Ancient lake

An ancient lake is a lake that has consistently carried water for more than one million years. Many have existed for more than 2.6 million years, the full Quaternary period. Ancient lakes continue to persist due to plate tectonics in an active rift zone. This active rift zone creates lakes that are extremely deep and difficult to naturally fill with sediment. Due to the prolonged life of ancient lakes (1–30 million years old), they serve as models for isolated evolutionary traits and speciation.

There are 6 major types of lakes (Listed below). The majority of lakes dry up as the result of the filling with lacustrine deposits; sediment deposited from a river into a lake over thousands of years. Factors that influence the water level decreasing includes fluvial-lacustrine sediment build up, evaporation, natural drainage and geophysical processes. Ancient Lakes have such a prolonged life when compared to younger more traditional lakes due to the local active rift zones and subsided sections of land called grabens.

For example, Lake Baikal in Russia, the deepest lake in the world is an ancient lake created by the Baikal Rift Zone; 25-30 million years old, 5,387 feet (1,642m) deep. Compared to the Great Lakes in North America, which were formed by the last glacial period by glacial scouring and the pooling of meltwater: 14,000 years old, max depth of lakes ranging from 200-1,300 feet deep.

Ancient lake formation is similar to that of a rift valley. Formation occurs within a graben that is located on an active rift zone. Grabens are sections of land, formed along divergent plate boundaries, which have subsided between two parallel plates. The location of the graben above the active rift zone results in a lake bottom that is constantly dropping in depth and walls increasing in height.

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