Near the end of the Pleistocene Ice Age, about 13,000 years ago, a lobe of the Cordilleran Glacier that covered the Rocky Mountains blocked the flow of the Clark Fork River, in northwestern Montana. Behind this dam of ice, a massive lake developed; 200 miles long and 2000 feet deep, Glacial Lake Missoula contained 500 cubic miles of glacial meltwater.
Eventually, the ice dam failed and a torrent of water rushed across the Idaho Panhandle, eastern Washington and the Columbia River Valley. In fact, as the glacier advanced and retreated over 2500 years, the lake repeatedly formed and drained, eroding the Channeled Scablands of the Columbia Plateau. Characterized by broad, braided canyons, dry falls, rippled rock formations, massive gravel bars and countless erratic boulders, this unique topography attests to the power of the recurrent floods; indeed, the Columbia River Gorge was primarily carved by these torrents.
While similar glacial lake floods occured elsewhere across the Northern Hemisphere (including the Bonneville Flood of southern Idaho), none were as powerful as those arising from Lake Missoula. Geologists and hydrologists estimate that the flow of these deluge events (which numbered three dozen or more) exceeded the current total flow of all rivers on Earth and emptied the Lake within a few days.