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glacial lake outburst flood
A glacial lake outburst flood (GLOF) is a type of outburst flood that occurs when the dam containing a glacial lake fails. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a Jökulhlaup. The dam can consist of glacier ice or a terminal moraine. Failure 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.
==Definition==
A glacial lake outburst flood is a type of outburst flood occurring when water dammed by a glacier or a moraine is released. A water body that is dammed by the front of a glacier is called a marginal lake, and a water body that is capped by the glacier is called a sub-glacial lake. When a marginal lake bursts, it may also be called a marginal lake drainage. When a sub-glacial lake bursts, it may be called a jökulhlaup.
A jökulhlaup is thus a sub-glacial outburst flood. Jökulhlaup is an Icelandic term that has been adopted into the English language, originally referring only to glacial outburst floods from Vatnajökull, which are triggered by volcanic eruptions, but now is accepted to describe any abrupt and large release of sub-glacial water.
Glacial lake volumes vary, but may hold millions to hundreds of millions of cubic metres of water. Catastrophic failure of the containing ice or glacial sediment can release this water over periods of minutes to days. Peak flows as high as 15,000 cubic metres per second have been recorded in such events, suggesting that the v-shaped canyon of a normally small mountain stream could suddenly develop an extremely turbulent and fast-moving torrent some deep. Glacial Lake Outburst Floods are often compounded by a massive river bed erosion in the steep moraine valleys, as a result, the flood peaks increase as they flow downstream until the river reaches, where the sediment deposits. On a downstream floodplain, it suggests a somewhat slower inundation spreading as much as wide. Both scenarios are significant threats to life, property and infrastructure.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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