Glaciers are large masses of ice that move over a land surface. They originate in areas that receive large amounts of snow during the winter and which is greater than the amount that melts during the summer months. Such areas of the world include Greenland, Antarctica and several high mountain ranges, such as the Rockies, the Andes, the Alps and the Himalayas. They are also present on some of the high mountain peaks in eastern Africa.
Glaciers form as a result of layers of snow pressing together. Over a period of time these layers change into pieces of ice and as more snow falls on them each year, they become thicker and thicker. Eventually they become large masses of ice.
Types of Glaciers
There are four main types of glaciers: valley, piedmont, continental and icecap.
A valley glacier originates high in the mountains and gradually moves down the mountain valley. An example of this type of glacier is the Hubbard Glacier in Alaska.
Piedmont glaciers form from valley glaciers that spread over the land at the base of a mountain. It is often formed when the glacier fans out in a fan shape. Piedmont glaciers are flat and can cover a very large area, such as the Malaspina Glacier in Alaska.
Continental glaciers are the largest type and cover almost all of the surface of a continent, such as that of Antarctica. Some continental glaciers are more than 10,000 feet thick and can cover entire mountain ranges.
These glaciers are small continental glaciers found on a mountaintop or a small plateau high in the mountains. The Penny Ice Cap on Baffin Island is the largest icecap glacier in the world.
Movement of Glaciers
As a rule, glaciers move slowly, sometimes only a few inches a day. However, valley glaciers have been known to move as much as 100 feet or more in one day. They move faster during the summer months because of the melting ice, which reduces the friction.
Scientists have suggested that the movement of glaciers is the result of the lower layers of ice losing some of their rigidity and this causes them to move downhill. Water freezing on both sides of the glacier also exerts force on the ice causing the middle layers to move forward.
The effect that glaciers have on the land over which they move is known as glaciations. Valley glaciers, for example, cause the formation of U-shaped valleys and bowl shaped depressions in the land. As the glaciers move they also pick up rocks and carry them along with them. Then when melting occurs in warmer areas, these rocks are then deposited in locations far away from their source. Many of the lakes and rivers that cover the surface of the earth were created through the movement of glaciers during the last Ice Age.