Glacial Lake Missoula
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Glacial Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about 7,770 square kilometres (3,000 sq mi) and contained about 2,100 cubic kilometres (500 cu mi) of water, half the volume of Lake Michigan.[1]
The lake was the result of an ice dam on the Clark Fork River caused by the southern encroachment of a finger of the Cordilleran Ice Sheet into the Idaho Panhandle (at the present day location of Lake Pend Oreille). The height of the ice dam typically approached 610 metres (2,000 ft), flooding the valleys of western Montana approximately 320 kilometres (200 mi) eastward. It was the largest ice-dammed lake known to have occurred.[2]
The periodic rupturing of the ice dam resulted in the Missoula Floods--cataclysmic floods that swept across Eastern Washington and down the Columbia River Gorge approximately 40 times during a 2,000 year period. The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream.[3] These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through gradual processes.
[edit] See also
[edit] Cited references
- ^ Bjornstad, Bruce N. (c2006). On the trail of the Ice Age floods : a geological field guide to the mid-Columbia basin / Bruce Bjornstad.. Sandpoint, Idaho: Keokee Books, p. 4. ISBN 9781879628274.
- ^ Alt, David; Hundman, Donald W. (1995). Northwest Exposures: A Geologic History of the Northwest. Mountain Press. ISBN 0-87842-323-0.
- ^ Allen, John Eliot; Burns, Marjorie and Sargent, Sam C. (c1986). Cataclysms on the Columbia : a layman's guide to the features produced by the catastrophic Bretz floods in the Pacific Northwest. Portland, OR: Timber Press, p. 104. ISBN 0881920673.
[edit] External links
- PBS's NOVA (TV series): Mystery of the Megaflood for information on the Missoula Floods
- The Seattle Times' Pacific NW magazine - "Trailing an Apocalypse" - 30-Sep-2007
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