Desert message. Tropical deserts: general characteristics; the brightest representatives Climatic conditions of the desert of the tropical and temperate zones

It lies in the climatic zone of the same name. On our planet, almost all desert areas are located precisely in the tropics, but, unlike paradises on the coasts of the sea, weather here are much more severe and not at all suitable for life. Well, let's consider what characterizes such tropical deserts, where they can be found and which of them are the most famous.

What characterizes the desert zones of the tropics?

The relief and origin of each of the deserts known to us vary greatly. Somewhere these are based on plateaus, in other places they are surrounded by rocks and elevated plateaus, sometimes deserts are found on the shores of the oceans, that is, in the lowlands. But it is the climate that unites all tropical deserts. The first characteristic is the sharp diurnal fluctuations in air temperature. During the day in most of these natural areas, the thermometer can exceed 50, and at night the air cools down to 10. The second characteristic is the difference between winter and summer. In such zones, it is insignificant, but the further the desert lies from the equator, the more the range of annual temperature fluctuations expands. Well, the third common feature are the winds. Some regions of our planet have become completely devastated not because there are barren lands. It's just that atmospheric flows are arranged so that there are no clouds over the deserts - they are always dispersed by the wind. Due to this, the percentage of solar radiation increases and, accordingly, all living things die out.

Sands of the Middle East

Considered the Sahara. It occupies the entire northern part of Africa and smoothly passes into a small isthmus. Both natural zones are very similar to each other in terms of landscape, origin and climate. They also form a pronounced climatic zone on the surface of the Earth. Numerous tropical deserts, named only by locals, are part of this natural area. Here, yellow sands predominate, which are collected either in single dunes or in huge ridges of dunes stretching for kilometers. It is in this Afro-Asian geographic area that very high temperature fluctuations are observed. During the day, the thermometer does not fall below 45, and the maximum reaches 58. Therefore, only insects and reptiles live in the sands of the Sahara and Arabia, which crawl out to the surface only at night.

smallest continent

The deserts of the tropical belt are also concentrated on Australian lands. locals they are also divided into numerous "sovereign" territories, but their landscapes are very similar to each other. Climatic conditions here are not as severe as in Asia. The temperature during the day is within 30 degrees, and at night it does not fall below 15. The amount of precipitation that falls per year is up to 300 mm (which is a lot for a desert). The Australian sand flats are characterized by their red soils. The local sands have a crimson hue, the glow of which intensifies at sunset.

Mysterious valleys of Chile

In the west, perhaps, there are the most extraordinary tropical deserts. Photos of these masterpieces of nature are presented in the article, and they do not look like pictures of the Sahara or any other natural area. Here in leading role not sands protrude, but valleys that are surrounded by rocks. In (as it is called) precipitation has not fallen for 400 years. All the moisture that the local land is content with is fogs that occur only in the summer.

Other sandy areas

Desert areas can also be found in southern Africa. These are Kalahara and Namibia. The landscape and origin of this natural area can be compared to the Sahara. In North America, as well as in Mexico, there are narrow deserts that stretch from North to South. Their landscapes can be compared with the Atacama. There are few sands, but there are a lot of various other rocks that create incredible beauty.

The content of the article

DESERT, areas earth's surface, where, due to the too dry and hot climate, only very scarce vegetation and animal world; usually these are areas with low population density, and sometimes generally uninhabited. This term also applies to areas that are unfavorable for life due to the cold climate (the so-called cold deserts).

Physical and geographical characteristics.

Aridity

deserts can be explained by two reasons. The deserts of the temperate zone are arid because they are remote from the oceans and inaccessible to moisture-bearing winds. The dryness of tropical deserts is due to the fact that they are located in the area of ​​prevailing downward air currents coming from equatorial zone, where, on the contrary, strong upward currents are observed, leading to the formation of clouds and heavy precipitation. When descending, the air masses, already deprived of most of their moisture content, heat up, further moving away from the saturation point. A similar process also occurs when air currents cross high mountain ranges: most of the precipitation falls on the windward slope during the upward movement of air, and the areas located on the leeward slope of the ridge and at its foot are in the “rain shadow”, where the amount of precipitation is low.

Desert air is everywhere extremely dry. Both absolute and relative humidity are close to zero for most of the year. Rainfall is extremely rare and usually falls in the form of heavy showers. At the Nouadhibou weather station in the west of the Sahara, the average annual rainfall, according to long-term observations, is only 81 mm. In 1912, only 2.5 mm of rain fell there, but the next year one very heavy rain brought 305 mm. High temperatures, which increase evaporation, also favor the aridity of deserts. The rain that falls over the desert often evaporates before reaching the surface of the earth. Most of the moisture that reaches the surface is quickly lost to evaporation, and only a small fraction seeps into the ground or runs off as surface streams. Water seeping into the soil replenishes the reserves groundwater and can travel long distances until it comes to the surface as a source in an oasis. It is believed that most deserts can be turned into a flowering garden with the help of irrigation. This is generally true, but very great care is needed when designing irrigation systems in arid areas, where there is a great danger of large losses of water from irrigation canals and reservoirs. As a result of water infiltration into the soil, the groundwater table rises, which, under arid climate and high temperatures, leads to capillary pulling of groundwater to the surface and evaporation, and the salts dissolved in these waters accumulate in the near-surface soil layer, contributing to its salinization.

Temperatures.

The temperature regime of the desert depends on its specific geographical location. Desert air, which contains very little moisture, does little to protect the land from solar radiation (unlike humid areas with higher cloudiness). Therefore, in the daytime, the sun shines brightly there and there is a sizzling heat. The usual temperatures are approx. 50 ° C, and the maximum recorded in the Sahara is 58 ° C. The nights are much cooler, as the soil heated during the day quickly loses heat. In hot tropical deserts, daily temperature amplitudes can be more than 40 ° C. In the deserts of the temperate zone, seasonal temperature fluctuations exceed daily ones.

Wind.

A characteristic feature of all deserts are constantly blowing winds, often reaching very great strength. main reason the occurrence of such winds is excessive heating and the convective air currents associated with it, however great importance also have local factors, such as large landforms or position in relation to the planetary system of air currents. Wind speeds of up to 80–100 km/h have been recorded in many deserts. Such winds capture and transport loose material on the surface. This creates sand and dust storms - a common occurrence in arid regions. Sometimes these storms are felt at a great distance from the source of their origin. It is known, for example, that dust carried by the wind from Australia sometimes reaches New Zealand, which is 2,400 km away, while dust from the Sahara is transported more than 3,000 km and deposited in northwestern Europe.

Relief.

Desert landforms differ significantly from those found in humid regions. Of course, there are mountains, plateaus and plains here and there, but in the deserts these large forms have a completely different appearance. The reason is that the desert relief is created mainly by the work of the wind and turbulent water currents that occur after rare showers.

Forms created by water erosion.

There are two types of streams in the desert. Some rivers, the so-called. transit (or exotic), such as the Colorado in North America or the Nile in Africa, originate outside the desert and are so full of water that, flowing through the desert, they do not dry out completely, despite the large evaporation. There are also temporary, or episodic, streams that occur after intense rainstorms and dry up very quickly as the water completely evaporates or seeps into the soil. Most desert watercourses carry silt, sand, gravel and pebbles, and although they do not have a constant flow, it is they that create many of the features of the relief of desert areas. The wind also creates sometimes very expressive landforms, but they are inferior in importance to those worked out by water flows.

Flowing down steep slopes into wide valleys or desert depressions, streams deposit their sediment at the foot of the slope and form alluvial fans - fan-shaped accumulations of sediment with a top facing up the stream valley. Such formations are extremely widespread in the deserts of the Southwestern United States; cones often located nearby merge, forming at the foot of the mountains an inclined piedmont plain, which here is called "bajada" (Spanish bajada - slope, descent). Such surfaces are composed of loose deposits, in contrast to other gentle slopes, called pediments, and worked out in bedrock.

In deserts, water quickly flowing down steep slopes erodes surface deposits and creates gullies and ravines; sometimes erosional dissection reaches such a density that so-called. badlands. Such forms, formed on the steep slopes of mountains and mesas, are characteristic of the desert regions of the whole world. One shower is enough to form a ravine on the slope, and once formed, it will grow with each rain. Thus, as a result of rapid gully formation, large sections of different plateaus were destroyed.

Forms created by wind erosion.

The work of the wind (the so-called aeolian processes) creates various forms relief typical of desert regions. The wind captures dust particles, carries them and deposits them both in the desert itself and far beyond its borders. Where sand particles have been blown out, deep depressions several kilometers long or smaller shallow depressions remain. In places, air vortices create strange cauldron-shaped recesses with steeply overhanging walls or caves. irregular shape. Wind-blown sand acts on bedrock ledges, revealing differences in their density and hardness; this is how bizarre forms arise, reminiscent of pedestals, spiers, towers, arches and windows. Often, the entire fine earth is removed from the surface by the wind, and only a mosaic of polished, sometimes multi-colored, pebbles remains, the so-called. "Desert Pavement" Such surfaces, purely "swept" by the wind, are widespread in the Sahara and the Arabian Desert.

In other areas of the desert there is an accumulation of sand and dust brought by the wind. Of the forms formed in this way, sand dunes are of the greatest interest. Most often, the sand that composes these dunes consists of quartz grains, but on coral islands there are dunes of limestone particles, and sand dunes in the White Sands National Natural Monument ("White Sands") in the state of New Mexico in the USA are formed by pure white gypsum. Dunes form where the air current encounters an obstacle in its path, such as a large boulder or bush. The accumulation of sand begins on the leeward side of the barrier. The height of most dunes is in the range from a few meters to several tens of meters, but dunes are known that reach a height of 300 m. If they are not fixed by vegetation, they move in the direction of the prevailing winds. As the dune moves, the sand is blown up the gentle windward slope and falls off the crest of the leeward slope. The speed of dune movement is low, on average 6–10 m per year; however, a case is known when in the Kyzylkum desert, with an exceptionally strong wind, the dunes moved 20 m in one day. When moving, the sand covers everything that is in its path. There are cases when entire cities were covered with sand.

Some dunes are heaps of irregularly shaped sand, while others, formed under the predominance of winds of a constant direction, have a clearly defined gentle windward slope and a steep (about 32 °) leeward slope. A special kind of dune is called dunes. These dunes have a regular crescent shape in plan, with a steep and high lee slope and pointed “horns” stretched in the direction of the wind. In all areas of the distribution of the dune relief, there are many depressions of irregular shape; some of them are created by eddy currents of air, others were formed simply as a result of uneven deposition of sand.

Temperate deserts

usually located in the depths of the continents, away from the oceans. They occupy the largest area in Asia, the largest part of the world; North America is in second place. In many cases, such deserts are surrounded by mountains or plateaus that block access to wet sea ​​air. Where high mountain ranges are close to the ocean and parallel coastline like in the west North America, deserts come quite close to the coast. However, with the exception of the desert regions of Patagonia, located in the rain shadow of the Andes in the south South America, and the Sonoran Desert in Mexico, none of the temperate deserts open directly to the sea.

The temperatures of the deserts of the temperate zone show significant seasonal fluctuations, but it is difficult to name typical values, since these deserts have a large extent from north to south (in Asia and North America up to 15–20 ° in latitude). Summers in such deserts are usually warm, even hot, while winters tend to be cold; winter temperatures can stay below 0°C for quite some time.

Consider the climate and relief of deserts Central Asia(on the territory of Kazakhstan, Uzbekistan and Turkmenistan) and the Gobi Desert in Mongolia, typical of the temperate zone. All these deserts are located in the interior regions of Asia, inaccessible to humid oceanic winds, since the moisture contained in them falls in the form of precipitation before reaching these regions. The Himalayas block the wet summer monsoons from the Indian Ocean, while the mountains of Turkey and Western Europe significantly reduce the amount of moisture coming from the Atlantic. In the Western Hemisphere, typical examples of temperate deserts are the deserts of the Great Basin in the southwestern United States and the deserts of Patagonia in Argentina.

Deserts of Central Asia

include the Ustyurt plateau between the Aral and Caspian seas, the Karakum south of the Aral Sea, and the Kyzylkum southeast of it. These three desert regions form a vast inland drainage basin where rivers flow into the Aral or Caspian Sea. Three-quarters of the area is occupied by desert plains, bounded by the high mountain ranges of the Kopetdag, Hindu Kush and Alay. The Karakum and Kyzylkum are sandy deserts with dune ridges, many of which are fixed by vegetation. The annual amount of precipitation does not exceed 150 mm, but on mountain slopes it can reach 350 mm. Snow rarely falls on the plains, but is quite common in the mountains. Temperatures are high in summer, and in winter they drop to 2° ... -4° C. The main source of irrigation water is the Amudarya and Syrdarya rivers, which originate in the mountains. The most valuable varieties of cotton, wheat and other grains are grown on irrigated lands, but high evaporation contributes to soil salinization, which hinders the normal development of plants. From minerals, gold, copper and oil are mined.

Desert Gobi.

Under this name, a vast desert region is known, the area of ​​\u200b\u200bwhich is approx. 1600 thousand km 2; surrounded on all sides high mountains: in the north - Mongolian Altai and Khangai, in the south - Altyntag and Nanshan, in the west - Pamir and in the east - Greater Khingan. Within the large depression occupied by the Gobi desert, there are many small depressions in which water flowing from the mountains collects in summer. This is how temporary lakes are formed. The average annual rainfall in the Gobi is less than 250 mm. In winter, some snow occasionally falls on the lowlands. In summer, the temperature reaches 46 ° C in the shade, and in winter it sometimes drops to -40 ° C. Strong winds, dusty and sandstorms. For many thousands of years, dust and silt have been carried by the wind to the northeastern regions of China, where powerful loess covers have formed as a result.

The relief of the desert itself is quite diverse. large area occupy outcrops of ancient rocks. In other areas, the dune relief of shifting sands alternates with undulating pebbly plains. Often a "pavement" is formed on the surface, consisting of fragments of rocks or multi-colored pebbles. The most amazing formations of this kind are areas of rocky desert, covered with a black film of iron and manganese oxides (the so-called "desert tan"). Around oases and drying lakes there are saline clays with salt crusts on the surface. Trees grow only along the banks of rivers flowing down from the mountains. Various animals are found on the outskirts of the Gobi. The population is mainly concentrated in oases or near wells and wells. Railways and highways are laid through the desert.

The Gobi has not always been a desert. In the Late Jurassic and Early Cretaceous, rivers flowed here, depositing sandy-silt and gravel-pebble sediments. Trees grew in the river valleys, sometimes even forests. Dinosaurs flourished here, as evidenced by egg clutches discovered in the 1920s by expeditions from the American Museum of Natural History. From the end jurassic and during the Cretaceous and Tertiary natural conditions were favorable for the habitat of mammals, reptiles, insects and, probably, birds. It is also known that a man lived here, as evidenced by the finds of Neolithic, Mesolithic, Late and Early Paleolithic tools.

Big Pool.

The desert region of the Great Basin in the western United States occupies about half the area of ​​the physiographic province of the Basins and Ranges; it is bounded on the east by the Wasatch Range (Rocky Mountains), and on the west by the Cascade and Sierra Nevada ranges. On its territory fit almost the entire state of Nevada, partly - southern Oregon and Idaho, as well as part of eastern California. These are the most unfavorable areas for human life in North America. With the exception of a few oases, this is really a desert, where small depressions alternate with short mountain ranges. The depressions are usually endorheic, and many of them are occupied by salt lakes. The largest - Big Salt Lake in Utah, Pyramid Lake in Nevada and Mono Lake in California; all of them are fed by streams flowing down from the mountains. The only river, crossing the Great Basin - Colorado. The climate is arid, the amount of precipitation does not exceed 250 mm per year, the air is always dry. Summer temperatures are usually above 35°C, winters are quite warm.

In a large part of the Great Basin, water cannot be obtained even from wells. At the same time, the soils are quite fertile in places and can be used for agriculture under irrigation. However, the only area where irrigation has managed to develop desert lands is around Salt Lake City in Utah; in the rest of the territory Agriculture represented almost exclusively by cattle breeding.

The Great Basin is a vivid example of various types and forms of desert relief: in southern California there are vast fields of sand dunes, in Nevada - sloping accumulative plains (bajada), intermountain depressions with a flat bottom - bolsons (Spanish bolson - bag), slightly sloping denudation plains near at the foot of steep slopes - pediments, the bottoms of dry lakes and solonchaks. Near the city of Wendover in Utah, there is a vast flat plain (the former bottom of Lake Bonneville), where car races are held. Throughout the desert, there are multi-colored rocks of bizarre shapes cut by the wind, arches, through holes and narrow ridges with sharp ridges, separated by furrows (yardangs). The Great Basin is rich in minerals (gold and silver in Nevada, borax in California's Death Valley, common and Glauber's salt and uranium in Utah), and intensive exploration and development of deposits continues. In the south, the Great Basin merges into the Sonoran Desert, similar in appearance to the other Basin deserts, but most of it drains into the ocean. Sonora is located mainly in Mexico.

Patagonian desert region

stretches in a narrow strip at the foot and in the lower part of the eastern slope of the Andes in Argentina. Its driest part extends from the Tropic of the South to about 35°S, since all the moisture contained in air masses ah, coming from the Pacific Ocean, falls in the form of rain over the Andes, not reaching the eastern foothills. The population is extremely small. Summer (January) temperatures average 21°C, and average winter (July) temperatures range from 10 to 16°C. Mineral resources are limited, and due to inaccessibility, it is one of the least explored deserts in the world.

Tropical or trade wind deserts.

This type includes the deserts of Arabia, Syria, Iraq, Afghanistan and Pakistan; the exceptionally peculiar Atacama Desert in Chile; the Thar Desert in northwest India; vast deserts of Australia; Kalahari in South Africa; and finally, the greatest desert in the world - the Sahara in North Africa. Tropical Asian deserts, together with the Sahara, form a continuous arid belt stretching for 7200 km from Atlantic coast Africa to the east, with an axis approximately coinciding with the Tropic of the North; in some areas inside this belt it almost never rains. The regularities of the general circulation of the atmosphere lead to the fact that downward movements of air masses prevail in these places, which explains the exceptional aridity of the climate. Unlike the deserts of America, the Asian deserts and the Sahara have long been inhabited by humans who have adapted to these conditions, but the population density is very low.

Sahara Desert

extends from the Atlantic Ocean in the west to the Red Sea in the east, and from the foothills of the Atlas and the Mediterranean coast in the north to about 15°N. in the south, where it borders on the savannah zone. Its area is approx. 7700 thousand km 2. Average July temperatures over most of the desert exceed 32°C, average January temperatures range from 16 to 27°C. the nights are quite cold. Strong winds are frequent, which can carry dust and even sand far beyond Africa, in Atlantic Ocean or to Europe. The dusty winds originating in the Sahara are known locally as sirocco, khamsin and harmattan. Precipitation everywhere, with the exception of a number of mountainous regions, falls below 250 mm per year, and this happens very irregularly. There are several places where rains have never been recorded at all. During rains, usually torrential, dry channels (wadis) quickly turn into turbulent streams.

In the relief of the Sahara, a number of low and medium-altitude table heights stand out, above which isolated mountain ranges rise, such as Ahaggar (Algeria) or Tibesti (Chad). To the north of them are closed saline depressions, the largest of which turn into shallow salt lakes during the winter rains (for example, Melgir in Algeria and Dzherid in Tunisia). The surface of the Sahara is quite varied; vast areas are covered with loose sand dunes (such areas are called ergs), rocky surfaces are widespread, worked out in bedrock and covered with rubble (hamada) and gravel or pebbles (regi).

In the northern part of the desert, deep wells or springs provide water to oases, thanks to which date palms, olive trees, grapes, wheat and barley are grown. It is assumed that the groundwater that feeds these oases comes from the slopes of the Atlas, located 300–500 km to the north. In many parts of the Sahara, ancient cities were buried under a layer of sand; this may be indicative of a comparatively recent desiccation of the climate. In the east the desert is cut by the Nile valley; since ancient times, this river has provided residents with water for irrigation and created fertile soil, depositing silt during annual floods; the regime of the river changed after the construction of the Aswan Dam.

In the 1960s, oil production began in the Algerian and Tunisian sectors of the Sahara and natural gas. The main deposits are concentrated in the Hassi-Messaoud region (in Algeria). In the late 1960s, even richer oil fields were discovered in the Libyan sector of the Sahara. The transport system in the desert has undergone significant improvements. Several highways crossed the Sahara from north to south, but did not displace the time-honored camel caravans.

Arabian deserts

are considered the most typical on Earth. Their vast spaces are occupied by moving dunes and sandy massifs, and in the central part there are outcrops of bedrock. Precipitation is insignificant, temperatures are high, with large diurnal amplitudes common for deserts. Strong winds, sand and dust storms are frequent. Most of the territory is completely uninhabited.

Atacama Desert

located in northern Chile at the foot of the Andes on the Pacific coast. This is one of the driest areas on Earth; on average, only 75 mm of precipitation falls here annually. According to long-term meteorological observations, in some areas there was no rain for 13 years. Most of the rivers that flow from the mountains are lost in the sands, and only three of them (Loa, Copiapó and Salado) cross the desert and flow into the ocean. The Atacama Desert is home to the world's largest sodium nitrate deposit, 640 km long and 65–95 km wide.

Deserts of Australia.

Although there is no single "Australian desert" as such, the central and western parts of this continent with a total area of ​​​​more than 3 million km 2 receive less than 250 mm of precipitation per year. Despite such meager and irregular rainfall, most of this area has a vegetation cover dominated by very thorny grasses of the genus Triodia and acacia flat-leaved, or mulga ( Acacia aneura). In places, such as in the Alice Springs area, grazing is possible, although pasture forage productivity is very low and per head of large cattle 20 to 150 ha of pasture land is required.

Vast areas covered with parallel sandy ridges, having a length of up to several kilometers, are real deserts. They include the big sandy desert, the Great Victoria Desert, the Gibson, Tanami and Simpson Deserts. Even in these areas, most of the surface is covered with sparse vegetation, but their economic use hindered by lack of water. There are also large expanses of stony deserts that are almost completely devoid of vegetation. Any significant areas occupied by moving sand dunes are rare. Most of the rivers are filled with water episodically, and most of the territory does not have a developed runoff system.

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.

Deserts are areas of the earth's surface where, due to the too dry and hot climate, evaporation exceeds precipitation by many times, and therefore there is only a very meager flora and fauna; usually these are areas with low population density, and sometimes generally uninhabited. This term also applies to areas that are unfavorable for life due to the cold climate (the so-called cold deserts).

What are the causes of deserts? Deserts are located in places where moisture does not get. Many are either located far from the seas and oceans and are closed from them by mountains; or are close to the equator. The spiers of the mountains do not allow rain clouds to reach these lands and irrigate them with moisture. Near the equator, the climate is very dry due to the constant heat, which burns everything out and much more moisture is needed here than usual.

It is drought that is a sign of desert or semi-desert lands. And such lands are called an arid, that is, arid, zone. It does not include all areas of land where there are droughts, but only those where the life of man, plants and animals is under their influence and depends on them. This is such a geographical area of ​​​​the earth where the features of aridity (aridity) are most pronounced and reach such an extreme, beyond which the complete destruction of the biological life of the landscape begins. Arid lands on our planet are almost one third of the entire land surface. And this is 48 million km. sq. But less than 23% of the earth's surface belongs to real deserts.

general characteristics

Deserts are common in the temperate zone of the Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres. All of them are characterized by moistening conditions (the annual amount of precipitation is less than 200 mm, and in extra-arid regions - less than 50 mm; the moisture coefficient, which reflects the ratio of precipitation and evaporation, is 0-0.15). The relief of the deserts is diverse: there is a complex combination of highlands, hillocks and insular mountains with structural layered plains, ancient river valleys and closed lake depressions. The erosional type of landform formation is strongly weakened, eolian landforms (landforms formed under the action of wind) 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 adjacent plants varies from a few tens of centimeters to several meters or more) and usually covers less than 50% of the soil surface; practically absent under extraarid conditions.

Huge drainless depressions are found almost everywhere in deserts. Some of them are of great depth, for example, the Turfan basin - 154 m below the level of the World Ocean, Akchakaya in the north of the Karakum - 81 m, Karagiye on Mangyshlak - 132 m.

Climate

The main difference between deserts and other places is the almost complete absence of water: rivers, streams, fresh lakes. Rain falls 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.

Most of the world's deserts receive most of their precipitation in winter and spring, and only in a few - in the Gobi and large deserts of Australia - maximum amount Precipitation falls in the summer 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 up 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%.

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 are distinguished, first of all, by cold, very severe, but practically snowless winters, without thaws with frosts down to -40 °C.

More favorable climate in the deserts along the Atlantic and Pacific coasts, 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 - brikfielderi, 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.

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 huge force hit them on all protruding objects. The wind lifts huge masses of sand into the air, carrying them over long distances. The air temperature at this time rises to +50 ° C, accompanied by a sharp drop in humidity.

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 great height in the form of a rotating funnel, expanding upward. scary legends they talk about Saharan sandstorms - "samum", which means "poison" in translation.

It is deadly dangerous for a person to fall into sandy winds. 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. People try to protect themselves in all sorts of ways. But sandstorms rarely come back alive.

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. Mirages also occur in the early morning, before sunrise, when the air is saturated with fine dust. 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. 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.

Desert types

By surface type, all the deserts of the world can be divided into:

• sandy (erg);
• sandy-gravelly;
• rubble-gypsum (serir, reg);
• rocky (gamada, gobi);
• loess-clay (takyr);
• solonchak (dayas, sebkhs, shotts).

But in its pure form, each of the listed types of deserts is almost never found. Most often, the desert is a combination of stony and clay plateaus, dune sands, drainage basins, isolated table-like hills, solonchaks and takyrs (this is a relief form formed when saline soils dry out). In some places, impassable areas of the smallest, like flour, dust, which is called puff, are formed. And yet, each type of desert has its own, only its inherent features.

Sandy deserts (ergs)

Many imagine boundless distances of sand. Sandy deserts indeed - they took over more than half of all the arid territories of the world. True, they are also different. Some of them are long dune chains devoid of any vegetation, while others, on the contrary, are covered with rather dense grassy and shrubby vegetation.

Each sandy desert has its own wind regime, which determines the features of the construction of sand massifs, which can take various forms. Where the direction of the winds is changeable and chaotic, the dunes take on bizarre shapes, terrifying travelers with their obstruction.

Where the winds of one direction prevail, the dunes are higher than in those areas where the winds often change direction. The main type of such sandy relief in deserts is large parallel sandy ridges several hundred meters long, 10 m to 1 km wide and 5 to 60 m high on average. In some deserts, the height of dunes exceeds 300 m. Sometimes the ridges are connected by bridges and , when viewed from above, resemble a honeycomb. But it happens that not ridges are obtained from the sand, but randomly located mounds.

Where there are no plants, the sand, driven by the wind, sometimes moves over long distances. Loose sands are dangerous not only in motion, but also at rest. During movement, legs get stuck in such sand, each step requires great effort, and literally after some half an hour, if there is no habit and ability to walk on them, a person is not able to go further. Cars also make their way through the sands with difficulty, and even then only with front and rear driving wheels and wide cylinders - they have a larger support area, and the car does not get stuck in the sand so much.

The world's largest sandy desert is the Takla Makan in northwestern China, located between the Tien Shan and Tibet. Its length is 1200 km, and its width is up to 400 km.

In the rest of the deserts of the world, sand occupies a far from dominant place. The sands of the Sahara occupy only 10% of its area, and the rest are rocky plateaus - gammads, separated by shallow valleys and depressions. Desert areas with small gravel, often covered with the so-called desert tan (black shiny crust), are called serir.

The Arabian deserts are only 25% covered with sand, while the rest of the territory is characterized by rocky areas and takyrs.

Clay deserts

Clay deserts are widespread on all continents. These are huge, lifeless spaces stretching for many tens of kilometers, covered with a smooth, like a table, hard clay layer, cracked into four- and six-sided tiles and similar to a honeycomb.

They differ from sandy ones in much lower mobility and worse water properties. Their surface eagerly absorbs precipitation, however, the upper layers, when moistened, quickly swell and cease to pass water. Only the top layer of 2-5 cm is moistened. With the onset of drought, it dries quickly. But if there is sand in the composition of clay deposits, then the permeability of such soils increases, and a larger supply of water is formed in them.

Such areas in Central Asia are called takyrs, and in the Gobi - toyrims. When it rains or snow melts, the clay swells and becomes almost impermeable. At this time, takyrs turn into shallow muddy lakes. On small takyrs in the spring you can often find small small puddles fresh water- "kakk". But with the onset of a hot period, the water is filled with various putrefactive bacteria and becomes undrinkable. With the onset of dry and hot weather, the water in them evaporates.

As a rule, large takyrs are surrounded by high dune ridges. And on the border of takyr and sand arise small towns shepherds, in Central Asia they are called - "charva".

rocky deserts

One of the most common types of deserts are stony, gravel, gravel-pebble and gypsum deserts. They are united by roughness, hardness and surface density. The permeability of rocky soils is different. The largest pebble and rubble fragments, which occur rather loosely. They easily pass water, and precipitation quickly seeps to great depths inaccessible to plants. But surfaces are more common where pebbles or crushed stone are cemented with sand or clay particles. In such deserts, stony fragments lie densely, forming the so-called desert pavement.

The relief of rocky deserts is different. Among them there are areas of even and flat plateaus, slightly inclined or flat plains, slopes, gentle hills and ridges (elongated hills with a flat, slightly convex or wavy top and gentle slopes). On the slopes, ravines and gullies are formed.

The rocky deserts of the Sahara (hamadas), occupying up to 70% of its area, are often devoid of higher vegetation. Cushion-like shrubs of freodolia and limonastrum are fixed only on separate stone screes. The more humid deserts of Central Asia, although sparsely, are evenly covered with wormwood and saltworts. On the sandy-pebble plains of Central Asia, undersized thickets of saxaul are common.

In tropical deserts, succulents settle on rocky surfaces. In South Africa, these are cissuses with thick barrel-shaped trunks, spurges, "tree lily"; in the tropical part of America - a variety of cacti, yucca and agave. There are many different lichens in the stony deserts, covering the stones and coloring them in white, black, blood red or lemon yellow.

Scorpions, phalanges, geckos live under stones. Here, more often than in other places, the muzzle is found.

Salt marshes

Almost all desert soils are saline to some extent. Usually they are located along the banks and on the bottoms of salty drying lakes or in places where groundwater comes out. Where the concentration of salts is especially high, a hard crust of salt, cracked in places, forms on the surface of the salt marsh. Its thickness reaches 10-15 cm.

In addition to table salt (sodium chloride), calcium and potassium salts, mirabilite and gypsum can be found here. The largest solonchaks of this type are common in the Deshte-Kevir desert in Iran ("kevir" in Iranian means "saline marsh"). Here, salt layers form thick layers, split by cracks into polygons with a diameter of up to 50 m, separated by salt hummocks and partitions up to 1 m high.

Depending on the concentration of the brine and its depth under the surface, salt marshes are covered with a dense saline crust, cracked like takyrs, or they are a quagmire in which legs get stuck deep (it can completely drag a person or animal). Such salt marshes, as a rule, are impassable at any time of the year. Cortical solonchaks become sour only during the rainy season, and in the dry season their surface is even and hard.

Flora and fauna

The vegetation is diverse, which is due to the structure of the desert surface, the variety of soils, and often changing moisture conditions. In the nature of the desert vegetation of different continents, there are many common features arising in plants in similar habitat conditions: strong sparseness, poor species composition.

For the inland deserts of temperate zones, plant species of the xerophilic type are typical (xerophiles are organisms that live in conditions of extremely low humidity and cannot tolerate high humidity), including leafless shrubs and subshrubs (saxaul, dzhuzgun, ephedra, saltwort, wormwood, etc.). An important place in the phytocenoses of the southern subzone of deserts of this type is occupied by herbaceous plants - ephemera ( environmental group herbaceous annuals with a very short growing season (some full cycle its development in just a few weeks)) and ephemeroids (an ecological group of perennial herbaceous plants with a very short growing season, falling on the most auspicious time of the year).

The subtropical and tropical inland deserts of Africa and Arabia are also dominated by xerophilous shrubs and perennial grasses, but succulents also appear here. Barkhan sands and areas covered with a salt crust are completely devoid of vegetation.

The vegetation cover of the subtropical deserts of North America and Australia is richer (in terms of the abundance of plant mass, they are closer to the deserts of Central Asia) - there are almost no areas devoid of vegetation. On clay depressions between the ridges of sands, stunted acacia and eucalyptus trees predominate; the pebbly-rubbly desert is characterized by semi-shrub saltworts - quinoa, prutnyak, etc. In subtropical and tropical oceanic deserts (Western Sahara, Namib, Atacama, California, Mexico), succulent-type plants dominate.

On the salt marshes of the deserts of the temperate, subtropical and tropical zones, there are many general types. These are halophilic and succulent shrubs and shrubs (tamarix, saltpeter, etc.) and annual saltworts (hodgepodge, sveda, etc.).

Phytocenoses of oases, tugai (a specific mini-ecosystem that occurs along the never-ending river banks), large river valleys and deltas differ significantly from the main desert vegetation. The valleys of the desert-temperate zone of Asia are characterized by thickets of deciduous trees - turanga poplar, dzhida, willow, elm; for subtropical and tropical belts- evergreens - palm, oleander.

Deserts are inhabited mainly by specialized forms (with adaptations both morpho-physiologically and in lifestyle and behavior).

Deserts are characterized by fast moving animals, which is associated with the search for water and food, as well as protection from persecution. Due to the need for shelter from enemies and harsh climatic conditions, a number of animals have highly developed devices for digging in the sand (brushes made of elongated elastic hair, spines and bristles on the legs, which serve to shovel and throw sand; incisors, as well as sharp claws on the front paws - in rodents). They build underground shelters, or are able to quickly dig into loose sand. Many animals are able to run fast.

The desert fauna is characterized by a “desert” coloration - yellow, light brown and gray tones, which makes many animals hardly noticeable. Most of the desert fauna in summer leads night image life. Some hibernate, and in some species (for example, ground squirrels) it begins at the height of the heat (summer hibernation, directly turning into winter hibernation) and is associated with plant burnout and lack of moisture.

Moisture deficiency, especially drinking water, - one of the main difficulties in the life of the inhabitants of the desert. Some of them drink regularly and a lot, and therefore move in search of water over considerable distances (grouse) or move closer to water during the dry season (ungulates). Others drink water rarely or do not drink at all, limiting themselves to moisture obtained from food. A significant role in the water balance of many representatives of the desert fauna is played by metabolic water formed in the process of metabolism (large reserves of accumulated fat).

The desert fauna is characterized relatively a large number species of mammals (mainly rodents, ungulates), reptiles (especially lizards, dragons and monitor lizards), insects (dipterans, hymenoptera, orthoptera) and arachnids.

Amazing deserts

Deserts are characterized by amazing phenomena:

• "dry fog"
• "sound of the sun"
• "singing sands"
• "dry rain"
• mirages, etc.

"Dry fog" occurs when calm reigns in the desert and the air is filled with dust, visibility completely disappears.

"Dry rain" occurs when precipitation evaporates before reaching the ground due to high temperatures.

"Singing sands" occur when tons of moving sand make enchanting sounds: high, melodious, with a strong metallic tinge.

The "sound of the sun" occurs at 40 degrees of heat, when rocks burst in the desert, making a special sound.

The "whisper of the stars" occurs at 70-80 degrees below zero, when the water vapor exhaled by a person instantly turns into ice crystals. Colliding with each other, they begin to rustle.

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"Natural zones of the temperate zone of Eurasia" - Mixed forest. Taiga. Mixed and broadleaf forests. Steppes and forest-steppes. The southern taiga in the European part of Russia is changing mixed forests. Numerous and widespread: Brown bear, lynx, wolverine, chipmunk, marten, sable, squirrel, etc. Flora. Deserts and semi-deserts of the temperate zone.

"Desert Life" - Lions. Kalahari Desert. The Kalahari Desert is a large arid sandy area in Southern Africa. Hyenas. The Arabian Desert has the most sand and lots of sand dunes. Flamingos. Australian desert. The Kalahari supports a variety of fauna and flora. Nearly half of Australia is a desert. Cheetahs. Previously havens for wild animals from elephant to giraffe.

"Belts of Russia" - A small area of ​​the temperate zone is occupied by steppes. Representatives of the flora of the tundra. Sedge. Tundra from a bird's eye view. A small part of the temperate zone is occupied by mixed and broad-leaved forests. Representatives of the plant world of semi-deserts and deserts. Forest-steppe. Semi-desert. Sheep.

"Belts of the Earth" - Wet equatorial forest(EKP). Diversity of Earth's climates. Climate-forming factors are the reasons for the formation of the climate of any part of the earth's surface. Savannah (Subequatorial CP). In transitional climatic zones, seasonal precipitation falls unevenly. Climatic zones of the Earth. Recall the "properties of air masses".

"Climatic zones of the Earth" - Game "Finish the sentence." Large volumes of the troposphere, which have the same properties, are called ... The air shell of the Earth is called ... Climatic zones of the Earth. Equatorial Tropical Moderate Arctic (Antarctic). Warm-up on the map. Main climatic zones: Earth's climate is influenced by..

"Thermal zones of the Earth" - Physical, political and map of the hemispheres. Two - bend, unbend. Summary of the lesson. Thermal belts. 3. Half the globe. Sands. Three - three claps in the hands, Three nods with the head. Water. Work in a workbook. Globe. Belts of the Earth. Australia. Each card has its own ... . Guess the crossword. And the conditional image of the Earth's surface on a plane is called ....

desert

desert

areas of the earth's surface where, due to the too dry and hot climate, only very scarce flora and fauna can exist; usually these are areas with low population density, and sometimes generally uninhabited. This term also applies to areas that are unfavorable for life due to the cold climate (the so-called cold deserts).
Physical and geographical characteristics.
Aridity deserts can be explained by two reasons. The deserts of the temperate zone are arid because they are remote from the oceans and inaccessible to moisture-bearing winds. The dryness of tropical deserts is due to the fact that they are located in the area of ​​prevailing descending air flows coming from the equatorial zone, where, on the contrary, strong ascending currents are observed, leading to the formation of clouds and heavy precipitation. When descending, the air masses, already deprived of most of their moisture content, heat up, further moving away from the saturation point. A similar process also occurs when air currents cross high mountain ranges: most of the precipitation falls on the windward slope during the upward movement of air, and the areas located on the leeward slope of the ridge and at its foot are in the “rain shadow”, where the amount of precipitation is low.
Desert air is everywhere extremely dry. Both absolute and relative humidity are close to zero during most of the year. Rainfall is extremely rare and usually falls in the form of heavy showers. At the Nouadhibou weather station in the west of the Sahara, the average annual rainfall, according to long-term observations, is only 81 mm. In 1912, only 2.5 mm of rain fell there, but the next year one very heavy downpour brought 305 mm. High temperatures, which increase evaporation, also favor the aridity of deserts. The rain that falls over the desert often evaporates before reaching the surface of the earth. Most of the moisture that reaches the surface is quickly lost to evaporation, and only a small fraction seeps into the ground or runs off as surface streams. Water seeping into the soil replenishes groundwater and can travel long distances until it comes to the surface as a spring in an oasis. It is believed that most deserts can be turned into a flowering garden with the help of irrigation. This is generally true, but very great care is needed when designing irrigation systems in arid areas, where there is a great danger of large losses of water from irrigation canals and reservoirs. As a result of water infiltration into the soil, the groundwater table rises, which, under arid climate and high temperatures, leads to capillary pulling of groundwater to the surface and evaporation, and the salts dissolved in these waters accumulate in the near-surface soil layer, contributing to its salinization.
Temperatures. The temperature regime of the desert depends on its specific geographical location. Desert air, which contains very little moisture, does little to protect the land from solar radiation (unlike humid areas with higher cloudiness). Therefore, in the daytime, the sun shines brightly there and there is a sizzling heat. The usual temperatures are approx. 50 ° C, and the maximum recorded in the Sahara is 58 ° C. The nights are much cooler, as the soil heated during the day quickly loses heat. In hot tropical deserts, daily temperature amplitudes can be more than 40 ° C. In the deserts of the temperate zone, seasonal temperature fluctuations exceed daily ones.
Wind . A characteristic feature of all deserts are constantly blowing winds, often reaching very great strength. The main reason for the occurrence of such winds is excessive heating and the associated convective air currents, but local factors are also of great importance, for example, large landforms or position in relation to the planetary system of air currents. Wind speeds of up to 80–100 km/h have been recorded in many deserts. Such winds capture and transport loose material on the surface. This creates sand and dust storms - a common occurrence in arid regions. Sometimes these storms are felt at a great distance from the source of their origin. It is known, for example, that dust carried by the wind from Australia sometimes reaches New Zealand, which is 2,400 km away, while dust from the Sahara is transported more than 3,000 km and deposited in northwestern Europe.
Relief. Desert landforms differ significantly from those found in humid regions. Of course, there are mountains, plateaus and plains here and there, but in the deserts these large forms have a completely different appearance. The reason is that the desert relief is created mainly by the work of the wind and turbulent water currents that occur after rare showers.
Forms created by water erosion. There are two types of streams in the desert. Some rivers, the so-called. transit (or exotic), such as the Colorado in North America or the Nile in Africa, originate outside the desert and are so full of water that, flowing through the desert, they do not dry out completely, despite the large evaporation. There are also temporary, or episodic, streams that occur after intense rainstorms and dry up very quickly as the water completely evaporates or seeps into the soil. Most desert watercourses carry silt, sand, gravel and pebbles, and although they do not have a constant flow, it is they that create many of the features of the relief of desert areas. The wind also creates sometimes very expressive landforms, but they are inferior in importance to those worked out by water flows.
Flowing down steep slopes into wide valleys or desert depressions, streams deposit their sediment at the foot of the slope and form alluvial fans - fan-shaped accumulations of sediment with a top facing up the stream valley. Such formations are extremely widespread in the deserts of the Southwestern United States; cones often located nearby merge, forming at the foot of the mountains an inclined piedmont plain, which here is called "bajada" (Spanish bajada - slope, descent). Such surfaces are composed of loose deposits, in contrast to other gentle slopes, called pediments, and worked out in bedrock.
In deserts, water quickly flowing down steep slopes erodes surface deposits and creates gullies and ravines; sometimes erosional dissection reaches such a density that so-called. badlands ( see also BADLAND). Such forms, formed on the steep slopes of mountains and mesas, are characteristic of the desert regions of the whole world. One shower is enough to form a ravine on the slope, and once formed, it will grow with each rain. Thus, as a result of rapid gully formation, large sections of different plateaus were destroyed.
Forms created by wind erosion. The work of the wind (the so-called aeolian processes) creates a variety of landforms typical of desert areas. The wind captures dust particles, carries them and deposits them both in the desert itself and far beyond its borders. Where sand particles have been blown out, deep depressions several kilometers long or smaller shallow depressions remain. In places, air vortices create strange cauldron-shaped recesses with steeply overhanging walls or irregularly shaped caves. Wind-blown sand acts on bedrock ledges, revealing differences in their density and hardness; this is how bizarre forms arise, reminiscent of pedestals, spiers, towers, arches and windows. Often, the entire fine earth is removed from the surface by the wind, and only a mosaic of polished, sometimes multi-colored, pebbles remains, the so-called. "Desert Pavement" Such surfaces, purely "swept" by the wind, are widespread in the Sahara and the Arabian Desert.
In other areas of the desert there is an accumulation of sand and dust brought by the wind. Of the forms formed in this way, sand dunes are of the greatest interest. Most often, the sand that composes these dunes is composed of quartz grains, but dunes of limestone particles are found on coral islands, and sand dunes in the White Sands National Natural Monument ("White Sands") in New Mexico in the USA are formed by pure white gypsum . Dunes form where the air current encounters an obstacle in its path, such as a large boulder or bush. The accumulation of sand begins on the leeward side of the barrier. The height of most dunes is in the range from a few meters to several tens of meters, but dunes are known that reach a height of 300 m. If they are not fixed by vegetation, they move in the direction of the prevailing winds. As the dune moves, the sand is blown up the gentle windward slope and falls off the crest of the leeward slope. The speed of dune movement is low, on average 6–10 m per year; however, a case is known when in the Kyzylkum desert, with an exceptionally strong wind, the dunes moved 20 m in one day. When moving, the sand covers everything that is in its path. There are cases when entire cities were covered with sand.
Some dunes are heaps of irregularly shaped sand, while others, formed under the predominance of winds of a constant direction, have a clearly defined gentle windward slope and a steep (about 32 °) leeward slope. A special kind of dune is called dunes. These dunes have a regular crescent shape in plan, with a steep and high lee slope and pointed “horns” stretched in the direction of the wind. In all areas of the distribution of the dune relief, there are many depressions of irregular shape; some of them are created by eddy currents of air, others were formed simply as a result of uneven deposition of sand.
Temperate deserts usually located in the depths of the continents, away from the oceans. They occupy the largest area in Asia, the largest part of the world; North America is in second place. In many cases, such deserts are surrounded by mountains or plateaus, blocking access to humid sea air. Where high mountain ranges are close to the ocean and parallel to the coastline, as in western North America, the deserts come fairly close to the coast. However, with the exception of the desert areas of Patagonia, located in the rain shadow of the Andes in the south of South America, and the Sonoran Desert in Mexico, not a single temperate desert goes directly to the sea.
The temperatures of the deserts of the temperate zone show significant seasonal fluctuations, but it is difficult to name typical values, since these deserts have a large extent from north to south (in Asia and North America up to 15–20 ° in latitude). Summers in such deserts are usually warm, even hot, while winters tend to be cold; Winter temperatures can stay below 0°C for quite some time.
Consider the climate and relief of the deserts of Central Asia (on the territory of Kazakhstan, Uzbekistan and Turkmenistan) and the Gobi Desert in Mongolia, which are typical of the temperate zone. All these deserts are located in the interior regions of Asia, inaccessible to humid oceanic winds, since the moisture contained in them falls in the form of precipitation before reaching these regions. The Himalayas block the wet summer monsoons from the Indian Ocean, while the mountains of Turkey and Western Europe significantly reduce the amount of moisture coming from the Atlantic. In the Western Hemisphere, typical examples of temperate deserts are the deserts of the Great Basin in the southwestern United States and the deserts of Patagonia in Argentina.
Deserts of Central Asia include the Ustyurt plateau between the Aral and Caspian seas, the Karakum south of the Aral Sea, and the Kyzylkum southeast of it. These three desert regions form a vast inland drainage basin where rivers flow into the Aral or Caspian Sea. Three-quarters of the area is occupied by desert plains, bounded by the high mountain ranges of the Kopetdag, Hindu Kush and Alay. The Karakum and Kyzylkum are sandy deserts with dune ridges, many of which are fixed by vegetation. The annual amount of precipitation does not exceed 150 mm, but on mountain slopes it can reach 350 mm. Snow rarely falls on the plains, but is quite common in the mountains. Temperatures are high in summer, and in winter they drop to 2° ... -4° C. The main source of irrigation water is the Amudarya and Syrdarya rivers, which originate in the mountains. The most valuable varieties of cotton, wheat and other grains are grown on irrigated lands, but high evaporation contributes to soil salinization, which hinders the normal development of plants. From minerals, gold, copper and oil are mined.
Desert Gobi. Under this name, a vast desert region is known, the area of ​​\u200b\u200bwhich is approx. 1600 thousand km 2; it is surrounded on all sides by high mountains: in the north - Mongolian Altai and Khangai, in the south - Altyntag and Nanshan, in the west - Pamir and in the east - Greater Khingan. Within the large depression occupied by the Gobi desert, there are many small depressions in which water flowing from the mountains collects in summer. This is how temporary lakes are formed. The average annual rainfall in the Gobi is less than 250 mm. In winter, some snow occasionally falls on the lowlands. In summer, the temperature reaches 46° C in the shade, and in winter it sometimes drops to -40° C. Strong winds, dust and sand storms are common in these places. For many thousands of years, dust and silt have been carried by the wind to the northeastern regions of China, where powerful loess covers have formed as a result.
The relief of the desert itself is quite diverse. A large area is occupied by outcrops of ancient rocks. In other areas, the dune relief of shifting sands alternates with undulating pebbly plains. Often a "pavement" is formed on the surface, consisting of fragments of rocks or multi-colored pebbles. The most amazing formations of this kind are areas of rocky desert, covered with a black film of iron and manganese oxides (the so-called "desert tan"). Around oases and drying lakes there are saline clays with salt crusts on the surface. Trees grow only along the banks of rivers flowing down from the mountains. Various animals are found on the outskirts of the Gobi. The population is mainly concentrated in oases or near wells and wells. Railways and highways are laid through the desert.
The Gobi has not always been a desert. In the Late Jurassic and Early Cretaceous, rivers flowed here, depositing sandy-silt and gravel-pebble sediments. Trees grew in the river valleys, sometimes even forests. Dinosaurs flourished here, as evidenced by egg clutches discovered in the 1920s by expeditions from the American Museum of Natural History. From the end of the Jurassic through the Cretaceous and Tertiary, natural conditions were favorable for the habitat of mammals, reptiles, insects, and probably birds. It is also known that a man lived here, as evidenced by the finds of Neolithic, Mesolithic, Late and Early Paleolithic tools.
Big Pool. The desert region of the Great Basin in the western United States occupies about half the area of ​​the physiographic province of the Basins and Ranges; it is bounded on the east by the Wasatch Range (Rocky Mountains), and on the west by the Cascade and Sierra Nevada ranges. On its territory fit almost the entire state of Nevada, partly - southern Oregon and Idaho, as well as part of eastern California. These are the most unfavorable areas for human life in North America. With the exception of a few oases, this is really a desert, where small depressions alternate with short mountain ranges. The depressions are usually endorheic, and many of them are occupied by salt lakes. The largest are the Great Salt Lake in Utah, Pyramid Lake in Nevada and Mono Lake in California; all of them are fed by streams flowing down from the mountains. The only river that crosses the Great Basin is the Colorado. The climate is arid, the amount of precipitation does not exceed 250 mm per year, the air is always dry. Summer temperatures are usually above 35°C, winters are quite warm.
In a large part of the Great Basin, water cannot be obtained even from wells. At the same time, the soils are quite fertile in places and can be used for agriculture under irrigation. However, the only area where irrigation has managed to develop desert lands is around Salt Lake City in Utah; in the rest of the territory, agriculture is represented almost exclusively by cattle breeding.
The Great Basin is a vivid example of various types and forms of desert relief: in southern California there are vast fields of sand dunes, in Nevada - sloping accumulative plains (bajada), intermountain depressions with a flat bottom - bolsons (Spanish bolson - bag), slightly sloping denudation plains near at the foot of steep slopes - pediments, the bottoms of dry lakes and solonchaks. Near the city of Wendover in Utah, there is a vast flat plain (the former bottom of Lake Bonneville), where car races are held. Throughout the desert, there are multi-colored rocks of bizarre shapes cut by the wind, arches, through holes and narrow ridges with sharp ridges, separated by furrows (yardangs). The Great Basin is rich in minerals (gold and silver in Nevada, borax in California's Death Valley, common and Glauber's salt and uranium in Utah), and intensive exploration and development of deposits continues. In the south, the Great Basin merges into the Sonoran Desert, similar in appearance to the other Basin deserts, but most of it drains into the ocean. Sonora is located mainly in Mexico.
Patagonian desert region stretches in a narrow strip at the foot and in the lower part of the eastern slope of the Andes in Argentina. Its driest part extends from the Tropic of the South to about 35°S, since all the moisture contained in the air masses coming from the Pacific falls as rain over the Andes without reaching the eastern foothills. The population is extremely small. Summer (January) temperatures average 21°C, and average winter (July) temperatures range from 10 to 16°C. Mineral resources are limited, and due to inaccessibility, it is one of the least explored deserts in the world.
Tropical or trade wind deserts. This type includes the deserts of Arabia, Syria, Iraq, Afghanistan and Pakistan; the exceptionally peculiar Atacama Desert in Chile; the Thar Desert in northwest India; vast deserts of Australia; the Kalahari in South Africa; and finally, the greatest desert in the world - the Sahara in North Africa. Tropical Asian deserts, together with the Sahara, form a continuous arid belt, stretching 7200 km from the Atlantic coast of Africa to the east, with an axis approximately coinciding with the Northern Tropic; in some areas inside this belt it almost never rains. The regularities of the general circulation of the atmosphere lead to the fact that downward movements of air masses prevail in these places, which explains the exceptional aridity of the climate. Unlike the deserts of America, the Asian deserts and the Sahara have long been inhabited by humans who have adapted to these conditions, but the population density is very low.
Sahara Desert extends from the Atlantic Ocean in the west to the Red Sea in the east, and from the foothills of the Atlas and the Mediterranean coast in the north to about 15°N. in the south, where it borders on the savannah zone. Its area is approx. 7700 thousand km 2. Average July temperatures over most of the desert exceed 32°C, average January temperatures range from 16 to 27°C. the nights are quite cold. Strong winds are frequent, which can carry dust and even sand far beyond Africa, to the Atlantic Ocean or to Europe. The dusty winds originating in the Sahara are known locally as sirocco, khamsin and harmattan. Precipitation everywhere, with the exception of a number of mountainous regions, falls below 250 mm per year, and this happens very irregularly. There are several places where rains have never been recorded at all. During rains, usually torrential, dry channels (wadis) quickly turn into turbulent streams.
In the relief of the Sahara, a number of low and medium-altitude table heights stand out, above which isolated mountain ranges rise, such as Ahaggar (Algeria) or Tibesti (Chad). To the north of them are closed saline depressions, the largest of which turn into shallow salt lakes during the winter rains (for example, Melgir in Algeria and Dzherid in Tunisia). The surface of the Sahara is quite varied; vast areas are covered with loose sand dunes (such areas are called ergs), rocky surfaces are widespread, worked out in bedrock and covered with rubble (hamada) and gravel or pebbles (regi).
In the northern part of the desert, deep wells or springs provide water to oases, thanks to which date palms, olive trees, grapes, wheat and barley are grown. It is assumed that the groundwater that feeds these oases comes from the slopes of the Atlas, located 300–500 km to the north. In many parts of the Sahara, ancient cities were buried under a layer of sand; this may be indicative of a comparatively recent desiccation of the climate. In the east the desert is cut by the Nile valley; since ancient times, this river has provided residents with water for irrigation and created fertile soil, depositing silt during annual floods; the regime of the river changed after the construction of the Aswan Dam.
In the 1960s, oil and natural gas production began in the Algerian and Tunisian sectors of the Sahara. The main deposits are concentrated in the Hassi-Messaoud region (in Algeria). In the late 1960s, even richer oil fields were discovered in the Libyan sector of the Sahara. The transport system in the desert has undergone significant improvements. Several highways crossed the Sahara from north to south, but did not displace the time-honored camel caravans.
Arabian deserts are considered the most typical on Earth. Their vast spaces are occupied by moving dunes and sandy massifs, and in the central part there are outcrops of bedrock. Precipitation is insignificant, temperatures are high, with large diurnal amplitudes common for deserts. Strong winds, sand and dust storms are frequent. Most of the territory is completely uninhabited.
Atacama Desert located in northern Chile at the foot of the Andes on the Pacific coast. This is one of the driest areas on Earth; on average, only 75 mm of precipitation falls here annually. According to long-term meteorological observations, in some areas there was no rain for 13 years. Most of the rivers that flow from the mountains are lost in the sands, and only three of them (Loa, Copiapó and Salado) cross the desert and flow into the ocean. The Atacama Desert is home to the world's largest sodium nitrate deposit, 640 km long and 65–95 km wide.
Deserts of Australia. Although there is no single "Australian desert" as such, the central and western parts of this continent with a total area of ​​​​more than 3 million km 2 receive less than 250 mm of precipitation per year. Despite such meager and irregular rainfall, most of this area has a vegetation cover dominated by very thorny grasses of the genus Triodia and acacia flat-leaved, or mulga ( Acacia aneura). In places, such as in the Alice Springs area, grazing is possible, although the forage productivity of pastures is very low and 20 to 150 hectares of grazing land are required for each head of cattle.
Vast areas covered with parallel sandy ridges, having a length of up to several kilometers, are real deserts. They include the Great Sandy Desert, the Great Victoria Desert, the Gibson, Tanami and Simpson Deserts. Even in these areas, most of the surface is covered with sparse vegetation, but their economic use is hindered by a lack of water. There are also large expanses of stony deserts that are almost completely devoid of vegetation. Any significant areas occupied by moving sand dunes are rare. Most of the rivers are filled with water episodically, and most of the territory does not have a developed runoff system.
LITERATURE
Fedorovich B.F. The face of the desert. M., 1950
Babaev A. Desert as it is. M., 1980
Babaev A. G., Drozdov N. N., Zonn I. S., Freikin Z. G.