isostasy

The equilibrium between the earth's crust and the denser mantle beneath it — the principle that the crust floats on the mantle the way an iceberg floats in water, and that adding or removing weight from the surface causes the crust to sink or rise in response. Load a continent with an ice sheet and the crust depresses beneath the weight; remove the ice and the crust slowly rebounds. Isostasy explains why Scandinavia and northern Canada are still rising — they are recovering from the weight of glaciers that melted thousands of years ago, and they are not done yet.