About 12,000 years ago, the valleys of western Montana lay beneath a lake nearly 2,000 feet deep. Glacial Lake Missoula formed as the Cordilleran Ice Sheet dammed the Clark Fork River just as it entered Idaho. The rising water behind the glacial dam weakened it until water burst through in a catastrophic flood that raced across Idaho, Oregon, and Washington toward the Pacific Ocean. Thundering waves and chunks of ice tore away soils and mountainsides, deposited giant ripple marks, created the scablands of eastern Washington and carved the Columbia River Gorge. Over the course of centuries, Glacial Lake Missoula filled and emptied in repeated cycles.
The Ice Dam's collapse can largely be attributed to faults that were created by
frost wedging and repeated expansion and pressurization of water deep below the surface. As a result, you see unprecedented examples of weathering, erosion, and mass wasting across the entire pacific northwest.
In addition to explaining the mystery of the scablands, the discovery of glacial lake missoula provides examples for other similar catastrophic events across the globe, including the biblical story of the great flood.
