|MadSci Network: Earth Sciences|
Contrary to popular belief, the natural sandstone arches found in the southwestern United States (such as Arches NP) are not entirely the result of wind erosion by wind-blown sand. Their formation has more to due with differential weathering of the rocks (sandstones) by water and the effects of freeze-thaw cycles than erosion by wind-blown sand. Sandstone rock is made up of small grains of sand-sized rock (usually quartz sand but, it can also be other rock material) that are cemented together by another rock material (such as silica, iron oxide, or calcium carbonate). It is common to have varying degrees of cementation within any mass of rock; that is, some rock will be “harder” and some will be “softer." The softer rock will tend to be easier to erode by water than the harder rock. The differential weathering between the hard and soft rock over long periods of time can eventually lead to creating alcoves (caves) in a rock face in the softer rock. These caves may eventually develop into the natural stone arches common at Arches National Park. Along with weathering by water, the desert regions of the southwest United States also experience a high number of days of freeze-thaw cycles. Freeze-thaw cycles are the daily freezing on moisture at
Try the links in the MadSci Library for more information on Earth Sciences.