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sahara: eco info: topography
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It's easy to dismiss a desert as being sand, and nothing but mountains of sand. But, just like the less dry areas of Africa, the Sahara is a place of changing topography, from rocky stream beds to powdery piles of sand.


Ergs Otherwise known as sand seas, ergs are the Saharan dunes of popular imagination. They cover about 20 percent of the Sahara and can stretch for hundreds of miles at heights of up to 1,000 feet. The Grand Erg Occidental and Oriental cover most of Algeria; the Selima Erg blankets more than 3,000 square miles in Libya; the Erg Cherch stretches for 600 miles across Mali and Algeria. Formed in depressions, ergs, such as the Grand Erg of Bilma in Nigeria, can also contain large quantities of salt from dried-up ancient lakes that fuel the Sahara's salt trade.


Regs These plains of sand and black, red or white gravel make up 70 percent of the Sahara. The Libyan reg stretches for 340,000 square miles; the Tanezrouft reg, to the west of the Ahaggar Mountains, stretches for 200,000 square miles. The remains of prehistoric seas and rivers, the regs are now nearly completely waterless. Plant life is sparse; animal life is mostly limited to rodents.


Hamadas The Sahara's elevated plateaus of rock and stone, known as hamadas, can soar over 11,000 feet. They include the Atlas Mountains in southern Morocco and western Algeria; Tassili N'Ajjer massif in southeastern Algeria (up to 7,800 ft.); Tibesti Mountains of southern Libya and northern Chad (up to 11,204 ft.); the Ahaggar Mountains (9,852 feet), product of a volcanic explosion in the center of the Sahara. The Sahara's highest point? The summit of Mount Koussi in the Tibesti Mountains. (11,204 ft.)


Wadis Wadis are temporary water sources located primarily in the mountains and fed by rainfall. They are home to most of the Sahara's trees and large bushes.


ChottsChotts are depressions that fill with salt once moisture from the Sahara's winter rains evaporates in the spring and summer. Large chotts occur throughout the northern Sahara. Key scenes from "The English Patient" and "Star Wars" were filmed in a large chott in western Tunisia called wChott el Djerid.


Oasis OAn oasis can vary in size from about 2.5 acres for a tiny village to larger farm lands. At its hub is water, often in the form of natural springs, artesian wells or entire irrigation systems. About 75 percent of the Sahara's population live in oases, which make up only a tiny 800 square miles of the desert's vast sea of sand and gravel. The date palm is most characteristic of the vegetation that flourishes there. Other typical food sources grown in Saharan oases include figs, peaches, citrus fruits, wheat and barley. The word "oasis" is believed to come from an ancient Egyptian word, "wah," meaning "fertile place in the desert."

Erg Photo Credit/Copyright: Van Acker/FAO

Reg and Wadi Photo Credit/Copyright: Yves Larboulette/Sahara Info - www.sahara-info.ch

Chott Photo Credit/Copyright: Gus Lopez

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