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.
Physiographically New Guinea can be divided into three parts:
A. The western peninsula or Vogelkop (Birds- head), connected by a narrow neck to the mainland (130°-135° E. long.).
B. The Mainland or Trunk (between 135 ° and 143~ E. long.).
C. The eastern part, including the tail (143t 0- 151 ° E. long.).
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).
To the South, the Sahul Shelf (Arafura Sea) and Strait Torres connects New Guinea with the Australian Continent.
4.1.1. "BIRDHEAD" (VOGELKOP in Dutch) AND "NECK"
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).
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).
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.
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.
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.
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.
4.1.2. MAINLAND OR TRUNK
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".
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).
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.
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.
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.
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.
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.
The divide area between the Idenburg River and the Sepik River forms a threshold in this longitudinal depression. This area is still little known.
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).
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).
The highest summits of the Snow Mountain Range are situated at its southern side, forming sharp crests and fim basins.
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).
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.
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.
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.
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.
4.1.3. EASTERN PART, INCLUDING THE "TAIL"
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.
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).
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.
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.
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.
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).
4.2. THE SAHUL SHELF
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.
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.
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.
4.3. CHRISTMAS ISLAND
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).
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.
|Fig.4.3.1. Christmas Island (source: appszoom)|