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Deserts

Areas of the world with almost no rainfall, and which also experience extremes of heat and cold, are called deserts. The vast ice areas of the North and South Poles are deserts in a sense, but the name is more usually given to huge dry areas found in the middle of continents.

The Earth's desert belt stretches from the Sahara in Africa across Arabia to the Gobi desert of Central Asia. Beyond the Himalayan mountains in northwestern India is the Desert of Sindh (Pakistan). There are huge deserts in the United States, east and south of the Sierra Nevada Mountains, and also in the western regions of South America, in southwestern Africa (Kalahari), and Australia (Victoria and Sandy). Deserts are generally found in the middle of continents, because winds from the sea have lost all their moisture by the time they reach the center. The extreme dryness of these regions is intensified between mountain barriers, and desert basins are created, such as the Tarim Basin in China and the Great Basin in North America. There are very great differences in temperature between day and night, and summer and winter, in all these regions. The sun's heat is taken up very quickly by the dry soil, but after sunset the soil gives up heat equally rapidly and the temperature quickly drops.

At certain intervals, often years apart, rain does fall and plants spring to life. Though plant and animal life is sparse, few deserts lack some life, owing to the great adaptability of living things. Bushes develop enormously long roots, and plants evolve that do not lose water by evaporation, such as the cactus.

Desert animals can travel long distances without drinking or eating. Camels, for example, have padded feet to walk on sand, and are able to store food in them humps, and water in their stomachs.

Human beings living in deserts are mainly nomads (wanderers), who drive their animals from one grazing or watering area to another. Settlements are usually found only where there are wells, or oases (rare pools of water surrounded by trees and bushes).

Deserts are often rich in minerals. Gold is found in Australian deserts, oil in Arabia and the Sahara, and nitrates (chemicals that can be used as fertilizers) in Chile. The Mojave Desert in southeastern California is one of the world's leading sources of boron, an important mineral used in high-energy fuels. Much of western United States is covered by desert. Regions such as the brightly colored Painted Desert in north-central Arizona and Death Valley in eastern California are rugged infertile regions that cannot be used. However, much work has been done to make some of the desert land useful to man. By means of irrigation, some of the once barren regions are made fertile for farming. Water is pumped up from under the surface or led from rivers and streams over the dry land.

Extensive irrigation has been used in several regions, including the Colorado Desert in southern California. Dams such as the Hoover Dam on the Colorado River have been built to provide water for irrigation. In this way, two highly fertile areas, the Imperial and Coachella Valleys, have been created in the barren desert. Crops such as artichokes, asparagus, carrots and peas are now cultivated.