RELIEF AND STRUCTURE: DRAINAGE

RELIEF AND STRUCTURE: DRAINAGE

General Characteristics

The vast land-mass of Asia dwarfs the other continents in size, as a glance at any world map on an equal area projection will confirm. In latitude it extends from nearly 80° N. to nearly 10° S. (if we include the Indonesian Islands). In longitude it stretches from 28° E. to 165° W., a total of 167°, or nearly half-way round the globe. This means that when the people of Western Turkey are finishing their midday meal, those of Eastern Siberia are fast asleep at 1.30 a.m. on the next night.

It is obvious that over such an enormous area there must be great differences of relief, climate, and other geographical features, which in their turn have much affected the multi- farious peoples so that there are also many different types of human society. Asia has indeed been called the “Continent of Contrasts”; here are a few examples which bear out the truth of this:-

1. It contains the highest parts of the earth’s land-surface (Mt. Everest, 29,000 ft.) and the lowest (the Dead Sea Rift-1300 ft. below sea-level).
Off its shores, too, near the Philippine Islands is the deepest known part of the ocean floor (5900 fathoms).

2. It has the coldest place in the Northern Hemisphere in January and the hottest in July. Verkhoyansk in North-Eastern Siberia has a mean January temperature of – 51° C. (-60° F.), and several places in North- West India and the Persian Gulf area record a mean of over 35° C. (95° F.) in July. Incidentally, Verkhoyansk has the greatest known annual range of temperature, i.e. 67° C. (120° F.).

3. The greatest known annual rainfall in the world is that of Cherrapunji in Assam (432 in.), but Asia also contains the largest area in the world with less than 10 in. This area extends from the Red Sea to Mongolia.

RELIEF AND STRUCTURE: DRAINAGE

4. The natural vegetation of Asia varies from the mosses and the lichens of the Arctic Tundra to the impenetrable tropical jungle of the south-east.

5. In the fertile alluvial lowlands of the monsoon lands there are the most densely peopled areas of the world. In the belt extending from India to China are packed about one-half of the world’s population. Yet in the area of less than 10 in. rainfall and north of it to the Arctic shores is the most extensive area of sparse population. Asia may also be called the “Continent with a Past and a Future”. In Iraq and the lower Indus Valley there were civilizations contemporary with that of Ancient Egypt and of equal standard.

Another developed somewhat later in China. All were flourishing when the peoples of North-West Europe were still savages. Then came a decline. There are many signs that the Giant of the East is awakening, prodded by the impact of the Western civilizations. The huge terri- tories of the Soviets in Asia have been steadily developed; Japan has become the third largest trading nation in the world, and most other countries are modernising their agriculture and developing mining and manufacturing industries. The Turks have become Westernised and this process is well under way in Iran. By Westernization we do not mean merely the wearing of European dress and the adoption of the roman handwriting. It goes much further than that, and includes, e.g., legal procedure, and the methods of government.

The transition from sleep to wakefulness is seldom completed without a period of restlessness. There is no continent with so many grave problems as those of Asia, not even Europe. In the Levant there is the seemingly insoluble problem of reconciling conflicting interests and viewpoints, in India the disputes between the two countries and the antagonism of Hindu and Moslem, in the Far East the rivalries of the Nationalists and Communists in North and South Viet- nam, North and South Korea and between China and Taiwan. Ultimately, so great are the natural resources and so numerous the population, with such varied abilities, that the peoples of Asia cannot fail to play a leading part in world affairs. If they, and particularly those of the south and east, rigidly adhere to the guiding principles of their great religions, it may well be for the world’s good. We must remember that all the great religions originated in Asia, i.e. Christianity, Muham- madanism, Hinduism, Buddhism, Judaism, and the philosophy of Confucius.

One of the most serious problems is that of the resettlement of millions of refugees displaced by political changes since the Second World War. (i) At the partition of India some 8,500,000 Hindus moved eastwards and 7,500,000 Moslems westwards. In 1971 some 9 millions crossed from East Paki- stan into West Bengal, but nearly all have returned. (ii) With the expansion of Israel in 1949 there were 880,000 Arab refu-gees; of these, Jordan received 476,000; Gaza (Egypt), 209,000; Lebanon, 104,000; Syria, 84,000; Iraq, 5,000. Most of these are still in refugee camps maintained by U.N.R.R.A. (United Nations Refugees Relief Association), and their presence is a major factor accounting for the bitterness of the Arabs towards the Jews. Most of Jordan’s troubles have sprung from the discontent among its Palestinian Arab refu- gees. (iii) The Chinese Civil War led to the flight of unknown numbers. (iv) The Korean War caused 2,750,000 North Koreans to take flight to the South, and well over 14 million moved from North to South Vietnam for a similar reason.

Apart from the involuntary movement of refugees, there has for many years been a voluntary migration on a large scale from over-populated areas of India, and especially China, to the rapidly developing lands of South-East Asia, particularly Malaysia and the East Indies. As Chinese do not assimilate with the indigenous population their presence in such numbers is bound to cause misgivings, particularly as they have strong ties with their homeland and as the latter is now under a Communist régime. This is one of the greatest sources of worry to the Federation of Malaysia and to Singa- pore. Most of these Chinese immigrants come from the island of Hainan and the southern provinces of Kwantung and Fukien. There are 350,000 in Burma, 180,000 in Cam- bodia, 2,200,000 in Indonesia, 2,550,000 in Malaysia, 200,000 in the Philippines, 920,000 in Singapore (over 80 per cent. of the population), 800,000 in South Vietnam, and 100,000 in North Vietnam.

RELIEF AND STRUCTURE: DRAINAGE

As to the western boundary of Asia with Europe, this is usually taken to be the line of the Ural Mountains to their southern end, where it turns westwards along a line of low hills towards the Volga River, but before reaching the latter it again turns southwards to the Caspian, keeping parallel with the river and about 50 miles from it. Finally, in the area between the Caspian and the Black Seas, the crest of the Caucasus Mountains is normally regarded as the boundary. All this is very arbitrary as, apart from the Caucasus, there is no effective barrier between the continents. With the expansion of Russian government across Siberia and beyond the Caucasus it has become increasingly difficult to regard the boundary as a real one. Indeed, some authorities prefer to think of the U.S.S.R. as an Oriental rather than as an Occidental Power, basing this opinion upon the general outlook and mental make-up of the population of the European section.
Relief and Structure.

Extending from the Ural Mountains in the west to the Lena River in the east is the greatest continuous lowland in the world-the Siberian Plain. The western half as far as the River Yenisei is a flat area composed mainly of recent sedimentary rocks, but beyond the Yenisei there is an eroded plateau formed of Palaeozoic rocks of a more resistant type. Structurally the whole of the lowland is a table of great solidity which has resisted folding, and the Primary rocks of Palaeozoic sedimentaries extend throughout the area, but in the western part they remain covered with glacial debris deposited during the Ice Age. The debris has been removed The latter is a complex from the higher eastern part. drainage area, the main and secondary watersheds forming ranges which rise to 3,000 ft.

Pressing on this area to the west, south and south-east there is a great but broken crescent of ancient fold ranges including the Altai and Sayan Mountains, some of which reach 14,000 ft. To the south-east there are the lower and broken Yablonovyy and Stanovoi Ranges. Fringing the southern edges of these up-folds there is a series of depres- sions some of which form great basins partly flooded by such

TERTIARY FOLD SYSTEM

inland seas as the Northern Caspian, the Aral Sea, and Lake Balkash. It should be noted that the Khirghiz Steppe is structurally one of these lowlands and not an extension of the Siberian Plain. The Dzungarian Gate, a depression between the Altai and Tien Shan Ranges, has played a major
30°
60°
90°
120°
150°
SIBERIAN
TERTIARY

FOLDS
SHIELD
60%
BALTIC
SHIELD
45°
CARBONIFE
TERTIARY
FEROUS
FOLDS
FOLDS
-15°
0
–RIFT
Pre-Cambrian Tables
CHINESE
TABLE
Tertiory Folds
Carboniferous Folds
120
150°
60
45
15
0
Fig. 1. ASIA-GEOLOGICAL STRUCTURF.
part in determining the routes of Central Asia. All these depressions are synclinal. Every wave consists of a trough and a crest. Fold ranges are the crests of earth waves and are said to be anti-clinal, whilst the corresponding troughs are synclinal. (See Book I, pp. 76-7, for an explanation of fold mountains.)

RELIEF AND STRUCTURE: DRAINAGE

To the south-west of this fold system is another much younger one which provides the most impressive mountain scenery in the world. The folding occurred during the Tertiary, or third, period of geological history, i.e. about 50 million years ago, compared with the 400 million years ago of the older ones. It is an extension of the ranges which border the shores of North-West Africa and Southern Europe. The system enters Asia in the west of the Peninsula of Anatolia (Asia Minor) by two east-west ranges-the Pontic Mountains in the north and the Taurus Ranges in the south. These are continuations of the Greek Pindus Ranges to which they are linked by lines of islands which trace for us the submerged parts of chains.

The two ranges enclose like pincers a great massif of ancient rock which forms the core of the peninsula. At their eastern end they converge in Armenia to form the knot of Mount Ararat, the central and culminating point of a volcanic area. It is a characteristic of fold ranges that volcanic outbursts and earthquakes are liable to occur along their flanks, no doubt because the very folding that gave rise to these ranges has weakened the crust and enabled the lava to burst through. Nowhere is this more probable than where two or more crests converge, as is the case with the Armenian area. That the Anatolian area is still in a very unsettled state is proved by the several disastrous earthquakes of recent years. To the north-east of this volcanic mass there is a synclinal lowland mainly drained into the South Caspian, itself part of this syncline.

Beyond this again are the Caucasus Mountains, a continuation of another European fold which, after forming the curving Carpathians and Transylvanian Alps, turn eastwards to the Black Sea as the Balkan Range. The fold system reappears as the mountains of Southern Crimea, and then as the much more majestic Caucasus which rise in Mount Elbruz to 18,000 ft. Where the fold ranges reach the Caspian they form the Apsheron Peninsula. The narrow part of the Caspian links the two synclines that we have already mentioned, and then the fold recovers again in the Asiatic Balkans only to die away to a northward curving line of downs, regaining height in the Altai Mountains.

Returning to Mount Ararat, we find that two groups of ranges diverge to the east and south-east to enclose the next resistant mass, the plateau of Iran. The northern group forms the Elburz Mountains which skirt the southern shores of the Caspian and then run in a general eastwards direction through the Koh-i-Baba to the Hindu Kush. The southern group, the Zagros Mountains, which overlook Iraq and the Persian Gulf, continues along the northern shore of the Arabian Sea, sending a spur across the Strait of Hormuz to the mountains of Muscat in South-East Arabia. The main fold continues almost to the mouth of the Indus and then turns suddenly northwards, making an S-shaped bend at Quetta. Here again there has been a weakening of the earth’s crust, as proved by the destruction of Quetta by earthquake. This is a normal type of event where fold ranges make sudden bends.

Flanking the Punjab the fold continues northwards as the Sulaiman Range. In the tangled region to the north-west of India there is a meeting place of ranges in the highest mountain knot of all, the Pamir Plateau or “Roof of the World” as the local people call it. It is at this point that there begins the highest part of the earth’s surface. From the Pamirs towards the north-east run the Tien Shan (24,000 ft.) and to the east-the Kun-lun (25,000 ft.). These two sys- tems partly enclose the Tarim Basin. To the south-east run the successive ranges of the Karakoram (K2, 28,000 ft., the second highest peak in the world) and the Himalayas (Mt. Everest, 29,000 ft.). Between these and the Kun-lun is the Tibetan Plateau which averages about 15,000 ft. and is crossed by yet more ranges, in places exceeding 25,000 ft. At the eastern end of the plateau relief becomes very complicated, for suddenly every one of these fold systems, each consisting of several ranges, turns southwards to form the parallel chains of Burma.

The most westerly, the Arakan Yoma, is con- tinued through the Andaman and Nicobar Islands to become the “backbones” of Sumatra and Java and parallel Metawa Isles off the south of Sumatra. The eastern Burmese Ranges are squeezed into the Malay Peninsula and then, via the “Tin Isles” of Bangka and Biliton, swing north-eastwards through Borneo and the Philippines, Formosa and the Japanese Archi- pelago to the complex folded areas of North-Eastern Siberia, east of the Lena River.

The presence of this huge obstacle across the entire width of the development of the various major civilisations. It has meant that, throughout the whole of the north, human movements have been mainly along the latitudes, Russian from the west, Mongolian from the east. It has meant the development of the Indian civilisation in the south in its turn isolated from the Chinese in the east.
The remainder of the continent consists chiefly of more tables of resistant rock forming the tilted massifs of Arabia, the Indian Deccan, and parts of Indo-China and China. Between the two former of these and the Tertiary anticlines there are the great synclines of the Tigris-Euphrates Valley, the Persian Gulf, and the Indo-Gangetic Plain.

The only other structural feature worthy of mention in this brief survey is the great Rift Valley which, commencing in Syria, forms the deep depressions of the Dead Sea and the Red Sea. It is thought that this great fissure in the Earth’s surface was in some way caused by the great stress exerted upon the crust by the gigantic east-west earth waves.

Drainage

Disregarding minor details one may see that the waterways of Asia are divided into four groups, viz.:-
1. An area of the centre, which can be called the Heart- land, extending from Anatolia in the west to Manchuria in the east and penetrating well into Europe in the great Volga Basin. It is a region of inland drainage where the rivers either flow into lakes such as the Caspian and Aral Seas or, like the streams of the Tarim Basin, become swallowed up in sandy wastes. Apart from the Syr and Amu Darias which flow into the Aral Sea there are no rivers of major importance on the Asiatic side. The lakes are the outstanding feature of the drainage system and of these the Caspian is by far the greatest. As we have mentioned, it has been formed by the flooding of the lower parts of two synclines.

The Caspian is well below open sea-level and at its northern end there is a large area of land known as the Caspian Depression which is also below sea-level. The American geographer, the late Ellsworth Huntington, proved by his observation of the past shore-lines of the Caspian that its level has fluctuated, showing that there must have been climatic changes over its drainage area, because the volume of an inland sea depends upon the amount of rain falling in the basins of its contributary rivers in relation to the volume of moisture evaporated over the whole of the basin. In wet cycles the amount received exceeds the amount evaporated so that the volume of the lake is increased and the shore-lines expand. In dry cycles evapora- In tion exceeds precipitation, therefore the lake shrinks.

Fig. 2. CATCHMENT AREAS.

Persia and the high depressions of the Tarim Basin, and in the Gobi Desert, most of the areas shown as lakes are really salt pools, for they are fed only by streams which flow to them seasonally after the melting of the winter snows on the surrounding heights.
2. The Indian Ocean drainage area extends from the headwaters of the Tigris and the Euphrates to the Malay

RELIEF AND STRUCTURE: DRAINAGE

Peninsula. The most important streams are the Indus and the Ganges-Brahmaputra, the two last named sharing the same delta. One interesting fact emerges from a study of the courses of these streams. The Himalayas, greatest of all mountain systems, do not form a major watershed, for the Indus and one of its chief tributaries, the Sutlej, and the Tsang-po, headstream of the Brahmaputra, all rise north of the ranges and break through them by narrow gorges into the Indo-Gangetic Plain. The three rivers have their sources very close to each other and can be compared with the Rhone, the Rhine, and the Aar in Southern Switzerland. It is probable that both drainage systems may be accounted for in the same way. There was once a river flowing in a single longitudinal valley, in the Asiatic case from the east to west via the Amu Darya to the Aral Sea. Short, very swift rivers on the opposite slopes of the mountains, eroding their courses very steeply, undercut the higher valley and so “captured” the longitudinal stream in three places. There are signs that other captures will one day take place, for several tributaries of the Ganges appear to be making gaps in the Himalayas.

There are numerous examples of river-capture (or behead- ing) in this drainage area, e.g. there used to be another Indus tributary rising to the east of the present series, but its head- waters were captured by the Jumna so that, now, deprived of its flood waters, the beheaded stream loses itself in the sands of the Thar Desert. Then again, in Burma, the Irrawaddy had as its original source the Chindwin. Flowing parallel to the Chindwin and separated from it by the Pegu Yoma, central range of Burma, was the less energetic Sittang. A powerful tributary of the old Irrawaddy cut a gap in the Pegu Yoma and drained off the upper part of the Sittang near the site of Mandalay.

3. The Pacific drainage area is a relatively small one, the outstanding rivers being the Chinese Yangtse and Hwang-Ho. The watershed between this drainage area and the Indian Ocean area is very finely drawn, for in South-East Tibet there is a succession of rivers flowing towards the south-east, and those flowing to the Pacific are divided from the others by a narrow mountain ridge which ultimately becomes the back- bone of Malaya. Here again we could find plenty of examples of river-capture but we must content ourselves with pointing out the excellent one of the beheading of the Sikiang by the
C
A
Amu-Dary
Ob
Indu
Sutle
X Yenisex
NORTH-WEST INDIA
Ganges
SIBERIA
Lower Tunguska
Stony Tunguska
San-po
B
BURMA
Chindwin
Irrawad
Sittang
D
S.W. CHINA & INDO-CHINA
Song-Ka
Si-Kiang
Fig. 3. SOME EXAMPLES OF RIVER-CAPTURE IN ASIA. In A, B, and D numbers represent the former drainage lines. In C points of river-capture are marked “x.”
Yangtse. Note, too, that the Song-ka of Tonking appears to be about to rob the Mekong.

4. The largest drainage or catchment area is that feeding the Arctic. The three principal rivers are the Ob, Yenisei, and Lena, all rising in the northern fold area, but the former

RELIEF AND STRUCTURE: DRAINAGE

two flow across the Quaternary rocks of the western section, whilst the last named flows across the ancient rocks of the eastern. They all have one feature in common-they rise in warmer southerly latitudes and flow to the Arctic. There- fore in spring the upper courses thaw before the lower and are fed by the melting of the winter snows. This results in extensive flooding in the lower basins followed by more flooding in the autumn when the lower courses freeze first. An examination of the map shows that the West Siberian rivers have similar features to those of Northern Europe in that they zig-zag across the plain in a general S.E.-N.W. direction with well-developed east-west tributaries. In both areas the great ice-sheets deposited accumulations of debris, called moraines, which stretch roughly from east to west.

When a warmer climate returned at the close of the Glacial Age and the rivers began to flow again, they were forced into parallel east-west courses along the southern edges of the moraines. The Siberian ones then drained into the great Gulf of Ob. Next, swift streams rising on the northern edges of the moraines undercut the lower east-west rivers, resulting in another type of river-capture. Fig. 3C shows how the present Lower and Middle Yenisei have played a big part in this process. Note particularly how the three right bank tributaries, the Tunguskas, must have once continued west- wards to the Ob basin until they were diverted. A further capture seems imminent by a tributary of the Ob in the foothills of the Sayan Mountains, and the Lower Tunguska has robbed its fellow, the Stony Tunguska, of its headwaters.

These rivers rank amongst the longest in the world, but are of little importance because they flow into the Arctic. Taking the main streams only, the Ob measures over 2000 miles, the Yenisei nearly 2,000 miles, and the Lena nearly 2,500 miles. In the extreme north-east there is a series of shorter, swifter streams draining the Chersk and the Anadyr Mountains.

Coast Lines

The coasts of the three oceans bordering the continent each represents a very different type. That of the Indian Ocean describes two great bays, the Arabian Sea and the Bay of Bengal, with two large gulfs projecting from the former, the Red Sea-Gulf of Aden and the Persian Gulf. The former is part of the Great Rift Valley and the latter the flooded part of the Mesopotamian Syncline. Note how the main lines of direction of the Red Sea, Mesopotamia, the west coast of India, the Arakan Range, and Malaya turn generally from north-west to south-east, whilst there are indications of minor direction lines at right angles in the coast of Arabia, the north- east coast of India, and the Indus Valley. This parallelism of surface features is common in areas where there has been much faulting and fracturing of the crust, e.g. the Scottish Highlands. Note, too, that the phenomenon is continued along the east coast of Africa.

Turning to the Pacific, we find a similar north-west to south-east trend (in, e.g., the Malayan coast, Indo-China, the north-east coast of China, the Korean Peninsula, Sakhalin, and Kamchatka) with minor trends at right angles (e.g. Cochin China, S.E. China, and the south-east coast of Honshu, Japan). This feature is overshadowed in the Pacific by the “festoons” of islands where archipelagoes appear to hang from the main- land, e.g. the Japanese group. On examination, however, it is clear that these festoons are themselves part of the same north-west to south-east and north-east to south-west structure lines.

Compared with the other two, the Arctic coast has few outstanding features. We may note, however, that in the west the rivers flow into long estuaries and in the east they form deltas. This difference is largely caused by the different characters of the respective basins. The rivers of the west wander over relatively flat areas so that their rate of flow is slow. Therefore, they drop most of the load derived from the upper courses before they reach the sea. Those of the east are much swifter so that they bring the silt right down to their mouths. In addition the tidal scour in the Western Arctic is much more vigorous than that of the eastern part.

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