Volcanic Dam

A volcanic dam is a natural dam produced directly or indirectly by volcanism, holding or temporarily restricting the flow of surface water in an existing stream much like an artificial dam. There are two main types, those created by the flow of molten lava and those created by the deposition of pyroclastic material and debris; the classification generally excludes the larger, often longer-lived crater lakes, though a volcano's own confining rim may itself be considered such a dam where the lake level within a crater runs relatively high.