Missoula History & Museums: Glacial Lake Missoula

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Glacial Lake Missoula

About 12,000 years ago, a catastrophic flood occurred that would forever change the geological face of western Montana, Idaho, Washington and Oregon. The glacial dam that had formed Glacial Lake Missoula crumbled, sending out torrents of water that would slice through the northwest like a razor. Read More

Glacial Lake Missoula was formed during the Pleistocene Ice Age, which is the most contemporary of the five ice ages that have occurred in Earth's history. The ancient lake was formed when Cordilleran Ice Sheet dammed the Clark Fork River, which trapped water behind the dam to create the lake. This rising water behind the dam destabilized the dam until it finally burst with violent force.

The catastrophic flood waters spread across the northeasterly stretches of America with force equal to the flow of sixty Amazon Rivers. Because the force was so dramatic, Glacial Lake Missoula probably emptied within a week. The flood waters tore away layers of topsoil and bedrock, and even carried mammoth boulders over 500 miles away. The impact of the flood can still be viewed today, particularly in the "scablands" of Washington State, where otherwise pristine land is scarred by ripped away land.

The unique geological landscape had puzzled geologists. It took the pioneering work of J. Harlen Bretz and Joseph T. Pardee to solve the riddle of the unusual formations in the northwest. Their work lead to the theory that the disintegration of Glacial Lake Missoula was the cause of the region's "scablands."