The Sahara Desert in Africa is almost 8.6 million square kilometers of secrets, mysteries and mysticism. Some of them have been practically solved, others cannot be explained. Its size is rapidly increasing, sands are advancing from the south and southeast at a speed of 50 km per year. Why is this happening? This is another inexplicable mystery, and there is no way to stop the sand invasion.
The Sahara Desert is located in the north of the African continent, it occupies almost a quarter of its area. Length – 4800 km from west to east, 800-1200 km from north to south. Libya, Algeria, Egypt, Tunisia, Morocco - these are not all the countries that border the largest desert in Africa and the entire planet.
The Sahara Desert Was Once a Green Savannah
The Sahara Desert appeared about 4 thousand years ago, but literally 2 thousand years before that, rivers flowed here, and the water was crystal clear. The fertile land was covered with lush vegetation, and herbivores and predators lived in the forest thickets.
Interesting fact. There were no camels, which are invariably associated with the Sahara Desert. "Ships of the Desert" appeared much later. African savannah inhabited by a variety of animals and numerous tribes engaged in farming and hunting.
The dunes of the Sahara Desert sometimes reach 300 m
The dunes of the Sahara resemble the lifeless landscapes of Mars
Another legend? Not at all, this is a long-proven fact. Back in 1933, the German explorer of the African continent Leo Frobenius discovered rock art in the heart of the Sahara Desert. Ancient artists decorated the rocks close to the riverbed ancient river, drawings of antelopes, giraffes, birds, lions and even hippos. The paintings are painted with white clay and red ocher. Isn't this proof of the existence of a once diverse fauna in these places?
Among the dunes of the Sahara rise black rocks of volcanic origin
Lake Ubari in the Sahara Desert (Libya) is filled with underground springs
Rock art in the Sahara Desert
What happened to the African savanna? About 5 thousand years ago, a drought occurred, the fertile land of the Sahara began to rapidly lose moisture, and rivers and lakes gradually dried up. Vegetation disappeared, animals began to leave these places, they went into the forests Central Africa. People also had to leave their homes; a few remained in the Sahara Desert, turning into nomads moving from oasis to oasis.
Are there rivers and lakes in the Sahara Desert?
By southern territory The Niger flows through the Sahara Desert, or rather, a small part of it. The deep Nile carries its waters across the entire desert territory. These are the main water arteries"sandy country"
However, things were different before. The Sahara rivers originated on the slopes of the Atlas Mountains and brought life-giving moisture to the ancient inhabitants. Their dry riverbeds are imprinted in an intricate grid into the desert landscape. Their name is wadi. Many of them are striking in their size - in the Sahara there are wadis that are 30 km wide and more than 400 km long. During the period of mountain rains, some wadis are filled with water for a short time.
Wadi in the Sahara Desert - dry river beds and lake bowls
Lake Ubari in the Sahara Desert, Libya
There were also lakes in the Sahara Desert, and they are reminiscent of huge depressions, at the bottom of which there are shottas - miniature salt lakes. The water level in them is not constant, it fluctuates depending on the height groundwater. In summer they dry out completely, revealing only a dense salty crust. The chotts are treacherous; in the spring, bottomless bogs form here, which are masked only by a thin layer of thoroughly salted clay. In some of them, entire caravans disappeared without a trace; safe paths are known only to the Tuaregs.
Lake Yoa is located in the Sahara and is part of the Unianga lake system
Drying red Lake Trona - a salty spring in the Sahara Desert
Although there are no deep rivers in the Sahara Desert, except for the legendary Nile, there is no shortage of water here. Even if it's underground. If it were different, then this “sandy country” would become a real hot hell without any signs of life. In some places, water seeps out of the ground, and oases are located near such springs.
Gelta Darshey in the Sahara Desert - a source of water among the rocks
Amazing landscapes in the vicinity of Gelta Darshey
The most famous oasis of the Sahara Desert is the legendary Nefta. According to legend, he appeared at this place immediately after the end global flood. It was found by none other than the grandson of Noah himself - Kostel. He planted the first date palm near the spring, today there is a grove of 35 thousand trees. The largest oasis of the Sahara Desert is the valley of the deep Nile, whose area is more than 20 thousand km.
The dunes of the Sahara Desert take on a bluish-gray hue at sunset
Trees of the Sahara Desert are adapted to extreme conditions: minimum leaves, maximum spines
Immortals from the Sahara Desert
Dates from the Sahara oasis - Nefty
Springs in the Sahara Desert are rare, so today, like many centuries ago, water is obtained from deep wells, of which there are many thousands. Back in the 11th century, there were more than 3 thousand of them. Some man-made springs are capable of watering only a small caravan, others are so full of water that oases have formed around them, where numerous tourists take refuge in the shade of date palms and Tuaregs settle.
Flora and fauna of the Sahara Desert
Animals of the Sahara Desert are individuals that can withstand the harshest living conditions. Speaking modern language– extreme sportsmen. They must move very quickly in search of food and water, and endure high temperatures and scorching heat.
Desert fox of the Sahara - fennec fox
Fenech - a faithful companion Little Prince from the famous fairy tale by Antoine de Saint-Exupéry
Desert hedgehog adapts to hard life in the Sahara
Hyenas survive well in climatic zone Sugars
The Sahara Desert is home to graceful antelopes: oryx and addax. In the endless sands there are gazelles and mountain goats. Many species of artiodactyls are at the stage of extinction, the reason for this is their valuable skins and tasty meat, which is valued by the Tuaregs, and tourists consider it an African delicacy. The predator population includes hyenas and jackals, wild fennec foxes and cheetahs. The kings of animals, lions, also live in the vastness of the Sahara.
Funny pillars in the Sahara Desert - meerkats
And even little meerkats, just being born, already know how to stand in a column
The world of reptiles of the Sahara Desert is incredibly diverse. Lizards, snakes and turtles tolerate drought well, and long years They have adapted well to such living conditions; they are at home here. It is in the Sahara Desert that the most poisonous scorpion on the planet lives. From its bite, a person dies within four hours, a dog or cat - immediately. The deep Nile is a habitat for crocodiles.
Thunderstorm of the Sahara Desert - horned viper
Black scorpion from the Sahara desert - shining example how amphibian species became terrestrial, adapting to new climatic conditions
The vegetation of the Sahara Desert is the most persistent, but this does not make it any less beautiful. Although the sands seem lifeless, more than 1000 species of plants grow here, most of them are xerophytes or ephemerals that tolerate drought and heat well.
Flowers grow in the Sahara Desert
Desert hyacinth Cistanche tubulosa
Rose of Jericho during the dry season in the Sahara
Rose of Jericho comes back to life after rain in the Sahara
An amazing flower grew in the sands of the Sahara
The most famous is the rose of Jericho, which can exist for up to 30 years without a drop of water, curling up into a ball of dry stems, and immediately throwing out color at the slightest presence of moisture. But the most common vegetation of the Sahara Desert is lichens with small spines. Date palms, pistachios, and oleanders grow in the oases.
The tribes of the Sahara Desert are proud and unyielding inhabitants of the sands
The vast territory of the Sahara Desert is home to many nationalities. The total population is only 2.5 million people. Vast areas of the Sahara are deserted, and the highest density of inhabitants is recorded in the cities of Algeria, a country where a significant part is occupied by the Sahara Desert.
Interesting fact. There are many tribes in the Sahara Desert, but the most famous are the proud Tuaregs. A stern rider, covered with a bandage right up to his eyes, sitting on a camel or horse, is a symbol of the great “land of sands.”
Sahara desert mountains
Amazing mosaic of salt lakes in the Sahara region of Niger
The Tuaregs lived in the vast expanses of the Sahara Desert long before the Arabs arrived here. They are light-skinned, there is not a drop of black blood in their veins. How did the Tuaregs appear in the Sahara? This is another secret. They still live a nomadic life, stubbornly rejecting all the benefits of civilization. Pride is their main asset and the meaning of life.
The White Desert is an iconic landmark of the Sahara.
In the east of the Sahara, on the territory of Egypt, is located one of the attractions of the “land of sands” - White Desert. Its area is only 300 km2, and the sands here really shine with pearly whiteness. Karst formations give them this shade.
White desert in the Sahara
Amazing mushroom formations in the Sahara Desert
White Desert in Egypt, Sahara Desert territory
At night, the White Sahara Desert resembles an Arctic landscape. Wind and erosion have carved bizarre pillars, castles and towers from the pliable karst deposits. Many of them are so intricate that they seem almost ephemeral.
Miracle of the Sahara - “Eye of the Desert” Richat
One of the Sahara Deserts and one of its main secrets is the “eye of the Sahara” - Guel El Richat. This is a geological formation in the form of rings with a diameter of more than 50 km. Richat's age is more than 500 million years.
“Eye” of the Sahara Desert - Richat
The Eye of the Sahara Richat Desert seen from space
It is noteworthy that the iconic landmark for a long time served as... a landmark for astronauts, it was this object that stood out among the vast sands of the world's largest desert. The era of astronautics made Richat famous; until the beginning of the 20th century, only the Tuaregs knew about the existence of the “Eye of the Sahara,” considering it a miracle.
Multi-tiered, amphitheater-like Richat structure in the Sahara Desert
Satellite photo of the Richat structure in the Sahara Desert
The reason for the blue concentric rings of Richat are stones of an unearthly shade of ultramarine
For a long time it was believed that the appearance of rings in the Sahara Desert was the result of a meteorite fall. However heavenly body There is no way he can get to the same place several times. The multi-tiered nature of Güell Er Richat is the result of centuries of erosion. However this scientific explanation does not in any way detract from the majesty of this attraction and its perfect shapes. Perhaps this is a gift from other civilizations?
Will judgment day come?
The climate of the Sahara Desert continues to change. Floods have been recorded here over the past 100 years, and snow fell in 1979. The snowfall was so heavy that within half an hour it practically paralyzed traffic in Algeria. Locals were quite surprised, to say the least. This unique phenomenon has excited scientists all over the world. And it’s not surprising, because it is the world’s largest desert that is the place of the most high temperatures, where the thermometer sometimes rises to +57.
Snow fell in the Sahara Desert
According to the Koran, the Day of Judgment will come when the Sahara Desert turns into a blooming oasis. Well, anomalies occurring with the local climate are a significant prerequisite. It is quite possible that our descendants will see the African savannah again.
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Let's take a little break from serious topics and take a walk... through the Sahara Desert. Although in real life many of us are unlikely to be able to do this. The hot sand will not allow you to walk, as in some summer days the sand heats up to 80 degrees. And not everyone will be able to travel to Africa to take a tour through the desert by bus.
But we can take a virtual walk through the desert, and it’s also possible to learn interesting facts about this amazing desert. So, let's go!
The Sahara Desert is the most big desert peace. Located in the north and occupying a third African continent, which is slightly larger than the territory of a state like Brazil. It stretches over an area of about 8.6 million km². From west to east the length of the desert is 4800 km, from north to south – 800-1200 km. On the western side, the desert borders the Atlas Mountains and is washed by Mediterranean Sea, and from the east - the Red Sea, from the south is the Sahel - a transition region to the Sudanese savannah.
There are 10 countries in the desert: Algeria, Egypt, Western Sahara, Libya, Mauritania, Mali, Morocco, Sudan, Tunisia and Chad.
Life in the desert without water is impossible, but despite this, almost 2.5 million people live in the desert. They lead a sedentary lifestyle in oases in the valleys of the Nile and Niger rivers, where there is water and vegetation. The most numerous peoples of the desert are the Tuaregs and Berbers.
Features of the Sahara Desert
In our minds, the desert is sands and dunes that move with the help of the wind. But the sands in the Sahara Desert occupy only a fifth. The thickness of the sand is approximately 150 meters. The sands are swept into dunes, some of which sometimes reach the height of the Eiffel Tower in Paris. There is so much sand in the desert that if every person living on our planet had to scoop up sand using 10-liter buckets, they would have to carry out 3 million buckets.
70% of the desert territory is occupied by sandstone mountains, and the remaining 10% is sand and pebble wasteland, on which you cannot even see a trace of vegetation - it is barren rocky land and salt marshes.
Sahara Desert. Safari
In the Sahara there is a city called Tegazi, where the walls of the houses are made of rock salt. But the residents of this city are not afraid that their houses may dissolve from the rains. This is the driest place on Earth.
Climate
Until recently, it was believed that the Sahara Desert appeared about 5 million years ago. But scientists currently believe that the lands of modern Sahara became deserted only 2.7 thousand years ago.
It's still so hot in the desert! It’s simply impossible to be in the sun, or rather in the open. In summer, the air temperature rises to 58°, and in winter – to 15-28° C, which is typical for annual temperature changes. We have this temperature in summer, and in the desert - in winter! Such differences annual temperatures are observed more often in northern regions deserts. But differences between day and night are observed within 20-25°.
The climate of the Sahara is determined by the northeast trade wind, very often there are sandstorms, which even reach Europe. The climate in the north of the desert is dry subtropical, in the south it is dry tropical.
Water
Life in the desert is concentrated only near water. Most big river, flowing through the Sahara Desert, is the Nile. Its main tributaries - Blue And White Nile- merge in the southeast of the Sahara, passing along the eastern side of the desert, flowing into the Mediterranean Sea. In the sixties of the 20th century, a large Nasser reservoir was created, which, when overflowed, formed Lake Toshka. The Niger River flows along the southwestern edge of the Sahara, near the inner delta of which there are lakes Fagibin, Garou, Niangai, and others.
Nile River near Luxor
Precipitation is rare in the desert. And what sometimes falls in the rains does not reach the ground, evaporating from the hot sand along the way. The Sahara is one of the places where evaporation is several times higher than the amount of precipitation.
But the most interesting thing is that under the sands of the Sahara there are huge “deposits” groundwater, which are larger in area than our Baikal.
Saharan groundwater is used for irrigation. For the first time, mentions of irrigation systems relate to culture Ancient Egypt. It is safe to say that the Egyptians developed a method of irrigating land. The Egyptians dug many parallel small canals perpendicular to the movement of the Nile. Some of them converge into basins, from which water was distributed over irrigated lands, providing them with moisture.
Mirages
Mirages are another interesting fact about the Sahara Desert. How many people, traveling through the desert, have suddenly seen oases with water and palm trees, thinking that it is located about 2-3 km from them? In fact, sometimes you have to walk 500 kilometers or more to get to the nearest water.
A mirage is an optical phenomenon in the atmosphere; a stream of light is refracted at the boundary between layers of air of different density and temperature.
Where is the Sahara Desert located?
The Sahara Desert is the largest SANDY desert on our planet and it is located in the northern part of the continent of Africa. It also ranks second as the largest desert in the world by area, second only to Antarctic desert. The area of the Sahara covers about 8.6 million km2 and partially occupies the territory of 10 states. From west to east its length is 4800 m, and from south to north its length ranges from 800 to 1200 meters. Moreover, the size of the desert is not constant; it grows annually by 6-10 km from south to north.
Sahara desert landscape
The landscape of the Sahara consists of 70% plains and 30% of the Tibesti and Ahaggar highlands, the stepped plateaus of Adrar-Iforas, Air, Ennedi, Tademait, etc., as well as cuesta ridges.
Sahara desert climate
The desert climate is divided into subtropical in the north and tropical in the south of the desert. In the northern part of the desert there are large temperature fluctuations, both average annual and average daily. In winter, temperatures in the mountains can drop to -18 degrees. Summer, on the other hand, is very hot. The soil can warm up to 70-80 degrees Celsius.
In the southern part of the desert, temperature fluctuations are slightly less, but also in winter, temperatures in the mountains can drop below zero degrees Celsius. Winters are milder and drier.
The desert is characterized by large temperature fluctuations between night and day. This figure is expressed by up to 30-40 degrees difference between night and day temperatures! Therefore, sometimes you can’t do without warm clothes there at night, as the temperature can drop below zero. Also in the desert there are often sandstorms, in which winds can reach up to 50 meters per second. Central parts of the desert may not see rain for years, and other parts may even experience heavy downpours. In other words, the Sahara Desert is full of surprises when it comes to weather.
Sahara Desert - amazing place. It is incredible how animals, plants, and people were able to adapt to life in this part of the earth, given the constant drought and heat.
1) The size of the desert is as big as half of Russia, or the whole of Brazil!
The Sahara Desert is the largest desert in the world, covering 30% of Africa. But this is half Russian Federation, or the entire area of Brazil, which is the fifth largest country on Earth.
2) “A sea without water.” On Arabic The Sahara is a desert, and some people called it the “Sea without Water” because once upon a time there were many rivers and lakes in its place.
3) Mars on Earth. Desert dunes move from a couple of centimeters to hundreds of meters per year, and the dunes themselves resemble the landscapes of Mars! Sometimes they reach a height of 300 meters!
4) There are fewer and fewer oases. Villages and towns usually appear near oases, but every year there are fewer and fewer oases.
5) average temperature in the desert it's about 40 degrees Celsius! The sand itself heats up to 80 degrees Celsius! But at night the temperature can drop to -15 degrees Celsius.
6) Over the past fifty years, storms have begun to appear more and more often, in some places their occurrence has increased forty times!
7) 3 million people live in the Sahara. However before people there was more, once upon a time, caravans of traders passed through the desert, carrying various riches. But crossing the entire desert took 1.5 years!
8) The roots of some plants are at a depth of 20 meters! In this way, plants try to get water for themselves in order to retain it for a long time and use it carefully.
9) There are about 4 thousand in the Sahara various types animals and plants.
10) Camels live without water for 14 days, and without food for as many as 30! They can smell moisture from 50 kilometers away, and drink one hundred liters of water at a time! And they don't sweat at all! Their humps are fat, thanks to which they can survive for a long time without food.
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One of the largest and most famous deserts on the planet is the Sahara, which covers the territory of ten African countries. In ancient writings the desert was called “great”. These are endless expanses of sand, clay, stone, where life is found only in rare oases. Only one river flows here, but there are small lakes in oases and large reserves of groundwater. The desert territory occupies more than 7,700 thousand square meters. km, which is slightly smaller in area than Brazil and larger than Australia.
The Sahara is not a single desert, but a combination of several deserts that are located in the same space and have similar climatic conditions. The following deserts can be distinguished:
Libyan
Arabian
Nubian
There are also smaller deserts, as well as mountains and dormant volcano. You can also find several depressions in the Sahara, among which we can highlight Qatar, 150 meters deep below sea level.
Climatic conditions in the desert
The Sahara has an extra-arid climate, that is, dry and hot tropical, but in the far north it is subtropical. Recorded in the desert temperature maximum on the planet +58 degrees Celsius. As for precipitation, it is absent here for several years, and when it falls, it does not have time to reach the ground. A common phenomenon in the desert is the wind that raises dust storms. Wind speed can reach 50 meters per second.
There are strong differences in daily temperatures: if during the day the heat is over +30 degrees, which makes it impossible to breathe or move, then at night it becomes cool and the temperature drops to 0. Even the hardest people cannot withstand these fluctuations. rocks which crack and turn into sand.
In the north of the desert there is the Atlas mountain range, which prevents Mediterranean air masses from entering the Sahara. Wet ones move from the south atmospheric masses from the Gulf of Guinea. The desert climate affects neighboring climatic zones.
Plants of the Sahara Desert
Vegetation is distributed unevenly throughout the Sahara. More than 30 species of endemic plants can be found in the desert. Flora is most represented in the Ahaggar and Tibesti highlands, as well as in the north of the desert.
Among the plants are the following:
Acacia
Animals in the Sahara Desert
The fauna is represented by mammals, birds and various insects. Among them in the Sahara are jerboas and hamsters, gerbils and antelopes, maned sheep and miniature foxes, jackals and mongooses, sand cats and camels.
There are lizards and snakes here: monitor lizards, agamas, horned vipers, sandy f-holes.
The Sahara Desert is special world, where an extra-arid climate formed. This is the hottest place on the planet, but there is life here. These are animals, birds, insects, plants and nomadic peoples.
Desert location
The Sahara Desert is located in North Africa. It occupies an area from the western part of the continent to the eastern part for 4.8 thousand kilometers, and from north to south 0.8-1.2 thousand kilometers. total area The Sahara is approximately 8.6 million square kilometers. WITH different parts The desert is bordered by the following objects:
- in the north – the Atlas Mountains and the Mediterranean Sea;
- in the south – the Sahel, a zone transitioning to savannas;
- in the west – the Atlantic Ocean;
- to the east is the Red Sea.
Most of the Sahara is occupied by wild and uninhabited spaces, where nomads can sometimes be found. The desert is divided between states such as Egypt and Niger, Algeria and Sudan, Chad and Western Sahara, Libya and Morocco, Tunisia and Mauritania.
Sahara desert map
Relief
In fact, sand occupies only a quarter of the Sahara, and the rest of the territory is occupied by stone structures and mountains of volcanic origin. In general, we can distinguish the following objects in the desert:
- Western Sahara - plains, mountains and lowlands;
- Ahaggar - highland;
- Tibesti - plateau;
- Tenere – sandy expanses;
- Air - plateau;
- Talaq – desert;
- Ennedi – plateau;
- Algerian desert;
- Adrar-Iforas - plateau;
- El Hamra;
The largest accumulations of sand are in such sandy seas as Igidi and the Great Eastern Erg, Tenenre and Idehan-Marzuk, Shesh and Aubari, the Great Western Erg and Erg Chebbi. There are also different shapes dunes and dunes. In some places there is the phenomenon of moving and also singing sands.
If we talk in more detail about the topography, sands and the origin of the desert, then scientists say that previously the Sahara was ocean floor. There is even a White Desert here, in which white rocks are the remains of various microorganisms of antiquity, and during excavations paleontologists find skeletons of various animals that lived millions of years ago.
Now sands cover some parts of the desert, and their depth in some places reaches 200 meters. Sand is constantly transported by winds, forming new landforms. Under the dunes and sand dunes there are deposits of various rocks and minerals. When people discovered oil and natural gas deposits, they began to extract them here, although it is more difficult than in other places on the planet.
Water resources of the Sahara
The main source of the Sahara Desert is the Nile and Niger rivers, as well as Lake Chad. Rivers originated outside the desert and are fed by surface and groundwater. The main tributaries of the Nile are the White and Blue Nile, which merge in the southeastern part of the desert. The Niger flows in the southwest of the Sahara, in the delta of which there are several lakes. In the north there are wadis and streams that form after heavy rainfall and also flow from the mountain ranges. Inside the desert itself there is a network of wadis that was formed in ancient times. It is worth noting that under the sands of the Sahara there is underground water that feeds some reservoirs. They are used for irrigation systems.
River Nile
Among interesting facts One thing to note about the Sahara is that it is not completely deserted. More than 500 species of flora and several hundred species of fauna are found here. Animal diversity and flora forms a special ecosystem on the planet.
In the bowels of the earth beneath sandy seas deserts have sources of artesian water. One of interesting phenomena– this is that the territory of the Sahara is changing all the time. Satellite images show that the desert area is either increasing or decreasing. If the Sahara was previously a savannah, now it is a desert, it is very interesting what several thousand years will do to it and what this ecosystem will turn into.
Geographical position. Tropical deserts occupy a vast territory in northern Africa. Desert and semi-desert landscapes are common throughout the Atlantic Ocean to the Red Sea, from the foot of the Atlas Mountains and the Mediterranean coast to a line running approximately from the lower reaches of the Senegal River through Lake Chad to Khartoum on the Nile (see map of the physiographic zoning of Africa with links to photographs of nature in this region). This huge space with an area of about 7 million km 2 is united under a common geographical name- Sugar.
The geographical boundaries of the Sahara are quite defined. Only in the south. where natural conditions change more or less gradually from semi-deserts to savannas, the physiographic boundary is somewhat blurred and separates areas with a pronounced rainy season.
Geological structure. Most of the Sahara is a plateau, composed of crystalline and volcanic rocks at the base and overlain by strata of horizontal sedimentary deposits. In some places, an ancient folded foundation protrudes to the surface, forming high highlands, or ancient intrusions emerge in the form of dome-shaped hills.
In the extreme east, between the Red Sea and the Nile, the crystalline basement is uplifted and in places overlain by layers of Mesozoic sandstone. There rise table plateaus up to 2000 m high, intersected by deep dry gorges, indicating strong erosional dissection in the previous wetter era. This part of the region is known as the Arabian and Nubian deserts.
West of the Nile stretches the plateau of the Libyan Desert with the greatest accumulations of sand in the world. In the north, the surface of the Sahara gradually decreases, with some deep depressions located below sea level. The Qattara Depression, with an absolute bottom elevation of 133 m below sea level, is one of the deepest dry depressions on Earth.
In the central part of the Sahara, high highlands and plateaus rise, composed of crystalline and volcanic rocks: the Tibesti, Ahaggar, Iforas highlands, etc. highest peak Tibesti highlands - the extinct volcano Emi-Kusi (3415 m) with a crater with a diameter of 12 km; it is the highest peak in the Sahara. The relief of the massifs is highly dissected, their slopes are steep and rocky, and masses of coarse clastic material have accumulated at the foot.
The surface of the rest of the Sahara, with prevailing altitudes of 300-400 m, is covered with strata of limestone, sandstone and clayey rocks of various ages.
Relief. Many areas of the Sahara have a monoclinal structure and form well-defined cuesta scarps. This type of relief is typical for the Tassilin-Adjer plateau, bordering the Ahaggar highlands from the northeast, for the Tademait plateau located to the north and the Bani plateau adjacent to the Anti-Atlas, etc. In the formation of the cuesta relief of the Sahara, the role of tectonics and erosion processes, which manifested themselves in the post-glacial period, is great. wetter than the modern era.
The surface of the desert plateaus of the Sahara is crossed by a network of channels bearing the Arabic name “wedd”, or “wadi”. Only after rare rains do they fill with water, which dries up after a few days, and sometimes after a few hours. Most of the water diverges radially along the slopes of the central Sahara massifs, which served as watersheds during the pluvial period, when a network of erosional depressions in the Sahara formed. Their bottoms are currently covered with alluvial sandy material, and sometimes they represent a hard clay surface.
Many wadis end in closed depressions of various sizes and depths, which are also one of the features of the Sahara topography. After rains, the depressions are filled with water for a short time. The bottoms of some depressions (sebkhs) are covered with a crust of salts, but those that have underground drainage are usually not saline. The origin of the depressions is determined by tectonics, underground erosion processes, karst processes and the blowing out of weathering products.
With the high intensity of weathering processes and the absence of removal, clastic material accumulated in huge quantities in the Sahara. Some parts of the desert, especially the depressions between cuesta plateaus and vast closed basins, are characterized by huge accumulations of dune sand, the so-called ergs. Along with areas of motionless, “dead” sands large areas occupied by sand dunes constantly moving in the direction prevailing winds. Particularly powerful accumulations of sand have been noted in the Libyan Desert. The relative height of the dunes there reaches 300 m. In the Sahara, there are often vast flat areas with a layer of pebble material, sometimes covered with sand (“reg” or “serir”) on the surface. Large spaces are cluttered with rubble formed as a result of the destruction of crystalline rocks. Such rocky deserts are called “hamada”. Among the rubble accumulations of Hamads, isolated plateaus with steep rocky slopes rise - “gara”.
Climatic conditions. The continental Sahara deserts owe their existence to the dominance of dry tropical air throughout the year. The climate of most of it is sharply continental, the annual precipitation almost everywhere is less than 50 mm (Fig. 114).
Rice. 114. Annual course temperatures, precipitation and relative humidity in the Algerian Sahara
In inland areas there is sometimes no precipitation for several years in a row and rainfall is random. However, sometimes heavy rains cause floods. Known to have drowned in the Sahara more people than died from the heat. Caravan routes usually passed along the bottoms of dry riverbeds, and people did not have time to escape from sudden heavy rains.
A slight increase in precipitation is observed only on the slopes of high uplands, but even there the annual amount does not reach 100 mm. On the northern and southern edges of the desert, more constant precipitation is confined to certain periods of the year. In the north they fall in autumn, winter and spring, and in the south in summer. These bands of more or less constant rainfall serve as a transition from the Sahara to the Atlas country in the north and the Sudan natural region in the south. The air in the Sahara is always dry and full of dust; relative humidity it is very small, sometimes below 25%. On hot days, with strong and uneven heating of the air, visibility conditions can be distorted, mirages appear with non-existent rivers, lakes or mountains on the horizon. Along with low precipitation, the Sahara has the highest evaporation rate in the world. Over the course of a year, a layer of water up to 6 m thick can evaporate in this hot desert. Strong winds increase evaporation. The most constant summer winds are the trade winds, which carry dry and hot air from the north and northeast. Atmospheric depressions that occur in summer cause severe sand and dust storms - one of the main disasters in the Sahara.
Temperature variations are characterized by sharp daily and annual contrasts. IN summer time the heat reaches 30...50 °C, it is aggravated by constant hot and dry winds carrying dust and sand. The absolute maximum of 58 °C, observed in the Sahara in the shade, is the absolute maximum for the entire Earth. The soil surface heats up to 60... 80 °C. In summer, even at night, the temperature usually does not drop below 30 °C, but daily fluctuations of 30...50 °C are possible.
IN winter months the air is cooler and more stable as anticyclonic weather sets in. During the day, the temperature stays around 20...25 °C; at night, due to strong heat transfer, the air cools to 0 °C, and sometimes there are such severe frosts that water in vessels and artificial reservoirs freezes. Frosts down to -18 °C were observed in the mountains.
The western edge of the Sahara, located off the coast of the Atlantic Ocean with its cold Canary Current, is a different type of desert - coastal. Due to the proximity of the ocean, temperatures become more moderate, relative humidity reaches 75-80%, refreshing breezes blow on the coast, but there is little more rain than in the interior of the Sahara.
Natural water. There is almost no surface water in the Sahara; the source of water supply is groundwater, on the proximity of which the existence of people, animals and plants depends. Sandy deserts are richest in underground water. Under the sand in some places there are quite thick groundwater horizons that give rise to springs. Sub-channel watercourses are characteristic of many wadis. Water in the Sahara is mostly taken from wells. Recently, deep artesian wells and wells, equipped with pumps that pump out the most reliable and permanent water from pressure horizons, have begun to play a significant role in water supply. There is evidence of huge reserves artesian waters in the depths of the Sahara and other areas of North Africa.
In the outlying parts of the Sahara and some mountainous regions there are lakes with clear water, preserved from the time of the last pluvial and fed by groundwater.
The only major permanent watercourse within the region is the Nile. This river, flowing for many hundreds of kilometers through the barren desert and bringing it to life, is one of the most remarkable natural phenomena in Africa. But the Nile's existence is supported by the waters it receives outside the desert.
Vegetation. The soils of the Sahara do not form a continuous cover. Vast areas of sandy and rocky deserts are almost completely devoid of soil. However, when the land is irrigated, the Sahara can become very fertile, as it contains many salts necessary for plants. But rising groundwater levels are often associated with excess salinization and the appearance of salt marshes.
IN vegetation cover There are 1,200 plant species that contain sugars. The vast majority of them are xerophytes or ephemerals. Only relatively few areas, mostly rocky, seem completely lifeless. But even on them there are plants that are amazing in their ability to adapt to the harsh conditions of the desert. For example, among the stones or on the sand you can find the rose of Jericho - a plant with a short stem and branches bent like fingers with seeds clutched. When it rains, the branches unclench, the seeds fall to the ground and germinate very quickly, using every drop of moisture. Seeds or tubers of other plants are stored in the ground and also germinate quickly after rains that occur every few months or even several years. In some places, on sand and rocks, there are thorny, squat or creeping plants with small leaves or spines. Sometimes the stones are covered with a thick crust of lichens. In some places there are tree-like spurges. The vegetation cover is dominated by gray-green, gray and yellow tones, which gives it a particularly sad, lifeless appearance.
U southern border Communities of shrubs and some tough grasses appear in the sugars. In the north, along the border with the Atlas Mountains, there are wild pistachios, oleanders and jujubes.
Animal world. Poor in species, but quite rich in individuals, the fauna of the Sahara includes animals that are hardy and move quickly in search of water and food, or constantly live near water sources. The most typical species for the Sahara are addax and oryx antelopes, Dorcas gazelle, dama gazelle, and mountain goats. They are hunted for their meat and skins, some of which have almost disappeared.
The most famous predators are jackals, hyenas, foxes, and cheetahs. There are birds, both migratory and permanent. Among the latter, the desert raven is especially characteristic. Of the reptiles, lizards predominate; snakes and turtles are found. Rare bodies of water in strictly localized habitats have preserved relics of pluvial eras - crocodiles.
The existence of relict fauna, as well as many other facts (for example, dry erosion depressions, terraces on the slopes of lake depressions) indicate that in the recent geological past the climate of the Sahara was wetter than it is now. Particularly convincing are the rock paintings discovered in the caves of the Central Sahara massifs depicting plants and animals that are now absent from the Sahara, hunting scenes, etc. It is assumed that during the last pluvial, i.e. 10-15 thousand years ago, the Sahara was watered and quite densely populated.
Population and environmental problems. The modern population of the Sahara is concentrated mainly in oases. Oases are one of the attractions of the Sahara, green spots among vast desert spaces. They occur where there is water on or close to the surface. In some oases, water is taken from springs that sometimes feed small rivers, in others - from wells. The largest oases in the Sahara are formed near artesian wells. Many of them exist for a relatively short time and then disappear if the source dries up or the well dries up. But there are oases dating back hundreds and even thousands of years. The largest and most ancient oasis of the Sahara is the Nile Valley, irrigated by Nile water and representing one of the oldest centers of agricultural culture.
As in the oases of South-West Asia, the main cultivated plant of the Saharan oases is the date palm, in the shade of which fruit trees and shrubs are grown and cereals are sown. Some oases have no permanent population; Arabs come there only at certain times of the year to collect dates. Noting the close connection date palm with the Sahara, some scientists consider it possible to draw the border of the Sahara as a geographical region along the border of the distribution of the date palm.
On the outskirts of the Sahara, some Berber-Arab tribes lead a nomadic or semi-nomadic lifestyle, breeding camels and sheep. They live in large tents and dress in loose, long clothes that protect their bodies from overheating.
In some areas of the Sahara, salt has long been mined and exported, and iron and other metals have been smelted. But the real use of natural resources in the Sahara countries is just beginning. And the riches of this desert territory are incalculable, first of all its mineral reserves. After World War II, large oil and gas deposits were discovered in Libya, Algeria and other countries. There are also large reserves of iron, manganese, copper ores, uranium.
Great amount solar energy, which the surface of the Sahara receives, represents inexhaustible possibilities for agriculture; soils contain many nutrient minerals. Mention has already been made of the supposed vast reserves of groundwater that make it possible to exploit the climatic and land resources of the Sahara.
In the decades that have passed since the formation of independent states in North Africa, paved roads have been laid across the Sahara, new cities and towns have arisen in mining areas, and the number of people engaged in mining has increased. agriculture. But these essentially positive processes in the conditions of the extremely vulnerable nature of the Sahara also entailed undesirable phenomena. Currently, the area of deserts in northern Africa is increasing. The observed process of desert advance to the south, towards savannahs, is proceeding very quickly. Trampling the soil by livestock, burning and cutting down shrubs and trees along the desert border contribute to the destruction soil cover, fluttering sands and drying out water bodies.
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