GLACIAL LAKE MISSOULA AND THE ICE AGE FLOODS
courtesy of Mark Alan Wilson and The Nature Center

Strandlines (ancient lakeshores) on Mount Jumbo. Photo courtesy of National Park Service

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 where 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. Over the course of centuries, Glacial Lake Missoula filled and emptied in repeated cycles, leaving its story embedded in the land.Thundering waves and chunks of ice tore away soils and mountainsides, scoured out the scablands of eastern Washington, and carved the Columbia River Gorge.

The floods left a visual legacy that can be seen all along its path, though few places are as grand as the waterfalls of the Columbia River Gorge. The floodwaters scoured and steepened the walls of the Gorge. Creek junctions with the Columbia were torn away, leaving the creeks to plunge over the lip of the newly cut gorge in a series of spectacular waterfalls.

Channeled scablands at Palouse River Canyon, Washington.

Flood Facts:

   • The ice dam was more than 2000 feet tall.

   • Glacial Lake Missoula was as big as Lakes Erie and Ontario combined.

   • The flood waters ran with the force equal to 60 Amazon Rivers.

The impact from Glacial Lake Missoula and the Ice Age Floods can be seen in parts of Montana, Idaho, Washington, and Oregon. Testifying to the cataclysm are the ancient shorelines, ripple marks, scoured lakes, dry channels, and waterfalls that are still visible after nearly 12,000 years. Without seeing this evidence it is hard to imagine the enormity of the geologic event.

Find out more at www.glaciallakemissoula.org.