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How were the Great Lakes formed?
from Michael in Hatfield, PA, Age 10

The Great Lakes basin is a relatively new phenomenon because it was formed by glacier activity only during the last 10,000 years. Geologically speaking, this is as short a time for the planet as a single second is out of your busy day! The foundation of the Lakes, however, was laid through several geologic eras spanning millions and millions of years.

The continental glaciers repeatedly moved from what is now Canada over the Great Lakes region again and again as they thawed and melted, only to be later reformed. As these glaciers inched forward -- some of them up to 2,000 meters (that's about 6,500 feet) thick -- they scoured the surface of the earth, leveled hills, and altered forever the previous ecosystem. Small valleys created by the river systems of the previous era were deepened and enlarged to form the basins for what are now the Great Lakes.

Related references:
TEACH: How the lakes were formed
Great Lakes Atlas, 3rd ed. Two Natural Processes in the Great Lakes: Geology and Climate

Thank you for your question!

Answered on May 16, 2001

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