Why is the desert hot during the day and cold at night? Desert natural zone: characteristics, description and climate. The most famous hot deserts of the Earth

About ten thousand years ago, the territory where the most great desert our planet, the Sahara, was covered with grass, low bushes and was densely populated. After our planet slightly changed the tilt of its axis, the climate began to gradually change, it became hot, the rains stopped - and many representatives of the animal world left the formed desert.

The Sahara (in the translation from Arabic - "desert") is the largest desert on our planet, which is located in northern Africa and is located on the territory of ten states. On the geographic map it can be found at the following coordinates: 23 ° 4 ′ 47.03 ″ s. latitude, 12 ° 36 ′ 44.3 ″ E etc.

The Sahara occupies about thirty percent of the African continent, and its area is about 9 million km2:

• From east to west, the length of the desert is 4,800 km: the Sahara begins off the coast Atlantic Ocean and ends off the coast of the Red Sea.
• The length of the Sahara from south to north ranges from 800 to 1200 km. The desert begins in the north of the mainland off the coast of the Mediterranean Sea and Atlas Mountains, the southern border is limited to 16 ° N. sh., in the area of ​​inactive ancient dunes, to the south of which begins the tropical Sahel savanna, a transitional area between the desert and Sudan.

When exactly the Sahara desert was formed on the territory of the African continent, scientists do not have a unanimous opinion: earlier its age was estimated at 5.5 thousand years, then at four, recently they began to tend to think that it is even younger, and its lands became deserted only about three thousand years ago.

The desert is located in the northwest of the stable ancient African platform, so ground shuddering is rarely observed today. In the center of the platform, the relief rises from west to east: one of the largest high-mountain regions of the desert are the Ahaggar and Tibesti plateaus, where, unlike other regions of the Sahara, for a short time almost every year.

From the northern and southern parts of the uplifts - the deflections of the platform, where in the past there was a sea, and therefore the presence of marine sedimentary rocks is characteristic of the soil. In the south of the desert, the platform trough has led to the formation of large lakes, which are the main suppliers of fresh water for their region. First of all, we are talking about Lake Chad and the Unianga group of lakes.

Sands occupy only one fourth of the Sahara, while the thickness of the sandy layer is about 150 meters. Stony soil predominates: it occupies about 70% of the desert area, the rest is volcanic mountains, as well as pebble and sandy-pebble soil.

There are also many aquifers (sedimentary rocks with varying degrees of water permeability, cracks and voids of which are filled with water), which are the main suppliers of water to the oases.

Sometimes fertile lands are found in the desert - mainly near oases that take water from underground rivers and reservoirs, the water of which, due to its own pressure, was able to reach the ground.

On the map of Africa, the Sahara is divided into several regions:

• Western Sahara - located in northwest Africa, the territory is characterized by coastal lowlands, which turn into elevated basement plains and plateaus.
• The central highlands of Ahaggar - on the map it is located in the south of Algeria, the highest point is Mount Tahat with a height of 2918 meters, so it often snows here in winter.
• Tibesti mountain plateau - located in the center of the desert, in the north of the state of Chad and partly in the south of Libya. Highest point The plateau is the Emi-Kusi volcano, almost 3.5 km high, on top of which snow falls annually.
• Desert Tenere - located in the south of the central Sahara. It is a sandy plain with an area of ​​about 400 thousand km2, which is located in the northeastern part of Niger and in the west of Chad.
• Libyan Desert - on the map of Africa, it is located in the north and is the driest region of the desert.

Climate

The Sahara is the hottest and hottest place on our planet: not even the driest desert in the world, the Atacama, in South America, can compare with it.

The weather here is extremely hot in summer: air temperature at this time often exceeds 57 ° С, and the sands heat up to 80 ° С. At the same time, the Sahara Desert is one of the few places on our planet where evaporation significantly exceeds the amount of precipitation (with the exception of narrow coastal strips). While the average values ​​of precipitation are only 100 mm (while in the center they may not be for several years in a row), 2 to 5 thousand mm of moisture evaporates.

Conventionally, the Sahara can be divided into two climatic zones, northern (subtropical) and southern (tropical):

The northern part of the desert is characterized by hot summers (up to 58 ° C) and cold winters (especially cold, where temperatures can drop to -18 ° C). The annual rainfall is 80 mm, rainy weather is here from December to March and in August, with frequent thunderstorms and even severe short-term floods. In winter, snow falls briefly on the high mountain plateaus Ahaggar and Tibesti almost every year.

The south is characterized by mild winters, and rains fall at the end of the hot and dry period. There is little precipitation in mountainous regions, and it goes evenly throughout the whole year. In the lowlands, it rains in the summer, often accompanied by thunderstorms, about 130 mm of precipitation falls a year. In the west, near the coast of the Atlantic Ocean, humidity is higher than in the rest of the Sahara, and there are often fogs here.

The difference between daytime and nighttime air temperatures in the Sahara is often about forty degrees: the average temperature in the center of the desert in July is 35 ° C, while at night the air temperature drops to + 10 or + 15 ° C. The weather here is also warm in winter: the temperature of the coldest month of the year is + 10 ° C (therefore, snow is an extremely rare phenomenon).

The climate of the Sahara is very strongly influenced by constantly blowing strong winds, especially in the north of the desert (only 20 days a year are calm). Winds blow mainly from north to east: the movement of moist air masses of the Mediterranean air stops the Atlas mountain range.

As for the air currents that move from the south, when they reach the central part of the desert, they have time to lose moisture, so the winds in the northern part of the desert are especially destructive. They move at a speed of about 50 m / s and, raising dust, sand, small stones to a height of more than a thousand meters, cause tornadoes and the strongest, often moving the dunes.

Water resources

The only river in North Africa that passes through the eastern part of the Sahara towards Mediterranean Sea is the Nile, the length of which is 6852 km (the river is the second longest after the Amazon, and flows through South America).

Since a considerable part of the water evaporates as we move through the desert, its two tributaries, the White and Blue Nile, play an important role, which flow into it in the southeast of the desert (they are very clearly distinguishable on the map). In the 60s of the last century, the Nasser reservoir was created between Egypt and Sudan, total area which exceeds 5 thousand km2.

In the south of the Sahara, several river flows flow into Lake Chad, the area of ​​which ranges from 27 to 50 thousand km2 (depending on precipitation in the region), after which part of the water leaves the lake - and the water continues to flow in the northeastern direction, replenishing the watersheds.

In the southwest flows the Niger River, which flows into the Gulf of Guinea of ​​the Atlantic Ocean. This river is interesting because it starts almost near the ocean, 240 km from the coast, it flows in the opposite direction, to the Sahara, after which it turns sharply to the right and continues its way to southeast direction(the shape of the river, if you look at the map of Africa, resembles a boomerang).

In the northern part of the desert, water comes from wadi streams, temporary water flows that appear after showers and flow down from the mountains. Also, wadis feed the soil of the desert in its central part. A lot of rainwater is in the dunes: once in the sand, water seeps down the slopes and flows down.

Under the sands of the desert there are huge pools of groundwater, thanks to which oases are formed (especially in the north of the Sahara, while the aquifers are located deeper in the south).

Another source of water in the largest desert of the planet is relict lakes located on the outskirts and in mountain ranges (remnants former seas), often swampy and salty, although freshwater is often found among them (for example, the water of most of the lakes of the Uniang group).

Flora

There is not much vegetation in the Sahara - mainly shrubs, grasses and trees that grow near a natural reservoir, along a wadi or in high-altitude regions, including olives, cypress, dates, thyme, citrus fruits.

In areas where water is scarce, there are only those types of vegetation that tolerate drought well. There are no plants at all in rocky massifs, in places of accumulation of sand.

Fauna

The desert is inhabited by almost 4 thousand representatives of the animal world, most of which are invertebrates. The animals of the Sahara Desert live mainly near the water (they are practically not found in arid regions) and are nocturnal.

Most of the animals are monitor lizards, cobras, lizards, chameleons, snails. Crocodiles, frogs, crustaceans are found in reservoirs. There are about sixty species of mammals, among them - cheetah, sand fox, mongooses.

The Sahara is home to about 300 species of birds, 50% of them are migratory. These are primarily ostriches, African owl, trumpet and desert crows and others.

Desert and people

Despite its huge area, the desert is hardly inhabited: only 2.5 million people live here. Some peoples are nomadic, but most prefer to settle. People settle only near oases, as well as in the valleys of the Nile and Niger rivers, where there is enough water and vegetation to survive on their own and feed livestock. At the same time, breeding of cattle: goats and sheep prevails over fishing and hunting.

The desert windswept Atacama Plateau, which stretches off the coast of Chile, is rightfully considered the driest place on the planet. You rarely see a bird flying over the desert. And the Pan American Highway - the only road here - rushes into the distance, not meeting on its way even a hint of any greenery. At a distance of 1000 km along the Chilean coast, you can see only a bare landscape with rocks scorched by the sun, rubble and dunes. At a distance of 100 km from the ocean, a plateau almost undisturbed by civilization, rising to an altitude of 900 m, is replaced by the harsh and windy foothills of the Andes.

No matter how bare it may seem here, the nomadic sands of the desert make it "move" - ​​the dunes are strewn with the wind, poured on top of each other in sickle-shaped layers, moving from place to place. Harsh sandstorms with occasional showers, they polished and smoothed the surface of the rocky rocks, turning them over time into gentle hills. In the rays of the setting sun, the exposed rocks play with brown, purple-red and green hues.

There is no heat in the Atacama Desert, only at noon the temperature reaches 50 ° C, and the average summer temperature is about 18 ° C. In the evenings, literally within an hour, the temperature drops by 40 degrees. Such a sharp change in temperature deforms even stones, which crack from compression, filling the surroundings with the sounds of pistol shots.

The Loa River flows through the central part of the desert, originating in the foothills of the Andes. The deep river bed makes it sometimes invisible from the outside. There is an opinion that in some areas of the desert it never rained at all. It is well known that no more than four times in a century it rains in the ports of Iquique and Antofagasta, necessarily bringing with them natural disasters... The determining percentage of moisture in the desert is caused by fog, which does not allow the sun to reach the outskirts, due to which cacti grow here. In the north, the deserts are swept by the winds sand dunes... At the tip of the desert, where the Atacama meets the Pacific Ocean, rains have washed deep ravines on the desert slopes. This is despite the fact that it rarely rains here.

The Atacama Desert is virtually devoid of rain moisture. On the eastern slopes of the Andes, moisture from the Amazon remains, condensing on the mountain surface. In the western part, the climate is influenced by the Antarctic Humboldt Current, passing in coastal waters The Pacific... Moist sea winds do not bring the desired moisture, but, on the contrary, pull it out of the land, since it is colder than the latter. In this case, "kamanchaka" is formed - a fog that cannot penetrate into the depths of the desert. He does not rise above 300 m and is unable to cross the edge of the plateau.

Among the dunes, a surprise awaits tourists - the sculpture "Hand of the Desert"

The dryness of the desert climate "preserves" traces of human presence for a long time. Surprisingly, the track from the horse-drawn carriages that passed here 100 years ago can still be seen on the stones covered with a soft coating of rubble mixed with salt crystals. Unique stone patterns and geoglyphs (figures) gigantic- "Atakamskiy Giant" reaches a length of 120 meters. The feeling of novelty of their creation, given that the true age is millennia, is somewhat strange.

On the gentle bank, you can find foxes and pig-nosed skunks, for which birds and Marine life... For example, crabs. Gray gulls also prefer them. However, in summer, birds migrate 100 km inland to safely raise chicks. It is interesting that the mother's wings protect the babies from the burning sun rays during the day, with which she covers them, like an umbrella.

The Atacama Desert is not a lifeless plain. a real home for dozens of animal species

There are many vampire bats in the caves - night hunters. Biting through the skin of sleeping birds or sea lions, they lick their blood so that the victim sometimes does not even notice it.

But in the coastal waters life is in full swing. Upwelling (upward current) rises from ocean depths minerals necessary for plankton. Plankton, in turn, becomes food for numerous fish, and those for seabirds. On the coastal islets, you can observe not only their countless nesting sites, but also "maternity homes" of fur seals and lions.