Desert - a natural area characterized by a flat surface, sparseness or lack of flora and specific fauna. Natural area desert Description of the desert

Desert - a natural area characterized by a flat surface, sparseness or lack of flora and specific fauna.

There are sandy, rocky, clayey, saline deserts. Separately, the Arctic deserts are distinguished (eng. polar desert) in Antarctica and the Arctic. They can be snowy and snowless (dry). The area of ​​snowy deserts is more than 99% of the total area Arctic deserts. A snowless (dry) desert is the McMurdo Dry Valleys. The area of ​​these valleys is 8 thousand km² (less than 0.06% of the 14.1 million km² of the total area of ​​Antarctica). Katabatic winds (cold air currents directed down the slopes earth's surface, arising from the cooling of air on glaciers and entrained due to greater strength gravity down) cause the evaporation of moisture. Thanks to this, the valleys are practically free of ice and snow for about 8 million years.

The most famous sandy desert– Sahara (the largest sandy desert by area), occupying the entire northern part of the African continent. Close to deserts are semi-deserts, also related to extreme landscapes.

In total, deserts occupy more than 16.5 million km² (excluding Antarctica), or about 11% of the land surface. With Antarctica more than 20%.

general characteristics

Deserts are common in temperate zone Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres. They are characterized by humid conditions (the annual amount of precipitation is less than 200 mm, in extra-arid regions - less than 50 mm, and in some deserts there has been no precipitation for decades). In the relief there is a complex combination of highlands, low hills and insular mountains with structural layered plains, ancient river valleys and closed lake depressions. The erosional type of relief formation is strongly weakened, eolian relief forms are widespread. For the most part, the territory of the deserts is drainless, sometimes they are crossed by transit rivers (Syr Darya, Amu Darya, Nile, Huang He and others); there are many lakes and rivers that dry up, often changing their shape and size (Lob Nor, Chad, Eir), periodically drying up watercourses are characteristic. Groundwater is often mineralized. Soils are poorly developed, characterized by the predominance of water-soluble salts in the soil solution over organic matter, salt crusts are common. The vegetation cover is sparse (the distance between neighboring plants varies from several tens of cm to several meters or more) and usually covers less than 50% of the soil surface; practically absent under extraarid conditions.

Sandy deserts are inhabited from plants mainly by thorny bushes, from animals - by reptiles and small steppe animals. AT sandy deserts over the places of occurrence groundwater there are oases - "islands" with dense vegetation and reservoirs. The snowy deserts are mostly found above the Arctic Circles and are inhabited by cold-hardy animals.

Desert classification

By the nature of soils and soils:

• Sandy - on loose deposits of ancient alluvial plains;
• Loess - on loess deposits of piedmont plains;
• Loamy - on slightly carbonate cover loams of the plains;
• Clay takyr - on the piedmont plains and in ancient river deltas;
• Clay - in low mountains, composed of saline marls and clays,
• Pebble and sand-pebble - on gypsum plateaus and piedmont plains;
• Rubble gypsum - on the plateau and young piedmont plains;
• Stony - on low mountains and small hills;
• Solonchakous - in saline depressions of the relief and along the sea coasts.

According to the dynamics of precipitation:

• Coastal - develop where cold sea currents approach the hot coasts (Namib, Atacama): there is almost no precipitation; life, respectively.
• Central Asian type (Gobi, Betpak-Dala): the rate of precipitation is approximately constant throughout the year - and therefore life is here all year round, but barely warm.
• Mediterranean type (Sahara, Kara-Kum, Great Sandy Desert in Australia): there is the same amount of precipitation as in the previous type, but only they all pour out at once, in two to three weeks; here there is a brief and stormy flowering of life (various ephemera), which then passes into a latent state - until the next year.

How do deserts form?

Historical experience shows that degradation natural environment as a result of the destruction of forests occurred in the following sequence: deforestation - the emergence of savannas - desertification. Several millennia ago, the Sahara arose on the site of the savannas, and even earlier, a significant part of this territory was occupied by forests.

Desertification is the final stage of soil destruction. After deforestation, the climate changes, go to the depth fresh water, erosion begins, and then the winding of the soil. Desertification has become a global problem in the 20th century. Every year, the advancing deserts capture up to 50 thousand square kilometers of territory, where people lived quite recently, and forests rustled in the recent past. The threat of desertification now affects 150 states to one degree or another. If it develops at a modern pace, 600-700 million people, a seventh of the world's population, will be under the threat of resettlement. The arid lands, which are threatened by the desert, now supply meat, wool, cotton, grain. These lands have considerable potential for further development of agricultural production. Their loss will turn into another tragedy for humanity. Deserts need to be stopped.

The process of desertification has also affected the territory of our country. It is observed in Kazakhstan, in the plains Central Asia, on the territory of Kalmykia. The main reason is mismanagement Agriculture: plowing of dry steppes, ill-conceived irrigation, lack of protective forest plantations. Today, the annual increase in the area of ​​semi-deserts in a number of regions of our country reaches 10 percent. The true extent of this process has only now begun to be clarified with the help of satellite observations.

Peculiarities

Relief

The relief of hot deserts is very diverse. Only some of them are completely covered with sand. The surface of others consists of stones, pebbles and other rocks. Deserts are practically open to weathering. Strong winds pick up small fragments of stones from the surface and throw them onto the rocks. Erosion is most intense near the surface, where the winds throw the most sand and stones onto the rocks.

In sandy deserts, winds carry sand over the surface, forming undulating sediments - dunes. The shape of the dunes depends on the direction of the wind and the size of the sand particles. The most common form of dunes is dunes. The dunes are crescent shaped. They form in deserts where the winds blow in any one direction. The dunes move slowly, and sand pours over their tops. Their height can reach 30m. Ridged dunes are long sandy ridges formed by winds blowing from two directions. They can be up to 100 km long and up to 100 m high.

Temperatures

During the day, the temperature in the desert can rise to 52°C, as there are no clouds in the atmosphere and nothing protects the surface from the sun's rays. It is much cooler underground, and therefore most animals hide during the day from the heat in deep holes. At night, the temperature drops very quickly due to the absence of clouds to trap the heat radiated from the surface. During the day, the phoenix fox hides from the heat in a deep hole. She hunts at night when it is cool. Blood vessels pass under the very skin of the fox's large ears. Flowing through them, the roof cools, releasing heat into the air. This reduces the body temperature of the animal.

rain in the desert

Although little rain falls in hot deserts, very heavy showers occasionally occur, after which water does not soak into the soil, but quickly flows down the surface, washing away pebbles and soil particles from it into dry channels - wadis.

The seeds of some plants in deserts can lie in the soil for many months, and even years. After rain, they germinate very quickly, bloom, produce seeds, and then die when conditions become unbearable. Many desert plants have an extensive root system that draws moisture deep from the ground. The leaves of such plants are very small in order to minimize the evaporation of moisture from their surface. Cacti, shaped to minimize evaporation, are covered with sharp spines that do not animals to eat them. When it rains, cacti absorb water with juicy pulp.

Tropical desert flora

The primitive soils of tropical deserts are very poor in humus, and gray soils form only in relatively humid areas. The soil cover in tropical deserts, as a rule, is absent. Vast areas are covered with sands or placers of rubble and pebbles, on the surface of which a characteristic shiny dark crust forms, the so-called desert tan, which protects rocks from rapid weathering and destruction.

Only plants that can grow in deserts can grow in deserts. extreme conditions drought and high temperatures. There are many xerophytes, ephemera and ephemeroids that do not form a closed vegetation cover, unusual shrubs and semi-shrubs of the "tumbleweed" type. In the sandy deserts of Asia, leafless shrubs (white saxaul, sand acacia) are common, in America and Africa, succulents (cacti, agaves, aloe, etc.) are common. A variety of wormwood and saltwort are characteristic of clay deserts. Hamads, at first glance, devoid of vegetation, also have a vegetation cover - lichens.

Where groundwater comes close to the surface, oases are located. The largest of them are in the river valleys. Irrigated agriculture and horticulture are developing here, cotton, wheat, barley, sugar cane, olive, etc. are cultivated. The date palm grows in the Arabian and North African deserts - a beautiful, slender tree up to 30 m high. dried. The apical buds, flower shoots of palm trees - palm cabbage, as well as the powdery core of young palm trees are used for food.

Tropical desert fauna

The hot and extremely dry climate of tropical deserts is extreme for living organisms. However, the animals living in these places have managed to adapt to such conditions. They can go without drinking for a long time and travel great distances in search of water. During the hottest season of the year in tropical deserts, many invertebrates go into suspended animation, while reptiles and rodents go into hibernation. Some animals spend almost all their lives underground, and ungulates and most bird species migrate from hot regions for the summer. Many desert animals are nocturnal. They crawl out of their holes only for a short period of time between the night cold and the scorching heat of the day, and some animals hide in the shade of bushes or climb high branches away from the hot earth during the day.

In tropical deserts, jerboas, voles, mole rats, hyenas, cheetahs, desert cats, miniature chanterelles are common; ungulates are represented by antelopes, donkeys, mountain sheep; birds - grouse, larks. There are many reptiles (geckos, lizards, snakes), arachnids and insects (dark beetles, phalanges, scorpions) in the deserts.

The one-humped camel (dromedary) is often called the “ship of the desert” for its endurance and reliability. Previously, the dromedary lived only in the arid regions of the Middle East, northern India and North Africa, but later one-humped camels were introduced to central Australia. Brownish or sandy-gray dromedaries weigh from 300 to 690 kg and reach a height of 2 m, sometimes black and white individuals are found. The dromedary has a long curved neck, a narrow chest and a single hump consisting of fat deposits - food reserves - approx. from geoglobus.ru. The size of the hump varies depending on the amount of food and the time of year. The dromedary feeds on dry grass and young shoots of shrubs, chewing each portion of food thoroughly (40-50 times). It needs salt to conserve water.

The camel's hooves are perfectly adapted for moving on the sands, and thick lips allow the animal to eat even thorny plants. Usually dromedaries live in family groups of 20 individuals: one male, one or more females and their offspring. Camels give birth to one cub in winter, during the first year of life it gains weight very quickly. One-humped camels live 40-50 years.

Typical desert birds - grouse have long and sharp wings, adapted for fast flight. They feed on the seeds of grasses and shrubs, and when they arrive at a watering place, they moisten their abdominal feathers, which have a special structure. In the goiter and wet feathers, the grouse carry water to the chicks. The nest of the grouse is arranged on the ground, the parents take turns incubating 3 laid eggs.

In the deserts, jerboas are often found: in the Sahara - sandy, and in Central Asia and Iran - crested, thick-tailed and upland. Funny animals with long hind legs and short "handles" resemble miniature kangaroos. Their soft thick fur is colored in the color of sand - approx. from geoglobus.ru. From their shallow, complexly branched burrows with several exits, jerboas emerge at nightfall. On long hind legs, they jump in search of food, reaching speeds of up to 50 km / h. The animals feed mainly on plant foods, but do not neglect insects and carrion.

And in Russia there are deserts

As a rule, at the mention of deserts, the Sahara, Kalahari and Gobi come to mind, and not everyone thinks about Russia at such moments. Mostly motherland associated with the taiga and endless snowy expanses. However, this phenomenon is not completely alien to our country. The desert in Russia is much richer in flora than one might imagine. Don't believe? Read on! Oddly enough, one of the Russian deserts is located just 800 km from the capital. Archedinsky-Don sands - this is the name of the local wasteland. Most of this territory is covered with sandy massifs left from the time of the Ice Age by the Don.

The plants of the Russian deserts make this territory truly unique in its kind - birch bushes stretch among the sandy hillocks, black alder and aspens grow. There are juniper, a special kind of cinquefoil and buckthorn. There are also saxauls, common in desert areas around the world. In the spring, in especially humid areas of the desert, numerous tulips bloom, and the harsh nature turns into a real parade of colors and shades. They can be called the brightest accent among the desert spring. Dangerous animals are almost non-existent here. The most common representatives of the Russian desert fauna are ground squirrels and jerboas. Of the larger animals, saigas are common in this area, and the number of bird species here is truly enormous.

Where sand turns to ice

Note that the desert in Russia is not only the Tsimlyansk and Archedinsky-Don sands. These territories also include the Arctic wastelands, where the heat is replaced by frost. For most of the year, these expanses are covered with a thick layer of ice, and here you can only find moss that is very resistant to low temperatures. Only at the height of summer, white wastelands are transformed beyond recognition - mosses and lichens acquire new colors, forming green-red carpets. Sow thistle and some types of cereals make their way out of the frozen soil.

There are also flowering plants of the Russian deserts - foxtail, buttercup, arctic pike, snow saxifrage and even polar poppy. In some places, sky-blue forget-me-nots and fluffy white reindeer moss peep through. The icy, harsh desert turns into a real wonderful world during this period, where the beauty and riot of life compete with low temperatures and strong winds. Much more striking is the diversity of the fauna of the Arctic wastelands - walruses, seals and polar bears coexist here with a huge number of bird species, deer, narwhals and beluga whales.

The driest deserts in the world

Dry deserts in Antarctica

The Dry Valleys of Antarctica can be considered the driest place on the planet, as there has been no precipitation in these places for more than two million years. The Dry Valleys include the Victoria, Taylor and Wright valleys. They are located near McMurdo Sound. This desert of Antarctica is not covered with ice, its area is about eight thousand square kilometers.

Causes of dryness in Katabatic winds. They blow at a speed of at least three hundred and twenty kilometers per hour, which is maximum speed wind on the planet. It is the wind that evaporates all the moisture. For nearly eight million years the valleys have remained free of snow and ice. Dry Valleys is a protected area of ​​particular value, where it is very convenient to conduct various kinds of research. By natural conditions these valleys are close to the conditions of Mars. This similarity is used by NASA for testing purposes.

On the territory of the valleys there is Lake Vida and the Onyx River. The water of the lake is extremely salty and surpasses even the water of the Dead Sea in the amount of salt. Animal world in the Dry Valleys is extremely poor, despite the complete absence of ice and snow cover. This is due precisely to increased dryness, which makes it difficult for animals to survive there.

The driest places in Eurasia

There are several deserts on the territory of Eurasia. They are located in Central, Central Asia, Kazakhstan. In Kazakhstan, the most famous deserts are the Ustyurt plateau, Betpak-Dala, Kyzylkum, Moyunkum, the Aral Karakum. The desert expanses of Kazakhstan are truly immense. The fauna is represented by jerboas, vipers, gray monitor lizards and gazelles. In Central Asia, the sandy desert of Takla-Makan can be distinguished. It is recognized as the largest in the world, while its conditions are among the most severe. The desert of Dzungaria, the desert of Alashan and the Gobi are known. The deserts of Central Asia have cold winters with maximum precipitation in summer.

In Central Asia, vast territories are occupied by deserts, there is an extremely dry and extremely hot climate. They can be attributed to the southern deserts, which are a continuation of the North African deserts and the deserts of Asia Minor. The largest Central Asian deserts are the Karakum and Kyzylkum. The rest are much smaller.

The hottest desert in India

One of the most significant in India and the most populated desert in the world is the Thar Desert. It is located in the Indian state of Rajasthan. The climate of the Thar Desert cannot be called harsh; it is a living eco-system.

The Thar Desert is inhabited by animals. Common representatives are the Indian gazelle, jungle cat, nilga antelope, jackals and foxes. Due to the low population of desert expanses by people, animals have the opportunity to live in vivo environment. It is common to find lizards of prehistoric appearance, rat snakes, vipers and sand boas there. It is surprising that in the place of the Thar Desert in the last two hundred and eighty million years there has been a sea four times.

In the area of ​​the village of Akal, petrified trees have been preserved, which are the remains of ferns and forests that grew in those places about one hundred and eighty million years ago. One of the largest petrified trees with a girth of one and a half meters, and a length of almost seven meters.

8 most unusual deserts of the planet

1. Desert with lagoons - Lencois Maranhensis, Brazil

It's hard to believe, but this desert that stretches into national park in the state of Maranhao in Brazil, full of lagoons. The impressive view creates a contrast between the white dunes and the blue lagoons formed by the rains, the water from which collects in the lowlands between the dunes, forming small ponds with clear water. The lagoons themselves, where fish, turtles and shellfish live, can only be seen after the winter has passed and before the onset of summer.

2. Colored desert, USA

The colored desert in the state of Arizona in the USA is an expanse of hills, plateaus and individual hills with steep slopes. It is a dry, sparsely vegetated land that has been heavily eroded. The name "Colored Desert" refers to the variety of colorful sedimentary rock layers that are visible against this rugged landscape. The relief of the Colored Desert is often compared to the colorful layers of a cake. The variety of shades of the sandstone and mudstone layers is the result of the different mineral content of the sedimentary rocks and the rate at which they were deposited.

3. The smallest desert in the world - Carcross Desert, Canada

The Carcross Desert in Yukon is called the smallest desert in the world. The dry climate and winds have created sand dunes here and contributed to the growth of sparse vegetation that has adapted to environment. The size of the Kacross desert is about 2.6 square meters. km.

4. The largest gypsum desert - White Sands, USA

Rising right in the middle of the Tularos Basin, one of the greatest natural wonders state of New Mexico in the USA - the shimmering sands of the gypsum desert. The dunes cover about 712 sq. km of land, which makes this desert the largest gypsum desert in the world. Unlike other deserts, here the sand is really cool to the touch due to the high evaporation and moisture on the surface and the fact that the sands reflect rather than absorb the sun's rays.

5. Black Desert, Egypt

The Black Desert is an area where volcanic hills are covered with a large number of small black pebbles. Pebbles lie on top of the orange-brown earth, and therefore the desert is not completely black. Climbing one of the tops of numerous hills, you can admire an indescribable landscape consisting of many equally beautiful gloomy hills. However, it is worth remembering that the Black Desert is uninhabited and there are no amenities here.

6. The largest salt desert - Uyuni Salt Flats, Bolivia

This desert, located in Bolivia, can significantly change your idea of ​​​​deserts. It is actually a dried-up salt lake whose relief is completely flat, and is so large and transparent that it seems as if the sky is reflected, creating a landscape of different shades of blue. Another attractive aspect of this desert is the many colorful lakes that have acquired their color from a variety of minerals.

The Uyuni salt marsh is the largest wet salt marsh, stretching over 10,582 sq. km. The salt marsh contains a large number of sodium, potassium, lithium, magnesium, and borax. According to some estimates, it contains about 10 billion tons of salt, of which about 25,000 tons are mined annually.

7. Desert covered in snow - Takla Makan, China

Takla Makan is one of the largest sandy deserts in the world, being the 15th in the list of the largest non-polar deserts. It extends over 270,000 sq. km of the Tarim River Basin, its length is 1000 km and its width is 400 km. From the northern and southern edges, it is crossed by two branches of the Silk Road, which travelers usually sought to avoid the arid wasteland.

In 2008, China's largest desert experienced the largest snowfall and recorded the most low temperatures after 11 days of continuous snowfall.

8. Red Sand Desert - Simpson Desert, Australia

Located in Australia, the Simpson Desert is striking in its beauty due to the red sand dunes.

Another attractive aspect is that here are the longest parallel dunes on the planet. The most famous dune is the Big Red dune, whose height reaches 40 m.

Although the climate here is rather harsh, the spinifex plant grows here, which fixes loose sand, and is a habitat for 180 species of birds, as well as lizards and marsupials.

Sources

https://ru.wikipedia.org/wiki/Desert https://www.factroom.ru/facts/16538 https://uznayvse.ru/interesting-facts/samyie-suhie-pustyini-v-mire.html

Despite the fact that its very name "desert" comes from words such as "empty", "emptiness", this amazing natural object filled with varied life. The desert is very diverse: in addition to the sand dunes that our eyes habitually draw, there are saline, stony, clay, and also snowy deserts of Antarctica and the Arctic. Taking into account the snowy deserts, this natural zone belongs to one fifth of the entire surface of the Earth!

Geographic feature. The meaning of deserts

The main distinguishing feature of the desert is drought. The reliefs of the deserts are very diverse: insular mountains and complex highlands, small hills and layered plains, lake depressions and dried up centuries-old river valleys. On the formation of the relief of deserts big influence exerts the wind.

Man uses deserts as pastures for livestock and areas for growing some cultivated plants. Plants for feeding livestock develop in the desert thanks to the horizon of condensed moisture in the soil, and desert oases, flooded with sun and water, are exceptionally good places for growing cotton, melons, grapes, peach and apricot trees. Of course, only small areas of deserts are suitable for human activity.

Characteristics of deserts

Deserts are located either next to the mountains, or almost on the border with them. High mountains prevent the movement of cyclones, and most of the precipitation they bring falls in the mountains or foothill valleys on the one hand, and on the other side - where the deserts lie - only a small remnant of rain reaches. That water, which manages to reach the soil of the desert, flows down the surface and underground watercourses, gathering in springs and forming oases.

Deserts are characterized by various amazing phenomena that are not found in any other natural area. For example, when there is no wind in the desert, the smallest grains of dust rise into the air, forming the so-called "dry fog". Sandy deserts can "sing": the movement of large layers of sand generates a high and loud slightly metallic sound ("singing sands"). Deserts are also known for their mirages and terrible sandstorms.

Natural areas and types of deserts

Depending on the natural zones and the type of surface, there are such types of deserts:

• Sandy and sandy-gravel. They are distinguished by great diversity: from chains of dunes devoid of any vegetation, to territories covered with shrubs and grass. Moving through the sandy desert is extremely difficult. Sands do not occupy the largest part of the deserts. For example: the sands of the Sahara make up 10% of its territory.

• Stony (hamadas), gypsum, gravel and gravel-pebble. They are combined into one group according to a characteristic feature - a rough, hard surface. This type of desert is most common in globe(hamadas of the Sahara occupy 70% of its territory). Succulents and lichens grow in tropical rocky deserts.

• saline. In them, the concentration of salts prevails over other elements. Salt deserts can be covered with a hard cracked salt crust or salt bog that can "suck in" a completely large animal and even a person.

• clayey. They are covered with a clayey smooth layer stretching for many kilometers. They are characterized by low mobility and low water properties (the surface layers absorb moisture, preventing it from going deep, and dry quickly during the heat).

Desert climate

Deserts occupy the following climatic zones:

• temperate (Northern Hemisphere)
• subtropical (both hemispheres of the Earth);
• tropical (both hemispheres);
• polar (ice deserts).

The deserts are dominated by a continental climate (very hot summers and Cold winter). Precipitation is extremely rare: from once a month to once every few years and only in the form of showers, because. small precipitation does not reach the ground, evaporating in the air.

The daily temperature in this climatic zone varies greatly: from +50 ° C during the day to 0 ° C at night (tropics and subtropics) and up to -40 ° C (northern deserts). Desert air is especially dry: from 5 to 20% during the day and from 20 to 60% at night.

The largest deserts in the world

Sahara or Queen of the Desert- the most big desert world (among hot deserts), the territory of which occupies over 9,000,000 km 2. Located in North Africa, it is famous for its mirages, which happen here on average 150,000 a year.

Arabian desert(2,330,000 km 2). It is located on the territory of the Arabian Peninsula, also capturing part of the land of Egypt, Iraq, Syria, Jordan. One of the most capricious deserts in the world, known for especially sharp fluctuations in daily temperature, strong winds and dust storms. From Botswana and Namibia to South Africa extends over 600,000 km2 Kalahari, constantly increasing its territory due to alluvium.

Gobi(more than 1,200,000 km2). It is located in the territories of Mongolia and China and is the largest desert in Asia. Almost the entire territory of the desert is occupied by clay and stony soils. In the south of Central Asia lie Karakum("Black Sands"), occupying an area of ​​350,000 km 2.

Desert Victoria- occupies almost half of the territory Australian continent(over 640,000 km 2). It is famous for its red sand dunes, as well as a combination of sandy and rocky areas. Also located in Australia Great Sandy Desert(400,000 km 2).

Two South American deserts are very notable: Atacama(140,000 km 2), which is considered the driest place on the planet, and Salar de Uyuni(more than 10,000 km 2) - the largest salt desert in the world, the salt reserves of which are more than 10 billion tons.

Finally, the absolute champion in terms of occupied territory among all world deserts is ice desert Antarctica(about 14,000,000 km 2).

Even the word "desert" itself evokes associations of emptiness and the absence of life, but for the people who live on these lands, it seems beautiful and unique. The natural zone of the desert is a territory very difficult, but life. There are sandy, clayey, rocky, saline and snowy (yes, in the Arctic and Antarctica - arctic desert) desert. The most famous is the Sahara, it is also the largest in area. In total, deserts occupy 11% of the land, and if you count with Antarctica - more than 20%.

See the geographical position of the natural zone of deserts on the map of natural zones.

Deserts are located in the temperate zone of the Northern Hemisphere and the subtropical and tropical zones of the Northern and Southern Hemispheres (they are characterized by special moisture conditions - the amount of precipitation per year becomes less than 200 mm, and the moisture coefficient is 0-0.15). Most deserts were formed on geological platforms, occupying the most ancient land areas. Like other landscapes of the Earth, deserts arose naturally, due to the peculiar distribution of heat and moisture over the earth's surface. In simple words, deserts are located in places where very little or no moisture enters. The reasons for this are the mountains that cover the desert from the oceans and seas or the proximity of the desert to the equator.

The main feature of semi-desert and desert lands is drought. Arid, arid zones include lands where the life of people, plants and animals is completely dependent on it. Arid lands make up almost a third of the entire land mass of the planet.

The relief of the desert zone is very diverse—complex uplands, hillocks and insular mountains, stratified plains, ancient river valleys, and closed lake depressions. The most common are eolian landforms, which were formed under the action of the wind.

Sometimes the territory of the deserts is crossed by rivers (Okavango - a river flowing into the desert, Huang He, Syr Darya, Nile, Amudarya, etc.), there are many drying streams, lakes and rivers (Chad, Lop Nor, Air).

Soils poorly developed - water-soluble salts predominate over organic substances.
Groundwater is often mineralized.

Climate features.

The climate in the deserts is continental: winters are cold and summers are very hot.

Rains fall once a month or only once in a few years, in the form of heavy downpours. Small rains simply do not reach the surface of the earth, evaporating under the influence of high temperature. The driest regions of the world are the deserts of South America.

Most deserts receive the main precipitation in spring and winter, and only in some deserts the maximum amount of precipitation falls in summer in the form of showers (in big deserts Australia and Gobi).

The air temperature in this natural area can fluctuate greatly - during the day it rises to + 50 ° C, and at night it drops to 0 ° C.
In the northern deserts, the temperature in winter drops to -40 °C.

One of the most important features is the dryness of the air - during the day the humidity is 5-20%, and at night it is within 20-60%.

Winds are of great importance in deserts. Each of them has its own name, but they are all hot, dry, carrying dust and sand.

The sandy desert is especially dangerous during a hurricane: the sand turns into black clouds and overshadows the sun, the wind carries the sand over long distances, destroying absolutely everything in its path.
Another feature of the deserts are mirages created by the sun's rays, which, when refracted, create very amazing pictures on the horizon.

The main difference between deserts and other places is the almost complete absence of water - rivers, streams, fresh lakes. It rains very rarely - once a month or once every few years, mainly in the form of heavy showers. A small rain due to high temperatures does not reach the surface of the earth - the water evaporates on the way to it.

Large intermountain depressions and basins are characterized by particularly high air dryness. But the driest regions of the world are the deserts of South America. On the Pacific coast, in the town of Iquique, only 1 mm of precipitation falls per year.

Most of the world's deserts receive most of their precipitation in winter and spring, and only a few - in the Gobi and the great deserts of Australia - receive the maximum amount of precipitation in summer time in the form of showers.

In deserts, air temperature can fluctuate widely. During the day up to +50 °С in the shade, and at night - almost to 0 °С. In winter, the temperature in the northern deserts drops even to -40 °C. Desert air is extremely dry, and this is one of their most important features. During the day, humidity ranges from 5-20%, and at night - from 20 to 60%. For a long time summer period temperature + 40 ... + 50 ° C in the shade is a common occurrence.

When the sun disappears below the horizon in the evening, the air temperature drops by 30-35 ° C, and sometimes much more. The soil during the day heats up more than the air, and then cools more. The climate in the deserts is continental: summers are very hot, and winters are relatively cold.

Extratropical deserts - the Gobi, Karakum and Kyzylkum, Takla-Makan, Alashan and Ordos - are distinguished primarily by cold, very severe, but practically snowless winters, without thaws with frosts down to -40 ° C (for example, the Gobi desert).

A more favorable climate is in the deserts located along the coasts of the Atlantic and the Pacific Ocean, the Persian Gulf, where it softens somewhat, and in connection with this, the humidity increases to 80-90%, and the range of daily fluctuations decreases. Periodically in such deserts in the mornings there are dews and fogs.

The wind is of great importance in the deserts. Desert winds have their own names, as follows: in the Sahara - sirocco, in the Libyan and Arabian deserts - gabli and khamsin, in Australia - brickfielder and Afghan in Central Asia. All winds are dry, hot, carrying sand or dust. They are distinguished by an enviable constancy of direction, its duration and frequency, which plays a positive role in the problems of orientation and maintaining the direction of movement. But the winds often turn into dust or sand storms, carrying away millions of tons of sand and dust per day, and the air temperature at this time rises to +50 ° C, accompanied by a sharp drop in humidity.

The sandy desert is especially terrible during a hurricane. Black clouds of sand rush in the air and outshine the light. Air whirlwinds carry sharp grains of sand and strike them with great force at all protruding objects. Dust blinds the eyes, burns the face and hands. The wind lifts huge masses of sand into the air, carrying them over long distances.

It happens that the sand raised by the wind stands in the air with such a dense wall that the sun is not visible. And sometimes it twists into a spiral, rising to a great height in the form of a rotating funnel, expanding upwards. Small hot grains of sand, raised by the wind, painfully cut the skin, fit into all the cracks - into clothes, shoes, seep under the glasses of dustproof glasses and watches. They creak on the teeth, cut the eyes, clog the pores of the skin ...

Terrible legends circulate about the Sahara sandstorms- "Samum", which means "poison" in translation.

Another feature of deserts is mirages. As a rule, this happens in deserts of all types in the afternoon, when the soil is as hot as possible, and layers of air with different densities are formed in the surface atmosphere. The sun's rays, refracting, create the most amazing pictures on the horizon. In the trembling, as if tangible, air, an image appears either of a lake, or a city, or domes of minarets, or mountains, or alluring palm trees. Mirages also occur in the early morning, before sunrise, when the air is saturated with fine dust. Pictures of mirages are so bright and realistic that they can confuse even an experienced traveler and direct him in the opposite direction from the chosen direction of travel.

Deserts are a certain geographical phenomenon, a landscape that lives its own, special life, has its own laws, has features inherent only to it, forms of change.

The desert can be gentle and gentle, but it can also be formidable. The desert is like a chameleon, constantly changing its color and its temper.

Deserts and semi-deserts are waterless, dry regions of the planet, where no more than 25 cm of precipitation falls per year. The most important factor their formation is the wind. However, not all deserts have hot weather, some of them, on the contrary, are considered the coldest regions of the Earth. Representatives of flora and fauna have adapted to the harsh conditions of these areas in different ways.

How do deserts and semi-deserts arise?

There are many reasons for the formation of deserts. For example, there is little rainfall because it is located at the foot of the mountains, which, with their ridges, cover it from rain.

Ice deserts formed for other reasons. In Antarctica and the Arctic, the main snow mass falls on the coast; snow clouds practically do not reach the interior regions. Precipitation levels generally vary greatly, for one snowfall, for example, an annual norm can fall. Such snow drifts form over hundreds of years.

Hot deserts are distinguished by the most diverse relief. Only some of them are completely covered with sand. The surface of most is littered with pebbles, stones and other miscellaneous rocks. Deserts are almost completely open to weathering. Strong gusts of wind pick up fragments of small stones and hit them on the rocks.

In sandy deserts, the wind carries the sand across the area, creating undulating sediments, which are called dunes. The most common type of dunes are dunes. Sometimes their height can reach 30 meters. Ridge dunes can be up to 100 meters high and stretch for 100 km.

Temperature regime

The climate of deserts and semi-deserts is quite diverse. In some regions, daytime temperatures can reach up to 52 ° C. This phenomenon is due to the absence of clouds in the atmosphere, so nothing saves the surface from direct sunlight. At night, the temperature drops a lot, again due to the lack of clouds that can trap the heat radiated from the surface.

In hot deserts, rain is rare, but sometimes there are heavy downpours. After rain, water does not soak into the ground, but rapidly flows from the surface, washing away particles of soil and pebbles into dry channels, which are called wadis.

Location of deserts and semi-deserts

On the continents located in northern latitudes, there are deserts and semi-deserts of the subtropical and sometimes also tropical - in the Indo-Gangetic lowland, in Arabia, in Mexico, in the southwestern United States. In Eurasia, extratropical desert regions are located in the Central Asian and South Kazakh plains, in the basin of Central Asia and in the Near Asian highlands. The Central Asian desert formations are characterized by a sharply continental climate.

In the southern hemisphere, deserts and semi-deserts are less common. Here are located such desert and semi-desert formations as the Namib, Atacama, desert formations on the coast of Peru and Venezuela, Victoria, Kalahari, the Gibson Desert, Simpson, Gran Chaco, Patagonia, the Great Sandy Desert and the Karoo semi-desert in southwestern Africa.

The polar deserts are located on mainland islands near-glacial regions of Eurasia, on the islands of the Canadian archipelago, in the north of Greenland.

Animals

Animals of deserts and semi-deserts for many years of existence in such areas have managed to adapt to harsh climatic conditions. From cold and heat, they hide in underground burrows and feed mainly on underground parts of plants. Among the representatives of the fauna there are many types of carnivores: fennec fox, cougars, coyotes and even tigers. The climate of deserts and semi-deserts has contributed to the fact that many animals have perfectly developed a thermoregulation system. Some desert dwellers can withstand fluid loss of up to a third of their weight (for example, geckos, camels), and among invertebrates there are species that can lose water up to two thirds of their weight.

AT North America and Asia there are a lot of reptiles, especially a lot of lizards. Snakes are also quite common: ephs, various poisonous snakes, boas. Of the large animals, there are saiga, kulans, camels, pronghorn, it has recently disappeared (it can still be found in captivity).

The animals of the desert and semi-desert of Russia are a wide variety of unique representatives of the fauna. The desert regions of the country are inhabited by sandstone hares, hedgehogs, kulan, dzheyman, poisonous snakes. In the deserts that are located on the territory of Russia, you can also find 2 types of spiders - karakurt and tarantula.

They live in polar deserts polar bear, musk ox, arctic fox and some species of birds.

Vegetation

If we talk about vegetation, then in deserts and semi-deserts there are various cactus, hard-leaved grasses, psammophyte shrubs, ephedra, acacias, saxaul, soap palm, edible lichen and others.

Deserts and semi-deserts: soil

The soil, as a rule, is poorly developed, and water-soluble salts predominate in its composition. The ancient alluvial and loess-like deposits predominate, which are reworked by the winds. Gray-brown soil is inherent in elevated flat areas. Deserts are also characterized by solonchaks, that is, soils that contain about 1% of easily soluble salts. In addition to deserts, salt marshes are also found in steppes and semi-deserts. Groundwater, which contains salts, when it reaches the soil surface, is deposited in its upper layer, resulting in soil salinization.

Completely different are characteristic of such climatic zones like subtropical deserts and semi-deserts. The soil in these regions has a specific orange and brick red color. Noble for its shades, it received the appropriate name - red soil and yellow soil. In the subtropical zone in northern Africa and in South and North America there are deserts where gray soils have formed. Red-yellow soils have developed in some tropical desert formations.

Natural and semi-desert - a huge variety of landscapes, climatic conditions, flora and fauna. Despite the harsh and cruel nature of the deserts, these regions have become home to many species of plants and animals.