Once glaciers become thick enough, they begin to move under their own weight. Pressure from gravity causes the glacier to spread out. This is called internal deformation of the ice. Glaciers slide on a thin layer of water at their base. This water may come from glacial melting due to the pressure of the overlying ice or from water that has flowed through cracks in the glacier. Glaciers can also slide over rocks and sediment.
Most glaciers move very slowly at only a few centimeters a day. Some, however, can move 160 feet a day and are known as galloping glaciers.
The Kutiah Glacier in Pakistan holds the record for the fastest glacial movement. In 1953, it moved more than 7.5 miles in three months, averaging about 367 feet per day.