Copyright Information: All images are in the public domain and available for free. If you use this image, credit NOAA/NGDC, John Lockridge, Longmont, Colorado. |
Glacial crevasses (deep cracks in the ice) open from the downslope movement of the glacier and generally form perpendicular to the direction of glacial movement. As glaciers move, they quarry and pluck away at the lead surface on valley floors and along the sides. They also erode headward into mountain sides, carving steep but rounded valley headwalls called cirques (middle background). These cirques form as glacial ice flows down hill, and a crevasse forms between the glacier and the rock headwall. In summer, melt water flows between the glacier and the headwall. It then refreezes, rejoining the glacier to the headwall. As the glacier moves away from the headwall, it pulls away pieces of the rock headwall with it, enlarging the cirque. Image Credit: John Lockridge, Longmont, Colorado. The hydrologic system, which includes all possible paths of motion of Earth's near-surface fluids including air and water, is largely responsible for the variety of landforms found on the continents. Heat from the sun evaporates water from oceans, lakes, and streams. Although most of the water returns directly as precipitation to the oceans, some of the water is recipitated over land as rain or snow. If it is precipitated over land, it then begins its journey back to the sea as "runoff." The relentless action of surface runoff, streams, and rivers, glaciers, and waves sculpts the rock into intriguing and bizarre shapes. This set of slides includes examples of wave erosion, wind and water erosion, valley shapes, and glacial rosion. The views are often dramatic. Many were taken at U.S. National Parks and Monuments. |
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