Overview
Glaciers form on land when the amount of snow falling in winter is greater than the amount that melts in the summer. The compact snow and ice form sheets that flow under their own weight. Those moving rivers of ice are especially found in mountainous areas and in the polar regions on Earth.
Types of Glaciers
Alpine glaciers form near mountain summits, especially in areas where the winter snows are deep and do not melt completely during relatively short summers. The largest glaciers flow great distances, down high elevations to the lowlands. Continental glaciers, or ice sheets, cover more than 50,000 square kilometers, and exist mostly in Greenland and Antarctica. By contrast, the Arctic area is more oceanic, and glaciers do not form on oceans.
Movement of Glaciers
Glaciers move at different rates depending upon landforms and weather conditions. Over steep terrain, glaciers can move several meters at a time, especially if their inner temperature is relatively high. However, when terrain is not as steep and the weather is cold and dry, glaciers only move at the rate of a few centimeters a day. For the most part, glaciers move by a combination of friction and low pressure. Crevasses open as brittle upper ice cracks, making it dangerous for mountaineers to travel along them.
Glacial Erosion
Glaciers pick up rocks and sediment and carry them along, scraping and gouging the bedrock as it freezes, melts, and moves. In addition, water seeps through cracks beneath the glacier, causing more weathering and erosion. U-shaped valleys are gouged out of mountain landscapes by glacial action, and mountain peaks are carved into steep formations. The Matterhorn in the Alps is an example of this type of erosion, as glaciers sculpted a steep peak from three different sides of the mountain.
Glaciers and Global Warming
Glaciers store fresh water, and are a very important reservoir for much of the fresh water on the earth. However, many areas that were covered in ice, such as the ice sheets in Greenland and glaciers throughout the world, are melting more rapidly than ever before. Even Antarctica is losing mass along its great ice shelves at a greater rate than they are growing.
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