great desert area, N Africa, the W portion of the broad belt of arid land that extends from the Atlantic Ocean eastward past the Red Sea to Iraq. The entire desert, the largest in the world, is about 1610 km (about 1000 mi) wide and about 5150 km (about 3200 mi) long from E to W. The total area of the Sahara is more than 9,065,000 sq km (more than 3,500,000 sq mi), of which some 207,200 sq km (some 80,000 sq mi) consist of partially fertile oases.

The boundaries of the Sahara are the Atlantic Ocean on the W, the Atlas Mts. and the Mediterranean Sea on the N, the Red Sea and Egypt on the E, and the Sudan and the valley of the Niger R. on the S. The boundaries, however, are not clearly defined and have been shifting for millennia. The Sahara was once a fertile area; millet was cultivated there over 8000 years ago. As conditions gradually became drier, however, and desertification set in, farmers abandoned their land.

Geographically distinct are the W Sahara, which is sometimes called the Sahara proper; the central Ahaggar Mts. and the Tibesti Massif, a plateau region; and the Libyan Desert in the E. The W Sahara is an area of rock-strewn plains and sand deserts of varying elevation. The land is almost entirely without rainfall or surface water but possesses a number of underground rivers that flow from the Atlas and other mountains. Occasionally the waters of these rivers find their way to the surface; in these naturally irrigated oases, plants grow freely. The soil of this region of the Sahara is fertile and, where irrigation is possible, produces excellent crops. The central plateau region of the Sahara runs for about 1610 km (about 1000 mi) in a NW to SE direction. The plateau itself varies in height from about 580 to 760 m (about 1900 to 2500 ft), and peaks in the several mountain ranges that rise from the plateau are from about 1830 to more than 3414 m (about 6000 to more than 11,200 ft) high. Notable peaks include Emi Koussi (3415 m/11,204 ft), in the Tibesti Massif, and Tahat (3003 m/9852 ft), in the Ahaggar range. Although rainfall is scanty in the area, a number of the central Saharan peaks are snowcapped during part of the year.

The Libyan Desert is considered the most arid part of the Sahara. Moisture is almost totally absent and few oases exist. The land is characterized by sandy wastes and large dunes of sand 122 m (400 ft) or more in height. The valley of the Nile R. and the mountainous area of the Nubian Desert to the E of the Nile are, geographically, part of the Sahara, but the irrigation afforded by the Nile transforms the desert into fertile agricultural land throughout much of Egypt.

The Sahara as a whole is a tableland with an average elevation from about 395 to 490 m (1300 to 1600 ft). Only comparatively small areas are elevated as little as 150 m (500 ft) above sea level. In Egypt and Algeria, limited areas, such as the Qattarah Depression, are below sea level. The climate is uniformly dry; most areas average less than 127 mm (less than 5 in) of rain per year, and some get none at all for years at a time. The temperature range is extreme, ranging between freezing to more than 54.4° C (130° F) in the W and central portions. Except in the oases the desert is almost devoid of vegetation, although some stunted, thorny shrubs grow in the W Sahara. Artificial oases have been created by drilling water wells more than 1000 m (more than 3280 ft) deep. The chief trees of the oases are the date palm and a form of acacia. Gazelle and antelope are found in many parts of the desert, as are jackal, fox, badger, and hyena. The Libyan Desert is virtually devoid of any form of animal or vegetable life. The N Sahara has assumed economic importance with the discovery of extensive petroleum deposits in Algeria and Libya.

Politically, the Sahara lies largely in Morocco, Algeria, Tunisia, Libya, Egypt, Mauritania, Mali, Niger, Chad, and Sudan.

For further information on this topic, see the Bibliography, section 427. Desert.