Glaciers are moving masses of ice. Glaciers are formed by the effects of snowfall and cold temperatures. They are formed over many years in areas where the rate of snowfall is more than the rate of melting. Approximately 10% of the earth is covered by glaciers. Major portion of this is in polar regions. A glacier does not move until the ice is about 200 ft deep. Then under tremendous pressure, normally brittle ice begins to flow. The speed of glaciers depends on thickness of ice and temperature.
There are lots of reasons that cause movement of glacier. One among them is the pull of gravity. It may also be due to the slippage of ice crystals over each other. Melting along the bottom of glacier also helps its motion by oiling the surface. Compared to the lower layers, the upper layer is at less pressure. Hence it is brittle and crack quite easily under stress.
The glacier can move very slowly with ice advancing less than a foot a day or an amazing speed of 90 meters or more a day. The speed of glaciers varies depending on ice thickness and temperature. Some glaciers do not move at all. World’s fastest glacier is in Greenland. The largest glacier in west Greenland is Jakobshavn Glacier. It is found to move about 30 meters per day.
Glacial surges are temporary shocks that could cause them move many times faster than normal. The surges can be unpredictable or occur in regular cycles. They may also lead to a slow start rising to a maximum velocity and a sudden stop. Thus surges exhibit different behavior at different times. A glacier can advance in winter and retreat in summer. An advancing glacier moves ahead more than it melts and a retreating glacier melts more than it moves. There has been a great decline in the number of glaciers recently due to climate change and global warming.