What external forces affect the relief of our planet. The relief of the earth and its main forms Table of the influence of external forces on the relief of the earth
So far, we have considered internal relief-forming factors, such as movements earth's crust, folding, etc. These processes are due to the action of the internal energy of the Earth. As a result, large landforms such as mountains and plains are created. In 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 on the destruction of 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 in water, others (limestone, gypsum) dissolve very intensively. If water penetrates along cracks into layers of soluble rocks, then these cracks expand. In those places where water-soluble rocks are close to the surface, numerous sinkholes, funnels and depressions are observed on it. This karst landforms(see Fig. 4).
Rice. 4. Karst landforms
Karst is the process of dissolution of rocks.
Karst landforms are developed on the East European Plain, Cis-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 destruction processes, the destruction products are transferred to lower areas, thus, the relief is smoothed out.
Consider how the Quaternary glaciation shaped the modern relief of our country. Glaciers have survived to this day only on the Arctic islands and on the highest peaks of Russia. (See Fig. 5).
Rice. 5. Glaciers in the Caucasus Mountains ()
Going down steep slopes, glaciers form a special, glacial relief. Such a relief is common in Russia and where there are no modern glaciers - in the northern parts of the East European and West Siberian plains. This is the result of an ancient glaciation that arose in the Quaternary era due to a cooling of the climate. (See Fig. 6).
Rice. 6. Territory of ancient glaciers
The largest centers of glaciation at that time were the Scandinavian mountains, the Polar Urals, the islands of Novaya Zemlya, the 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 advancing on the territory of our plains in several waves. Scientists believe that there were about 3-4 glaciations, which were replaced by interglacial epochs. The last ice age ended about 10,000 years ago. The most significant was the glaciation on the East European Plain, where the southern edge of the glacier reached 48º-50º N. sh.
To the south, the amount of precipitation decreased, therefore, in Western Siberia, glaciation reached only 60º N. sh., and east of the Yenisei, due to the small amount of snow, it was even less.
In the centers of glaciation, from where the ancient glaciers moved, there are widespread traces of activity in the form of special relief forms - Sheep foreheads. These are ledges of rocks with scratches and scars on the surface (slopes facing towards the movement of the glacier are gentle, and the opposite ones 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 the way, they smoothed out the relief. A characteristic glacial relief is observed in Russia on the territory of the Kola Peninsula, the Timan Ridge, 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 the ice formed moraine(deposits of rock fragments formed by glaciers during their movement and melting). These rocks were deposited in more southerly regions where the glacier was melting. 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 the relief, they are represented by curved rows tens or sometimes even hundreds of kilometers long, for example, Northern Uvaly on the East European Plain (see fig. 8).
During the melting of glaciers, streams of melt water were 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 "zander" - sand). Examples of outwash plains are the Meshcherskaya lowland, the Upper Volga, Vyatka-Kama lowland (see fig. 9).
Rice. 9. Formation of outwash plains
Among the flat-low hills, water-glacial landforms are widespread, ozes(from Swedish "oz" - ridge). These are narrow ridges, up to 30 meters high and up to several tens of kilometers long, resembling railway embankments in shape. They were formed as a result of settling on the surface of loose sediments formed by rivers flowing along the surface of glaciers. (see fig. 10).
Rice. 10. Formation of lakes
All water flowing on land, under the influence of gravity, also forms a relief. Permanent streams - rivers - form river valleys. The formation of ravines is associated with temporary streams formed after heavy rains. (see fig. 11).
Rice. 11. Ravine
Overgrown, the ravine turns into a beam. The slopes of uplands (Central Russian, Volga, etc.) have the most developed ravine 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 sediment
They consist of river floodplains, stretching in strips along the riverbeds. (see fig. 13).
Rice. 13. The structure of the river valley
Sometimes the latitude of the floodplains varies from 1.5 to 60 km (for example, near the Volga) and depends on the size of the rivers (see Fig. 14).
Rice. 14. The width of the Volga in various sections
Along the river valleys there are traditional places of human settlement and a special kind of economic activity- Animal husbandry in floodplain meadows.
On the lowlands, experiencing slow tectonic subsidence, there are extensive floods of rivers and wanderings of their channels. As a result, plains are formed, built by river sediments. This 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 flows into the depth and prevails near mountain rivers and rivers of plateaus, which is why deep river valleys with steep slopes are formed here. Lateral erosion is aimed at erosion of 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 the seas advance on the flooded land, sedimentary rocks accumulate in horizontal layers. The surface of the plains, from which the sea retreated long ago, is greatly changed by flowing waters, wind, glaciers (see fig. 16).
Rice. 16. Retreat of the sea
The plains, relatively recently abandoned by the sea, have a relatively flat relief. In Russia, this is the Caspian lowland, as well as many flat areas along the shores of the Arctic Ocean, part of the low plains of Ciscaucasia.
The activity of the wind also creates certain landforms, which are called eolian. Aeolian landforms are formed in open spaces. In such conditions, the wind carries a large amount of sand and dust. Often a small bush is a sufficient barrier, the wind speed decreases, and the sand falls to the ground. Thus, at first small, and then large sandy hills are formed - dunes and dunes. In terms of plan, the dune has the shape of a crescent, with its convex side facing the wind. As the direction of the wind changes, so does the orientation of the dune. Wind-related landforms are distributed mainly on 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 fragments and sand from the bare mountain peaks. Many of the grains of sand he carries out again hit the rocks and contribute to their destruction. You can observe bizarre weathering figures - remnants(see fig. 18).
Rice. 18. Remains - bizarre landforms
The formation of special species - forests - is associated with the activity of the wind. - 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. Russian territories covered with forest (shown in yellow)
It is believed that the formation of the forest is associated with dust and strong winds. The most fertile soils are formed on the forest, but it is easily washed away by water and the deepest ravines appear in it.
- The formation of the relief occurs under the influence of both external and internal forces.
- Internal forces create large landforms, and external forces destroy them, transforming them into smaller ones.
- Under the influence of external forces, both destructive and creative work is carried out.
Bibliography
- Geography of Russia. Nature. Population. 1 hour Grade 8 / V.P. Dronov, I.I. Barinova, V.Ya Rom, A.A. Lobzhanidze.
- V.B. Pyatunin, E.A. Customs. Geography of Russia. Nature. Population. 8th grade.
- Atlas. Geography of Russia. population and economy. - M.: Bustard, 2012.
- V.P. Dronov, L.E. Savelyeva. UMK (educational-methodical set) "SPHERES". Textbook “Russia: nature, population, economy. 8th grade". Atlas.
- The influence of internal and external processes on the formation of relief ().
- External forces that change the relief. Weathering. ().
- weathering().
- Glaciation in Russia ().
- Physics of dunes, or how sand waves are formed ().
Homework
- Is the statement true: “Weathering is the process of destruction of rocks under the influence of wind”?
- Under the influence of what forces (external or internal) did the peaks of the Caucasus Mountains and Altai acquire a pointed shape?
Remember
- Due to what source of energy do external forces act to change the surface of the Earth? What happens to solid rocks when heated and then cooled? How do tree roots and burrowing animals affect rocks?
How external forces affect the terrain. You already know that internal forces make the Earth's surface vary in height. External forces act in the opposite direction. They destroy large relief elevations, carry rock fragments and fill depressions with them. Thus, external forces smooth, level the surface. However, external processes are not only destroyers, but also creators of the relief. Destroying its large forms, they create medium and small irregularities.
The main external forces are weathering, the work of flowing waters, wind, glaciers, and the sea. Human economic activity has also become a significant external force.
Weathering. Weathering occurs due to the impact on the surface of temperature fluctuations, water with substances dissolved in it and living organisms. Wind work has nothing to do with weathering.
Weathering is the destruction and change of rocks on the land surface under the influence of environmental conditions.
During weathering, physical, chemical and biological processes simultaneously operate everywhere on the surface of the land. However, in different natural conditions one or the other of these processes may predominate. Therefore, physical, chemical and biological weathering is distinguished.
Rice. 60. Placers of stones at the foot of the mountains
main reason physical weathering- temperature fluctuations. During the day, the rocks heat up and expand, at night they cool and narrow. Because of this, monolithic rocks crack and break up into fragments. This is how placers are formed from blocks, crushed stone and sand (Fig. 60). Physical weathering is typical for areas with large and sharp temperature changes and dry air: deserts, mountain peaks not covered with snow (Fig. 61).
chemical weathering- this is the dissolution, decomposition of some minerals and the formation of other minerals and rocks instead. It occurs under the influence of air oxygen, water and substances dissolved in it. In humid and hot climates, chemical weathering occurs more actively than in cold and dry ones. The main result of chemical weathering is the formation of clay from hard and durable rocks: granites, basalts, gneisses, etc.
biological weathering occurs under the influence of plant and animal organisms. The roots of trees growing on rocks spread cracks like wedges. Animals, especially burrowing rodents, also contribute to the destruction of rocks. But the main effect of living organisms is something else. They supply the soil organic matter, which contribute to the decomposition of minerals. Therefore, where lush vegetation grows, biological weathering is especially active.
Rice. 61. Bizarre landforms formed by weathering
The strength of different breeds is not the same. Some break down faster, others slower. Therefore, when weathering rocks of different strengths, bizarre landforms arise: pillars, columns, balls, gates.
Even microorganisms, lichens, mosses have an impact on rocks. If you tear off the moss from the stone, then under it you can find small depressions filled with loose matter. This is the result of the destruction of hard rock by organic acids secreted by mosses.
Physical, chemical and biological weathering occurs everywhere and all the time. Under its influence, even the most durable rocks turn into loose material - debris and clay. Loose material is carried by water currents, wind, glaciers over great distances. When it enters lakes, seas and oceans, clastic and clay sedimentary rocks accumulate from it.
Questions and tasks
- How do external forces act on the earth's surface?
- What is weathering? How does it affect rocks?
- What types of weathering process consists of?
- How do living organisms affect rocks?
- How are animals and plants involved in physical and chemical weathering?
Class: 8
Presentation for the lesson
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Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.
Target: to reveal to students ideas about internal (endogenous) and external (exogenous) processes as necessary condition relief development, to teach to independently identify cause-and-effect relationships, to show the continuity of relief development, to identify especially dangerous natural phenomena, the causes of occurrence.
Equipment: physical and tectonic maps of Russia; map of recent tectonic movements; interactive whiteboard; visual and illustrative material about mudflows, erosional activity of rivers and ravines, landslides and other exogenous processes; filmstrip "Formation of relief".
DURING THE CLASSES
1. Organizational moment
2. Repetition of the studied material.
– Find 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. What do you think is the difference between the life of people in the mountains and on the plain?
- Give examples of the influence of relief on the nature of our country.
- The plains of Russia are among the greatest in the world. With what plains of the globe can they be compared in size and structure?
4. Learning new material(Presentation )
(Slide 1) The surface of the Earth 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 were especially strongly reflected in the modern relief: the latest tectonic movements, ancient glaciations, the advance of the seas. (Slide 2)
Among the internal (endogenous) processes, the most recent tectonic movements and volcanism had the greatest influence on the relief in the Quaternary. Endogenous processes are relief-forming processes that occur mainly in the bowels of the Earth and are due to its internal energy, gravity and forces arising from 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, uplands, lowlands and intermountain basins is largely due to the amplitude (range) 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 uplift at that time. But the northern outskirts of the Asian part of Russia sank and was flooded by the waters of the seas of the Arctic Ocean. Some sections of the low plains (the central regions of the West Siberian Plain, the Caspian lowland) also descended and were filled with loose deposits. The scope of the newest movements on the platforms is measured in tens and hundreds of meters. In more mobile folded areas, the amplitude of the latest tectonic movements is measured in kilometers.
earthquakes.
(Slide 5) Earthquakes are evidence of ongoing tectonic movements.
The most frequent and strong earthquakes are observed in Kamchatka, the Kuril Islands, and in the mountains of the Baikal region. The Greater Caucasus, the southeastern part of Altai, Tuva and the lower reaches of the Lena are subject to significant earthquakes.
Volcanism.
(Slide 6) Active volcanoes in our country are only on Kamchatka and the Kuril Islands, where powerful processes of crushing rocks into folds and creating young mountain structures are actively continuing to this day. There are about 60 active and 3 times more extinct volcanoes. Almost all the time, some of the volcanoes are active. From time to time, powerful explosions are heard, accompanying volcanic eruptions, streams of red-hot lava break out of the crater and flow along the slopes. When lava comes into contact with snow and glaciers, mud flows are formed. Clouds of ash rise up for several kilometers, and with the wind they form huge plumes. The volcanoes of the Kuriles and Kamchatka have not yet caused big troubles, but this is an uncontrollable force, and it is difficult to predict what surprises they are preparing.
Traces of recent volcanism are also found in other parts of our country. There are lava plateaus and cones of extinct volcanoes in the Caucasus (Elbrus and Kazbek), in Transbaikalia and in the Far East.
Volcanic eruptions and earthquakes bring innumerable disasters to people, are a catastrophe for many living in areas prone to them. Volcanoes and earthquakes have long evoked superstitious fear in people, giving rise to faith in supernatural forces. Man is unable to prevent these phenomena. But, knowing about their approach, it is possible to avoid human casualties and reduce the damage they cause. Therefore, the study of volcanoes and earthquakes and their prediction is of great importance. The Institute of Volcanology was established in Petropavlovsk-Kamchatsky for this purpose.
Among external (exogenous) processes the formation of the relief, the greatest influence on its modern appearance was exerted by ancient glaciations, the activity of flowing waters and, in areas covered with sea waters, the activity of the sea.
Exogenous processes- processes caused by external forces of the Earth.
Ancient glaciations.
(Slide 7) The general uplift of the land, changes in the outlines of the Eurasian continent and the cooling of the climate on the globe led to the emergence of a cover glaciation in the Quaternary.
In total there were 3-4 epochs of glaciation. The mountains of Scandinavia, the Polar Urals, Putorana and the mountains of Taimyr served as centers of glaciation. From here, the ice spread to the adjacent territories.
Moving, the glacier greatly changed the surface of the Earth. From the center of glaciation, he carried away with him stones frozen into the lower layers of ice, like a powerful bulldozer, removed loose deposits (sand, clay, crushed stone) and even rather large stones from the surface. The glacier smoothed and rounded the rocks, leaving deep longitudinal scratches (strokes) on them.
In the more southern regions, where the ice melted, the brought material, the moraine, was deposited on the plains. The 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 arose. Since there were several glaciations and their boundaries did not coincide, several terminal moraine ridges arose.
During the melting of glaciers, huge masses of water were formed, which washed the moraine, carried and deposited sandy material, leveling the surface. Thus, water-glacial plains were created in low areas along the outskirts of the glacier.
The landforms created by ancient glaciation are best expressed on the Russian Plain, where the thickness of the glacier was greatest.
Significant was the ancient glaciation of the mountainous regions. Its traces are sharp peaked peaks and valleys with steep slopes and wide bottoms (troughs), including where there is no modern mountain glaciation.
Sea activity. On the shores of the seas of the Arctic Ocean in Russia there are narrow strips of marine sediments. They make up flat coastal plains that arose during the advance of the seas in the post-glacial period. In the southeastern part of the Russian Plain, the extensive Caspian lowland is composed of marine sediments. In the Quaternary time, the advance of the sea repeatedly took place here. During these periods, the Caspian through the Kuma-Manych depression connected with the Black Sea.
Activity of flowing waters.
(Slide 8) Flowing waters constantly change the surface of the land. Their relief-forming activity continues at the present time. The processes of destruction of rocks and soils by flowing waters (erosion processes) are especially vigorous in areas with a large amount of precipitation and significant surface slopes.
Erosive relief is especially characteristic of mountains and uplands. Erosion relief prevails in all mountainous regions. A dense network of mountain gorges and deep river valleys dissects the slopes of the ridges.
On the plains, in areas that were not subjected to ancient glaciation, the erosional dissection of the surface continued throughout the entire Quaternary period. An extensive system of river valleys, ravines and deep ravines has formed here, dividing the watershed surfaces (Central Russian, Volga Uplands).
Flowing waters not only dissect the surface, creating an erosive relief, but also deposit destruction products in river valleys and on gentle slopes. Especially a lot of material is carried by rivers. Flat plains created by river accumulation (accumulation of river sediments) stretch in stripes along the river beds. They are especially characteristic of low plains and intermountain basins. These forms occupy large areas in the West Siberian Plain.
Processes caused by the action of gravity. (Slide 9) In areas with a highly dissected relief, the effect of gravity plays an important role in the transformation of the relief. It causes the movement of rock fragments down the slopes and their accumulation on gentle and concave slopes and foothills. In the mountains, with a steep slope, large masses of large detrital material often move: boulders and rubble. Falls and screes occur. Sometimes these processes also occur on the plains, on the steep slopes of river valleys and ravines.
With a shallow occurrence of water-resistant rocks, and especially with the alternation of aquifers and water-resistant layers, the waterlogged upper layers slip along the aquiclude. Landslides occur.
Landslide
called the displacement (sliding) of rock masses down the slope under the influence of gravity.
The landslide relief is characterized by a hilly surface, waterlogged depressions between hillocks. Landslide processes are intensified during earthquakes, erosion of landslide slopes by watercourses, heavy precipitation, etc.
Landslides can destroy homes and highways, demolish gardens and crops. Sometimes landslides resulted in human casualties. In densely populated areas, landslides cause great damage to the state.
The change in relief occurs especially rapidly in areas composed of loose rocks. Solid rocks are more stable, but they are gradually destroyed. Weathering processes play an important role in this. The material prepared by weathering is then moved under the action of gravity, water and wind, and the rock surface freed from it is again subjected to weathering.
With the accumulation of a large amount of weathering products in depressions on the slopes of mountains, and sometimes uplands and heavy precipitation, water-stone and mud-stone flows arise - sat down
moving at high speed and destroying everything in its path.
Aeolian landforms.
Eolian, that is, created by the wind and named after the Greek god Eol, the lord of the winds, landforms are found in arid, desert regions of the Caspian lowland, in areas devoid of vegetation and composed of loose loose sands. Most often they are represented by blowout basins, knolls 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. Loesses are very valuable soil-forming rocks; the most fertile soils are always formed on them. However, loess is easily eroded by water, so ravines often appear in the area of their distribution.
How a person changes the terrain? (Slide 10)
A person in the process of his economic activity also changes the relief. It creates such landforms as pits during open-pit mining, reaching a depth of tens, and sometimes even hundreds of meters, railway embankments, canals, etc.
To reduce the speed of modern relief-forming processes, to prevent them, it is necessary to observe certain rules for managing the economy in areas subject to their action. In erosion-prone areas, it is necessary to tin the ravine slopes, fix the tops of growing ravines, and plow across the slope. In the areas of development of landslide processes, it is recommended to arrange drains that reduce the seepage of precipitation, limit the load on the soil during construction work.
5. Consolidation of the studied material
What causes the surface of the earth to change?
- Name the relief-forming processes known to you.
- What phenomena of nature known to you, associated with the formation of mountains, caused superstitious fear among our ancestors?
- Think, for mountainous or flat areas, erosional relief is most characteristic. Which rocks are most susceptible to erosion?
– What 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. Summary of the lesson
Relief formation of the Earth.
The surface of the Earth 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 | Cover - 3-4 epochs with centers: Scandinavian mountains, Polar Urals, Putorana, Taimyr mountains; the formation of moraines, strokes and furrows. On the Russian Plain, the thickness of the glacier is the largest. |
| Sea activities | Along the coasts of the seas 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 a large amount of precipitation, with a significant slope of the surface (gorges, caves, river valleys, gullies, 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 unusually diverse and has a long history. A wide variety of forces and processes are involved in its formation, manifesting themselves unequally and with varying intensity in different regions of our country.
7. Homework:§8
8. Test yourself.
Task for strong students - Computer testing ( Attachment 1
).
Task for weak students - Modern development of the relief. interactive whiteboard (Annex 2
).
Literature
- Alekseev A.I. Geography of Russia: nature and population: a textbook for grade 8. M.: Bustard, 2009.
- Alekseev A.I. Toolkit on the course "Geography: population and economy of Russia": A book for the teacher. M.: Education, 2000.
- Rakovskaya E. M. Geography: nature of Russia: Textbook for grade 8. M.: Education, 2002.
- Encyclopedia: Physical and economic geography of Russia. M.: Avanta-Plus, 2000.
Until now, we have considered internal relief-forming factors, such as movements of the earth's crust, folding, etc. These processes are due to the action of the internal energy of the Earth. As a result, large landforms such as mountains and plains are created. In the lesson, you will learn how the relief was formed and continues to form under the influence of external geological processes.
Relief-forming processes
It would be wrong to assume that the relief of our planet was formed in those ancient geological epochs under the influence of internal (endogenous) forces. Even in such stable forms of the earth's surface as platforms, changes occur under the influence of external factors. All relief-forming processes can be divided into two large groups: internal (endogenous) and external (exogenous).
The main exogenous processes that change the relief of our country include weathering, glaciation, the activity of flowing waters and wind processes (see Fig. 1).
Rice. 1. External relief-forming factors
Weathering
Weathering- this is the process of destruction and change of rocks under the influence of the mechanical and chemical effects of the atmosphere, ground and surface waters and organisms.
Rocks are destroyed by temperature changes due to the fact that the minerals of which they are composed have different coefficients thermal expansion. Over time, cracks appear in the once monolithic rock. Water penetrates into them, which freezes at negative temperatures and, turning into ice, literally “breaks” the rocks. Their destruction occurs, and along with this, the “smoothing” of the relief forms. Such processes are called physical weathering. They occur most intensively in the mountains, where solid monolithic rocks come to the surface. The rate of physical weathering processes (about 1 mm per year) seems to be very low. However, over millions of years, the mountains will already drop by 1 kilometer. Thus, for the complete destruction of the highest mountains of the Earth, the Himalayas, it would take 10 million years. By geological standards, this is a very short time period (see Fig. 2).
Rice. 2. Physical weathering
Other forces are also working on the destruction of 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 in water, others (limestone, gypsum) dissolve very intensively. If water penetrates along cracks into layers of soluble rocks, then these cracks expand. In those places where water-soluble rocks are close to the surface, numerous sinkholes, funnels and depressions are observed on it. This karst landforms(see Fig. 4).
Rice. 4. Karst landforms
Karst is the process of dissolution of rocks.
Karst landforms are developed on the East European Plain, Cis-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 destruction processes, the destruction products are transferred to lower areas, thus, the relief is smoothed out.
Glaciation
Consider how the Quaternary glaciation shaped the modern relief of our country. Glaciers have survived today only on the Arctic islands and on the highest peaks of Russia (see Fig. 5).
Rice. 5. Glaciers in the Caucasus Mountains
Going down steep slopes, glaciers form a special, glacial relief. Such a relief is common in Russia and where there are no modern glaciers - in the northern parts of the East European and West Siberian plains. This is the result of an ancient glaciation that arose in the Quaternary due to a cooling of the climate (see Fig. 6).
Rice. 6. Territory of ancient glaciers
The largest centers of glaciation at that time were the Scandinavian mountains, the Polar Urals, the islands of Novaya Zemlya, the 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 advancing on the territory of our plains in several waves. Scientists believe that there were about 3-4 glaciations, which were replaced by interglacial epochs. The last ice age ended about 10,000 years ago. The most significant was the glaciation on the East European Plain, where the southern edge of the glacier reached 48º-50º N. sh.
To the south, the amount of precipitation decreased, therefore, in Western Siberia, glaciation reached only 60º N. sh., and east of the Yenisei, due to the small amount of snow, it was even less.
In the centers of glaciation, from where the ancient glaciers moved, there are widespread traces of activity in the form of special relief forms - Sheep foreheads. These are protrusions of rocks with scratches and scars on the surface (the slopes facing towards the movement of the glacier are gentle, and the opposite ones 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 the way, they smoothed out the relief. A characteristic glacial relief is observed in Russia on the territory of the Kola Peninsula, the Timan Ridge, 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 the ice formed moraine(deposits of rock fragments formed by glaciers during their movement and melting). These rocks were deposited in more southerly regions where the glacier was melting. 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 the relief, they are represented by curved rows tens or sometimes even hundreds of kilometers long, for example, Northern Uvaly on the East European Plain (see Fig. 8).
During the melting of glaciers, streams of melt water were 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 "zandr" - sand). Examples of outwash plains are the Meshcherskaya lowland, the Upper Volga, Vyatka-Kama lowlands (see Fig. 9).
Rice. 9. Formation of outwash plains
Among the flat-low hills, water-glacial landforms are widespread, ozes(from the Swedish "oz" - ridge). These are narrow ridges, up to 30 meters high and up to several tens of kilometers long, resembling railway embankments in shape. They were formed as a result of sedimentation on the surface of loose sediments formed by rivers flowing along the surface of glaciers (see Fig. 10).
Rice. 10. Formation of lakes
Activity of flowing waters
All water flowing on land, under the influence of gravity, also forms a relief. Permanent streams - rivers - form river valleys. The formation of ravines is associated with temporary streams formed after heavy rains (see Fig. 11).
Rice. 11. Ravine
Overgrown, the ravine turns into a beam. The slopes of uplands (Central Russian, Volga, etc.) have the most developed ravine 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 sediment
River floodplains consist of them, stretching in strips along the riverbeds (see Fig. 13).
Rice. 13. The structure of the river valley
Sometimes the latitude of the floodplains varies from 1.5 to 60 km (for example, near the Volga) and depends on the size of the rivers (see Fig. 14).
Rice. 14. The width of the Volga in various sections
Along the river valleys there are traditional places of human settlement and a special type of economic activity is being formed - animal husbandry in floodplain meadows.
On the lowlands, experiencing slow tectonic subsidence, there are extensive floods of rivers and wanderings of their channels. As a result, plains are formed, built by river sediments. This relief is most widespread 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 flows into the depth and prevails near mountain rivers and rivers of plateaus, which is why deep river valleys with steep slopes are formed here. Lateral erosion is aimed at erosion of 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 the seas advance on the 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. Retreat of the sea
The plains, relatively recently abandoned by the sea, have a relatively flat relief. In Russia, this is the Caspian lowland, as well as many flat areas along the shores of the Arctic Ocean, part of the low plains of Ciscaucasia.
wind activity
The activity of the wind also creates certain landforms, which are called eolian. Aeolian landforms are formed in open spaces. In such conditions, the wind carries a large amount of sand and dust. Often a small bush is a sufficient barrier, the wind speed decreases, and the sand falls to the ground. Thus, at first small, and then large sandy hills are formed - dunes and dunes. In terms of plan, the dune has the shape of a crescent, with its convex side facing the wind. As the direction of the wind changes, so does the orientation of the dune. Wind-related landforms are distributed mainly on the Caspian lowland (dunes) and on the Baltic coast (dunes) (see Fig. 17).
Rice. 17. Formation of a dune
The wind blows a lot of small fragments and sand from the bare mountain peaks. Many of the grains of sand he carries out again hit the rocks and contribute to their destruction. You can observe bizarre weathering figures - remnants(see fig. 18).
Rice. 18. Remains - bizarre landforms
The formation of special species - forests - is associated with the activity of the wind. - this is a loose, porous, silty 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. Russian territories covered with forest (shown in yellow)
It is believed that the formation of the forest is associated with dust and strong winds. The most fertile soils are formed on the forest, but it is easily washed away by water and the deepest ravines appear in it.
Summing up
The formation of the relief occurs under the influence of both external and internal forces. Internal forces create large landforms, and external forces destroy them, transforming them into smaller ones. Under the influence of external forces, both destructive and creative work is carried out.
Bibliography
Geography of Russia. Nature. Population. 1 hour Grade 8 / V. P. Dronov, I. I. Barinova, V. Ya Rom, A. A. Lobzhanidze. V. B. Pyatunin, E. A. Customs. Geography of Russia. Nature. Population. 8th grade. Atlas. Geography of Russia. population and economy. - M.: Bustard, 2012. V. P. Dronov, L. E Savelyeva. UMK (educational-methodical set) "SPHERES". Textbook “Russia: nature, population, economy. 8th grade". Atlas.
Influence of internal and external processes on the formation of relief. External forces that change the relief. Weathering. . Weathering. Glaciation in Russia. Physics of dunes, or how sand waves are formed.
Homework
Is the statement true: “Weathering is the process of destruction of rocks under the influence of wind”? Under the influence of what forces (external or internal) did the peaks of the Caucasus Mountains and Altai acquire a pointed shape?
External forces - weathering, the work of the wind, the work of flowing waters (erosion), the work of snow and ice, the activity of waves and tides, the action of gravity
The activity of external forces as a whole leads to the destruction of the rocks that make up the earth's surface, and the demolition of the products of destruction from high places to lower ones. This process is called denudation. Demolished material accumulates in low places - valleys, hollows, depressions. This process is called accumulation. The destruction of rocks near the Earth's surface under the influence of various factors - weathering prepares the material for movement. Weathering can be of three types - physical, chemical and biological.
The role of water that has fallen into cracks, which are almost always present in rocks, is especially great. Freezing, it expands, pushes the edges of the crack; thawing, flows out of it, taking with it the destroyed particles.
An equally important force, under the influence of which the relief changes, is a manifestation of the action of gravity. These are such natural phenomena as mudflows, landslides, landslides and talus. The activity of flowing waters forms beams, ravines and huge canyons in the relief. Thanks to karsts, mountain caves and funnels appear.
Sea waves and tides contribute to the change in relief. They destroy the shores, carry away the destroyed material and move it to different distances along the coast, forming coastal ramparts and beaches, constantly changing the coastline.
Rock fragments, sand, dust from surrounding rocks and valley slopes move on the surface of mountain glaciers and in their thickness. When a glacier melts, all this material falls on the earth's surface. The ice mass itself is capable of exerting a strong shaping effect on the relief. Under its influence, trough-shaped glacial valleys are formed - troughs, pointed peaks - carlings, huge bulk shafts - moraines. Glaciers contribute to the formation of sands and mountain ranges. As a result of erosion, the earth and rocks acquire a strange shape, change color, and form bizarre shapes.
Another important element that affects the state of the relief is the wind. The most striking example of his activities are the sand dunes.
And the last external force, which is not related to natural phenomena, is human activity. With the help of mechanisms, he is able to pull out giant quarries or waste heaps.
1. Temperature differences. With the first rays of the sun, snow and ice begin to melt high in the mountains. Water penetrates into all cracks and depressions of rocks. At night, temperatures drop a few degrees below zero and the water turns to ice. At the same time, it increases in volume by 9% and pushes the cracks apart, expanding and deepening them. This continues day after day, year after year, until some crack separates a piece of rock from the main massif and it rolls down the slope. Rocks are also subjected to heating and cooling. The minerals they contain have different thermal conductivity. Expanding and contracting, they break strong bonds between themselves. When these bonds are completely destroyed, the rock turns into sand.
2. The active impact of plant and animal organisms on rocks causes biogenic weathering. The roots of plants perform mechanical destruction, and the acids released in the course of their vital activity perform chemical destruction. As a result of many years of activity of living organisms, coral reefs and a special type of islands arise - atolls formed by calcareous skeletons of marine animals.
3. The absolute master of open spaces is the wind. Encountering obstacles on its way, it forms majestic hills - dunes and dunes. In the Sahara desert, some of them are up to 200-300 meters high. In the mountain ranges located in the desert, there is almost never loose material that fills the depressions and cracks. That is why aeolian landforms appear, reminiscent of towers, pillars and bizarre castles.
4. Human economic activity also causes changes in the relief. Man extracts minerals, as a result of which quarries are formed, builds buildings, canals, makes embankments and fills up ravines. This is all a direct impact, but it can also be indirect, which is the creation of favorable conditions for relief-forming processes (plowing of slopes causes rapid growth of ravines).
