Volcanic eruptions under a glacier or ice sheet can lead to sudden releases of meltwater. Such releases occur in Iceland, and their name, jökulhlaup, is taken from the Icelandic (“glacier-flood”). The jökulhlaup that began on 5 November 1996 following eruptions under the Vatnajökull ice sheet released an estimated 3 to 4 cubic kilometers of water over two days, with a peak discharge of 45,000 cubic meters per second. See wdcgc.spri.cam.ac.uk/jokulhlaup/.
The word is also applied to sudden releases of water from glaciers due to causes other than volcanism. For example, in Wyoming the Grasshopper Glacier dammed a lake at its head. In early September 2003 the ice dam gave way. See www.watershed.org/wmc/modules.php?op=modload&name=News&file=article&sid=13 A similar event occurred when the dam formed by the Perito Moreno glacier in Lago Argentina, Argentina, collapsed on 19 March 2004. See www.esa.int/esaEO/SEM2OFX5WRD_index_0.html
A video of the Eyjafjallajökull jökulhlaup of 14 April 2010: www.youtube.com/watch?v=fJII-u-41Lg
A collection of photographs of another Icelandic jökulhlaup of 5 November 1996, taken by Magnús Tumi Guðmundsson and Finnur Pálsson, with comments from the Science Institute at the University of Iceland: www.astrogeology.usgs.gov/Projects/VolcanoIceWorkshop/website_archives/jokulhlaup.pdf
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Last revised: 21 October 2010.