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The Origin of lake basins

 

The lake basin can be both endogenous and exogenous origin that have the most significant impact on their size, shape, water regime.

The largest lake basins of tectonic origin. They are located either in a simple tectonic structures in the basin in the plains (Ilmen, Chad) or in foothill and intermountain depressions (Balkhash), or in the grabens of the rift (Baikal, Nyasa, Tanganyika). But most of the major lake basin has a complex tectonic origin, in their education are involved as concave folds and breaks of the earth’s crust (Issyk-Kul lake. Victoria, etc.). All tectonic lakes are large in size and significant depth, and rift – an elongated and narrow shape in plan, very large depth, steep slopes. The bottoms of many deep lakes lie below the sea level, having a mirror above the water level, is cryptodepression (Baikal, Ladoga, etc.). In the location of tectonic lakes are observed certain regularities: they are concentrated along faults of the earth’s crust (the Syrian-African and Baikal rift zone), or framed panels: along the Canadian shield is a Large bear, Great Slave, Winnipeg, Athabasca, Great North American lakes; the Baltic shield along the Vyg, Segozero, Onega, Ladoga, etc.

The lakes occupy volcanic craters and calderas of extinct volcanoes or depressions in the surface of solidified lava flows (Kronotsky lake on the Kamchatka Peninsula, lake Java, New Zealand).

Along with lake basins created by the internal processes of the Earth, are very numerous bath lake, formed by exogenous processes.

Among the most common glacial (moraine) lake on the plains and in the mountains as in basins, wymaganych the glacier and in the depressions between the hills, with uneven deposition of the moraine. Destructive activities of ancient glaciers owe their origin to the lakes of Karelia and Finland, which are elongated in the direction of movement of the glacier from the North-West to South-East along tectonic cracks (actually they are of mixed glacial and tectonic origin, like Ladoga, Onega and other lakes on the periphery of the Baltic and Canadian shields). To a glacial hollow in the mountains are numerous small glacial lake in a bowl-shaped hollows on mountain slopes below the snow line (in the Alps, the Caucasus, the Altai) and the lake trough – shaped valleys in the mountains (Geneva, Constance). With an uneven accumulation of glacial deposits associated with lake surrounded by hilly moraine relief in the North-West of East European plain, especially in the Valdai hills, in the Baltic States, Poland. Germany, Canada and the Northern United States. These lakes are usually shallow, broad, lobed shores, with Islands (Seliger, Valdai, etc.). In the mountains such end of the lake arose on the site of the former languages of glaciers (Como, Garda in the Alps). In areas of former glaciations numerous lakes in streambeds melt waters of a glacier – they are elongated, trough-shaped, usually small and shallow (Long, Round on the klinsko-Dmitrovskaya ridge).

Karst thermokarst or thaw lakes are formed in places where leaching of rocks (gypsum, salt, limestone, etc.) underground and partly surface water, they are deep, but small, often rounded in shape (in the Crimea, the Caucasus, the Dinaric mountains).

Suffusion lakes are formed in the subsiding basins of origin in place of intensive removal of groundwater fine-grained mineral particles (in the South of Western Siberia).

Thermokarst thermokarst or thaw lakes occur when the ground is thawing permafrost or the melting of the ice. Thanks to them, the Kolyma lowland is one of the lake regions of Russia. Many relict thermokarst lake basins situated North-West of Eastern European plain in the former glacial and periglacial zones.

Aeolian lakes occur in depressions blowing (lake Teke, Selects in Kazakhstan).

Ice-dammed lakes formed in the mountains, often after earthquakes, avalanches and landslides, blocking the river valley. The most famous of them is lake Sarez was formed in 1911, after the fallout from the earthquake, giant landslide, zabrodivshie the river Murghab in the Pamirs.

In the valleys of lowland rivers are the most numerous floodplain oxbow lakes are characteristic horseshoe shape formed by periodic straightening of bends in the beds of meandering rivers and their separation from river currents. During the drying of the rivers of their pools in the Creek are stored in the form of bochagov – river lakes in the deltas of the rivers there are small lakes, ilmens in place of ducts, often overgrown with reeds and rushes (ilmens of the Volga Delta, the lakes of the Kuban’).

Low-lying coasts of the seas is typical of coastal lakes estuaries and lagoons, if the latter is separated from the sea by a sandy alluvial ridges: spits, bars. For a particular type of organogenic lakes are among swamps and coral structures.

These are the main genetic types of lake basins due to natural processes. But lately there are more “man-made” lakes, man-made, man– made lakes-dams on the rivers, lakes, ponds, quarries, salt mines, in place of peat, etc.

Literature.

Lyubushkin G. S. General physical geography. Proc. a manual for students of higher educational institutions on special. “Geography” / S. G. Lyubushkin, V. K. Passing, A. V. Chernov; edited by A. V. Chernov. – M. Education, 2004. – 288 S.

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