The major drainage is northward. Long, wide, deep rivers which meander across the vast marshy and forested, lake-strewn plain to the Arctic Ocean. The coastline is irregular, broken by long embayments and numerous close islands. Soils and vegetation. Three distinctive zones are present: (1) North of the Arctic Circle, highly organic soils of peat over sand and clay are widespread and are especially thick along rivers. North of about 72°N, Arctic barrens have only spotty turf of dwarf grass, herbs, and lichens less than a foot tall and scattered shallow peat bogs. Southward, grassland, grassy tundra, and dense scrub tundra also include scattered shallow peat bogs. (2) South of the tree line, which is near the Arctic Circle, to the latitude of Tyumen and Tomsk, very deep sand, clay, and peat soils support dense evergreen and deciduous taiga forest. Numerous peat bogs with thick peat over sand and clay also characterize this zone. (3) In the southernmost areas, cropland with patches of forest and fields of grass are common on deep to very deep fine-grained soils. A few areas of very deep sand are also present. Permafrost. Permafrost occurs in much of the area north of about 60°N in three zones: (1) North of the Arctic Circle, permafrost is mostly continuous and generally more than 200 m thick; the active layer is only .5-1.0 m thick. In places, the permafrost is more than 600 m thick. Along river valleys, the thickness of permafrost decreases. (2) From the Arctic Circle south to about 62°N, permafrost is not continuous, but commonly there are two layers of permafrost separated by unfrozen ground (talik). The upper (Recent) permafrost layer ranges from 10-100 m in thickness and the talik from 10-50 m. The top of the lower (Pleistocene) permafrost occurs at depths of 80-200 m, and extends down to 200-300 m below the surface. (3) Between 62°N and 60°N, only Pleistocene permafrost is present, the top is generally 150-200 m below the surface and its thickness is 100-200 m. In much of West Siberia, especially in areas with permafrost, icings (masses of surface ice formed in winter by freezing of groundwater seepage) are common, and they may attain a thickness of 10 m, cover several kilometers, and remain unthawed for several years. Drainage characteristics. Riverflow regime and ice regime vary considerably from north to south. In most of the area, high water, ice jams, and extensive flooding occur from May to August or September. Floods rise as much as 20 m in the lower Yenisey River and extend over 48 km in width in the lower Ob f River. Large areas are more than 50 percent lake covered part of the year. Most rivers and lakes have 2 m of ice or are frozen solid from early December to late March and those in the extreme north freeze in October. The southernmost areas have interior drainage. Many streams and lakes are intermittent, having an abrupt rise after snowmelt in May and a swift fall in late May or mid-June. Many lakes are saline. Ice cover of less than one meter is common from early December to April or May. Clima...
The most higly contaminated surface areas from cesium-137 fallout from the April 1986 accident at the Chernobyl' nuclear power station in Ukraine occur within the 30-km radius evacuation zone set up around the station, and an 80-km lobe extending to the west-southwest. Lower levels of contamination extend 300 km to the west of the power station. The deposition of this radioactive dust on the surface and the subsequent entombment of the damaged reactor effectively result in the de facto establishment of an above-ground nuclear waste storage site. This site is located on a thick sedimentary sequence of loose, mostly clastic deposits, with a shallow (generally 3-5 m) water table. The geology, the presence of surface water, a shallow water table, and leaky aquifers at depth make this an unfavorable environment for the long-term containment and storage of the radioactive debris. An understanding of the general geology and hydrology of the area is important to assess the environmental impact of this unintended waste storage site, and to evaluate the potential for radionuclide migration through the soil and rock and into subsurface aquifers and nearby rivers.
A seismic event of October 4, 1979, east of the Ural Mountains was described by the U. S. Department of Energy as an underground nuclear explosion. The location of this event by the U. S. Geological Survey places it in the oil-rich Middle Ob region of West Siberia in the vicinity of the Salym oil field. The field, which was discovered in 1965, has seven oil pools, of which the main pay is the bituminous shale of the Upper Jurassic Bazhenov Formation. This formation is one of the few examples of a primary oil-bearing pelite reservoir having a high content of organic matter that was also the source of the oil. A characteristic of the Bazhenov Formation is the wide range of fracture permeability and oil flow rates. Where fracture permeability is high, wells yield more than 2,100 bbl/day. Elsewhere, wells yield less than 35 bbl/day or are dry. The seismic event of October 4, 1979, may have been an underground nuclear explosion experiment designed to stimulate production by fracturing the tight bituminous shale. Previous attempts to stimulate oil production in the U.S.S.R. by using nuclear explosions were carried out in carbonate reservoirs.
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