What is a Desert?
A desert generally is thought of as a hot, barren area with little rainfall. However, this is not always true. Polar deserts (barren areas around the North and South Poles) have a lot of snow and ice, and are very cold. They usually receive less than five inches of rainfall in a year’s time. There is not much plant growth, and land animals are scarce. However, a few varieties of lichens and mosses may grow in areas where rocks are exposed, and penguins are found along the shores of Antarctica.
Hot deserts are close to the equator. The world’s highest temperatures have been recorded in these places. Even so, the nights can cool down quickly when the air is dry, and there are no clouds to stop the daytime heat from escaping into space.
Rainfall is scarce in all desert regions. In some deserts, months or even years may pass without rainfall. When the rain finally arrives, it usually comes in short but violent storms, and the downpour may cause flash floods.
Deserts have a wide variety of land formations. Usually they are caused by water and wind erosion. Parts of a desert may be covered by windswept piles of sand called "dunes." Dunes have many shapes that are changed continually by the wind. The rest of the land consists of gravel, boulders, mountains, and various types of soil.
The drainage system of a desert is made up of dried streams called "arroyos" in the Americas, and "wadis" in North Africa and the Middle East. Playas or pans are very flat areas that fill with water after a rain, and have no outlet. The water either evaporates, or seeps into the Earth. Salts from the soil can build up on the surface of the ground. Erosion forms mesas (MAY-sahs), and smaller buttes (byoots), which are flat-topped, steep-sided hills. Canyons are well developed in deserts because the lack of rainfall does not erode the valley walls very much.