Geology
The West Siberian Plain consists mostly of Cenozoic alluvial deposits and is extraordinarily flat. A rise of fifty metres in sea level would cause all land between the Arctic Ocean and Novosibirsk to be inundated (see also Turgai Straits, West Siberian Glacial Lake). It is a region of the Earth's crust that has undergone prolonged subsidence and is composed of horizontal deposits from as much as 65,000,000 years ago. Many of the deposits on this plain result from ice dams; having reversed the flow of the Ob and Yenisei Rivers, redirecting them into the Caspian Sea, and perhaps the Aral Sea as well. It is very swampy and soils are mostly peaty Histosols and, in the treeless northern part, Histels.
It is one of the world's largest areas of peatlands, which are characterized by raised bogs. It is believed that Vasyugan Swamp is the world’s largest single raised bog, covering approximately 20,309 mi² (51,600 km²).
In the south of the plain, where permafrost is largely absent, rich grasslands that are an extension of the Kazakh Steppe formed the original vegetation (almost all cleared now).
Large regions of the plains are flooded in the spring, and marshlands make much of the area unsuitable for agriculture. The principal rivers in the West Siberian Plain are the Ob, Irtysh, and Yenisei. There are many lakes and swamps, as well as large petroleum and natural gas reserves. Most of Russia's oil and gas production was extracted from this area during the 1970s and 80s.
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