Garrett Rice, age 13, of Twin Falls, Idaho, for his question:

WHAT CAUSES DESERTS TO FORM?

A desert is an area of land that is so dry that few plants can grow on it. Deserts form because they are located in regions which have little water.

Deserts are rarely flat, featureless wastes of bare sand. They may be mountainous or rocky. Parts of them may be cut deeply by rushing streams of water that follow occasional bursts of rain.

Some deserts, such as the Sahara, are extremely hot. Others, such as the Gobi, are hot in summer and very cold in winter.

The term "cold desert" sometimes is applied to Siberia and to the frozen arctic regions of Europe and North America. There is water in cold deserts, but it is usually frozen, so few plants can grow.

Nearly one fifth of the earth's entire land surface is made up of deserts. That means that about 20 percent of the world's land is located in regions which have little water and few plants.

All continents except Europe have large deserts. The greatest desert area in the world stretches across Asia and Africa. It extends all the way from the Sahara across the Great Arabian Desert and the deserts of Afghanistan and Iran.

Much of the southwestern part of the United States and northern Mexico is desert. Another large desert is the Atacama on the Pacific coast of South America.

There's another vast desert in central western Australia as well as the Gobi in China and Mongolia, and the Kalahari in southern Africa.

Many deserts are almost totally without water. Winds blow the sands of these deserts into dunes which shift and move endlessly across the desert's surface. Few plants can live in these dry, moving sands.

An oasis in the desert is a spot where irrigation from wells or water from springs gives plants the water they need to grow. Oases are like green islands in the middle of deserts. People living in an oasis can grow many kinds of fruits and cereals:

Large areas of some deserts have been irrigated by engineers.

Engineers have built dams on rivers crossing some desert regions and have made the river water flow into desert canals. They have also dug artesian wells in desert regions.

Many desert areas have very rich soil. When these deserts are irrigated, they grow abundant and useful crops where once nothing grew but cacti and other desert plants.

California's Imperial Valley is a desert region that was turned into valuable farmland by irrigation. In India and Pakistan, water from the Indus River is carried in canals to irrigate huge areas of desert land.

Large desert areas around the Nile Delta in Egypt have been turned into valuable farming land by irrigation.