Jökulhlaup

A jökulhlaup is a sudden flood released from a glacial or ice-dammed lake, often through or beneath a glacier. It can carry enormous volumes of water, sediment, and ice.

Subglacial lake: A body of water stored beneath a glacier or ice sheet. Many jökulhlaups begin when a subglacial lake drains through or beneath its ice cover.
Grímsvötn: A subglacial volcanic lake beneath Vatnajökull in Iceland. Its lake repeatedly drains in jökulhlaups that flow toward the Skeiðarársandur plain.
Glacial lake outburst flood: A sudden flood caused by the failure or drainage of a lake associated with a glacier. Jökulhlaup is commonly used for this flood type, especially in Icelandic and glaciological contexts.
Jökulhlaup deposit: A sediment deposit laid down by a glacial outburst flood. Its grain sizes and layers preserve evidence of a flood’s power and changing flow.
Ice-dammed lake: A lake held back by a glacier or ice sheet. A jökulhlaup can begin when rising water or changing ice opens a route through the dam.
Skeiðarársandur: A broad sandur plain on Iceland’s south coast, built by glacial rivers. Repeated jökulhlaups from Vatnajökull have deposited sediment across this plain.
Flood hydrograph: A graph showing how river discharge changes over time during a flood. Its rising limb and peak help distinguish gradual lake release from rapid outburst drainage.
Outwash fan: A fan-shaped deposit of sediment spread by meltwater beyond a glacier or valley mouth. Large jökulhlaups can build outwash fans where floodwater loses speed.
Nye channel: A subglacial water conduit whose roof and walls are formed by ice and bedrock. A growing Nye channel can carry an outburst flood beneath a glacier.
Katla: A volcano beneath the Mýrdalsjökull ice cap in southern Iceland. Subglacial eruptions at Katla can melt ice and trigger jökulhlaups.

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