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. |
A natural bridge forms when a river's meandering course creates a bend that nearly doubles back on itself. Water washes into and scours the inside wall of the canyon. After the river or stream cuts an opening through the narrow wall, the stream may change course taking a short cut under the bridge and eliminating the meander. The same erosional forces that enlarge arches also work to expand the opening under the new natural bridge. In this view a small canyon has been cut by the stream below the pillars of Rainbow Bridge. 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. |
|
