Arid regions experience weathering relative to physical and chemical processes.
In arid regions, weathering is a slow process because of the absence of water. As a result, it often takes large spans of geological time for weathering to cause arid landforms. These processes depend upon any number of natural factors, including wind, the amount of soluble rocks on the landscape and water sources, such as dew that forms on the rocks each morning. With such elements in place, weathering can begin to influence the landscape.
Isolation Weathering
Isolation weathering is a physical process that shatters rocks during alternating hot and cold temperatures. Daily heating and cooling of the ground, depending on the sun's relationship to the Earth, is thus important to rock formations. Those minerals that compose rocks expand and contract when heated by solar radiation. With time, the stress that results can weaken bonds within the rocks and cause fragments to flake or break apart.
Surface cracks that occur in boulders and cobbles are thought to be the result of thermal stresses that arise from inconsistent solar heating. Once the cracks are formed, they can extend and widen, leading to a breakdown of the rock or facilitating other weathering processes. Desert rainstorms may also produce cool rain that falls on hot rock, thus initiating the process of isolation weathering.
Salt Crystallization
To demonstrate that chemical and physical weathering processes are dependent upon each other, salt crystallization relies on water as well. This is a chemical process by which water on rock surfaces evaporates. Dissolved minerals then form crystals, which grow with time. As the volume of these crystals expands, it exerts force on the rocks. Mineral grains then split and break apart the rocks, thus causing them to lose their original shapes.
Sandblasting
Wind is a common geologic agent in arid regions because these areas have little or no soil moisture to retain rock fragments. Those pieces can therefore travel to erode and deposit sediments. In turn, particles carried by wind create a sandblasting effect that can alter rock formations. Researchers are today convinced that this process can shape and polish ground-level rocks, and some believe pedestal or mushroom rocks are the result of sandblasting.
Biological Weathering
Biological weathering can be the result of either physical or chemical processes. Trees and other plant life, for example, form deep roots through surface rocks and ledges. Those roots exert unrelenting pressure on rocks, often forcing them to crack. Rock particles can also fracture from animal burrowing and chelation -- a chemical process by which organisms produce substances known as chelates, which can decompose minerals and rocks.
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