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|How Glaciers Shape the Land
As glaciers pass over an area, they help shape its features, creating a variety of land forms by means of erosion and by transporting and depositing rock debris.
Glacial Erosion occurs when an advancing ice mass scoops up rock fragments and drags them along its base. In doing so, the glacier grinds the bedrock, producing a polished but often scratched surface. When a glacier decreases in size, it leaves behind broad humps of scratched bedrock called roches moutonnÚs. One side of this kind of land form is smoothly rounded while the other side is rough and irregular. One of the best examples of such a formation is New York City's Central Park, where huge mounds of glacier-scarred bedrock are exposed.
A glacier in a mountain valley may produce a rounded hollow, called a cirque, near the peak of the mountain. A cirque forms when the upper part of a glacier removes blocks of rock from the surrounding cliffs. The Swiss Alps contain many well-known cirques, as does Glacier National Park in Montana. A glacier can also gouge out a U-shaped depression in a river valley. California's Yosemite National Park is home to a marvelous example of a glacier-carved valley. Such a depression that forms below sea level and is flooded by the ocean is called a fjord; the coast of Norway is well known for its fjords.
Glacial Deposits consist of clay, sand, and rocks of various sizes. Glaciers pile up these materials, forming uneven ridges called moraines. The ridges along the sides of a valley glacier are known as lateral moraines. When two valley glaciers come together, the lateral moraines between them merge to form a medial moraine along the center of the combined ice mass. The hilly ridge at the lower end of a valley glacier is called a terminal moraine. Long Island, New York, is a terminal moraine that was left behind when the North American ice sheet retreated at the end of the last Ice Age.
A drumlin is an oval-shaped hill that usually consists of rock debris. Most drumlins occur in groups, and thousands of such groups are found throughout southeastern Canada and New England. The islands of Boston Harbor Islands National Recreation Area are drumlins that became islands when sea levels rose as the glaciers melted.
An esker is a long, narrow ridge of sand and gravel deposited by a stream of water that flowed in a tunnel beneath a melting glacier.
The Finger Lakes of New York were formed when the last great North American ice sheet retreated, exposing gouges in the earth that were subsequently filled by glacial meltwater. In addition, the immense weight of a glacier can literally cause the land beneath it to sink. As the glacier retreats, releasing the weight, the land gradually rises back up again. In some areas, however, the depressed areas may fill with water before the land has a chance to "rebound." The Great Lakes were formed in such a manner, as was the Kettle Lakes region of Canada's Northwest Territories.
Library >> Geography >> Physical Geography
Glaciers, Ice Sheets, Sea Ice
This page was last updated on 12/16/2017.