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How a Desert Forms
Deserts form thanks to a variety of natural mechanisms that change the composition of the environment. Subtropical deserts, for example, are formed when atmospheric circulation deposits dry subtropical air at mid-latitudes. The hot, dry air brings with it extreme drought which makes it difficult for life to persist. Deserts, such as the Sahara, the Kalahari and the Great Australian Desert were formed by this natural mechanism. Continental deserts, on the other hand, form because they are deep in land where little water is available. In these areas, summers are incessantly hot and winters are relentlessly cold which make them hostile to life. The Gobi desert, for example, is a continental desert that formed because of the land's location in relation to a water source. In short, deserts form as a result of natural environmental changes and conditions that isolate the land from water.
Rocks in a Desert
Rocks are formed when sediments such as mud, sand and gravel settle to the bottom of an ocean where they are compacted over thousands of years. Rocks are also formulated when a volcano spews magma, molten rock, on the Earth's surface where it eventually cools. Rock found deep in the Earth's crust is also brought to the surface by the collision of tectonic plates which formulate mountains. Furthermore, rocks are also moved, crushed and deposited around the surface of the Earth by the movement of powerful glaciers. Water and wind erosion break down mountains over time, which makes smaller rocks and boulders. When the conditions are right, deserts form around these already formulated rocks. The rocks found in a desert are then shaped and eroded by wind.
Wind Erosion
Wind erosion works through a process called - deflation and abrasion. Deflation is characterized by the lowering of the land surface by the wind removal of all fine-grained particles, such as sand. Eventually, deflation concentrates the coarser-grained particles of the surface until only coarse-grained particles remain. The particles are no longer movable by the wind. Abrasion is the blasting of a coarse rock surface with small particles -- sand -- carried by wind. The process is similar to sand blasting. Any abraded bedrock is called a "ventifact" and the ridges caused by abrasion are called "yardangs."
Desertification
Desertification is the process by which a desert grows and forms as a result of changing environmental circumstances caused by human impact. Overgrazing, draining water reserves through over irrigation, and the lowering of the water table all contribute to desertification. If the vegetation around an area dies, it destabilizes the soil, making it possible for it dry up. Drying soil makes it difficult for other vegetation to grow. Eventually the area becomes arid and the desert expands