Information Page: Jökulhlaup Iceland
Jökulhlaup Iceland, April 2010
|Domain:||terrestrial, hydrology, marine|
|Keywords:||glacial outburst flood|
|Model name:||Animation model name|
|Name:||RUV, Icelandic TV|
Grade level: Under graduate (13-16)
Statement: jökulhlaup resulting from volcanic eruption
Abstract: April 2010, a jökulhlaup resulting from the volcanic eruption near Eyjafjallajökull.
This movie shows how the generated meltwater and debris spills out of side-gullies and along the valley wall. When the flow reaches the local valley bottom, the sandur surface it fans out. The helicopter flies low over the flow in the sandur plain and one can see standing waves being generated by the shallow fast-moving water. This is an indication that large bedforms are actively formed and migrating over the bottom. It can also been seen that even over the floodplain the flow has erosive effect and incises an estimated > 1,5 m banks.
A glacial lake outburst flood occurs when massive amounts of meltwater are dramatically released. This can be for several reasons: when a lake contained by a glacier or a moraine dam drains. One distinguishes between a ‘Jökulhlaup’, if the lake formed subglacially, or a ‘marginal lake drainage’ if it was dammed between ice and the ground. Glacial outburst flows can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, volcanic eruptions under the ice, or if a large enough portion of a glacier breaks off and massively displaces the waters in a glacial lake at its base.
A jökulhlaup is thus a sub-glacial outburst flood. Jökulhlaup is an Icelandic term that has been adapted into the English language, and originally only referred to glacial outburst floods, which are triggered by volcanic eruptions, but now is accepted to describe any abrupt and large release of sub-glacial water. Glacial lakes come in various sizes, but may hold millions to hundreds of millions of cubic meters of water. Catastrophic failure of the containing ice or glacial sediment can release this water over a timespan of minutes to days. Peak flows as high as 15,000 cubic meters per second have been recorded in these events. On a downstream floodplain, inundation can spread as much as 10 kilometers wide. Both scenarios are horrific threats to lives, property and infrastructure.
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