Glaciers are not a rarity today. The most common type is called “valley glaciers”. In the Alps alone there are more than 1,200 valley glaciers, and in the high mountains of southern Alaska, there are tens of thousands of them.
Valley glaciers creep downward like great rivers of ice snowy The source of the large quantities of snow that form most valley glaciers is a valley head that is shaped like an amphitheater with steep walls. Snow is blown into this area or slides down in avalanches. It does not melt during the summer but gets deeper year by year.
Eventually, the increasing pressure from above, together with some melting and refreezing, forces the air out of the lower part of the mass and changes it to solid ice. Further pressure from the weight of ice and snow above eventually squeezes this mass of ice until it begins to creep slowly out of the basin and down the valley.
When the glacier moves down below the region of snow, the front of it starts to melt. If the melting takes place as rapidly as the glacier moves, the front edge remains at the same position in the valley. But if melting takes place faster than the advance of the glacier, the front of the glacier retreats back up the valley. Where valley glaciers move into the sea they break off in huge blocks and we have icebergs.
How Quickly Do Glaciers Move?
Glacial motion can be fast (up to 30 meters/day, observed on Jakobshavn Isbræ in Greenland) or slow (0.5 m/year on small glaciers or in the center of ice sheets), but is typically around 25 cm/day.