Wind and flowing waters change the topography of the mountains. External forces that create relief. Examples of famous plains that arose on the site of mountains

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

Can a plain be formed on the site of a mountainous country

Wind and flowing waters change the topography of mountains. This process is called " denudation"(outcrop") when rocks are breaking down under the influence of the mentioned waters and wind, as well as ice, its own gravity, tectonic transformations or other chemical and physical processes and phenomena. Wherein fragments of mountains fill the lower areas, which leads toterrain leveling. Thus, on the site of a mountainous country, a plain may well be formed, however, a rather specific landscape and geological composition. Of course, this process is extremely long (the only exceptions are, perhaps, the explosions of volcanoes, the results human activity and environmental disasters). "Born" from the destroyed mountains of the plains are called peneplains.

Examples of famous plains that arose on the site of mountains

The result of denudation is the following geographic features:

• Kazakh uplands. 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 spaces are mixed with deep, mountainous valleys;
• Bugulma-Belebeevskaya Upland in the Cis-Urals on the territory of my native Bashkortostan;
• Pribelskaya ridged-wavy plain;
• Ufa plateau;
• Transural plateau;
• all mountain system , which is still in mesozoic era was turned into the notorious peneplain.

Separately, I would like to note Mesopotamian lowlands, 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 following processes influence the relief of the Earth's surface: the activity of wind, water, glaciers, organic world and a person.

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

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

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

Temporary (formed after rains or melting snow) and rivers erode rocks (this process is called erosion). Temporary streams of water cut through ravines. Over time, erosion can decrease, then the ravine gradually turns into a beam. Rivers form river valleys. The groundwater dissolve some rocks (limestone, chalk, gypsum, salt), resulting in the formation of caves. The destructive work of the sea is provided by the impact of waves on the shore. Wave blows form niches in the shore, and from the remains of rocks, first stony, and then a sandy beach is formed. Sometimes the waves along the coast wash up narrow spits. The wind performs three types of work: destructive (blowing and blowing loose rocks), transport (transportation of rock fragments by wind over long distances) and creative (deposition of the transferred debris and the formation of various eolian 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 influence did the ancient glaciation have on the relief?

Glaciers have a significant impact on the underlying surface. They smooth out uneven terrain and demolish rock fragments, and widen river valleys. In addition, they create landforms: troughs, karts, circuses, carlings, hanging valleys, "sheep's foreheads", eskers, drumlins, stained ridges, kams, etc.

5. On the map in Figure 30, determine: a) where were the main centers of glaciation; b) where the glacier flowed from these centers; c) how is the boundary of maximum ice cover; d) which territories were covered by the glacier, which did not reach.

A) The centers of glaciation were: the Scandinavian Peninsula, the islands New Earth, Taimyr Peninsula. B) The movement from the center of the Scandinavian Peninsula was directed radially, but the south-easterly direction received the advantage; the glaciation of the islands of Novaya Zemlya was also radial and generally directed to the south; glaciation of the Taimyr Peninsula was directed to the southwest. C) The boundary of maximum glaciation passes through the northwestern part of Eurasia, while in the European part of Russia it has more distribution to the south than in Asia, where it is limited only by 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 northern latitude V Western Siberia and 62-630 north latitude in the Serden-Siberian Plateau. Territories of the north-east of the country ( Eastern Siberia And Far East), as well as the belt of the mountains of Southern Siberia, the south of Western Siberia and the East European Plain, the Caucasus were outside the glaciation zone.

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

Approximately 65% ​​of the territory of Russia is occupied by permafrost. It is mainly distributed in Eastern Siberia and Transbaikalia; while her western border starts from the areas of the extreme north of the Pechersk lowland, then goes through the territory of Western Siberia in the region of the middle course of the Ob River, and descends to the south, where it begins at the headwaters of the right bank of the Yenisei; in the east it turns out to be limited by the Bureinsky ridge.

7. Carry out the following work but the definition of the concept of "weathering": a) give a definition you know; b) find other definitions of the concept in reference books, encyclopedias, 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 place of occurrence: under the influence of temperature fluctuations, freezing cycles and chemical effects of water, atmospheric gases and organisms”; “Weathering is the process of destruction and change of rock under conditions earth's surface under the influence of mechanical and chemical effects of the atmosphere, ground and surface waters and organisms”. Synthesis of my own definition and definitions taken from the Internet: "Weathering is a constant process of destruction of rocks under the influence of the external forces of the Earth, in a physical, chemical and biological way"

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

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

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

IN Chelyabinsk region, now you can meet all types of weathering: physical - destruction Ural mountains with constantly blowing winds, also constant temperature changes lead to the physical destruction of rocks, flowing waters mountain rivers, although slowly but constantly expanding the channel and increasing the river valleys, in the east of the region every spring, with abundant snowmelt, ravines are formed. Also on the border with the Republic of Bashkortostan, in the mountainous regions, processes of karstization occur - the formation of caves. Also, biological weathering occurs on the territory of the region, so in the east beavers create dams, 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.

So far, we have considered internal relief-forming factors, such as movements earth's crust, folding, etc. These processes are due to the action internal energy Earth. As a result, large forms terrain such as mountains and plains. 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 date 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 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. Last glacial period ended about 10 thousand 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 terrain. A characteristic glacial relief is observed in Russia on the territory Kola Peninsula, Timan Ridge, 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).

When glaciers melt, streams form melt water, 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 out of bounds 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 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 banks of the Northern 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. Under such conditions, the wind carries a large number 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. The landforms associated with the wind are distributed mainly in 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

covered with forest large territories 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 winding dust and strong winds. On the forest, the most fertile soils, however, it is easily washed out by water and the deepest ravines appear in it.

1. The formation of the 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 hour Grade 8 / 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-methodical 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 relief. Weathering. ().
3. weathering().
4. Glaciation in 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) the vertices Caucasus mountains and Altai acquired a pointed shape?

Moving rivers destroy the rocks adjacent to them and create river valleys, ravines. A river valley is a lowering of the relief, elongated along the river and resulting from the long work of the flowing waters of the river.

On the other hand, rivers carry rock fragments into depressions or their river valleys. As a result, river sediments appear.

A glacier is a collection of ice that moves along the earth. Moving, the ice captures stones, sand and other fragments of rocks, destroys rocks, plows out depressions. After the glacier melts, the debris will settle in another area, forming the so-called glacial deposits.

According to the accumulation of certain hills, they now conclude which area the glacier used to occupy. So tens of thousands of years ago there were more glaciers on Earth.

The wind is able to carry small fragments of rocks and accumulate them in certain places. This effect of the wind is most noticeable in deserts and other places on the earth's surface where there is no vegetation.

The wind can destroy even strong rocks. When the wind contains many grains of sand and they strike hard rocks with great force, they gradually destroy them and, as they say, grind them.

In sandy areas, the wind, carrying the sands, forms depressions and hills. In deserts, such sandy hills are called dunes, and on the shores of the seas and oceans - dunes.