The lake Formation
Looking at a map, on all continents, you can see the lake. Some of them elongated, others rounded. Some lakes are located in mountainous areas, others on vast flat plains, some very deep and some very shallow. The shape and depth of the lake depend on the size of the basin which it occupies. Lake basins are formed by different ways.
Most of the major lakes of the globe is of tectonic origin. They are located in major deformations of the earth crust in the plains or fill the deep tectonic crack — rift (lake Baikal, Tanganyika, Nyasa, etc.).
Lake basins can become craters and calderas of extinct volcanoes, and sometimes depressions on the surface of lava flows. These lakes are called volcanic, are found, for example, on the Kuril and Japanese Islands, in Kamchatka, on the island of Java and in other volcanic regions of the Earth. It happens that the lava and fragments of igneous rocks dammed the river valley in this case also there is a volcanic lake.
The basin of the lake Kaali in Estonia is of meteoritic origin. It is located in the crater formed by the fall of a large meteorite.
Glacial lakes fill hollows formed as a result of the glacier activity. Moving, the glacier plowed over the soft ground, creating depressions in the topography: in some places long and narrow, while others are oval. Over time they filled with water, and glacial lakes. Such lakes is very much on the North American continent, in Eurasia, the Scandinavian and Kola peninsulas, Finland, Karelia and on the Taimyr Peninsula. In mountainous areas, for example in the Alps and the Caucasus, glacier lakes are located in qarah — bowl-shaped recesses in upper parts of mountain slopes, which involved a small mountain glaciers and snowfields. Melting and retreating glacier leaves a moraine — an accumulation of sand, clay with inclusions of pebbles, gravel and boulders. If Morena stem of the river flowing from under the glacier that formed glacial lake, often having a circular shape.
In the areas composed of limestone, dolomite and gypsum, as a result of chemical dissolution of these surface rocks and groundwater occur karstic lake basin – approx.The layer of sand and clay overlies karst rocks, sinking into underground cavities, forming on the earth’s surface deepening, which will eventually fill with water and become lakes. Karst lakes are found in the caves, you can see them in the Crimea, the Caucasus, the Urals and other regions.
In the tundra, and sometimes in the forest, where widespread permafrost during the warm season, the soil melts and sags. Small pits appear of the lake, called thermokarst. In river valleys, when meandering, the river straightens its course, the old section of the channel is outlined. It formed oxbow lakes, often having the shape of a horseshoe. Dammed or dammed lakes occur in the mountains, when the result of the collapse of a mass of rocks traverses the bed of the river. For example, in 1911 in Pamir during the earthquake occurred giant mountain collapse, he blocked the river Murgab and formed the Sarez lake – approx. Dam are lake Tana in Africa, Sevan in the Caucasus and many other mountain lakes.
Near the shores of seas, sand bars can separate the shallow area from the coastal marine area, the result is a lake-lagoon. If sandy-clayey sediments from the submerged fence off the sea estuaries are formed of estuaries, shallow bays with very salty water. Many such lakes on the coast of Black and Azov seas.