The Depth of the Great Lakes

Question

I understand that the Great Lakes were formed by the glacial terminus of one of the Ice Ages. What I don’t understand is the extreme depth of Superior, Huron and Michigan. These lakes are over 500 ft deep, even over 1000 ft deep, which seems fantastical based on their other dimensions.

In comparison, Long Island and the Sound were also formed by a glacial terminus, and the Sound is only about 230 ft deep.

I’m having trouble visualizing how glaciers slowly spreading down from the north would leave a deep scar at the terminus. I would expect a large pile of agglomerate (like Long Island), not a deep scar.

What gives?

In: Other

Answer 1

Besides glacial action, there’s the failed Midcontinent Rift. Lake Superior sits inside of the ancient rift valley. The massive structure also extends into the lower peninsula of Michigan.