| row 3, column 1 |
The Story of the Glacial Lake Missoula Outburst Floods
During the last Ice Age (15,000 to 20,000 years ago), a finger of the Cordilleran ice sheet crept southward into the Idaho Panhandle, blocking the Clark Fork River and creating Glacial Lake Missoula. As the waters rose behind this 2,000-foot ice dam, they flooded the valleys of western Montana. At its greatest extent, Glacial Lake Missoula stretched eastward a distance of some 200 miles, essentially creating an inland sea.
Periodically, the ice dam would fail. These failures were often catastrophic, resulting in a large flood of ice- and dirt-filled water that would rush down the Columbia River drainage, across northern Idaho and eastern and central Washington, through the Columbia River Gorge, back up into Oregon’s Willamette Valley, and finally pour into the Pacific Ocean at the mouth of the Columbia River.
The glacial lake, at its maximum height and extent, contained more than 500 cubic miles of water. When Glacial Lake Missoula burst through the ice dam and exploded downstream, it did so at a rate 10 times the combined flow of all the rivers of the world. This towering mass of water and ice literally shook the ground as it thundered towards the Pacific Ocean, stripping away thick soils and cutting deep canyons in the underlying bedrock. With flood waters roaring across the landscape at speeds approaching 65 miles per hour, the lake would have drained in as little as 48 hours.
But the Cordilleran ice sheet continued moving south and blocking the Clark Fork River again and again, creating other Glacial Lake Missoulas. Over thousands of years, the lake filling, dam failure, and flooding were repeated dozens of times, leaving a lasting mark on the landscape of the Northwest. Many of the distinguishing features of the Ice Age Floods remain throughout the region today.
National Park Service
|
 "Palouse Falls - Washington - Click to view")
 "Bitterroot blooms - Click to view")
 "Giant Current Ripples - Camas Prairie Montana - Click to view")
 "Bison wallowing in Glacial Lake Missoula deposits - Western Montana - Click to view")
 "Ice-Rafted erratic boulder stranded high above the Columbia River at Wallula Gap - Click to view")
