Book 30, Question 3
How were the Great Lakes scooped out?
About two million years ago, huge ice sheets began advancing over the region, and each one dug deeper into the old river valleys.
Moving ice is heavy and acts like a giant bulldozer. When the glaciers melted about 14,000 to 10,000 years ago, meltwater filled the carved basins. The lakes took their current shape as the land slowly rose after the ice weight was lifted.