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Glacial Lake Missoula

© Copyright 1996, Jim Loy

The last Ice Age was at its most southern extension about 15,000 years ago. Back in the Ice Ages, there were a number of fairly large lakes in what is now northwestern United States, at the southern edge of the north polar ice cap. One of these is called Glacial Lake Missoula, in what is now western Montana. It was created when a glacier blocked the Clark Fork River. At times, Glacial Lake Missoula was about as large as Lake Ontario. Sometimes the ice dam would break, sending a wall of water downstream into Idaho and Eastern Washington, digging out the deep canyons of the Scablands of Washington, perhaps in minutes, probably in a few days. There is evidence that Glacial Lake Missoula filled and emptied as many as 41 times. The last flood was about 13,000 years ago.

Addendum:

Other even larger lakes in the area were Glacial Lake Columbia, in eastern Washington, and the really huge Lake Bonneville, which covered much of western Utah and parts of Nevada and Idaho. When the ice dam emptied Glacial Lake Missoula, the rush of water overflowed Lake Columbia, and that overflow scoured out the Scablands, and other canyons down to the ocean near Portland. There were other huge lakes in eastern Washington.

Glacial Lake Missoula was discovered by geologist Joseph T. Pardee, in about 1910. And J Harlen Bretz (J was his first name) was the geologist who first proposed catastrophic flooding as the cause of the Scablands, and received much ridicule from other geologists. Geologists had shown that the Grand Canyon had been dug by the Colorado River over millions of years. And here was a man who claimed that other canyons had been dig out in days.

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