Soromandi have produced leucitic rocks. They might be compared with the alkaline volcanoes of the Ngawi Subzone on Java (Lurus and Ringgit Beser). For the rest, tertiary sediments and calc- alkaline volcanic rocks, like those of the southern mountains of Java, are widely distributed. This gives the impression that the zone of the Southern Mountains of Java occupies the whole island and that the median depression, called Solo Zone, is no longer present East of Lombok. The Saleh Bay might be considered as an isolated apical depression of this Solo Zone on Sumbawa. (See chapter V).<br />
Flores. The island is separated from Sumbawa by Strait Sape, a narrow, more than, 200 m deep trench. Komodo and Rintja belong to the geanti- clinal culmination of West- and Central Flores, which consists of older (tertiary) volcanic rocks and igneous intrusions comparable with those of the Southern Mts of Java. Younger volcanoes occur along the South coast of West Flores. In Central Flores they are present not only along the South coast but also at the northern side of the island (Paluweh). In East Flores the geanticline shows an axial plunge so that the older volcanic rocks and granodioritic intrusions are no longer exposed; only young volcanoes are found, crowning its crest.<br />
The geanticline continues along Solor, Adonara, Lomblen and Pantar, which islands also carry young and active volcanoes 1).<br />
The axis then crosses Alor or Ombai, Kambing, Wetar and Romang. In this section of the inner arc active volcanoes are absent; the islands consist of late tertiary, partly submarine volcanic deposits.<br />
BROUWER (since 1917) attaches a special importance to the extinction of the volcanism in this section of the inner arc from Alor to Romang. We will discuss this problem more in detail in the chapter on the geological evolution (Chapter V B).<br />
<br />
3.5.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>INTERDEEP WITH SUMBA<br />
Interdeep of the Lesser Sunda Islands. Between the volcanic inner arc of Java-Bali-Lombok and the submarine ridge, South of Java (about -2000 m), there occurs a trough of 175 km width. Its greatest depth, South of Lombok, is 5,160 m. This trough bifurcates eastward into two branches North and South of the Island of Sumba (Strait Sumba -1,020m and Strait Sawu -1,160 m).<br />
These branches form the connection between the trough South of Java and the Sawu Basin (-3,440m); e greatest width of the latter is about 200 km tween East Flores and Roti).<br />
It then gradually narrows eastward to the threshold, 25 km in width and 1,815 m depth, between Kambing and Timor, which separated the Sawu Basin from the Wetar Trough. The latter is 60 km wide with a maximum depth of -3,460 m and is limited at its eastern end by Kisar.<br />
The steep slopes of the Wetar- and Sawu Basins and their relatively flat bottoms give them the appearance of down-thrown crustal blocks which are bordered at their eastern and western end by the horst-like elevations of Kisar and Sumba. These islands belong physiographically to the interdeep zone.<br />
Sumba is the most important geological link between the inner- and outer arc of the Sunda Mountain System. Young volcanoes are absent; an almost horizontal cover of marine neogene-quater nary deposits has a wide distribution, forming typical "bad land" sceneries, which are elsewhere almost lacking in the Indian Archipelago.<br />
<br />
3.5.4.<span class="Apple-tab-span" style="white-space: pre;"> </span>OUTER ARC<br />
The Lesser Sunda Islands belonging to the outer arc are Dana, Raidjua, Sawu, Roti, Semau, and Timor. The distinct submarine ridge South of Java, rising to -1,200 m, plunges eastward, to -4000 m. Its elevation above the adjacent interdeep is at most some hundreds of metres. Then the geanticlinal axis rises again to the Sawu Islands (Dana, Raidjua, Sawu).<br />
Sawu has elevated coral reefs of 300 m above sealevel around a nucleus of pre-tertiary rocks. The Dana-Raidjua-Sawu Ridge has an "en echelon" position in respect to the Roti-Timor Ridge, from which it is separated by the Strait of Dao, which is more than 1000 m deep.<br />
Roti has a core of strongly folded sediments, overlain by quaternary coral reefs up to 430 m above sealevel.<br />
Timor. Like the other broad geanticIinal elevations in the Indian Archipelago, West Timor has a longitudinal depression on its crest, which can be traced from the Kupang Bay to Timor Leste border, where it seems to end at the Lois River.<br />
<br />
3.5.5.<span class="Apple-tab-span" style="white-space: pre;"> </span>FOREDEEP<br />
Between Christmas Island and the median sub- marine ridge South of Java, a prominent deep stretches West and East (-7,450 m). This fore- deep of the Java sector of the Sunda Mountain System extends eastward as a narrow trough of 6000-7000 m depth. Off Sumba its depth diminishes, and South of Sawu it curves northeastward, parallel to Timor. Off Roti ,a rise to -1,940 m separates this western part from the Timor Trough (-3,310 m). The South Java Trough is limited to the South by an ill-defined rise of the Ocean floor (passing from Christmas Island to the swell of 3000-4000 m depth between 108lo and 114lo eastern longitude, the isolated shoal on 1180 40' eastern long and 120 30' southern latitude). The bathymetrical data are yet insufficient to decide whether it forms a continuous• ridge on an ocean floor of 5000-6000 m depth, or belongs to a more complicated submarine relief of this part of the Indian Ocean. The eastern part of the foredeep of Timor is bordered by the Australian- or Sahul Shelf (Arafura Sea).<br />
<br />
<b>3.6. THE SUNDA MOUNTAIN SYSTEM IN THE JAVA-SUMATRA SECTOR</b> (See fig, 11 on pl. 2)<br />
The islands of Java and Sumatra, belonging to the central sector of the Sunda Mountain System, have been outlined under the heading of the Sunda area, because they are 'connected with the Asiatic Continent by the Sunda Shelf, whereas the outer arc of this Sumatra-Java sector belongs physiographically to the circum-Sunda Archipelago. The same general trendlines as in the eastern part can be discerned in the central sector.<br />
The backdeep is represented by the oilbearing basins of East Sumatra and North Java. It differs physiographically from the backdeep in the eastern part of the Sunda Mountain System in being filled by folded neogene sediments (so that it forms at present a land surface which connects the inner arc with the central Sunda Land), whereas in the eastern part the backdeep is formed by sea basins.<br />
The volcanic inner arc is marked by the Barisan Range on Sumatra and the geanticline of South Java.<br />
The interdeep is a trench of 3000-4000 m depth South of Java ending off the Wijnkoops Bay of West Java. It is interrupted SW of Strait Sunda in the bending point between Java and Sumatra. Here the bathymetrical data show a gradual slope of the sea- bottom from Strait Sunda (-1,575 m) to the foredeep (-6,960 m).<br />
Along the Southwest coast of Sumatra this inter- deep reappears as a series of troughs between the Barisan and the islands west of Sumatra. It is 2,260 m deep SW of Lake Ranau, and this basin is separated by a rise of -936 m from the Mentawei Basin (-1,760 m). The islet of Pini forms a threshold between the latter and the Nias Basin (-705 m), while the Banjak Islands in their turn are the separation between the Nias Basin and the basin SW of Atjeh (North Sumatra). The latter has a depth of more than 1000 m.<br />
The outer are, South of Java, is a submarine geanticlinal ridge rising from -7,450 m to the South of it up to -1,200 m. It is not developed as a distinct ridge in the submarine relief SW of Strait Sunda, where the general trend of the Sunda Mountain System changes from East-West to SE-NW. But it reappears West of Sumatra as the island festoon from Enggano to Sirneulue (Simular).<br />
The foredeep, South of Java, has been outlined in connection with the foredeep of the Sunda Islands; West of Sumatra it is represented by an uninterrupted, though hardly pronounced trough of 5000- 6000 m bordered by the floor of the Indian Ocean which has a mean depth of 4000-5000 m. This fore- deep ends West of Simeulue.<br />
<br />
<b>3.7. NICOBARS AND ANDAMANS</b> (See fig. lIon pl. 2, and fig. 375)<br />
The Nicobars (total area 1,645 sq km) consist of 10 small islands and 9 still smaller islets. The Andaman group (6,497 sq km) is formed by 4 larger, mountainous islands. These islands form the northern end of the Sunda Mountain System in so far as this is treated in this book, though this mountain system can be traced still farther northward to the Arakan Y oma of Burma on the Asiatic Continent.<br />
The backdeep. The geosynclinal trough of Northeast Sumatra opens northward into the Andaman Sea which is 450 km wide and -3,600 m deep. This basin forms the connecting link between the Sumatran backdeep and the Sittang depression (Toungoo) in Burma. The Sittang River flows through the eastern part of the Central Belt of Burma (CHHIB- BER, 1934).<br />
This Andaman Basin is connected with the Indian Ocean by a strait of 200 km width and over 2000 m deep between the Nicobar Islands and Sumatra. It is this interruption of the geanticlinal trend which makes it difficult to decide how the Andaman-Nicobar Arc is connected with the Sumatran sector.<br />
The volcanic inner arc of North Sumatra plunges via the Island of Weh (with the harbour of Sabang) down into the Andaman Sea. Here, it cannot be traced clearly between 60 and 110 northern latitude, but it rises again to the Invisible Bank, and from there it runs across the volcanic islands of Barren (with an active volcano) and Narcondam to the volcanic zone between the Sittang and the Irawadi in Burma. This is the igneous line of the Central Belt of Burma, distinguished by CHIBBER (1934, p. 288).<br />
The interdeep is ill defined between the northern spur of Sumatra and the Invisible Bank owing to the lack of bathymetrical data. Perhaps it can be traced northward via the trough of -3,136 m East of the Nicobar Islands. Its course is clear, however, between the Andaman Islands and the volcanic inner arc, and northward it passes into the Irawadi depression of Burma.<br />
The outer arc is interrupted between Simeulue and the Nicobar Islands by the above mentioned passage between the Andaman Sea and the Indian Ocean. The Nicobar and Andaman Islands have often been pictured by geographers and geologists as the continuation of the Sumatran Range. For instance CHHIBBER (1934) in his "Geology of Burma" is of the opinion that the Arakan Yoma of Burma (with the Waga and the Manipur Hills) "continues southwards through the Andaman and Nicobar Islands to Sumatra and Java". UMBGROVE (1930, Geological History of the East Indies, p. 67) prefers the conception "that the western part of Sumatra (the so-called Barisan geanticline), as well as the series of islands West of Sumatra, did indeed during the Tertiary form one zone, which must be considered as the continuation of the Arakan Yoma". The above analysis of the trendlines of the Sunda System, indicates that the Andamans and Nicobars are physiographically an element of the outer arc of this system; in other words, they are the continuation of the chain of islands West of Sumatra. Their non-volcanic character is also in favour of this conception 1).<br />
Narcondam and Barren Island, on the other hand, are situated on the inner arc, which is a continuation of the Barisan geanticline of Sumatra.<br />
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Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.com0tag:blogger.com,1999:blog-7274248385186471083.post-47334517540543777852014-08-09T09:23:00.002-07:002014-12-06T07:29:29.507-08:002.SUNDALAND<br />
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The Sunda area is the partly submerged south- eastern outgrowth of the Asiatic continent, being connected with it by the Malay Peninsula and the Isthmus of Kra. The so called "Sunda Land" comprises Malay Peninsula, Borneo, Java, Sumatra and the interjacent shallow seas from which emerges a number of smaller islands.<br />
We will first discuss the physiography of this shelf-sea and the smaller islands; thereafter that of the three Larger Sunda Islands: Borneo, Java and Sumatra. <br />
<br />
<b>2.1. THE SUNDA SHELF AND THE SMALLER ISLANDS</b><br />
2.1.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>THE SUNDA SHELF<br />
The Sunda Shelf is a shallow sea, generally less than a hundred meters deep, comprising the Gulf of Thailand, Malacca Strait, the SW part of the South China Sea, the Java Sea and the adjoining southwestern part of the Makassar Strait. With its area of 1.850,000 sq km, it is the most extensive, coherent shelf in the world (K. KRUMMEL, Ozeanographie I, 1907, p. 113). It was EARLE (1845) who more than a century ago drew attention to this extensive submerged flat and to its counter part on the Australian side ("Great Asiatic Bank" and "Great Australian Bank"). About 75 years later, after the results of the Siboga Expedition had become known, MOLENGRAAFF & WEBER (1919) took up again EARLE'S conception. MOLENGRAAFF advanced a number of arguments for the idea that these shelf seas were submerged peneplains, resulting from the marine transgression after the Pleistocene glaciation.<br />
In the relief of the bottom of the Sunda Shelf the course of submerged drainage systems can be distinguished: the river system in the Malacca Strait, the river system in the South China Sea, the river systems in the Java Sea.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-2t5GZgo4dUg/U_l8nK4B8RI/AAAAAAAA0iE/kd2f0ofGYnI/s1600/physiography-sunda-shelf.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-2t5GZgo4dUg/U_l8nK4B8RI/AAAAAAAA0iE/kd2f0ofGYnI/s1600/physiography-sunda-shelf.jpg" height="400" width="348" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.1. Map of Sundaland</td></tr>
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The zoogeographic studies of WEBER demonstrated that there is a closer relationship between the fresh water fishes in the present rivers of West Borneo (Kapuas River) and South East Sumatra, than between the Kapuas and the Mahakam River of East Borneo. This proves that the rivers of SE Sumatra and West Borneo have formerly been the tributaries of a large river in the South China Sea. A symposium on the geomorphology of the Java- and Sunda Sea (held at Utrecht in 1944) has been edited by SMIT SIBINGA in 1947 (see BAARTMANS, etc., 1947).<br />
The structural framework of the Sundah Shelf and vicinity was studied by Ben-Avraham (1973) based on several surveys.<br />
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2.1.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>THE ISLANDS ON THE SUNDA SHELF<br />
The Sunda Shelf carries a number of islands, which were formerly high parts on the Sunda peneplain. Therefore, they are nearly all rocky islands, often covered by a deep crust of lateric weathering. The arrangement of these islands forms an indication of the major structural trendlines which connect SE Asia with the three Larger Sunda Islands.<br />
The Natuna Islands in the North (total area 1,875 sq km) lie on a belt which points from the western promontory of Borneo (Cape Datuk) northwest- ward to Pulu Condor and Indo China. This rise of the shelf floor is transversely cut by the gullies of the submerged drainage pattern. BOTHE (1928, p. 147) mentions a slight recent elevation of Natuna major or Bunguran, which has rejuvenated the erosion at some places, but it seems also possible that such a rejuvenation has resulted from the recent abrasion along the coasts.<br />
Midai, South of Natuna major, is a young (though extinct) basalt volcano.<br />
The Anambas and Tambelan Islands (total area of 625 sq km) form the next belt with a NW -SE trend. In the chapter on the geological evolution arguments will be advanced that this belt is the central part of the Sunda area, from which orogenic systems have spread to the NE and the SW.<br />
The Riau Archipelago (Bintan and surrounding islands, with a total area of 2,313 sq km) forms the southern extension of Singapore and the eastern part of the Malay Peninsula. The islands are covered in many places by a thick lateritic crust, which is mined in Bintan as bauxite ore. Workable tin ores are absent in the Riouw Archipelago, though cassiterite is occasionally found in alluvial deposits and in contact-metamorphic rocks. This belt, extending from eastern Malaya to the Riouw Archipelago, can be traced to the Karimata Islands off the coast of West Borneo, giving it a slightly convex outline to the SW.<br />
The Lingga Archipelago (Singkep, Lingga, and surrounding islands, with a total area of 2,188 sq km) belongs to the great Tin-belt. This belt extends from the western part of the Malay Peninsula (with the Main Range) via the Lingga Archipelago with Singkep, to Bangka and Billiton. These islands belong to a mountain range which had largely been baseleveled 1) and which was partly abraded. It has been dissected into a great number of islands owing to a rise of the sea in late quaternary time. They represent a drowned topography.<br />
Singkep, Bangka, and Billiton are surrounded by an aureole of submerged river valleys, containing alluvial tin-ores. Bangka and Billiton are the most important tin producing islands. Bangka has an area of 11,340 sq km, being the 19th island in size of the whole Indian Archipelago. The Maras Mts in North Bangka attain a height of 692 m above sealevel and the Pading Mts in the southern part of the island are 654 m high. Billiton measures 4,595 sq km and the two summits in its centre (Tadjem Laki and Tadjem Bini) both attain an altitude of 510 m.<br />
The Karlmundjawa Islands in the Java Sea are a group of rocky islands consisting of pre-tertiary rocks covered by basaltic lava. The basalt occurs also as E- W trending dikes in the basement complex. These islands are situated south of the great Tin-belt. They belong to the southernmost belt of the Sunda landmass, ending at its western side in the massif of crystalline schists and granites in the Lampong Districts of South Sumatra, which is also covered by a shield of young basaltic effusions.<br />
The Island of Bawean in the southeastern part of the Java Sea has quite another character. It is the only island in the Sunda Shelf area which consists of marine tertiary strata and alkaline volcanic rocks. This part of the Java Sea does not belong to the more or less stable Sunda Land, but it has been subjected to tertiary processes of diastrophism. It bears a close resemblance to the Muriah on the North coast of Java. This extinct volcano was also an island, but it has been linked to the mainland in historical time by the silting up of the Semarang- Rembang passage.<br />
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<b>2.2. BORNEO</b><br />
Borneo is the second largest island of the SE Asian Archipelago (736,000 sq km), being slightly larger than France. Sarawak, Labuan, and Sabah belong politically to Malaysia (196,000 sq km), West-, South- and East-Kalimantan are a part of Indonesia (539,500 sq km) and Brunei Darussalam<br />
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<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-9gyOBz1QIc0/U_mA7pfz2gI/AAAAAAAA0iQ/9iroASO_Oxk/s1600/physiography-borneo.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://4.bp.blogspot.com/-9gyOBz1QIc0/U_mA7pfz2gI/AAAAAAAA0iQ/9iroASO_Oxk/s1600/physiography-borneo.jpg" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.2. Topographic map of Borneo</td></tr>
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2.2.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>OROGRAPHIC AND HYDROGRAPHIC TRENDLINES<br />
The island has roughly a triangular outline with three small peninsulas at its northeastern side (Mangkalihat Peninsula, and the two promontaries bordering Darvel Bay; Fig. 2.2). It has extensive hilly and mountainous relief which, however, in most localities does not exceed 1500 m. The altitude levels are indicated on the map Fig. 2.2.<br />
This map shows that the orographic trendlines are not as prominent as in most of the other islands. The older maps of Borneo show mountain-ranges which are too high and much too coherent. The divide mountains of the older cartography still haunts the geotectonic conceptions; even the border ranges have often been inferred between the major administrative and political divisions. A broad mountain system traverses the island from the Kinabalu Range in the north (with Mt Kinabalu, 4,095 m, forming the highest summit of the island), via the Iran and the Muller Mts to the Schwaner Mountain (with Bukit Raja, 2,278 m) in. the SW. This complex mountain system forms the main divide of the island, from which other orographic units branch off to the East and West, whilst the North- and South trending Meratus Mountain (with highest summit Besar 1,892 m) in the SE-part of the island has a more isolated position.<br />
Westward branches are:<br />
a) the Upper Kapuas Mts between the Redjang Valley to the North. and the Upper Kapuas Basin and the Batang Lupar Valley to the South. and<br />
b) the Madi plateau between the Upper Kapuas Basin and the Melawi River. The latter branch can be traced farther westward. along an axial depression, which is traversed by the probably antecedent Kapuas River, to the mountain complex in the western promontory formed by the Chinese Districts (highest summit Niut, 1,701 m). This mountain complex is dissolved into a great number of isolated summits. a peculiar topography of residual mountains. The belt curves northwestward via Cape Datu(k) to the submerged ridge in the Sunda Sea. carrying the Natuna Islands. Eastward branches are:<br />
a) mountain system in North Borneo. ending in the peninsulas at both sides of Darvel Bay. and<br />
b) another complex mountain system, ending in the Mangkalihat Peninsula.<br />
The Kapuas River should be distinguished from another Kapuas River, which starts on the other side of the same mountain range in central Borneo, but flows to the south, merging with the Barito River and discharging into the Java Sea.<br />
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2.2.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>STRUCTURAL TRENDLINES<br />
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<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-bQ1nMbjNU7g/VIMZCoZlCFI/AAAAAAAA0uY/_JRWDdPkkcg/s1600/physiography-borneo-04.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-bQ1nMbjNU7g/VIMZCoZlCFI/AAAAAAAA0uY/_JRWDdPkkcg/s1600/physiography-borneo-04.jpg" height="640" width="564" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.3. SAR Image of Borneo</td></tr>
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Ridges lineations onshore Borneo are clearly seen on satelite immageries especially by Synthetic Aperture Radar (SAR) image as shown in Fig. 2.3. The bending of Rajang-Crocker range is almost like the core of the island. Meratus Mountains in the southeast of the island also appear as long continuous ridges. In a detail image, the Samarinda Anticlinorium is also comes out as log ridges in the east of Borneo (Fig. 2.4). Karst topography occur in places like in Mulu (Sarawak) and Sangkulirang-Mangkalihat area in East Borneo. The highest peak of Borneo is <a href="http://en.wikipedia.org/wiki/Mount_Kinabalu">Mount Kinabalu</a> in Sabah. A granitic intrusion which reach 4095 meters above sea level.<br />
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<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-xopvLi4Se84/VIMbPbvbSEI/AAAAAAAA0uk/m3CzS8a-UWc/s1600/samarinda-ridges.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-xopvLi4Se84/VIMbPbvbSEI/AAAAAAAA0uk/m3CzS8a-UWc/s1600/samarinda-ridges.jpg" height="120" width="200" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.4. Samarinda Anticlinorium ridges.</td></tr>
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It then appears that Northwest Borneo region forms a part of the major trendlines of the Philippine Archipelago, whilst the bulk of the island belongs to the Sunda structure.<br />
The Palawan festoon ends in the Kinabalu Range and the Sulu festoon in the Darvel Bay area. The NNE-SSW trending Kinabalu Range consists of highly interfolded pre-tertiary and lower tertiary strata which are intruded by the granodiorites of the Kinabalu Massif.<br />
The East-to-West trending ranges North of Darvel Bay consist also of pre-tertiary and lower tertiary rocks. Less folded younger tertiary strata are found on the flanks of these ranges and in the basin between them, which forms the southwestern extension of the Sulu trough.<br />
This complex of Northwest Borneo region has geological affinities to the Philippine trendlines, and it is separated from the mainland of Borneo by a neogene tract, which extends across the island from the Sulawesi Basin, in the East, to Labuan Bay, on the NW coast.<br />
The Sundaic part of the island consists of a triangular continental core in SW-Borneo, which is flanked by the tertiary basin of Sarawak on the one side and the tertiary basins of the Southern and Eastern Divisions of Borneo on the other.<br />
Only the western part of Borneo, comprised by the triangle Müller Mts - Cape Datu(k) - Cape Sam bar is a proper continental mass. It contains at its eastern side the Melawi Basin with Lower Tertiary in brackish-water facies. FEHN (1933) is also of the opinion that only SW -Borneo may be called an old land ("Alte Rumpfebene").<br />
This continental core forms a part of the old Sunda landmass. Its northern boundary is formed by the mountain complexes extending from Cape Datu(k) via Mt Niut and the Madi Plateau to the Milller Mts. Its southern margin is formed by the Schwaner Mts and the low mountainous land extending from there to the Southcoast. Both marginal zones of the old Sunda landmass are, moreover, characterized by volcanic intrusions and extrusions of tertiary age. These tertiary volcanic belts unite in the Muller Mts and extend thence farther northeastward via the Batuajan (1,652 m) to the Kongkemal (2,053 m), ending in the low Latong Mts, West of Tarakan. Near the northern edge of the continental mass of West Borneo Quaternary basalt flows are found around the old Niut- stock, and along its southwestern edge WITKAMP has described some Quaternary, though extinct, volcanoes near Lonigram (Murai, Beluh, Bawang Aso).<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-HbezxlUvjTo/VIML-BwA-tI/AAAAAAAA0t8/ohoVhTBKHOY/s1600/physiography-borneo-03.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://4.bp.blogspot.com/-HbezxlUvjTo/VIML-BwA-tI/AAAAAAAA0t8/ohoVhTBKHOY/s1600/physiography-borneo-03.jpg" height="320" width="277" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.5. Relief of Borneo Island</td></tr>
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<br />From the Kongkemal, a complex ridge branches off eastward to the Niapa Mts (1,275 m) and thence the basement complex definitely plunges under the tertiary strata of the Mangkalihat Peninsula.<br />
The Sunda landmass penetrates into Borneo like a huge wedge, which has its base (of 600 km width) along the SW-coast between Cape Datuk and Cape Sambar, and thence it extends northeastward into the island, gradually narrowing. Northeast of the Schwaner Mts it begins to plunge under marine tertiary strata, but exposures of it can be traced farther NE, to the KongkemaI. Thence it tapers out to the Latong Mts in NE-Borneo.<br />
This wedge of pre-tertiary rocks forms the structural backbone of Sundaic Borneo. NW of it lies a great. 1000-2000 m high mountain range, concave to the NW, which comprises the Kapuas Mts and the Iran (or Nieuwenhuis) Mts. This mountain range consists of pre-tertiary and lower tertiary marine rocks which are intensely folded and thrusted to the NW.<br />
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<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-V1Ue7Vwuwg4/VIMMx7qIhgI/AAAAAAAA0uI/9PNFqcFwvC0/s1600/physiography-borneo-01.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-V1Ue7Vwuwg4/VIMMx7qIhgI/AAAAAAAA0uI/9PNFqcFwvC0/s1600/physiography-borneo-01.jpg" height="320" width="280" /></a><br />
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<tr><td class="tr-caption" style="text-align: center;">Fig. 2.6. Physiographic units of Borneo</td></tr>
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It is separated by the Redjang Valley from a ridge, generally less than 1000 m high, which is also concave to the Northwest. This ridge is called in this book the "UIarbulu Ridge". It is an anticlinorium, consisting for the greater part of tertiary strata, and separated from the coast of Sarawak and Brunei by a rather narrow stretch of low hilly land.<br />
Both, Kapuas-Iran Range and Ularbulu Ridge, are tertiary mountain ranges, belonging to the circum-Sunda Mountain System. Southeast and East of the structural backbone of Borneo the pre-tertiary basement complex disappears under the basins of the Southern- and Eastern Division of the island, on which were deposited many thousands of metres of tertiary sediments.<br />
Thebasement complex rises again towards the East coast, lying less deeply buried along the Strait of Makassar, and being exposed again in the small islands of Pulu Laut and Sebuku, off the SE corner of Borneo.<br />
In this marginal tertiary basin of SE- and E-Borneo is situated a SSW-NNE trending median ridge. It begins with the Meratus Mts in the South, which consist largely of pre-tertiary rocks, and joins on to the great Samarinda anticlinorium which separates the lakes district of the Mahakam River from the coast. This Samarinda anticlinorium has an axial depression in the Samarinda section, where it is cut by the antecedent Mahakam River, and thence the axis rises again northward. towards the transverse threshold, formed by the Kongkemal-Niapa-Mangkalihat system. This Meratus-Samarinda Range is the result of the tertiary orogenesis at the southeastern side of the structural backbone of the island. It forms the counterpart of the tertiary mountain ranges of Sarawak at its northwestern side. It appears from this sketch that it is necessary, for a clear insight into the arrangement of the orographic elements of the island, to consider also its paleo-geographic evolution. The reader therefore is referred to the paleo-geographic maps of the tertiary evolution, pictured in fig. 148.<br />
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2.2.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>THE THREE LARGEST RIVERS OF BORNEO<br />
The three largest rivers of Borneo are the Kapuas, the Barito, and the Mahakam. The Kapuas source is on the Tjemaru (1,681 m) in the centre of the island. The river flows westward through the Western Division, emptying with some ramifications into the Sunda Sea near Pontianak. It is probably the longest river in Indonesia (1.143 km), being somewhat shorter than the Rhine in Europe (1.320 km). Its upper course crosses. between Putussibau (898 km from the mouth) and Semitau (623 km from the mouth), a marshy lake district, which is an intermontane basin surrounded by the upper Kapuas Mts in the North, the Miiller Mts in the East, the Madi Plateau in the South, and the Kelingkang Mts in the West. After cutting through some East-to-West trending ridges between Semitau and Singkang (469 km from the mouth), it reaches the Melawi basin. From Sekadau (348 km from the mouth) the river flows' through a low mountain land to Tajan (182 km from the mouth). There it reaches its delta. a large, marshy tract of land, with some isolated hills •of Pre-Tertiary. The delta is at present still growing by coastal accretion. This delta has an area of 5,400 sq km, according to FERN (1933, p. 14). Upon reaching the delta the average water supply of the Kapuas is 6000-7000 cbm per second.<br />
The second largest river of Borneo is the Barito, which rises in the Muller Mts, from which it flows 900 km southward. from Muaratewe through the marshy Barito Basin. This basin is framed at its eastern side by the Meratus Range, whilst its broad western part is traversed by several other important rivers, flowing from the Schwaner Mts southward. This western part of the Barito Basin is covered by a rather thin section of tertiary and quaternary strata, which gradually increases in thickness towards the Barito. It is still a rather stable area, underlain by the basement complex of the old Sunda land, which tilts towards the axis of the Barito Basin, being hinged on the old landmass of Western Borneo.<br />
The third largest river is the Mahakam (about 775 km long), which rises, like the Kapuas river, on the Tjemaru in the centre of the island. It cuts through the pre-tertiary axis of the island East of the Batuajan (1.652 m) and then reaches the tertiary basin of Kutei. Its middle course traverses a lowland plain with many marshy lakes. This intermontane depression is seperated from the Barito depression by a broad hilly tract of less than 500 m altitude.<br />
Thereafter, the Mahakam cuts through the Samarinda anticlinorium and reaches, near the oilfield of Sanga-Sanga, its alluvial delta. This delta spreads like a broad fan over the shelf-sea, having a base of 65 km and a radius of about 30 km.<br />
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<b>2.3. SUMATRA</b><br />
This island has an area of 435,000 sq km being about the size of Great Britain. Economically it is the second island in importance, next to Java, and it offers great possibilities for further development.<br />
The island has an elongated form, measuring 1650 km from Kota Radja in the North to Cape Vlakke-Hoek (Tanjung Cina) in the South. Its width amounts to 100-200 km in the northern part and-to about 350 km in the southern part. There are few indentures along the coastline.<br />
The West coast is only slightly indented by the Bay of Tapanuli, whereas along the East coast the larger rivers form wide, but shallow estuaries at their mouths. Only at the southern end of the island, two important bays penetrate about 50 km inland. These are the Lampong Bay (with Teluk Betung and Oosthaven or "East Harbour") and the Semangko Bay (with Kota Agung). Natural harbours are scarce. The West coast is dangerous owing to the ocean breakers. Barus (20 north. lat.) is one of the very few safe landing points, which has been used, according to VOLZ, by the Malayans and Indians in former times. The East coast, along the Strait of Malacca, is safer and, therefore, it was visited in early historic times by sailors coming from India and China.<br />
The heavily silt laden rivers along the shallow East coast have necessitated the dredging of navigation channels for modern ships. The East coast in historical time has shifted outward many kilometres due to deposition by these streams. In the middle ages the sea still entered with large embayments in the East coast, forming, for instance, the large embayment in the vicinity of Palembang. The large marshy islands off the central part of the East coast, such as Rupat, Bengkalis, Padang, Tebingtinggi, Rangsang, are still separated by narrow, shallow straits from the mainland, but they will be united with the mainland in the near geological future in consequence of deposition.<br />
The main physiographic trendlines of the island are rather simple. Its backbone is formed by the Barisan Range along its western side, which is the divide between the West- and the East coast. The slope towards the Indian Ocean is generally steep and consequently the West coast belt is mostly mountainous, with the exception of two lowland embayments in North Sumatra (Meulaboh and Singkel or Singkil), which have a width of about 20 km.<br />
The eastern side of the island is occupied by broad, hilly tracts of tertiary formations and alluvial lowland. This low eastern belt has at Diamond Point in Aceh a width of about 30 km; southward its width increases to 150-200 km in Central and South Sumatra.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-4-8zzRtNFoM/U_JzCYRZ5uI/AAAAAAAA0gM/8eOjELvwZcQ/s1600/physiography-sumatra.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-4-8zzRtNFoM/U_JzCYRZ5uI/AAAAAAAA0gM/8eOjELvwZcQ/s1600/physiography-sumatra.jpg" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.3. Physiographic and relief map of Sumatra</td></tr>
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2.3.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>THE BARISAN MOUNTAIN RANGE<br />
The most prominent orographic element of the island is the Barisan Mountain Range, 1.650 km long and about 100 km wide (highest summit is the Peak of Kerinci or Peak of Indrapura, 3,800 m). The Tigapuluh Mts occupy an isolated position in the eastern lowland, forming a dome- or horst-like elevation (90 km long and 40 km wide, highest summit the Tjengeembun, 722 m).<br />
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<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-ddnQTocIbdU/U_efZjUONmI/AAAAAAAA0hM/xjrMyNy86F4/s1600/Slide3.JPG" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-ddnQTocIbdU/U_efZjUONmI/AAAAAAAA0hM/xjrMyNy86F4/s1600/Slide3.JPG" height="320" width="280" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.4. Barisan Mountain / Range a 3D view of a satellite image, with vertical scale exageration.</td></tr>
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In the older descriptions the Barisan Range is commonly described as a number of parallel ranges or "coulisses", which one after the other branch off from the main NW -SE trending range, assuming a more West to East direction, and plunging toward the eastern lowland (see map of the Malayan Archipelago by BLOM. 1934). The coulisses repeat on a smaller scale the arcuate outline of the Sunda Mountain System as a whole, changing from NW-SE in Sumatra to WoE in Java. This pattern would be suggestive for those geotectonic interpretations, that accept a general compressive force in the crust from the N or NNE as the chief cause of the formation of this mountain system.<br />
However, on closer inspection this explanation is definitely inadequate.<br />
In northern Atjeb (or Atchin) there is indeed a tendency of the ranges to curve from NW -SE into a West-to-East direction. This can be observed in the ranges, flanking the Atjeh Valley near Kotaradja, which pass along the Southern Mountains into sliver blocks which form the WoE trending Y-Mountains, X-Mountains, and the Central Gajo Range (or Intemintem Mts with the Abongabong, 2,985 m) (Fig. 14). These ranges skirt the southern end of the Andaman Basin. Also their stratigraphy and tectonic structure correspond more with the northern part of the Sunda Mountain System than with that of the Sumatran section. The Sumatran trendlines, paralleling those of the Malayan Peninsula, begin with the N -S trending van Daalen Range. The latter meets the above mentioned ranges at right angles. Here an intersection occurs of the pretertiary trendlines, which we find belong to two different centres of orogenic activity, that of Mergui and that of the Sunda land. The foothills, formed by truncated tertiary anticlines and skirting the central pre-tertiary mountains of northern Atjeh, have a prevailing WoE trend along the North coast and curve around into a NW -SE direction South of Diamond Point. Therefore, the separation between the pre-tertiary trendlines of the Mergui section of the Sunda Mountain System (around the Andaman Basin) and those of the Sumatra section (around the Sunda Land), can no longer be made for the tertiary trendlines, which are all governed by the Barisan Range.<br />
The Pundak Lembu (2,983 m) is a central knot, from which the van Daalen Range extends northward, the Central Gajo Range westward, and the Wilhelmina Range southeastward. In Southern Atjeh, South of Blangkedjeren, the NW-SE trend of the Barisan System prevails.<br />
Between the Wampu- and the Barumun River, the Barisan Range shows a typical oblong culmination (NW-SE axis of 275 km length, and 150 km broad) (Fig. 15.) This culmination has been called by the author the "Batak-tumor", In its top part. which is about 2000 m high (Sibuatan, 2,457 m), lies the great Toba cauldron with Lake Toba. The cauldron is 100 km long and 31 km wide, an area of 2.269 sq km, while Lake Toba has a length of 87 km and an area (inclusive of Samosir Island) of 1,776.5 sq km. A geographical description of the southern part of the Batak culmination was lately given by HELBIG (1940).<br />
The Barisan System of Central Sumatra consists of a number of NW-SE trending block-mountains. It is narrowest at the transition into the Batak- tumor near Padang Sidempuan (75 km) and then gradually widens southeastward to 175 km in the Padang section. These block-mountain ranges are highest at the southwestern side of the Barisan System, where they attain altitudes of over 2000 m, becoming lower towards the East-Sumatran lowland (Lisun-Kwantan-Lalo Range. about 1000 m, and Suligi-Lipat Kain Range up to 500 m). The pre-tertiary core of the Suligi-Lipat Kain Range can be traced via some anticlinal ridges of tertiary formations to the northwestern corner of theTigapuluh Mts, which are situated in the middle of the tertiary basin of East Sumatra. The Lisun-Kwantan-Lalo Range, however, plunges southeastward, disappearing under a 50 km wide basin, called the Sub-barisan Depression, which separates the Tigapuluh Mts from the main Barisan System.<br />
In this section of Sumatra TOBLER (1917) distinguished the following tectonical and morphological elements (from NE to SW):<br />
a.<span class="Apple-tab-span" style="white-space: pre;"> </span>Alluvial East coast plain.<br />
b.<span class="Apple-tab-span" style="white-space: pre;"> </span>Tertiary foreland (peneplain) with the Tigapuluh Mts.<br />
c.<span class="Apple-tab-span" style="white-space: pre;"> </span>Sub-Baris an depression.<br />
d.<span class="Apple-tab-span" style="white-space: pre;"> </span>Fore-Barisan with overthrust masses.<br />
e.<span class="Apple-tab-span" style="white-space: pre;"> </span>Schiefer Barisan with intensely folded and metamorphic pre-tertiary rocks.<br />
f.<span class="Apple-tab-span" style="white-space: pre;"> </span>High-Barisan with young volcanoes.<br />
g.<span class="Apple-tab-span" style="white-space: pre;"> </span>Alluvial West coast plain.<br />
This is still a useful distinction of the main physiographic elements in Central- and South- Sumatra. The Fore-Barisan begins in the Umbilin area, East of Lake Singkarak, were it wedges out between the Lisun-Kwantan-Lalo Range and the Schiefer Barisan; southeastward it disappears under the tertiary deposits of the East-Sumatran basin.<br />
The Schiefer' Barisan can be traced along the entire length of .the island. The High-Barisan is especially well developed in the southern half, South of Padang. In the northern half of the island no distinction can be made between Schiefer-Barisan and High-Barisan, because pre-tertiary rocks are exposed over the entire cross-section and they are capped by more or less isolated young volcanoes. In the chapter on the geological evolution of Sumatra (V B) the tertiary basin of East Sumatra (a-c) will be called Zone I. The block- mountain ranges North of Umbilin, such as Suligi- Lipat Kain and Lisun-Kwantan-Lalo will be called Zone II. The overthrust masses of the Fore-Barisan (d) are united in Zone III. The Schiefer-Barisan (e) comprises Zone IV, but North of Padang the Schiefer-Barisan (e) coincides with the High-Barisan (f). The High-Barisan sensu stricto (f) forms Zone V, South of Padang. See fig. 126.<br />
The Zones II and III are foreign elements, lying on the East flank of the main Barisan Range, as will appear from the geological analysis in the sub- chapter VB. The geanticlinal arch of the Barisan Range, which was elevated in plio-pleistocene time, comprises the Zones IV and V.<br />
<br />
2.3.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>THE SEMANGKO ZONE<br />
There is one typical feature, which characterizes the Barisan geanticline along its entire length, namely a median depression zone on its top, called the Semangko(-rift) Zone after its type section in the Semangko Valley of South Sumatra.<br />
This Semangko Zone begins in the Semangko Bay of South Sumatra and can be traced from there to the trough of the Atjeh Valley with Kotaradja at the northern end of the island. Some sections were filled and capped by young volcanoes.<br />
The series of narrow trough-valleys and volcano- tectonic sinks, forming this median Semangko-rift Zone on the top of the Barisan geanticline consists of the following units (from South to North): Semangko Valley with the Suoh and Antatai sinks; Liwa Basin; Warkuk Valley; Ranau cauldron; Kuala-Mekakau Valley; between Pulaubringin and Tandjong Sakti it is filled by the volcanoes Bepagut (2,732 m) and Patah (2,817 m) and it reappears in the Upper Mana Valley; Keruh Valley; Upper Musi Valley with Kepahiang; the Ketaun Basin with Muaraaman; upper Seblat Valley; interruption by the volcanic Gedang Massif (2,446 m); Upper Dikit Valley (Mentenang) with Muara Manderas; interruption by volcanic massifs; Upper Merangin Valley with the lake of Kerintji and Sungeipenuh; interruption by the Kerintji volcano (Peak of Indrapura, 3800 m, highest summit of Sumatra); Upper Batang Hari with Muara Labuh; the lakes Danau-di-Atas and Danau-di-Bawah; the Singkarak Valley with Solok and Lake Singkarak; interruption by the Marapi volcano (2,891 m); intermontane basin of Fort de Kock; Upper Masang Valley with Bondjol; Upper Rokan-kiri Valley (Batang .Sumpur) with Lubuksikaping and Rau (Rao), Here the Semangko-Zone bifurcates; the main fault-zone, called "Ulu-Aer fault" by DURHAM (1940), extends first northward and then curves NE to Sibubuhan and Sipirok; West of Rau the Angkola fault- trough branches off in a western direction and then sweeps northwestward along the Batang Gadis and Batang Angkola Valleys, in the vicinity of Muara Sipongi, Siabu, Sarumai- tinggi, and Padang Sidempuan. Near the last mentioned settlement occurs the transition between the Barisan of Central Sumatra and the Batak culmination of North Sumatra. At this point the Semangko zone is capped by the volcanic massif of Lobukraja-Buabuali (described by HELBIG, 1940, p. 189). It then can be traced farther, across the Batak-tumor, along the Batang Toru Valley with Tarutung and the Renun Valley with Sidikalang, This part has a crescentic outline, concave to the SW. The great Toba cauldron has a position somewhat off-side the main depression zone, cutting across its northeastern fault margin. In Atjeh the course of the Semangko-rift Zone becomes more complicated. The Renun Valley joins on to the Alas Valley, which has also a crescentic outline, concave to the SW. The Alas depression can be traced farther NW to the intermontane basin of Blangkedjeren (760 m), and from there along the upper course of the Tripa and the Seunagan Rivers in a western direction towards the embayment of Meulaboh on the West coast. The continuation of this depression zone is the upper course of the Teunom and the Atjeh River. Finally, it ends in the marine trough between the islands Breueh and Peunasoe at its SW-side and the volcanic island of Weh at its NE-side.<br />
<br />
2.3.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>MAIN STRUCTURAL TRENDLINES<br />
After this analysis, the main trendlines of Sumatra may be outlined as follows: The West flank of the Barisan geanticline extending west of the Semangko Zone is rather regularly formed in the southern half of the range, South of Padang. In this southern part the West flank is formed by a long crustal block which has been tilted toward the Indian Ocean, whilst its elevated northeastern edge breaks down along the Semangko Zone. This tilted block, called the Benkulen Block, can be compared with the Southern Mountains of Java, which are blocks tilted oceanward and forming the South flank of the geanticline of Java. The escarpment along the Semangko Zone is in general the divide between the East- and the West coast. This is the Barisan sensu stricto or High-Barisan. The West coast rivers are short, having a steep grade towards the Indian Ocean. The rivers descending eastward are much longer, flowing through the erosional plain, which truncates the anticlines of the neogene basin, and through the wide alluvial lowlands, until they empty on the Sunda Shelf-sea and Strait Bangka (see, for instance, the description of the Musi drainage basin by LEHMANN, 1933).<br />
The southern end of the Barisan in the Lampong Districts is nearly 150 km wide, and here one may distinguish between the West flank or Bengkulu Block, the top part or Lampung Block, and the Eastflank or Sekampong Block (see fig. 355).<br />
North of Ranau the range narrows to less than 100 km, because the Sekampong Block disappears under the neogene oil basin of Palembang and the Lampong Block is also covered by neogene strata. The pre-tertiary basement complex of the latter reappears in the culminations of the Garba, Gumai-, and Tambesi-Rawas Mts, which belong to the Schiefer Barisan, whilst the edge of the Benkulen Block, capped by a series of young volcanic cones, forms the High-Barisan.<br />
Between Padang and Padang Sidempuan the geanticlinal structure of the Barisan Range is less distinct. It is cut into a number of longitudinal block-mountains on the East flank (described by VON STEIGER, 1922), as well as the West flank. The latter are indicated, for instance, by the subsequent tributaries of the lower course of the Batang Gadis, after it has left the Batang Angkola trough of the Semangko Zone.<br />
The next part of the Barisan Range, that of the Batak-tumor, is a great geanticlinal dome, traversed by an arcuate section of the Semangko-rift Zone (see fig. 15). The northern part of the Barisan Range, in Atjeh, is the most complicate portion, broken into a number of block-mountain structures. The Leuser Block and the West Mountains occupy a position on the West flank, comparable with that of the Benkulen Block in the South.<br />
The Barisan Range forms a section of the volcanic inner arc of the Sunda Mountain System. It is separated from the old Sunda landmass by the oil-bearing basin of East Sumatra. This downwarp of the pretertiary basement complex is the "back- deep" of the Sunda Mountain System. This back- deep is filled by neogene sediments which were folded in plio-pleistocene time.<br />
During or after the main phase of folding a dome was elevated in the centre of this back deep, now forming the Tigapuluh Mts. Also in other places the basement complex is exposed in the cores of the tertiary anticlines (Limau Mts., Duabelas Mts., Bukit Pendopo). The anticlines were eroded to baselevel during their folding, so that a primary peneplain of subaerial erosion truncates the tertiary anticlines. The pre-tertiary basement complex of the Sunda Land crops out at some places in the alluvial marshes along the East coast. These are in fact former islands in the Sunda Shelf Sea, which are now connected with the mainland of Sumatra by the deposition in subrecent time. Physiographic ally the back deep of the Sunda Mountain System now forms a low land in the Sumatra section, whilst in other sections, with less strong sedimentation in neogene time, it is represented by a sea basin; for instance, the Andaman Basin of the Mergui section, North of Sumatra.<br />
West of the Barisan Range stretches the interdeep of the Sunda Mountain System, which forms the sea basin between Sumatra and the island-festoon to the West of it. The latter represents the non-volcanic outer arc of the Sunda Mountain System. Because it is not connected by a land surface with the central Sunda Land, like Sumatra, the physiography of this island-festoon in the Indian Ocean will be described under the heading of the circum- Sunda Archipelagoes.<br />
<br />
<b>2.4. JAVA AND MADURA</b><br />
These islands, like Sumatra, are connected with the Sunda Shelf-sea, so that they belong physiographically to the central Sunda Land. They will be described in this chapter under the heading of the Sunda Shelf area. Geologically, however, they belong entirely to the young tertiary mountain systems around the pre-tertiary Sunda Land, forming, like Sumatra, a section of the Sunda Mountain System.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-2FNPilKqozg/U_BR6VpuvxI/AAAAAAAA0fs/CeY_SzU5VPY/s1600/physiography-java.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-2FNPilKqozg/U_BR6VpuvxI/AAAAAAAA0fs/CeY_SzU5VPY/s1600/physiography-java.jpg" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 2.4.1. Physiographic sketchmap of Java and Madura, modified from van Bemmelen (1949) using satellite images (above) and an example of a satellite image based relief map by <a href="http://www.maphill.com/">Maphill</a> (below) .</td></tr>
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Java has an area of 127,000 sq km and Madura measures 4000 sq km, being in total nearly four times as large as the Netherlands 1). Java is about 1000 km long and Madura 160 km. The main structural elements of the island are the geanticline of South Java extending along the southern half of the island, and the geosyncline of North Java, occupying its northern half. From Serna rang eastward this geosynclinal basin becomes considerably wider, bifurcating into a northern branch, which occupies the hilly country of Rembang and Madura, and a southern branch which comprises the Kendeng Ridge and Strait Madura. The geanticline of South Java is less regularly built than the Barisan Range, which forms the geanticlinal backbone of Sumatra. This is because the top part of the geanticline of Java has broken down, now being physiographically a depressed zone with island-like elevations of the former geanticlinal crest. The southern flank of the Java-geanticline is formed by the Southern Mts. These are crustal blocks, tilted towards the Indian Ocean, like the Benkulen Block in South Sumatra. In the middle part of Java the Southern Mts have disappeared below sea level, so that here the median depression is bordered by the Indian Ocean. A similar phenomenon has been observed in North Sumatra, where the Semangko depression is bordered by the low- land embayments of Singkil and Meulaboh on the Westcoast. On account of physiographic and structural differences four sections can be distinguished:<br />
1.<span class="Apple-tab-span" style="white-space: pre;"> </span>West Java (West' of Cheribon)<br />
2.<span class="Apple-tab-span" style="white-space: pre;"> </span>Central Java (between Cheribon and Semarang)<br />
3.<span class="Apple-tab-span" style="white-space: pre;"> </span>East Java (between Semarang and Surabaja)<br />
4.<span class="Apple-tab-span" style="white-space: pre;"> </span>The eastern spur of Java (Neth. "Oosthoek") with the Strait of Madura and the Island of Madura.<br />
<br />
2.4.1.<span class="Apple-tab-span" style="white-space: pre;"> </span>WEST JAVA<br />
The trendlines, typical for Java, begin east of the Wijnkoops Bay. The westernmost part of the island, called Bantam, has in some respects more affinities with the Strait Sunda area and Sumatra, than with Java.<br />
In NW-Bantam some volcanic complexes rise above the northern lowland plain of Java: Firstly, the Gede (595 m) with the harbour of Merak at its western foot, and secondly the Danau complex with the cones of the Karang 0,778 m) and the Pulasari 0,346 m). These volcanoes belong to the eruptive activity which accompanied and followed the en- gulfment of the Sunda Strait, like the volcanoes of Prinsen Island, Krakatau group, Sebesi, Sebuku, Sangiang ("Dwars-in-de-weg") in the Sunda Strait, and the volcanoes Tanggamus, Ratai, Betung, and Radjabasa on the Sumatran border of this strait. The Lampong Districts and Bantam at both sides of the Sunda Strait are covered by acid, pumiceous tuffs, called respectively Lampong tuffs and Bantam tuffs, which are at least partly eruption products of cataclysmic outbursts in the Sunda Strait area during its engulfment in plio-pleistocene time.<br />
The Udjung Kulon Peninsula (Pajong, 480 m) and the Hondje Ridge (620m) in SE Bantam were separated from Java by the sea in pliocene time, forming presumably the southeastern end of the Barisan Range of Sumatra. The connecting link between the Semangko Bay at the Sumatran coast and the Welkomst Bay at the Java coast broke down in the plio-pleistocene phase of diastrophism. It is at present the more than 1000 m deep southern part of the Sunda Strait.<br />
The Hondje Ridge is connected by a low ridge of pliocene strata with the Bajah culmination in SE Bantam. This uplift forms a transition between the structural trendlines of the Sunda Strait area and those of Java proper. The Sunda Strait area is supposed to have been a large culmination in upper tertiary time, which formed a threshold between the geosynclinal basins of eastern Sumatra and of northern Java.<br />
It is bounded on its northern side, like the Strait Sunda area, by a crescent of young volcanoes: Malang (909 m), Endut 0,297 m), Halimun I (1,929 m), Halimun II 0,750 m).<br />
The lowland plain of NE Bantam, North of the Bajah dome and East of the volcanic Danau complex, consists of slightly folded young tertiary strata, overlain by quaternary tuffs and alluvial deposits. The trend of the folds is N-S, which is at right angles to the WoE trend of the folds in the geosyncline of North Java. This N-S direction appears also in the arrangement of the coral reef islands off the North coast of Java, North of Tangerang.<br />
The proper trendlines of Java begin East of the connecting line between these "Duizend" Islands (Thousand Islands) and the Wijnkoops Bay.<br />
The part of West Java between this line and Cheribon has a width of 150-175 km. It is formed by an alluvial lowland plain in the North and a mountainous belt in the South, which comprise respectively t and!' of the cross section.<br />
The plain of Batavia is about 40 km wide, extending from Serang and Rankasbitung in Bantam to Cheribon. It consists largely of alluvial river deposits and lahars (mud flows) from the volcanoes in the hinterland, with occasional exposures of slightly folded marine tertiary sediments.<br />
To the South follows a complex belt of hills and mountains, also about 40 km in cross section, which extends from the Djasinga area near the boundary of Bantam to the Pemali River and Bumiaju in Central Java.<br />
This belt might be called the Bogor Zone, after the main place Bogor (Buitenzorg) situated in its western part. It is an anticlinorium of strongly folded neogene strata with many, intrusions of hyp- abyssal volcanic necks, stocks, bosses, etc. (e.g. the conspicuous Sangabuana Complex, West of Purwakarta). Its western part extends west to east, whilst its eastern part assumes a more WNW-ESE direction, giving it a slightly arcuate outline, convex to the North. Its eastern part is crowned by young volcanoes, such as the Sunda Complex, North of Bandung (highest summit the Bukittunggul, 2,209 m), the Tampomas (1,684 m), and the Ciremai (3,078 m),<br />
The third physiographic unit is a longitudinal belt of intermontane depressions, from which emerge island-like ridges of tertiary strata. This belt has generally a width of 20-40 km. It extends from the Wijnkoops Bay in the East, via the Tjimandiri Valley (with Sukabumi, 600 m), the up- land plains of Cianjur (459 m), Bandung (715 m), and Garut (711 m), to the Citanduy Valley (with Tasikmalaja, 351 m) in the West, ending in the Segara Anakan (or "Kinderzee") at the South coast of Central Java.<br />
This depressed zone might be called, after the main town in it, the Bandung Zone. It is structurally the top part of the geanticline of Java, which has broken down after or during its arching up at the end of the Tertiary. In some respects it can be compared with the Semangko Zone on the crest of the Barisan geanticline in Sumatra. However, the latter is only 5-15 km wide, whereas the Bandung Zone attains a width of over 40 km. This is because the Semangko Zone is only a belt of rifts and graben on the top of the Barisan geanticline, whereas the Bandung Zone comprises the top part as well as the North flank of the Java geanticline.<br />
The border between the Bogor Zone and the Bandung Zone is capped by a series of quaternary volcanoes (Kendeng, 1.370 m; Gagak, 1.511 m: Salak, 2,211 m; Pangrango-Gedeh, resp. 3.019 m and 2.958 m; Sunda Complex. North of Bandung, with Burangrang, 2.064 m, Tangkuban Prahu, 2,076 m, and Bukittunggul, 2,209 m, Tjalantjang, 1,667 m; Tjakrabuwana, 1,721 m).<br />
The border between the Bandung Zone and the Southern Mountains is also marked by a series of volcanoes (Kendeng, 1.852 m; Patuha, 2,429 m; Tilu, 2,040 m; Malabar. 2.321 m; Papandajan, 2,622 m; Tjikoraj, 2,821 m). The Garut section of the Bandung Zone is flanked by two transverse rows of volcanoes, one separating it from the Bandung plateau (with the Guntur, 2,249 m, and the Mandalawangi, 1.663 m), and the other forming a divide with the Citanduy Valley (with the Galunggung. 2,241 m, Telagabodas, 2,201 m, and the Sedakeling, 1.676 m). The extinct Sawal volcano (1,733 m) occupies an isolated position amidst of the Cidanduy Valley, North of Tasikmalaja.<br />
The Bandung Zone is partly filled by young volcanic and alluvial deposits, but these upland plains are occasionally interrupted by hills and ridges of tertiary rocks. Among these are, for instance, the ridges of lower tertiary and Miocene strata near Sukabumi and the oligo-miocene Radjamandala ridge, South of Tjiandjur. A morphological analysis of this part of the Bandung Zone was given by PANNEKOEK (1946, Map A & C).<br />
In its eastern part, similar island-like mountains rise above the marshy lowlands of the Citanduy, e.g. Mt Sangkur (365 m) near Bandjar at the western side of the great Lakbok swamp, and the low mountain ridge extending from Wonoredjo at the NE side of this swamp in a southeastern direction to Maos at the Seraju River. This ridge consists of lower neogene strata and volcanic rocks. It is bordered at its southwestern side by the railroad Meluwung-Sidoredjo-Maos, and at its northeastern side by the highroad Wonoredjo-Majenang-Jatilawang. Due to the presence of this ridge the eastern end of the Bandung depression zone bifurcates; the southern and widest branch follows the Citanduy Valley to the Segara Anakan, whilst a narrow branch follows the alluvial plain of the Tjikanring and the intermontane valley of Karangputjung- Lumbir-Karangajam-Wangon. The latter valley separates the median ridge from the southeastern end of the Bogor anticlinorium. This median ridge in the eastern end of the Bandung Zone might be called after its highest summits the Kebanaran (360 m) or Kutadjaja (339 m) ridge. It is arranged "en echelon" with the South-Seraju Range of Central Java. which is to be discussed in the next paragraph.<br />
The fourth physiographic unit of West Java is formed by the mountain land of South Priangan, called Southern Mountains. This unit extends from the Wijnkoops Bay to Nusa Kembangan Islands, South of the Segara Anakan near Tjilatjap. It has an average width of 50 km, but for its eastern end, which narrows down to some kilo metres in the Island of Nusa Kembangan. As a whole it represents the southern flank of the Java geanticIine, being a crustal block which has been tilted some degrees to the South. Physiographically three parts can be distinguished. The western part, called the Jampangs, has been described morphologically by PANNEKOEK (1946). Its erosional surface rises gradually from the Indian Ocean to a height of about 1000 m, with some resistant volcanic necks of greater altitude (Mt Malang 1.305 m) and then breaks down with a fault or flexure to the Bandung Zone.<br />
The central part or Pengalengan section is the highest one. It is crowned by several extinct volcanoes (e.g. Kantjana, 2,182 m) and then breaks down by stepfaults and flexures to the Bandung Zone. The transition between the elevated edge of the central part of the Southern Mts and the Bandung Zone. is masked by the series of quaternary volcanoes already mentioned with the Bandung Zone.<br />
The eastern section of the Southern Mts, called KarangnunggaI section, resembles again the Djampang section, being a rather low mountain land, seldom reaching altitudes of over 1000 m (Bongkok, 1,144 m). This difference in altitude between the central part on the one hand, and the Djampangs to the West and the Karangnunggal area to the East on the other hand, must also have existed in the Neogene, for the upper-miocene transgression of the Bentang-Beser Series did not submerged entirely this central part, which was an island at that time.<br />
<br />
2.4.2.<span class="Apple-tab-span" style="white-space: pre;"> </span>CENTRAL JAVA.<br />
The central part of Java is much narrower than West- and East Java, measuring only 100-120 km across. This is because the Java Sea extends inland with a broad bight between Ceribon and Semarang, so that the northern lowland is more restricted or even absent, and because the Southern Mountains disappear for the greater part below sea level between Nusa Kembangan and the Southern Mountains of East Java.<br />
The northern coastal plain of Central Java has its maximum width (40 km) South of Brebes, where the Pemali Valley separates the Bogor Range of West Java from the northern mountains of Central Java. Farther East it narrows to about 20 km South of Tegal and Pekalongan, until it disappears completely East of Pekalongan where the headland of the mountains reaches the coast. Between Weliri and Kaliwungu another fertile alluvial stretch is formed by the delta of the Bodri River. The mountainland of Central Java is formed by two geanticlinal culminations, the North- and the South-Seraju Range.<br />
The North-Seraju Range forms the connecting link between the Bogor Range in West Java and the Kendeng ridge in East Java (to be discussed in the next paragraph). The South-Seraju Range is a new element rising from the longitudinal Bandung-depression of West Java. The North-Seraju-Range has a width of 30-50 km. Its western end is capped by the Slamet volcano:~•(3,428 m), and its eastern part is covered by the young volcanic products of the Rogojembangan Mts (2,177 m), the Dieng complex (Prahu, 2,565 m), and the Ungaran (2,050 m). The border- line with the Bogor Range of West Java runs across Prupuk-Bumiaju-Ajibarang.<br />
Between the North- and the South-Seraju Range there is again a longitudinal depression, the Seraju Zone, in which are situated the places Madjenang, Adjibarang, Purwokerto, Bandjarnegara, Wonosobo.<br />
Between Purwokerto and Bandjarnegara the Seraju Zone has a width of 15 km; East of Wonosobo it becomes broader, but here the depression is partly filled and masked by the young volcanic cones of the Sundoro (3.155 m) and Sumbing (3,371 m). Orographically it appears again in the plain of Temanggung-Magelang, which is the first of a series of intermontane plains in East Java.<br />
The South-Seraju Mts consist of a western and an eastern part. The western one (with Kabanaran 360 m) might be described as an elevation in the Bandung-depression Zone of West Java, or as a new structural element belonging to Central Java. It is separated from the Bogor Range by the Majenang plain and the upper course of the Cihaur and Pasir.<br />
The eastern part of the South-Seraju Range forms a geanticlinal elevation in this depression zone of Bandung, comparable with the culmination of the Bajah Mts at its western end. The eastern part of the South-Seraju Range is completely separated from the western one by the Djatilawang Valley. It starts near Adjibarang as a simple, narrow anticline, transversely cut by the Seraju River. East of Banjumas this anticline develops into an anticlinorium of some 30 km width in the Lukulo (Loh Ulo) area, South of Bandjarnegara (Midangan 1,043 m). The eastern end of the South-Seraju Range is formed by the more or less independent dome of the West-Progo Mts (1,022 m), between Purworedjo and the Progo river. The Coastal Plain of South Central Java is 10-25 km wide. This part of the South coast forms a sharp contrast with the rocky South coasts of West and East Java, lying not more than 10 m above sea- level. Three shore bars with dunes of 5-15 m height and 100-500 m width run parallel to the coast, the youngest one still being subjected to changes. This low coastal stretch joins on to the Bandung Zone of West Java. It is interrupted in the middle part by the Karangbolong Mts (475 m), which are the physiographical and structural equivalent of the Southern Mts in West and East Java. Apart from this relic, these Southern Mts have subsided below sealevel between Nusa Kambangan and the mouth of the Opak river.<br />
<br />
2.4.3.<span class="Apple-tab-span" style="white-space: pre;"> </span>EAST JAVA<br />
East of the line Semarang-Yogyakarta a number of parallel zones can be distinguished, the southern ones forming the direct continuation of the zones of West and Central Java, whereas the northern ones are new physiographic and structural elements.<br />
In the North the Murjo or Muriah Massif (1,602 m), known for its leucite-bearing rocks, and the andesitic Lasem volcano (806 m) are situated off- side the main series of Javanese volcanoes.<br />
The Muriah is now connected with Java by the alluvial plain of Semarang-Demak-Kudus-Pati- Djuwono-Rembang, but during the Holocene it was still an island (Present shift in the shoreline near Demak 30 m per year).<br />
The hilly district of Rembang consists of a number of more or less East-and-West trending ridges, alternating with alluvial plains (near BIora, Djodjogan, and along the lower course of the Solo). This Rembang anticlinorium has an average width of 50 km, the highest tops reaching about 500 m above sealevel (Gading 535 m, Tungangan 491 m). The hills almost reach the North coast, from which they are separated by narrow sandy beaches with dunes.<br />
The flat topped ridges near Tuban, consisting of reef limestones, look from the sea like gigantic coffins.<br />
The Rembang hills are separated from the Kendeng ridge by a synclinal zone, called Randublatung Zone, which can be traced from Semarang via Purwodadi-Randublatung-Ngimbang to Wonokromo near Surabaja.<br />
Near Randublatung and Ngimbang it has a cross section of some kilometres only, being wider at those places where it links up with the lowland plains between the ridges of Rembang (e.g. the lower Solo Valley). The structural importance of this synclinal zone follows from the fact that the direction of the folding movement in the Rembang area is generally southward, whereas the Kendeng strata have been pushed northward.<br />
The Kendeng Ridge or Kendeng anticlinorium is the eastward continuation of the North-Seraju Range of Central Java. It has a length of 250 km and a width of 40 km South of Semarang, narrowing down eastward to 20 km. Its height is seldom more than 500 m. Near Ngawi an axial depression occurs. where the ridge is transversely cut by the Solo River. thus being divided into a western and an eastern part.<br />
The eastern part attains its maximum width (30 km) near the small Pandan volcano (897 m) which pierces the tertiary strata at its southern rim. From here on the height and width of the Kendeng Ridge gradually decrease eastward. its anticlines disappearing near Modjokerto one after the other under the alluvial deposits of the Brantas delta. till only" two anticlinal ridges of about 10 km width reach the Strait of Madura near Surabaja.<br />
Between the Kendeng Ridge and the eastern Southern Mountains a depression zone occurs. which is the physiographical and tectonical equivalent of the Bandung Zone in West Java. The latter bifurcates in Central Java into the Seraju Zone and the southern coastal plain of Central Java. thus embracing the South-Seraju Range. In the Progo Valley near Djokjakarta both branches unite. forming the wide Solo Zone of East Java. Like the Bandung Zone this longitudinal depression of East Java is partly filled and capped by a series of young volcanoes. It can be subdivided into three parallel strips. viz. the Ngawi Subzone. the Solo Zone (sensu stricto) and the "BIitar Subzone.<br />
The Ngawi Subzone is the synclinal depression bordering the Kendeng Ridge at its southern side. It begins near Simo and can be considered as the eastward continuation of the Seraju Zone of Central Java. It can be traced via Sragen and Ngawi to Djombang where it links up with the alluvial plain of the Brantas delta. Structurally, however, this Ngawi Subzone has to be traced eastward across the saddle between the Penanggunan 0.653 m) and the Andjasmoro Mts via Bangil to the North coast of the eastern spur of Java ("Oosthoek"). The Solo Zone (sensu stricto) is formed by a series of giant quaternary volcanoes with intermontane plains,beginning with the Sundoro (3.135 m) and Sumbing (3.371 m) in Central Java:<br />
The Brantas River is, after the Bengawan Solo, the second longest river of Java. It rises on the southern slope of the Andjasmoro; flows southward through the Malang Plain and bends sharply westward near Kepandjen; after a westward stretch of about 70 km it turns to the North near Tulungagung till it reaches the Kendeng Zone. which is partly covered by its alluvial deposits in the area of Djombang and Modjokerto; here the river takes an eastward course. Near Modjokerto the Brantas delta is reached and the river bifurcates into the Mas (emptying near Surabaja) and the Porong (reaching the Strait of Madura near Bangil). The present mouth of the Porong is situated at a distance of only 40 km from the head waters of the river." so that an almost closed noose is formed round the volcanic complex of the Andjasmoro Mts- Kelud - Kawi. The catchment area measures about 11.000 sq km, while the silt load of the Brantas River is 1.3 kg per cbm, less than half of the load of the Solo River which amounts to 2.75 kg per cbm. The shift in the coast line amounts to 7 m per year near the mouth of the Brantas and 9-15 m near the mouth of the Porong. In historical times (lOth century) the Brantas mouth still was a wide estuary, forming a good natural harbour.<br />
South of the zone of quaternary volcanoes (Solo Zone s.str.) a third subzone, called Blitar Subzone, can be distinguished. in which the places Wonogiri. Balong, Tulungagung and Blitar are situated.<br />
The Blitar Subzone is bounded on the South by the Southern Mts of East Java. Like those of West Java. the Southern Mts of East Java are in general an elevated block tilted oceanward in which the erosion has been rejuvenated. The northern border is marked by a complicated escarpment. The maximum width of these Southern Mts is 55 km South of Surakarta, whilst south of Blitar they measure only 25 km across.<br />
The eastern part (between Opak and Patjitan), consisting partly of limestones with typical Karst- phenomena. is called "Duizend" (Thousand) Mts or Gunung Sewn (See morphological analysis by LEHMANN. 1936). Between Patjitan and Popoh the northern part of the Southern Mts consists of older volcanic deposits; here also remnants of the pre- quaternary peneplain can be observed (Gembes 1.243 m). The southern part is covered by the limestones of the Thousand Mts. The narrow stretch South of the Brantas River consists mainly of limestones, with steep abrasion cliffs along the Indian Ocean.<br />
4.THE EASTERN SPUR ("OOSTHOEK") AND MADURA<br />
Madura (area 4,382 sq km, length 160 km, max. width 38 km, max. height 471 m) forms the east- ward extension of the Rembang Hills. Its seperation from Java possibly occurred in 80 A.D. accor- ding to STUTTERHEIM (1929, p. 22, note 1). TheStrait of Madura, having nowhere a depth of more than 100 m and a maximum width of 68 km, forms the continuation of the Kendeng Ridge which plunges eastward under the Brantas delta. Eastward this strait passes into the Bali Sea which belongs to the backdeep of the Lesser Sunda Islands. The narrow North coast of the eastern spur shows folded plio-pleistocene deposits, capped by small volcanoes. From East to West the following elements can be distinguished: Bangil anticline, Semongkrong tuff hill (84 m), Hills of Probolinggo (38 m, 104 m), Lurus volcano (539 m), Ringgit- Beser Mts (resp. 1,250 m, 1,303 m), Baluran volcano (1,247 m). This coastal stretch represents the eastward extension of the southern margin of the Kendeng anticlinorium (which comprises Pandan volcano, the anticlines of Jombang and Mojokerto, and the Penanggungan volcano).<br />
South of this narrow coastal stretch follows the eastward continuation of the Ngawi Subzone, which can be traced via Tampung plain (between Bangil and Lawang), and Grati Lake (between Semongkrong and Tengger) to the plains of Probolinggo and Bondowoso.<br />
Then comes the Solo Zone (sensu stricto) which is composed of a series of volcano complexes and intermontane plains, just as in East Java. Table 4.<br />
The Blitar Subzone of East Java extends east- ward by way of Kepandjen and Turen to Pasirian. Here the lowland of Lumadjang-Djember reaches the South coast at Puger, due to the absence of the Southern Mts, and by the same reason the lowland of Rogodjampi reaches the South coast at Gradjogan.<br />
The Southern Mountains in the eastern spur of Java are discontinuous, consisting of three more or less isolated parts. The western part (South of Turen), about 25 km wide, is directly connected with the Southern Mts of East Java. Between Pasirian and Turen the Southern Mts are interrupted by the lowland of Lumadjang. However, the island of Nusa Barung (South of Puger) belongs structurally to them, forming a link with the next part of the Southern Mts between Puger and the river Baru (Betiri, 1,223 m). South of Rogodjampi the lowland again reaches the South coast, from which the isolated Pumpangpitu hill rises to a height of 489 m. Finally, the eastern-most fragment of the Southern Mts in this section of Java is represented by the Peninsula of Blambangan or Purwo (360 m), linked to the main island by an alluvial isthmus, 22 km wide. This breaking down of the Southern Mts continues eastward in Bali and Lombok, where the parts are separated by sea- straits in stead of alluvial plains.<br />
<div>
<br /></div>
Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.com2tag:blogger.com,1999:blog-7274248385186471083.post-68857879215787263852014-08-09T05:42:00.001-07:002014-08-23T08:55:14.735-07:001.INTRODUCTION<div class="MsoNormal" style="margin-bottom: 6pt;">
<span style="line-height: 19.200000762939453px;">Physiography (also known as geosystem or physical geography) </span><span style="line-height: 19.200000762939453px;"> is one of the two major sub-fields of geography.It is a branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, hydrosphere, biosphere, and geosphere, as opposed to the cultural or built environment, the domain of human geography.</span><br />
<span style="line-height: 19.200000762939453px;"><br /></span>
<br />
<span style="line-height: 19.200000762939453px;">Within the body of physical geography, the Earth is often split either into several spheres or environments, the main spheres being the atmosphere, biosphere, cryosphere, geosphere, hydrosphere, lithosphere and pedosphere. Geomorphology, hydrology, biogeography, climatology, meteorology, pedology (soil science), paleogeography, coastal geography, oceanography, quarternary science, landscape ecology, geomatics, and environmental geography are parts of physiography. The following sections discuss the majority of these subjects in Indonesia and its vicinity.</span><br />
<div style="line-height: 120%;">
<b><br /></b></div>
<div style="line-height: 120%;">
<span style="font-family: inherit;"><b>1.1. SITUATION
AND EXTENT </b><o:p></o:p></span></div>
</div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<span style="font-family: inherit;">The main topic
of this book is the geology of the Indonesian Archipelago which extend between 6<sup>o</sup>08'northern and 11<sup>o</sup>15'southern latitude, and between 94<sup>o</sup>45'and
141<sup>o</sup>45' eastern longitude. This archipelago, however, is not a regional
unit in a geo-tectonical sense. It forms the central part of the great
archipelago which extends between SE-Asia and Australia, and between the
Pacific and the Indian Ocean. <o:p></o:p></span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<span style="font-family: inherit;">The East Indian
Archipelago in this sense comprises also: the Philippine Islands, Malaysian Northwest
Borneo (Sabah and Sarawak), Brunei, Papua New Guinea, Christmas Island and the
Andaman and Nicobar Islands. </span><o:p></o:p><br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-zUCNmokyNs8/U-Y6LnrTKhI/AAAAAAAA0a4/orn5JgiGIR0/s1600/Eastern+hemisphire+of+the+globe.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-zUCNmokyNs8/U-Y6LnrTKhI/AAAAAAAA0a4/orn5JgiGIR0/s1600/Eastern+hemisphire+of+the+globe.jpg" height="150" width="200" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.1. Eastern hemisphere geographic grid</td></tr>
</tbody></table>
<br /></div>
<div class="MsoNormal" style="margin-bottom: 6pt;">
<div style="line-height: 120%;">
For a better
insight in its geological evolution it is necessary to consider this
archipelago in its larger sense as the entire realm of islands extending
between 21<sup>o</sup> northern and 11<sup>o</sup> southern latitude, and
between 92<sup> o</sup>15' and 150<sup> o</sup>48' eastern longitude (Fig. 1.1). Moreover,
the Malay Peninsula forms structurally a part of the Sunda Shelf area, so that
a short discussion of its geology will be necessary. The total land area of the
Southeast Asian Archipelago sensu largo amounts to more than 2,800,000 sqkm, which are
divided among the political units, islands, and island groups as follows:</div>
<br />
<ul>
<li style="line-height: 120%;"><span style="line-height: 120%;">Indonesia 1,904,569 km2</span><span style="line-height: 120%;"> </span></li>
<li><span style="line-height: 120%;">Papua New Guinea </span><span style="line-height: 19.200000762939453px;">462,840 km2</span></li>
<li><span style="line-height: 19.200000762939453px;">Philippines: 298,170 </span><span style="line-height: 19.200000762939453px;">km2</span></li>
<li><span style="line-height: 19.200000762939453px;">Northwest Borneo (East Malaysia & Brunei): 198,847 </span><span style="line-height: 19.200000762939453px;">km2</span></li>
<li><span style="line-height: 19.200000762939453px;">Timor Leste: 15,410 km2</span></li>
<li><span style="line-height: 19.200000762939453px;">Christmas Island: 161 </span><span style="line-height: 19.200000762939453px;">km2</span></li>
</ul>
<span style="line-height: 19.200000762939453px;">The total land area covers 2,879,997 km2.</span></div>
<div class="MsoNormal" style="margin-bottom: 6pt;">
<span style="line-height: 120%;">Besides these 19 large islands, there are many thousands of smaller islands, ranging in size from several
thousands of square kilometres to mere isolated rocks. Indonesia itself has </span><span style="line-height: 19.200000762939453px;"> 13,466 islands listed in Wikipedia. </span><span style="line-height: 120%;">The physiographic
position of the SE Asian Archipelago is shown in fig. 1.2.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<o:p></o:p><br />
<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-cNL-UMQBCEI/U-YhITr5n1I/AAAAAAAA0ao/R_09hovpppY/s1600/Eastern+hemisphire+of+the+globe.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-cNL-UMQBCEI/U-YhITr5n1I/AAAAAAAA0ao/R_09hovpppY/s1600/Eastern+hemisphire+of+the+globe.jpg" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.2. Eastern hemisphere of the globe</td></tr>
</tbody></table>
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The
cartographic basis for the geological maps of the East Indies has been provided
by the excellent work of the Topographical Survey of the Netherlands Indies.
The summary in the work of the Topographical Survey in the Netherlands
Indies has been given by SCHEPERS (1941). During the 2nd World War the allied geographical
section of the Southwest Pacific area issued a number of Terrain Studies on Papua,
the eastern part of Indonesia and the Philippines, in which a wealth of
geographical, ethnological and other data are collected, illustrated by
excellent maps and air photographs. These days satellite images are available from public domain such as Google earth (Fig. 1.2). Higher resolution images are also available from several commercial, research and governmental institutions.<o:p></o:p><br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-Vjgb5Ts1p2A/U-Z8SFVBgCI/AAAAAAAA0bo/WsDKutklZ7c/s1600/indian-archipelago.JPG" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img alt="" border="0" src="http://4.bp.blogspot.com/-Vjgb5Ts1p2A/U-Z8SFVBgCI/AAAAAAAA0bo/WsDKutklZ7c/s1600/indian-archipelago.JPG" height="496" title="Fig. 3. Indian Archipelago" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.3. SE Asian Archipelago (darker color) as treated in this book. The brown outline shows Indonesian border.</td></tr>
</tbody></table>
<span style="line-height: 120%;">The area
discussed in this book, with the major political boundaries, appears on fig. 3. The red outline shows Indonesian maritime boundaries in general.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<span style="line-height: 120%;">The combined outline map of Europe, USA and Indonesia (fig. 1.4)
demonstrates the dimensions of the latter, which should be kept in mind during
the study of its geology. Total Area of Indonesia is 1,919,440 sq km (Land Area: 1,826,440 sq km; Water Area: 93,000 sq km).</span><br />
<o:p></o:p><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-meXrLLo27yg/U-ZJgQO30_I/AAAAAAAA0bI/eQwflIDvrA8/s1600/Area-size-comparison-with-US-Europe.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-meXrLLo27yg/U-ZJgQO30_I/AAAAAAAA0bI/eQwflIDvrA8/s1600/Area-size-comparison-with-US-Europe.jpg" height="400" width="300" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.4. Areal comparison of Indonesia to USA (above) and to Europe (below) </td></tr>
</tbody></table>
<b style="line-height: 120%;">1.2. DENOMINATION</b></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
This book deals
with the complex archipelago between SE-Asia and Australia. We might call it
the "Australasiatic Archipelago" as was done by the SARASIN'S, or the
"Indo-Australian Archipelago" (ZEUNER, 1943). However, these are
somewhat uncommon names, and it is not clear that the Philippine Islands would
belong geologically to this group. The term "Indian Archipelago" is
easier to pronounce, but it neither clearly implies the Philippine Islands, nor
Papua. Nevertheless, because of its shortness, this expression will often be
used in this book for the whole of the island-system between the continents of
Asia and Australia. The East Indies were called "Indonesia" by LOGAN
in 1850, and by BASTIAN in 1884; this name has often been used in a political
sense, but also as a geographical term in scientific papers. In August 1945, the people in this area have declare their independence and since October 1948
"Indonesia" became the official name for the Netherlands East Indies.
The name "Insulinde" was created for the East Indies by the author
DOUWES DEKKER (Multatuli) in 1860. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The term
"Malayan Archipelago" has often been used for the East Indies and the
Philippine Islands. However, New Guinea (Papua), not being inhabited
prehistorically by Malayans, does not belong to this unit. This name seems to
be inadequate as a name for the whole area, although it is a suitable name for
the belt of islands between the continent of Asia and New Guinea. The name
"Sunda Archipelago" also has a restricted meaning and should be used
only for the islands grouped on and around the Sunda Shelf area of SE-Asia and
not for the whole region between Asia and Australia, as was done for instance
by CLOOS in his book "Einftihrung in die Geologie" (1936. p. 425).
The name "Sunda Seas" was given by SCHOTT in 1935 to the water areas
between the Strait of Malacca and the line Philippines- Papua. But the Moluccas
lie outside the Sunda area, thus this name is inadequate. These seas between
SE-Asia and Australia are more aptly called the "Austral- Asiatic
Mediterranean" (Winkler Prins Encycl., Vth edit., 1937, Vol. 12. p. 625).
The author decided to call this volume "The Geology of Indonesia and
adjacent archipelagoes", thus laying stress on the Indonesia as the
central area, and indicating that also the neighboring archipelagoes are treated
in it. For simplicity Southeast Asia Archipelago will also be used.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.3. GEO<span style="line-height: 120%;">LOGICAL
IMPORTANCE OF THE SE ASIAN ARCHIPELAGO</span></b></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<span style="line-height: 120%;">The SE Asian Archipelago is the most intricate part of the earth's surface. Even the Caribean Archipelago between North and South America, although bearing a close
resemblance with it in many respects, does not attain such a diversity of forms
and geological structures.</span><br />
<div class="separator" style="clear: both; text-align: center;">
</div>
<span style="line-height: 120%;"><br /></span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-CNclV3R74vg/U-vCcgAwnBI/AAAAAAAA0do/q4d-ENgSO_o/s1600/physiography-seasia.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-CNclV3R74vg/U-vCcgAwnBI/AAAAAAAA0do/q4d-ENgSO_o/s1600/physiography-seasia.jpg" height="315" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.5. Relief map of the Southeast Asian Archipelago and its vicinity.</td></tr>
</tbody></table>
MOUNTAIN
SYSTEMS <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In Indonesian region the interlacing of the Tethys mountain system with the western Pacific
island festoons and the circum-Australian mountain system can be studied. This
archipelago forms the border area between continental nuclei of Asia which
belongs to the northern hemisphere, and the great Gondwana land of the southern
hemisphere. In this archipelago both continental areas are being welded together
by an active process of mountain building. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
One may
distinguish the more or less stable portion of the Sunda Shelf area in the NW,
and that of the Sahul Shelf in the SE. The Sunda area is surrounded by the
circum-Sunda Mountain System, which cuts across the trend lines of the circum-Australian
Mountain System (Fig. 1.5). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The
circum-Sunda System consists of two main parts; its northern portion
(Philippine Islands) belongs to the island festoons along the western Pacific;
its southern portion forms a part of the great Sunda Mountain System, which
extends from the Southern Moluccas to the Bramahputra Valley in Assam. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
This Sunda
Mountain System has a length of about 7000 km, being traceable from the noose
formed by the Banda arcs in the East along the Lesser Sunda Islands, Java,
Sumatra, Andamans and Nicobars, to the Arakan Yorna in Burma, where it meets
the Himalayan System with a sharp angle of intersection. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The Sunda
Mountain System is one of the greatest coherent mountain belts of the world,
comparable in length with the Cordillera de los Andes in South America. Along
its entire length it consists of two parallel belts of mountain arcs, island-festoons
and submarine ridges. The inner one has a volcanic nature whereas the outer one
is non- volcanic. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The circum-Australian
System extends along the central axis of Papua Island, and farther along the
archipelagoes, situated East of Australia, to New Zealand. It may perhaps be
traced along a sub- marine swell between Australia and Antarctica (Macquari
threshold) to the Kerguelen rise in the southern part of the Indian Ocean. An
indistinct branch of the median threshold in the Indian Ocean extends
northeastward, via the Cocos Islands to Christmas Island, South of Java. The
segment between Christmas Island and New Guinea is overlapped by the trendlines
of the above mentioned Sunda Mountain System. Another geotectonic unit is
formed by the mountain system which stretches from the Halmahera group via the
northern part of Papua to the New Britain group.<o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
OCEANIC BASINS<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The
Southeast Asian Archipelago is bordered to the NE and the SW by oceanic
basins. The NE oceanic basin consist of the Philippine Basin and the Carolinan Basin at the Pacific side, and the Indo-Australian Basin at the
side of the Indian Ocean. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The sea basins are
4000-6000 meters deep; however, they are presumably not primeval oceanic
receptacles, but submerged borderlands of Asia and Australia. The Galathea Deep in the west of Philippines trench is 10540 meters deep. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In his 1949 book van Bemmelen wrote: "Vertical
oscillations of large blocks of the earth's crust, attaining a diameter of
thousands of kilometers, may cause the subsidence of such blocks to oceanic
depths or their uplift to high continental plateau. Such epeirogenetic
movements are of another type and of larger extent than the crustal waves or
"Plis de fond" which form mountain ranges and adjoining deeps. The
latter are the expression of the process of mountain building or orogenesis in
a stricter sense. Both, epeirogeny and orogeny are the effect of the endogenic
forces of the crust. Both are at present active in the Indian Archipelago,
causing actual rising and sinking movements, which are accompanied by normal
and deep-focus earthquakes, anomalies of the isostatic equilibrium, and
volcanic activity."<o:p></o:p><br />
<br />
The <a href="http://en.wikipedia.org/wiki/Plate_tectonics">plate tectonics</a> concept, which was introduced in late 1950's (after the publication of van Bemmelen's book) suggests that these oceanic basins developed at the plate margins. The plate movement generate collisions and the oceanic plates in this region subducted underneath other plates. These subductions oceanic plates generated low reliefs. In many parts the collisions are still active and generate earth quakes (Fig. 1.6).The positive relief in Himalaya is caused by a collision of Indian-Australian continent and Asian continent.<br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
SEISMICITY<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-hKfwDMl4zvc/U-aFTkHT_bI/AAAAAAAA0cA/QVETfcJbpLQ/s1600/indonesia-seismicity-usgs.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-hKfwDMl4zvc/U-aFTkHT_bI/AAAAAAAA0cA/QVETfcJbpLQ/s1600/indonesia-seismicity-usgs.jpg" height="200" width="200" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.6. Epicentre distribution in Indonesia (source: USGS)</td></tr>
</tbody></table>
The mountain
belts skirting the continental Sunda and Sahul blocks belong to the most
seismic areas of the world. In Indonesia about 500 earth- quakes per year are
registered (Fig. 1.6). The deep-focus shocks in the Flores Sea are the deepest of their
kind (-720 km). <o:p></o:p><br />
<br />
In 2004 a major earth quake in the Indian Ocean, close to Aceh has killed at least 280,000 people. Further detail of this incident is available in wikipedia (<a href="http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami">Click here for link</a>)<br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br />
<br />
<span style="line-height: 120%;">GRAVITY
ANOMALIES</span><br />
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-kI3YmFq-zDY/U-p0QuWZ1rI/AAAAAAAA0ck/JDvNhx71sz4/s1600/indo-gravity-anomaly.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-kI3YmFq-zDY/U-p0QuWZ1rI/AAAAAAAA0ck/JDvNhx71sz4/s1600/indo-gravity-anomaly.jpg" height="214" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.7. Gravity anomaly map of Indonesia by Sandwell and Smith (2009)</td></tr>
</tbody></table>
The rising
outer arc of the circum-Sunda Mountain System is underlain by an uncompensated
rnountain root, causing considerable negative isostatic anomalies (the negative
anomaly belt of VENING MEINESZ). The anomaly found between Sulawesi and
Halmaheira (-204 millidyne after application of VENING MEINESZ' method of
regional isostatic reduction) is the largest isostatic gravity anomaly thus far
known on the world. Figure 1.7 shows the gravity anomaly in the SE Asian archipelago.<o:p></o:p><br />
<br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
VOLCANISM<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-NpJh0mKlq-Q/U-aE4xiLyZI/AAAAAAAA0b4/Q-Za8u2ESPg/s1600/map_indonesia_volcanoes_usgs.gif" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-NpJh0mKlq-Q/U-aE4xiLyZI/AAAAAAAA0b4/Q-Za8u2ESPg/s1600/map_indonesia_volcanoes_usgs.gif" height="222" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.8. Major volcanoes of Indonesia (USGS, 2001)</td></tr>
</tbody></table>
The inner arcs
of the orogenic systems in the Indian Archipelago are characterized by strong
volcanic activity. The number of active volcanic centres in this area (at least
177) is greater than in any other coherent volcanic region of the world (Fig. 1.8). For
more than twenty years the Netherlands Indies Volcanological Survey has
systematically collected data on this orogenic volcanism. The Directorate of Vulcanology in Bandung is now monitoring the volcanoes and their observations could be found in their <a href="http://www.bgl.esdm.go.id/">website</a>. Its organization was
unique, using Indonesian volcano-observers on permanent observation posts
equipped with concrete refuge tunnels. Volcanic activity occurred in all stages
of the geological evolution of this area. For the older stages the hypabyssal
and abyssal intrusions of igneous rocks can be studied. <o:p></o:p><br />
<br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
CRUSTAL RELIEF<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The differences
of altitude between the mountain ranges and the adjacent deep sea troughs in
the present orogenic belts are enormous. The Emden Deep of -10,830 m in the
Philippine trough is the greatest sea-depth ever measured. The Wilhelmina Range
in New Guinea, now called Jayawijaya Mountain (with the Carstensz Summit of +
5,030 m, and it is called Puncak Jaya now), rises into the zone of perennial
snow in this equatorial area.<br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
STRATIGRAPHY
AND PALEONTOLOGY<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The study of
the stratigraphy in this area has provided many interesting results. All types
of facies are encountered, ranging from continental deposits to abyssal
sediments. Quick changes of facies occur in the vertical section as well as in
the horizontal distribution. The sedimental columns of the tertiary - (idio- ) geosynclines
attain stupendous thicknesses (up to 10,000-15,000 m). The facies of the
sediments reflects the differential vertical oscillations of the earth's crust,
which were partly very rapid (orogenesis), partly slow (epeiro- genesis).
Igneous intrusions have in places penetrated into these sediments changing
their texture and composition, often to such a degree that the exogenous origin
of the deposits becomes practically unrecognizable. The crystalline schists of
the basement complex are often poly-metamorphic rocks, which were subjected to
more than one cycle of mountain building. In some areas, tertiary rocks have
already attained a phyllitic appearance. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The fossil
faunae and florae have been described in numerous paleontological publications
by a great many international specialists, thus greatly advancing this branch
of science. We can mention the faunae of Foraminifera (DOUVILLE, RUTTEN, TAN
SIN HOK, VAN DER VLERK, UMBGROVE, LEROY, etc.), Mollusca (MARTIN, OOSTINGH,
BEETS, VAN REGTEREN ALTENA, etc.), Corals (UMBGROVE, etc.), Vertebrates
(DUBOIS, VON KOENIGSWALD, HOOIJER, etc.), the permian and mesozoic faunae of
Timor, Misool, Ceram, Buru, etc. (WANNER, and many others), the permo-carboniferous
flora of Sumatra and New Guinea (JONGMANS). <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
CONCLUSION<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It appears that
the endogenic forces were extremely active in these areas since the oldest
traces of its history. Moreover, at present the orogenesis still is in full
swing in the crustal tracts between Asia and Australia. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Therefore, the Indian
Archipelago is an extremely favourable object for the study of the tecto-genesis
in relation with allied endogenic phenomena, like igneous activity (volcanism
in its wider sense), seismicity, and isostatic anomalies. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It is to be
expected that most branches of geological science will be advanced by the work
done in this area. The East Indies are an important touchstone for conceptions
on the fundamental problems of the geological evolution of our planet, as has
been pointed out, for instance, by CLOOS in his book "Einfiihrung in die
Geologie" (1936, p. 473). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.4. FAUNA AND
FLORA</b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Much work on
our knowledge of the flora of the East Indies has been done in the past
decades. A review of this work has been written by LAM (1948). Also many
studies on the recent faunae appeared, as appears from the article by DE BEAUFORT
(1948) in the report of the scientific work done in the Netherlands on behalf
of the Dutch overseas territories in the period 1918-1943. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The fact that
the Malay Archipelago separates the Australian continent from the Asiatic
territory makes it a favourable object for the study of faunal migrations. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
As A. R.
WALLACE stated in his classical essay of 1860 (which laid the foundation for the
modern science of zoogeography): "The western and eastern islands of the
Archipelago belong to regions more distinct and contrasted than any other of
the great zoological divisions of the globe. South America and Africa,
separated by the Atlantic, do not differ so widely as Asia and Australia".<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
There is much
truth in this statement. The boundary line between both faunal realms, known as
"Wallace's line", has since been much criticized as well as defended.
Of the more comprehensive zoogeographic publications on the East Indies we
might mention the books by DE BEAUFORT (1926) and RENSCH (1936), and the
symposium by SCRIVENOR et al. (1943). Some other recent papers were written by
ZEUNER (1942, 1943) and MAYR (1944 a&b). In relation with the faunistic
boundaries in this Archipelago, MAYR (1944 a) arrives at the following conclusions:
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
1. Wallace's
line is not the boundary between the Indo-Malayan and the Australian Regions,
but it rather indicates the edge of the area (Sunda Shelf) that was dry at the
height of the pleistocene glaciations.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
2. The
equivalent line along the edge of the Sahul Shelf separates New Guinea and the
Aru Islands from the Moluccas and Kai Islands. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
3. Weber's line
separates the islands in the West on which the Indo-Malayan element is
predominant from the islands in the East on which the Australo-Papuan element
has a numerical superiority. <o:p></o:p><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-jUF10360Myk/U-Zw4qY1deI/AAAAAAAA0bY/Urrhkl_OHHA/s1600/biodeversity-map.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://4.bp.blogspot.com/-jUF10360Myk/U-Zw4qY1deI/AAAAAAAA0bY/Urrhkl_OHHA/s1600/biodeversity-map.jpg" height="372" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.10. Zoogeographic border lines in the Malay Archipelago.</td></tr>
</tbody></table>
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
These
zoogeographic border lines are marked on the map (fig. 1.10) which also shows
clearly the continental shelves as shaded areas. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Besides the
migration of the faunal elements, also the spreading of the plant species
presents many interesting problems.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In this
connection we might mention the papers of BACKER (1929), DOCTERS VAN LEEUWEN
(1936), ERNST (1934) who studied the returning fauna and flora of Krakatau;
JONGMANS & GOTHAN (1935), and JONGMANS (1940 & 1941) who made important
contributions to our knowledge of the late-paleozoic flora in the East Indies;
MUSPER (1938 b, 1939 b) who studied the stratigraphy of tertiary fossil woods; POSTHUMUS
(1945) on the paleobotanical research in the Netherlands Indies; VAN STEENIS
(1934/1936) on the origin of the Malaysian mountain-flora. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
A synopsis of
some important books on pure and applied botany in Malaysia, which appeared in
the period 1921-1939, has been given by VAN STEENIS (1939). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The present
flora of the Indian Archipelago is estimated to comprise at least 24000 species
of flowering plants, belonging to circa 2200 genera.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
No
comprehensive treatments on this huge flora have thus far been published. The
dozens of theories advanced for an explanation of the plant geography of the
Archipelago in the static sense (floristics) and the dynamic sense (history and
origin) have not been based on a complete survey of the flora. A first attempt
consisting of an analysis of the complete flora, based on the statistics of the
genera, led VAN STEENIS (1948) to a delimitation of the area and a distiction
of provinces and districts. This paper is preliminary to a full treatment of
the floristics in volume 3 of the forthcoming Flora Malesiana (see VAN STEENIS,
1947). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.5. CLIMATE </b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the past
decades many important papers have appeared on the climate and meteorology,
especially by the staff of the Royal Magnetic and Meteorological Observatory at
Batavia (now Jakarta). A number of articles were also written in Europe by W. VAN BEMMELEN,
B. BRAAK, S. W. VISSER, and E. VAN EVERDINGEN (see review by BRAAK, 1948).<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The Indian
Archipelago lies completely between the tropics and within the Indo-Australian
monsoon region, which is characterized by high temperatures, high humidity, and
abundant rains. The average sunshine is about 50-70 % in the coastal plains. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-v2n__fb7B4w/U-p-oZ15GoI/AAAAAAAA0c8/KpBiPqGi2EM/s1600/pola-curah-hujan-bmg.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-v2n__fb7B4w/U-p-oZ15GoI/AAAAAAAA0c8/KpBiPqGi2EM/s1600/pola-curah-hujan-bmg.jpg" height="226" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.11. Rain fall distribution in Indonesia (source BMG)</td></tr>
</tbody></table>
Due to the
influence of the continents of Asia and Australia it is the most typical
monsoon region in the world. Figure. 1.11 shows Badan Meteorologi, Klimatologi dan Geofisika (Indonesian Agencey for Meteorology, Climatology and Geophysic) rain fall distribution in Indonesia. D. Kirono has provided the average seasonal rain distribution map of Indonesia from 1979 to 2001 (Fig. 1.12).<br />
<span style="line-height: 120%;"><br /></span>
<span style="line-height: 120%;">The Philippine
Islands are often struck by typhoons. These are cyclones revolving counter
clockwise, which form over the Pacific Ocean, as a rule east of the Ladrone
Islands. Of those passing across the Philippine Archipelago, practically all
occur North of Mindanao, and most of them strike Luzon.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the
southeastern part of the Indian Archipelago the climate is drier due to the
influence of the Australian winter anticyclone. Therefore, a savanne landscape
prevails in the eastern part of the Lesser Sunda Islands. See fig. 1.12. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Elsewhere the
Archipelago is covered by dense forests. Part of these forests have been
destroyed or replaced by man. But even on Java, with a mean population density of many
hundreds pro square kilometre, still 20-30 % of the surface is covered with
forests. In the sparsely populated eastern part of Borneo forests cover more
than 80 % of the land. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-HQd4tMGJ498/U_bbtQBKRkI/AAAAAAAA0g8/U7LFzK3eoAc/s1600/peta_hujan_musiman_indo_1979-2001.gif" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-HQd4tMGJ498/U_bbtQBKRkI/AAAAAAAA0g8/U7LFzK3eoAc/s1600/peta_hujan_musiman_indo_1979-2001.gif" height="640" width="385" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.12 Seasonal changes of rain distribution in SE Asia from 1979-2001 (D. Kirono, Pers Comm, based on the CMAP data set of Xie et al 2003).</td></tr>
</tbody></table>
On the averag<span style="font-family: Times, Times New Roman, serif;">e
two thirds of the</span> Malayan Archipelago is covered by forests. See fig. 8. The
mean annual temperature at sea level is slightly above 26° C (78.8° F) and the
mean humidity is 80 %. The high humidity coupled with moderate heat is
oppressive, but the heat is often tempered by breezes and the living conditions
are greatly ameliorated thereby. Of the larger dwelling places along the coast,
Surabaya has an average temperature of 26.4° C (79° F) and Manila of 26.6° C
(79.9° F), which classes these cities as the hottest. The averages of some
other coastal places are 26.2° C (79.2° F) for Batavia, 25.8° C (78.4 ° F) for Makassar, and Menado, 25.r C (78.3° F) for Balikpapan, and 25.2° C (77.4 ° F)
for Medan. The mean temperature of dwelling places in the mountains more inland
is considerably lower, e.g. at Bandung, at 730 m above sealevel, it is 22.10 C
(71.8° F) and at Tosari, at an altitude of 1,735 m, only 15.9°C (60.6° F),
these climates being more temperate. The decrease of temperature is from 5t to
60 C (10-11° F) for a rise of 1000 m. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Comparing the
climatic living conditions of Indonesia with those in the neighbouring
countries, BRAAK (1929) arrives at the following conclusion:<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
"Although
the heat of the coast plains is far from pleasant, yet the climate compares
favorably with that of the neighboring areas at a greater distance from the
equator. As a matter of fact, the mean annual temperature decreases as the
latitude increases, but the favourable effect of the cooler winter months is
more than counter balanced by the unbearable heat of the hottest summer months.
In this case a more equable temperature distribution over the year is better
than the more usually praised variety. We may conclude from the wet-bulb
temperatures that there exists on both sides of the equator a zone with more
oppressive weather in the hottest month than is found on the equator. The
following figures, which represent the mean wetbulb temperature in the hottest
month, may serve as a proof (in degrees of Celsius): Jakarta 24.4, Shanghai
24.8, Manila 25.2, Hongkong 25.4, Port Darwin 25.4, Nhatrang (Annam) 25.8,
Bombay 25.9, Madras 26,2, Calcutta 26.4, Lahore 26.6, Hanoi 26.9. Whereas it
Jakarta the maximum heat, although disagreeable, can be endured without too
much discomfort, the same cannot be said of most other places. At Calcutta, for
instance, the climate is almost unbearable at the most oppressive time of the
year".<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The 1934
rain-gauge statistics for the Indonesia shows the majority of the
recorded annual rainfall to be more than 2000 mm: <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Palu in the
Moluccas has the lowest average rainfall (557 mm per annum) and Tenjo in
Central Java the highest (7,026 mm per annum). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The average
annual rainfall for the Philippine Archipelago is 2,366 millimeters (94.6
inches). The greatest annual rainfall, 9,038.3 mm, was recorded at the Baguio
weather station in the highlands of Luzon, in 1911. The greatest rainfall at
Baguio for a single period of 24 hours was 1,168.1 mm (46 inches) (SMITH, 1924,
p. 35). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Tropical rains,
generally torrential, though mostly of short duration, are of geological
importance. These, in combination with the high temperature and high humidity,
cause rapid weathering of rocks, resulting in a denudation which is much more
effective than in more tempered climatic zones (BEHRMANN, 1921; SAPPER, 1935). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.6. DENUDATION</b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The main
factors, responsible for a rapid denudation, are the tropical climate and the active
process of mountain building. The high temperature and high humidity cause
rapid weathering of a chemical character, whilst torrential rains cause
leaching and surface erosion. The denudation is promoted by uplift of mountains
and/or unconsolidated sedimentaries. L. M. R. RUTTEN (1917, 1938) collected
some data on rivers of Java and Sumatra and found an annual denudation
considerably above similar figures for rivers of Europe and North America<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Many drainage
basins show values of over 1 mm per annum 1), and in one case, that of the
Pengaron River near Semarang, it amounts to 4 mm. The drainage area of the
Pengaron is only 40 sq km. Here a mean denudation of 1 mm in one day has been
calculated, corresponding with the denudation by the Marne in two centuries.
Such areas on Java with excessive erosion are called "stervende
landen" (dying lands). Recently VAN DUK & VOGELZANG (1948) have
published some.i data on one of these dying lands, the Tjilutung drainage basin
on the SW slope of the Tjarerne volcano in West Java. Measurements on the
erosion were carried out in 1911/1912 and 1934/1935:<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It appears that
the gradually increasing deforestation, reckless cultural methods, and
pasturing after 1917 caused doubled soil erosion. Under the conditions now
prevailing and calculated over the whole area, a soil layer of 10 em depth is
removed in about 50 years for the entire area. However, the erosion is almost
exclusively confined to the most erodable soils from the Miocene marly clays.
According to the values given by RUTTEN (1917), it may be presumed that the
rate of erosion on these soils surpasses that on volcanic soils by about ten
times. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The Cilutung
basin consists for 34 % of quaternary volcanic rocks, 60 % of Miocene breccias,
sandstones, and marly clays (VERBEEK'S m<sub>1</sub>-Formation), and 6 % of
creeping Miocene argillaceous marls (VERBEEK'S m<sub>2</sub>- Formation). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It may be
safely estimated that 90 percent of the eroded material originates from the Miocene
deposits, covering nearly 2/3 of the total area. Hence under' conditions
prevailing at present a loss of arable soil of 10 em depth is to be registered
here in about 35 years. The quantity of bed load in the river has not been
determined, so that the calculated rates of erosion are surely not too high. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Exceptionally
strong floods cause an excessive devastation of the land, as
occurred during the floods on Java in 1861 (KLINKERT, 1917). Heavy showers
are about 60 times more numerous on Java than in Germany, and 11 times more
numerous than in the most rainy southeastern part of the United States of North
America, according to VAN KOOTEN (1927, see COSTER 1938, p. 459). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Therefore, the
maximum water transport of the rivers on Java, and especially of the smaller
rivers, is very much greater than elsewhere in the world, where the rainfall is
less intensive. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The minimum
flow-off in the dry seasons is strongly influenced by the geological
formations. ROESSEL(1941)pointed out, that the "forest-sponge" theory
is no longer up to date. This theory for the regulation of the water run-off in
drainage basins has long been advocated by foresters as an argument for the
preservation of protective forests in the catchment areas. The forests and the
vegetation in general are certainly of importance for the maximum run-off after
heavy rainshowers, but the minimum flow-off depends in the first place on the
permeability of the underground and the infiltration-capacity of the surface.
ROESSEL found no clear relation between the minimum run-off in the dry season
on the one hand, and the percentage of protective forests in the catchment area
on the other for several drainage basins in the young vol- canic area of the
Andjasmoro Mts in East Java. On the other hand, there is a conspicuous difference
in the minimum run-off of the dry seasons between the young volcanic areas and
the young-tertiary marl areas of Java. Many of them have completely dry rivers
in the dry season, and this is independant of the fact whether or not forests
are present. This shows that there is no direct relation between forests and
drought in the dry season, but the relation between geological formation and
drought is evident. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-jDZ3cxXcGA8/U_i3DH_4uvI/AAAAAAAA0h0/Fm5OQWIQv6s/s1600/river-length-discharge-comparison.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-jDZ3cxXcGA8/U_i3DH_4uvI/AAAAAAAA0h0/Fm5OQWIQv6s/s1600/river-length-discharge-comparison.jpg" height="320" width="276" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.13. Comparison of SE Asian rivers (with red underline) and other rivers in the world.</td></tr>
</tbody></table>
Some data on
the denudation in the Philippines are given by FELICIANO & CRUZ (1933). The
Angel River, NE of Manila has a drainage area of 732 sq km and an average
run-off amounting to 83,631 cb m per second. Near Matictic (Prov. of Bulacan)
it transports yearly approximately 5,343,610 tons of load and dissolved matter
into the ocean. This means a denudation of nearly 3 mm per annum, if the
average rock density is taken at 2.5. <o:p></o:p><br />
<br />
Coleman and Huh from Lousiana State University did a comparison of world river systems, including a number of rivers from Southeast Asia. Fig. 1.13 shows examples of the graphs they prepared on river length and average annual discharge. The Southeast Asian rivers are generally have small catchment areas and relatively short. The size of islands limit the river system. Mekong River is an exception as it is located in the Asian continent. On the other hand Chao Praya, which is also in the Asian continent is relatively small as it is controlled by fault zones.<br />
<br />
<span style="line-height: 120%;">LIXIVIATION OF
THE SOIL</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The heavy
rainfall of 1 to 7 metres per year, which is particularly characteristic for
the Indian Archipelago, strongly affects the soil and, consequently, the
vegetation. For the abundance of rain water not only wets the soil, but most
distinctly leaches it at the same time. All substances that are soluble in
water, however slight the solubility may be, are dissolved in the long run.
They are carried away into deeper levels and to springs, and thence to rivers
and the sea. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
This process
also takes place in the very damp areas of the temperate zones, but there it
works more slowly; firstly, because the rainfalls are less, and secondly,
because the temperature is lower, a condition which greatly decreases
solubility. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Among these
soluble substances are those which serve to feed the vegetation. Hence the soil
in these tropical regions is constantly being impoverished, a fact which has
been stressed by MOHR in numerous publications. Finally, real laterites are
formed on which vegetable growth is nearly impossible, like the aluminous
laterites of Bintan, described by the author (1940 e).<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
REJUVENATION OF
THE SOIL<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Fortunately
there is a number of factors which greatly, in some cases vey greatly, retards
the process towards this fatal end, or even vey largely prevent its
accomplishment. In the lowlands the silt of water floods may enrich the soils.
But this means only a postponement or prevention of complete exhaustion. There
is, however, pone radical factor which may at any time bring about a fun damental
change in the whole situation, namely, the action of young volcanoes, ejecting
great quantities of ashes, sand and stones over the surrounding country. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
At first everything
in the immediate neighbour- hood of the centre of eruption, on the slopes of
the mountain, is in ruins, buried under all those ejecta. But it is surprising
how quickly a new surface becomes covered with a fresh mantle of vegetation.
This fact was noted in connection with the eruption of Krakatau in 1883
(BACKER, 1929; DOCTERS VAN LEEUWEN, 1936), and those of the Kelud in 1902 and
1919. If there is no immediate recurrence of the eruption, the new soil remains
extraordinarily fertile for centuries, to be finally subjected once more to
gradual impoverishment as a result of leaching by tropical rains.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
MOHR'S opinion
seems to be somewhat pessimistic, because not only leaching out of the soils
occurs, buyt on the other hand erosion brings continuously fresh rocks within
the reach of the process of weathering and soil formation. The active mountain
building in this archipelago creates considerable relief, so that hypabyssal
and plutonic intrusions are exposed by erosion, the mineral content of which
supplies new feeding substances for vegetable growth. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Nevertheless,
there is such a close relation bet ween the presence of young volcanoes and the
density of the population, as has been pointed out for instance by MOHR (1938
b) that the process of lixiviation of the soil occurs apparently at a greater
rate than its rejuvenation by the exposure of fresh rocks. From a human point
of view the volcanic activity is the most important factor for soil
rejuvenation. The population density varies from less than 1 to more than 1000
souls per sq km. In other words, the differences are enormous. According to the
Census of 1930 in theIndonesia, the average density of population was 31.89.
For Java, with its numerous volcanoes, it amounted to 316.11 and for Borneo,
where not a single active volcano is known, it was only 4.02. 1) <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
DENUDATION AND
MOUNTAIN RELIEF<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The very high
rate of denudation and baseleveling in the Indian Archipelago is confirmed by
the study of the geological sections through young mountain ranges, which have
been elevated in plio-pleistocene time. In some instances thousands of metres
have already been removed by the combined effect of gravity flow (viz. creep)
and surface erosion. Consequently these young ranges were already more or less
baseleveled during their elevation ("Primare Rumpfflache" in the
sense of W. PENCK). Many such young peneplains, highly dissected by the
rejuvenated erosion, showing narrow divides and numerous gullies, are to be
found in extensive areas of the Indian Archipelago. 2) In Sulawesi they reach
altitudes of well above 2000 m, and in Ceram to about 1000-1200 m. PANNEKOEK (1946) gave a morphological analysis of the changes in the pliocene
peneplain of SW Java by the rejuvenated erosion due to the uplift and tilting
of the crustal block of the Southern Mountains. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The young
volcanic cones represent another typical feature of the East Indian landscape.
What would be left of the charming and grandiose landscapes of Sumatra, Java,
Bali, and Lombok, without their imposing volcanic cones? These are very young
structures, often built upon pleistocene plains. Only the very active volcanoes
show superb conical outlines (Merapi, Semeru, Mayon). When the activity
decreases they are quickly worn down by erosion. Older quaternary, extinct
volcanoes are at present mere ruins; neogene volcanoes are mostly reduced to
their very basement, exposing the feeding stocks and other hypabyssal intrusions.
Therefore, the volcanoes are indeed only an ephemeral feature of the landscape.
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The strong denudation
in this tropical area, removing and impoverishing the soils, forms a social
problem of great importance. It appears that the terracing of the wet
rice-fields provides an ideal protection against erosion and floods, seeing
that each rice field (sawah square) forms a water reservoir capable of
absorbing a considerable rainfall before overflowing. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
DENUDATION AND
VEGETATION<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It is thought
necessary to preserve a forest cover in the mountainous catchment areas of the
rivers in order to protect the lowlands against floods from the torrential
rains ("bandjirs"), and to prevent excessive erosion of the soil. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The
experimental station for forestry at Buitenzorg (W Java) has studied the
influence of forests on the hydrology and erosion (DE HAAN, 1933 & 1936; COSTER,
1938).<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
From all
observations the main fact stands out that the run-off and the erosion are
determined in the main by one supreme factor, namely the extent to which the
mineral soil lies bare. According to COSTER (1938) the surface run-off of the
rainwater is small on a good forest soil (less than 1-2 %) and there is
practically no surface erosion. Upon removing the vegetable growth the surface
run-off increases to 30-50 %, and the erosion to 5-12 kg/sq m/year. On loose
sandy ashes of volcanoes the erosion may assume catastrophic proportions.
Comparing the denudation on Java with that of the Alps in Europe, DE HAAN
(1936) arrives at the following conclusion: <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-Zku74kILNZo/U_OyTqtxM2I/AAAAAAAA0gc/5b42OMgCCNU/s1600/forest-coverage.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-Zku74kILNZo/U_OyTqtxM2I/AAAAAAAA0gc/5b42OMgCCNU/s1600/forest-coverage.jpg" height="480" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1. 14. Forest distribution of Southeasian Archipelago (<a href="http://earthenginepartners.appspot.com/science-2013-global-forest?hl=nl&llbox=9.24%2C-4.87%2C121.88%2C106.12&t=ROADMAP&layers=2%2Clayer4%2Clayer0%2C11%2C12">University of Maryland</a>).</td></tr>
</tbody></table>
"The
factors which influence stream flow and erosion on Java are quite different
from those in the Alps. In a volcanic area, such as Java, the slopes of the
mountains are not steep and diminish gradually, so that here we do not find the
erosion cones ("Schutthalden") which are so common in the Alps.
Furthermore, in the tropics with a high and equable temperature and heavy rainfall,
chemical decay is predominant against mechanical decay in the Alps. This
results in a more or less thick layer of soil in the mountains of Java against
a thin layer of soil or even bare rocks in the higher mountain regions above
the tree limit in Europe.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The vegetation
in the tropics is dense and nearly unbroken, the types of vegetation are very
varied, and agriculture is possible up to a great altitude. In the Alps the
forests do not mount above 2000 m; the higher regions are covered with grass,
stones, snow, and glaciers. The flow of a glacier river is determined by the
melting of snow and ice. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The flow of a
river from the middle mountains is of a mixed type, influenced by the melting
of snow and by rainfall. With the first type the vegetation will be of no
consequence, with the second one its influence will be greater. The rivers on
Java belong to the pure rain type, a third type, where the vegetation in the
basins influences greatly the stream flow. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Inconsequence
of the greater amount of precipitation and the thicker layers of soils, the
minimal flow of the rivers on Java is much greater than that of Alpine rivers.
But the maximal flow also is higher on Java than in the Alps, because of the
long periods of heavy rainshowers. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the Alps the
rivers transport mostly coarse material, gravel and stones; on Java mostly sand
and mud. These fine particles can not be chequed by engineering works
("Wildbach- Verbauung"). The only practical means to combat this kind
of erosion is by keeping the soil-cover closed and dense, or by
reafforestation. Only in exceptional cases technical works may be of value. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
As the
irrigation of the agricultural crops on Java depends on the local rivers and
streams (irrigation water can not be transported .easily), a sufficient care of
the agricultural land in the plains requires good and dense vegetation in the
mountains all over the island. In general we may expect that the soil cover in
the tropics has a greater effect on stream-flow and erosion than in the Alps.
Engineering works may be useful, but do not stand on the first plan." <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
DENUDATION BY
CREEP<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The presence of
a thick cover of weathered rock drenched with water causes also a considerable
creep of the soils towards the floors of the valleys. STAUBER (1944) draws
attention to the fact that also in the Alps the engineering works
("Wildbach- Verbauung"), which have cost in the past century more
than 200 million Swiss francs, have had little effect on the gravity movements
of the cover of detrital matter, which blankets the lower parts of the mountain
slopes (land-slides, earth glaciers and mud flows). The detrital material of
the mountain flanks often slides in large portions into the ravines, and are
thence removed by river erosion. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The humid
tropical climate of the Indian Archipelago is responsible for the formation of
a deep mantle of disintegrated rocks up to high on the mountains. Moreover, the
active process of mountain building has created considerable relief. It is
clear that the combination of both factors highly promotes the occurrence of
hillside and mountainside creep, which is accompanied by frequent landslides,
cold "lahars" (mud flows), and the like. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
This kind of
denudation is quantitatively much more effective than mere surface erosion, the
value of which is estimated by such experiments as has been made on Java by the
Forestry Station. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the
Karangkobar area of Central Java, where the core of the mountains consists of
neogene mudstones, the creep of the surface layers is so strong that the sawah
fields have to be reparceled from time to time (HARLOFF, 1930, VAN BEMMELEN,
1937 d). In the tin-islands, Bangka and Billiton, the process of creep has been
studied in relation with the formation of the "Kulit" and
"Kaksa" ores (ADAM, 1932-1933). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
This hillside
creep towards the valley floors is also very effective in those instances,
where unconsolidated sediments are folded up or elevated above the local
erosion base. In such cases it is not the disintegrated rock formation, but the
primary deposit, yet unaffected by exogenic weathering, that is subjected to
gravity flow.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the chapter
on the geological evolution of the regional units it will be demonstrated that
this gravity flow is of utmost importance for the restoration of gravitational
balance (secondary tectogenesis). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
There is a
gradual transition in the quantity of mass transport from the process of
surface erosion, via hillside and mountain side creep, to the gravitational
extension and spreading of elevated areas. The difference between both is that
the process of denudation (by surface erosion and creep) is influenced by
climatic factors, whereas gravitational tectogenesis depends only on the field
of gravitational stress-gradients created by differential vertical movements
and the physical properties of the elevated formations. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
DENUDATION AND
GEOLOGICAL FORMATIONS<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Last but not
least, there is of course a close relation between the rate of denudation and
the geological formations. The rate of denudation will be much more rapid in
unconsolidated sediments which are subjected to the erosion due to the process
of mountain building, than in exposures of solid igneous rocks or those of the
crystalline basement complex. RAVEN (1944) is of the opinion that the rate of
denudation is approximately twenty times more rapid for the former than for the
latter. This he considers is a conservative (low) estimate. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
THE HUMAN
STRUGGLE AGAINST DENUDATION<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The process of
erosion has far reaching cons quences for agriculture, forestry, cattle breeding,
various types of civil engineering, particularly for irrigation and transport.
Therefore, the knowledge of the causes, results, and methods of fighting
erosion are of great cultural importance. In view of this the Government of the
Netherlands Indies sent in 1946 a special commission of scientists to the
United States of America to study the modem methods of combating erosion in
that country. The original report of that commission, which consisted of nine
members, has been summarized by VAN BAREN and was issued by the Department of
Economic Affairs in 1947.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.7. SOIL SCIENCE
AND SEA SEDIMENTS </b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Though not belonging
to the scope of this work, something has to be said about the study of the
soils in Indonesia. A few decades ago private and government experimental stations
for agriculture were established. The publications of these experimental
stations give us an uninterrupted picture of the stages of development of
scientific and practical soil science in the Netherlands Indies. M. TREUB
founded in 1905 the Laboratory for Agrogeology and Soil Research. Its task was
to become the link between geology in the widest sence of the word on the one
hand, and of agriculture on the other. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-g5ZTeazR64c/U-eYPLZ9k4I/AAAAAAAA0cU/34d8CGFTeaY/s1600/soil-map.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-g5ZTeazR64c/U-eYPLZ9k4I/AAAAAAAA0cU/34d8CGFTeaY/s1600/soil-map.jpg" height="231" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.15. Asia soil map by ISRIC, 1997</td></tr>
</tbody></table>
A review on the
development of the tropical soil science in the period 1918-1943 was recently
published by MOHR (1948). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
An excellent
treatise on the soils of the East Indies has been written in 1933-1938 by Prof.
Dr E. C. J. MOHR, the nestor of the pedologists who worked in the Netherlands
Indies. Recently EDEL- MAN (1941) published a book on this subject with an
extensive list of literature references. Further might be mentioned the work of
VAN HEURN 14 PHYSIOGRAPHY
(1923) and DRUIF (1932-1934) on the soils of Sumatra's Eastcoast; that
of SZEMIAN (1929/30 a, 1930) and IDENBURG (1937) on the pedological survey of
South Sumatra, besides the pedological notes by SZEMIAN, accompanying the
explanations of sheet 3 (Bengkunat) of the 1 : 200,000 geological map of
S-Sumatra, and the sheets 30 (Purwakarta), 36 (Bandung), and 58 (Bumiaju) of
the 1 : 100,000 geological map of Java. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
There have been
some discussions whether the pedological surveys were to be conducted as a
branch of the geological survey, or by the agrogeological laboratory (VAN
BEMMELEN, 1928 b&c; DE IONGH, 1929/30, SZEMIAN 1929/30 b, WHITE, 1930;
OPPENOORTH, 1930; discussions "Algemeen Landbouw Weekblad" 15, 1930,
by WHITE, DE IONGH, DEN BERGER, REITSEMA, SCHEIBENER, BOTHE, Roos, BERNARD). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the decade
before the outbreak of the war with Japan the general survey has been done by
the Agrogeological Institute ("Bodemkundig Instituut") at Buitenzorg
(Bogor). The privately financed experimental stations for sugar, coffee,
tobacco, etc. had their own pedologists for the more local researches of the
soil. <i>The institute is now called Institut
Pertanian Bogor (IPB = Agricultural Institute of Bogor).<o:p></o:p></i></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Beside the
survey of the soils of the islands, we may also mention in this paragraph the
research of sea sediments. A map of the sediments in the Java Sea has been
composed by MOHR (1919). The bottom samples of the Moluccan Seas, collected by
the Snellius Expedition in 1929-1930, have been studied by NEEB (1943). See
fig. 10. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
MYERS (1945)
wrote an article on the sediments of the Java Sea and their significance in
relation to stratigraphic and petroleum geology. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In 1948 the
Swedish deep sea expedition of the Albatros under the leadership of H.
PETTERSON visited the East Indies. This expedition collected samples of
sea-sediments of 20 metres depth. The profiles obtained by the Snellius
expedition were 2.5 metres deep, which was a record depth at that time. Also
seismic measurements of the thicknesses of the sediments at the sea floor will
be made. So the results of the Albatros expedition, which at present are not
yet available, will greatly augment our knowledge of the history of the sea
floors (HARDENBERG, 1948).<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.8. MAJOR
PHYSIOGRAPHIC DIVISIONS</b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The major
relief features of the Indian Archipelago are fundamental for its division into
regional physiographic units. There can be distinguished a partly submerged
land mass in the West, the Sunda Shelf area, and the partly submerged northern
extension of the Australian Continent in the East, the Sahul Shelf area. These
are separated by an intervening belt of deep-sea basins and island-festoons.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The shelf seas
are generally less than 100 m deep, although the edges of the shelves are indicated
on the map by the 200 m isobath, as is common use. The islands emerging from
the shelf seas are mostly less than 1000 m high. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
These shelf seas
largely are old peneplains, which are only gently warped by later epeirogenic
movements, being more or less stable land masses with low seismicity, low
isostatic gravity anomalies and no active volcanoes. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
During the
tertiary cycle of mountain building the marginal parts of the Sunda Shelf area
have subsided considerably. In these marginal troughs thousands of metres of
sediments have accumulated, on which are located the productive oilfields of NW
and E-Borneo, N-Java, and E-Sumatra. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
There can be
distinguished in the Sunda Shelf area, an old central land mass (comprising the
Malay Peninsula, the Riau-Lingga Archipelago, Bangka, Billiton, Karimondjawa
Islands, Karimata Islands, Tambelan Islands, Anambas Islands, Natuna Islands,
and the western part of Borneo) and more unstable marginal parts, which have
been subjected to the tertiary cycle of mountain building (the remaining part
of Borneo, Bawean Island, Java and Madura, Sumatra). As the latter are physiographically
connected with the Sunda Shelf area, their physiographic description will be
given under that heading; but, geologically, they belong to the circum-Sunda
Mountain System, to be discussed hereafter. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The Sahul Shelf
area comprises the Arafura Shelf Sea, the Aru Islands and the southern part of Papua
(Merauke swell). Perhaps also the shelf-sea, extending West of the
"Vogelkop" (Birds- head) to Misool, may be assigned to it. North of
the Merauke ridge the pre-tertiary basement complex plunges down under the
tertiary geosyncline of New Guinea, which forms a part of the circum-
Australian Mountain System. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
SUBMERGED
BORDERLANDS<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The crustal
blocks of SE-Asia (i.e. Sunda) and of NW-Australia (i.e. Sahul) have a mean
elevation corresponding more or less with the sealevel. The bordering parts of
the Pacific and Indian Ocean are considered by the author to be crustal blocks
of former border lands, which have subsided to oceanic depths, now forming the
China Basin, the Philippine Basin, the Carolinan Basin, at the north- eastern
(Pacific) side of the Archipelago, and the Indo-Australian Basin, at its
southwestern (Indian) side. The floors of these basins are rather level, showing
differences in depth which are generally less than 1000 m. The floor of the
China Basin is at about 4000 m depth, and that of the Philippine Basin at
5000-6000 m; the Carolinan Basin, forming the northern part of Melanesia, is
about 4000 m deep. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The part of the
Indo-Australian Basin, extending between the Cocos or Keeling Islands and
Australia, is 5000-6000 m deep, whilst the part of it extending from the
fore-mentioned islands north- east- and northward to the Gulf of Bengal
gradually shoals in that direction from 5000 to 3000 m. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
There are
several geological and geophysical reasons for supposing that these crustal
blocks have been above sealevel in pretertiary times, forming-parts of the
Asiatic continent and of the former Gondwana continent. They subsided, later
on, to oceanic depths, but the discussion thereof is outside the scope of this
chapter (See chapter IV). These differential vertical movements of such extensive
crustal blocks, measuring thousands of kilometres across, are major geotectonic
movements separated by very long phases of relative stability. They are
generally described as epeiro- genic movements. In this book they will be
called "geoundations". For the description of the present
physiographic situation they can be considered as more or less stable crustal
parts, lying at various depths with respect to the datum plain which is given
by the sealevel. <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
OROGENIC BELTS<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Between these
crustal blocks are belts of much stronger relief, characterized by
island-festoons or submarine ridges, which are paralleled by deep-sea troughs
or trenches. The width of the unstable tract varies from some hundreds of kilo
metres at the northern end of the Philippines, to more than two thousand
kilometres between central Borneo and the Aru Islands. These belts are zones of
active orogenic movements along which ranges have been elevated at times to
some thousands of metres above sealevel, whilst the intervening basins sub-
sided, reaching depths of 5000 to more than ,10,000 m (-10,830 m in the
Philippine Deep).<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
An important
advance in our knowledge of the oceanography of the Indo-Australian
Mediterranean has been made by the cruise of the Snellius Expedition in the
eastern part of the Netherlands East Indies in 1929-1930. A list of
publications concerning the Snellius Expedition till 1943 is published in Vol.
V, Geological Results, pp. 266-268 (KUENEN & NEEB, 1943). See also fig. 78
on pl. 8. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The
bathymetrical results of the Snellius Expedition include more than 30,000 echo
soundings. On these figures is based the large bathymetrical chart designed by
the expeditionary staff and published by VAN RIEL (1934). This chart has been
copied in varous publications (e.g. the "Atlas van Tropisch
Nederland", 1938) and has thus become widely known. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
It is, however,
not the only bathymetrical chart designed from the depth figures of the
Snellius Expedition. The late P. J. B. VAN KESSEL of the Topographical Service
at Batavia was of the opinion that the course of the isobaths on the Snellius
chart was too much influenced by preconceived ideas about submarine folds. This
led him to design a bathymetrical chart based on the same soundings, but eliminating
as much as possible any indication of the direction of the folds. The chart
constructed by VAN KESsEL in 1933 was published posthumously by PANNE- KOEK
(1941). On this chart most of the shallows are circular, even though there may
be strong arguments in favour of a shallow being elongated in a certain
direction. Because the shallows were rounded and but rarely linked together in
the form of longitudinal ridges, the deeper parts of the seas occupy more space
than on the Snellius chart. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
A. J.
PANNEKOEK, who was VAN KESSEL'S successor at the Topographical Service,
compared critically both constructions of the isobaths, based on the same depth
figures, and came to the following conclusions (1941): "Although,
generally speaking, VAN KESSEL's construction of the isobaths seems to be less
probable than that of the Snellius Expedition, it is, nevertheless, an
interesting piece of work in that it shows up immediately where the Snellius
chart may be subject to doubt. For certain areas it may even be said to be an
improvement over the Snellius chart. Particular attention is called to the
different representations of the central ridge of the Banda basin between Buru
and the Tukangbesi Islands, Southeast of Sulawesi." <o:p></o:p><br />
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>1.9. PHYSIOGRAPHIC
DISTINCTION OF THE MAIN UNITS <br />
THE GROUPING FOLLOWED IN THIS BOOK </b><o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
As has been
pointed out in the preceding .paragraphs, the main physiographic units are: 1)
The continental platforms, 2) the oceanic basins (or engulfed borderland), and
3) the orogenic belts. These three groups can be subdivided into a number of
smaller physiographic units. Thus we come to the following scheme: <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in; text-indent: -.5in;">
<b>A. The Sunda area. </b><br />
a. The Sunda shelf and smaller
islands. <br />
b. Larger Sunda Islands
bordering the Shelf Sea (Borneo, Sumatra, Java and Madura). <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in; text-indent: -.5in;">
<b>B. The circum-Sunda orogenic belts. </b><br />
a. Sin Cowe Reefs in the South
China Sea. <br />
b. The Philippine Archipelago. <br />
c. Sulawesi. <br />
d. Moluccas.<br />
<span style="line-height: 120%;">d</span><sub style="line-height: 120%;">1</sub><span style="line-height: 120%;">. Northern Moluccas.</span><span style="line-height: 120%;">d</span><sub style="line-height: 120%;">2</sub><span style="line-height: 120%;">. Southern Moluccas.</span><br />
<span style="line-height: 120%;">e. Lesser
Sunda Islands.</span><br />
<span style="line-height: 120%;">f. Ridges South of Java and
West of Sumatra.</span><br />
<span style="line-height: 120%;">g. Andamans and Nicobars.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
<b>C. The circum-Australian belt.\</b><br />
<span style="line-height: 120%;">a. New
Guinea.</span><br />
<span style="line-height: 120%;">b. Sahul Shelf with the Aru
Islands.</span><br />
<span style="line-height: 120%;">c. Christmas Island. This
grouping will be followed in this chapter.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
From this
physiographic description it will appear that the structural relations are
somewhat more complicated than this simple scheme suggests. Therefore, in the
part, on the regional geology (Chapter V) a slightly different scheme had to be
used.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the first
place, Sumatra, Java and Madura, though bordering on the Sunda Shelf, belong
almost entirely to the young Sunda Mountain System. Therefore, they will be
treated under the heading of the circum-Sunda orogenic belts. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the second
place, a short discussion of the geology of the Malay Peninsula will be
necessary for the understanding of the structural relations in the Sunda area.<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
In the third
place, the Aru Islands on the Sahul Shelf do not belong to the young
circum-Australian orogenic belts, being a marginal part of the Australian
continental block. Consequently, the scheme for the discussion of the regional
geology in Chapter V will be: <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
A. The Sundaland<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
1. Sunda
Shelf. <br />
2. Smaller Islands on the Sunda
Shelf. <br />
3. Borneo. <br />
4. The Malay Peninsula. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
B. The Circum-Sunda orogenic systems <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
1. The
Philippines. <br />
2. Northern Moluccas. <br />
3. Sulawesi. . <br />
4. Southern Moluccas (Banda
Arcs). <br />
5. Lesser Sunda Islands. <br />
6. Java. <br />
7. Sumatra and the Islands to
the West of it.<br />
8. Andamans and Nicobars. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
C. The Circum-Australian orogenic
systems <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
1. New
Guinea. <br />
2. Christmas Island.<br />
<span style="line-height: 120%;">3. The Sahul area</span><span style="line-height: 120%;"> a. The
Sahul Shelf.</span><span style="line-height: 120%;"> b. The Aru Islands.</span></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt; margin-left: .5in; margin-right: 0in; margin-top: 0in;">
<o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
The geological
analysis in Chapter V shows that the geotectonic relations are still more
complicated. Beside the continental
nuclei of SE Asia and Australia, we can distinguish four main orogenic systems,
which meet and interlace in the focal part of the Archipelago, between Borneo
and New Guinea. These four major mountain systems are: <br />
1. The Sunda Mountain System. <br />
2. The East-Asiatic Arcs. <br />
3. The Melanesian System. <br />
4. The circum-Australian
System. <o:p></o:p></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
A synthesis of
the general geotectonic picture will be given at the end of this volume,
Chapter VI. FIG. 11. Main physiographic and tectonic outlines of the
Indonesian and adjacent archipelagoes.<br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-povf2D2qaB0/U-wzTC-QO_I/AAAAAAAA0d4/gmn6l1v-GWk/s1600/tectonics-seasia.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-povf2D2qaB0/U-wzTC-QO_I/AAAAAAAA0d4/gmn6l1v-GWk/s1600/tectonics-seasia.jpg" height="320" width="284" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig. 1.16. Simplified tectonic map of SE Asia</td></tr>
</tbody></table>
<br /></div>
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
Figure 1.16 illustrates the main physiographic and tectonic outlines of the SE Asian Archipelago and its geotectonic relations. The numbers and letters indicate the
subchapters in which they are treated. The roman cipher I refers to the chapter
on physiography, II to the chapter on stratigraphy, and V to that on the
regional geology. The subchapters on stratigraphy, marked on this map, refer
only to the discussion of the tertiary stratigraphy, in sofar as this has not
been treated in chapter V. <o:p></o:p></div>
<br />
<div class="MsoNormal" style="line-height: 120%; margin-bottom: 6.0pt;">
We will now
continue with the description of the physiographic features of the various
units. It has to be born in mind, that this description is meant as an
introduction to the regional geology. Therefore, stress is laid on the
structural trendlines which can be derived from the orographic features.<o:p></o:p></div>
</div>
Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.com0tag:blogger.com,1999:blog-7274248385186471083.post-22887780814865788582014-08-09T05:20:00.005-07:002015-02-20T20:01:48.412-08:00Outline<b><a href="http://phsyiography-indonesia.blogspot.nl/2014/08/general.html">1. INTRODUCTION</a></b><br />
1.1. Situation and Extent<br />
1.2. Denomination<br />
1.3. Geological importance of the Indian Archipelago<br />
1.4. Fauna and flora<br />
1.5. Climate<br />
1.6. Denudation<br />
1.7. Soil science and sea sediments<br />
1.8. Major physiographic divisions<br />
1.9. Physiographic distinction of the main units<br />
<br />
<b><a href="http://phsyiography-indonesia.blogspot.nl/2014/08/sundaland.html">2. THE SUNDALAND AREA</a></b><br />
2.1.The Sunda Shelf and the smaller islands<br />
2.1.1. The Sunda Shelf<br />
2.1.2. The Islands on the Sunda Shelf<br />
<br />
2.2. Borneo<br />
2.2.1. Orographic and hydrographic trendlines<br />
2.2.2. Structural trendlines<br />
2.2.3. The three largest rivers of Borneo<br />
<br />
2.3. Sumatra<br />
2.3.1. The Barisan Range<br />
2.3.2. The Semangko Zone<br />
2.3.3. Main structural trendlines<br />
2.3.4. Java & Madura<br />
<br />
2.4. Java & Madura<br />
2.4.1. West Java<br />
2.4.2. Central Java<br />
2.4.3. East Java<br />
2.4.4. The eastern spur and Madura<br />
<br />
<b><a href="http://phsyiography-indonesia.blogspot.nl/2014/08/circum-sunda-archipelago.html">3. THE CIRCUM-SUNDA ARCHIPELAGO</a></b><br />
3.1. The-Sin-Cowe Reefs in the South China Sea<br />
<br />
3.2. The Philippine Archipelago<br />
3.2.1. General outlines<br />
3.2.2. Luzon<br />
3.2.3. Luzon arc<br />
3.2.4. Samar arc<br />
3.2.5. summary of the main structural trendlines<br />
3.2.6. Actual shore lines<br />
<br />
3.3. SULAWESI<br />
3.3.1. North arm<br />
3.3.2. East arm<br />
3.3.3. Banggai archipelago<br />
3.3.4. Southeast arm<br />
3.3.5. Buton archipelago and Tukang Besi Islands<br />
3.3.6. South arm<br />
3.3.7. Central Sulawesi<br />
<br />
3.4. HALMAHERA AND BANDA ARC<br />
3.4.1. Halmahera<br />
3.4.2. Northern Banda Arc<br />
3.4.3. Southern Banda Arc<br />
<br />
3.5. LESSER SUNDA ISLANDS<br />
3.5.1. Back deep<br />
3.5.2. Inner arc<br />
3.5.3. Interdeep with Sumba<br />
3.5.4. Outer arc<br />
3.5.5. Foredeep<br />
<br />
3.6. THE SUNDA MOUNTAIN SYSTEM IN THE JAVA-SUMATRA SECTOR<br />
<br />
3.7. NICOBARS AND ANDAMANS<br />
<br />
<b><a href="http://phsyiography-indonesia.blogspot.nl/2014/08/circum-australian-belt.html">4. THE CIRCUM-AUSTRALIAN BELT</a></b><br />
4.1. PAPUA<br />
4.1.1. "Birdhead" and "neck"<br />
4.1.2. Mainland and trunk<br />
4.1.3. Eastern part, including the "tail"<br />
<br />
4.2. THE SAHUL SHELF<br />
4.3. CHRISTMAS ISLAND<br />
<br />
5. DISCUSSION<br />
<br />
6. REFERENCES LIST<br />
.<br />
<div>
<br /></div>
Darmanhttp://www.blogger.com/profile/02782732581537482284noreply@blogger.com0