Grand Erg Oriental

The Grand Erg Oriental is a Saharan sand sea spread mainly across the lowlands of northeastern Algeria, with its northeastern edge entering Tunisia. It covers about 185,000 square kilometres, including roughly 30,000 square kilometres in Tunisia, and is Algeria's second-largest erg after Erg Chech. The Atlas, Aurès and Tunisian Jebel Dahar uplands close its northern horizon; the Hamada of Tinrhert and the Tademait Plateau lie to the south. Wind-scoured gassi corridors cut between immense dune chains, linking otherwise separate stretches of the desert.

Its sand arrived through a long geological history. Rivers from the Ahaggar brought sediment north through the Oued Igharghar, while streams from the Atlas and Aurès supplied material from the northwest. Dry phases during the Pleistocene and between 5,000 and 3,000 years ago exposed the deposits to stronger winds and allowed the dunes to grow. Sand then covers about 70 percent of the erg. Northwest winds build longitudinal dunes; barchanoid ridges shape the Tunisian side; and complex winds have created an enormous field of star dunes across the southern half, some reaching 230 metres high.

The climate is hyper-arid, becoming drier southward, yet substantial fossil water is stored in the Continental Intercalaire aquifer. Ancient caravans avoided open dunes and followed corridors such as Gassi Touil. Oases at Touggourt and Ouargla served trans-Saharan routes, while Ghadames stands near the southeastern edge. These corridors remain the practical lines through an expanse dominated by mobile sand.