Deserts of the World the Sahara Desert

About the African Sahrara desert, size, history, and geography of the largest desert in the world.

DESERTS

SAHARA DESERT

North Africa's Sahara Desert is the largest in the world. At its greatest length it stretches 3,200 mi. east from the Atlantic Ocean to the Red Sea; and from the Mediterranean Sea southward it varies in width from 800 to 1,400 mi. In all, this desert encompasses some 3.5 million sq. mi., one third of Africa. Sahara is the plural of the Arabic noun sahra, which means simply "desert."

Contrary to what most people think, the Sahara isn't all soft sand. Only one fifth of its surface consists of dunes. The rest is barren rock and sun-scorched rubble. But the dunes are the most impressive feature of the desert--many of them, the whalebacks, 100 mi. long. 2 mi. wide, and 200 ft. high. The Sahara's level varies from the Qattara Depression in Egypt (436 ft. below sea level) to the Emi Koussi mountain in Chad (11,204 ft. high).

Daily temperatures fluctuate as much as 80 deg. F, sometimes climbing to well over 100 deg. F in the afternoon or falling below freezing at night.

To the north, the 14,000-ft.-high Atlas Mountains of Morocco and Algeria create a rain shadow that blocks moist air from the Atlantic and Mediterranean. Three or four inches of rain a year is generous; the central desert receives far less, often at intervals of several years. At one time, during the Cretaceous period, the Sahara was covered with a vast sea, which created rich mineral deposits. The sea eventually dried up, followed by a succession of wet and dry periods. During its earliest human habitation, the Sahara was comparatively green and fertile, but not until the Romans introduced well-digging tools and the camel to the desert could humans sustain themselves there, and then only on the fringes or near oases.

Orbital photography from Apollo-Soyuz space missions has confirmed what scientists long suspected, that the desert is moving south and growing larger. Most dunes are migrating an average of 2 ft. a day, pushed by the Mediterranean dry winds, and claiming roads and fertile land. So far, only a line of imported Australian eucalyptus trees has been able to stem the tide of sand.

Arab geographer Ibn Batuta recorded the first detailed observations about the Sahara between 1325 and 1345. European explorers didn't take notice of the desert until the 19th century, because of its alien hostility. One sandstorm alone, in 1805, resulted in the death of an entire caravan of 2,000 men and 1,800 camels.

Recently men have come to respect the rich Sahara, with its storehouse of oil, natural gas, tin, copper, iron, uranium, and other valuable resources.

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