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. |
This formation is composed of ancient sand dunes, produced when winds, blowing across an ancient desert, piled up grains of sand. Over time, the dunes shifted and were reworked. Eventually calcium-bearing solutions cemented them in place. The resulting formation seen in this Navajo sandstone is called "cross-bedding." The frozen dunes reveal that the wind direction was from north to south (from left to right, in the photo). The "checkers" that groove the surface of this formation are formed by the weathering of horizontal bedding planes and vertical cracks. Vertical cracks and joints in the sandstone were created in the stress of uplift. As water is channeled into the crevice, it dissolves the cement holding the rock particles. The cement may be redeposited in another location hardening the rock in that area. Other physical cracking results from the freezing and expansion of the water. 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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