Dependence of relief on external geological processes. What external forces influence the topography of our planet? How do external forces influence changes in mountains?

External forces- these are forces that act only on the surface of an object, but do not penetrate into it. These forces include all forces developed by a material object.

Inner forces- these are forces that act immediately on all atoms of a moving object, regardless of where they are: on the surface or in the middle of the object. These forces include inertial forces and field forces: gravitational, electric, magnetic. And this happens because the field and the carrier of inertia, the physical vacuum, freely penetrate into any body.

In mechanics external forces in relation to a given system of material points(i.e. such a set of material points in which the movement of each point depends on the positions or movements of all other points) are those forces that represent the action on this system of other bodies (other systems of material points) not included by us in composition of this system.

Internal forces are the forces of interaction between individual material points of a given system. The division of forces into external and internal is completely conditional: when the given composition of the system changes, some forces that were previously external can become internal, and vice versa. So, for example, when considering

PRIMER the movement of a system consisting of the earth and its satellite the moon, the interaction forces between these bodies will be internal forces for this system, and the gravitational forces of the sun, the remaining planets, their satellites and all the stars will be external forces in relation to the specified system. But if you change the composition of the system and consider the movement of the sun and all planets as the movement of one common system, then external the forces will be only the forces of attraction exerted

If a loaded body is in equilibrium, then the internal forces are equal in value to the external forces and opposite in direction. Obviously, they prevent the development of deformation. Work of internal forces(U), taking into account their direction with respect to the deformation, is always negative.

Work of external forces equal to taken with the opposite sign work of internal forces:

Let a rod element with a length experience tension (Fig. 15.3, a).

Let us replace the action of the discarded parts of the rod on the element under consideration with longitudinal forces N. These forces are shown in the figure by dashed lines. In relation to the element they are, as it were, external. The element elongation they cause is equal to: .

The effect of the element in question on the discarded parts is shown in the figure by solid lines. The elementary work of internal longitudinal forces, gradually increasing and counteracting the development of elongation, according to Clapeyron’s theorem, will be expressed by the formula: .

ELEMENTARY WORK OF INTERNAL TRANSVERSE FORCES () IN PURE SHEAR (FIG. 15.3, B)

In pure shear, shear stresses are uniformly distributed over the entire section and are determined by the formula: .

The absolute shift of the right section of the element relative to the left section, taking into account Hooke’s law, is equal to: ,

Then .

During transverse bending, tangential stresses are distributed unevenly over the section. In this case, the expression for the elementary work of internal shear forces can be presented as: , where k is a coefficient depending on the shape cross section rod. For example, for a rectangular cross section.

ELEMENTARY WORK OF INTERNAL FORCES DURING TORSION

The rotation of the right section of the element relative to the left section, occurring under the influence of torques external to it (), shown (see Fig. 15.3, c) by dashed lines, is equal to: .

Then the work of internal torques (they are not shown in the figure) at this angle of rotation is determined by the formula: .

Let the rod element now experience bending. And let its right cross section rotate by an angle of rotation relative to the left section (see Fig. 15.3, d).

Then the internal bending moments, shown (see Fig. 15.3, d) by solid lines, will do work at this angle of rotation:

.

With simultaneous stretching, torsion and direct transverse bending of the rod (taking into account the fact that the work of each of the internal forces on the displacements caused by the other forces is equal to zero), we obtain the following expression for the elementary work of internal elastic forces:

Integrating the expression over the entire length of the rod, we finally obtain formula for the work of internal forces.

External forces smooth out those created by the internal forces of the Earth. Destroying protruding surface irregularities, they fill depressions with sedimentary rocks. Flowing waters, glaciers, and humans create a variety of smaller landforms on land.

Weathering

One of the main external processes is weathering- the process of destruction and transformation of rocks.

Weathering itself does not lead to the formation of relief forms, but only turns hard rocks into loose ones and prepares the material for movement. The result of this movement is various forms of relief.

Effect of gravity

Under the influence of gravity, rocks destroyed by weathering move across the Earth's surface from elevated areas to lower ones. Blocks of stone, crushed stone, and sand often rush down steep mountain slopes, causing landslides and screes.

Under the influence of gravity there are landslides and mudflows. They carry huge masses of rocks. Landslides are the sliding of rock masses down a slope. They form along the banks of reservoirs, on the slopes of hills and mountains after heavy rains or melting snow. The upper loose layer of rocks becomes heavier when saturated with water and slides down the lower, water-impervious layer. Heavy rains and rapid snow melting also cause mudflows in the mountains. They are with destructive force moving down the slope, demolishing everything in its path. Landslides and mudflows lead to accidents and loss of life.

Activity of flowing waters

The most important transformer of relief is moving water, which performs great destructive and creative work. Rivers cut wide river valleys on the plains and deep canyons and gorges in the mountains. Small water flows create gully-gully relief on the plains.

Flowing bottoms not only create depressions on the surface, but also capture rock fragments, transport them and deposit them in depressions or their own valleys. This is how flat plains are formed from river sediments along rivers

Karst

In those areas where readily soluble rocks (limestone, gypsum, chalk, rock salt), amazing natural phenomena. Rivers and streams, dissolving rocks, disappear from the surface and rush into the depths earth's bowels. Phenomena associated with the dissolution of surface rocks are called karst. The dissolution of rocks leads to the formation of karst landforms: caves, abysses, mines, funnels, sometimes filled with water. Beautiful stalactites (multi-meter calcareous “icicles”) and stalagmites (“columns” of limestone growths) form bizarre sculptures in the caves.

Wind activity

In open, treeless spaces, the wind moves giant accumulations of sand or clay particles, creating aeolian landforms (Aeolus is the patron god of the wind in ancient greek mythology). Most of the world's sandy deserts are covered with sand dunes and hills. Sometimes they reach a height of 100 meters. From above the dune has the shape of a sickle.

Moving at high speed, particles of sand and crushed stone process stone blocks like sandpaper. This process goes faster near the surface of the earth, where there are more grains of sand.

As a result of wind activity, dense deposits of dust particles can accumulate.
Such homogeneous, porous, grayish-yellow rocks are called loess.

Glacier activity

Glaciers form a special glacial topography. Moving along the surface of the land, they smooth out rocks, plow out basins, and move destroyed rocks. The deposits of these rocks form moraine hills and ridges. When glaciers melt, sandy plains called outwash are formed from sand brought by water. Basins formed by glaciers often fill with water, turning into glacial lakes.

Human activity

Humans play a major role in changing the relief. The plains are especially strongly changed by its activities. People have been settling on the plains for a long time; they build houses and roads, fill up ravines, and construct embankments. Man changes the relief during mining: huge quarries are dug, heaps of heaps are piled up - dumps of waste rock.

The scale of human activity can be comparable to natural processes. For example, rivers develop their valleys, carrying out rocks, and humans build canals of comparable size.

Landforms created by humans are called anthropogenic. Anthropogenic changes in relief occur with the help of modern technology and at a fairly rapid pace.

Moving water and wind do a huge amount of destructive work called erosion (from the Latin word erosio to eat away). Land erosion is a natural process. However, it intensifies as a result economic activity people: plowing slopes, deforestation, excessive grazing, building roads. In the last hundred years alone, a third of all the world's cultivated land has been eroded. These processes reached their greatest scale in large agricultural regions of Russia, China and the USA.

Formation of the Earth's relief

Features of the Earth's relief

Class: 8

Presentation for the lesson

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Target: reveal to students ideas about internal (endogenous) and external (exogenous) processes as necessary condition relief development, teach how to independently identify cause-and-effect relationships, show the continuity of relief development, identify particularly dangerous natural phenomena and their causes.

Equipment: physical and tectonic maps of Russia; map of the latest tectonic movements; interactive whiteboard; visual and illustrative material about mudflows, erosion of rivers and ravines, landslides and other exogenous processes; Filmstrip “Formation of Relief”.

PROGRESS OF THE LESSON

1. Organizational moment

2. Repetition of the material studied.

– Find it on physical map main plains and mountains. Where are they located?
– Highlight the main features of the relief of our country. Give an assessment of the structure of the surface from the point of view of the possibilities of economic development of the territory. How do you think the life of people in the mountains and on the plain differs?
– Give examples of the influence of relief on the natural features of our country.
– The plains of Russia are considered to be the greatest in the world. What plains of the globe can they be compared with in size and structure?

4. Studying new material(Presentation )

(Slide 1) The Earth's surface is constantly, although very slowly, changing as a result of the interaction of internal and external processes. The relief that we see on the territory of our country now is the result of such interaction during the last geological period of time. The most important events of the Quaternary period had a particularly strong impact on the modern relief: the latest tectonic movements, ancient glaciations, and the advance of the seas. (Slide 2)

Among the internal (endogenous) processes, the most recent tectonic movements and volcanism had the greatest impact on the relief in Quaternary times. Endogenous processes are relief-forming processes that occur mainly in the bowels of the Earth and are caused by its internal energy, gravity and forces arising during the rotation of the Earth.

How do the internal forces of the Earth affect the relief?

Recent (neotectonic) movements. (Slide 3) The height of modern mountain ranges, hills, lowlands and intermountain basins is largely determined by the amplitude (span) of tectonic movements of the Neogene-Quaternary time. These movements are called the latest tectonic (neotectonic).(Slide 4) Almost the entire territory of our country experienced an upsurge at this time. But the northern edge of the Asian part of Russia sank and was flooded by the waters of the seas of the Arctic Ocean. Some areas also sank and were filled with loose sediments. low plains(central regions of the West Siberian Plain, Caspian Lowland). The scope of the latest movements on platforms is measured in tens and hundreds of meters. In more mobile folded areas, the amplitude of recent tectonic movements is measured in kilometers.

Earthquakes. (Slide 5) Earthquakes are evidence of ongoing tectonic movements.
The most frequent and powerful earthquakes are observed in Kamchatka, Kuril Islands, in the mountains of the Baikal region. The Greater Caucasus, the southeastern part of Altai, Tyva and the lower reaches of the Lena are subject to significant earthquakes.

Volcanism. (Slide 6) There are active volcanoes in our country only in Kamchatka and the Kuril Islands, where powerful processes of crushing rocks into folds and creating young mountain structures actively continue to this day. There are about 60 active ones and 3 times more - extinct volcanoes. Some of the volcanoes are active almost all the time. From time to time, powerful explosions are heard that accompany volcanic eruptions; streams of hot lava burst out of the crater and flow down the slopes. When lava comes into contact with snow and glaciers, mud flows are formed. Clouds of ash rise up several kilometers, and with the wind they form huge plumes. The volcanoes of the Kuril Islands and Kamchatka have not yet caused any major troubles, but they are an uncontrollable force, and it is difficult to predict what surprises they are preparing.
Traces of recent volcanism are also found in other areas of our country. Lava plateaus and cones of extinct volcanoes are found in the Caucasus (Elbrus and Kazbek), Transbaikalia and the Far East.
Volcanic eruptions and earthquakes bring untold disasters to people and are catastrophic for many living in areas affected by them. Volcanoes and earthquakes have long aroused superstitious fear among people and given rise to belief in supernatural forces. Man is unable to prevent these phenomena. But, knowing about their approach, you can avoid human casualties and reduce the damage they cause. Therefore, the study of volcanoes and earthquakes and their prediction are of great importance. In Petropavlovsk-Kamchatsky, the Institute of Volcanology was created for this purpose.

Among external (exogenous) processes The formation of the relief had the greatest influence on its modern appearance by ancient glaciations, the activity of flowing waters and, in areas covered by sea waters, the activity of the sea.
Exogenous processes– processes caused by external forces of the Earth.

Ancient glaciations. (Slide 7) The general rise of land, changes in the contours of the Eurasian continent and the cooling of the climate on the globe led to the emergence of cover glaciation in the Quaternary.
There were 3-4 glaciation epochs in total. The centers of glaciation were the mountains of Scandinavia, the Polar Urals, Putorana and the Taimyr mountains. From here the ice spread to the surrounding areas.
As it moved, the glacier greatly changed the surface of the Earth. From the center of glaciation, he carried away stones frozen into the lower layers of ice, like a powerful bulldozer, and removed loose sediment (sand, clay, crushed stone) and even quite large stones from the surface. The glacier smoothed and rounded the rocks, leaving deep longitudinal scratches (striations) on them.
In the more southern regions, where the ice melted, the brought material, the moraine, was deposited on the plains. A moraine consists of mixed sand, clay, small fragments of hard rocks and large stones (boulders) and forms moraine hills on the surface. Where the edge of the glacier passed, the thickness of the moraine turned out to be especially large and terminal moraine ridges appeared. Since there were several glaciations and their boundaries did not coincide, several terminal moraine ridges arose.
When the glaciers melted, huge masses of water were formed, which washed over the moraine, transported and deposited sandy material, leveling the surface. Thus, water-glacial plains were created in low areas along the outskirts of the glacier.
The relief forms created by ancient glaciation are best expressed on the Russian Plain, where the thickness of the glacier was greatest.
The ancient glaciation of mountainous areas was significant. Its traces are sharp peaks and valleys with steep slopes and wide bottoms (troughs), including where there is no modern mountain glaciation.

Sea activity. Along the shores of the seas of the Arctic Ocean in Russia there are narrow strips of marine sediments. They are composed of flat coastal plains that arose during the advance of the seas in post-glacial times. In the southeastern part of the Russian Plain, the vast Caspian Lowland is composed of marine sediments. During the Quaternary period, the sea advanced here several times. During these periods, the Caspian Sea was connected to the Black Sea through the Kuma-Manych depression.

Activity of flowing waters. (Slide 8) Flowing waters constantly change the surface of the land. Their relief-forming activities continue to this day. The processes of destruction of rocks and soils by flowing waters (erosion processes) are especially vigorous in areas with a large number precipitation and significant surface slopes.
Erosion relief is especially characteristic of mountains and hills. All mountainous areas are dominated by erosional terrain. A dense network of mountain gorges and deep river valleys dissects the slopes of the ridges.
On the plains, in areas not subject to ancient glaciation, erosional dissection of the surface continued throughout the Quaternary period. Here a branched system of river valleys, gullies and deep ravines was formed, dividing watershed surfaces (Central Russian, Volga Uplands).
Flowing waters not only dissect the surface, creating erosional relief, but also deposit destruction products in river valleys and on gentle slopes. Rivers especially transport a lot of material. Flat plains created by fluvial accumulation (accumulation of river sediment) stretch in stripes along river beds. They are especially characteristic of low plains and intermountain basins. These forms occupy large areas on the West Siberian Plain.

Processes caused by gravity. (Slide 9) In areas with highly dissected relief, the action of gravity plays a large role in transforming the relief. It causes rock fragments to move down slopes and accumulate on gentle and concave slopes and foothills. In mountains with very steep slopes, large masses of large clastic material often move: stone blocks and crushed stone. Landslides and screes occur. Sometimes these processes also occur on plains, on steep slopes of river valleys and ravines.

When aquicluded rocks are shallow and especially when aquifer-bearing and impermeable layers alternate, the waterlogged upper layers slide down the aquitard. Landslides occur.
Let's landslide called the displacement (sliding) of rock masses down a slope under the influence of gravity.
Landslide relief is characterized by a hilly surface and waterlogging in the depressions between the hillocks. Landslide processes intensify during earthquakes, erosion of landslide slopes by watercourses, heavy rainfall, etc.
Landslides can destroy houses and highways, and destroy gardens and crops. Sometimes landslides resulted in human casualties. In densely populated areas, landslides cause great damage to the state.
Relief changes occur especially quickly in areas composed of loose rocks. Hard rocks are more stable, but they also gradually collapse. Weathering processes play a major role in this. The material prepared by weathering then moves under the influence of gravity, water and wind, and the rock surface freed from it is again subjected to weathering.
When a large amount of weathering products accumulates in depressions on the slopes of mountains, and sometimes on hills, and heavy precipitation falls, water-stone and mud-stone flows arise - sat down , moving at high speed and destroying everything in its path.

Aeolian landforms. Aeolian, that is, created by the wind and named after the Greek god Aeolus - the lord of the winds, landforms are found in arid, desert areas of the Caspian lowland, in areas devoid of vegetation and composed of loose loose sand. Most often they are represented by blowing basins, mounds and dunes - crescent-shaped hills moving at a speed of up to 5 m per year.
In the southern regions of our country - in the south of the Russian Plain and Western Siberia, in the foothills of the Caucasus, the Baikal region and Transbaikalia - loose, porous rocks called loess are widespread. Loess is a very valuable soil-forming rock; the most fertile soils are always formed on them. However, loess is easily washed away by water, so ravines often appear in the area where it is distributed.

How a person changes the terrain? (Slide 10)

Man, in the process of his economic activity, also changes the relief. It creates such relief forms as pits during open-pit mining, reaching depths of tens and sometimes even hundreds of meters, railway embankments, canals, etc.

To reduce the speed of modern relief-forming processes and to prevent them, it is necessary to follow certain rules of farming in areas exposed to their action. In erosion-hazardous areas, it is necessary to turf the ravine slopes, secure the tops of growing ravines, and plow across the slope. In areas where landslide processes develop, it is recommended to install drains that reduce the seepage of precipitation and limit the load on the ground during construction work.

5. Consolidation of the studied material

– What causes the Earth’s surface to change?
– Name the relief-forming processes known to you.
– What natural phenomena do you know associated with the formation of mountains that caused superstitious fear among our ancestors?
– Think about whether erosive terrain is most characteristic of mountainous or flat areas. Which rocks are most susceptible to erosion?
– What natural natural phenomena are associated with the processes of relief formation?
– Tell us about the spread of natural disasters throughout the country, explain it.
– What modern relief-forming processes are most typical for your area?

6. Lesson summary

Relief formation of the Earth.

The Earth's surface has changed as a result of the interaction of internal and external processes. Internal processes include neotectonic movements, earthquakes and volcanism.

Relief formation of the Earth

Reasons for change: external processes
Ancient glaciations	Pokrovnoe - 3-4 eras with centers: Scandinavian mountains, Polar Urals, Putorana, Taimyr mountains; formation of moraines, streaks and furrows. On the Russian Plain the thickness of the glacier is greatest.
Sea activity	Along the coasts of the seas there are narrow strips of marine sediments (coastal plains): the coast of the Arctic Ocean and the Caspian Lowland.
Activity of flowing waters	Erosion processes in areas with large amounts of precipitation, with a significant surface slope (gorges, caves, river valleys, ravines, ravines).
Processes under the influence of gravity	Landslides, screes, landslides, mudflows (mountainous areas)
Human activity	Almost the entire accessible territory of Russia: pits, embankments, canals, waste heaps, dams, etc.

The relief of Russia is extremely diverse and has a long history. A wide variety of forces and processes are involved in its formation, manifesting themselves differently and with varying intensity in different regions of our country.

7. Homework:§8

8. Test yourself.

Assignment for strong students – Computer testing ( Appendix 1 ).
Assignment for weak students - Modern development of relief. Interactive whiteboard ( Appendix 2 ).

Literature

1. Alekseev A. I. Geography of Russia: nature and population: textbook for 8th grade. M.: Bustard, 2009.
2. Alekseev A. I. Methodological manual for the course “Geography: population and economy of Russia”: A book for teachers. M.: Education, 2000.
3. Rakovskaya E. M. Geography: nature of Russia: Textbook for 8th grade. M.: Education, 2002.
4. Encyclopedia: Physical and economic geography of Russia. M.: Avanta-Plus, 2000.

Question: PLEASE HELP!!! DO NOT LEAVE GIANT TEXTS! 1.Define external forces, which have the greatest impact on the mountain topography. 2. Using a map of recent tectonic movements, identify the cause of the different relief created by flowing waters in Western Siberia and on the Central Siberian Plateau. 3. Compare the boundaries of ancient glaciation and the distribution of the relief created by its activities.

PLEASE HELP!!! DON'T LEAVE GIANT TEXTS! 1. Determine the external forces that have the greatest impact on the mountain topography. 2. Using a map of recent tectonic movements, identify the cause of the different relief created by flowing waters in Western Siberia and on the Central Siberian Plateau. 3. Compare the boundaries of ancient glaciation and the distribution of the relief created by its activities.

Answers:

1) External forces - weathering, wind work, flowing water work (erosion), snow and ice work, waves and tides, gravity. 3) There were 3-4 glaciation epochs in total. As it moved, the glacier greatly changed the surface of the Earth. From the center of glaciation, he carried away stones frozen into the lower layers of ice, like a powerful bulldozer, and removed loose sediment (sand, clay, crushed stone) and even quite large stones from the surface. The glacier smoothed and rounded the rocks, leaving deep longitudinal scratches (striations) on them. The relief forms created by ancient glaciation are best expressed on the Russian Plain, where the thickness of the glacier was greatest.

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So far we have considered internal relief-forming factors, such as movements earth's crust, folding, etc. These processes are caused by the action of the internal energy of the Earth. As a result, large landforms such as mountains and plains are created. During the lesson you will learn how the relief was formed and continues to form under the influence of external geological processes.

Other forces are also working to destroy rocks - chemical. Seeping through cracks, water gradually dissolves rocks (see Fig. 3).

Rice. 3. Dissolution of rocks

The dissolving power of water increases with the content of various gases in it. Some rocks (granite, sandstone) do not dissolve with water, others (limestone, gypsum) dissolve very intensively. If water penetrates along cracks into layers of soluble rocks, then these cracks widen. In those places where water-soluble rocks are close to the surface, numerous dips, funnels and basins are observed on it. This karst landforms(see Fig. 4).

Rice. 4. Karst landforms

Karst is the process of dissolving rocks.

Karst landforms are developed in the East European Plain, the Urals, the Urals and the Caucasus.

Rocks can also be destroyed as a result of the vital activity of living organisms (saxifrage plants, etc.). This biological weathering.

Simultaneously with the processes of destruction, the products of destruction are transferred to low areas, thus the relief is smoothed out.

Let's consider how the Quaternary glaciation shaped the modern topography of our country. Glaciers have survived today only on the Arctic islands and the highest peaks Russia (see Fig. 5).

Rice. 5. Glaciers in the Caucasus Mountains ()

Going down steep slopes, glaciers form a special glacial landform. This type of relief is common in Russia and where there are no modern glaciers - in northern parts East European and West Siberian plains. This is the result of ancient glaciation that arose in the Quaternary era due to climate cooling (see Fig. 6).

Rice. 6. Territory of ancient glaciers

The largest centers of glaciation at that time were the Scandinavian mountains, the Polar Urals, and the islands New Earth, mountains of the Taimyr Peninsula. The thickness of the ice on the Scandinavian and Kola Peninsulas reached 3 kilometers.

Glaciation occurred more than once. It was approaching the territory of our plains in several waves. Scientists believe that there were approximately 3-4 glaciations, which were followed by interglacial eras. Last ice age ended about 10 thousand years ago. The most significant glaciation was on the East European Plain, where the southern edge of the glacier reached 48º-50º N. w.

To the south, the amount of precipitation decreased, so in Western Siberia glaciation reached only 60º C. sh., and east of the Yenisei due to the small amount of snow there was even less.

In the centers of glaciation, from where ancient glaciers moved, traces of activity in the form of special forms relief - Ram's foreheads. These are rock protrusions with scratches and scars on the surface (slopes facing the movement of the glacier are gentle, and those opposite are steep) (see Fig. 7).

Rice. 7. Lamb forehead

Under the influence of their own weight, glaciers spread far from the center of their formation. Along their route, they smoothed out the terrain. A characteristic glacial relief is observed in Russia on the territory of the Kola Peninsula, the Timan Ridge, and the Republic of Karelia. The moving glacier scraped soft, loose rocks and even large, hard debris from the surface. Clay and hard rocks frozen into ice formed moraine(deposits of rock fragments formed by glaciers as they move and melt). These rocks were deposited in more southern areas where the glacier melted. As a result, moraine hills and even entire moraine plains were formed - Valdai, Smolensk-Moscow.

Rice. 8. Moraine formation

When the climate did not change for a long time, the glacier stopped in place and single moraines accumulated along its edge. In relief they are represented by curved rows tens or sometimes even hundreds of kilometers long, for example the Northern Uvaly on the East European Plain (see Fig. 8).

When glaciers melted, flows of meltwater formed, which washed over the moraine, therefore, in the areas of distribution of glacial hills and ridges, and especially along the edge of the glacier, water-glacial sediments accumulated. Sandy flat plains that arose along the outskirts of a melting glacier are called - outwash(from German “zandra” - sand). Examples of outwash plains are the Meshchera lowland, the Upper Volga, and the Vyatka-Kama lowlands. (see Fig. 9).

Rice. 9. Formation of outwash plains

Among the flat-low hills, water-glacial landforms are widespread, oz(from Swedish “oz” - ridge). These are narrow ridges, up to 30 meters high and up to several tens of kilometers long, shaped like railway embankments. They were formed as a result of the settling on the surface of loose sediment formed by rivers flowing along the surface of glaciers (see Fig. 10).

Rice. 10. Formation of eskers

All water flowing over land also forms a relief under the influence of gravity. Permanent watercourses - rivers - form river valleys. The formation of ravines is associated with temporary watercourses that form after heavy rains (see Fig. 11).

Rice. 11. Ravine

Overgrown, the ravine turns into a ravine. The slopes of the hills (Central Russian, Volga, etc.) have the most developed ravine-gully network. Well-developed river valleys are characteristic of rivers flowing outside the boundaries of the last glaciations. Flowing waters not only destroy rocks, but also accumulate river sediments - pebbles, gravel, sand and silt (see Fig. 12).

Rice. 12. Accumulation of river sediments

They consist of river floodplains, stretching in strips along river beds (see Fig. 13).

Rice. 13. River valley structure

Sometimes the latitude of floodplains ranges from 1.5 to 60 km (for example, near the Volga) and depends on the size of the rivers (see Fig. 14).

Rice. 14. Width of the Volga in various sections

Traditional places of human settlement are located along the river valleys and a special type of economic activity is being formed - livestock raising on floodplain meadows.

In lowlands experiencing slow tectonic subsidence, extensive river floods and wandering of their channels occur. As a result, plains are formed, built by river sediments. This type of relief is most common in the south of Western Siberia (see Fig. 15).

Rice. 15. Western Siberia

There are two types of erosion - lateral and bottom. Deep erosion is aimed at cutting streams into the depths and prevails in mountain rivers and rivers of plateaus, which is why deep river valleys with steep slopes are formed here. Lateral erosion is aimed at eroding the banks and is typical for lowland rivers. Speaking about the impact of water on the relief, we can also consider the impact of the sea. When seas advance on flooded land, sedimentary rocks accumulate in horizontal layers. The surface of the plains, from which the sea retreated long ago, has been greatly altered by flowing waters, wind, and glaciers. (see Fig. 16).

Rice. 16. Sea retreat

The plains, relatively recently abandoned by the sea, have a relatively flat topography. In Russia, this is the Caspian lowland, as well as many flat areas along the shores of the Arctic Ocean, part of the low-lying plains of the Ciscaucasia.

Wind activity also creates certain forms of relief, which are called aeolian. Aeolian landforms form in open spaces. In such conditions the wind carries large number sand and dust. Often a small bush is a sufficient barrier, the wind speed decreases and the sand falls to the ground. This is how small and then large sand hills are formed - barchans and dunes. In plan, the dune has the shape of a crescent, with its convex side facing the wind. As the wind direction changes, the orientation of the dune also changes. Landforms associated with wind are distributed mainly in the Caspian lowland (dunes), on the Baltic coast (dunes) (see Fig. 17).

Rice. 17. Formation of a dune

The wind blows a lot of small debris and sand from the bare mountain peaks. Many of the grains of sand it carries out hit the rocks again and contribute to their destruction. You can observe bizarre weathering figures - remnants(see Fig. 18).

Rice. 18. Remnants - bizarre landforms

The formation of special species - forests - is associated with the activity of wind. - this is a loose, porous, dusty rock (see Fig. 19).

Rice. 19. Forest

Forest covers large areas in the southern parts of the East European and West Siberian Plains, as well as in the Lena River basin, where there were no ancient glaciers (see Fig. 20).

Rice. 20. Territories of Russia covered with forest (shown in yellow)

It is believed that the formation of the forest is associated with the blowing of dust and strong winds. The most fertile soils form on the forest, but it is easily washed away by water and the deepest ravines appear in it.

1. The formation of relief occurs under the influence of both external and internal forces.
2. Internal forces create large landforms, and external forces destroy them, transforming them into smaller ones.
3. Under the influence of external forces, both destructive and creative work is carried out.

References

1. Geography of Russia. Nature. Population. 1 part 8th grade / V.P. Dronov, I.I. Barinova, V.Ya Rom, A.A. Lobzhanidze.
2. V.B. Pyatunin, E.A. Customs. Geography of Russia. Nature. Population. 8th grade.
3. Atlas. Geography of Russia. Population and economy. - M.: Bustard, 2012.
4. V.P. Dronov, L.E. Savelyeva. UMK (educational and methodological set) “SPHERES”. Textbook “Russia: nature, population, economy. 8th grade." Atlas.

1. The influence of internal and external processes on the formation of relief ().
2. External forces that change the terrain. Weathering. ().
3. Weathering().
4. Glaciation on the territory of Russia ().
5. Physics of dunes, or how sand waves are formed ().

Homework

1. Is the statement true: “Weathering is the process of destruction of rocks under the influence of wind”?
2. Under the influence of what forces (external or internal) did the peaks of the Caucasus Mountains and Altai acquire a pointed shape?