Sunday Roast: Glacial Lake Missoula

Photo by Zooey

I took this photo on my recent trip to Glacier National Park, having taken a detour down to the National Bison Range.  Over 13,000 years ago, this lush farmland was the site of a huge glacial lake; today we refer to it as Lake Missoula.

The lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran Ice Sheet into the Idaho Panhandle (at the present day location of Clark Fork, Idaho at the east end of Lake Pend Oreille). The height of the ice dam typically approached 610 metres (2,000 ft), flooding the valleys of western Montana approximately 320 kilometres (200 mi) eastward. It was the largest ice-dammed lake known to have occurred.

Approximately forty times over a 2000 year periodthe glacial ice dam ruptured, and the contents of Lake Missoula went screaming across the Idaho Panhandle, Eastern Washington (creating the Scablands), and the Columbia River Gorge.  You can see that the flood even reached my little corner of the world on the Snake River.

The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream. These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through more typical gradual processes.

If you drive across Eastern Washington, you’ll see that even today it looks like a virtual wasteland.  Being in the rain shadow of the Cascades has something to do with it, but the main culprit was flood after flood after flood scouring off the land.  It’s really quite fascinating to imagine the raw and determined power of WATER.

This is our daily open thread — Hey, you learned something new today!