Sahara

desert in western Libya, part of the Sahara]] on the surface of the Sahara. The bottom (using radar) is the rock layer underneath, revealing black channels cut by the meandering of an ancient river that once fed the oasis.]]

The Sahara ( , , "The Greatest Desert") is the world's largest hot desert. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The only larger desert in the world is Antarctica, classified as such due to very low precipitation rates. The Sahara stretches 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 that comprises the northern region of central and western Sub-Saharan Africa.

Some of the sand dunes can reach in height. The name comes from the Arabic word for desert: (صَحراء), "ṣaḥrā´" ( ; ).

Overview

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 Air Mountains (a region of desert mountains and high plateaus), Ténéré 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 the last ice age. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles 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 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 5000 years ago. Some 2.5 million people currently 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 Toubou, 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, and El Oued (Algeria), Timbuktu (Mali), Agadez (Niger), Ghat (Libya), as well as Faya-Largeau (Chad).

Geography

The Sahara covers large 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 (Aeolian processes) 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 the 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 central part 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 scrub 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 drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel. During the last glacial period, the Sahara was even bigger than it is today, extending south beyond its current boundaries. The end of the glacial period brought more rain 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, northern Sahara dried out. In the southern Sahara though, the drying trend was soon counteracted by the monsoon, which brought rain further north than it does today. The monsoon is due to heating of air over the land during summer. The hot air rises and pulls in cool, wet air from the ocean, which causes rain. Thus, though it seems counterintuitive, the Sahara was wetter when it received more insolation in the summer. This was caused by a stronger tilt in Earth's axis of orbit than today, 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 desertification of the Sahara. The Sahara is now as dry as it was about 13,000 years ago. Half of the Sahara receives less than of rain per year, and the rest receives up to per 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 moved south overall during that period. Deforestation has also caused the Sahara to advance south in recent years , as trees and bushes continue to be used as fuel source.

Recent signals indicate that the Sahara and surrounding regions are greening due to increased rainfall. Satellites show extensive regreening of the Sahel between 1982 and 2002, and in both Eastern and Western Sahara a more than 20 year long trend of increased grazing areas and flourishing trees and shrubs has been observed by climate scientist Stefan Kröpelin.

Snow and ice

On February 18, 1979, snowfall in several places in southern Algeria, including a half-hour snowstorm that stopped traffic in Ghardaïa, was reported in newspapers around the world as '[snow in the Sahara] for the first time in living memory'. The snow was gone within hours.

Several Saharan mountain ranges, however, receive snow on a more regular basis. Although relative humidity is low in the arid environment, the absolute humidity is sufficiently high to condense when driven up a mountain range. In winter, temperatures drop low enough on the Tahat summit, highest peak of the Ahaggar Mountains, to cause snow every third year; the inaccessible Tibesti Mountains are said to receive snow on peaks over every seventh year.

Ecoregions

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:

* Atlantic coastal desert: The coastal desert occupies a narrow strip along the Atlantic coast, where fog generated offshore by the cool Canary Current provides sufficient moisture to sustain a variety of lichens, succulents, and shrubs. It covers 39,900 square kilometers (15,400 square miles) in Western Sahara and Mauritania.

North Saharan steppe and woodlands: This ecoregion lies along the northern desert, next to the Mediterranean forests, woodlands, and scrub ecoregions of the northern Maghreb and Cyrenaica. Winter rains sustain shrublands and dry woodlands that form a transition between the Mediterranean climate regions to the north and the hyper-arid Sahara proper to the south. It covers 1,675,300 square kilometers (646,800 square miles) in Algeria, Egypt, Libya, Mauritania, Morocco, Tunisia, and Western Sahara.

Sahara desert: This ecoregion covers the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Vegetation is rare, and this ecoregion consists mostly of sand dunes (erg, chech, raoui), stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. It covers 4,639,900 square km (1,791,500 square miles) of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, and Sudan.

South Saharan steppe and woodlands: The South Saharan steppe and woodlands occupy a narrow band running east and west between the hyper-arid Sahara and the Sahel savannas to the south. Movements of the equatorial Intertropical Convergence Zone (ITCZ) bring summer rains during July and August which average , but vary greatly from year to year. These rains sustain summer pastures of grasses and herbs, with dry woodlands and shrublands along seasonal watercourses. The ecoregion covers 1,101,700 km² (425,400 mi²) in Algeria, Chad, Mali, Mauritania, and Sudan.

West Saharan montane xeric woodlands: Several volcanic highlands in the western portion of the Sahara provide a cooler, moister environment that supports Saharo-Mediterranean woodlands and shrublands. The ecoregion covers 258,100 km² (99,700 mi²), mostly in the Tassili n'Ajjer of Algeria, with smaller enclaves in the Aïr of Niger, the Dhar Adrar of Mauritania, and the Adrar des Iforas of Mali and Algeria.

Tibesti-Jebel Uweinat montane xeric woodlands: The Tibesti and Jebel Uweinat highlands foster higher, more regular rainfall and cooler temperatures, which support woodlands and shrublands of palms, acacias, myrtle, oleander, Tamarix, and several rare and endemic plants. The ecoregion covers 82,200 km² (31,700 mi²) in the Tibesti of Chad and Libya, and Jebel Uweinat on the border of Egypt, Libya, and Sudan.

Saharan halophytics: Seasonally flooded saline depressions in the Sahara are home to halophytic, or salt-adapted, plant communities. The Saharan halophytics cover 54,000 km² (20,800 mi²), including the Qattara and Siwa depressions in northern Egypt, the Tunisian salt lakes of central Tunisia, Chott Melghir in Algeria, and smaller areas of Algeria, Mauritania, and Western Sahara.

Tanezrouft: One of the harshest regions on Earth and the driest in the Sahara, contains no vegetation and very little life.

Flora and fauna

, in north-eastern Chad.]]

Dromedary camels and goats are the most domesticated animals found in the Sahara. Because of its qualities of endurance and speed, the dromedary is the favorite animal used by nomads.

The Leiurus quinquestriatus (aka deathstalker) scorpion which can be long. Its venom contains large amounts of agitoxin and scyllatoxin and is very dangerous; however, a sting from this scorpion rarely kills a healthy adult.

The monitor lizard. It has been suggested that the occasional habit of varanids to stand on their two hind legs and to appear to "monitor" their surroundings led to the original Arabic name waral ورل, which is translated to English as "monitor".

Sand vipers, which average less than in length. Many have a pair of horns, one over each eye. Active at night, they usually lie buried in the sand with only their eyes visible. Bites are painful, but rarely fatal.

The African Wild Dog has some populations confirmed in the southern Sahara. or perhaps only 14 countries. .

The fennec fox, pale fox and Rüppell's fox, are omnivorous canids living in many parts of Sahara.

The hyrax. It first appears in the fossil record over 40 million years ago, and for many millions of years hyraxes were the primary terrestrial herbivore in Africa.

The ostrich which is a flightless bird native to Africa. They have become rare.

The addax, a large white antelope, is a threatened species. Adapted to the desert, they can remain months without drinking, even a whole year.

The Saharan cheetah lives in Algeria, Togo, Niger, Mali, Benin, and Burkina Faso. There remain less than 250 mature cheetahs which are very cautious, fleeing any human presence. The cheetah avoids the sun from April to October. It then seeks the shelter of shrubs such as balanites and acacias. They are unusually pale.

The dorcas gazelle is a north African gazelle that can also go for a long time without water.

There exist other animals in the Sahara (birds in particular) such as African Silverbill and Black-throated Firefinch among others. There are also small desert crocodiles in Mauritania and the Ennedi Plateau of Chad.

The central Sahara is estimated to include only five hundred species of plants, which is extremely low considering the huge extent of the area. Plants such as acacia trees, palms, succulents, spiny shrubs, and grasses have adapted to the arid conditions, either by reducing water loss or storing water. Plant leaves may dry out totally and then recover. Human activities are more likely to affect the habitat in areas of permanent water (oases) or where water comes close to the surface. Here, the local pressure on natural resources can be intense. The remaining populations of large mammals have been greatly reduced by hunting for food and recreation. In recent years development projects have started in the deserts of Algeria and Tunisia using irrigated water pumped from underground aquifers. These schemes often lead to soil degradation and salinization.

==History==

Berbers

Berbers are one of the oldest known inhabitants of the Sahara Desert. They are the people that occupied (and still occupy) more than two thirds of the Sahara's total surface. The Garamantes Berbers built a prosperous empire in the heart of the desert. The Tuareg nomads continue, to present day, to inhabit and move across wide Sahara surfaces in Algeria, Mali, Niger, Mauritania, and Libya. Some of the oldest Berber Tifinagh inscriptions are found in Southern Algeria, Northern Mali and Niger.

Egyptians

By 6000 BC predynastic Egyptians in the southwestern corner of Egypt were herding cattle and constructing large buildings. Subsistence in organized and permanent settlements in predynastic Egypt by the middle of the 6th millennium BC centered predominantly on cereal and animal agriculture: cattle, goats, pigs and sheep. Metal objects replaced prior ones of stone. Tanning of animal skins, pottery and weaving are commonplace in this era also. There are indications of seasonal or only temporary occupation of the Al Fayyum in the 6th millennium BC, with food activities centering on fishing, hunting and food-gathering. Stone arrowheads, knives and scrapers are common. Burial items include pottery, jewelry, farming and hunting equipment, and assorted foods including dried meat and fruit. Burial in desert environments appears to enhance Egyptian preservation rites, and dead are buried facing due west. Megaliths found at Nabta Playa are overt examples of probably the world's first known Archaeoastronomy devices, predating Stonehenge by some 1000 years. This complexity, as observed at Nabta Playa, and as expressed by different levels of authority within the society there, likely formed the basis for the structure of both the Neolithic society at Nabta and the Old Kingdom of Egypt. salt caravan. As recently as 1906, a 20,000- camel caravan left Agadez to collect salt at Bilma.]]

Phoenicians

The people 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 people of Ancient Libya, who were the ancestors of people 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.)

Greeks

By 500 BC, a new influence arrived in the form of the Greeks. Greek traders spread along the eastern coast of the desert, establishing trading colonies along the Red Sea coast. The Carthaginians explored the Atlantic coast of the desert. But the turbulence of the waters and the lack of markets never led to an extensive presence further south than modern Morocco. Centralized states thus surrounded the desert on the north and east; it remained outside the control of these states. Raids from the nomadic Berber people of the desert were a constant concern of those living on the edge of the desert. (1971)]]

Urban civilization

An urban civilization, the Garamantes, arose around this time in the heart of the Sahara, in a valley that is now called the Wadi al-Ajal in Fazzan, Libya.

Trans-Saharan trade

Following the Islamic conquest of North Africa in the mid-seventh to early eighth centuries, 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. It has been estimated that from the 10th to the 19th century some 6,000 to 7,000 slaves were transported north each year. once controlled the central Sahara desert and its 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 imperialism

At the beginning of the 19th century, most of the northern Sahara, including most of present-day Algeria, Tunisia, Libya, and Egypt, was part of the Ottoman Empire. The Sahel and southern Sahara were home to several independent states.

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.

Spain captured present-day Western Sahara after 1874. In 1912, Italy captured Libya from the Ottomans.

To promote the Roman Catholic religion in the desert, the Pope in 1868 appointed a delegate Apostolic of the Sahara and the Sudan; later in the 19th century his jurisdiction was reorganized into the Vicariate Apostolic of Sahara.

Modern times

Egypt became independent of Britain in 1936, although the Anglo-Egyptian Treaty of 1936 allowed Britain to keep troops in Egypt and maintained the British-Egyptian condominium in the Sudan. British military forces were withdrawn in 1954.

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, but Morocco continues to hold the territory.

The modern era has seen a number of mines and communities develop to utilize 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.

Peoples and languages

The Sahara is home to a number of people and languages. Arabic is the most widely spoken language in the Sahara, from the Atlantic to the Red Sea. Berber people are found from western Egypt to Morocco, including the Tuareg pastoralists of the central Sahara. The Beja live in the Red Sea Hills of southeastern Egypt and eastern Sudan. The Arabic, Berber, and Beja languages are part of the Afro-Asiatic language family.

See also

List of deserts by area

Arid Lands Information Network

Azaouad

Sahara Conservation Fund

Saharan explorers

Green Sahara

References

Notes

Bibliography

Michael Brett and Elizabeth Frentess. The Berbers. Blackwell Publishers, 1996.

Charles-Andre Julien. History of North Africa: From the Arab Conquest to 1830. Praeger, 1970.

Abdallah Laroui. The History of the Maghrib: An Interpretive Essay. Princeton, 1977.

Hugh Kennedy. Muslim Spain and Portugal: A Political History of al-Andalus. Longman, 1996.

Richard W. Bulliet. The Camel and the Wheel. Harvard University Press, 1975. Republished with a new preface Columbia University Press, 1990.

External links

hydrology and planned usage of the aquifers">About Sahara subsurface hydrology and planned usage of the aquifers

Tassili and Ahaggar National Parks

Category:Deserts Category:Palearctic Category:Deserts and xeric shrublands Category:Arabic words and phrases Category:Geography of the Arab League Category:Physiographic provinces Category:Geography of Africa