Crater lake
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- This page describes the geological feature. For the lake of the same name, see Crater Lake.
A crater lake is a lake that forms in a volcanic crater or caldera after the volcano has been inactive for some time. Incoming precipitation fills the depression to form a deepening lake, until an equilibrium is reached between the rate of water coming in and the rate of water loss due to evaporation, subsurface drainage, and possibly also surface outflow if the lake fills the crater up to the lowest point on its rim. Some crater lakes are acidic, while other lakes' water remains fresh. Some also have geothermal activity, especially if the volcano is merely dormant rather than extinct.
A well-known crater lake, which bears the same name as the geological feature, is Crater Lake of Crater Lake National Park, in Oregon, USA. It is formed in the caldera of Mount Mazama. (The Mount Mazama article features a detailed description of the geologic events leading to a crater lake's formation.) It is isolated from rivers and streams, and therefore has no inflow or outflow at the surface, and hence no pollution from river input. It is fed by melting snow. Crater Lake is the deepest lake in the United States with a depth of 594 m (1949 feet). It should also be noted that the name "Crater Lake" is a misnomer, since this particular lake occupies a caldera.
Lakes can also fill impact craters, but these are not usually referred to as crater lakes except in a few isolated cases. Example of such impact crater lakes include Lake Bosumtwi in Ghana and Siljan in Sweden.
[edit] Notable crater lakes
