Glacial Isostatic Adjustment
Glacial isostacy is the upward or downward land motion caused by the weight of ice sheets deforming the Earth's crust. The weight of the ice sheet deforms the underlying crust downward and displaces the underlying lithosphere, creating an indentation. Raised ridges called forebulges form at the edges of the ice sheet from where displaced mantle rock causes the crust to bulge upward. When the ice sheets retreat, the forebulges slowly collapse while the indentation rebounds. This is called post-glacial isostatic adjustment.