How were the Channelled Scablands formed?

The Channeled Scabland of eastern Washington was formed by a series of cataclysmic glacial floods that occurred between approximately 17,000 and 12,000 years ago.12

These floods were triggered by the periodic failure of an ice dam created by a lobe of the Cordilleran Ice Sheet, which blocked the Clark Fork River and impounded a massive body of water known as Lake Missoula. When the ice dam failed, it released up to 2,500 cubic kilometers of water in sudden, immense torrents that swept westward and southward across the Columbia Plateau and down the Columbia River valley.312

The force of these floods stripped away the region's loess cover and eroded the underlying basalt bedrock. This process carved a complex system of dry channels, steep-walled ravines known as coulees, waterfalls, and potholes. Other diagnostic features left by these floods include giant current ripples and massive gravel bars. The hypothesis that these landforms were created by such catastrophic flooding was first proposed by the geologist J. Harlen Bretz in the 1920s.3241