Lakes - Lentic Ecosystems
Most lakes occur in regions which have recently been subjected to geological changes; say within the past 20,000 years. However, a few lakes, such as Lake Baikal in Russia and Lake Tanganyanitia in Africa are ancient and are estimated to have originated twenty million years ago. Lakes arise in several ways. Some, like the tectonic lakes, are formed in basins created by geological activities such as warping and faulting of the earth's crust. Most of the Himalayan lakes are tectonic in origin.
Some are formed in crater depressions of extinct volcanoes and are called crater lakes, for example lake Konsar nag in Kashmir. Others may be a result of glacial activity. For example most lakes of North America originated due to glacial erosions and deposition, whereby glacial abrasions of slopes in high mountain engraved basin which later became filled with melting snow and rain. Still others have been formed by deposition of silt, drift-wood and other debris in beds of slow moving streams. Lakes may also arise by landslides blocking off streams and valley.