The lobes of the Cordilleran Ice Sheet would have been close to maximum extension during the Late Wisconsin glaciation 12,700 and 15,300 years B. Evidence in the Priest Lake area indicates this happened at least 14 times, causing catastrophic floods.
(Fig 01) The ancient lake created by the ice dam across the Clark Fork River is known as Glacial Lake Missoula. The Cordilleran Ice Sheet is present and the maximum size of Lake Missoula with the areas affected by the floodwaters shown.
Several other large glacially dammed lakes also formed along the margins of the Cordilleran Ice Sheet (Breckenridge, 1989). (Map courtesy of USGS, used with permission.) Other glacial lakes were created as the lobes off the Cordilleran Ice Sheet moved southward into Washington.
Several lobes were associated with the Cordilleran Ice Sheet.
The Purcell Trench lobe moved southward (to 48° 10N) into Northern Idaho through the Purcell Trench and blocked the Clark Fork of the Columbia River with an ice dam (Booth, 2003).
This great flood created a distinctive landscape across Washington and Oregon that has been studied by many geologists.
J Harlen Bretz started a great controversy in 1923 when he suggested that a catastrophic flood created the Channeled Scablands of Washington State (Baker, 1995).The Channeled Scabland was just one feature Bretz investigated. Pardee, contributed to the understanding evidence of great flooding and the glacial Lake Missoula through his research in the Montana basins.Return to: Table of Contents J Harlen Bretz and Joseph T.Glacial Lake Missoula in northwestern Montana was created when a lobe of the Cordilleran Ice Sheet blocked the Clark Fork River.With the rivers outlet blocked by a huge ice dam a glacial lake formed behind that dam and became known as glacial Lake Missoula.The 610 m ice dam created by the glacier impounded water behind it stretching 322 km southward.