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The Sahara ( / səˈhɑːrə /, / səˈhærə /) is a desert spanning across North Africa. With an area of 9,200,000 square kilometres (3,600,000 sq mi), it is the largest hot desert in the world and the third-largest desert overall, smaller only than the deserts of Antarctica and the northern Arctic.
- 9,200,000 km² (3,600,000 sq mi)
- 1,800 km (1,100 mi)
- 4,800 km (3,000 mi)
- Overview
- Physiography
The Sahara exhibits great climatic variability within its borders, with two major climatic regimes differentiating along a north-south axis: the desert’s northern latitudes are arid subtropical and have two rainy seasons, while the southern ones, although also arid, are more tropical and have only one rainy season. The southern reaches of the Sahara end in the Sahel, a semiarid buffer zone that separates the desert from the more temperate savanna biomes beyond. A number of other factors affect climatic variability within the Sahara as well: topography does so, as do ocean currents, the latter of which are responsible for the slightly cooler and more humid conditions found on the desert’s western margins. Some scientists estimate that the Sahara became arid about two to three million years ago, while others contend that it happened before this.
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Read more about the Sahel.
How did the Sahara get its name?
In Arabic the Sahara is called Al-Ṣaḥrāʾ al-Kubrā, or “the Great Desert.” The Arabic word ṣaḥrāʾ simply means “desert,” and its plural form, ṣaḥārāʾ, is where the northern African desert gets its Anglicized name. The word ṣaḥrāʾ shares its roots with the Arabic word aṣḥar, which translates to “desert-like” and specifically connotes the yellowish red color that characterizes the Sahara’s sandy expanses.
The principal topographical features of the Sahara include shallow, seasonally inundated basins (chotts and dayas) and large oasis depressions; extensive gravel-covered plains (serirs or regs); rock-strewn plateaus (hammadas); abrupt mountains; and sand sheets, dunes, and sand seas (ergs). The highest point in the desert is the 11,204-foot (3,415-metre) summit of Mount Koussi in the Tibesti Mountains in Chad. The lowest, 436 feet (133 metres) below sea level, is in the Qattara Depression of Egypt.
The name Sahara derives from the Arabic noun ṣaḥrāʾ, meaning desert, and its plural, ṣaḥārāʾ. It is also related to the adjective aṣḥar, meaning desertlike and carrying a strong connotation of the reddish colour of the vegetationless plains. There are also indigenous names for particular areas—such as the Tanezrouft region of southwestern Algeria and the Ténéré region of central Niger—which are often of Berber origin.
The Sahara sits atop the African Shield, which is composed of heavily folded and denuded Precambrian rocks. Because of the stability of the shield, subsequently deposited Paleozoic formations have remained horizontal and relatively unaltered. Over much of the Sahara, these formations were covered by Mesozoic deposits—including the limestones of Algeria, southern Tunisia, and northern Libya, and the Nubian sandstones of the Libyan Desert—and many of the important regional aquifers are identified with them. In the northern Sahara, these formations are also associated with a series of basins and depressions extending from the oases of western Egypt to the chotts of Algeria. In the southern Sahara, downwarping of the African Shield created large basins occupied by Cenozoic lakes and seas, such as the ancient Mega-Chad. The serirs and regs differ in character in various regions of the desert but are believed to represent Cenozoic depositional surfaces. A prominent feature of the plains is the dark patina of ferromanganese compounds, called desert varnish, that forms on the surfaces of weathered rocks. The plateaus of the Sahara, such as the Tademaït Plateau of Algeria, are typically covered with angular, weathered rock. In the central Sahara, the monotony of the plains and plateaus is broken by prominent volcanic massifs—including Mount ʿUwaynat and the Tibesti and Ahaggar mountains. Other noteworthy formations include the Ennedi Plateau of Chad, the Aïr Massif of Niger, the Iforas Massif of Mali, and the outcroppings of the Mauritanian Adrar region.
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Sand sheets and dunes cover approximately 25 percent of the Sahara’s surface. The principal types of dunes include tied dunes, which form in the lee of hills or other obstacles; parabolic blowout dunes; crescent-shaped barchans and transverse dunes; longitudinal seifs; and the massive, complex forms associated with sand seas. Several pyramidal dunes in the Sahara attain heights of nearly 500 feet, while draa, the mountainous sand ridges that dominate the ergs, are said to reach 1,000 feet. An unusual phenomenon associated with desert sands is their “singing” or booming. Various hypotheses have been advanced to explain the phenomenon, such as those based upon the piezoelectric property of crystalline quartz, but the mystery remains unsolved.
Oct 29, 2021 · Learn about the Sahara Desert, the world's largest hot desert and the third most extensive desert after Antarctica and the Arctic. Explore its geography, climate, ecology, and features such as sand dunes, volcanoes, oases, and rivers. See maps, photos, and facts about the Sahara Desert's location, size, history, and culture.
- Diptarka Ghosh
Feb 5, 2024 · Learn about the largest hot desert in the world, its location, climate, people, animals, and plants. Find out how the Sahara is not only a harsh environment but also a land of diversity and life.
A new study suggests that humans and their goats may have caused the end of the humid period in the Sahara, which was once a green oasis with lakes, rivers and forests. The researchers propose that humans overgrazed the grasslands, reduced the amount of moisture and enhanced albedo, triggering the desertification of the region.
Kerzaz oasis on Wadi Saoura, western Sahara, Algeria. Sahara, Largest desert in the world, encompassing almost all of northern Africa. Covering an area of about 3.3 million sq mi (8.6 million sq km), it is bounded by the Atlantic Ocean, the Atlas Mountains, the Mediterranean Sea, the Red Sea, and the Sahel region.
Sahara - Exploration, Climate, Geography: Classical accounts describe the Sahara much as it is today—a vast and formidable barrier. The Egyptians controlled only their neighbouring oases and, occasionally, lands to the south; the Carthaginians apparently continued the commercial relationships with the interior that had been established during the Bronze Age.
