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 of some 185,000 sq. km (about the size of North Dakota or twice the size of Portugal). "Open Street Map", surface. It is the second largest erg in Algeria after Erg Chech. The erg's northeastern edge spills over into neighbouring Tunisia (about 30,000 sq. km)David Mallon, "Slender-horned Gazelle, Gazella leptoceros", Conservation Strategy 2020-20, IUCN SSC Antelope Specialist Group, UK, 2020, pp. 17, 21. It borders the Atlas and the Aurès Mountains as well as the mountainous region of Jebel Dahar in Tunisia to the north, and the Hamada of Tinrhert and the Tademait Plateau to the south.Robert Capot-Rey, "Remarques sur les ergs du Sahara", Annales de géographie, 1970, p. 4. Retrieved on November 6, 2025. - Erg is a Tamachek Berber word, and also a geographic term of art.Erg is an Afroasiatic word similar to Amharic 'arǎgǎ: "rise, ascend". Said to be "Hamitic" in origin (as opposed to "Semitic"). "Webster's Third New International Dictionary" (Springfield: "Merriam", 1971) p.770. The Berber language is included in "Hamitic".
Formation and development
Ground-penetrating radar (GPR) can be used to map the internal structure of large dunes, and Radiocarbon dating of organic material or thermoluminescence dating can be used to determine the time frame within which the individual sand layers of a dune were deposited.Nick Lancaster, "Development of large aeolian bedforms - time matters", Desert Research Institute, Reno, USA, without year, pp. 2, 8ff. Retrieved on November 6, 2025. A few measurements are available for the Grand Erg Oriental, which indicate the following possible development:
Towards the end of the Pliocene, until about 2,5 million years ago, the Sahara had a humid tropical climate. During this time, large river systems washed considerable amounts of sand into the basins of the Sahara. In the area of the Grand Erg Oriental, it was the Oued Igharghar, which rises in the Ahaggar Mountains, that brought sand from the south. From the north and northwest, the sand was brought in by various river courses from the Atlas and Aurès Mountains.Francis Tack, Paul Robin, "Dünen, Sandmeere der Wüsten", National Geographic Deutschland, 2003, ISBN 978-3-934-38596-2, pp. 23, 27ff, 51 (in German).Sebaa Abdelkamel, "Etude du rôle des Draas dans l’évacuation des dunes menaçant les routes dans le Bas Sahara Algérien", Université Aboubakr Belkaïd, Tlemcen, Algeria, p.117, (in French). Retrieved on November 6, 2025. The formation of the sand seas in the Sahara began in the Pleistocene, around 1,6 million years ago. This occurred during the various dry periods of this era until 11,000 years ago and in the subsequent Holocene between 5,000 and 3,000 years ago.Christopher Swezey, "Eolian sediment responses to late Quaternary climate changes: Temporal and spatial patterns in the Sahara", ResearchGate, 2001, pp. 123, 219. Retrieved on November 6, 2025. During these arid epochs, the sand was not stabilized by vegetation, and the wind strength and thus its mobilizing power was considerably higher than today during certain periods. Nicholas Lancaster, "Low latitude dune fields", ResearchGate, 2007, p. 1. Retrieved on November 6, 2025. This allowed much more massive dunes to form than is possible under today's wind conditions. The northeast trade winds drove the sand from the area of today's Chott Melghir and Chott el Jerid with their salty clay crust soils to the southwest, so that there are no dunes there today.Michael Martin, "Das Wesen der Wüste", Ludwig Verlag, 2019, ISBN 978-3-453-28121-9, p. 81 (in German).
Topography
The Grand Erg Oriental is about 70% covered with sand.Edwin D. McKee et al., "A Study of Global Sand Seas", Geological Survay Professional Paper, 1979, p. 336. Retrieved on November 6, 2025. An estimate of the sand volume comes to several hundred cubic kilometers. Every year, about 6 million tons of sand are added by wind transport from the north. However, there is also a certain amount of sand flowing southward. But with the exception of its southwestern part, the erg has a positive sediment balance, while the ergs of the central Sahara lose sand to the ergs on the southern edge of the Sahara.Monique Mainguet, "Où il faut parler d'éologie, d'épilithe, d'actions éoliennes et de protection des cadres de vie humaine sur la terre", Persé, 1984, p. 5, (in French). Retrieved on November 6, 2025. – The sand of the erg consists mainly of quartz, with a small amount of tourmaline and zircon. In the northern and northeastern edges of the erg, the grains are generally larger than further south.
The size of the dunes increases continuously from north to south.Thomas Baird et al., "Measuring Sand Dune Migration Rates with COSI-Corr and Landsat", MDPI, 2019, p. 16. Retrieved on November 6, 2025. Nearby the cities of Ouargla and Touggourt, within the boundaries of this erg, the landscape is described as being "practically free from [sand] dunes" evidently due to strong, persistent winds.E.-F. Gautier, "Le Sahara", Payot, 2d ed. 1928, translated and augmented as "Sahara. The great desert" (Columbia University, 1935; reprint: Octagon, 1970; reprint: Hippocrene, 1987) p. 93. In the northwest, there are mainly seif dunes (longitudinal dunes) whose crests run from northeast to southwest, following the main wind direction. These dunes have long, sharp ridge lines. Cross-winds, however, may alter the height or width of such lengthy dunes, with the slope being steep on both sides.W. G. Moore, "A Dictionary of Geography" (Penguin 1949, 3d ed. 1963), p. 64 (erg), 58-59 (dune), 146 (reg (gravel), 157 (seif dune). The dunes in the east, in Tunisia and the adjacent Algerian region, are barchanoid and interconnected barchanoid ridges that form a net-like pattern. On Barchan dunes the slope on the windward side is gradual, on the leeward steep, and such dunes may "roll" forward being blown in the direction of the wind is taking. These dunes tend to be perpendicular to the wind's direction. The southern part on the border with Tunisia and the southern tip of Tunisia are covered by approximately 400 dome dunes, covering an area of around 2,600 km². "Google Earth", measurement and counting (dome dunes).
The southern half of the erg is dominated by star dunes. They lie within an area of approximately 66,000 km². It is the largest accumulation of star dunes in the world.Andrew S. Goudie et al., "The distribution and nature of star dunes: A global analysis", Elsevier, 2021, pp. 1, 9. Retrieved on December 26, 2025. Star dunes are formed under complex wind conditions. In the southwestern part of the erg, within an area of approximately 27,000 km², these star dunes sit on longitudinal dunes. Such dunes are also called draa or mega dunes and were subject to a change in wind regime during their formation. The largest star dunes of the erg reach a diameter of 2.4 km and a height of 230 m. Star dunes appear to migrate.Geof Duller, Charles Bristow, "Structure and chronology of a star dune at Erg Chebbi, Morocco", Scientific Reports, 2024, p. 4. Retrieved on December 26, 2025.
Between the dune chains lie the gassi, wind-swept deflation corridors of hard-pressed reg (gravel), such as the Gassi Touil, which follows the old course of the Oued Igharghar, or the Gassi El Mouilah, both of which are up to 20 km wide and show that the sediment balance here is negative.Monique Mainguet et al., "Sédimentation éolienne au Sahara et sur ses marges", persée, 1984, p. 19ff, (in French). Retrieved on November 6, 2025.
Hydrology
The climate is hyper arid, with average annual precipitation of 60 mm in the north of the erg. Further south, it decreases, reaching 25 mm at the southern edge. "Global Watersheds", watersheds - report - precipitation. Retrieved on November 6, 2025. However, there is a lot of water stored underground: the Aquifer Continental Intercalaire, one of the largest closed aquifers in the world, stores around 60,000 cubic kilometers of water and extends over large areas of the Algerian, Tunisian, and Libyan northern Sahara.Michael Daum, "Tomaten aus der Sahara", Le Monde diplomatique, 2016, (in German). Retrieved on November 6, 2025 Most of this water is fossil water that seeped into the ground during the wet periods of the Pleistocene in the Atlas Mountains and Aurès region, the M'zab ridge west of Touggourt, and the Dahar mountain range in southern Tunisia."Der Aquifer Continental Intercalaire", Freie Universität Berlin, (in German). Retrieved on November 6, 2025 These elevations are located in the vicinity of the erg. In addition, the Oued Igharghar and its groundwater probably also made a contribution.Naima Koull, "Paléo-hydrologie de la région de l’Oued Righ", ResearchGate, 2010, p.3, (in French). Retrieved on December 12, 2025.
In recent decades, the aquifer's water has been exploited on a large scale with the construction of thousands of wells, including for agricultural production centers. However, this has led to problems such as falling or rising groundwater levels and deterioration in groundwater quality.
Flora and fauna
Commonly found are Drinn grass (stipagrostis pungens), a good pasture for gazelles, but also for camels, and Euphorbia guyonia, a spurge used in traditional medicine as a remedy for warts, coughs, and scorpion stings.Fellous Amina et al., "Inventaire de la Faune Sauvage des zones désertiques d'Algérie. Grand Erg Oriental", ResearchGate, 2009, p. 20, (in French). Retrieved on November 5, 2025. Among the shrubs, one finds broom (Retama raetam), sea lavender (Limoniastrum guyonianum), and foxtail (Hammada schmittiana). There are also four species of Calligonum (knotweed family). Three of these species are shrubs 1 to 3 m high. The fourth species, Calligonum arich, grows only on the high dune ridges and can reach a height of up to 10 m with its tree-like growth. However, its population is endangered in the Tunisian part of the erg. Its wood, mostly in the form of charcoal, is highly sought after by locals for baking flatbread and making tea. Off-road vehicles are used to search increasingly remote regions of the interlocking dunes for firewood, even though logging was banned some time ago.Frédéric Médail, Pierre Quézel, "Biogéographie de la flore du Sahara", IRD Editions, 2018, p. 257f, (in French). Retrieved on November 6, 2025.
Between 2006 and 2009, an inventory of large mammals was carried out in selected sectors of the erg on the Tunisian and on the Algerian side. The following animals or traces of them were sighted: The Rhim gazelle (Gazella leptoceros loderi Thomas, 1894). Today, its population is classified as critically endangered by the IUCN. Illegal hunting seems to be the main possible cause. The Cape hare (Lepus capensis) The fennec fox (Vulpes zerda) The Rüppell's fox (Vulpes rueppelii) The Jebil National Park in the Tunisian part of the erg, covering an area of 1,500 sq. km and located 70 km south of the city of Douz (pop 2014: 30,245), serves to protect the flora and fauna in this region. A group of addax antelopes (Addax nasomaculatus) lives in a 77 sq. km enclosure within the park with the aim of breeding and reintroduction into the wild."Le parc national de Jbil, présentation générale et opportunités de valorisation écotouristique", Ministère de l'Equipement, de l'Aménagement du Territoire et du Développement Durable, Tunisia, (in French). Retrieved on December 14, 2025.Tania Gilbert et al., Re-introduction of addax to Djebil National Park, Tunisia, IUCN, 2018, pp. 120 - 124. Retrieved on December 14, 2025.
Routes, cities, settlements