Grand Erg Oriental

Grand Erg Oriental العرق الشرقي الكبير
Erg
Landscape of the sand dune 'seas' of the Grand Erg Oriental. Other areas are bare rock. There are also Oases, and oil extraction zones.
Map of the Maghreb showing the Grand Erg Oriental.
Country	Algeria and Tunisia
Elevation	280 m (920 ft)

The Grand Erg Oriental (English: 'Great Eastern Sand Sea') is a large erg or "field of sand dunes" in the Sahara Desert. Situated for the most part in Saharan lowlands of northeast Algeria, the Grand Erg Oriental covers an area some 600 km wide by 200 km north to south. The erg's northeastern edge spills over into neighbouring Tunisia.

The Grand Erg Oriental is a desert natural region receiving very little rainfall. It is the largest Erg in Algeria, the next in size being the much smaller Grand Erg Occidental ('Western Sand Sea'). The largest erg of the Sahara is probably As-Sahra al-Libiyah, which straddles the inland border of Libya and Egypt. Erg is a Tamachek Berber word, and also a geographic term of art.

The Grand Erg Oriental used to be associated with the Wadi Igharghar, a mostly dry and buried river with a sizable network of tributaries which, should it possess any water, would flow north into the erg from the Ahaggar mountains of the central Sahara. Yet such dry, anciently-made river beds, lying seemingly useless beneath the desert sands, can preserve the infrequent rain water, by carrying it off underground and so rescue the moisture from an otherwise "intense and almost instantaneous" evaporation.

A buried river bed "not only serves in certain cases to carry into the heart of the desert the waters of distant rains which have fallen outside the desert domain, but in it the waters of the local storms are concentrated and carried swiftly to the alluvial basins where they are imbibed by the lighter earth and form lasting reserves within its depths. The result is that what vegetation survives is localized along the wadi beds or in their basins; in fact the words wadi and pasturage are interchangeable in the language of the nomads, who habitually reside in such places."