Australia is the smallest continent on the globe, located in the southern hemisphere. Australia's area with islands is less than 8 million square meters. km, population - about 23 million people.

The western and southern coasts of the mainland are washed by the Indian Ocean, the northern ones are the Timor and Arafur Seas of the Indian Ocean, the eastern ones are the Coral and Tasman Seas of the Pacific Ocean. The extreme points of Australia: in the north - Cape York, in the west - Cape Steep Point, in the south - Cape Southeast, in the east - Cape Byron. The distance from the northernmost to the southernmost points of the mainland is 3200 km, from the western to the eastern - 4100 km. Parallel to the eastern coast, the Great Barrier Reef stretches for 2300 km.

The coast of the mainland is poorly indented. There are large bays of Great Australian in the south and Carpentaria in the north. The northern part of Australia has two of the largest peninsulas, Cape York and Arnhemland. This continent includes the adjacent islands - Tasmania, Melville, Kangaroo, etc.

The mainland lies on the ancient Australian platform, which becomes the East Australian folded belt... The average height of Australia is 215 m above sea level, and most of the mainland is occupied by plains and up to 95% of the territory is below 600 m. In the eastern part of the mainland along the coast, the Great Dividing Range stretches, which includes several flat-topped mountain systems. In the western part of the continent there is a plateau with a height of up to 500 m with mesas and ridges, in the central part there is a lowland with a large Lake Eyre. On the territory of the mainland there are deposits of minerals such as coal and brown coal, copper, iron ore, bauxite, titanium, polymetallic and uranium ores, diamonds, gold, natural gas, oil.

The main part of Australia's territory is located in the tropical climatic zone, the northern regions are in the equatorial zone (with a hot climate and frequent summer rains), the southern regions are in the subtropics (with a predominance of precipitation in winter). In the middle of the continent, 70% of the territory is dominated by a desert and semi-desert climate. The east coast has a hot tropical maritime climate with rainfall in the summer. Average annual precipitation decreases from east to west.

Large river systems of the mainland - Murray, Darling, Flinders. A characteristic feature of Australia is the presence of screams - rivers that fill with water only after heavy rains.

On the vast interior spaces of the mainland, there are the Great Gibson Desert, Victoria, the Great Sandy Desert, etc. Salt lakes can often be seen here. Around the deserts there is a belt of semi-deserts with bushes. In the northern, eastern and southeastern regions of the semi-desert are replaced by savannas. In the mountainous areas and along the coast, forests of palms, tree ferns and eucalyptus grow. Among the wild animals in Australia, there are large numbers of rabbits, pigs, and wild dogs. Among the endemic animals there are many marsupial forms (kangaroos, wombats, marsupial wolves, marsupial moles).

The entire territory of the mainland and the island of Tasmania is occupied by the country of the Australian Union. The state is divided into six states: Victoria, New South Wales, Queensland, Western Australia, South Australia, Tasmania. The number of indigenous people is only 2% of the total population, the rest of the inhabitants are descendants of Europeans and Asians who colonized the mainland after its discovery in the 17th century. High level development Agriculture and the mining industry brought the country to a leading position as a supplier of wheat, coal, gold, iron ore to the world market.

The modern river network, lake and artesian basins were formed within each of them, mainly at those stages of the development of nature, when Gondwana had already disintegrated, and the continents existed in isolation from each other, therefore, the similar features of the hydrosphere of the Southern Tropical continents are explained mainly by the similarity of modern natural conditions.

Among the sources of water supply for water bodies, rainfall is absolutely dominant due to the fact that South America, Africa and Australia are located for the most part in equatorial-tropical latitudes. Ice and snow supply is of some importance only for mountain rivers and lakes in the Andes and the East Australian mountains.

The regime of rivers flowing in similar climatic regions on different continents has a certain similarity. So, the rivers of the equatorial regions of South America and Africa and the eastern shores in the tropical zone of all three continents are full of water all year round. On the rivers of the subequatorial belt, the summer maximum is well expressed, and in the areas of the Mediterranean type of climate - the winter maximum flow.

Lakes in arid and semi-arid regions are similar in properties. They, as a rule, are highly mineralized, do not have a constant coastline, their area varies within wide limits depending on the supply, often lakes dry up completely or partially, and salt marshes appear in their place.

However, these features practically limit the similarity of the water bodies of the southern continents. Significant differences in the properties of the inland waters of the southern continents are explained by differences in the history of the formation of the hydrographic network at the last stages, in the structure of the surface, in the ratio of the areas of arid and humid climatic regions.

First of all, the continents differ sharply from each other in terms of water content. The average runoff layer in South America is the largest in the world - 580 mm. For Africa, this figure is about three times lower - 180 mm. Africa occupies the penultimate place among the continents, and the last (not counting Antarctica, where there is no hydrographic network usual for the continents) belongs to Australia - 46 mm, more than ten times less than for South America.

Large differences can be seen in the structure of the hydrographic network of the continents. Areas of internal flow and closed areas occupy about 60% of Australia and 30% of Africa. In South America, such areas make up only 5-6% of the territory.

This is due to both climatic features (in South America, there are relatively few arid and semi-arid regions), and with differences in the structure of the surface of the continents. In Africa and Australia, large and small basins play an important role in the relief. This contributes to the formation of centers of internal flow, such as, for example, Lake Chad, the Okavango Basin in Africa, Lake Eyre in Australia. Such a relief structure also affects the aridization of climates, which in turn determines the predominance of closed-drainage areas in low-water regions of the continents. There are almost no closed basins in South America. Small areas with internal drainage or completely devoid of surface waters there are in the Andes and Precordillera, where they occupy intermontane basins with a dry climate.

The history of the development of the hydrographic network is also important. Neotectonic movements in South America were predominantly inherited. The pattern of the river network was already determined at an early stage. geological history platform part of the mainland.

The largest waterways - the Amazon, Orinoco, Parana, Parnaiba, San Francisco, and their main tributaries occupy most of the axial zones of the ancient syneclises. The ascending neotectonic movements along the peripheral parts of the river basins contributed to the incision of the erosion network and the drainage of the existing lakes. Only lake-like extensions in the valleys of some rivers have survived from them.

In Africa, the most active ascending neotectonic movements are confined to the continent's margins. This led to a significant restructuring of the river systems. In the recent past, the areas of the internal runoff regions were apparently much larger than they are now.

Vast lakes occupied the bottoms of many basins, including Congo, Okavango, Kalahari, Chad, Middle Niger, and others. They collected water from the sides of the basins. Short, deep rivers flowing from the well-irrigated rising margins of the continent, in the process of backward erosion, intercepted part of the flow of these basins. It is likely that this happened, for example, in the lower reaches of the Congo and the Niger, in the middle reaches of the Nile. Lake Chad has lost part of its basin and shrank in size, and the bottoms of other basins have completely lost lakes. This is evidenced by lacustrine sediments in the central regions of vast inland depressions, the presence of internal deltas, an undeveloped equilibrium profile in some parts of river valleys, and other signs characteristic of the results of such a process.

In Australia, due to the widespread arid climatic conditions, more or less full-flowing short rivers flow from the elevated margins in the east and north of the continent into the seas of the Pacific and Indian oceans.

On the west coast south of 20 ° S. NS. river beds are filled with water only during rather rare, mainly winter rains. The rest of the time, the rivers of the Indian Ocean basin turn into chains of small reservoirs connected by weak under-channel runoff. In the south, the karst Nullarbor Plain is generally devoid of surface runoff. The only relatively long river in Australia - Murray (2570 km) flows in the southeast. It has a distinct summer maximum runoff, but this river does not dry up in winter either. The tributary of the r. Murray - p. The Darling is almost the same length, in the middle and lower reaches it flows through arid regions, does not receive any tributaries, and in dry time there is no runoff through it. All inland areas of the continent with a continental tropical and subtropical climate are practically devoid of runoff into the ocean, and most of the year are generally waterless.

Rivers of the Southern continents

A number of rivers of the southern continents are among the largest in the world. First of all, this is the Amazon - unique in many properties. The river system is unmatched: the river carries 15-17% of the entire river flow of the Earth into the ocean. It desalinates sea water at a distance of up to 300-350 km from the mouth. The channel width in the middle reaches is up to 5 km, in the lower reaches - up to 20 km, and the main channel in the delta is 80 km wide. The water depth in some places is over 130 m. The delta begins 350 km before the mouth. Despite a slight drop (from the foot of the Andes to the confluence with, it is only about 100 meters), the river carries out into the ocean great amount suspended sediment (estimated at up to a billion tons per year).

The Amazon begins in the Andes with two sources of the rivers - Maranyon and Ucayali, receives a huge number of tributaries, which themselves are large rivers, comparable in length and water flow rate to Orinoco, Parana, Ob, Ganges. The rivers of the Amazon system - Zhurua, Rio Negro, Madeira, Purus, etc. - for the most part of their course are typically flat, meandering, slowly flowing. They form the widest floodplains with swamps and many oxbows. The slightest rise in water causes spills, and with an increase in precipitation or during high tides or surge winds, the bottoms of the valleys turn into huge lakes. It is often impossible to determine which river the floodplain, branches, oxbows belong to: they merge with each other, forming "amphibious" landscapes. It is not known what is more here - land or water. Such is the appearance of the western part of the vast Amazonian lowland, where muddy rivers carrying fine earth are called rios brancos - "white rivers". The eastern part of the lowland is narrower. The Amazon here flows along the axial zone of the syneclise and retains the same flow pattern as above. However, its tributaries (Tapajos, Xingu, etc.) flow down from the Guiana and Brazilian highlands, cut through outcrops of solid rocks and form rapids and waterfalls 100-120 km from the confluence of the main river. The water in these rivers is clear, but dark from the organic matter dissolved in it. These are Rios Negros - "Black Rivers". A powerful tidal wave enters the mouth of the Amazon, which is here called vice. It has a height of 1.5 to 5 m and with a roar with a wide front of tens of kilometers moves upstream, damming the river, destroying the banks and washing off the islands. The tides do not allow the delta to grow, since the ebb currents carry the alluvium into the ocean and deposit it on the shelf. The effect of the tides is felt 1400 km from the mouth. In the rivers of the Amazonian basin, there is a unique world of aquatic plants, fish, freshwater mammals. The river is full-flowing all year round, as it receives tributaries with a summer maximum flow from both the Northern and Southern hemispheres. The river arteries connect the inhabitants of the Amazon with the rest of the world - sea vessels rise along the main river for 1,700 km (however, the channel in the delta has to be deepened and cleaned of sediment).

The second major river on the continent, Parana, is significantly inferior to the Amazon in terms of the length and area of ​​the basin, and especially in terms of water content: the average annual water discharge at the mouth of the Amazon is more than 10 times higher than that of the Parana.

The river has a difficult regime. In the upper reaches, there is a summer flood, and in the lower reaches, an autumn one, and the fluctuations in discharge can be very significant: deviations from the average values ​​are almost 3 times in either direction. Catastrophic floods also occur. In the upper course, the river flows along a lava plateau, forming numerous rapids and waterfalls on its steps. On its tributary - r. Iguazu, near the confluence of the main river, is one of the largest and most beautiful waterfalls in the world, bearing the same name as the river. In the middle and lower reaches, the Parana flows along the flat Laplat lowland, forming a delta with 11 large branches. Together with r. Uruguay The Parana flows into the La Plata estuary. The muddy waters of the rivers can be traced in the open sea 100-150 km from the coast. Sea vessels rise upstream up to 600 km. There are a number of large ports on the river.

The third significant river in South America is the Orinoco.Its regime is typical for rivers of the subequatorial climate: the difference between water discharge in dry and wet seasons is very significant.

During the period of especially high floods, the discharge at the top of the delta can be more than 50 thousand m 3 / s, and in the dry season of a dry year, it decreases to 5-7 thousand m 3 / s. The river originates in the Guiana Highlands and flows through the Orinoco Lowland. Before the mouth of the left tributary - Meta, there are a number of rapids and rapids on the main river, and in the middle reaches of the Orinoco it turns into a real flat river, 200 km before the mouth, it forms a vast swampy delta with 36 large branches and numerous channels. On one of the left tributaries of the Orinoco - r. Casiquiare, the phenomenon of classical bifurcation is observed: about 20-30% of its waters are carried out to the Orinoco, the rest enter through the upper reaches of the river. Rio Negro in the river basin. Amazon. Orinoco is navigable 400 km up from the mouth for ocean-going ships, and in the wet season river ships can pass up to the river. Guaviar. The left tributaries of the Orinoco are also used for river navigation.

On African continent the most full-flowing river. Congo (the second largest in the world after the Amazon). With the Amazon river. Congo bears great similarities in many ways. This river is also full-flowing throughout the year, as it flows a considerable distance in the equatorial climate and receives tributaries from both hemispheres.

In the middle reaches of the river. Congo occupies the flat, boggy bottom of the basin and, like the Amazon, has a wide valley, a winding channel, many branches and oxbows. However, in the upper reaches of the river. Congo (on this stretch of more than 2000 km long, it is called Lualaba) sometimes forms rapids with a steep fall, then flows calmly in a wide valley. Under the very equator, the river descends from the ledges of the plateau into the basin, forming a whole cascade of Stanley Falls. In the lower reaches (length - about 500 km), the Congo breaks through the South Guinean Upland in a narrow deep valley with numerous rapids and waterfalls. They are collectively referred to as Livingstone Falls. The mouth of the river forms an estuary, the continuation of which is an underwater canyon with a length of at least 800 km. Only the lowest section of the current (about 140 km) is accessible to sea-going vessels. In the middle reaches of the Congo, it is navigable for river vessels, and waterways are widely used in the countries through which this river and its large tributaries flow. Like the Amazon, the Congo is deep throughout the year, although it has two rises associated with floods on its tributaries (Ubangi, Kasai, etc.). The river has a huge hydropower potential, which is just beginning to be used.

The Nile is considered the longest river artery on Earth (6671 km), has a vast basin (2.9 million km 2), but its water content is ten times less than other large rivers.

The source of the Nile is the river. Kagera flowing into Lake Victoria. Coming out of this lake, the Nile (under various names) crosses plateaus and forms a series of waterfalls. The most famous waterfall Kabarega (Murchison) with a height of 40 m on the river. Victoria Nile. After passing through several lakes, the river reaches the plains of Sudan. Here, a significant part of the water is lost for evaporation, transpiration, and filling of depressions. After the confluence of the river. El-Ghazal river is called the White Nile. Khartoum White Nile merges with Blue, originating in Lake Tana in the Ethiopian Highlands. Most of the lower course of the Nile runs through the Nubian Desert. There are no tributaries, water is lost for evaporation, percolation, and is disassembled for irrigation. Only a small part of the runoff reaches the Mediterranean Sea, where the river forms a delta. Neil has a difficult regime. The main water rise and floods in the middle and lower reaches occur in the summer-autumn period, when precipitation falls in the Blue Nile basin, which brings 60-70% of the water into the main river in summer. A number of reservoirs have been built to regulate the flow. They protect the Nile Valley from floods, which used to happen quite often. The Nile Valley is a natural oasis with fertile alluvial soils. No wonder the river delta and its lower valley are one of the centers ancient civilization... Before the construction of dams, navigation on the river was difficult due to low water levels and the presence of six large rapids (cataracts) between Khartoum and Aswan. Now the navigable sections of the river (using canals) are about 3000 km in length. There are a number of hydroelectric power plants on the Nile.

In Africa there are also large rivers of great natural and economic importance: the Niger, Zambezi, Orange, Limpopo, etc. Victoria Falls on the river is widely known. Zambezi, where channel waters (1800 meters wide) fall from a height of 120 meters into a narrow tectonic fault.

In Australia, the largest river is the Murray, which originates in the Snowy Mountains of the East Australian mountain system. Flowing through the arid plain, the river is shallow (the average annual water discharge is only 470 m 3 / sec). In the dry season (in winter), it becomes shallow, and sometimes dries up in places. Several reservoirs have been built to regulate the flow on the river and its tributaries. Murray has great importance for irrigation: the river flows through an important agricultural area in Australia.

Lakes of the southern continents

In the arid regions of Africa and Australia, there are numerous drainless salt lakes, mainly of residual origin. Most of them are filled with water only during rare heavy rainfall. Rain moisture enters through the channels of time streams (weddam and screams). There are few similar lakes on the highland plains of the Central Andes, in the Precordillera and the Pampan Sierras of South America.

Large freshwater lakes are found only on the African continent. They occupy the tectonic depressions of the East African and Ethiopian highlands. The lakes located within the eastern branch of the rift fault are elongated in the submeridional direction and are very deep.

The depth of Lake Tanganyika, for example, reaches almost one and a half kilometers and is second only to Lake Baikal. It is the largest of the rift lakes in Africa (34,000 km 2). Its banks are steep in places, steep, usually straight. In some places, lava flows form narrow peninsulas that jut deep into the lake. Tanganyika has a rich fauna with many endemics. Several national parks are located along its banks. The lake is navigable and connects a number of countries by waterways (Tanzania, Zaire, Burundi). Another large lake East Africa- Victoria (Ukereve) - the second after the North American Lake Superior in terms of area fresh water body (68,000 km 2), located in a tectonic trough. Compared to rift lakes, it is shallow (up to 80 meters) and has a round shape, low-lying winding shores, and many islands. Due to its large area, the lake is subject to the action of tides, during which its area increases significantly, as water floods the low shores. The river flows into the lake. Kagera, which, not without reason, is considered the source of the Nile: it has been experimentally established that the Kagera stream crosses Victoria and gives rise to the Victoria Nile River. The lake is navigable - there are connections between Tanzania, Uganda and Kenya.

There are many small freshwater lakes in the East Australian Mountains, in the South Andes, and at the foot eastern slopes There are also quite large lakes of glacial origin in the Patagonian Andes. The alpine lakes of the Central Andes are very interesting.

On the plains of Pune there are many small, usually salty bodies of water. Here, at an altitude of over 3800 m, in a tectonic depression, there is the largest of the alpine lakes in the world - Titicaca (8300 km 2). The runoff from it goes to the salt lake Poopo, which is similar in properties to the reservoirs of arid regions of Africa and Australia.

There are very few lakes on the plains of South America, except for oxbows in the floodplains of large rivers. On the northern coast of South America there is the vast Maracaibo lagoon. There are no large bodies of water of this type on any of the southern continents, but there are many small lagoons in the north of Australia.

Underground waters of the southern continents

Significant reserves of groundwater play a significant role in natural processes and in the lives of people on the southern continents. In the tectonic depressions of the platforms, vast artesian basins are formed. They are widely used in the economy, but are of particular importance in the arid regions of Africa and Australia. Where groundwater comes closer to the surface - in relief depressions and along thalweg of temporary watercourses, conditions for the life of plants and animals appear, natural oases are formed with completely special compared to the surrounding deserts environmental conditions... In such places, people in all possible ways extract and store water, create artificial reservoirs. Artesian waters are widely used in water supply of arid territories of Australia, Africa and some regions of South America (Gran Chaco, Dry Pampa, intermontane basins).

Swamps and wetlands of the southern continents

Many areas of the Southern Tropical continents are swampy due to the flat relief and close to the surface of the occurrence of water-resistant rocks. To a large extent, they are subject to the process of waterlogging of the bottoms of depressions in the humid zones of Africa and South America, where the amount of precipitation exceeds the evaporation rate and the moisture coefficient is greater than 1.00. These are the Congo basin, the Amazonian lowland, the interfluve of the rivers Paraguay and Uruguay, the low plains of the Moist Pampa and some other areas. However, in some places even such territories are swampy, within which there is a moisture deficit.

A hollow in the upper reaches of the river. Paraguay, which bears the name Pantanal, which means "swamp" in translation, is very swampy. However, the moisture coefficient here barely reaches 0.8. In some places, even arid areas are swampy, for example, the White Nile Basins in North Africa and the Okavango in South Africa. The deficit of precipitation here is 500-1000 mm, and the moisture coefficient is only 0.5-0.6. There are swamps in the Dry Pampa - arid areas on the right bank of the river. Paranas. The reason for the formation of marshes and wetlands within these territories is poor drainage due to the small slopes of the surface and the presence of impervious soils. In Australia, swamps and wetlands occupy very small areas due to the dominance of arid climates. A number of marshes are found on the flat, low-lying northern coasts, on the eastern shores of the Great Australian Bight, and along river valleys and temporary watercourses in the low-lying basin of the Darling-Murray Basin. Moisture coefficients in these areas are different: from exceeding 1.00 in the very north of the Arnhemland Peninsula to 0.5 in the southeast, but small surface slopes, the presence of impermeable soils and the close occurrence of groundwater contribute to waterlogging even with a sharp moisture deficit.

Glaciers of the southern continents

Glaciation within the southern tropical continents has a limited distribution. There are no mountain glaciers at all in Australia and very few in Africa, where they cover only individual peaks in the equatorial regions.

The lower boundary of the chionosphere is located here at an altitude of 4550-4750 m. Mountain ranges exceeding this level (Kilimanjaro, Kenya, some peaks of the Rwenzori mountains) have ice caps, but their total area is about 13-14 km2. The largest area of ​​mountain glaciers in the Andes of South America. There are regions where mountain-cover glaciation is also developed: the North and South Glacial plateaus south of 32 ° S. NS. and the mountains of Tierra del Fuego. In the North and Central Andes, mountain glaciers cover many peaks. Glaciation here is the largest in the equatorial and tropical latitudes of the Earth, as there are high and highest mountains crossing the lower boundary of the chionosphere even in those regions where it is located at high altitudes. The snow line varies greatly depending on the amount of precipitation. In equatorial and tropical latitudes, it can be located at altitudes from 3000 m to 7000 m in mountains with different moisture conditions, which is mainly associated with the exposure of the slopes in relation to the prevailing air currents carrying moisture. South 30 ° S NS. the height of the snow line with an increase in the amount of precipitation, and with a decrease in temperatures in higher latitudes, rapidly decreases and already at 40 ° S. NS. on the western slopes it does not even reach 2000 m. In the very south of the continent, the height of the snow line is not more than 1000 m, and the outlet glaciers descend to the ocean level.

The ice sheet occupies a special place. It arose about 30 million years ago, and since then its size and shape, apparently, have changed little. This is the largest ice accumulation on the globe (area - 13.5 million km 2, including about 12 million km 2 - the continental ice sheet and 1.5 million km 2 - ice shelves, especially extensive in the Weddell and Ross). The volume of fresh water in solid form is approximately equal to the runoff of all the rivers of the Earth for 540 years.

Antarctica has ice sheets, mountain-cover, shelf and various mountain glaciers. Three ice sheets with their own feeding areas contain about 97% of the mainland's total ice reserve. From them, ice spreads at different speeds and, reaching the ocean, forms icebergs.

The Antarctic ice sheet is fed by atmospheric moisture. In the central parts, where predominantly anticyclonic conditions, feeding is carried out mainly by sublimation of steam on the surface of ice and snow, and closer to the coast, when cyclones pass, snow falls. Consumption ice goes due to evaporation, melting and runoff into the ocean, the removal of snow by winds outside the continent, but most of all - due to the breakaway of icebergs (up to 85% of the total ablation). Icebergs are already melting in the ocean, sometimes very far from the Antarctic shores. Ice consumption is uneven. It does not lend itself to accurate calculations and forecasts, since the size and speed of icebergs spalling is influenced by many different factors that cannot be taken into account simultaneously and completely.

The area and volume of ice in Antarctica are changing literally by day and hour. Different sources indicate different numerical parameters. It is equally difficult to calculate the mass balance of the ice sheet. Some researchers obtain a positive balance and predict an increase in the area of ​​ice, while others have a negative balance, and we are talking about the degradation of the ice sheet. There are calculations according to which the state of the ice is assumed to be quasi-stationary with fluctuations throughout the year and over longer periods. Apparently, the last assumption is closest to the truth, since the average long-term data on the assessment of the area and volume of ice produced at different times and by different researchers differ little from each other.

The presence of a powerful continental glaciation, comparable in size to the Pleistocene glaciation of the Northern Hemisphere, plays a huge role both in the general global moisture turnover and heat exchange, and in the formation of all natural features Antarctica. The existence of this continent, completely covered with ice, has a large and varied effect on the climates, and through them on other components of the nature of the southern continents and the entire Earth.

The ice of Antarctica is a huge supply of fresh water. They are also an inexhaustible source about the past of the Earth and about the processes characteristic of glacial and periglacial regions of the Earth in the past and present. It is not without reason that the Antarctic ice sheet is an object of comprehensive study by specialists from many countries, despite the difficulties associated with research work in the extremely harsh conditions prevailing on the continent.

Remember how important water is for other components of nature and for humans. What properties does water have? Which ones are geographically significant? What water bodies are terrestrial waters?

Distribution of inland waters of the land. Waters are distributed extremely unevenly across the continents. There are areas where there is an abundance of rivers, lakes, there are vast swamps, and in some areas there is practically no surface water, except for rare drying up lakes. Of all the continents, the "wettest" (water-supplied) one is South America. If all the waters flowing down from this continent in a year are distributed in an even layer over its area, then a layer of water with a thickness of more than 500 mm will turn out. This quantity is called the runoff layer (8.1). In Antarctica, almost all water is in solid form, and does not flow into the ocean, but falls in large blocks, forming icebergs. But in terms of the volume of fresh water, Antarctica is many times larger than all continents combined. It is estimated that the reserves of fresh water contained in the Antarctic ice are approximately equal to the flow of all rivers on Earth for more than 500 years.

The distribution of inland waters across continents is most dependent on climate, but other factors are also important. The distribution of rivers, lakes, swamps, glaciers, the shape of river valleys and lake depressions, geological structure terrain. For example, even with a low amount of precipitation, swamps can arise if the terrain is flat and it is difficult to drain from it.

All types of inland waters play a huge role in nature and in human life. However, the most prominent place is occupied by rivers.

Rivers. On all continents of the Earth, except for Antarctica, there are large and small river systems. South America has the most ramified river network, receiving the most precipitation.

There are almost no territories on this continent without rivers. The huge basins of the Amazon, Orinoco, Parana occupy most of the mainland (8.2). Most rivers originate in the mountains, cut through mountain ranges and high plateaus and plateaus, forming rapids and waterfalls. Then they go out onto flat plains, spread widely, and turn into a dense network of waterways. Material carried by rivers from high places fills depressions crust... Amazonian, Orinokskaya, Laplatskaya lowlands are vast flat plains, composed of river sediments.

The river network of North America has a similar structure. Here, the areas of drainless areas are also small. Many rivers carry water to the Atlantic Ocean and the Gulf of Mexico. The largest of these is the Mississippi system, which collects water from the Cordilleras, the Appalachians, and the American plains (8.3). Rough rivers flow into the Pacific Ocean, cutting through the Cordillera. The Mackenzie River, which has an extensive network of tributaries, flows into the Arctic Ocean. Short, deep, rapids flow into Hudson Bay.

Rivers Eurasia carry out into the oceans almost half of all waters flowing down from the planet's land. In terms of river flow, the continent surpasses all continents. Of the 14 greatest rivers in the world (more than 3 thousand km long), most are in Eurasia: Yangtze, Yellow River, Mekong, Indus, Lena, Ob, Yenisei, Volga.

Rivers are unevenly distributed across the mainland. The most powerful river systems are found in Asia - in its northern, eastern and southeastern parts. In the central regions, the river network is almost absent. Small rivers predominate in Europe. The largest rivers of Eurasia originate deep in the mainland high in the mountains and spread in all directions to the marginal plains. In the upper reaches they are all mountainous, in the lower ones they are flat, calm and wide. Flowing out of the mountains, the rivers lose their speed, expand the valley and deposit the brought material - alluvium - in it. The largest plains of Eurasia are alluvial.

Rivers of Eurasia extremely diverse in types of food and flow regime. One and the same river, crossing different climatic zones, feeds water from different sources in different sections, floods and grows shallow at different times. Most of the rivers have atmospheric nutrition: mixed - snow and rain, or mainly rain. These are rivers on the outskirts of the mainland with non-continental climates. High water on different rivers occurs at different times of the year, depending on the onset of the rainy seasons or the melting of snow. In the rivers of continental regions, groundwater plays the main role in feeding. During low water periods, some dry up completely. Rivers originating in the mountains of Europe, in the center, in the east and southeast of Asia, are fed by the waters of melting glaciers. Asian rivers flowing through permafrost also have a glacial type of feeding.

River basins. Water collected from 65% of the territory of Eurasia is carried by rivers to all four oceans of the planet. A third of the continent's surface has no flow into the World Ocean. Accordingly, the territory of Eurasia is divided into five drainage basins. Four of them are ocean basins, and the fifth is an internal drainage basin. It is the largest internal drainage basin on the planet.

Pool Arctic Ocean occupies the northern outskirts of Eurasia. "Record holders" of the basin: Lena - has the greatest length - 4400 km; Ob (3650 km, with the Irtysh 5410 km) - the largest catchment - about 3000 km 2 (Fig. 39); The Yenisei (from the confluence of the Big and Small Yenisei - 3487 km) - carries the largest amount of water into the ocean - 630 km 3 / year (Fig. 40). These rivers originate in the mountains. They flow to the ocean along the plains - low or high, from south to north - crossing several natural zones. A significant part of their valleys is located in the permafrost zone. They feed on melted snow, rain and glacial waters. In winter they freeze, and many of their small tributaries freeze to the bottom.

Basin rivers The Pacific - Yangtze (6380 km) (Fig. 41), Yellow River (4845 km), Mekong(4500 km) (Fig. 42), Amur(2850 km) - have a monsoon type of regime and are distinguished by high water content. The summer, when the rainy season begins and the snow melts in the mountains, account for up to 80% of their annual runoff. The water level at this time rises by 20-40 m. Floods are accompanied by severe floods. At this time, the rivers flood their valleys and fill them with a thick layer of loose sediment. The longest river on the continent second only to the Nile, Amazon and Mississippi - Yangtze... It begins in Tibet, breaks through the rapids into the alluvial plain, where it flows among boundless lakes and swamps. When it flows into the East China Sea, it forms a narrow long estuary - a funnel-shaped widened mouth. It is formed by the force of sea tides that rise up the river for several hundred kilometers. By the rivers of the basin Indian Ocean also a monsoon regime. The largest are Indus (3180 km), Brahmaputra (2900 km) (Fig. 43), Ganges(2700 km), Tiger, Euphrates- originate high in the mountains. Bo Ђ Most of their valleys lie in the foothill troughs, and the rivers tirelessly fill them with alluvium. Its thickness in the Ganges valley reaches 12 km. The Ganges - Brahmaputra system in terms of water content is the third after the Amazon and Congo: every second 7700 m 3 of water is carried into the ocean. 500 km from the ocean, the Ganges begins to form the branches of a giant delta - the largest on the globe (with an area of ​​more than 80 thousand km 2).

From rivers of other basins of the river basin Atlantic Ocean are distinguished by their diversity. They do not form large systems, have a smaller and more uniform drain, all possible power sources. Some of them freeze in winter, on others there is no freeze-up. Polomaputry (space image)

waters and floods occur at different times. The largest river - Danube(2850 km) - begins in the Black Forest mountains and flows through the territory of nine countries. Mountainous, rapids in the upper reaches, in the middle and lower reaches, it becomes a typical flat river - calm, with a wide floodplain and numerous oxbows. The river cuts through the Carpathians through a narrow valley and, splitting into branches, flows into the Black Sea.

Pool internal drain occupies the central part of the mainland. Its rivers are usually short and do not form a dense network. They feed mainly on groundwater and often do not bring water to rare lakes, being lost in the sands of the deserts.

Its main river is not at all typical for the basin. Volga(3530 km) - largest in Europe... It crosses the East European Plain from north to south. In the upper and middle reaches, the river is very full-flowing - it is fed by abundant waters of melted snow and rains. To the south, they dry up, but the consumption increases - for evaporation and economic needs. The Volga flows into the Caspian, forming a powerful delta consisting of hundreds of channels and islands.

Lakes Eurasia is many and varied. They are unevenly distributed over the territory and differ in the origin of the basins, in size, nutrition, temperature regime, salinity.

The northern part of the continent, covered with ancient ice sheets, is dotted with glacial lakes. The largest (including the largest in Europe Ladoga and Onega lakes) are occupied by tectonic troughs deepened by a glacier. There are also many glacial lakes in the mountains of Central Asia and in the Himalayas. In the south of Europe, west and southeast of Asia, common karst lakes. Far East and the Japanese islands are rich volcanic lakes. Widespread in river valleys floodplain oxbow lakes. A significant part of the Eurasian lakes have depressions tectonic origin. This is the largest lake in the world - the Caspian, and also Aral and Balkhash... Their depressions are remnants ancient ocean Tethys. The largest lakes in central Europe are Constance and Balaton- are located in the foothill troughs. Sections of continental rifts are occupied by the deepest lakes - Baikal (1637 m) and The Dead Sea... There is a lake in a tectonic depression Issyk-Kul.

The lakes of regions with a humid climate are fresh, with a continental climate, saline to varying degrees. The salinity of the internal drainage lakes is especially high.

The surface of this closed lake in Arabia is the lowest place on the Earth's land - below sea level by 405 m. In some years, the water level drops to -420 m, and the salinity, usually 260-270 ‰, rises to 310 ‰. Organic life in the waters of the lake is impossible, hence its name - the Dead Sea (Fig. 45).

The groundwater. Swamps. The underground waters of Eurasia are concentrated in large basins. East and Southeast Asia are especially rich in them. The widespread occurrence of swamps and wetlands is another feature of Eurasia. Swamps are typical in the tundra and forest-tundra, in the permafrost zone, very widespread in areas with a monsoon climate.

Permafrostnot on any continent planets(except Antarctica) not as widespread as in Eurasia... In the Asian part of the continent, it extends south to 48 ° N. w (Fig. 47). Permafrost was formed during the ancient glaciation. The modern climate in high latitudes contributes to its preservation (relict permafrost), and in the inland regions of the temperate zone - its formation (modern). The thickest layer of frozen rocks reaches the upper reaches of the Vilyui River in Yakutia - 1370 m.

Referring to Figure 47, compare the distribution of permafrost in North America and Eurasia, Europe and Asia. What explains the differences in its distribution?

Glaciation in Eurasia it is significantly in area - 403 thousand km 2, but it accounts for only 0.75% of the mainland. Almost 90% of the glaciers of Eurasia are mountain ... In Europe, the most powerful mountain glaciation is in the Alps, in Asia - in the Himalayas (30 times more extensive than the Alpine). Covering glaciation is developed on the northern islands.

In the Caucasus, in Scandinavia, in the Polar Urals, Taimyr, northeastern Siberia, Kamchatka, the Japanese islands, glaciation is facilitated by the oceanic (or coastal) position of the mountains, which allows to delay atmospheric precipitation. The formation of glaciers in Central Asia - in the Pamirs, Tibet, Kunlun, Karakorum, Tien Shan - is hindered by the dryness of their continental climate, but the huge height contributes.

Rice. 47. Distribution of permafrost

Changes in the state of water bodies under the influence of economic activities. The huge water wealth of the mainland is intensively used in the economy. However, due to the uneven distribution of inland waters over the territory, some regions experience an extreme shortage of water resources, while others face the problem of excessive surface moisture.

The shortage of water resources is especially acute within the continent - in the basin of internal flow. Farming and human life here are possible only with artificial irrigation - irrigation. Often the water of the rivers is withdrawn completely, depriving the water bodies of the internal runoff. It causes the chain environmental issues: soil salinization, increased wind erosion, desertification. Over the past decades, many small rivers and lakes have disappeared from the map of Eurasia, and some large rivers, for example Amu Darya and Syrdarya in Central Asia, cannot bring their waters to The aral sea, which turned because of this into several small lakes.

To remove excess moisture from the swampy Woodlands of Europe and the waterlogged lowlands of South and Southeast Asia, drainage reclamations are carried out . Drainage, which does not take into account the hydrological regime of biocenoses, often entails a chain of negative ecological consequences. The continentality of the climate is growing, peat bogs are being destroyed, species of plants and animals are disappearing forever, small rivers and lakes are drying up, and soil erosion is increasing.

Intensive farming leads to the pollution of surface and underground waters with pesticides, mineral and organic waste, synthetic substances, oil products. The "circulatory system" of the mainland, "infected" with harmful substances, soaking the surface rocks, transports these pollutants over long distances, spreading the "infection", and then carries it out into the World Ocean. Despite the fact that the most densely populated regions of Eurasia are located in the basins of the largest rivers, in many of these territories there is an acute shortage of water resources, including clean water.

As a consequence global warming, one of the reasons for which is human economic activity, there is a rapid degradation of permafrost, intensive melting of glaciers, which leads to a gradual rise in the level of the World Ocean.

Bibliography

1. Geography grade 9 / Tutorial for grade 9 institutions of general secondary education with Russian as the language of instruction / Edited by N. V. Naumenko / Minsk "Narodnaya Asveta" 2011