Glacial Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago.
The lake was the result of an ice dam on the Clark Fork River caused by the southern encroachment of a finger of the Cordilleran ice sheet into the Idaho Panhandle. The height of the ice dam typically approached 2,000 feet, flooding the valleys of western Montana approximately 200 miles eastward.
GlacialLake Columbia (west) and GlacialLakeMissoula (east) are shown south of Cordilleran Ice Sheet.
The Missoula Floods (also known as the Spokane Floods or the Bretz Floods) refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age.
Bretz, however was not able to explain the source of the huge volume of water and his hypothesis was controversial, partly due to the popularity at that time of the principle of uniformitarianism in geologic processes.
Glaciers did not continually cover the earth during this time; there have been interglacial periods where temperatures warm slightly and the glaciers melt and retreat.
It was during this glacial advance that a finger from the glacial ice sheet moved south through the Purcell Trench in northern Idaho, near present day Lake Pend Oreille, damming the Clark Fork River creating GlacialLakeMissoula.
Pardee attributed this phenomenon to the sudden failure of the ice dam that impounded GlacialLakeMissoula.
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