Lakes, glaciers and groundwater

A lake is water collected in a natural hollow on land; unlike a sea, a lake is not joined to the ocean. The largest lake is the Caspian (area about 371 thousand km²) and the deepest is Baikal (≈ 1642 m). By origin lakes are tectonic (Baikal, Issyk-Kul), dammed (Sarez) and oxbow lakes; by water regime they are outflowing (a river leaves them) or closed (the Caspian). Closed lakes in hot climates are salty because water evaporates and the salt stays; the Dead Sea has more than 300 g of salt per litre (the textbook gives 270 g). The Aral Sea was once a large lake, but its water has greatly decreased. Glaciers are long-lasting ice formed when snow accumulates and compacts on land; they form above the snow line, above about 3500 m in the Tien Shan and Pamirs. In Antarctica and Greenland ice is several km thick; large ice mountains that break off a glacier and float on water are icebergs, most of which is under water, so they are dangerous for ships. Groundwater is water in the pores of rocks: ground water, interlayer (pressure) water, artesian wells and springs, and mineral waters (Chimyon, Chortoq).