The Great Lakes Frozen, Canada–United States Border, North America

Land below the glaciers "rebounded" as it was uncovered. Because the glaciers covered some areas longer than others, this glacial rebound occurred at different rates.
Climate
The Great Lakes have a humid continental climate, Köppen climate classification Dfa (in southern areas) and Dfb (in northern parts) with varying influences from air masses from other regions including dry, cold Arctic systems, mild Pacific air masses from the West, and warm, wet tropical systems from the south and the Gulf of Mexico. The lakes themselves also have a moderating impact on the climate, they can also increase precipitation totals and produce lake-effect snowfall.