Isostatic depression is the sinking of large parts of the Earth's crust into the asthenosphere. The sinking is caused by a heavy weight placed on the Earth's surface. Often this is caused by the heavy weight of glacial ice due to continental glaciation. This is a process in which permanent ice places pressure on the Earth's crust, thereby depressing it with its weight. After continental glaciation has receded, it is common for isostatic rebound to occur.