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In lakes of our planet contains four times more waters, than in the rivers, but their life is much less long. And if lakes do not replenish with arriving waters, they can shoal, dry up or turn to bogs.

Geographers classify lakes on a way of their formation, the maintenance of salts and life presence. Only in most salty of them there is no life. The majority of lakes were generated owing to earth movements or eruptions of volcanoes. Some have been left by receding glaciers, and only the few have appeared as a result of branch from the sea. Many lakes are created by people. They are called as water basins as contain a reserve of water for hydroelectric power stations and other economic needs.

Tectonic lakes

Tectonic lakes Breaks and earth movement folds - the reason of formation of Caspian sea, the biggest lake of the Earth, and Baikal in Siberia, deepest of lakes. For the last some millions years its sizes constantly varied. Before lifting of the Caucasian ridge Caspian sea incorporated with Black. And lake Baikal has arisen owing to a break of the block of earth crust therefore there was a hollow filled with water.

East African riftovaja system - one more example of a huge break. It is stretched since Ju.-century of Africa on S to JU.-Z. Asia also it is filled by a chain of lakes. Most known of them - Albert, Edward, Tanganyika and Njasa (Malawi). The Same system (in territory of Israel) posesses also the most low-sited lake in the world - the Dead Sea (-399.

Volcanic lakes

The Most widespread form of volcanic lake is the crater of a volcano filled with water. Lake Oregon (USA) Krej-rubbed in a crater of a volcano of Mazama, was formed 6600 years ago and has diameter of 10 km and depth of 589 m.

Some lakes were generated at blocking of volcanic valleys by streams of a lava and skaplivanii in them waters. As an example lake Kivu, a hollow in East African riftovoj serves system on border of Zaire and Ruanda. Once the river Ruzizi following from lake Tanganyika, on a valley to Kivu flew on the north to Nile but since eruption of a nearby volcano has blocked a channel of the river, its waters have filled a hollow.

The Lakes created by glaciers during last glacial age, are most extended in Northern hemisphere.

Glaciers left after themselves deep hollows. In them thawed snow accumulated. A moraine (glacial adjournment) zapruzhivala hollows, forming lakes. An example - Lake-land reservoirs on S.Anglii.

In emptiness of calcareous breeds underground lakes also can be formed. Water dissolves limestone, creating the huge caves filled with water. Similar lakes can be formed in areas of underground salt deposits.

Salty lakes

Salty lakes the Majority of lakes presnovodny also eat at the expense of streams, the rivers, rain waters, but at the limited receipt of fresh water minerals and the soils which are washed off from coast, gradually collect. Fresh water evaporates, and in lake there is a hydrochloric solution rich with minerals. The big Salty lake in the State of Utah, the USA, - a typical example of the given kind of formation.

Caspian and Aral exhausting in the Russian Federation - too salty lakes. Aral was the fourth lake on size in the world before channels of the rivers filling up it therefore it began to dry up have been changed. Its area has decreased about 77 451 km - to 40 000 km that gives the grounds to speak about gradual  destruction of lake.

The Most salty lake - the Dead Sea in the Jordanian valley between Israel and Jordan (it the most low-sited). Its water in 9 times solonee the oceanic. As a result of its density it is so great that on a lake surface it is possible to lie easy as on a bed, reading the newspaper.

Artificial lakes

Water basins - the most known example of artificial lakes. Among the largest - lake Naser on border of Egypt and Sudan, created by a way zapruzhivanija valleys of Nile, and lake Mid in the USA, appeared after overlapping by a dam of the river of Colorado. All of them serve HYDROELECTRIC POWER STATION. There is also a set of artificial lakes for maintenance with water of large settlements and for industrial use.