Ancient lake

There are six 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 include fluvial-lacustrine sediment build-up, evaporation, natural drainage, and geophysical processes. Ancient lakes have a prolonged life when compared to younger, more ordinary 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 which is 25–30 million years old and 5,387 feet (1,642 m) deep. This is compared to the North American Great Lakes, which were formed by the last glacial period by glacial scouring and the pooling of meltwater which are 14,000 years old and have maximum depths ranging from 200–1,300 feet (60–400 m) deep.

• Rift lakes^{[clarification needed]}
• Landslide and ice dam lakes
• Salt lakes
• Oxbow lakes
• Crater lakes
• Glacial lakes
• Subglacial lakes

Ancient lakes allow scientists to study the mechanisms of environmental changes over glacial-interglacial timescales. Evolutionary characteristics including sexual selection, adaptive radiation and punctuated equilibrium are studied in ancient lakes due to their prolonged existence and general geographic isolation. Most of the research has been associated with the endemic fauna and diatoms that exist in these isolated lakes, concentrating on Lake Baikal, the Caspian Sea and the African Great Lakes. Information is derived from the associations of the fluvial-lacustrine, fluctuating profundal and evaporative facies.^{[citation needed]}

These are the ancient lakes in the world that have existed for more than 1 million years, excluding the many subglacial lakes whose age is yet to be determined.^[1]