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Name: Stacey
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 2000-2001


Question:
How do deserts form?


Replies:
Stacey,

If you look at the general atmospheric circulation and topography, you will find that most desert areas are downwind of some fairly large mountain ranges or long expanses of land. Mountains lift the air, causing condensation and precipitation that "dries" the air. As the air drops down off of the mountain range it naturally warms, thereby causing increased evaporation of water from the land that it passes over. That keeps the land dry.

Northern and sub-central Africa are a little different. These areas have been stripped of their vegetation by man and animals, thereby reducing transpiration from plants and making evaporation from the soil easier. This has combined with long expanses of land and long distances from water bodies (moisture sources) to cause a large desert area.

Then there are plateaus of land of high elevation that are dry, such as the Tibetan plateau. The precipitation rains and snows out in the mountains around them leaving little moist air to flow over the plateau, leaving it dry.

So, there are various causes of deserts. Actually, Antarctica is a cold desert. It is so cold that moisture quickly condenses out into ice crystals, leaving some snow, but almost no water vapor in the air.

I hope that this information helps you.

David Cook
meteorologist
Argonne National Laboratory


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