Lake

Although several geological phenomenon account for the formation of numerous lakes on Earth, most lakes were formed as a result of glacier activity. Earth's glacial ice formed and extended into what is now Canada, the northernmost United States, and northern Europe. As the heavy, thick ice pushed along, it scoured out top soil, creating crevices in the former landscape. Glacial growth peaked about 20,000 years ago, after which time the ice slowly began to melt. As the ice melted, the glaciers retreated, but the basins formed by glaciers remained and filled with water from the melting glaciers. Lake basins formed at the edge of glaciers were generally not as deep as basins underneath glaciers. The shallower lakes are called ice-block or depression lakes; the lakes formed under glaciers (some more than 1 mi [1.6 km] high) are called ice-scour lakes.

Movements of earth, water, and wind can also form lakes. Rock deformations of the earth's crust occur as folds, tilts, or sinking, usually along fault lines. Depressions Kettle lakes like this one in Dundee, Wisconsin, are formed when blocks of ice buried by moving glaciers melt and leave a depression. JLM Visuals. Reproduced by permission.
created can fill with water, forming lakes such as Lake Baikal in Siberia. It may seem peculiar to state that water forms lakes also, but water currents and land erosion by water form specific types of lakes: oxbow and solution lakes. Oxbow lakes are created as windy rivers change course. Windy rivers such as the Mississippi meander, carrying water through twists and turns; when they change direction at a particular twist or turn in the river, a loop can become separate from the main water flow. As deposits build up and separate the loop from the river, an oxbow lake such as Lake Whittington in Mississippi forms. Solution lakes result from ground water eroding the bedrock above it, creating a sinkhole. Sinkholes are the predominant type in Florida and on the Yucatan Peninsula. Wind can also create lake basins called blowouts; such lakes usually occur in coastal or arid areas. Blowouts created by sand shifted in arid regions are typical of lakes in northern Texas, New Mexico, southern Africa, and parts of Australia.

A few lakes result from meteors or volcanic activity. Gases at high pressure under crests of volcanic lava can explode, forming basins that collect water. Volcanic basins up to 1 mi (1.6 km) in diameter are called craters, and those with diameters greater than 1 mi (1.6 km) are called calderas. Crater Lake in Oregon is a caldera 1,932 ft (590 m) deep, 20 ft (6 m) in length, and 16 ft (5 m) in width. This makes it the seventh deepest lake in the world. The largest well-documented meteorite-formed lake in the world is Chubb Lake in Quebec. Lake Chubb is 823 ft (250 m) deep inside a crater 10,990 ft (3,350 m) wide.

Dams made by streams, beavers, and humans have also created lakes. Natural dams can be formed as a stream deposits debris at the point that it enters a river; the accumulated material can close off the stream, creating a lake. Man-made lakes have many characteristics in common with natural lakes, although water level can be less consistent in man-made lakes.