Algeria is bounded to the east by Tunisia and Libya; to the south by Niger, Mali, and Mauritania; to the west by Morocco and Western Sahara (which has been virtually incorporated by the former); and to the north by the Mediterranean Sea. It is a vast country—the largest in Africa and the 10th largest in the world—that may be divided into two distinct geographic regions. The northernmost, generally known as the Tell, is subject to the moderating influences of the Mediterranean and consists largely of the Atlas Mountains, which separate the coastal plains from the second region in the south. This southern region, almost entirely desert, forms the majority of the country’s territory and is situated in the western portion of the Sahara, which stretches across North Africa.
The main structural relief features in Algeria were produced by the collision of the African and Eurasian tectonic plates along the Mediterranean margin, giving the country its two geographic regions. The Tell, home to most of the country’s population, contains two geologically young massifs, the Tell Atlas (Atlas Tellien) and the Saharan Atlas (Atlas Saharien), that run generally parallel from east to west and are separated by the High Plateau (Hauts Plateaux). The south, consisting of the Sahara, is a solid and ancient platform of basement rock, horizontal and uniform. This region is uninhabited desert with the exception of several oases, but it conceals rich mineral resources, most significantly petroleum and natural gas.
- THE TELL
In succession from north to south are intermittent coastal folded massifs and coastal plains. Along with the Tell Atlas, High Plateau, and Saharan Atlas, they form a sequence of five geographically variegated zones that roughly parallel the coast.
The coastal ridges and massifs are indented with numerous bays and are often separated from each other by plains—such as the plains of Oran and Annaba—that extend inland. In the same way, the Tell Atlas is not continuous; in the west it forms two distinct ranges separated by interior plains. Thus, the Maghnia Plain separates the Tlemcen Mountains to the south from the Traras Mountains to the northwest. Similarly, the plains of Sidi Bel Abbès and Mascara are nestled between hill ranges to the north and south. The Dahra Massif forms a long range extending from the mouth of the Chelif River in the west to Mount Chenoua in the east; it is separated from the Ouarsenis Massif to the south by plains of the Chelif valley.
The relief as a whole, therefore, does not constitute a barrier to communications in the western Tell. However, this is not the case in the central Tell, where the Blida Atlas merges with the Titteri Mountains and the mountainous block of Great Kabylia (Grande Kabylie) joins with the Bibans and Hodna mountains to make north-south communications more difficult. Only the valley of the Wadi Soummam permits communication with the port of Bejaïa.
Farther east, from Bejaïa to Annaba, one mountain barrier follows another to separate the plains of Constantine from the sea. The lands south of the plains are dominated by the Hodna, Aurès, and Nemencha ranges. The plains themselves, which have long been used for growing cereal grains, have a distinct local topography and do not present the same features as the High Plateau, which extends westward from the Hodna Mountains into Morocco. The latter is broken by sabkhahs (lake beds encrusted with salt) and is much less favourable to agriculture because it receives less precipitation.
To the south of the High Plateau and the plains of Constantine runs the Saharan Atlas, which is formed from a series of ranges oriented southwest to northeast. These decline in elevation from the west, where Mount Aïssa reaches 7,336 feet (2,236 metres) in the Ksour Mountains, to lower summits in the Amour and Oulad Naïl mountains. Higher summits are again found in the Aurès Mountains, where the highest peak in northern Algeria, Mount Chelia, which reaches 7,638 feet (2,328 metres), is located.
Only the northern Tell ranges, lying along the tectonic plate boundary, experience much seismic activity. Severe earthquakes there have twice destroyed the town of Chlef (El-Asnam), in 1954 and 1980. An earthquake in 1989 caused severe damage in the zone between the Chenoua massif and Algiers, as did another in 2003 just east of Algiers.
- THE SAHARA
The Algerian Sahara may be divided roughly into two depressions of different elevation, separated from one another by a central north-south rise called the Mʾzab (Mzab). Each zone is covered by a vast sheet of sand dunes called an erg. The Great Eastern Erg (Grand Erg Oriental) and the Great Western Erg (Grand Erg Occidental), which average 1,300 to 2,000 feet (400 to 600 metres) in height, decline in elevation northward from the foot of the Ahaggar (Hoggar) Mountains to below sea level in places south of the Aurès Mountains. The Ahaggar Mountains in the southern Sahara rise to majestic summits; the tallest, Mount Tahat, reaches an elevation of 9,573 feet (2,918 metres) and is the highest peak in the country.
Most of the rivers of the Tell Atlas are short and undergo large variations in flow. The largest river is the Chelif, which rises in the High Plateau, crosses the Tell Atlas, and flows through an east-west trough to reach the sea east of Mostaganem. The Chelif has been so intensively exploited for irrigation and drinking water that it has ceased to flow in its lower reaches during the summer months. South of the Tell Atlas there are only ephemeral rivers (wadis), and much surface runoff ends in chotts (salt marshes) within inland depressions. Several Saharan watercourses, in particular those flowing off the Ahaggar uplands, occupy valleys formed largely during pluvial periods in the Pleistocene Epoch (2,600,000 to 11,700 years ago). Some southward-flowing wadis feed the water tables beneath the Saharan surface, and desert oases appear in locations where the water, under hydrostatic pressure, rises to the surface in artesian wells or springs.
Continued vegetation clearance and erosion have limited the area of fertile brown soils to those uplands where evergreen oak forests are still found. Mediterranean red soils occupy the lower elevations in much of the northern Tell. Farther south the soils become progressively immature as aridity increases; they are characterized by little chemical weathering or accumulation of organic matter. In the desert areas soil development is further impeded by strong and nearly constant wind erosion. An ambitious project was initiated in the mid-1970s to create a “green barrier” against Saharan encroachment northward, reforesting a narrow strip up to 12 miles (19 km) in width and some 1,000 miles (1,600 km) in length; it proved only somewhat successful. Another plan, however, was introduced in the mid-1980s to reforest an additional 1,400 square miles (3,600 square km).
Climate, more than relief, is the country’s major geographic factor. The amount of precipitation and, above all, its distribution throughout the year, as well as the timing and magnitude of the sirocco—a dry, desiccating wind that emanates seasonally from the Sahara (often with gale force)—constitute the principal elements on which agriculture and many other activities depend.
Algeria’s coastal zone and northern mountains have a typical Mediterranean climate, with warm, dry summers and mild, rainy winters. Algiers, for example, has afternoon temperatures in July of 83 °F (28 °C), which drop to about 70 °F (21 °C) at night, while in January daily temperatures range between 59 and 49 °F (15 and 9 °C). Four-fifths of the city’s 30 inches (760 mm) of annual precipitation falls between October and March, and July and August are usually dry. Total annual precipitation increases along the coast from west to east but diminishes rapidly from the coast southward into the interior. The greatest amount of precipitation occurs in the mountainous regions of the eastern littoral, which are directly exposed to the humid winds that blow inland from the Mediterranean. From a point about 50 miles (80 km) west of Algiers to the Tunisian frontier, annual precipitation exceeds 24 inches (600 mm), and in certain places—for example, in the Great Kabylia, Little Kabylia (Petite Kabylie), and Edough regions—it reaches about 40 inches (1,000 mm). West of this location a considerable part of the Chelif Plain and the plains of the littoral and the region immediately to the south of it in the vicinity of Oran are insufficiently watered, receiving less than 23 inches (580 mm). Precipitation also diminishes after crossing the Atlas ranges to the south, except in the Aurès and in a section of the Amour Mountains, which still receive about 16 inches (400 mm).
This east-west boundary roughly separates the two principal agricultural zones of the country. Dry farming is generally possible and commercially profitable in the eastern zone, where fine forests and abundant vegetation also exist. In the western zone cereal crops can be cultivated only with irrigation; pastoral activities dominate, and the forests disappear.
Northern Algeria’s relief, parallel to the coastline, limits the southward penetration of the Mediterranean climate. The plains and hills in the region immediately to the south of the coastal mountains still receive sufficient precipitation but have a much drier atmosphere, and temperature ranges are more varied. The High Plateau, on the other hand, is characterized by daily and annual extremes of temperature, hot summers and cold winters, and insufficient precipitation. Summer temperatures are typically above 100 °F (38 °C) in the afternoon and drop to about 50 °F (10 °C) at night, while in winter they range from about 60 °F (16 °C) during the day to about 28 °F (−2 °C) at night. Annual precipitation varies from 4 to 16 inches (100 to 400 mm).
The Sahara proper begins on the southern border of the Saharan Atlas. The demarcation coincides with a diminution of the precipitation to less than 4 inches (100 mm) per year. The landscape and vegetation differ greatly from those in the north, with life and activity limited to a few privileged locations. Daily and annual temperature ranges are even more extreme than on the High Plateau, and precipitation is marked by greater irregularity. Three years may pass without precipitation in the Tademaït region, as many as five years on the Ahaggar plateau.
- Plant and animal life
Natural vegetation patterns generally follow the country’s north-south climatic gradient, and elevation produces additional variations. All vegetation in Algeria, where all areas are subject to some seasonal aridity, is characteristically drought-resistant. Forests cover only about 2 percent of the entire land area and are found primarily in the less-accessible mountain regions, where remnants of evergreen forests remain on the moister slopes. Dominated by holm oak, cork oak, and conifers such as juniper, the forests today contain only limited patches of economically valuable cedar. Much of the entire Tell region in the north was once covered with woodland, but most of this has been replaced by a poor maquis scrubland consisting of evergreen, often aromatic, hard-leaved shrubs and low trees that include laurel, rosemary, and thyme. On limestone and poorer soils, however, maquis degenerates into garigue (or garrigue), a low-growing shrub association of gorse, lavender, and sage.
Farther south, increasing aridity reduces the vegetation to a discontinuous type of steppe (treeless plain) dominated by esparto grass. A richer association containing Barbary fig and date palm, however, is still found along the wadis. In the desert proper, plant life is highly dispersed and consists of tufts of several kinds of robust grass species that need almost no water, such as drinn (Aristida pungens) and cram-cram (Cenchrus biflorus); several types of shrubs, which are always stunted and sometimes spiny; tamarisk, acacia, and jujube trees; and some more varied species that are found in the beds of wadis with underground water or in mountainous regions.
The animal life of the northern mountains includes wild mouflons, Barbary deer, wild boars, and Barbary macaques. A multitude of migratory birds pass through the country, including storks and flamingos. In the Sahara, gazelles, fennecs, hyenas, and jackals can be found, together with many smaller mammals such as gerbils and desert hare. Insect life is abundant and is most spectacularly manifested in the region’s periodic massive swarms of locusts. Scorpions are common in the arid and semiarid regions.