Earth-Changing Drama...
In a Geologic Heartbeat
Map used by permission. Copyright 1995 Al Kettler. All rights reserved. First appeared in Smithsonian, April 1995, p. 50.
The Pacific Northwest was the stage for one of the world's greatest scientifically documented floods. Little more than 12,000 years ago during the last throes of the Ice Age, a "finger" of the continental ice sheet reached south into the Idaho panhandle, damming the mouth of the Clark Fork River and creating a monstrous lake known as Lake Missoula. Lake Missoula stretched for hundreds of miles across western Montana and contained more water than Lake Erie and Lake Ontario combined.
The ice could only temporarily restrain such an immense volume of water. When the lake reached its maximum depth, water burst through the ice barrier, shooting out of Clark Fork Canyon at a rate 10 times the combined flow of all the rivers in the world. At that rate the lake would have drained in as little as 48 hours!
In a scene belonging more to the realm of science fiction than to reality, this towering mass of water and ice, over 2,000 feet high at its source, literally shook the ground as it thundered toward the ocean at speeds approaching 65 miles per hour. The deluge quickly stripped away 200 feet of soil and cut deep canyons or "coulees" into the underlying bedrock, creating a vast maze-like network clearly visible from space. The torrent even widened and deepened the Columbia Gorge, baring the majestic cliffs seen today.
Flood waters carved out over 50 cubic miles of earth, depositing much of it to create other unique landforms. Mountains of gravel as tall as 30-story buildings were left behind, and huge boulders weighing more than 200 tons littered the ground like so much flotsam. Fast-moving water shaped giant ripple marks 50 feet high. Recent studies of flood-deposited sediments yield startling new evidence - the great flood occurred not once, but dozens of times!
Gone almost as quickly as they came, the floods left lasting marks across Montana, Idaho, Washington, and Oregon. Nowhere else in the world do these types of landforms exist on the scale and grandeur found here in the Pacific Northwest. Yet most who visit or live in the path of the floods know little about them or the enormous impacts they have had on our patterns of life. This may be the greatest story left untold.