The Great Floods of Glacial Lake Missoula: Page Two

PURCELL LOBE ICE DAM IS BREACHED

MAP #2

   Flowing down the Purcell Trench from British Columbia, the Purcell Lobe blocked the northwest-flowing Clark Fork River near Cabinet Gorge on the Idaho-Montana border. The dam formed by the Purcell Lobe created Glacial Lake Missoula. Covering 7,800 square kilometers of western Montana, Lake Missoula held more than 2,000 square km. of water and was approximately 600 meters deep at the Ice Dam. 1  By comparison, it contained more water than Lakes Erie and Ontario combined.

   Held back by a 2,500 foot wall of ice, when Lake Missoula reached sufficient depth it floated the Ice Dam and burst forth through the Clark Fork Canyon at a rate of ten times the combined flow of all the rivers of the world.

Model of Retreating Glacier

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