With around 9 million km², the Sahara is the largest desert on earth. It is located in North Africa and stretches from the Atlantic for more than 6000 km to the Red Sea in the east. From the Mediterranean Sea and the Atlas it extends from north to south over 2000 km with the transition zone Sahel to Sudan. The Sahara is a plateau with basins and depressions. Mountain massifs rise inside. To the south there are mountainous lands up to 1800 m. Scree and gravel deserts largely determine the landscape. Only around 10% are sandy deserts with blown dunes.
The climate is extremely dry and very hot with large daily temperature fluctuations. The only river with constant water is the Nile. The Sahara has no or only sparse vegetation. Of the approximately 5 million residents of the Sahara, around 60% are sedentary oasis farmers, nomads or semi-nomads. The Arabs, Berbers and Tuaregs have the largest share of the population. Carthaginians, Greeks and Romans penetrated the Sahara from the Mediterranean coast. The last unexplored areas were not explored until after World War II.
The Sahara is located in North Africa and extends from the Atlantic Ocean in the west for more than 6000 km to the Red Sea in the east. Its north-south extent extends from the Mediterranean Sea and the southern edge of the fold mountain system of the Atlas in the north over around 2000 km with the transition zone Sahel to Sudan in the south. The North African states of Morocco, Algeria, Tunisia, Libya, Egypt, Western Sahara, Mauritania, Mali, Niger, Chad and the Republic of Sudan make up part of the Sahara (Fig. 1).
The Sahara consists for the most part of an approximately 200 to 500 m high plateau. Wide basins and depressions are embedded in it like the Kattar depression up to 137 m above sea level. d. M. In the interior, this plateau is dominated by high mountain ranges. The most important are the Hoggar with a height of up to 3000 m and the Tibestigebirge with a height of up to 3400 m. To the south, up to 1800 m high mountain lands are connected to the table land. In the northeast the Libyan desert in the Djebel Uweinat reaches an altitude of 1892 m, east of the Nile the landscape rises to 2500 m.
The crystalline subsoil of the Sahara emerges in the mountains and thresholds. Sediments from ancient times to modern times are stored above it. In places, volcanic basalt chimneys pierce the subsoil.
Extreme drought, great heat and great fluctuations in temperature during the day are characteristic of the Sahara’s climate (Fig. 2). The cause is the sinking, extremely dry air masses over North Africa. The climatic conditions can be explained with the Passat cycle. In the equatorial region, the air rises and sinks again near the tropics at 20 to 30 ° north latitude. In doing so, it heats up constantly and becomes drier. On the desert floor, their humidity is only 5 to 10%. The result is low rainfall and sparse or no vegetation. The predominantly episodic precipitation falls in the north as winter rain, in the south also as tropical summer rain.
The highest air temperature in the Sahara of 57.7 °C was measured in the Libyan desert. In the Tibesti massif, the temperature drops to minus 16 °C even at night. This extreme temperature change is favored by the exceptional dryness of the air. A protective cloud cover is missing. The sun can shine unhindered and it gets very cold. The so-called Fata Morgana arises when the day is extremely hot and there is no wind. The sunlight refracts on the surface of heated layers of air and reflects cities, oases or lakes and rivers.
The high temperature changes and the heat are dangerous for people. At 50 °C, the body loses about 1 liter of water per hour through evaporation. His weight decreases by about 1 kg per hour. Thirst sets in. A water loss of 5 liters can mean death. Every 3rd day in the Sahara is a storm day. Dust storms with a height of up to 3000 m and a diameter of several kilometers are approaching. Up to 5 million tons of dust are constantly floating in the air of the Sahara.
Temperature, water and wind are the shaping forces in the desert. Strong and rapid temperature differences lead to tension in the rock skin. By expanding and contracting, the cohesion of the rock loosens and hairline cracks form. The rock bursts into different sizes of material. Constantly blowing winds have abrasive power. Sand and dust, the end products of weathering, are driven as if by a sandblasting fan and are constantly driven against solid rock. Depending on the nature of the rock, “mushrooms”, “pillars”, “towers”, “organs” or “alleys” are created in the Sahara (Figure 3). The sand is blown to form huge dunes.
Different weathering creates a multitude of different desert forms. Rock or stone deserts are common on the plateaus. They are called Hammada (Fig. 4). In the lower-lying areas, scree desert n occurs, so-called Reg. If the material is smaller, one speaks of gravel desert n or Seriren (Figure 5). Pure sand deserts take up only 10% of the area. They are called Erg or Edeien (Fig. 6). Blown dunes can often be found here. Salt sumps or pans, so-called bulkheads or sebcha, are typical for basins without drainage.
Waters and vegetation
The only continually flowing river in the Sahara is the Nile. It flows through the east of the Sahara from south to north as an alien river. The wadis, dry river beds, only carry water after occasional heavy rainfall. The Sahara has no or only very sparse vegetation. An exception are the oases, which are islands of rich vegetation due to the proximity of the groundwater or springs (Fig. 7). Prehistoric rock carvings in Tibesti and Tassili indicate what was once dense vegetation and a rich fauna. Due to human interference, the Sahara is gradually expanding southwards.
Population and economy
Around 5 million people live in the Sahara. The Berbers, Tuareg and Arabs have the largest share of the population. About 60% of the residents are settled oasis farmers, the rest are nomads or semi-nomads. A large part is active in oasis cities. Oil and natural gas are of great economic importance in Algeria, Libya (Great Syrte) and Egypt (Libyan Desert). Iron ores are mined in Mauritania, phosphates in Western Sahara and uranium ores in Niger. In Libya and Egypt there are plans to use irrigation to make the fertile soil usable for agriculture in many places.
The Greeks and Carthaginians had explored the northern edge of the Sahara more closely during their sea voyages. The Romans invaded the Fezzan and up the Nile into the Sudan. European exploration of the Sahara began in the 19th century. Only after the Second World War was it possible to explore the last unexplored areas with the help of aerial photographs.