The lake — it is a closed recess sushi filled with water and which has no direct connection with the ocean. Unlike rivers, lakes — the reservoirs slow water exchange. The total area of the lakes of the Earth about 2.7 million km2, or about 1.8% of the land surface. Lakes are everywhere, but unevenly. On the geographical distribution of lakes is greatly influenced by the climate, causing them to diet and evaporation, as well as the factors contributing to the formation of the lake basin. In areas with a humid climate, many lakes, they are flowing, fresh and mostly running. In areas with a dry climate, ceteris paribus smaller lakes, often dry, often closed, and that is often salty. Thus, the distribution of lakes and their hydrochemical characteristics due to the geographical zoning .
The largest lake — Caspian (area 368 km2). The largest are lake superior. Huron and Michigan (Sat. America), Victoria (Africa ), The Aral Sea (Eurasia ). The most profound — Baikal (Eurasia) — 1620 m and Tanganyika (Africa) — 1470 m.
Lakes are often classified by four characteristics:
the origin of lake basins;
the origin of the water mass ;
the water regime;
the salinity (amount of dissolved substances).
Origin of lake basins of the lake are divided into five groups.
1. Tectonic lake basins are formed as a result of the formation of cracks, fissures and subsidences of the earth’s crust. They have plenty of depth and steepness of the slopes (Baikal, North American and African Great lake Winnipeg, Great Slave, the Dead sea, Chad. Eyre, Titicaca, Poopo., etc.).
2. Volcanic. formed in craters of volcanoes or depressions in the lava fields (Kurilskoye and Kronotskoye Kamchatka. many lakes of Java island and New Zealand ).
3. Glacial lake basin formed in relation to viphavadee by the activity of glaciers (erosion) and the gathering of the waters before the glacial landforms. when the glacier during the melting of rocks portable material, forming hills, ridges, hills and depressions. These lakes are usually long and narrow, oriented along the lines of a melting glacier (lake of Finland. Karelia, The Alps. Urals, Caucasus, etc.).
4. Karst lakes basin which arose as a result of failures, subsidence of soils and erosion of rocks (limestones, gypsum, dolomite). Dissolution of these rocks with water leads to the formation of a deep, but small area of the lake basin.
5. Dammed (dammed or dammed) lakes result from block of the channel (valley) of the river boulders of rocks during a landslide in the mountains (O. Sevan, Tana, many lakes of the Alps, the Himalayas and other mountainous countries ). From a large landslide in Pamir in 1911, was formed the Sarez lake with a depth of 505 m.
A series of lakes formed due to other reasons:
flooded lakes are common on the shores of seas — that the coastal stretches of sea, separated from it by a coastal KOs;
oxbow lakes — of the lake that occurred in old river channels.
The origin of the water mass in the lake are of two types.
1. Atmospheric. This lake that have never been part of the ocean. Such lakes on Earth prevail.
2. Relict or residual, of the lake, which appeared in place of retreating seas (Caspian, Aral, Ladoga. Onega. Ilmen, etc.). In the recent past, the Caspian sea was connected with the Azov Strait that existed at the site of the present valley of the river Manych.
Water also there are two types of lakes — waste and bestacne.
1. Sewage lakes — this lake, in which flow of which flow rivers (lakes are sources ). These lakes are most often in the zone of excessive moisture.
2. Closed — in which rivers flow, but none flows out (lakes do not have a sink). These lakes are mostly located in the zone of insufficient moistening.
The amount of dissolved substances there are four types of lakes: fresh, salted, salty and mineral .
1. Freshwater lake — the salinity of which does not exceed 1‰ (one per Mille).
2. Brackish — such lakes salinity to 24‰.
3. Salt — the content of dissolved substances in the range of 24.7-47‰.
4. Mineral (47‰). These lakes are Sadovyi, sulfate, chloride. In lakes mineral salts can precipitate. For example, the self-deposited lakes Elton and Baskunchak, which produces salt.
Generally waste freshwater lake, as the water in them is updated continuously. Inland lakes are often salted, because the flow of water they dominated the evaporation, and all mineral substances remain in the reservoir.
Lakes, and rivers, — the most important natural resources used by man for navigation, water supply, fisheries, irrigation. production of mineral salts and chemical elements. In some places a small lake, often artificially created by humans. Then they are also called reservoir .