Regions of sand dunes (erg) occupy only about 15% of the Sahara; "stone deserts," consisting of plateaus of denuded rock (hammada) or areas of coarse gravel (reg), cover about 70% of the region; mountains, oases, and transition zones account for the remainder. Sparse vegetation is found in most parts of the Sahara, with the exception of the sand dune regions. High mountain massifs rise in the central regions; they are the Ahagger (Hoggar) in S Algeria, which rises to more than 9,000 ft (2,740 m); the Tibesti Massif in N Chad, which rises to more than 11,000 ft (3,350 m); and the Aïr Mountains (Azbine) in N Niger, which rise to more than 6,000 ft (1,830 m). The mountains are deeply dissected and were in the past infamous for the shelter they provided to marauders preying on desert traffic. From west to east the four principal land routes across the desert are from Colomb-Bechar to Dakar; from Colomb-Bechar to Gao and Timbuktu by way of Reganne; from Touggourt to Agadez and Kano by way of In-Salah; and from Tripoli to Ghat.
The Sahara has one of the harshest climates in the world. Located in the trade winds belt, the region is subject to winds that are frequently strong and that blow constantly from the northeast between a subtropical high-pressure cell and an equatorial low-pressure cell. As air moves downward from the high-pressure into the low-pressure cell, it becomes warmer and drier. The desiccating and dust-laden winds are sometimes felt north and south of the desert, where they are variously known as sirocco, khamsin, simoom, and harmattan. The northern slopes of the Atlas Mts. intercept most of the moisture from winds blowing inshore from the Mediterranean Sea.
Border zones on the north and south, where the desert merges with the steppe, receive about 10 in. (25 cm) of rain a year with some seasonal regularity, but over most of the region rainfall is sparser, with an average annual total of less than 5 in. (12.7 cm); rainfall is usually torrential when it occurs after long dry periods that sometimes last for years. The region's low relative humidity rarely exceeds 30% and is often in the 4% to 5% range.
Daytime temperatures are high; Azizia, Libya, recorded the world's highest official temperature in the shade (136°F;/58°C;) in Sept., 1922. Heat loss is rapid at night and a diurnal range of 86°F; (30°C;) is common. Freezing temperatures are not uncommon at night from December to February.
The Nile and Niger rivers, both fed by rains outside the desert, are the only permanent rivers in the region. Water is present at or just below the surface gravel in wadis (intermittent streams) that radiate from the mountain massifs, in scattered oases where the water table comes to the surface, and at greater depths in huge underground aquifers. The aquifers are believed to be filled with water dating from the Pleistocene epoch, when the Sahara was much wetter than it is today. The more than 20 lakes (called chotts in the north) and areas of salt flats and boggy salt marshes are also considered relics from this pluvial period.
Important discoveries of minerals, oil, and gas have been made in the Sahara. There are huge oil and gas deposits in Algeria and Libya, but in most cases, inaccessibility has delayed exploitation. In searching for oil reserves, underground deposits of water also have been found. Extensive iron ore deposits are worked in the Fort Gouraud area of Mauritania. Salt is still mined, as in the past, at Taoudenni, Mali, and at Bilma, Niger, and is transported, as in the days of the great medieval kingdoms of W Africa, by camel caravans across the desert.
Two thirds of the Sahara's estimated 2 million inhabitants (excluding those in the Nile valley) are concentrated in oases where date palms, fruits, vegetables, grains, and other crops are produced under irrigation. Nomads, with herds of sheep and goats and with camels for transportation, predominate in drier areas and continue to use oases (including modern oases created by the drilling of wells), as in centuries past, for water, trade, and provisioning stops. The principal ethnic groups of the Sahara are the Tuareg (of Berber origin), who dominate the mountains of the central Sahara; the peoples of mixed Berber and Arab origin in W Sahara; and the Tibu (Tébu), who dominate the Tibesti Massif.
The Sahara has undergone a series of wet periods, the most recent occurring c.5,000-10,000 years ago; it was not until c.3000 B.C. that the Sahara transformed into its present arid state. There is dispute as to whether the desertification of the region has continued into historic time. Those who support this theory contend that increasing aridity is the reason for the recorded advance of desert conditions into areas under cultivation in Roman times in the north and more recently (since the late 1960s) in the south. Opponents of this view explain such changes as being the result of alterations in land-use practices and neglect of water-supply and irrigation systems.
The camel was introduced probably in the 1st cent. A.D. and facilitated occupation by nomads (first the Berbers, later the Arabs), who lived in interdependence with the oasis dwellers, providing protection against enemies in exchange for supplies of food and water. A profitable trans-Saharan trade in gold and slaves from W Africa, salt from the desert, and cloth and other products from the cities on the Mediterranean coast was carried on by the nomads. The first European explorers to travel in the Sahara were Friedrich Horneman in 1805 and Mungo Park in 1806. Some areas of the Sahara remain virtually unexplored, although a network of air and automobile routes now crosses the desert and links the major oases and mining areas.
See C. Kruger et al., Sahara (tr. 1969); M. Williams and H. Faure, ed., The Sahara and the Nile: Quarternary Environments and Prehistoric Occupation in Northern Africa (1980); J. Cloudsley-Thompson, ed., Key Environments: Sahara Desert (1984); E. Gautier, Sahara (1987).
The Sahara (الصحراء الكبرى, aṣ-ṣaḥrā´ al-kubra, "The Great Desert") is the world's largest hot desert and the world's second largest desert after Antarctica. At over 9,000,000 square kilometers (3,500,000 sq mi), it covers most parts of Northern Africa; an area stretching from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel, a belt of semi-arid tropical savanna separating the Sahara from Sub-Saharan Africa. The Sahara is almost as large as the continental United States, and is larger than Australia. The Sahara has an intermittent history that may go back as much as 3 million years. Some of the sand dunes can reach 180 meters (600 ft) in height.
The Sahara's boundaries are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean Sea on the north, the Red Sea and Egypt on the east, and the Sudan and the valley of the Niger River on the south. The Sahara is divided into western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains (a region of desert mountains and high plateaus), Tenere desert and the Libyan desert (the most arid region). The highest peak in the Sahara is Emi Koussi in the Tibesti Mountains in northern Chad.
The Sahara divides the continent of Africa into North and Sub-Saharan Africa. The southern border of the Sahara is marked by a band of semiarid savanna called the Sahel; south of the Sahel lies the lusher Sudan and the Congo River Basin. Most of the Sahara consists of rocky hamada; ergs (large sand dunes) form only a minor part.
People lived on the edge of the desert thousands of years ago since, immediately after the last ice age, the Sahara was a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles (which still exist in parts of the desert) survive, with half found in the Tassili n'Ajjer in southeast Algeria. Fossils of dinosaurs, including Afrovenator, Jobaria and Ouranosaurus, have also been found here. The modern Sahara, though, is not as lush in vegetation, except in the Nile Valley, at a few oases, and in the northern highlands, where Mediterranean plants such as the olive tree are found to grow. The region has been this way since about 3000 BC. Some 2.5 million people live in the Sahara, most of these in Egypt, Mauritania, Morocco and Algeria. Dominant ethnicities in the Sahara are various Berber groups including Tuareg tribes, various Arabised Berber groups such as the Hassaniya-speaking Maure (Moors, also known as Sahrawis), and various "black African" ethnicities including Tubu, Nubians, Zaghawa, Kanuri, Peul (Fulani), Hausa and Songhai. Important cities located in the Sahara include Nouakchott, the capital of Mauritania; Tamanrasset, Ouargla, Bechar, Hassi Messaoud, Ghardaia, El Oued, Algeria; Timbuktu, Mali; Agadez, Niger; Ghat, Libya; and Faya-Largeau, Chad.
It has been reported that the Sahara is expanding south by as much as per year, overwhelming degraded grasslands, taking over the Sahel, the dry tropical savanna that has defined the Sahara's southern limit. Global warming and poor farming methods have been given as possible causes. The spreading of deserts is known as "desertification," and the phenomenon is occurring in other desert areas worldwide.
The Sahara covers huge parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia. It is one of three distinct physiographic provinces of the African massive physiographic division.
The desert landforms of the Sahara are shaped by wind (eolian) or by occasional rains, and include sand dunes and dune fields or sand seas (erg), stone plateaus (hamada), gravel plains (reg), dry valleys (wadi), and salt flats (shatt or chott). Unusual landforms include the Richat Structure in Mauritania.
Several deeply dissected mountains and mountain ranges, many volcanic, rise from the desert, including the Aïr Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and Red Sea Hills. The highest peak in the Sahara is Emi Koussi, a shield volcano in the Tibesti range of northern Chad.
Most of the rivers and streams in the Sahara are seasonal or intermittent, the chief exception being the Nile River, which crosses the desert from its origins in central Africa to empty into the Mediterranean. Underground aquifers sometimes reach the surface, forming oases, including the Bahariya, Ghardaïa, Timimoun, Kufrah, and Siwah.
The center of the Sahara is hyper-arid, with little vegetation. The northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis where moisture collects.
To the north, the Sahara reaches to the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Magreb, the Sahara borders Mediterranean forest, woodland, and shrub ecoregions of northern Africa, which have a Mediterranean climate characterized by a winter rainy season. According to the botanical criteria of Frank White and geographer Robert Capot-Rey, the northern limit of the Sahara corresponds to the northern limit of Date Palm cultivation (Phoenix dactylifera), and the southern limit of Esparto (Stipa tenacissima), a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the isohyet of annual precipitation.
To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a Chenopodiaceae), or northern limit of the Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the southern limit of the Sahara corresponds to the isohyet of annual precipitation (keeping in mind that precipitation varies strongly from one year to another).
The climate of the Sahara has undergone enormous variation between wet and dry over the last few hundred thousand years. During the last ice age, the Sahara was bigger than it is today, extending south beyond its current boundaries. The end of the ice age brought better times to the Sahara, from about 8000 BC to 6000 BC, perhaps due to low pressure areas over the collapsing ice sheets to the north. Once the ice sheets were gone, the northern part of the Sahara dried out. However, not long after the end of the ice sheets, the monsoon, which currently brings rain only as far as the Sahel, came further north and counteracted the drying trend in the southern Sahara. The monsoon in Africa (and elsewhere) is due to heating during the summer. Air over land becomes warmer and rises, pulling in cool wet air from the ocean, which causes rain. Paradoxically, the Sahara was wetter when it received more solar insolation in the summer. Changes in solar insolation are caused by changes in the Earth's orbital parameters (9,000 years ago the Earth's axis had a stronger tilt than it does presently, and perihelion occurred at the end of July).
By around 3400 BC, the monsoon retreated south to approximately where it is today, leading to the gradual rather than abrupt desertification of the Sahara. The Sahara is currently as dry as it was about 13,000 years ago. These conditions are responsible for what has been called the Sahara Pump Theory.
The Sahara has one of the harshest climates in the world. The prevailing north-easterly wind often causes the sand to form sand storms and dust devils. Precipitation, while rare, is not unknown. Half of the Sahara receives less than of rain a year, with the rest receiving up to a year. The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods, which can last for years.
The southern boundary of the Sahara, as measured by rainfall, was observed to both advance and retreat between 1980 and 1990. As a result of drought in the Sahel, the southern boundary showed an overall southward movement of during that period. . Deforestation has also caused the Sahara to advance southward in recent years, as trees and bushes continue to be used a fuel source.
The Sahara comprises several distinct ecoregions, whose variations in temperature, rainfall, elevation, and soils harbor distinct communities of plants and animals. According to the World Wide Fund for Nature (WWF), the ecoregions of the Sahara include:
The peoples of Phoenicia, who flourished between 1200-800 BC, created a confederation of kingdoms across the entire Sahara to Egypt. They generally settled along the Mediterranean coast, as well as the Sahara, among the peoples of Ancient Libya, who were the ancestors of peoples who speak Berber languages in North Africa and the Sahara today, including the Tuareg of the central Sahara.
The Phoenician alphabet seems to have been adopted by the ancient Libyans of north Africa, and Tifinagh is still used today by Berber-speaking Tuareg camel herders of the central Sahara.
Sometime between 633 BC and 530 BC, Hanno the Navigator either established or reinforced Phoenician colonies in Western Sahara, but all ancient remains have vanished with virtually no trace. (See History of Western Sahara.)
Following the Islamic conquest of North Africa in the seventh century CE, trade across the desert intensified. The kingdoms of the Sahel, especially the Ghana Empire and the later Mali Empire, grew rich and powerful exporting gold and salt to North Africa. The emirates along the Mediterranean Sea sent south manufactured goods and horses. From the Sahara itself, salt was exported. This process turned the scattered oasis communities into trading centres, and brought them under the control of the empires on the edge of the desert. A significant slave trade crossed the desert (See Arab slave trade).
This trade persisted for several centuries until the development in Europe of the caravel allowed ships, first from Portugal but soon from all Western Europe, to sail around the desert and gather the resources from the source in Guinea. The Sahara was rapidly remarginalized.
European colonialism in the Sahara began in the 19th century. France conquered Algeria from the Ottomans in 1830, and French rule spread south from Algeria and eastwards from Senegal into the upper Niger to include present-day Algeria, Chad, Mali, Mauritania, Morocco (1912), Niger, and Tunisia (1881).
Egypt, under Muhammad Ali and his successors, conquered Nubia (1820-22), founded Khartoum (1823), and conquered Darfur (1874). Egypt, including the Sudan, became a British protectorate in 1882. Egypt and Britain lost control of the Sudan from 1882 to 1898 as a result of the Mahdist War. After its capture by British troops in 1898, the Sudan became a Anglo-Egyptian condominium.
Most of the Saharan states achieved independence after World War II: Libya in 1951, Morocco, Sudan, and Tunisia in 1956, Chad, Mali, Mauritania, and Niger in 1960, and Algeria in 1962. Spain withdrew from Western Sahara in 1975, and it was partitioned between Mauritania and Morocco. Mauritania withdrew in 1979, and Morocco continues to hold the territory.
The modern era has seen a number of mines and communities develop to exploit the desert's natural resources. These include large deposits of oil and natural gas in Algeria and Libya and large deposits of phosphates in Morocco and Western Sahara.
A number of Trans-African highways have been proposed across the Sahara, including the Cairo-Dakar Highway along the Atlantic coast, the Trans-Sahara Highway from Algiers on the Mediterranean to Kano in Nigeria, the Tripoli-Cape Town Highway from Tripoli in Libya to Ndjamena in Chad, and the Cairo-Cape Town Highway which follows the Nile. Each of these highways is partially complete, with significant gaps and unpaved sections.
Speakers of the Nilo-Saharan language family also inhabit the Sahara, including the Fur of Darfur in western Sudan and the Saharan languages of Niger, Chad and western Sudan, which includes the Kanuri, Tedaga, and Dazaga.
The following countries are either fully or partially covered by the Sahara.