Deserts were formed as a result of uneven distribution of heat and moisture. And this happened because the air above the equator heats up more and, rising up and cooling, loses a large amount of moisture, which falls in the form of tropical showers. After this, in the uppermost layers of the earth's atmosphere, equatorial air begins to spread north and south, into the subtropical region. Gradually, the air masses descend to the heated earth's surface, they heat up even more, but there is no moisture in them anymore. This circulation of air masses occurs all year round.

As a result, the air becomes dry and hot - the average temperature in summer reaches 30-40 degrees and sometimes reaches 59 in the shade. The surface of the soil (sand and stone) sometimes heats up above 80 degrees. Rare precipitation - mostly heavy showers. Due to the high temperature, small rains do not reach the surface of the earth - the water evaporates on the way to it.

The driest areas of the world are the deserts of South America. On the Pacific coast, in the town of Iquique, only a millimeter of precipitation falls per year. And in the Nile River valley, near Aswan, for several years (1901-1905) there was only one rain in the form of a few drops!

Most of the world's deserts receive the most rainfall in winter and spring, and only in the Gobi and the great deserts of Australia in the summer.

When the sun disappears below the horizon in the evening, the air temperature drops by 30-35 degrees, and sometimes significantly more. The soil heats up more than the air during the day and then cools down more. In the morning, dew appears on the surface, and in winter, the desert is covered with a thick layer of frost.

Deserts occur not only in the subtropics, but also in the temperate zone, where there are arid areas, for example in Central Asia. There is very little precipitation here - 100-200 millimeters per year. Thus, atmospheric circulation (circular movement of air masses) and peculiar geographical conditions led to the formation of a desert zone north and south of the equator, between 15 and 45 degrees latitude. Most deserts are surrounded by or bordered by mountains. Mountains provide water to deserts - rivers flowing from the slopes irrigate the foothill plains and then disappear into the sands. Rivers carry a lot of sand, clay, and fine gravel to the flat desert areas, forming the surface layer. Over time, in some places a poor soil cover appears, saturated with salts and poor in organic matter. But more often the surface of deserts is covered with sand or rocky.

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The river flows quietly and smoothly across the plain, and on steep cliffs it accelerates its movement. The stream cuts deep into the soil and forms narrow gorges with steep and high walls. Water especially quickly erodes shores consisting of loose rocks. If the river’s path is blocked by mountains, it either goes around them or breaks through them, creating deep gorges and canyons. Sometimes…

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In this constellation, two bright stars are very close to each other. They received their name in honor of the Argonauts Dioscuri - Castor and Pollux - twins, sons of 3eus, the most powerful of the Olympian gods, and Leda, a frivolous earthly beauty, brothers of Helen the beautiful - the culprit of the Trojan War. Castor was famous as a skilled charioteer, and Pollux as an unsurpassed fist fighter...

The great Italian Galileo Galilei (1564-1642), who did a lot for the development of mathematics, mechanics, and physics, achieved amazing success in the study of celestial bodies. He became famous not only for a number of astronomical discoveries, but also for the enormous courage with which he defended the teachings of Copernicus, prohibited by the all-powerful church. In 1609, Galileo learned that a far-seeing device had appeared in Holland (as translated from Greek...

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The largest planet is named after the supreme god Olympus. Jupiter is 1310 times larger than Earth in volume, and 318 times larger in mass. In terms of distance from the Sun, Jupiter is in fifth place, and in terms of brightness it ranks fourth in the sky after the Sun, Moon and Venus. Through a telescope, a planet compressed at the poles is visible with a noticeable row...

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TYPES AND ORIGINDESERT EARTH

Introduction

Chapter 1. General information about the desert

1.1 Patterns of formation and distribution of deserts

1.2 Geographical features of the desert

1.3 Desert topography

1.4 Classification of deserts

1.5 Desert biota

Chapter 2. Characteristics of the largest deserts in the world

2.2 Deserts of Central Asia and Kazakhstan

2.3 Deserts of Central Asia

2.4 Deserts of the Hindustan Peninsula

2.5 Deserts of the Arabian Peninsula

2.6 North African Desert

2.7 Deserts of South Africa

2.8 Deserts of North America

2.9 Deserts of South America

2.10 Deserts of Australia

Chapter 3. Desert and man

3.1 Ecological-geographical and socio-economic aspects of the problem “desert and man”

3.2 Desert development

3.3 Desertification and nature conservation

Conclusion

Literature

Introduction

The problem of studying and developing the deserts of the world has recently attracted special attention of geographers from all countries. This was greatly facilitated by the activities of the Commission on the Arid Zone. Beginning in 1951, with the assistance of the International Geographical Union, it held a number of symposiums devoted to the most important problems of the study and development of the arid regions of the world; they were held in Ankara (1952), Karachi (1957), Madrid and Canberra (1959) and other cities.

The proceedings of the UNESCO Arid Zone Commission and symposiums are published in 30 issues of the Arid Zone Research series, containing valuable materials on the study and development of the world's deserts.

International conferences were convened at the initiative of individual countries: International Conference on Arid Areas in the Developing World (Tusan, Arizona, June 1969), International Conference on Arid Areas in Mexico in 1970.

In 2000, a major international conference on the problem of combating the encroachment of deserts was held in the United Arab Emirates, in which representatives of government public organizations from 70 countries of the world took part. 125 reports were heard and final recommendation documents were adopted. The reports stated that the threat of drought and desertification of fertile lands actually loomed over 110 countries of the world. Many of them are experiencing considerable difficulties in combating the advance of sands and are counting on international support, without which the situation could lead to catastrophic consequences. The United Nations Environment Program (UNEP) is urgently developing global and regional projects to assist developing countries and prevent environmental disasters. Similar conferences are held annually, and humanity is getting closer to achieving the goal of rational, mutually beneficial use of deserts with the environment.

The objective of this course work is to give a comparative overview of the natural features of the deserts of the globe, the results of the development of their natural resources, and also to discuss issues related to further plans for the study of arid territories.

The first chapter gives a general description of all types of deserts. One can notice the similarities in their geostructures, geomorphological processes and climatic features, and also note significant differences in their flora and fauna.

The second chapter assesses the specific features of the natural conditions of deserts, mainly sandy ones. It describes the nature, genesis of the aeolian relief and the processes of sand movement, characterizes the habitat in sandy deserts, and the environmental factors that determine organic life: the temperature and water regime of the sands, the geochemical features of arid regions.

The third chapter provides a general assessment of the natural resources of deserts and ways of using them. The problems of geographical study of the deserts of the world are also highlighted. In this work, 16 literature sources were used.

desert sandy geostructure natural

Chapter 1.General information about the desert

1.1 Patterns of formation and distribution of deserts

Desert is a type of landscape characterized by a flat surface, sparseness or absence of flora and specific fauna.

The process of formation and development of deserts is based, first of all, on the uneven distribution of heat and moisture on Earth, the zonality of the geographical envelope of our planet. The zonal distribution of temperatures and atmospheric pressure determines the specifics of the winds and the general circulation of the atmosphere. Above the equator, where the greatest heating of land and water occurs, ascending air movements dominate. Warm air rising above the equator, cooling somewhat, loses a large amount of moisture, which falls in the form of tropical showers. Then, in the upper atmosphere, the air flows north and south, towards the tropics. These air currents are called anti-trade winds. Under the influence of the rotation of the earth in the northern hemisphere, the antitrade winds bend to the right, in the southern hemisphere - to the left. Approximately above latitudes of 30-40C (near the subtropics), their deviation angle is about 90C, and they begin to move along parallels. At these latitudes, air masses descend to the heated surface, where they heat up even more, and move away from the critical saturation point. Due to the fact that in the tropics there is high atmospheric pressure all year round, and at the equator, on the contrary, it is low, a constant movement of air masses (trade winds) occurs at the surface of the earth from the subtropics to the equator. Petrov M.P.. Under the influence of the same deflecting influence of the Earth in the northern hemisphere, trade winds move from northeast to southwest, in the southern hemisphere - from southeast to northwest. Trade winds cover only the lower thickness of the troposphere - 1.5-2.5 km. The trade winds that dominate in equatorial-tropical latitudes determine the stable stratification of the atmosphere and prevent vertical movements and the associated development of clouds and precipitation. Therefore, cloudiness in these belts is very insignificant, and the influx of solar radiation is the greatest. As a result, the air here is extremely dry (relative humidity in the summer months averages about 30%) and extremely high summer temperatures. The average air temperature on continents in the tropical zone in summer exceeds 30-35C; Here the highest air temperature on the globe occurs - plus 58C. The average annual amplitude of air temperature is about 20C, and the daily range can reach 50C; the soil surface sometimes exceeds 80C. Precipitation occurs very rarely, in the form of showers. In subtropical latitudes (between 30 and 45C northern and southern latitudes), the amount of total radiation decreases, and cyclonic activity contributes to moistening and precipitation, confined mainly to the cold period of the year. However, sedentary depressions of thermal origin develop on the continents, causing severe aridity. Here, the average temperature in the summer months is 30C or more, but the maximum can reach 50C. In subtropical latitudes, intermountain depressions are the driest, where annual precipitation does not exceed 100-200 mm.

In the temperate zone, conditions for the formation of deserts occur in inland regions such as Central Asia, where precipitation falls less than 200 mm. Due to the fact that Central Asia is fenced off from cyclones and monsoons by mountain uplifts, a pressure depression forms here in the summer. The air is very dry, high temperature (up to 40C or more) and very dusty. Rarely penetrating here with cyclones, air masses from the oceans and the Arctic quickly warm up and dry out.

Thus, the nature of the general circulation of the atmosphere is determined by planetary features, and local geographical conditions create a unique climatic situation that forms a desert zone to the north and south of the equator, between 15 and 45C latitudes. Added to this is the influence of cold currents of tropical latitudes (Peruvian, Bengal, Western Australian, Canary and Californian). By creating a temperature inversion, cool, moisture-laden maritime air masses and easterly persistent wind pressure highs lead to the formation of coastal cool and foggy deserts with even less rainfall. Babaev A.G.

If land covered the entire surface of the planet and there were no oceans or high mountain rises, the desert belt would be continuous and its boundaries would exactly coincide with a certain parallel. But since land occupies less than 1/3 of the area of the globe, the distribution of deserts and their size depend on the configuration, size and structure of the surface of the continents. For example, Asian deserts spread far to the north - up to 48C north latitude. In the southern hemisphere, due to the vast water expanses of the oceans, the total area of the continents' deserts is very limited, and their distribution is more localized. Thus, the emergence, development and geographical distribution of deserts on the globe are determined by the following factors: high values of radiation and radiation, low amounts of precipitation or their complete absence. The latter, in turn, is determined by the latitude of the area, the conditions of the general circulation of the atmosphere, the peculiarities of the orographic structure of the land, and the continental or oceanic position of the area.

According to M.P. Petrov, deserts include territories with an extremely dry climate. Precipitation falls less than 250 mm per year, evaporation exceeds precipitation many times, agriculture is impossible without artificial irrigation, the movement of water-soluble salts predominates and their concentration on the surface, there is little organic matter in the soil.

The desert is characterized by high summer temperatures, low annual precipitation - usually from 100 to 200 mm, lack of surface runoff, often the predominance of sandy substrate and the large role of aeolian processes, groundwater salinity and migration of water-soluble salts in the soil, uneven amount of precipitation, which determines the structure , yield and feeding capacity of desert plants. One of the features of the distribution of deserts is the island, local nature of their geographical location. On no continent do desert lands form a continuous strip, like the Arctic, tundra, taiga or tropical zones. This is due to the presence within the desert zone of large mountain structures with their greatest peaks and significant expanses of water. In this regard, deserts do not completely obey the law of zonation [Fig. 1.].

Rice. 1. Deserts of the world, M.P. Petrov

In the northern hemisphere, the desert areas of the African continent lie between 15C and 30C latitude, where the world's largest desert, the Sahara, is located. In the southern hemisphere, they are located between 6 and 33C S, covering the Kalahari, Namib and Karoo deserts, as well as the desert areas of Somalia and Ethiopia. In North America, deserts are confined to the southwestern part of the continent between 22 and 24C N, where the Sonoran, Mojave, Gila, and other deserts are located. Large areas of the Great Basin and the Chihuahuan Desert are quite close in nature to the conditions of the arid steppe. In South America, deserts, located between 5 and 30C S, form an elongated strip (more than 3 thousand km) along the western, Pacific coast of the continent. Here, from north to south, stretch the deserts of Sechura, Pampa del Tamarugal, Atacama, and behind the Patagonian mountain ranges. The deserts of Asia are located between 15 and 48-50C N and include such large deserts as Rub al-Khali, Great Nefud, Al-Hasa on the Arabian Peninsula, Dasht-Kevir, Dasht-Lut, Dashti-Margo, Registan, Haran in Iran and Afghanistan; Karakum in Turkmenistan, Kyzylkum in Uzbekistan, Muyunkum in Kazakhstan; Thar in India and Thal in Pakistan; Gobi in Mongolia and China; Taklamakan, Alashan, Beishan, Tsaidasi in China. Deserts in Australia occupy a vast area between 20 and 34 C latitudes S. and are represented by the Great Victoria, Simpson, Gibson and Great Sandy deserts.

According to P. Meigs, the total area of arid territories is 48,810 thousand square meters. km [Table 1], that is, they occupy 33.6% of the earth's land, of which extra-arid accounts for 4%, arid - 15 and semi-arid - 14.6%. According to table. 1, the area of typical deserts, excluding semi-deserts, is about 28 million square meters. km, that is, about 19% of the earth's land area.

Table 1. Areas of arid territories by continent, million sq. km., P. Meigs

The ratio of arid areas to the area of continents is clearly shown in Fig. 2.

Fig.2. Arid continental regions, P. Meigs

Extra-arid zone. Precipitation less than 100 mm; deprived of vegetation cover, excluding ephemeral plants and shrubs along the beds of watercourses. Agriculture and animal husbandry (except in oases) is impossible. This zone is a pronounced desert with possible droughts for one or several years in a row.

Arid zone. Precipitation 100-200 mm. Sparse, sparse vegetation, represented by perennial and annual succulents. Rain-fed agriculture is impossible. Nomadic cattle breeding zone.

Semi-arid zone. Precipitation 200-400 mm. Shrub communities with intermittent herbaceous cover. Area of cultivation of rain-fed agricultural crops (“dry” farming) and livestock raising.

According to the above data on the amount of precipitation in arid territories, we draw a conclusion. Moisture is a decisive factor determining the biological productivity of arid lands and the living conditions of the population.

1.2 Geographical features of deserts

Most of the world's deserts were formed on geological platforms and occupy the oldest land areas. Deserts in Asia, Africa and Australia are usually located at altitudes from 200-600 m above sea level, in Central Africa and North America - at an altitude of 1 thousand m above sea level. Deserts are one of the landscapes of the Earth, which arose as naturally as all others, thanks primarily to the peculiar distribution of heat and moisture over the earth's surface and the associated development of organic life and the formation of biogeocenotic systems. A desert is a specific geographical phenomenon, a landscape that lives its own special life, has its own patterns, and, during development or degradation, has its own inherent features and forms of change. Most deserts are surrounded by mountains or, more often, bordered by mountains. In some places, deserts are located next to young high mountain systems, in others - with ancient, heavily destroyed mountains. The first include the Karakum and Kyzylkum deserts, the deserts of Central Asia - Alashan and Ordos, the South American deserts; The latter should include Northern Sahara. Fedorovich B.A.

Mountains and deserts are areas of formation of liquid runoff, which comes to the plain in the form of transit rivers and small, “blind” mouths. Underground and sub-channel flow, which feeds their groundwater, is also of great importance for deserts. Mountains are areas from which destruction products are removed, for which deserts serve as a place of accumulation. Rivers supply a lot of loose material to the plain. As a result of centuries-old work of rivers, the plains are covered with a multi-meter layer of alluvial sediments. The rivers of the sewage areas carry a huge mass of blown and debris material into the World Ocean. According to M.P. Petrov, the surface deposits of deserts are of the same type everywhere. Deserts are characterized by some similar natural processes that are prerequisites for morphogenesis: erosion, water accumulation, blowing and aeolian accumulation of sand masses. It should be noted that similarities between deserts are found in a large number of characteristics. The differences are less noticeable and limited to a few examples. The differences are most associated with the geographical location of deserts in different thermal zones of the Earth: tropical, subtropical, temperate. The first two zones contain the deserts of North and South America, the Near and Middle East, India, and Australia. Among them are continental and oceanic deserts. In the latter, the climate is moderated by the proximity of the ocean, which is why the differences between heat and water balances, precipitation and evaporation are not similar to the corresponding values that characterize continental deserts. However, for oceanic deserts, the ocean currents washing the continents - warm and cold - are of great importance. The warm current saturates the air masses coming from the ocean with moisture, and they bring precipitation to the coast. The cold current, on the contrary, intercepts the moisture of air masses, and they arrive on the mainland dry, increasing the aridity of the coasts. Oceanic deserts are located off the western coasts of Africa and South America.

Continental deserts are located in the temperate zone of Asia and North America. They lie inside the continents (deserts of Central Asia) and are distinguished by arid and extra-arid conditions, a sharp discrepancy between the thermal regime and precipitation, high evaporation, and contrasts in summer and winter temperatures. The differences in the nature of deserts are also influenced by their altitude.

Mountain deserts, like those located in intermountain depressions, are usually characterized by increased climate aridity. The variety of similarities and differences between deserts is primarily due to their location at different latitudes of both hemispheres, in the hot and temperate zones of the Earth. In this regard, the Sahara may have more similarities with the Australian desert and more differences with the Karakum and Kyzylkum in Central Asia. Equally, deserts formed in the mountains may have a number of natural anomalies among themselves, but there are even more differences with the deserts of the plains. Differences occur in average and extreme temperatures during the same season of the year, in the timing of precipitation (for example, the eastern hemisphere of Central Asia receives more precipitation in the summer from monsoon winds, and the deserts of Central Asia and Kazakhstan - in the spring). The sparseness of the cover largely determines the low humus content in desert soils. This is also facilitated by dry air in the summer, which prevents active microbiological activity (in winter, fairly low temperatures slow down these processes).

Arctic desert(ice desert) - natural (landscape) zone - part of the Arctic geographical zone, confined to many islands of the Arctic Ocean basin and individual sections of the mainland coast. There are numerous glaciers (Greenland, Spitsbergen, Novaya Zemlya, the Canadian Arctic Archipelago, islands near Antarctica and others). It has low air temperatures in winter (up to?50°C), on average?30?C in February and +1?C in July. It is formed not only due to the low temperatures of high latitudes, but also due to the reflection of heat (albedo) during daylight hours from snow and ice. The annual amount of precipitation is up to 400 mm. The widespread distribution of permafrost soils. The spaces are covered with rubble and fragments of stones with crustacean lichens. The soils are primitive, thin (1 - 5 cm), low in humus, with a patchy (island) distribution, mainly only under vegetation. The flora and fauna are not rich. Small isolated areas with moss-lichen and herbaceous vegetation look like peculiar oases among polar snows and glaciers. In the Arctic desert, several types of flowering plants are found: polar poppy, foxtail, buttercup, saxifrage, etc. Among the animals, lemmings, arctic foxes and polar bears are common, and in Greenland - musk ox. There are numerous bird colonies. To protect and study the Arctic desert, a number of national parks and reserves have been created, including Greenland National Park, Wrangel Island, etc. Ivanov N.N.

1.3. Desert terrain

Peculiarities of desert relief, according to N.P. Neklyukova, are determined by its formation in a climate characterized by a very small (no more than 200 - 250 mm) amount of precipitation with enormous evaporation and large daily amplitudes of air temperature fluctuations (30 - 35°). Surface runoff is either completely absent or occurs after short-term heavy rainfalls that occur once every few years. Temporary flows create channels that are devoid of water most of the time. On waterproof rocks, streams of storm precipitation, overloaded with debris, turn into mud-stone streams - mudflows. Large valleys have only “transit” rivers, starting in the mountains or on neighboring plains with a humid climate. The erosional dissection of the surface is very weak. Streams flowing across the surface of the desert do not reach the sea, but end in lakes or are lost in the sands. Characterized by extensive drainage basins. If groundwater is shallow in a basin, springs come to the surface and oases appear.

Climatic conditions contribute to vigorous, physical weathering (mainly temperature), which plays a very important role in the formation of the relief of deserts in general and especially the relief of rocky deserts. Intensive weathering is accompanied by the activity of the wind, which blows out loose products of rock destruction (deflation) and thereby creates conditions for their further destruction. The air flow, lifting dust particles, sand, and sometimes small rock fragments from the surface and moving them, grinds and polishes obstacles encountered along the way (corrosion process). Corrosion is most pronounced in the ground layer 1.5 - 2 m high, i.e. where the number of transported particles is greatest. Therefore, various mushroom-shaped rock shapes often appear. The ability of the wind to transport particles depends on its speed and the size of the particles. At a wind speed of up to 6.5 m/sec, it is capable of transporting sand and grains of sand with a diameter of up to 1 mm; at a speed of 20 m/sec, the diameter of the transported particles increases to 4 - 5 mm; hurricane-force winds lift small pebbles. Of all particles moved by the wind, up to 90% rise to a height of no more than 11 cm above the surface.

The relief-forming activity of wind consists of interconnected processes of destruction of irregularities, transfer of loose sediments and the creation of new, accumulative forms of relief.

Wind activity is manifested everywhere to one degree or another, but it leads to the formation of a special aeolian relief only with a combination of intense weathering, dry climate, the presence of loose sediments not fixed by vegetation and constant or frequent winds of significant strength. These conditions are primarily met by deserts.

Morphological types of deserts. Differences in desert morphology depend on the irregularities created by internal forces, on the lithology of the surface deposits, and on the influence of wind on this surface.

The deserts are rocky, sandy and clayey.

Rocky deserts developed mainly in mountainous desert areas. The surface of the flat rocky deserts is covered with gravelly material - products of the destruction of highlands. Near the mountains, the rubble that covers the desert surface can be carried by water currents. Protrusions of hard rocks, individual rocks, cliffs under the influence of wind and with the participation of weathering form bizarre shapes: cornices, columns, pillars, mushrooms, etc. Often there are such forms as blowing cauldrons and stone grates. The influence of the structure in the relief is very clear in rocky steps. Rocky deserts are common in North Africa (the Arabs call them “hamads”) and Asia. Fedorovich B.A.

Sandy deserts- the most common type of lowland deserts. Sands have different origins. These may be ancient alluvial deposits (for example, the sands of the Turkmen Karakum desert, deposited by the Amu Darya) and products of destruction of bedrock (for example, the sands of the central part of Alashan). In sandy deserts, the role of wind in shaping the relief is especially significant; eolian sandy forms dominate in them. At the same time, relief forms of unconsolidated (dune) and semi-consolidated sands are distinguished.

The relief of loose sands is predominantly that of subtropical deserts. Its most characteristic form is dunes. Dunes are asymmetrical crescent-shaped sand hills located perpendicular to the prevailing wind direction, with sharp ends (“horns”) forward. Their windward slopes are gentle (5-15?), their leeward slopes are steep (30-35?). The height of the dunes ranges from 1 - 2 to 15 m, and in some places (Libyan Desert) higher dunes are formed. The diameter of the dunes reaches 40-70 m, sometimes 140 or more meters. The dune chains are located perpendicular to the direction of the prevailing winds and have the appearance of asymmetrical waves (a gentle windward slope). The height of dune chains in the deserts of Central Asia reaches 100 m, in the deserts of Central Asia 60-70 m, length - from several hundred meters to 10-12 km. The distance between the ridges of neighboring chains is 150-3500 m. The formation and direction of dune chains is influenced by the relief; they can occur where the wind is reflected from an obstacle (from hills, from mountain ranges). A 2-3 km high ridge influences the direction of sand ridges at a distance of up to 100 km. Dune chains move noticeably when the winds of opposite directions displacing each other have unequal strength, but these chains are much less mobile than single dunes.

The ridges have an asymmetrical shape with a slope steepness of no more than 20°. Their height is very different and ranges from 1 - 3 m to hundreds of meters. Sand ridges reach large sizes in the Sahara. Longitudinal sand ridges arise as a result of the simultaneous processes of sand fluttering and its deposition. Jets of air in the wind flow move in a corkscrew fashion. This is mainly due to unequal heating of the slopes of the ridges. The air moves towards the heated slope, above which its upward movement occurs. At the same time, it transfers sand particles from the interridges to the slopes of the ridge.

The area of the earth's surface under sandy deserts is very large. In Africa alone it is 1,000,000 square meters. km. Huge sand massifs are located in the deserts of Asia: Karakum, Kyzylkum, Muyunkum, Balkhash sands, Sary-Ishikotrau, Taklamakan, etc. Large areas are occupied by sandy deserts in Iran, India, and the Arabian Peninsula. Colossal areas of sandy deserts in Australia and South America.

Clay deserts are formed on a surface covered with fine-earth sediments. Small clay particles are carried out by temporary flows and deposited in relief depressions or on foothill plains. When the water dries, these particles form a crust, in places covered with efflorescence of crystallized salts. Clay deserts are most often located in separate areas within sandy deserts, but they can also cover large areas (for example, in the northeastern and northwestern parts of Kyzylkum). They are usually sloping plains. The area of clay deserts on Earth is generally not much less than the area of sandy deserts. Significant areas of clayey deserts are found in North America, where they occupy depressions between ridges in mountainous regions. They occupy large areas in Central and Central Asia. Among the clay deserts in negative forms of relief, areas arise clay-salt marshes deserts. Salt marshes located in depressions with close-lying, highly mineralized groundwater are called sors (blinders). Litters are often subject to increased fluttering.

In Central Asia, areas of clayey - saline desert with a waterproof surface that cracks into polygons when drying are called takyrs. Sand brought to the surface of the takyr often forms single dunes. Neklyukova N.P.

The relief of deserts, which seems simple at first glance, turns out to be very complex and varied upon closer examination.

1.4 Desert classification

In arid territories, despite their apparent monotony, there is not at least 10-20 square meters. km of area within which the natural conditions would be exactly the same. Even if the topography is the same, the soils are different; if the soil is the same type, then the water regime is not the same; if there is a single water regime, then different vegetation, etc. Due to the fact that the natural conditions of vast desert territories depend on a whole complex of interrelated factors, the classification of desert types and their zoning is a complex matter.

There are classifications of deserts according to their geographical characteristics, they are more informative. One of these is presented in a table. 4.

Table 4. Main geographical characteristics of the deserts of the world, Ivanov N.N.

Name	Geographical position	Area, thousand sq. km.	Prevailing absolute heights, m	Absolute maximum temperature, C	Absolute minimum temperature, C	Average annual precipitation, mm. Hg
Central Asia and Kazakhstan
Karakum	37-42С N; 57-65С east
Ustyurt and Mangyshlak	42-45С N; 51-58С east
Kyzylkum	42-44С N; 60-67С east
Aral Kara-Kums	46-48С N; 57-65С east
Betpak-Dala	44-46С N; 67-72С east
	43-44С N; 67-73С east
central Asia
Taklamakan	37-42С N; 76-88С east
	39-41С N; 101-107С east
	40-42С N; 91-100С east
	38-40С N; 107-111С east
	36-39С N; 92-97С east
	42-47С N; 98-118С east
Iranian plateau
Dasht-Kevir	33-36С N; 52-57С east
Dasht-Lut	28-33С N; 56-60С east
Registan	29-32С N; 64-66С east
Arabia Peninsula
Rub al-Khali	17-23С N; 46-55С east
Big Nefud	27-30С N; 39-41С east
	21-28С N; 44-48С east
Syrian desert	31-34С N; 37-42С east
North Africa
	15-28С N; 15 W - 33 N E
Libyan desert	23-30С N; 18-30С east
Nubian desert	15-23С N; 31-37С east
South Africa
	19-29N S; 13-17С east
Kalahari	21-27N S; 20-27С east
	32-34N S; 18-26С east
Hindustan Peninsula
	26-29С N; 69-74С east
	30-32С N; 71-72С east
North America
Big Pool	36-44С N; 112-119N W
	35-37С N; 116-118N W
	28-35С N; 109-113N W
	22-30С N; 105-108С west
South America
	22-29N S; 69-70С west
Patagonian	39-53N S; 68-72N W
Australia
Bolshaya Peschanaya	18-23N S; 121-128С east
	23-25N S; 121-128С east
Great Victoria Desert	25-29N S; 125-130С east
	24-27N S; 135-138С east

1.5 Desert biota

All desert inhabitants, no matter how diverse they are, have one thing in common: they are all, to a greater or lesser extent, adapted to the lack of water, food, shelter and sudden temperature fluctuations.

Fig.3. Yucca shortifolia

Desert plants. Desert plants have a number of characteristic adaptations. For example, Yucca shortifolia [Fig. 3.] can dry out without any harm to itself. Old leaves dry out completely and die, but young leaves, although they also dry out and turn brown, continue to grow with the next precipitation.

Drought resistance is the most common method of protection. Some plants shed their leaves, others develop very long roots that draw moisture from the depths. Some desert plants, on the contrary, develop an extensive superficial root system that quickly absorbs moisture from short-term rains and pre-dawn dew. Many plants store excess moisture in leaves, like aloe, or in stems, like cacti [Fig. 4.]. In cacti, both the shape of the plant (cylindrical or spherical) and the reduction of leaves into spines, lumps and villi protect against herbivores and reduce evaporation. Babaev A.G., Freikin Z.G.

Fig.4. Cactus

Desert insects. Insects are very numerous in the desert and play an important role in the life of its inhabitants, who feed exclusively on insects, Zaletaev V.S. . The adaptations of these small desert inhabitants to arid conditions are varied. One of them, such as harvester ants, is not physiologically adapted to desert conditions; they make nests deep underground, where the outside temperature does not reach them. They make only short-term forays to the surface to stock up on seeds.

Amphibians and reptiles. The dry conditions of deserts prevent many species of amphibians from living in the desert, but the spadefoot frog is an example of adaptability. It is one of the very few desert amphibians that lives most of its life in burrows, emerging at night to hunt and waiting for rare rains to mate and lay eggs. Reptiles are another group of desert creatures that probably thrive here. When the temperature rises during the day, they hide either in burrows or on plants. But at night they seek shelter from the cold. Babaev A.G. . Perhaps the most numerous desert reptiles are snakes, but since most are nocturnal, they are less noticeable than the lizards that scurry here and there throughout the day.

Fig.5. Sychik-elf

Desert birds. There are many birds found in deserts - from the tiny elf owl [Fig. 5.] to the flightless giant ostriches. Desert birds feed on seeds or green plants (saxaul jay, bush jay, budgerigar, desert lark, ostrich and others). But among them there are many predators -

Mediterranean falcon, elf owl (up to 15 cm), ground cuckoo. Birds, as a more mobile type of animal, fly into deserts from neighboring more favorable territories, especially during the rains and autumn-spring period. Zaletaev V.S.

Desert mammals. There are fewer mammals, like birds, especially large ones, in deserts than in other zones, but still, surprisingly, many of them manage to survive in such harsh conditions thanks to adaptations in behavior, metabolism and structure.

Rodents are the most common small inhabitants of the desert. Most of them are active at night and spend the day in burrows where the humidity is higher. Many of them do not drink water, but extract it from plant foods. It is also known that some rodents obtain moisture by oxidizing dietary carbohydrates stored as fat. Zaletaev V.S.. Relatively few predators live in deserts: the cat family is represented only by the cheetah [Fig. 6.]. Babaev A.G., Freikin Z.G.

Fig.6. Cheetah

Chapter 2.Xcharacteristics of the largest deserts in the world

Aleshkovskyssands-- a sandy massif located in Ukraine 30 km east of the city of Kherson. The massif measures about 15 km in diameter. Aleshkovsky sands are the largest sand massif in Europe. They consist of endless dunes, about 5 m high, and sparse vegetation [Fig. 7.]

Fig.7. Aleshkovsky Sands

The name comes from the old (before 1925) name of the city of Tsyurupinsk - Aleshki. The Aleshkovo sands in their current form appeared very recently. Sands have always existed in the lower reaches of the Dnieper, but their advance was hampered by the cover of steppe vegetation. In the 18th and also in the 19th centuries, sheep began to be brought here (Baron Falz-Fein, the founder of the Askania-Nova reserve alone, owned huge herds of up to a million heads) which destroyed the grass, freed the sands, and wind erosion gave them the opportunity to expand. According to P. Kostychev, who studied the Aleshkovsky sands in the 1880s, no more than a hundred years before that time, the Aleshkovsky sands were completely fixed by vegetation, sometimes woody. Kostychev considers the opinion “that the appearance of sands occurred due to changes in the climatic conditions of the area” to be completely unfounded (“there is not the slightest evidence for this”). “The formation of shifting sands and the obstacle to their consolidation are determined by one reason: “intensified by the grazing of livestock.” The “Journal of Generally Useful Information” for 1837 indicates that the area of forests on the sands of the lower Dnieper, which amounted to more than 5,000 hectares in 1802, fell to almost zero by 1832.) Experimental work on fixing the sands began at the end of the 18th century, but the large-scale nature acquired in 1830-1840 in connection with activities to intensify afforestation and the formation of Aleshkovsky forestry. The period of general land surveying and allotment of land to peasants (1859-1890) turned into a disaster for forests and the area of sand increased significantly. Now the sands are stopped at the edges by huge artificial forests, with a total area of about 100 thousand hectares. The Dnieper sands themselves occupy an area of 161,200 hectares, and with inter-area lands - 210,000 hectares. Despite the fact that Aleshkovsky sands are often called a desert, this is not entirely true. Based on the temperature regime and amount of precipitation, they can be classified as semi-deserts. However, climatic conditions are such that in summer the sand heats up to 75 degrees. The air above the sands warms up more than above the surrounding area, air humidity decreases, so in the summer raindrops quickly evaporate, and the intensity of rain (according to some unconfirmed reports) here is somewhat less than in Kherson itself, which is located on the other side of the Dnieper. Although the sands are now contained by forests, they sometimes carry over the outskirts of nearby villages.

The main factors influencing the ecological situation in the region are a decrease in forest area and a decrease in the sand layer. The decrease in forest area is caused by deforestation, fires, and the natural death of pine plantations that are incapable of self-reproduction and can lead to the expansion of the sand massif. On the other hand, the uncontrolled use of sand for construction purposes and the placement of agricultural facilities in the region leads to a decrease in groundwater levels and their pollution, which can deprive residents of the region of high-quality drinking water and negatively affect the forest.

http://www.wiki.kherson.ua/

2.2 Deserts of Central Asia and Kazakhstan

Semi-deserts and deserts of Central Asia and Kazakhstan are located on the Turan Plain. The deserts extend from the Kopetdag and Paropamiz mountains framing the plain in the south to 48°N. and east of the Kazakhstan Sea up to the foothills of the Dzungarian Alatau, Tien Shan and Pamir-Altai. Within these vast boundaries there are deserts of different types in geological and landscape terms: sandy deserts (Karakum, Kyzylkum, Moyynkum, Aral Karakum, Big and Small Badgers, Volga-Ural), rocky (Betpak-Dala), gravelly (Ustyurt), clayey (Golodnaya steppe), Solonchakovaya (Kelkor, Dead Kultuk, etc.) Among the different types of deserts, remnant mountains rise, occupied by rocky and clayey deserts. The Kazakh small hills, Betpak-Dala and remnant mountains are the most ancient formations. The characteristic features of the desert relief include dry riverbeds and drainage basins, including very large ones. Some of them are basin-shaped in shape (Sarykamysh, Barsakelmes, etc.). the deepest depression - Karagiye (-132 m below sea level) - is located on the territory of Western Kazakhstan; other depressions are linear: Unguz, Western Uzboy. The life of sands and the natural processes occurring on their surface are closely related to the desert climate and, most of all, to the wind regime and the moistening of the sand. The wind moves bare sands, changes their shape, creates areas of sand removal or deflation, areas of dragging and areas of accumulation - accumulation. Wet sands are not mobile. Shifting sands under the influence of winds of different speeds form diverse forms of relief, genetically related to each other. The following sequence is distinguished: wind-sand flow, stationary accumulation of sand in the vortex zone and the formation of ripples on it, sand waves, ridges, dunes, dune chains and ridges, dune fields, etc. Petrov M.P. .

The climate of Central Asia is characterized by relatively long duration of sunshine, aridity and continentality. This is explained by its geographical location at the northern border of the subtropics, far from the oceans and inside the Eurasian continent, as well as atmospheric circulation, which contributes to the formation of predominantly cloudless and partly cloudy weather. On the plains of Central Asia, the duration of sunshine is high - 2500-3000 hours per year. The climate of Central Asia is often divided into two periods: from mid-May to mid-October - warm and dry, the rest of the year - wet and cold. The deserts of Kazakhstan are located to the north, their climate is characterized by longer and colder winters and shorter summers; shorter growing seasons and frost-free periods, more precipitation. Among the negative features of the desert climate, we note unstable weather in spring and winter, low precipitation, and excessively high summer temperatures, at which farming is possible only with artificial irrigation. Depending on the conditions of formation, the water content, length, and regime of rivers vary, as do the possibilities for their economic use. The central and western regions of Central Asia are the poorest in rivers. In Central Asia there are rivers glacial-snow fed (Amur Darya, Syr Darya, Ili), snow-rain fed (Murgab, Atrek), spring-rain fed (small rivers flowing from the Kopet Dag and other medium-high mountains). Within the Turanian Plain there are many small temporary rivers that form in the spring due to snow and rain feeding. They are especially numerous in Kazakhstan. Some rivers, such as Turgai and Sarysu, do not dry out completely, but only in certain places. Dry riverbeds are a noticeable phenomenon in the topography of deserts, its hydrographic network and watersheds. Dry riverbeds in the deserts of Central Asia and Kazakhstan are very long and seem to be rivers left without water. These are Western Uzboy and Kelif Uzboy in the Karakum Desert, Zhanadarya in the Aral Sea region. There are few large lakes in the desert. They only form where rivers with high flows carry their waters into deep basins.

Most desert plants belong to xerophytes, succulents, and halophytes and are highly adaptable to local conditions due to their morphological and physiological characteristics. Desert plants are exposed to dry and low-water conditions and find sufficient moisture and are protected from excessive heating and drying out; evaporation of moisture is reduced to a minimum.

The fauna of the deserts of Central Asia and Kazakhstan is very unique. It is distinguished by the great adaptability of animals to desert conditions, the protective coloration of the animal, a relatively poorer species composition, and the predominance of nocturnal activity of animals. When forming the structure of the animal world, it is important that mountains and plains are located here in close proximity and animals move freely from one natural zone to another. The deserts of Central Asia are home to the jackal, hyena, desert lark, large lizard monitor lizard, poisonous efa snake, sand boa, cobra, arrow snake, many birds fly from Kazakhstan and Siberia. The fauna of the sandy desert is richer than the fauna of clay, gypsum, and gravelly. In the sandy desert there are desert raven, saxaul jay, desert warbler, desert shrike, widow sandpiper, tolai hare, many rodents (gerbils, yellow and slender-toed ground squirrels, comb-toed and ruff-footed jerboas), long-eared hedgehog, many lizards, steppe turtles, at night butterflies fly - cutworms, beetles, mosquitoes, salpugs, scorpions, tarantula spiders, snakes leave their traces on the sand. The wolf has been greatly exterminated in the desert. During spring and autumn migrations, flocks of ducks, geese, coots, cranes, etc. appear in the desert zone. Among desert animals there are species that are gradually disappearing, these include: gray monitor lizard, goitered gazelle, poisonous snakes and others. Zaletaev V.S.

2.3 Deserts of Central Asia

Central Asia is a region of high plains and highlands framed by high climate-divided ridges. The dry climate characteristic of arid regions is formed here at great distances, often in isolation from Atlantic and Pacific air masses. The surface of the deserts is composed of aeolian sands, loess, as well as sand and pebble deposits; on the foothill plains there is proluvium. Central Asia is poor in surface water. In many places there are dry riverbeds, or sauries, confined to basins. Within Central Asia, there are ancient alluvial plains (Taklamakan in the Tarim Basin, Alashan in Northern China, Kuzupchi sands in Ordos), deserts of Tertiary and Cretaceous structures (parts of Dzungaria, Tsaidam, Alashani, Ordos), stony and rubble deserts on the site of destroyed and leveled ancient mountains (Beishan, Gashun and Mongolian Gobi). In the west of Central Asia, sandy deserts predominate, while in the central part there are rocky and sandy-pebble deserts. Deserts do not represent one continuous territory, but are dissected by mountain uplifts. Petrov M.P.

Alashan Desert occupies a depression lying between Nanshan and Gobi Altai. The absolute height is 800 m or more. Along with tectonic forms in the form of separate ridges, there are accumulative forms - chalk sand-pebble plains, as well as erosional forms - from dry channels and aeolian accumulative forms in the form of dune sands.

Dzungaria- a plain located in the east about 300 m. Here you can find small hilly uplifts of ancient crystalline rocks, gravel-pebble plains, takyr and takyr-like soils, salt marshes, hummocky sands overgrown with desert vegetation, and dune sands exposed to dispersal. Sandy deserts are located in the center and south of Dzungaria; on the southern outskirts, fixed sands turn into mobile ones.

Gobi - located between the mountains of the Mongolian Altai and Khangai, Eastern Tien Shan, Altyntag, Beishan and Yinshan. It stretches from west to east for 1750 km with a width of 600 km. Although the Gobi as a type of desert is found quite often in Central Asia, its proper name nevertheless refers to the Eastern Gobi, located in the north of Central Asia [Fig. 8.]

Fig.8. Gobi Desert

The Eastern Gobi is a plain lying in the east with an average height of about 1000 m. The flat terrain alternates with ridges and dry valleys. 200 mm of precipitation falls. The groundwater is slightly saline and lies shallow, feeding lakes and springs. The landscape is dominated by deserts and semi-deserts, but where there is more precipitation, steppes are formed.

The deserts of Central Asia lie in the temperate zone and belong to arid regions with cold winters and maximum precipitation in summer. Average annual air temperatures in the deserts of Central Asia range from 2.5C in the highlands of Tsaidam to 11.6C in Kashgar. The average July temperature in Tsaidam is plus 17.9C, in Chechnya - plus 27.3C. In other deserts, temperatures fluctuate within these limits. Precipitation per year is less than 100 mm. The eastern part of Central Asia up to Beishan is weakly influenced by the easterly monsoons and therefore receives the most precipitation in summer (in Alashan, 219 mm).

The fauna of Central Asia is small in species composition; Endemism at the species level is significant, and there are also endemic species among rodents. Only in this region lives the only modern representative of the camelid family in the Old World - the Bactrian camel. The basis of the rodent world is made up of jerboas; on dense soils, ground hares, the jumping jerboa, and the Mongolian jerboa are common. In addition to jerboas, gray and Djungarian hamsters are widespread in the deserts of Central Asia. Two species of gerbils, the midday and the clawed gerbil, inhabit sandy deserts. The small tolai hare is common in the sandy deserts of the region. Ungulates are not numerous. Only the gazelle is common, large herds of which are still found in sandy deserts. Over the past decade, the Przewalski's horse has completely disappeared from its former habitats in the Western Gobi and Dzungaria. Predators in the deserts of Central Asia are also few in number (the polecat, the steppe cat, and occasionally you can see traces of a fox and a wolf). The most noticeable birds are the larks (gray and larger Mongolian). Babaev A.G., Freikin Z.G.

2.4 Deserts of the Hindustan Peninsula

The deserts of Hindustan are confined to its western part and occupy significant areas. They are located in the vast ancient alluvial plain of the Indus and its tributaries, extending into the Deccan Plateau. There are two sandy deserts here - Thar and Thal and the small sandy-clayey desert Pyat.

Thar Desert located on the border of India and Pakistan [Fig. 9.] Its area is about 300 thousand square meters. km. The desert belongs to the type of sandy deserts of the subtropical zone in the north and tropical in the south. Most of the desert is covered with loose sands, on which areas of fixed or mobile dunes have formed. 90% of the territory is occupied by aeolian sands. Dunes occupy 58% of the area. The climate of the Thar Desert is dry and continental. Average annual precipitation varies from 105 to 500 mm. The distribution of precipitation is uneven.

Fig.9. Thar Desert

Precipitation falls towards the west. If the summer monsoon is strong enough to penetrate most of the desert, light rain falls as a consequence of convective currents of moist rising air. And in winter, sometimes several tens of mm of precipitation fall as a result of the movement of cyclones. In summer, the average daily maximum temperature is usually 40C, in winter - plus 22-28C. The average minimum temperature varies from 24C in summer to 4C in winter.

Groundwater lies too deep from the surface. Most of these waters are not suitable for water supply. Kunin V.N. In the Thar Desert, four types of soil formations predominate: thick, saline clayey alluvium on vast, seasonally flooded plains; sandy massifs north of the Rann; loamy, often silty modern alluvium of the Indus River in the west. Strong monsoon winds from the southwest and powerful dust storms carry away fine-grained fractions of sand and dust, leaving larger particles in place, resulting in increasingly sandy soils to the west of the Arabian ridge.

1.1 Patterns of formation and distribution of deserts

Desert is a type of landscape characterized by a flat surface, sparseness or absence of flora and specific fauna.

Rice. 1. Deserts of the world, M.P. Petrov

Table 1. Areas of arid territories by continent, million sq. km., P. Meigs

The ratio of arid areas to the area of continents is clearly shown in Fig. 2.

Fig.2. Arid continental regions, P. Meigs

Extra-arid zone. Precipitation less than 100 mm; deprived of vegetation cover, excluding ephemeral plants and shrubs along the beds of watercourses. Agriculture and animal husbandry (except in oases) is impossible. This zone is a pronounced desert with possible droughts for one or several years in a row.

Arid zone. Precipitation 100-200 mm. Sparse, sparse vegetation, represented by perennial and annual succulents. Rain-fed agriculture is impossible. Nomadic cattle breeding zone.

Semi-arid zone. Precipitation 200-400 mm. Shrub communities with intermittent herbaceous cover. Area of cultivation of rain-fed agricultural crops (“dry” farming) and livestock raising.

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The reasons for the origin of deserts have not yet been determined. Yes, they could not be defined under the dominance of the concept of mass attraction. The concept of electromagnetic interaction of celestial bodies easily explains this problem.

It must be said right away that the formation of deserts is very long process. Probably up to a thousand years. And it all starts with climate change, which could occur throughout the history of the Earth or after the drift of the entire earth's crust; either rapid continental drift early in Earth's history or after slower continental drift already during our era.

Let us take as a basis for our reasoning the largest desert on Earth - the Sahara. Without a doubt, the Sahara was once a fertile place on Earth. But a drift of the North and South Poles occurred, i.e. the drift of the entire earth's crust or the drift of the continents, and Africa, together with the Sahara, ended up where it is now. Or almost there, if you consider that, say, 1000 years after that, this continent gradually drifted to its current location. And the process of desertification of the Sahara began. It began because, due to the daily change in the angle of inclination of the northern end of the Earth's rotation axis to the Sun - at the culmination of the Sun over the oceans or from the Sun - at the culmination of the Sun over the continents over the Sahara region, the Northeast wind began to blow constantly. (See chapters: “Causes of movements of the Earth’s rotation axis in space, changes in the speed of rotation of the Earth around its axis and the consequences of these changes” and chapter: “Causes of the formation of trade winds”). This is a dry high pressure anticyclone. If we take the World Atlas and look at the natural zones of the world, we will notice that the zone of semi-deserts and deserts on the map of the Earth extends from the semi-deserts and deserts of Mongolia and China northeast stripe to the southernmost borders of the Sahara Desert. In the southern hemisphere, a dry, heavier Southeast wind blows through the deserts of Australia and the Southwestern deserts of Africa.

This dry, heavier North-East wind in the Northern Hemisphere and the similar South-East wind in the Southern Hemisphere, day after day, month after month, year after year, for centuries or more, first dries the top layer of soil, evaporates and drains swamps and lakes, and then - at a speed of at least 10 m/s, using the principle of spraying, sucks moisture from the ground through capillaries, lowering the groundwater level so that the root system of almost all trees and shrubs reaches the groundwater - for semi-deserts and all plants for deserts.

Having exposed and dried up some territory, the wind, when exceeding a certain speed threshold of approximately 10 m⁄s, creates “dust” (sand) storms and for hundreds, and maybe thousands of years, lifts particles of the fertile soil layer into the atmosphere and transports this fertile layer is thousands of kilometers long. That. the fertile layer of soil from the Sahara, by the same Northeast wind, was transported and sank partially to the bottom of the Atlantic Ocean off the West coast of Africa in such a layer that in this area of the Atlantic Ocean, over a huge water area up to 500 km from the coast, the depth of the Atlantic Ocean is from 100 meters to 2 km, and then - nearby the depth is already up to 6 km and more. In this area at the bottom of the Atlantic Ocean lies much of the fertile soil carried away by dust storms from the Sahara. Part of the fertile layer, carried away by dust storms from the Sahara, crossed the entire Atlantic Ocean and settled in the Antilles and the southern United States, as well as in the countries of Central America and northern South America.

All other semi-deserts and deserts on Earth were formed in a similar way.