It would seem that all the processes of forming the Earth’s landscapes have long been completed: the planet has high mountains and deep depressions, plains, lowlands, and hills. However, even today there is a continuous development of landforms. Under the influence of internal and external forces, the external appearance of the globe continues to undergo changes.

Relief formation

Modern relief is changing all the time: there is a continuous process of destruction, movement and accumulation of rocks, leading to the formation of new forms of landscape.

All processes influencing the formation of relief are divided into two large groups: internal (endogenous) and external (exogenous).

Endogenous processes are the latest tectonic processes occurring in the bowels of the earth. They appear equally in the mountains and on the plains.

Where the earth's crust, due to its antiquity, has lost its former plasticity, the rocks can no longer bend in the form of folds. As a result, under the influence of tectonic movements, powerful faults and faults are formed, which dismember the land into huge blocks.

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An example of endogenous processes is the movement of rocks in the Caucasus, which occurs at a speed of up to 8 cm per year. In the Altai, Urals, and Sayan Mountains, neotectonic movements lead to the formation of faults: some blocks descend, others, on the contrary, rise.

Rice. 1. Caucasus Mountains.

Exogenous processes are processes occurring under the influence of wind, permafrost, and flowing water. External factors include:

• glaciation (lakes, “ram’s foreheads”, moraines);
• flowing waters (ravines, hollows, river valleys);
• wind (barchans, dunes);
• Human (waste heaps, quarries, tunnels).

Weathered rock contains a huge number of microorganisms. Together with roots, lichens, insect larvae and earthworms, they have a noticeable effect on the rock, gradually crushing and dissolving it. These processes are called biological weathering.

Rice. 2. Biological weathering.

Development of relief forms in Russia

The formation of relief on the territory of modern Russia dates back to the Quaternary period. At this time, the vast majority of land areas on the planet were covered with glaciers. The centers of glaciation were the Central Siberian Plateau, the Taimyr Peninsula and the present-day Ural Mountains.

Rice. 3. Taimyr Peninsula.

Over time, when glaciers began their gradual conquest of the south, layers of clay, rubble, and sand began to move after them. However, in the southern regions, under the influence of heat, glaciers began to quickly melt. This led to the subsidence of loose rocks and the formation of moraine relief. This type of relief prevails, for example, in the Smolensk and Moscow regions.

The water formed after the melting of glaciers filled the depressions in the rocks, which, in turn, led to the formation of lakes in the northern part of the Russian Plain.

Lecture 3. Topic. The role of endogenous processes

1. Relief, general concepts. Classification of landforms.

2. Magmatism, its essence and significance in the formation of relief.

3. Metamorphism.

4. Slow oscillatory movements of the earth's crust (epeirogenesis - the birth of land).

5. Earthquakes, their causes, essence and forecasting.

6. Tectonic disturbances of the earth's crust (folded and discontinuous disturbances).

Literature:

1. Relief - this is a set of irregularities in the earth’s surface that characterize one or another part of the landscape.

Geomorphology– a science that studies the laws of relief development, its external features and geographical distribution.

The relief of the earth's surface is studied as one of the components of the geographic environment, taking into account its relationships with the geological structure, surface and underground waters, vegetation, soil and other elements of the natural environment. Relief is closely related to the age and composition of soil-forming and underlying rocks. Its influence on soil formation is associated with different inflows of water and heat. Soil properties also strongly depend on the topography, which must be taken into account in land management when organizing the territory of crop rotation fields.

The relief has various shapes, sizes and origins.

Landform– these are natural or artificial bodies and cavities, the simplest of which can be roughly compared with geometric figures (cone, pyramid, prism). Complex landforms are a combination of simple forms and can reach very large sizes (continent, sea basin, mountainous country, etc.). The main elements of relief forms are: faces - surfaces of slopes, edges - lines of articulation of faces, lines of watersheds, toes of slopes, points of peaks, saddles, mouths of valleys, ravines, etc.

By external signs and in relation to adjacent spaces differentiate positive And negative relief forms, closed And open. To the positive relief forms include areas of the earth's surface that rise above the surrounding area (mountains, hills, continent above the seabed), and to negative– areas that are low in relation to adjacent territories (craters, basins, depressions). Closed relief forms are limited on all sides by slopes or lines (bottoms of edges). Unclosed Landforms usually lack slopes on one and sometimes on both sides. For example, a mountain is positive, and a sinkhole is negative closed forms. A river valley is a negative, unclosed landform.

In different places on the earth's surface there is a wide variety of landforms in size and origin. In this regard, there are morphometric and genetic classification relief forms.

According to morphometric classification All landforms are divided according to size, height and horizontal extent.

Megarelief- the largest landforms, which include continents and their component parts.

Macrorelief– large landforms, the horizontal length of which ranges from 10 to 200 km. The areas of these landforms occupy hundreds of thousands of square meters (Ural Mountains, Russian Plain, West Siberian Lowland, etc.). The difference in absolute elevations above sea level is in the range of 500-4000 m or more.

Mesorelief– medium forms of relief, the length of which is measured in tens, less often hundreds of meters. The height difference is 10-20 m, sometimes more than 30 m (beams, ravines, moraine and sandy ridges, watersheds, river valleys, etc.).

Microrelief– small relief forms with height fluctuations within 1 m and a length of up to several tens of meters (small depressions and elevations, steppe saucers, low hills, runoff hollows, etc.).

Nanorelief– the smallest forms of relief in the form of roughness and unevenness of the surface with a difference in relative heights of several centimeters and a length of less than 1 m (hummocks, furrows, small gullies, sand ripples, pits, tubercles).

Genetic classification is based on combining landforms into groups depending on their origin and the most active factor of relief formation in given conditions. There are reliefs endogenous and exogenous origin. The main relief-forming factors are tectonic movements of the earth's crust and climate. Endogenous processes create unevenness on the earth's surface, and climate influences exogenous processes that tend to level out these unevennesses.

Endogenous processes are caused by the manifestation of the internal forces of the Earth, causing tectonic movements of the earth's crust, earthquakes, the formation of folds and faults.

Exogenous processes are caused by external forces, which include the activity of surface flowing waters, snow and ice, melted glacial waters, sea, lake and groundwater, the development of permafrost, the activity of wind, animals, plants and humans.

Let us consider landforms formed under the influence of endogenous and exogenous processes.

2. Magmatism- a complex process of the formation of magma deep in the earth and its movement to the surface.

It develops in those parts of the earth's crust where there is a violation of the thermodynamic regime. As a result, cracks form. The essence of magmatism is that a decrease in external pressure leads to melting and overheating of the material in the upper mantle. This substance turns into a fiery mass called magma. Magma rises through cracks to a zone of low pressure, where it cools and crystallizes, forming minerals and rocks. Depending on the nature of the movement of magma, two forms of magmatism are distinguished:

1) intrusive– penetrating into the upper layers of the earth, magma does not come to the surface, but solidifies at a certain depth, forming various body shapes. Intrusive massifs that lie conformably, that is, parallel to the bedding of the host rocks, are laccoliths– loaf-shaped body with a convex surface (found in the Crimea, in the North Caucasus in the vicinity of Pyatigorsk – Beshtau, Mashuk, Zheleznaya mountains; Lopolites– look like a flat dish or cup; strata deposits– bodies of great length. Unconformably occurring (this is when the shape of the intrusion is not parallel to the layering of surrounding forms) include batholiths– dome-shaped bodies of large area (200 km 2); rods– similar in shape to batholiths, but smaller in area; dykes and stocks– are formed when various destructions are filled with magmatic melt and repeat their shape.

2) Effusive magmatism– magma flows onto the surface of the earth’s crust, forming volcanoes.

The causes of volcanic eruptions are tectonic movements in the earth's crust with the formation of cracks and displacement of rock blocks of the earth's crust, during which magma is squeezed out to the surface. From the bowels of the Earth, a vent rises to the top of the volcanic cone, which is a pipe-shaped channel ending at the top with an extension - a crater.

Main types of volcanoes:

1) Maars- explosion of gases without outpouring of lava (Mexico, France, Africa, New Zealand islands).

2) Vesuvius– fiery breathing mountains in the form of pointed, high-rising cones. The eruption occurs with gases, lava and solids. They are found in Kamchatka, Vesuvius and Etna in Italy, on the Kuril Islands, etc.

3) Hawaiian Islands– this type has a conical shape with gentle slopes (slope angle from 3 to 10 degrees). This type of volcano includes several vents and erupts only with liquid matter. Found in the Hawaiian Islands, Iceland, Africa, etc.

A volcanic eruption occurs in 3 phases: 1) initial – there is an earthquake and the release of gases; 2) lava outpouring; 3) post-volcanic – weak release of gases and lava. All these phases are in their own sequence, and each volcano does not always exhibit all these phases.

Eruption products: 1) gaseous - represented by carbon dioxide, water vapor, oxygen, hydrogen and gases containing sulfur, chlorine, fluorine, etc.; 2) liquid products – these are lavas of various compositions (ultrabasic, basic, intermediate, acidic and ultraacidic); 3) solid products – this is volcanic ash, sand (0.25-10 mm), volcanic pebbles or lapilli the size of a walnut (1.5-3 cm); volcanic bombs (from 10 cm to several meters).

The significance of volcanic processes:

1) role in the formation of relief;

2) hot springs (Geysers) of different mineralization are associated with volcanoes;

3) role in soil formation. As a result of a volcanic eruption, the earth's crust is buried, and centuries later, new, most fertile soils are formed (such soils were formed in New Zealand, Italy, Central America, Chile, Indonesia, and the Philippines). As a result of ash fall, the surface of the earth is enriched with various compounds rich in plant nutrients. Volcanic soils have more stable fertility (Japan, Argentina, etc.).

3. Metamorphism- these are physical and chemical processes occurring inside the earth’s crust under the influence of high pressure and high temperatures.

These conditions cause changes and transformations in the chemical and mineralogical composition of rocks and minerals. The structure and texture (mutual placement of minerals in the rock) changes. As a result of metamorphism, rocks dehydrate, recrystallize, and replace some minerals with others.

Depending on the factors, several types of metamorphism are distinguished:

1) dynamometamorphism– high pressure takes part in the change of rocks, which is created inside the Earth due to the immersion of surface layers into the lower layers, displacement of layers, which causes fragmentation of rocks and the orientation of mineral aggregates is disrupted (a characteristic linear-parallel orientation is acquired). For example, granites turn into gneisses; Shales are formed from different rocks.

2) thermometamorphism– changes in rocks under the influence of high temperatures. The source of heat is the intruding hot magma, hot gases and aqueous solutions. In contact with the host rocks, they are heated for a long time, as a result of which the mineralogical composition and recrystallization change. For example, limestones turn into marble; clays - into hornfels; sandstones - into quartzites.

3) Contact metamorphism– associated with the impact of intrusive magma on the surface layers. At the contact of magma with side rocks, complex physical and chemical processes occur. Rock changes occur on both sides. The intensity of contact metamorphism is determined by the composition and physical properties of rocks. For example, calcite, dolomite together with magma form calc-silicate rocks - these are peroxenes and garnets; granites turn into greisen (quartz-mica rocks); gabbro turns into amphibolites, which are similar in composition to hornblende; dolomites - into talc.

Metamorphism plays a huge role in the formation of relief and in the formation of minerals (tungsten, tin ores, molybdenum, etc.). And metamorphic rocks that come to the surface are destroyed as a result of weathering, become loose and can participate in soil-forming processes.

4. Tectonic movements of the earth's crust- these are natural movements that create various surface shapes (Tektonos - creates, forms).

According to the nature of their manifestations they are divided into vertical and horizontal . By speed - to smooth and sharp . By time - on slow and fast . By duration - for permanent and periodic .

Slow oscillatory movements of the earth's crust cover large areas, proceed vertically, smoothly, constantly and very slowly (they are called secular oscillatory movements). The nature of their movement is pulsating, caused by the impulse of compression and expansion of the crust and mantle. Compression causes the land to sink, and expansion causes it to rise. These oscillatory movements cause the earth's crust to bend and sag and form hills and depressions. Oscillatory movements that cause uplift of the earth's crust are called epeirogenic. These movements are the most widespread and cover large areas of the globe. We don't see them, but they happen around the clock; They can be discovered after the passage of time and on the coasts of the seas and oceans. The rise of the land leads to the retreat of the sea and this process is called regression. And the opposite process - the subsidence of land leads to the advance of the sea and is called transgression.

The speed of these slow oscillatory movements is calculated in thousandths of a millimeter per day. This makes it possible to predict and prevent entire cities from sinking into the sea. The coast of the Arctic Ocean, the Western Baltic, Greenland, and the Scandinavian mountains are gradually rising. The direction from Moscow to St. Petersburg is omitted; The coast of the Black Sea, North America, and the southern coast of England are also sinking. Holland has been submerged for about 700 years.

5. Earthquakes- tectonic movements, but faster. The shaking of the earth's crust is caused by internal forces and is associated with: the release of internal stresses arising in the bowels of the Earth; Volcanic processes; rock falls. Earthquakes can occur from the surface, that is, from 0 to 800 km in depth. The place where tremors occur is called the focus of an earthquake. The center of the outbreak is called the hypocenter. The perpendicular projection onto the Earth's surface is called the epicenter.

As a result of an earthquake, catastrophic destruction occurs, the terrain changes, and colossal damage is caused. Predicting where an earthquake will occur is possible (a week in advance).

6. Tectonic disturbances– cause folding and rupture formation of mountains. The process of folding mountains is called orogenesis.

Wave movements of the earth's crust play a large role in tectonic disturbances. There is a disturbance, deformation of the surface of the earth's crust. The layers of the earth's crust bend and sag, forming a mountain range. These layers are folded, cracked and form folded mountains. Example: Caucasus Mountains, Himalayas.

The surface of the Earth, represented by the convex part of the folds, is called an anticline. The depressed areas or concave part is called a syncline. Oil deposits are associated with the anticline, and the accumulation of drinking water is associated with the syncline.

Fracture tectonic disturbances lead to ruptures in the surface of the earth's crust with the formation of cracks and faults.

There are various displacements of the Earth's surface:

1) a shift is two sections of the earth’s crust that have moved along a fracture in the horizontal direction;

2) fault – a rupture occurs in the vertical direction;

3) graben - tectonic disturbances, when the central part of the layers sinks down and reservoirs are formed at the site of subsidence (Lake Baikal, Balaton);

4) horst - this is when the central part rises. Do mountains or hills form? Example: Baikal region, Caucasus;

5) faults - deep cracks from 1 to 10 km in width and to great depth. These faults are subject to exogenous processes and are destroyed, forming cracks. Deposits of gases and other minerals are associated with these faults. Example: Elshanka is the place where the fault occurred. With faults and cracks, gorges, ledges, and ravines are created.

7. Categories of crustal structures- is a product of tectonic movement of various ages and nature, that is, it is the foundation of the earth’s surface, created as a result of tectonic movements. From the point of view of stability and mobility of various sections of the earth's crust, 3 categories of geological structures are distinguished: shield, platform, geosyncline.

Shield- areas of the earth's crust composed of the most ancient massive crystalline rocks - granite, gneisses, amphibolites. They are characterized by the greatest stability; for hundreds of millions of years they do not change their position. They are covered with a layer of glacial sediments or reach the surface of the earth's crust (Baltic, Siberian, Canadian shields).

Platform– consists of 2 layers: the lower one, represented by ancient crystalline rocks, and the upper one, a sedimentary layer (50-100 m).

There is no folding on the platforms, tectonic movements are extremely weak and are subject to slow oscillatory movements (Central Russian, North American, North Asian platforms, etc.)

Geosyncline- these are areas of the earth’s crust consisting of various sedimentary rocks, sometimes intensively crushed due to mountain-building processes. They have enormous power. These are the most mobile areas for tectonic disturbances. As a rule, they are confined to seas and oceans, and most often volcanic processes occur here.

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 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 “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. Structure of the river valley

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).

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?

From the moment of its formation to the present day, the earth’s crust has been under the continuous influence of two forces: internal - endogenous and external - exogenous.

Endogenous processes- This is a manifestation of the internal energy of the Earth that arises in its depths. Internal processes include: tectonic, igneous and metamorphic. Internal forces change the shape of the earth's surface: they create irregularities in the form of depressions and elevations and thereby give contrast to the relief.

Exogenous processes occur on the Earth's surface and at shallow depths in the earth's crust. Sources of exogenous forces are solar energy, gravity and the vital activity of organisms. External forces tend to smooth out the unevenness created by internal forces; they give the earth's surface a more or less flat shape, destroying hills and filling depressions with destruction products.

Internal and external processes are united under a common name geological.

Endogenous processes of relief formation

Tectonic movements of the earth's crust

All natural movements of the earth's crust or its individual sections are called tectonic movements.

Tectonic movements in the earth's crust occur constantly. In some cases they are slow, barely noticeable to the human eye (eras of peace), in others - in the form of intense stormy processes (tectonic revolutions). Mountain building, earthquakes, and volcanism are associated with tectonic movements in the earth's crust. The shape, nature and intensity of destruction of the earth's surface, sedimentation, and distribution of land and sea also depend on these movements.

The mobility of the earth's crust largely depends on the nature of its tectonic structures. The largest structures are platforms and geosynclines.

Platforms– stable, rigid, sedentary structures. The platforms are characterized by leveled landforms. They consist of a hard, non-foldable section of the earth's crust (crystalline base). They are characterized by calm, slow movements of a vertical nature.

Geosynclines- moving parts of the earth's crust. They are located between the platforms and are their movable connections. Geosynclines are characterized by various tectonic movements, seismic phenomena and volcanism.

Tectonic movements of the earth's crust are divided into three main interrelated types of movements:

Oscillatory;

Folded;

Explosive.

Oscillatory movements are movements in which, firstly, the direction of movement is vertical, and secondly, the direction of movement periodically changes (that is, during oscillatory movements, the same section of the earth’s crust experiences alternate descent or rise). They do not cause sudden disturbances in the original occurrence of rocks.

Oscillatory movements occurred at all geological stages of the development of the earth's crust and are still occurring now.

At folded movements, rocks under the influence of tectonic processes are crushed into folds. The formation of artesian groundwater basins and the formation of oil fields are associated with the folding movements of the earth's crust.

At explosive movements, cracks appear. Tectonic ruptures are shear or detachment faults. Rupture movements contribute to the formation of ore veins and mineral springs, but they also complicate the development of mineral resources.

Oscillatory movements

Oscillatory movements of the earth's crust are the most common type of tectonic movements. It has been established that there is not a single section of the earth's crust that is in a state of complete rest.

Oscillatory movements are expressed by slow (“secular”), uneven vertical uplifts of some sections of the earth’s crust and lowering of others located next to them. Movement signs change, and those areas that previously experienced upward, positive movements may begin to experience downward, negative movements. Consequently, oscillatory movements represent a constantly changing, but not repeating wave-like process, that is, successive rises and falls do not cover the same areas, but each time they shift in space in a wave-like manner.

Changes over time and travel speed. Within geosynclines it varies from a centimeter to several units of centimeters per year, and within platforms - from fractions of millimeters to 1.0 cm/year. Oscillatory movements in both the first and second areas occur slowly, calmly, people and existing devices do not feel them. The presence of movements is established only by carefully studying their results.

Development areas slow oscillatory movements can be different. Sometimes they cover vast territories (tens and hundreds of thousands of square kilometers), and then uplifts lead to the appearance of large, but very gentle arches, and subsidence leads to the formation of similar depressions.

Large arches and depressions are called first order structures. Movements that occur over smaller areas lead to the complication of first-order structures with second-order structures. In turn, third-order structures arise on second-order structures, etc.

Changing directions of vertical movements leads to changes in the outlines of sea basins, lakes, the direction of their geological activity, as well as the activity of other exogenous factors. When the continent sinks, the sea sometimes covers large areas of land (transgression), and sometimes it only invades the river valleys (ingression). When the continent rises, the sea regresses, the size of land is increasing.

Regressions are characterized by the vertical replacement of deep-sea sediments with shallow-water ones (clays are replaced by sands, sands by pebbles). During transgression, the opposite picture occurs—the replacement of shallow-water sediments with deep-water ones.

On slow raising indicate marine terraces, which represent a coastal platform developed as a result of the work of the sea. The width of these terraces in Norway is measured in tens of meters. As a result of slow uplifts of the earth's crust, some ancient ports now found themselves at quite a considerable distance from the coast; the islands were connected by land bridges to the continent.

On dives individual sections of the earth's crust are indicated by coastal terraces flooded with water, the presence of underwater river valleys at the mouth of rivers (Amazon, Congo), flooded river mouths - estuaries (Black Sea coast), flooded forests, peat bogs, roads, human settlements.

An example of modern uplift is Scandinavia (25 mm/year). There are about five ancient coastal terraces in Norway. The northern part of Finland is rising at a rate of 1 cm per year. The area of ​​Finland will increase by approximately 1000 km 2 in 100 years.

Subsidences are especially characteristic of the Netherlands (40–60 mm/year). Residents protect the country from flooding with a complex system of dams and dams, and constantly monitor their safety. 2/3 of the Netherlands is below sea level.

In Russia, the areas of Kursk (3.6 mm/year), the Central Russian Upland (1.5–2 mm/year), Novaya Zemlya, and the Northern Caspian region are rising. Subsidences occur in the area between Moscow and St. Petersburg (3.7 mm/year), in the Azov-Kuban depression (3–5 mm/year), in the Tver depression (5–7 mm/year) and in other places.

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

Weathering

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

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

Effect of gravity

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

Under the influence of gravity there are landslides and mudflows. They carry huge masses of rocks. Landslides are the sliding of rock masses down a slope. They form along the banks of reservoirs, on the slopes of hills and mountains after heavy rains or melting snow. The upper loose layer of rocks becomes heavier when saturated with water and slides down the lower, water-impervious layer. Heavy rains and rapid snow melting also cause mudflows in the mountains. They 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 world's sandy deserts are covered with sand dunes and hills. Sometimes they reach a height of 100 meters. From above the dune has the shape of a sickle.

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

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

Glacier activity

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

Human activity

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

The scale of human activity can be comparable to natural processes. For example, rivers 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 do a huge amount of destructive work called erosion (from the Latin word erosio to eat away). Land erosion is a natural process. However, it intensifies as a result 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 scale in large agricultural regions of Russia, China and the USA.

Formation of the Earth's relief

Features of the Earth's relief