How catastrophic Ice Age flooding shaped the unique landscape of the Pacific Northwest

[Emily]

http://www.iafi.org/floods.html

About the Ice Age Floods

Early settlers in eastern Washington State recognized that the landscapes were different than those seen in other places but were not sure why. A closer examination of the features in the Basin led one geologist, J. Harlen Bretz, to propose that only a sudden cataclysmic flood, on a scale never before considered possible, could account for the phenomenal size and distinctive characteristics of the landforms. This radical idea was not well received by fellow geologists, and a long-running scientific dispute followed. Ultimately his extensive field work, plus additional research by others, conclusively established that many extraordinarily huge and powerful Ice Age floods had shaped the region.
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During the most recent episode of major ice-sheet expansion, between about 18,000 and 13,000 years ago, a lobe of the Cordilleran ice sheet advanced into the Idaho Panhandle to the area that is now occupied by Lake Pend Oreille, thus blocking the Clark Fork River drainage and causing Glacial Lake Missoula to form. At its largest, the lake was deeper than 2,000 feet deep at the dam and held over 500 cubic miles of water?as much as Lake Erie and Lake Ontario combined. The ice dam, however, was subject to repeated failure.

When the dam broke, a towering mass of water and ice was released and swept across parts of Idaho, Washington, and Oregon on its way to the ocean. The peak rate of flow was ten times the combined flow of all the rivers of the world...

The Ice Age Floods Institute (IAFI) is an educational nonprofit founded in 1995.