How did the features of the formation of the territory's relief influence it? History of relief formation. How the Earth's crust was formed

Relief is all irregularities earth's surface, formed due to the interaction of internal and external forces of the Earth.
Landforms are distinguished by size, structure, origin, etc. There are convex (positive) and concave (negative) landforms.

At the heart of the territory of the Russian Federation there are large tectonic formations - shields, platforms, folded belts, the impact of which is expressed in the versatility of the relief of our state. Thus, Russia is characterized by numerous lowlands, hills, and mountain systems.

Structure of the earth's crust

The largest features of the country's relief are determined by the peculiarities of the geological structure and tectonic structures. The territory of Russia, like the whole of Eurasia, was formed as a result of the gradual convergence and collision of individual large lithospheric plates.
The structure of lithospheric plates is heterogeneous. Within their boundaries there are relatively stable areas - platforms and mobile folded belts. The location of the largest landforms - plains and mountains - depends on the structure of lithospheric plates. Areas with flat relief are confined to platforms - stable areas of the earth's crust, where folding processes have long since ended.

The most ancient of the platforms are the East European and Siberian. At the base of the platforms lies a hard foundation composed of igneous and highly metamorphosed rocks of Precambrian age (granites, gneisses, quartzites, crystalline schists). The foundation is usually covered with a cover of horizontally occurring sedimentary rocks, and only on the Siberian Platform (Central Siberian Plateau) are significant areas occupied by volcanic rocks - Siberian traps. The outcrops of the foundation, composed of crystalline rocks, to the surface are called shields. In our country, the Baltic Shield on the Russian Platform and the Aldan Shield on the Siberian Platform are known.

Mountain areas have a more complex geological structure. Mountains are formed in the most mobile areas of the earth's crust, where, as a result of tectonic processes, rocks are crushed into folds and broken by faults and faults. These tectonic structures arose at different times - during the eras of Paleozoic, Mesozoic and Cenozoic folding - in the marginal parts of lithospheric plates when they collided with each other. Sometimes fold belts are located in the internal parts of the lithospheric plate (Ural Range). This indicates that once there was a boundary between two plates, which later turned into a single, larger plate.

The youngest mountains of our country are located on Far East(Kuril Islands and Kamchatka). They are part of the vast Pacific volcanic belt, or the "Pacific Ring of Fire" as it is called. They are characterized by significant seismicity, frequent strong earthquakes, the presence of active volcanoes.

When looking at the map, two features of the relief of Russia are striking:
1) the predominance of plains in the western and central parts of the country, and mountains along its eastern and partially southern outskirts;
2) lower altitude position of the western part compared to the eastern part.
The border between them is clearly visible from the prevailing coloring of the map and clearly coincides with the Yenisei valley. The third feature can be seen upon closer examination of the map: the greater height of the southern mountains compared to the eastern ones. The Caucasus and Altai are among the highest mountains of Eurasia.

Plains occupy about 60% of the country's territory. They stretched from the western borders of Russia to the Lena, from the coast of the Arctic Ocean to the foothills of the Caucasus, Altai and Sayan Mountains. The two largest plains of Russia - East European and West Siberian - are among the greatest plains in the world.

The East European Plain stands out among other plains for its most diverse topography. There are large hills, individual elevations of which exceed 300 and even 400 m (the highest point of the Bugulmino-Belebeevskaya Upland reaches 479 m), and vast lowlands with small hills and ridges scattered across them (in the north) or quite monotonous (Caspian Sea). The lowest parts of the plain are located in the coastal strip of the Caspian Sea with a height of 26 m. The average height of the plain is 170 m.

In the extreme north-west of the country, within the Kola Peninsula, on the large intrusive massifs of Khibiny, Lovozersky and Monchetundra, some peaks exceed 1100 m; the highest of them is Mount Chasnachorr (1191 m) in the Khibiny Mountains.
The West Siberian Plain is characterized by an extremely uniform topography with slight fluctuations in elevation. Only some small areas in the outlying parts of the plain exceed 200 m. It reaches its maximum heights on the North Sosvinskaya (290 m) and Verkhnetazovskaya (285 m) hills. Almost half of the territory lies below 100 m above sea level. The average height of the plains is only 120 m.
The East European and West Siberian plains are separated by low and narrow (up to 150 km) Ural Mountains, only some peaks of which exceed 1500 m. The highest point of the Urals is Mount Narodnaya (1895 m).

In the area between the Yenisei and Lena rivers there is the Central Siberian Plateau, a plain raised to a considerable height (up to 400-600 m and higher) and deeply dissected by large river valleys. Greatest heights it reaches within the Putorana plateau (1701 m). The average height of the plateau is 480 m.
To the east, the Central Siberian Plateau gradually turns into the Central Yakut Plain, and to the north, a steep ledge descends to the North Siberian Lowland.

The mountain frame in the southwest is represented by the Greater Caucasus Mountains, stretching from the Black Sea to the Caspian Sea. Here is the highest point of Russia - the two-headed Elbrus (5642 m) and all the other “five thousand meters”. The southern mountain belt of Siberia begins from Altai. It is represented by high- and mid-mountain ridges of Altai (Mt. Belukha - 4506 m) and Sayan (Mount Munku-Sardyk - 3491 m), mountain ranges and highlands of Tuva, Baikal region and Transbaikalia. In Transbaikalia, the peaks of the Stanovoy Highlands reach the highest heights (highest point - 3073 m). Through the Stanovoy Range, the mountains of Southern Siberia are connected to the mountain structures of the eastern outskirts.

To the east of the Lena and right up to the shores of the Pacific Ocean there are medium-altitude ridges and highlands: Verkhoyansky (2389 m), Chersky Ridge (Pobeda - 3003 m), Suntar-Khayata (2959 m), Dzhugdzhur (1906 m), Yano-Oymyakonskoe , Kolymskoe, Chukotskoe, Koryakskoe (Mount Ledyanaya - 2453 m). To the south they pass into the low and medium-altitude ranges of the Amur region, Primorye (Sikhote-Alin) and Sakhalin, the maximum elevations of which do not reach 2500 m. The eastern outpost is represented by the folded and volcanic mountains of Kamchatka and the Kuril Islands. In Kamchatka there is the highest point of the Asian territory of Russia - the active volcano Klyuchevskaya Sopka (4688 m). All the highest peaks of Kamchatka and the Kuril Islands are active or extinct volcanoes.

The territory of Russia is characterized by the predominance of low and medium-altitude mountains. Mountains higher than 1500 m occupy less than 10% of the country's area.
Thus, the eastern and southeastern outskirts of Russia are represented by mountain structures. In the southwest, the lonely Caucasus rises at the southern border of the East European Plain.

The main forms of relief of Russia - plains, mountains and highlands - owe their origin to the internal forces of the Earth. But many essential details of their modern relief were created external forces. Almost everywhere, the formation of modern relief occurred and continues to occur under the influence of flowing waters. As a result, erosional landforms were formed - river valleys, gullies and ravines. The gully-gully network is especially dense on such elevations as Central Russian, Privolzhskaya, and in the foothills. Many coastal sea plains have flat, leveled topography, which was formed due to processes associated with the advance and retreat of the sea. Therefore, over vast areas of modern land, marine sediments lie horizontally. These are the plains of the Caspian, Black Sea, Azov, Pechora and northern parts of the West Siberian lowlands.

In large areas of our country, many relief forms were created as a result of the Quaternary glaciations. Their influence is especially great in the northern half of the European part of Russia, which was repeatedly covered by glaciers descending far to the south from the Scandinavian mountains and the Polar Urals. Traces of glacier activity on the plains are numerous hills and ridges composed of moraine. Landforms resulting from the activity of melted glacial waters are also widespread here. These are hills and flat sandy plains that vary in shape and material composition. Similar forms of relief associated with the activity of the glacier and its meltwater are found in the Western and Eastern Siberia. But here they occupy a smaller area, since glaciation in these areas was less intense: in conditions of a sharply continental climate, where there is little precipitation, glaciers of significant thickness could not form.

Mountain glaciers in Quaternary times existed in almost all mountains. There are still glaciers on the highest of them. Traces of former mountain glaciations are such landforms as cirques and trough valleys. They are widespread in the Caucasus, the Urals, the Sayans, Altai and many other mountains of Russia.
In a number of regions of Russia there are relief forms formed by wind activity. They are especially widely represented in the arid regions of the country. Thus, sand hills - dunes and ridges - formed in the deserts of the Caspian region. Aeolian forms are also found in humid areas. The Baltic dunes arose as a result of the winding of sand from sea beaches and spits.

In the north of the European part of the country and east of the Yenisei, landforms associated with permafrost strata are found almost everywhere. Particularly common are heaving mounds that arise as a result of the freezing of groundwater and various types of soil subsidence over areas of thawing of frozen rocks. These processes interfere with construction and are often accompanied by the destruction of roads, houses and industrial buildings.

The Caspian Lowland is the lowest point of the Russian relief

In order to understand the features of the relief, it is necessary to know the geological history of its formation. Scientists, studying layers of rocks, found that they all passed long haul formations and have different ages. You will learn about this from this lesson, taking a fascinating journey through the history of the development of the earth's crust. Also, learn to read a geochronological table and become familiar with a geological map.

Topic: Geological structure, relief and minerals

Lesson: Relief features as a result geological history formation of territory

To understand the pattern of formation of mountains and plains, it is necessary to become acquainted with the history of the geological formation of the territory. The history of the geological development of any territory is learned by studying the age, composition and occurrence of rocks. It is from these data that one can find out what happened to the territory in distant geological eras, whether the territory was covered by the sea or volcanic eruptions occurred, whether there were deserts or glaciers here.

Some areas of the earth's surface are composed of ancient metamorphic rocks, others are young volcanic, and still others are sedimentary. Rocks can lie horizontally or form folds. All rocks have an absolute or relative age . Relative age is determined by the concepts “older” and “younger”. Sedimentary and volcanic rocks accumulate in horizontal layers and therefore it is natural to assume that the older ones are deeper and the younger ones are closer to the surface. (see Fig. 1)

Rice. 1. Occurrence of layers of sedimentary rocks

help determine relative ages and ancient fossils. (see Fig. 2)

Rice. 2. Trilobite. Age about 380 million years

Thick layers of sedimentary rocks form at the bottom of the World Ocean. The ocean once covered vast areas of our planet and various animals lived in it, which died and settled to the bottom, were covered with sand, silt, soft tissues decomposed, and hard ones became fossils.

The more complex the organism is, the younger the rock; the simpler, the older. Absolute age breeds is the number of years that have passed since the formation of these breeds.

The study of rocks and extinct remains of animals and plants has made it possible to identify several stages in the formation of the geological history of our planet. These stages are reflected in the geochronological table (“geo” - earth, “chronos” - time, “logos” - teaching). The geochronological table is a geological record of events occurring on our planet. The table shows the sequence and duration of changes in various geological stages; the table can also present various geological events in different periods, typical animals, as well as minerals that were formed in different eras. The geochronological table is built on the principle: from ancient to modern, so you need to read it from bottom to top. (see Fig. 3)

Rice. 3. Geochronological table ()

According to the most significant changes that occurred on our planet in the geological past, all geological time is divided into two large geological segments - eons: cryptozoic- time of hidden life, Phanerozoic- time of apparent life. Eons include era: Cryptozoic - Archean and Proterozoic, Phanerozoic - Paleozoic, Mesozoic and Cenozoic. (see Fig. 4)

Rice. 4. Division of geological time into eons and eras

The last three eras: Paleozoic, Mesozoic, Cenozoic are divided into periods, due to the fact that the geological world was very complicated at that time. The names of the periods were given according to where rocks of a given age were first discovered, or according to the rocks that make up a particular area, for example: Permian and Devonian by the name of the area, and Carboniferous or Cretaceous by the rocks. We live in the Cainozoic era, the modern era, which continues to this day. It began approximately 1.7 million years ago. (see Fig. 3)

Let's consider some characteristics of geological eras. Archaea And Proterozoic are considered the time of hidden life (Cryptozoic). It is believed that the organic life forms that existed at that time did not have hard skeletons, so they did not leave any traces in the sediments of these eras. (see Fig. 5)

Rice. 5. Cryptose (Archaean and Proterozoic) ()

The time of dominance of invertebrates, crustaceans, insects, mollusks. In the late Paleozoic, the first vertebrates appeared - amphibians and fish. The plant kingdom was dominated by algae and pselophytes . Later, horsetails and mosses appear. (see Fig. 6)

Rice. 6. Paleozoic ()

In the Mesozoic, large reptiles dominate, and in flora gymnosperms .(see Fig. 7)

In the Cenozoic - the dominance of angiosperms, flowering plants, the appearance of mammals and, finally, humans. (see Fig. 8)

Rice. 8. Cenozoic ()

In each of the geological epochs and periods, the accumulation of the chemical and mechanical composition of rocks occurred. In order to find out what rocks a particular territory of our country is composed of, we can use the geological map of Russia. (see Fig.9)

Rice. 9. Geological map of Russia ()

Geological map contains information about the age of rocks and minerals. Information on the map is shown in different colors. If you look at the geological map, you will see that the most ancient rocks are composed of the territory of Transbaikalia and the Kola Peninsula.

Different periods are shown in different colors, for example, Carboniferous rocks are shown in gray and Mesozoic rocks are shown in green. Analyzing the geological map, you can pay attention to the fact that the East European Plain is composed of rocks of the Paleozoic era, and only in the Far North-West do we see outcrops of rocks of the Archean and Proterozoic periods. The West Siberian Lowland is composed of young Paleogene and Neogene sediments.

Using geological maps, you can obtain information about minerals, as well as predict their search.

The geological age of our planet is approximately 4.7 billion years. It was during this period that, as a result of differentiation of matter, the core, mantle, etc. were formed. (see Fig. 10)

Rice. 10. Internal structure Earth

Earth's crust divided into blocks - lithospheric plates. Moving through the mantle, lithospheric plates changed the outlines of continents and oceans. (see Fig. 11)

Rice. 11. Lithospheric plates

There were periods when the lithospheric plates sank, and then the land area decreased, and the area of the World Ocean increased. Such eras, which were geologically calmer, were called epochs of the seas. They alternated with more geologically stormy and shorter periods, which were called sushi eras. These eras were accompanied by active volcanism and mountain building.

Homework

Using a geochronological table, determine which periods are more ancient: Devonian or Permian, Ordovician or Cretaceous, Jurassic or Neogene?
Which era is more ancient: Proterozoic or Mesozoic, Cenozoic or Paleozoic?
What era and period are we living in?

Geography of Russia. Nature. Population. 1 hour 8th grade / author. V.P. Dronov, I.I. Barinova, V.Ya Rom, A.A. Lobzhanidze
Geography of Russia. Population and economy. 9th grade / author V.P. Dronov, V.Ya. Rum
Atlas. Geography of Russia. Population and economy / ed. "Drofa" 2012
UMK ( educational and methodological kit) "SPHERES". Textbook “Russia: nature, population, economy. 8th grade" author. V.P. Dronov, L.E. Savelyeva. Atlas.

Other lessons on this topic

The structure of the earth's crust (lithosphere) on the territory of Russia ().
Relief of Russia, geological structure and minerals ().

Find out more on the topic

Relief, geological structure and minerals ().
History of life on Earth ().
Interactive geological atlas of Russia ().
Website of the Mineralogical Museum named after. A.E. Fersman ().
Website of the State Geological Museum named after V.I. Vernadsky ().

Relief is a set of forms of the earth's surface, different in outline, size, origin, age and history of development. Relief influences the formation of climate, the nature and direction of river flows depend on it, and the distribution of flora and fauna is associated with it. Relief also affects a person’s lifestyle and his economic activity. Large landforms of Russia. The topography of our country is very diverse: high mountains are adjacent to vast plains. The highest point of the country (and Europe) - Mount Elbrus in the Caucasus reaches an altitude of 5642 m above sea level, and the Caspian lowland is located 28 m below this level. Territories with flat terrain predominate, occupying more than half of the country's area. Among the plains of Russia - one of largest plains globe (East European), Russian and vast Western Siberian. They are separated by short Ural Mountains. The south of the European part of Russia is occupied by young Caucasus Mountains, east - vast mountainous countries. From West Siberian Plain they are separated by the Central Siberian Plateau with a dense network of river valleys. To the east of the Lena there are mountain systems North-Eastern Siberia: Verkhoyansk ridge and Chersky ridge. In the south of the Asian part of Russia there are Altai, Sayan Mountains, Salair Ridge, Kuznetsk Alatau and the Baikal and Transbaikalia ranges, as well as the Stanovoy Range, Vitim Plateau, Stanovoy, Patom and Aldan Highlands. Along the Pacific coast, from south to north, the medium-altitude ranges of Sikhote-Alin, Bureinsky, Dzhugdzhur stretch, and in the north they are replaced by high plateaus: Kolyma, Chukotka, Koryak. High mountain ranges with volcanic peaks are located in Kamchatka.

Thus, the following conclusions can be drawn:

1) the relief of Russia is very diverse: there are vast plains, plateaus, high and medium-altitude mountains;

2) flat areas predominate;

3) the territory, this especially concerns the Asian part of the country, has a general decrease to the north, as evidenced by the direction of the flow of most large rivers;

4) mountain structures frame vast plains, with the main part of the mountains concentrated in the south of Siberia, the northeast and east of the country.

The structure of the earth's crust. The largest features of the country's relief are determined by the peculiarities of the geological structure and tectonic structures. The territory of Russia, like the whole of Eurasia, was formed as a result of the gradual convergence and collision of individual large lithospheric plates. The structure of lithospheric plates is heterogeneous. Within their boundaries there are relatively stable areas - platforms and mobile folded belts. The location of the largest forms of land relief - plains and mountains - depends on the structure of lithospheric plates. Areas with flat relief are confined to platforms - stable areas of the earth's crust, where folding processes have long since ended. The most ancient of the platforms are the East European and Siberian. At the base of the platforms lies a hard foundation composed of igneous and highly metamorphosed rocks of Precambrian age (granites, gneisses, quartzites, crystalline schists). The foundation is usually covered with a cover of horizontally occurring sedimentary rocks, and only on the Siberian Platform (Central Siberian Plateau) are significant areas occupied by volcanic rocks - Siberian traps. The outcrops of the foundation, composed of crystalline rocks, to the surface are called shields. In our country, the Baltic Shield on the Russian Platform and the Aldan Shield on the Siberian Platform are known. Mountain areas have a more complex geological structure. Mountains are formed in the most mobile areas of the earth's crust, where, as a result of tectonic processes, rocks are crushed into folds and broken by faults and faults. These tectonic structures arose at different times - during the eras of Paleozoic, Mesozoic and Cenozoic folding - in the marginal parts of lithospheric plates when they collided with each other. Sometimes folded belts are in internal parts lithospheric plate (Ural ridge). This indicates that once there was a boundary between two plates, which later turned into a single, larger plate. The youngest mountains of our country are located in the Far East (Kuril Islands and Kamchatka). They are part of the vast Pacific volcanic belt, or the "Pacific Ring of Fire" as it is called. They are characterized by significant seismicity, frequent strong earthquakes, and the presence of active volcanoes.

Various landforms are formed under the influence of processes that can be predominantly internal or external.

Internal (endogenous)- these are processes inside the Earth, in the mantle, core, which manifest themselves on the surface of the Earth as destructive and creative. Internal processes They create, first of all, large forms of relief on the surface of the Earth and determine the distribution of land and sea, the height of mountains, and the sharpness of their outlines. The result of their action is deep faults, deep folds, etc.

Tectonic(the Greek word "tectonics" means construction, the art of construction) movements of the earth's crust called the movement of matter under the influence of processes occurring in the deeper bowels of the Earth. As a result of these movements, the main relief irregularities on the Earth's surface arise. The zone of manifestation of tectonic movements, which extends to a depth of about 700 km, is called tectonosphere.

Tectonic movements have their roots in the upper mantle, since the cause of deep tectonic movements is the interaction of the earth’s crust with the upper mantle. Their driving force is magma. The flow of magma, periodically rushing to the surface from the bowels of the planet, provides a process called magmatism.

As a result of the solidification of magma at depth (intrusive magmatism), intrusive bodies arise (Fig. 1) - sheet intrusions (from lat. intrude- pushing), dykes (from English. dike, or dyke, literally - a barrier, a wall of stone), batholiths (from the Greek. bathos - depth and lithos - stone), rods (German. Stock, literally - stick, trunk), laccoliths (Greek. lakkos- hole, recess and lithos - stone), etc.

Rice. 1. Forms of intrusive and effusive bodies. Intrusions: I - batholith; 2 — rod; 3 - laccolith; 4 - lopolit; 5 - dike; 6 - sill; 7 - vein; 8 - paophysis. Effusions: 9 - lava flow; 10 - lava cover; 11 - dome; 12- nekk

Reservoir intrusion - a sheet-like body of magma frozen at depth, having the shape of a layer, the contacts of which are parallel to the layering of the host rocks.

Dykes - plate-shaped, clearly bounded by parallel walls of a body of intrusive igneous rocks that penetrate the surrounding rocks (or lie unconformably with them).

Batholith - a large massif of magma frozen at depth, having an area measured in tens of thousands of square kilometers. The plan form is usually elongated or isometric (has approximately equal dimensions in height, width and thickness).

Stock - an intrusive body, in vertical section having the shape of a column. In plan, its shape is isometric and irregular. They differ from batholiths in their smaller size.

Laccoliths - have a mushroom or dome-shaped overlying surface and a relatively flat lower surface. They are formed by viscous magmas entering either through dike-like supply channels from below or from the sill, and, spreading along the bedding, uplift the host overlying rocks without disturbing their bedding. Laccoliths occur singly or in groups. The sizes of laccoliths are relatively small - from hundreds of meters to several kilometers in diameter.

Magma frozen on the surface of the Earth forms lava flows and covers. This is an effusive type of magmatism. Modern volcanic magmatism is called volcanism.

Magmatism is also associated with the emergence earthquakes.

crustal platform

Platform(from French. plat - flat and form - form) - a large (several thousand km in diameter), relatively stable part of the earth's crust, characterized by a very low degree of seismicity.

The platform has a two-story structure (Fig. 2). Ground floor - foundation- this is an ancient geosynclinal area - formed by metamorphosed rocks, the upper - case - marine sedimentary deposits of low thickness, which indicates a small amplitude oscillatory movements.

Rice. 2. Platform structure

Age of platforms is different and is determined by the time of formation of the foundation. The most ancient platforms are those whose foundations are formed by Precambrian crystalline rocks crumpled into folds. There are ten such platforms on Earth (Fig. 3).

The surface of the Precambrian crystalline basement is very uneven. In some places it comes to the surface or lies near it, forming shields, in others - anteclises(from Greek anti- against and klisis - inclination) and syneclises(from Greek syn- together, klisis - mood). However, these irregularities are covered by sedimentary deposits with a quiet, nearly horizontal occurrence. Sedimentary rocks can be collected into gentle ridges, dome-shaped uplifts, step-like bends, and sometimes faults with vertical mixing of layers are observed. Disturbances in the occurrence of sedimentary rocks are caused by unequal speed and different signs oscillatory movements of crystalline foundation blocks.

Rice. 3. Pre-Cambrian platforms: I - North American; II - Eastern European; III - Siberian; IV - South American; V - African-Arabian; VI - Indian; VII - East China; VIII - South China; IX - Australian; X - Antarctic

The foundation of younger platforms was formed during periods Baikal,Caledonian or Hercynian folding. Areas of Mesozoic folding are not usually called platforms, although they are such at a relatively early stage of development.

In relief, the platforms correspond to plains. However, some platforms experienced serious restructuring, expressed in general uplift, deep faults and large vertical movements of blocks relative to each other. This is how folded block mountains arose, an example of which is the Tien Shan Mountains, where the revival of mountainous relief occurred during the Alpine orogeny.

Throughout geological history, the continental crust has seen an increase in the area of platforms and a reduction in geosynclinal zones.

External (exogenous) processes are caused by the energy of solar radiation entering the Earth. Exogenous processes smooth out unevenness, level surfaces, and fill depressions. They appear on the earth's surface both as destructive and creative.

Destructive processes - This is the destruction of rocks that occurs due to temperature changes, wind action, and erosion by water flows and moving glaciers. Creative processes are manifested in the accumulation of particles carried by water and wind in depressions of land, at the bottom of reservoirs.

The most difficult external factor is weathering.

Weathering- a set of natural processes leading to the destruction of rocks.

Weathering is conventionally divided into physical and chemical.

Main reasons physical weathering are temperature fluctuations associated with daily and seasonal changes. As a result of temperature changes, cracks form. Water entering them, freezing and thawing, widens the cracks. This is how the rock ledges level out and screes appear.

The most important factor chemical weathering is also water and dissolved in it chemical compounds. In this case, climatic conditions and living organisms play a significant role, the waste products of which affect the composition and dissolving properties of water. The root system of plants also has great destructive power.

The weathering process leads to the formation of loose products of rock destruction, which are called weathering bark. It is on it that soil gradually forms.

Due to weathering, the surface of the Earth is constantly renewed, and traces of the past are erased. At the same time, external processes create relief forms caused by the activity of rivers, glaciers, and wind. All of them form specific forms of relief - river valleys, ravines, glacial forms, etc.

Ancient glaciations and landforms formed by glaciers

Traces of the most ancient glaciation were discovered in North America in the Great Lakes region and then in South America and in India. The age of these glacial deposits is about 2 billion years.

Traces of the second - Proterozoic - glaciation (15,000 million years ago) were identified in the Equatorial and South Africa and in Australia.

At the end of the Proterozoic (650-620 million years ago), the third, most ambitious glaciation occurred - the Doxmbrian, or Scandinavian. Traces of it are found on almost all continents.

There are several hypotheses about the causes of glaciations. The factors underlying these hypotheses can be divided into astronomical and geological.

To astronomical factors causing cooling on Earth include:

change in the tilt of the earth's axis;
deviation of the Earth from its orbit towards distance from the Sun;
uneven thermal radiation Sun.

TO geological factors include mountain building processes, volcanic activity, and continental movement.

According to the continental drift hypothesis, huge areas of land throughout the history of the development of the earth's crust periodically moved from a warm climate to a cold climate, and vice versa.

The intensification of volcanic activity, according to some scientists, also leads to climate change: some believe that this leads to warming of the Earth's climate, while others believe that it leads to cooling.

Glaciers have a significant impact on the underlying surface. They smooth out uneven terrain and remove rock fragments, expanding river valleys. In addition, glaciers create specific relief forms.

There are two types of relief that arose due to the activity of a glacier: created by glacial erosion (from lat. erosio- corrosion, destruction) (Fig. 4) and accumulative (from lat. accumulatio- accumulation) (Fig. 5).

Glacial erosion created troughs, pens, circuses, carlings, hanging valleys, “ram's foreheads”, etc.

Large ancient glaciers carrying large rock fragments were powerful rock destroyers. They widened the bottoms of river valleys and made the sides of the valleys along which they moved steeper. As a result of such activity of ancient glaciers, trogs or trough valleys - valleys having a U-shaped profile.

Rice. 4. Landforms created by glacial erosion

Rice. 5. Accumulative glacial landforms

As a result of the splitting of rocks by water freezing in cracks and the removal of the resulting debris by sliding down glaciers, punishment- cup-shaped, chair-shaped depressions at the top of mountains with steep rocky slopes and a gently concave bottom.

A large developed cirque with an outlet into the underlying trough is called glacial circus. It is located in upper parts troughs in the mountains where large valley glaciers have ever existed. Many circuses have steep sides several tens of meters high. The bottoms of cirques are characterized by lake basins carved out by glaciers.

Pointed forms formed during the development of three or more carapaces different sides from one mountain are called Carlings. They often have a regular pyramidal shape.

In places where large valley glaciers received small tributary glaciers, hanging valleys.

"Ram's foreheads" - These are small rounded hills and elevations composed of dense bedrock that have been well polished by glaciers. Their slopes are asymmetrical: the slope facing down the movement of the glacier is slightly steeper. Often on the surface of these forms there is glacial hatching, and the streaks are oriented in the direction of glacier movement.

Accumulative forms of glacial relief include moraine hills and ridges, eskers, drumlins, outwash, etc. (see Fig. 5).

Moraine ridges - swell-like accumulations of products of destruction of rocks deposited by glaciers, up to several tens of meters high, up to several kilometers wide and, in most cases, many kilometers long.

Often the edge of the cover glacier was not smooth, but was divided into fairly clearly separated blades. Probably, during the deposition of these moraines, the edge of the glacier was in an almost motionless (stationary) state for a long time. In this case, not just one ridge was formed, but a whole complex of ridges, hills and basins.

drumlins- elongated hills, shaped like a spoon, turned upside down. These forms are composed of deposited moraine material and in some (but not all) cases have a core of bedrock. Drumlins are usually found in large groups of several dozen or even hundreds. Most of these landforms measure 900-2000 m long, 180-460 m wide and 15-45 m high. Boulders on their surface are often oriented with their long axes in the direction of ice movement, which was from a steep slope to a gentle one. Drumlins appear to have formed when lower layers of ice lost mobility due to overload of debris and were overlain by moving upper layers, which reworked moraine material and created the characteristic shapes of drumlins. Such forms are widespread in the landscapes of the main moraines of areas of glaciation.

Outwashplains composed of material carried by glacial meltwater streams and usually adjacent to the outer edge of terminal moraines. These coarsely sorted sediments consist of sand, pebbles, clay and boulders (the maximum size of which depended on the transport capacity of the streams).

Ozy - these are long narrow winding ridges, composed mainly of sorted sediments (sand, gravel, pebbles, etc.), extending from several meters to several kilometers and up to 45 m high. Eskers were formed as a result of the activity of subglacial meltwater flows flowing through cracks and gullies in the body of the glacier.

Kama - these are small steep hills and short ridges irregular shape composed of sorted sediments. This form of relief can be formed by both water-glacial flows and simply flowing water.

Perennial, or permafrost- thicknesses of frozen rocks that do not thaw for a long time - from several years to tens and hundreds of thousands of years. Permafrost affects the topography, since water and ice have different densities, as a result of which freezing and thawing rocks are subject to deformation.

The most common type of deformation of frozen soils is heaving, associated with an increase in the volume of water during freezing. The resulting positive relief forms are called heaving bumps. Their height is usually no more than 2 m. If heaving mounds formed within the peaty tundra, then they are usually called peat mounds.

In summer upper layer permafrost is thawing. The underlying permafrost prevents meltwater from seeping down; the water, if it does not flow into a river or lake, remains in place until autumn, when it freezes again. As a result, melt water ends up between a waterproof layer of permanent permafrost from below and a layer of new, seasonal permafrost that gradually grows from top to bottom. LSD takes up more volume than water. Water, caught between two layers of ice under enormous pressure, seeks a way out in the seasonally frozen layer and breaks through it. If it pours onto the surface, an ice field is formed - ice If there is a dense moss-grass cover or a layer of peat on the surface, water may not break through it, but only lift it,
spreading across the floor. Having then frozen, it forms the ice core of the mound; gradually growing, such a hillock can reach a height of 70 m with a diameter of up to 200 m. Such landforms are called hydrolaccoliths(Fig. 6).

Rice. 6. Hydrolaccolith

Work of flowing waters

Flowing water refers to all the water that flows over the surface of the land, from small streams that occur during rain or melting snow, to the largest rivers, such as the Amazon.

Flowing waters are the most powerful of all external factors that transform the surface of continents. By destroying rocks and transporting the products of their destruction in the form of pebbles, sand, clay and dissolved substances, flowing waters are capable of leveling the highest mountain ranges over the course of millions of years. At the same time, the products of rock destruction carried into the seas and oceans serve as the main material from which thick strata of new sedimentary rocks arise.

The destructive activity of flowing waters can take the form flat flush or linear erosion.

Geological activity flat flush lies in the fact that rain and melt water flowing down the slope pick up small weathering products and carry them down. In this way, the slopes are leveled out, and the washout products are deposited below.

Under linear erosion understand destructive activities water flows, flowing in a certain direction. Linear erosion leads to the dissection of slopes by ravines and river valleys.

In areas where there are easily soluble rocks (limestone, gypsum, rock salt), karst forms- funnels, caves, etc.

Processes caused by gravity. Processes caused by gravity include primarily landslides, landslides and scree.

Rice. 7. Landslide diagram: 1 - initial position of the slope; 2 - undisturbed part of the slope; 3 - landslide; 4 — sliding surface; 5 - rear seam; 6- supra-landslide ledge; 7- landslide base; 8- spring (source)

Rice. 8. Landslide elements: 1 - sliding surface; 2 - landslide body; 3 — stall wall; 4 – position of the slope before landslide mixing; 5 - bedrock of the slope

Masses of earth can slide down slopes with barely noticeable speed. In other cases, the rate of mixing of weathering products turns out to be higher (for example, meters per day), sometimes large volumes of rocks collapse at a speed exceeding the speed of an express train.

Collapses occur locally and are confined to the upper belt of mountains with sharply dissected relief.

Landslides(Fig. 7) occur when the stability of the slope is disrupted by natural processes or people. At some point, the cohesion forces of soils or rocks turn out to be less than the force of gravity, and the entire mass begins to move. The elements of the landslide are shown in Fig. 8.

In a number of mountain nodes, together with sloughing, collapse is the leading slope process. In the lower belts of mountains, landslides are confined to slopes that are actively being washed away by watercourses, or to young tectonic faults, expressed in the relief in the form of sheer and very steep (more than 35°) slopes.

Collapses of rock masses can be catastrophic, posing a danger to ships and coastal settlements. Landslides and screes along the roads impede the work of transport. In narrow valleys they can disrupt drainage and lead to flooding.

Scree in the mountains they happen quite often. Shedding tends to the upper zone of high mountains, and in the lower zone it appears only on slopes washed away by watercourses. The predominant forms of collapse are “peeling” of the entire slope or a significant section of it, as well as the integral process of collapse from rock walls.

Wind work (aeolian processes)

Wind work refers to the change in the Earth's surface under the influence of moving air jets. Wind can erode rocks, transport fine debris, collect it in specific locations, or deposit it in an even layer on the surface of the earth. The higher the wind speed, the greater the work it does.

A sand hill formed as a result of wind activity is dune.

Dunes are common wherever loose sands come to the surface and the wind speed is sufficient to move them.

Their sizes are determined by the volume of incoming sand, wind speed and the steepness of the slopes. Maximum speed dune movements are about 30 m per year, and the height is up to 300 m.

The shape of the dunes is determined by the direction and constancy of the wind, as well as the features of the surrounding landscape (Fig. 9).

Dunes - relief mobile formations of sand in deserts, blown by the wind and not fixed by plant roots. They only occur when the direction of the prevailing wind is fairly constant (Figure 10).

Dunes can reach a height of half a meter to 100 meters. The shape resembles a horseshoe or sickle, and in cross section they have a long and gentle windward slope and a short leeward one.