Sahara

Sahara, great desert, northern Africa , the western portion of the broad belt of arid land that extends from the Atlantic Ocean eastwards to the Red Sea. The entire desert, the largest in the world, is about 1,610 km (1,000 mi) deep and about 5,150 km (3,200 mi) wide from east to west. The total area of the Sahara is almost 9.1 million sq km (3.5 million sq mi), of which some 207,200 sq km (80,000 sq mi) consist of partially fertile oases.

The boundaries of the Sahara are the Atlantic Ocean to the west, the Atlas Mountains and the Mediterranean Sea to the north, the Red Sea and Egypt to the east, and the Sahel and the valley of the River Niger to the south. Politically, the Sahara lies largely in Morocco, Algeria, Tunisia, Libya, Egypt, Mauritania, Mali, Niger, Chad, and Sudan. However, the boundaries of the Sahara are not clearly defined and have been expanding for millennia as a result of climatic change, and the deleterious effects of human cultivation and overgrazing by animals in the modern era. The Sahara was once a fertile area; millet was cultivated there over 8,000 years ago. As conditions gradually became drier, however, and desertification set in, farmers abandoned their land. Nonetheless, the reverse is also true: in recent years, soil management and water conservation efforts, coupled with increased rainfall, have led to a significant increase in forest and grassland vegetation along the southern edge of the desert, particularly in many areas previously lost to drought in Chad, Mauritania, Niger, and Sudan.

Geographically distinct are the western Sahara, which is sometimes called the Sahara proper; the central Ahaggar Mountains and the Tibesti, a plateau region; and the Libyan Desert in the east. The western Sahara is an area of rock-strewn plains and sand deserts of varying elevation. Except in coastal areas there is virtually no rainfall or surface water; however, there are 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 approximately 1,610 km (1,000 mi) in a north-western to south-eastern direction. The plateau itself varies in height from about 580 to 760 m (1,900 to 2,500 ft); peaks in the several mountain ranges which rise from the plateau reach heights ranging from about 1,830 to more than 3,414 m (6,000 to 11,200 ft) high. Notable peaks include Emi Koussi (3,415 m/11,204 ft), in the Tibesti, and Tahat (3,003 m/9,852 ft), in the Ahaggar range. Although rainfall is scanty, 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 sand dunes 122 m (400 ft) or more in height. The valley of the River Nile and the mountainous area of the Nubian Desert to the east of the Nile are, geographically, part of the Sahara, but the irrigation transforms the desert into fertile agricultural land throughout much of the Nile Valley in Egypt.

The Sahara as a whole is a raised tableland with an average elevation from about 395 to 490 m (1,300 to 1,600 ft). Areas of lowland and depressions, where the elevation is as little as 150 m (500 ft) above sea level, are comparatively small. In Egypt and Algeria, a few areas, such as the Qattara Depression, are below sea level. The climate is uniformly dry; most areas average less than 127 mm (5 in) of rain per year, and some get none at all for years at a time. The temperature range is extreme, varying between freezing at night and on the highest peaks to more than 54.4° C (130° F) in the daytime, especially in the western and central portions. Except in the oases the desert is almost devoid of vegetation, although some stunted, thorny shrubs grow in the western Sahara. Artificial oases have been created by drilling water wells more than 1,000 m (3,280 ft) deep. In 2002 an underground river, lying 250-500 m (820-1,640 ft) beneath the Earth’s surface, was discovered in western Sahara near the town of Atar in Mauritania; the river contains significant water reserves.

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 northern Sahara has assumed contemporary economic importance with the discovery of extensive oil deposits in Algeria and Libya.

Although the Sahara may appear today to be a huge barrier between north and west Africa, historically it has been anything but divisive. Trans-Saharan trade began as early as 1000 bc, when the crossing was made by oxen, and carts and chariots. It was given new impetus by the Carthaginians in the 3rd century bc, and the Romans, who introduced the camel, three centuries later. It became of major importance after about the 8th century, with the rise of Arab power, and reached a peak between the 13th and 16th centuries, when the desert was crossed by numerous routes linking the medieval African kingdoms and empires of Ghana, Sanghai, Kanem-Bornu, and Hausaland, with the north African ports. The main items traded were gold and slaves, going north, and salt (from mines within the Sahara), cowrie shells (the major unit of currency), and weapons, going south. These items were state necessities. Luxury items were also carried on the caravans. Expensive cloth, pepper, ivory, kola nuts, leather goods, and, in the 19th century, ostrich feathers—all going north, and from there to Europe. Moroccan leather originally came from northern Nigeria, but gained its name because it was traded to the wider world through Moroccan ports. Copperware, beads, and other “fancy” items came south. The arrival of Europeans on the coast of west Africa undermined the Saharan trade, but did not finally finish it until well into the 19th century.