One third of Earth's land mass is desert. Deserts have low rainfall, sparse vegetation and extensive exposed rocky areas. Not all deserts are in hot climates; Antarctica is a desert.The desert environment effects how weathering changes the landscape. Since much of the desert landscape is bare rock and desert soil has little to hold it in place, water and wind play a much more dominant role in weathering than in other biomes. In contrast, evaporation exceeds precipitation in desert climes, retarding chemical-weathering processes.
Even though it rains little in the desert, when it does rain, extreme weathering occurs. The desert has few plants to hold its soil in place. When slow rain soaks a mountain slope, the added weight causes rock slides. Another issue is that rare rainfall often comes to the desert in large amounts; small rocks, mud and soil mix together with rain, creating a thick slurry that speeds down canyons. All of this churning action quickly wears rocks, resulting in various-sized sediments.
Temperature plays an important part in weathering in the desert. Deserts experience extreme temperature changes. Rocks expand and contract because of these changes and this can lead to fracturing. Another more common form of temperature weathering is a combination of water and temperature. Though water is scarce in the desert, many deserts are scattered with porous rocks often from volcanic processes. These rocks absorb water during infrequent rains. As the water within these rocks is heated to steam or frozen into ice, rocks split, and crack and flake.
The most spectacular form of weathering in the desert is caused by the wind. Wind sculpts rock by picking up tiny rock particles and abrading rock surfaces. Some rocks weather into unusual forms in deserts because of varying densities of the material within these rocks. Wind also causes "desert pavement;" on flat surfaces in the desert, wind removes all fine-grain particles, leaving behind a crust of coarse gravel. The wind also deposits fine-grain particles when it encounters objects such as large rocks or vegetation. These deposits form sand dunes.
Weathering due to chemical processes unfolds slower in deserts than in other climates due to a lack of water. One chemical process is a result of the physical breaking down of a rock called feldspar. This increase in the surface area of feldspar accelerates its conversion to granite and clays. Another kind of chemical weathering in deserts is called desert varnish. This rust-coloured patina found on many desert rocks is iron and manganese oxide created by a reaction between rock and clay particles embedded in the rock by the wind.