Oh, and to follow up on my followup: the case of New York shows one important subtlety, namely that glacial loads can cause both downward and upward motions at the same time.

/u/CrustalTrudger described the earth as a viscous trampoline. I'd like to suggest you think of it as a viscous air mattress. The overall volume of the mantle remains unchanged, so if the weight of glaciers pushes one area down, nearby areas must move up, as the mantle displaced under the glacier has to go somewhere. When the glacial load is removed, the opposite effect occurs.

This means that while most of Canada is currently rising as it recovers from the weight of the Laurentide ice sheet being removed, much of the United States is currently sinking by the same effect.