When do glaciers move?

Glaciers - moves when the pressure above it from rocks, loose ice and snow becomes greater than the strength of the ice. Under this enormous weight, the solid ice tends to flow like tar, although very slowly. The glacier must be quite old before enough material accumulates to exert the pressure needed to move it usually when it is about 60 feet thick. The movement of glaciers is too slow to be noticed by the eye, but measurements have shown they may travel as much as 150 feet a day. The bodies of mountaineers buried by avalanches have been carried several miles in a few years. Glaciers cover 10 per cent of the earth's land surface.