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In geology, a forebulge is created when an large static weight (such an ice sheet) causes the subsidence of a continent into the mantle. The resulting mantle deformation results in an upward displacement in the areas surrounding the ice load. This disturbance can spread, in a ripple effect, around the earth and affect even tropical regions that see no ice.

Sites of former forebulges (from the last glacial maximum), include Antarctica, the Netherlands and other areas adjacent the North Sea and the eastern coast of the U.S., have experienced prolonged relative sea level rise during the Quaternary as the forebulge subsided. The ripple effect from the multiple collapsing forebulges can last thousands of years resulting in varying relative sea levels and isostatic rebound leaving shorelines of the past hundreds of meters above present sea level.