Glacial Lake Missoula

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Wave-cut strandlines cut into the slope at left in photo. These cuts record former high-water lines, or shorelines of Glacial Lake Missoula near Missoula, Montana. Gullies above the highway are the result of modern-day erosion. (NPS Photo)

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 km² (3,000 square miles) and contained about 2100 cubic kilometers (500 cubic miles), 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 m (2,000 feet), flooding the valleys of western Montana approximately 320 km (200 miles) 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 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 km³ (50 mi³) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream.^[3]

[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.