A sudden, often annual, release of meltwater from a glacier or glacier-dammed lake, sometimes resulting in a catastrophic flood. Glacial outburst floods are triggered by melting of a drainage channel, buoyant lifting of ice by water, or subglacial volcanic activity. Glacier-dammed lakes may be subglacial (below the glacier), marginal (along the sides of the glacier), or proglacial (at the glacier terminus). Proglacial and ice-marginal dams develop behind moraines or in ice-dammed valleys.
