Glaciers erode the land in three primary ways: plucking, abrasion and freeze-thaw. All three manners of erosion combine to make glaciers one of the world’s most powerful agents of erosion.
Glaciers are essentially frozen rivers. They are common in the Northern Hemisphere as well as at high altitudes. Glaciers do not erode mountains and bedrock quickly, but over long periods, they cause drastic changes.
Glaciers usually have at least one side that is in contact with rock. When part of the glacier melts, it allows water to penetrate behind the glacier and pull broken rocks from the wall. This is called plucking. When the melted water near the top of the glacier repeatedly melts and freezes, the water forces its way into the cracks. When water freezes, it expands, causing the rock to break. This type of erosion is called freeze-thaw. Finally, when rocks stick to the glacier, they may rub against the bedrock, which is called abrasion.
Glaciers have carved a number of important geographic features. Glacier National Park features a number of valleys cut by ancient glaciers as well as glacially damaged mountains. A giant glacier carved the Matterhorn, a large sharp peak in Switzerland. Other times, glaciers break into small pieces and melt, which forms small lakes called kettle lakes.