The modern river network, lake and artesian basins were formed within each of, mainly at those stages of the development of nature, when Gondwana had already broken up, and the continents existed in isolation from each other, therefore, 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, rain absolutely prevails due to the fact that South America, Africa and Australia are located for the most part in equatorial-tropical latitudes. Glacial and snow nutrition 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. Thus, 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 zone, the summer maximum is well expressed, and in the areas of the Mediterranean type of climate - the winter maximum of the flow.
Lakes of arid and semi-arid regions are similar in properties. They, as a rule, are highly mineralized, do not have a permanent coastline, their area varies to a large extent depending on the inflow, lakes often dry up completely or partially, and solonchaks 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 internal 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 of 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 common to the continents) belongs to Australia - 46 mm, more than ten times less than that for South America.
Large differences can be seen in the structure of the hydrographic network of the continents. Areas of internal flow and drainless territories occupy about 60% of the area of Australia and 30% of the area of Africa. In South America, such areas make up only 5-6% of the territory.
This is due both to climatic features (there are relatively few arid and semi-arid regions in South America), and to 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 runoff, such as Lake Chad, the Okavango Basin in Africa, Lake Eyre in Australia. This structure of the relief also affects the aridization of climates, which in turn determines the predominance of drainage areas in dry regions of the continents. There are almost no closed basins in South America. There are small areas with internal runoff or completely devoid of surface water in the Andes and Precordillera, where they occupy intermountain 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 determined already at the early stages of the geological history of the platform part of the mainland.
The largest water arteries - the Amazon, Orinoco, Parana, Parnaiba, San Francisco and their main tributaries occupy for the most part the axial zones of ancient syneclises. Ascending neotectonic movements along the peripheral parts of the river basins contributed to the incision of the erosion network and the drainage of 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 margins of the continent. This led to a significant restructuring of river systems. In the recent past, the areas of internal runoff areas were, apparently, much larger than now.
Extensive lakes occupied the bottoms of many basins, including the Congo, Okavango, Kalahari, Chad, Middle Niger, and others. Water from the sides of the basins collected in them. Short full-flowing 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 Niger, in the middle reaches of the Nile. Lake Chad has lost part of its basin and shrunk in size, while the bottoms of other basins have completely lost their lakes. This is evidenced by lacustrine deposits in the central regions of vast inland depressions, the presence of inland deltas, an undeveloped equilibrium profile in some sections of river valleys, and other signs characteristic of the results of such a process.
In Australia, due to the widespread occurrence of arid climatic conditions, more or less full-flowing short rivers flow from the elevated margins in the east and north of the mainland into the seas of the Pacific and Indian oceans.
On the west coast south of 20° S. sh. river channels 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 underflow. In the south, the karsted Nullarbor Plain is completely devoid of surface runoff. The only relatively long river in Australia - Murray (2570 km) flows in the southeast. It has a distinct summer flow maximum, however, this river does not dry up in winter either. The tributary of the river. Murray - r. The Darling is almost the same length, in the middle and lower reaches it flows through arid regions, receives no tributaries, and in dry times there is no runoff. All the interior regions of the mainland with a continental tropical and subtropical climate are practically devoid of runoff into the ocean, and for most of the year they 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 ways. The river system is unparalleled: the river carries 15-17% of the total 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 width of the channel 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 small drop (from the foot of the Andes to its confluence with, it is only about 100 meters), the river carries a huge amount of suspended sediment into the ocean (estimated to be up to a billion tons per year).
The Amazon begins in the Andes with two sources of rivers - Maranion and Ucayali, receives a huge number of tributaries, which in themselves are large rivers, comparable in length and water flow with the Orinoco, Parana, Ob, Ganges. The rivers of the Amazon system - Zhurua, Rio Negro, Madeira, Purus, etc. - are typically flat, winding, slowly flowing for most of their course. They form the widest floodplains with swamps and many oxbow lakes. The slightest rise in water causes floods, 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, and oxbow lakes 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 flows here 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 hard rock outcrops, and form rapids and waterfalls 100-120 km from the confluence with the main river. The water in these rivers is clear, but dark from organic substances dissolved in it. This is rios negros - "black rivers". A powerful tidal wave enters the mouth of the Amazon, which is called pororoca here. It has a height of 1.5 to 5 m and with a roar of a wide front of tens of kilometers moves upstream, damming the river, destroying the banks and washing away the islands. The tides do not allow the delta to grow, as the ebb currents carry the alluvium into the ocean and deposit it on the shelf. The action 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 1700 km (although the channel in the delta has to be deepened and cleaned of sediments).
The second major river of the continent, the 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 flow 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 flow fluctuations can be quite significant: deviations from the average values by almost 3 times in both directions. There are also catastrophic floods. In the upper reaches, the river flows through 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 Parana flows into the bay-estuary of La Plata. Muddy waters of the rivers can be traced in the open sea for 100-150 km from the coast. Sea vessels rise upstream up to 600 km. There are a number of major 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 the flow of water in the dry and wet seasons is very significant.
During particularly high floods, the discharge at the head of the delta can be more than 50 thousand m 3 /sec, and in the dry season of a dry year, it decreases to 5-7 thousand m 3 /sec. The river originates in the Guiana Highlands and flows through the Orinoco Lowland. Before the mouth of the left tributary - the 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 from the mouth forming a vast marshy 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 to the Orinoco, the rest enter through the upper reaches of the river. Rio Negro in the river basin. Amazons. Orinoco is navigable up to 400 km from the mouth for ocean-going vessels, and during the wet season, river vessels can pass to the river. Guaviare. The left tributaries of the Orinoco are also used for river navigation.
On the African continent, the most full-flowing river. Congo (in terms of water content, the second in the world after the Amazon). With the Amazon Congo is very similar in many ways. This river is also full-flowing throughout the year, since it flows for a considerable distance in the region of the equatorial climate and receives tributaries from both hemispheres.
In the middle reaches of the river The Congo occupies a flat swampy 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 The Congo (in this section more than 2000 km long it is called Lualaba) either forms rapids with a steep drop, or flows calmly in a wide valley. Just below the 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 Guinea Upland in a narrow deep valley with numerous rapids and waterfalls. They bear the common name of Livingston 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 vessels. In the middle reaches of the Congo, it is navigable for river vessels, and the waterways are widely used in the countries through which this river and its large tributaries flow. Like the Amazon, the Congo is full of water throughout the year, although it has two rises in water 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 of the Earth (6671 km), has a vast basin (2.9 million km 2), but the water content is tens of times less than other large rivers.
The source of the Nile is the river. The Kagera flows 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 is Cabarega (Murchison) 40 m high on the river. Victoria Nile. After passing through several lakes, the river enters the plains of Sudan. Here, a significant part of the water is lost to evaporation, transpiration, and filling of depressions. After the confluence of the river El-Ghazal river gets the name of the White Nile. In Khartoum, the White Nile merges with the Blue Nile, which originates in Lake Tana in the Ethiopian Highlands. Most of the lower reaches of the Nile pass through the Nubian desert. There are no tributaries here, water is lost to evaporation, seepage, and is disassembled for irrigation. Only a small part of the flow reaches the Mediterranean Sea, where the river forms a delta. Neil has a difficult regime. The main rise of water and spills in the middle and lower reaches occur in the summer-autumn period, when precipitation falls in the Blue Nile basin, which in summer brings 60-70% of water into the main river. 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 valley in the lower reaches - one of the centers of ancient civilization. Prior to the construction of dams, navigation along the river was difficult due to low water and the presence of six large rapids (cataracts) between Khartoum and Aswan. Now the navigable sections of the river (using canals) are about 3,000 km long. There are a number of hydroelectric power plants on the Nile.
In Africa, there are also large rivers of great natural and economic importance: Niger, Zambezi, Orange, Limpopo, etc. The Victoria Falls on the river are widely known. Zambezi, where the waters of the channel (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 an arid plain, the river is shallow (average annual water flow 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 of the river and its tributaries. Murray is of great importance for the irrigation of land: the river flows through an important agricultural region of Australia.
Lakes of the Southern Continents
In the arid regions of Africa and Australia, there are numerous endorheic salt lakes, mainly of residual origin. Most of them are filled with water only during rare heavy rains. Rain moisture enters through the channels of temporary streams (weeddams and screams). There are few similar lakes in the high plains of the Central Andes, in the Precordillera and the Pampian 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 Baikal. This is the largest of the rift lakes in Africa (34,000 km 2). Its banks are sometimes steep, precipitous, usually rectilinear. In some places, lava flows form narrow peninsulas, deeply protruding into the lake. Tanganyika has a rich fauna with many endemics. There are several national parks along its banks. The lake is navigable and connects a number of countries (Tanzania, Zaire, Burundi) by waterways. Another large lake in East Africa - Victoria (Ukereve) - the second largest freshwater reservoir after the North American Lake Superior (68,000 km 2), is located in a tectonic trough. Compared to rift lakes, it is shallow (up to 80 meters), 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 banks. The river flows into the lake. Kagera, which is not without reason considered the source of the Nile: it has been experimentally established that the water flow of Kagera crosses Victoria and gives rise to the Victoria Nile River. The lake is navigable - it links between Tanzania, Uganda and Kenya.
There are many small fresh lakes in the East Australian mountains, in the Southern Andes, and at the foot of the eastern slopes of the Patagonian Andes there are also quite large lakes of glacial origin. The alpine lakes of the Central Andes are very interesting.
On the plains of Pune, there are many small, usually salty reservoirs. Here, at an altitude of over 3800 m, in a tectonic depression, there is the largest of the high mountain lakes in the world - Titicaca (8300 km 2). The runoff from it goes to the Poopo salt lake, which is similar in properties to the reservoirs of the arid regions of Africa and Australia.
There are very few lakes on the plains of South America, except for oxbow lakes in the floodplains of large rivers. On the northern coast of South America there is a vast lake-lagoon Maracaibo. There are no large reservoirs of this type on any of the southern continents, but there are many small lagoons in the north of Australia.
Groundwater of the Southern Continents
Significant reserves of groundwater play a significant role in natural processes and in the life of people on the southern continents. Extensive artesian basins are formed in the tectonic depressions of the platforms. 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 the depressions of the relief and along the thalwegs of temporary watercourses, conditions for the life of plants and animals appear, natural oases are formed with very special ecological conditions compared to the deserts surrounding them. In such places, people extract and store water in various ways, create artificial reservoirs. Artesian waters are widely used in the water supply of arid areas of Australia, Africa and some regions of South America (Gran Chaco, Dry Pampas, intermountain basins).
Swamps and wetlands of the Southern Continents
Many areas of the Southern Tropical Continents are swampy due to the flat relief and the occurrence of water-resistant rocks close to the surface. The bottoms of basins in the humid zones of Africa and South America are highly susceptible to the process of swamping, where the amount of precipitation exceeds the evaporation rate, and the moisture coefficient is more than 1.00. These are the Congo basin, the Amazonian lowland, the interfluve of the Paraguay and Uruguay rivers, the low plains of the Humid Pampa and some other areas. However, in some places even such territories are swamped, within which there is a shortage of moisture.
Basin in the upper reaches of the river. Paraguay, called Pantanal, which means "swamp" in translation, is very swampy. However, the moisture coefficient here barely reaches 0.8. In some places, even arid territories are swamped, for example, the White Nile basins in North Africa and the Okavango in South Africa. The precipitation deficit here is 500-1000 mm, and the moisture coefficient is only 0.5-0.6. There are swamps in the Dry Pampa - arid regions of the right bank of the river. Paranas. The reason for the formation of swamps and wetlands within these areas is poor drainage due to low surface slopes and the presence of water-resistant soils. In Australia, swamps and wetlands occupy very small areas due to the dominance of arid climates. There are some swamps on the flat, low 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. Humidity coefficients in these areas are different: from exceeding 1.00 in the very north of the Arnhem Land peninsula to 0.5 in the southeast, but small surface slopes, the presence of water-resistant soils and the close occurrence of groundwater contribute to swamping 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 areas where mountain-cover glaciation is also developed: the Northern and Southern Ice Plateaus south of 32 ° S. sh. and mountains of Tierra del Fuego. In the Northern and Central Andes, mountain glaciers cover many peaks. Glaciation here is the largest in the equatorial and tropical latitudes of the Earth, since there are high and highest mountains that cross the lower boundary of the chionosphere even in those areas where it is located at high altitude. 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 due to the exposure of the slopes to the prevailing air currents that carry moisture. South of 30°S sh. the height of the snow line with an increase in the amount of precipitation, and with a decrease in temperatures at higher latitudes, falls rapidly and already at 40 ° S. sh. on the western slopes, it does not even reach 2000 m. In the very south of the mainland, the height of the snow line is not more than 1000 m, and outlet glaciers descend to 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 accumulation of ice on the globe (the area is 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 flow of all the rivers of the Earth for 540 years.
In Antarctica there are ice sheets, mountain-cover, shelf and various mountain glaciers. Three ice sheets with their own feeding areas contain about 97% of the entire ice reserve of the mainland. From them, the ice spreads at different speeds and, reaching the ocean, forms icebergs.
The ice sheet of Antarctica is fed by atmospheric moisture. In the central parts, where there are predominantly anticyclone conditions, nutrition is carried out mainly by sublimation of steam on the surface of ice and snow, and closer to the coast, snow falls during the passage of cyclones. Ice consumption is due to evaporation, melting and runoff into the ocean, the removal of snow by winds outside the mainland, 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 is not amenable to accurate calculations and forecasts, since the magnitude and speed of iceberg breakaway is influenced by many different factors that cannot be taken into account simultaneously and completely.
The area and volume of ice in Antarctica change literally by the day and hour. Different sources indicate different numerical parameters. It is equally difficult to calculate the mass balance of the ice sheet. Some researchers have 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 cover. There are calculations according to which the state of ice is assumed to be quasi-stationary with fluctuations during 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, made 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 circulation and heat transfer, and in the formation of all the natural features of Antarctica. The existence of this continent, completely covered with ice, has a great and varied influence on climates, and through them on other components of the nature of the southern continents and the whole Earth.
The ice of Antarctica is a huge reservoir of fresh water. They are also an inexhaustible source about the past of the Earth and about the processes characteristic of the glacial and near-glacial regions of the Earth in the past and at the present time. It is not for nothing that the ice sheet of Antarctica 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.
LESSON 33 LARGEST RIVER SYSTEMS
Learning goal: to acquaint with the general features of the waters of the land of the mainland, the main river systems; promote understanding of the influence of climate and topography on the formation and distribution of land waters; to improve the skills and abilities to characterize the largest river systems of the mainland.
Equipment: physical map of South America, textbooks, atlases, contour maps.
Basic concepts: land waters, river basins, river system, regime, nutrition, waterfall, tectonic lake, lagoon lake, glacier, groundwater.
Type of lesson: learning new material.
II. Updating of basic knowledge and skills
Complete the sentences.
South America is located in climatic zones: equatorial ...
Rainfall on the east coast is about...
A special type of climate that forms in the Andes is called ...
The inland waters of the mainland include: rivers ...
The most full-flowing river in the world, located in South America, is called ...
III. Motivation of educational and cognitive activity
The idea is well-known: "The water network of the mainland is a mirror of its climate and relief." Do you agree with him? Today in the lesson, studying the inland waters of South America, you have the opportunity to confirm or refute this statement.
IV. Learning new material
1. General characteristics of the inland waters of South America
In terms of water supply, South America ranks first. The continent covers about 12% of the land area, but accounts for 27% of the total global water flow. This is primarily due to the exceptionally humid climate. Large river systems have formed here. The vast majority of them belong to the Atlantic Ocean basin. The most powerful rivers: Amazon, Parana, Sao Francisco, Orinoco.
Most of the rivers are fed by rain, only some rivers receive water from the melting of snow and ice in the mountains. Flowing in the Andes, crossing the plateau, the rivers of South America form numerous rapids and waterfalls. On one of the tributaries of the Orinoco River there is the highest waterfall in the world - Angel (1054 m), and on the tributary of the Parana there is a powerful waterfall - Iguazu (72 m).
There are relatively few lakes in South America. The largest lake on the mainland is the lake-lagoon of tectonic origin Maracaibo. In the Central Andes, in a depression at an altitude of 3812 m, there is the largest of the high mountain lakes in the world - Titicaca. Extensive swamps form on well-moistened lowlands. Significant areas of the mainland are well provided with groundwater, which is of great importance for the water supply of cities.
There are few mountain glaciers in the Andes. As you move south, the height of the snow line gradually decreases.
Student presentations with messages.
2. Major river systems
Make a brief description of the rivers of South America according to the plan. Arrange the results in the form of a table:
Name |
Leak location |
Current direction |
The nature of the flow |
Where does it flow |
1. Amazon |
||||
3. Orinoco |
Amazon (6516 km) - the deepest river in the world, has the largest river basin in the world (its area is equal to the area of the whole of Australia). It originates in the Peruvian Andes from its main source - the Maranhoin River. After its confluence with the Ucayali, the river is called the Amazon. The Amazon is second only to the Nile in length. It has as much water as the Congo, Mississippi, Yangtze and Ob combined. The Amazon has more than 1,100 tributaries, 20 of which are between 1,500 and 3,500 km long. More than a hundred tributaries of the Amazon are navigable. Thanks to numerous tributaries, the Amazon remains full-flowing all year round.
Other major rivers of South America - Parana and Orinoco, unlike the Amazon, have a pronounced seasonal flow. The maximum rise in the water level occurs in the summer season, and in the dry period they become very shallow. With the advent of moist equatorial air, the rainy season begins, the rivers overflow, flooding vast territories and turning them into swamps. Such floods are often catastrophic.
The rivers of the Parana system collect water on the Brazilian Plateau and the interior plains, the Orinoco River with tributaries - on the Gvian Plateau. In the upper reaches, these rivers are full of rapids and form numerous waterfalls. In the middle and lower reaches of the Parana and Orinoco - typical flat rivers, convenient for navigation.
The rivers of South America have significant hydro potential; in the arid regions of the interior plains, river water is used to irrigate fields.
V. Consolidation of the studied material
What are the reasons for the high rate of river flow in South America?
Which ocean basin does most of the rivers of South America belong to? What explains this?
What type of food is typical for most rivers on the mainland?
What is the origin of the lakes of South America? In which areas are the largest of them located?
What do the river systems of South America and Africa have in common? What makes them different?
Why did the process of glaciation in the Andes not become widespread?
V I. The result of the lesson
VII. Homework
Work on a paragraph...
Implementation of practical work 8 (continued). Outline the major rivers and lakes of South America on a contour map.
Leading (individual students): prepare reports on the natural areas of South America, individual animals and plants, changes in natural complexes by man.
Rivers Eurasia carry almost half of all the waters flowing from the land of the planet into the World Ocean. In terms of river runoff, the continent surpasses all continents. Of the 14 greatest rivers in the world (more than 3 thousand km long), most of them are located in Eurasia: Yangtze, Huang He, Mekong, Indus, Lena, Ob, Yenisei, Volga.
Rivers are unevenly distributed across the mainland. The most powerful river systems are located in Asia - in its northern, eastern and southeastern parts. In the central regions, the river network is almost absent. Europe is dominated by small rivers. The largest rivers of Eurasia originate in the depths of 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 reaches they are flat, calm and wide. Flowing out of the mountains, the rivers lose speed, expand the valley and deposit the material brought in it - alluvium. Alluvial are the largest plains of Eurasia.
Rivers of Eurasia are extremely diverse in terms of food types and runoff regime. The same river, crossing different climatic zones, feeds on water from different sources in its different sections, overflows with floods and becomes shallow at different times. Most of the rivers have atmospheric feeding: mixed - snow and rain or predominantly rain. These are the rivers of 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 season or the snow melting. In the rivers of continental regions, groundwater plays the main role in nutrition. During low water, 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 nutrition.
River basins. Rivers carry water collected from 65% of the territory of Eurasia to all four oceans of the planet. A third of the continent's surface has no runoff into the oceans. Accordingly, the territory of Eurasia is divided into five drainage basins. Four of them are ocean basins, and the fifth is an internal runoff basin. This is the largest internal runoff basin on the planet.
Swimming pool Arctic Ocean occupies the northern edge of Eurasia. "Record holders" of the basin: Lena - has the longest length - 4400 km; the Ob (3650 km, with the Irtysh 5410 km) - the largest catchment - about 3000 km 2 (Fig. 39); 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 elevated, 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 glacier waters. In winter they freeze, and many of their medium-sized tributaries freeze to the bottom.
Basin rivers Pacific Ocean - Yangtze (6380 km) (Fig. 41), Huang He (4845 km), Mekong(4500 km) (Fig. 42), Amur(2850 km) - have a monsoon type of regime and are distinguished by high water. In the summer, when the rainy season begins and the snow melts in the mountains, up to 80% of their annual runoff falls. 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 sediments. The longest river on the continent second only to the Nile, the Amazon and the Mississippi, Yangtze. It begins in Tibet, breaks through rapids into the alluvial plain, where it flows among boundless lakes and swamps. At the confluence with the East China Sea, it forms a narrow long estuary - a funnel-shaped extended mouth. It is formed by the force of the sea tides rising up the river for several hundred kilometers. By the rivers of the basin indian ocean also monsoonal. The largest are Indus (3180 km), Brahmaputra (2900 km) (Fig. 43), Ganges(2700 km), Tigris, Euphrates- originate high in the mountains. Bo Ђ Most of their valleys lie in 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 the Congo: 7700 m 3 of water is carried into the ocean every second. 500 km from the ocean, the Ganges begins to form branches of a giant delta - the largest on the globe (more than 80 thousand km 2 in area).
From the rivers of other river basins Atlantic Ocean are diverse. They do not form large systems, have a smaller and more uniform flow, all possible power sources. Some of them freeze in winter, while others do not freeze over. Polomaputra (space image)
water 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 it becomes a typical flat river - calm, with a wide floodplain and numerous oxbow lakes. The river cuts through the Carpathians in a narrow valley and, splitting into branches, flows into the Black Sea.
Swimming pool internal runoff 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, getting lost in the sands of deserts.
Not at all typical for the basin is its main river 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 rain. To the south, they dry up, but the consumption increases - for evaporation and household needs. The Volga flows into the Caspian, forming a powerful delta consisting of hundreds of channels and islands.
lakes Eurasia are numerous and varied. They are unevenly distributed over the territory and differ in the origin of the basins, size, nutrition, temperature regime, and salinity.
The northern part of the continent, covered by an ancient ice cover, is dotted with glacial lakes. The largest (including the largest in Europe Ladoga and Onega lakes) occupy tectonic troughs deepened by the glacier. There are also many glacial lakes in the mountains of Central Asia and in the Himalayas. Distributed in southern Europe, western and southeastern Asia karst lakes. The Far East and the Japanese islands are rich volcanic lakes. Widespread in river valleys floodplain old lakes. A significant part of the Eurasian lakes have basins tectonic origin. This is the largest lake in the world - the Caspian, and also Aral and Balkhash. Their depressions are the remains of the ancient Tethys Ocean. The largest lakes in central Europe - Constance and Balaton- located in foothills. Areas of continental rifts occupy the deepest lakes - Baikal (1637 m) and Dead Sea. Lake in a tectonic basin Issyk-Kul.
The lakes of areas with a humid climate are fresh, those with a continental climate are salty to varying degrees. The salinity of endorheic lakes is especially high.
The surface of this endorheic lake in Arabia is the lowest place on Earth's land - 405 m below sea level. In some years, the water level drops to -420 m, and salinity, usually 260-270 ‰, increases 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 wide distribution of swamps and wetlands is another feature of Eurasia. Bogs are typical in the tundra and forest-tundra, in the permafrost zone, and are very widespread in areas with a monsoon climate.
permafroston no 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). The permafrost was formed during the ancient glaciation. The modern climate in high latitudes contributes to its preservation (relic permafrost), and in the inland regions of the temperate zone - to its formation (modern). The thickness of frozen rocks reaches its greatest thickness in the upper reaches of the Vilyui River in Yakutia - 1370 m.
Using Figure 47, compare the distribution of permafrost in North America and in Eurasia, in Europe and in Asia. What explains the differences in its distribution?
Glaciation in Eurasia, it is significant in area - 403 thousand km 2, but it accounts for only 0.75% of the mainland. Almost 90% of the glaciers of Eurasia - mountain . In Europe, the most powerful mountain glaciation is in the Alps, in Asia - in the Himalayas (30 times more extensive than the Alpine). Integumentary glaciation is developed on the northern islands.
In the Caucasus, in Scandinavia, in the Polar Urals, Taimyr, northeast Siberia, Kamchatka, the Japanese islands, glaciation is facilitated by the oceanic (or coastal) position of the mountains, which makes it possible to retain 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 is facilitated by the enormous height.
Rice. 47. Distribution of permafrost
Changes in the state of water bodies under the influence of economic activity. 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 lack of water resources, while others face the problem of excessive surface moisture.
The shortage of water resources is especially acute inside the continent - in the basin of internal flow. Farming and people's lives here are possible only with artificial irrigation - irrigation. Often the water of the rivers is withdrawn completely, depriving water bodies of internal flow. This causes a chain of environmental problems: 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, they cannot carry their waters to the Aral Sea, which has turned into several small lakes because of this.
To remove excess moisture from the swampy woodlands of Europe and the lowlands of South and Southeast Asia, which are waterlogged by rains, drainage reclamation is carried out. . Often, drainage that does not take into account the hydrological regime of biocenoses entails a chain of negative environmental consequences. The continental climate is growing, peat bogs are being destroyed, plant and animal species are disappearing forever, small rivers and lakes are drying up, and soil erosion is intensifying.
Intensive management leads to pollution of surface and groundwater with pesticides, mineral and organic waste, synthetic substances, oil products. The “circulatory system” of the mainland “infected” with harmful substances, impregnating the surface rocks, carries these pollutants over long distances, spreading the “infection”, and then takes it to 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 areas there is an acute shortage of water resources, including clean water.
As a result of global warming, one of the causes of which is human economic activity, there is a rapid degradation of permafrost, intensive melting of glaciers, which leads to a gradual increase in the level of the World Ocean.
Bibliography
1. Geography grade 9 / Textbook for grade 9 institutions of general secondary education with the Russian language of instruction / Edited by N. V. Naumenko/ Minsk "People's Asveta" 2011
Remember the importance of water for other components of nature and for humans. What properties does water have? Which of them are geographically significant? What bodies of water are land waters?
Distribution of inland waters. Water is distributed across the continents extremely unevenly. There are areas where there is an abundance of rivers, lakes, there are extensive marshes, and in some areas there is practically no surface water, except for rare drying lakes. Of all the continents, the most "wet" (water-provided) 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 more than 500 mm thick will be obtained. This quantity is called the sink layer (8.1). In Antarctica, almost all water is in solid form, and does not flow into the ocean, but collapses in large blocks, forming icebergs. But in terms of the volume of fresh water, Antarctica is many times greater than all the continents combined. It has been calculated that the reserves of fresh water contained in the Antarctic ice are approximately equal to the flow of all the rivers of the Earth for more than 500 years.
The distribution of inland waters over the territory of the continents most of all depends on the climate, but other factors also play a role. The distribution of rivers, lakes, swamps, glaciers, the shape of river valleys and lake basins, the conditions for the occurrence of groundwater are affected by the relief and geological structure of the area. For example, even with low rainfall, swamps can occur if the terrain is flat and difficult to drain.
All types of inland waters play a huge role in nature and in people's lives. 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 extensive river network, receiving the most precipitation.
There are almost no territories on this continent devoid of 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 come out onto flat plains, overflow widely, turn into a dense network of water arteries. The material that rivers carry from elevated places fills the depressions of the earth's crust. The 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 endorheic regions 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 Cordillera, the Appalachians, and the American plains (8.3). Stormy 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 full-flowing rapids flow into the Hudson Bay.
Measuring the length of rivers is not an easy task, which, however, has been greatly simplified since the advent of artificial satellites. But even with the help of images from space, it is not possible to determine the exact length of the river. Difficulties in determining the beginning of a river may be due to the large number of tributaries. Of all the tributaries, the one that begins at the farthest point from the mouth is considered the beginning of the river, giving the river a total total length, and the name of this tributary is usually not the same as the name of the river. It can also be difficult to determine where the river ends, because the mouth of the river is often an estuary, gradually widening and opening into the ocean.
Estuary (from lat. aestuarium - flooded mouth of the river) - a single-arm, funnel-shaped mouth of the river, expanding towards the sea. One can think of an estuary as a place where the sea is wedged into the mainland/island due to the washing out of rocks.
Seasonal changes also contribute to the complexity of calculating the total length of river systems. This list shows the lengths of river systems, that is, rivers, taking into account their longest tributaries.
10. Congo - Lualaba - Luvua - Luapula - Chambeshi
The Congo is a river in Central Africa that flows into the Atlantic Ocean. The length of the river system of the Congo - Lualaba - Luvua - Luapula - Chambeshi - 4700 km (The length of the Congo River is 4374 km). This is the deepest and second longest river in Africa, the second river in terms of water content in the world after the Amazon.
The width of the river is on average 1.5-2 km, but in some places it reaches 25 km. The depth of the river reaches 230 m - this is the deepest river in the world.
The Congo is the only major river that crosses the equator twice.
9. Amur - Argun - Muddy channel - Kerulen
Amur is a river in the Far East in East Asia. It flows through the territory of Russia and the border between Russia and China, flowing into the Sea of Okhotsk. The length of the river system Amur - Argun - Mutnaya channel - Kerulen is 5052 km. The length of the Amur is 2824 km
8. Lena - Vitim
Lena - a river in Russia, the largest river in Eastern Siberia, flows into the Laptev Sea. The length of the Lena-Vitim river system is 5100 km. The length of the Lena is 4400 km. The river flows through the territory of the Irkutsk region and Yakutia, some of its tributaries belong to the Trans-Baikal, Krasnoyarsk, Khabarovsk territories, Buryatia and the Amur region. The Lena is the largest of the Russian rivers, whose basin lies entirely within the country. It freezes in the reverse order of opening - from the lower reaches to the upper reaches.
7. Ob - Irtysh
The Ob is a river in Western Siberia. It is formed in Altai at the confluence of the Biya and Katun. The length of the Ob is 3650 km. At the mouth it forms the Gulf of Ob and flows into the Kara Sea.
The Irtysh is a river in China, Kazakhstan and Russia, the left, main, tributary of the Ob. The length of the Irtysh is 4248 km, which exceeds the length of the Ob itself. The Irtysh, together with the Ob, is the longest watercourse in Russia, the second longest in Asia and the seventh in the world (5410 km).
Irtysh - the longest tributary river in the world
6. Huang He
Huang He is a river in China, one of the largest rivers in Asia. The length of the river is 5464 km. The Huang He originates in the eastern part of the Tibetan Plateau at an altitude of over 4000 m, flows through the lakes Orin-Nur and Dzharin-Nur, spurs of the Kunlun and Nanshan mountain ranges. At the intersection of the Ordos and the Loess Plateau, it forms a large bend in its middle course, then through the gorges of the Shanxi Mountains it enters the Great Chinese Plain, along which it flows for about 700 km until it flows into the Bohai Bay of the Yellow Sea, forming a delta in the area of its confluence.
Translated from Chinese, its name is “Yellow River”, which is associated with an abundance of sediment, giving a yellowish tint to its waters. It is thanks to them that the sea into which the river flows is called Yellow.
Yellow River - Yellow River
5. Yenisei - Angara - Selenga - Ider
Yenisei - a river in Siberia, one of the greatest rivers in the world and Russia. It flows into the Kara Sea of the Arctic Ocean. Length - 3487 km. The length of the waterway: Ider - Selenga - Lake Baikal - Angara - Yenisei is 5550 km.
The Angara is a river in Eastern Siberia, the largest right tributary of the Yenisei, the only river flowing from Lake Baikal. It flows through the territory of the Irkutsk region and the Krasnoyarsk region of Russia. Length - 1779 km.
4. Mississippi - Missouri - Jefferson
The Mississippi is the main river of the largest river system in North America. The source is located in Minnesota. The river mainly flows in a southerly direction and reaches a length of 3770 kilometers, ending in a vast delta in the Gulf of Mexico.
The Missouri is a river in the United States, the largest tributary of the Mississippi. The length of the river is 3767 km. It originates in the Rocky Mountains, flows mainly in east and southeast directions. It flows into the Mississippi near the city of St. Louis.
The length of the Mississippi - Missouri - Jefferson river system is 6275 km.
3. Yangtze
The Yangtze is the longest and most abundant river in Eurasia, the third river in the world in terms of full flow and length. It flows through the territory of China, has a length of about 6300 km, the basin area is 1,808,500 km².
2. Nile
The Nile is a river in Africa, one of the two longest rivers in the world.
The river originates in the East African Plateau and flows into the Mediterranean Sea, forming a delta. In the upper reaches, it receives large tributaries - Bahr el-Ghazal (left) and Achva, Sobat, Blue Nile and Atbara (right). Below the mouth of the right tributary of the Atbara, the Nile flows through the semi-desert, having no tributaries for the last 3120 km.
For a long time, the Nile water system was considered the longest on Earth. In 2013, it was established that the Amazon has the longest river system. Its length is 6992 kilometers, while the length of the Nile system is 6852 kilometers.
Feluca - a small deck vessel with peculiar oblique sails in the form of a trapezoid or a triangle cut from one corner.
1. Amazon
The Amazon is a river in South America, the largest in the world in terms of basin size, full flow and length of the river system. It is formed by the confluence of the Maranion and Ucayali rivers. The length from the main source of Maranyon is 6992 km, from the source of Apacheta discovered at the end of the 20th century - about 7000 km, from the source of Ucayali over 7000 km.
However, there are long rivers not only on the ground, but also under it. Hamza is an informal name for the underground current under the Amazon. The opening of the "river" was announced in 2011. The unofficial name is given in honor of the Indian scientist Valiya Hamza, who has been exploring the Amazon for more than 45 years. Hamza flows at a depth of about 4 km underground through porous soils parallel to the Amazon. The length of the "river" is about 6000 km. According to preliminary calculations, the width of Hamza is about 400 km. The flow rate of the Hamza is only a few meters per year - this is even slower than the glaciers move, so it can be called a river rather conditionally. Hamza flows into the Atlantic Ocean at great depths. The water of the Hamza River has a high salinity level.
20 longest rivers, excluding the length of tributaries
- Amazon - 6992 km
- Nile - 6852 km
- Yangtze - 6300 km
- Yellow River hotels - 5464 km
- Mekong - 4500 km
- Lena - 4400 km
- Parana hotels - 4380 km
- Congo - 4374 km
- Irtysh hotels - 4248 km
- Mackenzie hotels - 4241 km
- Niger - 4180 km
- Missouri - 3767 km
- Mississippi - 3734 km
- Ob - 3650 km
- Volga - 3530 km
- Yenisei hotels - 3487 km
- Madeira - 3230 km
- Purus - 3200 km
- Indus - 3180 km
- Yukon -3100 km