The speed of glaciers varies greatly depending on ice thickness, temperature, slope, snowfall and the presence of meltwater at the contact point between the ice bottom and the land underneath. Some glaciers do not move at all. Many move at a rate between zero and about half a kilometre (0.3 miles) per year.
The fastest moving glacier is in Greenland, rushing forward at 12.6 kilometres (7.8 miles) per year. The middle of a glacier moves much more quickly than its edges, which are held back by friction with the surrounding land. Large objects frozen in the ice may get stretched apart because of this different rate of movement.
Answered by: Dr Richard Hebda, curator of Botany and Earth History