About Our Lakes: Background

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Great Lakes Basin

The Laurentian Great Lakes were formed nearly 20,000 years ago when the earth's climate warmed and the last glacial continental ice sheet retreated. The glacier, up to 2 miles thick, was so heavy and powerful it gouged out the earth's surface to create the lake basins. Meltwater from the retreating glacier filled the newly created basins. Approximately 3,500-4,000 years ago, the Great Lakes attained their modern levels and area.

Glacial progression over the Great Lakes. 14,000 years ago, 9000 years ago, 7000 years ago & 4000 years ago

Diagram comparing depths of Great Lakes and other water bodies

Above three images from "Living with the Lakes."

Published by the U.S. Army Corps of Engineers and the Great Lakes Commission, 1999.

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