7.2 Formation of Deserts Deserts cover 30% of earth’s surface. Found on every continent except Antarctica. They lie within 2 broad belts called desert belts Deserts of northern belt are near Tropic of Cancer (230 North latitude) Deserts of southern belt are near Tropic of Capricorn (230 South latitude)

Natural Desert Formation    * Air over equator receives direct radiation from sun * This raises temperatures and causes rapid evaporation * This rapid evaporation causes air over equator to be moist *This causes frequent rainstorms over equator * This region is usually called the tropics *Once moisture falls over the tropics, the air becomes dry. It flows towards earth’s poles and becomes cooler and heavier. The dry, dense air sinks to earth’s surface generating dry winds that cause the formation of deserts.

Deserts in U.S. are formed this way and mountains are part of the geological feature which aids in the formation (p.114 fig. 7.4) Since the air blowing across the mountains drops its moisture on the western slopes, it is very dry when it reaches the eastern slope. The result is a semiarid region (a region that is dry but not as dry as a desert). The drying of the eastern side of the mountain is known as rainshadow effect

Desertification · Deserts are bordered by semiarid regions that support grasses and shrubs · Human activities like raising livestock cause many semiarid regions to become deserts. This is known as desertification Overgrazing causes soil to become compacted, topsoil erosion and reduced rainfall,