The
Sahara, the world's greatest dry hot desert, stretches right across the north
of Africa where there is almost no rainfall and, consequently, little or no vegetation
to anchor the soil. The sand is blown constantly by the wind, much of it into a
landscape of great shifting dunes which constantly change shape, while the
edges of the desert eternally encroach upon the land around.
The Sahara
extends over three and a half million square miles of and, where the average
rainfall is generally much less than 10 inches a year. The prevailing winds
come from the heart of Asia and carry little moisture.
The
temperature during the day exceeds 100°F in the summer, and even in the winter
averages 60°-70°F. The surface of the sand is sometimes as hot as 170°F. The
sun beats down from a clear sky all day, but at night the same cloudless sky
allows the land to cool quickly, and there is often frost at dawn in winter.
The wind acts
as a great sandblasting machine, constantly wearing down rocks and carrying
sand and small pebbles along. The few desert plants survive because they have
long roots or thick fleshy leaves, and stems that reduce water loss and may even
store moisture.
A desert
oasis is simply a place where there is water. The greatest oasis of all is
Egypt, where for thousands of years life has depended on the careful use of the
waters of the River Nile.
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