Jökulhlaups

Icebergs on dry land after a jökulhlaup drained Iceberg Lake (Wrangell-St. Elias National Park, AK)
Icebergs were left perched on dry land after a jökulhlaup drained Iceberg Lake (Wrangell-St. Elias National Park, Alaska)

NPS Photo

Jökulhlaups (an Icelandic word pronounced yo-KOOL-lahp) are glacial outburst floods. They occur when a lake fed by glacial meltwater breaches its dam and drains catastrophically. These lakes can take a number of forms:

  • Ice dammed lakes that are held in by the glacier ice itself
  • Moraine, rock, or sediment dammed lakes
  • Lakes that lie form beneath glaciers

In order for a jökulhlaup to occur, the lake water levels must reach a critical point such that the lake:

  • Causes its ice dam to float
  • Overtops its dam, causing rapid incision into the sediment, rock, or ice that contains it
  • Carves large meltwater channels beneath the glacier ice that allow for rapid drainage

Jökulhlaups may occur with a somewhat regular periodicity, but others drain without warning. 

To learn more about glaciers, glacier features, and glacial landforms, see the Glaciers & Glacial Landforms Page.

Last updated: February 9, 2018