Wind and flowing waters change the topography of the mountains. External forces creating relief

Mountains have always attracted me. True, I still haven’t climbed a single peak, but I’ve been in a cave, and even during road trips with my parents I couldn’t take my eyes off the majestic mountain silhouettes outside the window. It seemed that nothing had power over these age-old giants - neither time nor man. However, this is not quite true.

Can a plain form in place of a mountainous country?

Wind and flowing waters change the relief of mountains. This process is called " denudation"("exposure"), when rocks are destroyed under the influence of the mentioned waters and wind, as well as ice, gravity, tectonic transformations or other chemical and physical processes and phenomena. Wherein mountain debris fills lower areas, leading torelief leveling. Thus, in place of a mountainous country, a plain may well form, albeit with a rather specific landscape and geological composition. Of course, this process is extremely lengthy (the only exceptions are, perhaps, volcanic explosions, the results of human activity and environmental disasters). "Born" from the destroyed mountains of the plain are called peneplains.

Examples of famous plains that arose in place of mountains

The result of denudation is the following geographical objects:

• Kazakh small hills. The most famous mountain “successor”, one of the oldest representatives of the type of denudation relief;
• Donetsk Ridge. It has a unique landscape in which flat areas are mixed with deep, mountainous valleys;
• Bugulma-Belebeevskaya Upland in the Urals on the territory of my native Bashkortostan;
• Pribelskaya ridge-undulating plain;
• Ufa plateau;
• Trans-Ural Plateau;
• all mountain system, which was transformed into the notorious peneplain back in the Mesozoic era.

I would especially like to note Mesopotamian lowland, the cradle of ancient civilizations. No, there were no mountains in this place, however The lowland owes its existence to the flowing waters of the Tigris and Euphrates, the deposits of which led to the formation of this area. The Indo-Gangetic Plain also has a similar history.

1. What external processes and how do they affect the relief of Russia?

The relief of the Earth's surface is influenced by the following processes: the activity of wind, water, glaciers, the organic world and humans.

2. What is weathering? What types of weathering are there?

Weathering is a set of natural processes that lead to the destruction of rocks. Weathering is conventionally divided into physical, chemical and biological.

3. What effect do flowing waters, wind, and permafrost have on the relief?

Temporary (formed after rains or snow melting) and rivers erode rocks (this process is called erosion). Temporary streams of water cut through ravines. Over time, erosion may decrease, and then the ravine gradually turns into a gully. Rivers form river valleys. Groundwater dissolves some rocks (limestone, chalk, gypsum, salt), resulting in the formation of caves. The destructive work of the sea is ensured by the impacts of waves on the shore. The impacts of waves form niches in the shore, and from the remains of rocks, first rocky, and then sandy beaches are formed. Sometimes the waves form narrow spits along the shore. The wind performs three types of work: destructive (blowing and loosening of loose rocks), transport (wind transfer of rock fragments over long distances) and creative (depositing of transported fragments and the formation of various aeolian surface forms). Permafrost affects the relief, since water and ice have different densities, as a result of which freezing and thawing rocks are subject to deformation - heaving associated with an increase in the volume of water during freezing.

4. What impact did ancient glaciation have on the relief?

Glaciers have a significant impact on the underlying surface. They smooth out uneven terrain and remove rock fragments, expanding river valleys. In addition, they create relief forms: troughs, pits, cirques, carlings, hanging valleys, “ram’s foreheads”, eskers, drumlins, moraine ridges, kamas, etc.

5. Using the map in Figure 30, determine: a) where the main centers of glaciations were located; b) where from these centers the glacier spread; c) what is the boundary of maximum glaciation; d) which territories the glacier covered and which it did not reach.

A) The centers of glaciation were: the Scandinavian Peninsula, the Novaya Zemlya Islands, and the Taimyr Peninsula. B) The movement from the center of the Scandinavian Peninsula was directed radially, but the southeast direction received priority; glaciation of the Novaya Zemlya islands was also radial and generally directed south; glaciation of the Taimyr Peninsula was directed to the southwest. C) The boundary of maximum glaciation runs along the northwestern part of Eurasia, while in the European part of Russia it spreads more to the south than in the Asian part, where it is limited only to the north of the Central Siberian Plateau. D) The glacier covered the territories of the northern and central parts of the East European Plain, reached 600 north latitude in Western Siberia and 62-630 north latitude in the Serden-Siberian Plateau. The territories of the northeast of the country (Eastern Siberia and the Far East), as well as the mountain belt of Southern Siberia, the south of Western Siberia and the East European Plain, and the Caucasus were outside the glaciation zone.

6. Using the map in Figure 32, trace what part of the territory of Russia is occupied by permafrost.

Approximately 65% ​​of Russia's territory is occupied by permafrost. It is mainly distributed in Eastern Siberia and Transbaikalia; at the same time, its western border begins from sections of the extreme north of the Pechersk lowland, then goes through the territory of Western Siberia in the area of ​​​​the middle reaches of the Ob River, and descends to the south, where it begins at the sources of the right bank of the Yenisei; in the east it turns out to be limited by the Bureinsky ridge.

7. Do the following work to define the concept of “weathering”: a) give a definition known to you; b) find other definitions of the concept in reference books, encyclopedias, and the Internet; c) compare these definitions and formulate your own.

Weathering is the destruction of rocks. Definitions taken from the Internet: “Weathering is a set of processes of physical and chemical destruction of rocks and their constituent minerals at their location: under the influence of temperature fluctuations, freezing cycles and the chemical action of water, atmospheric gases and organisms”; “Weathering is the process of destruction and change of rock in the conditions of the earth’s surface under the influence of mechanical and chemical influences of the atmosphere, ground and surface waters and organisms.” Synthesis of our own definition and definitions taken from the Internet: “Weathering is a constant process of destruction of rocks under the influence of external forces of the Earth, by physical, chemical and biological means”

8. Prove that the relief changes under the influence of human economic activity. What arguments in your answer will be most significant?

The anthropogenic impact on the relief includes: A) technogenic destruction of rocks, through the extraction of minerals and the creation of quarries, mines, adits; B) movement of rocks - transportation of necessary minerals, unnecessary soils during the construction of buildings, etc.; C) accumulation of displaced rocks, for example, the construction of a dam, dam, formation of waste heaps (dumps) of empty, unnecessary rocks.

9. What relief-forming processes are most characteristic of your area in the modern period? What are they due to?

In the Chelyabinsk region, currently you can find all types of weathering: physical - the destruction of the Ural Mountains with constantly blowing winds, also constant temperature changes lead to the physical destruction of rocks, the flowing waters of mountain rivers, although slowly, but constantly expand the bed and increase the river valleys , in the east of the region, every spring when there is abundant melting of snow, ravines are formed. Also on the border with the Republic of Bashkortostan, in mountainous areas, karst processes occur - the formation of caves. Biological weathering also occurs in the region, for example, in the east, beavers create dams, and sometimes peat deposits burn out in swamps, forming voids. The developed mining industry of the region has a strong impact on the relief, creating quarries and mines, waste heaps and dumps, leveling uplifts.

Until now, we have considered internal relief-forming factors, such as movements of the 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 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 landform. This type of 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 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, the Novaya Zemlya Islands, and the mountains of the Taimyr Peninsula. The ice thickness 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. The 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 relief forms - Ram's foreheads - are widespread. 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 formed 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 amounts of 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.

Bibliography

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?

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, destroyed rocks move on the surface of the Earth 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 move down the slope with destructive force, demolishing everything in their 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 easily soluble rocks (limestone, gypsum, chalk, rock salt) lie close to the earth's surface, amazing natural phenomena are observed. Rivers and streams, dissolving rocks, disappear from the surface and rush deep into the bowels of the earth. 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 sandy ones are covered with dunes and sandy 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 at 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

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 carve out 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 perform enormous destructive work, which is called (from the Latin word erosio, corroding). Land erosion is a natural process. However, it intensifies as a result of human economic activity: plowing slopes, deforestation, excessive grazing, and 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 extent in large agricultural regions of Russia, China and the USA.

Formation of the Earth's relief

Features of the Earth's relief

If there is water and wind, then they behave no better on the plain. The only difference is that soft rocks are more common here, so the result of the activity of water and wind can be noticed faster.
You've probably seen streams of water flowing through clay soil after heavy rain. The water is cloudy because it carries many particles of soil that it has eroded. It is easy to guess that this is how water erodes the soil, creating river beds and ravines.

When the river floods, it floods a huge area, forming a floodplain.

Where water flows over hard rock, it erodes narrow passages in the rocks, creating canyons. If the soil is soft, water spreads widely during heavy rain or when snow melts, washing away a layer of soil from a large surface. This is how the river floodplain appears.


Dunes are crescent-shaped sand hills up to 150 m high, moving across the desert at speeds of up to hundreds of meters per year.

Water can not only erode the soil, but in some places even complete its construction. In fact, if a stone, bush or other obstacle gets in the way of water carrying many small particles, it will slow down and part of its burden will settle on the obstacle. This is how sandbanks and entire islands appear. This is especially noticeable at the mouths of powerful rivers flowing into the ocean. Sea water quickly precipitates river turbidity. Thus, the Siberian Lena River built a peninsula from soft tundra soil, the size of which is comparable to the average European country. And numerous rivers of North America have created a whole strip of small islands along the coast of the Gulf of Mexico.

In deserts, where water is rare, the wind takes on the role of destroyer and creator. It is he who pours out huge sand dunes - sand hills that slowly move across the desert. The wind carrying grains of sand hits the stones, rubbing them with streams of sand, like sandpaper, and in the waterless desert fantastic rocks appear, similar to coastal ones, corroded by sea water. Soft rocks erode faster, hard rocks more slowly. As a result, the wind creates bizarre arches, windows, and “mushrooms” that may seem like the creation of human hands. (In the picture on the left: the wind in the desert destroys rocks. It tears off small stones and brings them down on large ones, polishes the rocks with sand, like sandpaper).