GEOSCIENCE

Recurrent Flooding

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Science  14 Mar 2003:
Vol. 299, Issue 5613, pp. 1627
DOI: 10.1126/science.299.5613.1627a

When an ice dam broke during the last deglaciation, torrential floodwaters from Glacial Lake Missoula, which was located in western Montana, surged across eastern Washington, creating the now famous “channeled scabland.” Similar features have since been found near the former margins of receding glaciers throughout the Northern Hemisphere, and such flooding is recognized as a common, albeit extreme, process.

Whether the ice dam confining Lake Missoula was breached repeatedly has been debated, in part because the transitions between the layered floodwater deposits are subtle and hence it is not clear whether they represent scores of distinct events or the rhythmic sedimentation of just a few long-lived outflows. Clague et al. used paleomagnetic measurements and the demarcation of two volcanic horizons derived from Mount St. Helens preserved in the flood sediments to resolve this question. Their data imply that perhaps as many as 40 voluminous floods inundated the region over several thousand years. — BH

Geology31, 247 (2003).

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