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Figure 20. Moses Lake and coulees, Eastern Washington State. Glacial ice dams broke between 18,000 and 13,000 years ago, in response to volcanism near modern Lake Pend Oreille, ID. 500 mi3 of melt water stripped away the glacial soil and carved deep valleys (coulees) into the bedrock. The coulees were formed in five catastrophic events; glacial Lake Missoula was the source of the flood waters.