Magnitudes and implications of peak discharges from glacial Lake Missoula

New field evidence and discharge calculation procedures provide new estimates of maximum late Pleistocene glacial Lake Missoula Flood discharges for two important reaches along the flood route. Within the Spokane Valley, near the point of release, the peak discharge probably exceeded 17 ± 3 million m ³ .sec ^-1 , the largest known terrestrial fresh-water flow. Consideration of these discharge values constrains model for the failure of glacial Lake Missoula. The maximum discharges estimated here are larger than theoretical and empirical predictions of maximum subglacial jokulhlaup-style releases for Lake Missoula. We postulate, consistent with geological relations in the glacial Lake Missoula basin and in the Channeled Scabland, that the largest late Wisconsinan Missoula Flood resulted from a cataclysmic falure of the impounding ice dam of glacial Lake Missoula. This large release may have been the result of a complete rupture of the ice dam. Subsequent multiple flows of lesser magnitude may have resulted from repeated subglacial releases from the lake. -from Authors