Western Siberian Lowland
Western Siberian Lowland
one of the largest low-land aggradation plains in the world. It is situated to the north of the hillocky Kazakhstan Plain and the Altai Mountains, between the Urals in the west and the Central Siberian Plateau in the east. Length, 2,500 km north-south; width, 1,000-1,900 km east-west. Area, 2.6 million sq km. Its surface is flat and not very rugged with small ranges of elevations. Heights of the lowlands in the northern and central regions do not exceed 50-150 m. Small elevations (up to 220-300 m) are fairly characteristic of the western, southern, and eastern edges of the lowland. A zone of elevations also forms the so-called Siberian Uvaly, extending in the central part of the Western Siberian Lowland from the Ob’ River almost to the Enisei.
Extensive flat areas of interfluves prevail with small surface slopes that are highly swamped and in certain areas complicated by morainic hills and ridges (in the north) or by low, sandy crests (mainly in the south). Flat, ancient lacustrine basins (poles’e) occupy large areas. River valleys form a comparatively thin network; in the upper reaches they consist of shallow hollows with poorly pronounced slopes. Only a few of the largest rivers flow through the well-developed, deep (up to 50-80 m) valleys with a steep right bank and a system of terraces on the left bank.
The Western Siberian Lowland was formed in the area of the epihercynian Western Siberian platform, the foundation of which is composed of intensely dislocated Paleozoic deposits. They are covered with a mantle of loose marine and continental Mesocenozoic rock (clay, sandstone, marl) with an average thickness exceeding 1,000 m (and up to 3,000-4,000 m in basins of the foundation). The most recent, Anthropogenic, deposits in the south are alluvial and lacustrine, frequently covered with loess and loesslike loam; in the north, recent deposits are glacial, marine, and glacial-marine (in certain areas up to 200 m thick). Horizons of subterranean waters—both fresh and mineralized (including brines)—are contained in the mantle of loose deposits of the Western Siberian Lowland. Hot (up to 100°-150°C) waters are also encountered (in the Western Siberian Artesian Basin). Rich industrial deposits of oil and natural gas are contained in the interior of the lowland.
The climate is continental and rather severe. In winter, cold continental air masses from temperate latitudes prevail over the lowland. During warm periods of the year an area of reduced pressure is formed; this area is frequently visited by moist air masses from the North Atlantic. Average annual temperatures range from - 10.5°C in the north to 1°-2°C in the south; January temperatures vary from -28° to -16°C, and July temperatures, from 4° to 22°C. The length of the vegetation period in the extreme south is 175-180 days. The basic body of precipitation is delivered by air masses from the west, mainly in July and August. Total annual precipitation ranges from 200-250 mm in the tundra and steppe zones to 500-600 mm in the forest zone. Snowfall averages 20-30 cm in the steppe and 70-100 cm in the taiga of the Enisei regions.
The territory of the lowland drains more than 2,000 rivers, the total length of which exceeds 250,000 km. The largest of these rivers are the Ob’, Enisei, and Irtysh. Snow waters and summer and fall rains are the basic sources of the rivers. Up to 70-80 percent of the annual runoff occurs during spring and summer. There are many lakes; the largest are Lakes Chany and Ubinskoe. Some of the lakes in the southern regions are filled with salt water and bitter saline water. The large rivers are important shipping and floating routes, linking the southern regions to the north. In addition, the Enisei, Ob’, Irtysh, and Tom’ rivers have large hydroelectric potential.
The lowland nature of the topography of the Western Siberian Lowland results in clearly pronounced geographic longitudinal zones. Excess soil humidification and, consequently, widespread swamp terrain alternating in the south with black and white alkali soils are a distinctive feature of the majority of zones in Western Siberia. The north of the low-land is a tundra zone, in which arctic, moss, and lichen terrains are formed on tundra-arctic and tundra-gley soils.
In the south a terrain of underbrush tundra is formed. A narrow belt of foresttundra extends further to the south. Here intricate complexes of terrains consisting of underbrush tundra, sparse growths of spruce and larch trees, and sphagnum and lowland swamps have been developed on peatgley, gley-podzolic, and bog soils. A large part of the Western Siberian Lowland consists of a forest (forest-swamp) zone, where a taiga, consisting of spruce, fir, cedar, pine, and Siberian larch, predominates on podzolic soils. Only in the zone’s extreme south do taiga massifs alternate with a belt of small-leaved birch and aspen forests. Total area of the forests exceeds 60 million hectares; timber reserves total 9 billion cu m; annual increases in these reserves equal 100 million cu m. The forest zone is distinguished by extensive development of high peat ridge and hollow sphagnum swamps, which in certain locations account for over 50 percent of the land area.
Animals common to the forest zone include the brown bear, lynx, glutton, marten, otter, kolinsky, sable, elk, Siberian roe, squirrel, Siberian chipmunk, muskrat, and other representatives of the European-Siberian subregion of the Paleoarctic.
A forest-steppe zone is situated to the south of the subzone of small-leaved forests. Here leached and ordinary chernozems, meadow-chernozem and dark-gray forest and swamp soils, black alkali soils, and alkaline podzols are formed under not fully plowed herbage swamps, birch-aspen copses (kolki), and grassy swamps. A steppe zone occupies the extreme southern portion of the Western Siberian Low-land. In the north of this zone herbage and feather-grass predominated not long ago, and in the south, feather-grass and fescue steppes. Now these steppes with their abundant chernozem and dark-brown soils have been plowed, and only areas with saline soils have sometimes preserved their pristine character.
REFERENCESZapadno-Sibirskaia nizmennost’: Ocherk prirody. Moscow, 1963. Zapadnaia Sibir’. Moscow, 1963.
N. I. MIKHAILOV