Internal (endogenous) processes: slow vertical oscillatory movements, folded (plicative) and discontinuous (disjunctive) tectonic movements and disturbances of rock layers. Magmatism and volcanism, earthquakes. Main areas of volcanism and earthquakes.
Internal (endogenous) processes
formation of the Earth's relief
Relief is a collection of irregularities in the earth's surface of different scales, called landforms.
Relief is formed as a result of the influence of internal (endogenous) and external (exogenous) processes on the lithosphere.
Internal geological processes determine various tectonic movements: vertical and horizontal movements of individual sections earth's crust. The formation of the most significant unevenness of the earth's surface and its continuous change are associated with them. The source of internal processes is heat generated during the radioactive decay of the elements that make up the Earth's core.
According to the predominant direction, two types of tectonic movements are distinguished: vertical and horizontal. Both types of movements can occur either independently or in conjunction with each other. Often one type of movement gives rise to another. They manifest themselves not only in the movement of large blocks of the earth’s crust in vertical or horizontal directions, but also in the formation of folded and faulty faults of various types. scale.
Folds- wave-like bends of the layers of the earth's crust, created by the combined action of vertical and horizontal movements in the earth's crust. A fold whose layers are bent upward is called an anticlinal fold, or anticline. A fold whose layers are bent downwards is called a synclinal fold, or syncline. Synclines and anticlines are the two main forms of folds. Small and relatively simple in structure folds are expressed in the relief by low compact ridges (for example, the Sunzhensky ridge on the northern slope of the Greater Caucasus).
Larger and more complex folded structures are represented in the relief by large mountain ranges and depressions separating them (the Main and Side ranges of the Greater Caucasus). Even larger folded structures, consisting of many anticlines and synclines, form mega relief forms such as a mountainous country, for example the Caucasus Mountains, the Ural Mountains, etc. These mountains are called folded.
Faults- these are various discontinuities in rocks, often accompanied by movement of broken parts relative to each other. The simplest type of ruptures are single, more or less deep cracks. The largest faults, extending over a significant length and width, are called deep faults.
Depending on how the broken blocks moved in the vertical direction, faults and thrusts are distinguished (Fig. 16). Sets of normal faults and thrusts make up horsts and grabens (Fig. 17). Depending on their size, they form individual mountain ranges (for example, the Table Mountains in Europe) or mountain systems and countries (for example, Altai, Tien Shan).
In these mountains, along with grabens and horsts, there are also folded massifs, so they should be classified as folded-block mountains.
In the case when the movement of rock blocks was not only in the vertical direction, but also in the horizontal direction, shifts are formed.
In the process of developing the sciences Earth Many different hypotheses have been put forward about the development of the earth's crust.
The theory of lithospheric plates is based on the idea that all Lithosphere divided by narrow active zones - deep faults - into separate rigid plates floating in the plastic layer of the upper mantle.
The boundaries of lithospheric plates, both in places of their rupture and in places of collision, are moving sections of the earth's crust, to which most active volcanoes are confined, where earthquakes are frequent. These areas, which are areas of new folding, form the Earth's seismic belts.
The further from the boundaries of the moving areas to the center of the plate, the more stable the sections of the earth's crust become. Moscow, for example, is located in the center of the Eurasian plate, and its territory is considered seismically quite stable.
Volcano- a set of processes and phenomena caused by the penetration of magma into the earth’s crust and its outpouring onto the surface. From deep magma chambers, lava, hot gases, water vapor and rock fragments erupt onto the earth. Depending on the conditions and paths of magma penetration to the surface, three types of volcanic eruptions are distinguished.
Area eruptions led to the formation of vast lava plateaus. The largest of them are the Deccan Plateau on the Hindustan Peninsula and the Columbia Plateau.
Fissure eruptions occur along cracks, sometimes of great length. Currently, volcanism of this type occurs in Iceland and on the ocean floor in the area of mid-ocean ridges.
Central eruptions are associated with certain areas, usually at the intersection of two faults, and occur along a relatively narrow channel called a vent. This is the most common type. Volcanoes formed during such eruptions are called layered or stratovolcanoes. They look like a cone-shaped mountain with a crater on top.
Examples of such volcanoes: Kilimanjaro in Africa, Klyuchevskaya Sopka, Fuji, Etna, Hekla in Eurasia.
"Pacific Ring of Fire". About 2/3 of the Earth's volcanoes are concentrated on islands and the shores of the Pacific Ocean. The most powerful volcanic eruptions and earthquakes took place in this region: San Francisco (1906), Tokyo (1923), Chile (1960), Mexico City (1985).
Sakhalin Island, the Kamchatka Peninsula and the Kuril Islands, located in the very east of our country, are links in this ring.
In total, there are 130 extinct volcanoes and 36 active volcanoes in Kamchatka. The largest volcano is Klyuchevskaya Sopka. There are 39 volcanoes on the Kuril Islands. These places are characterized by destructive earthquakes, and the surrounding seas are characterized by seaquakes, typhoons, volcanoes and tsunamis.
Tsunami translated from Japanese - “wave in the bay”. These are waves of gigantic size generated by an earthquake or sea quake. In the open ocean they are almost invisible to ships. But when the path of the tsunami is blocked by the mainland and islands, the wave hits the land from a height of up to 20 meters. So, in 1952, such a wave completely destroyed the Far Eastern city of Severokurilsk.
Hot springs and geysers are also associated with volcanism. In Kamchatka, in the famous Valley of Geysers, there are 22 large geysers.
Earthquakes They are also a manifestation of endogenous earth processes and represent sudden underground impacts, tremors and displacements of layers and blocks of the earth's crust.
Studying earthquakes. At seismic stations, scientists study these formidable natural phenomena, using special instruments, and look for ways to predict them. One of these devices, the seismograph, was invented at the beginning of the 20th century. Russian scientist B.V. Golitsyn. The name of the device comes from the Greek words seismo (oscillation), grapho (writing) and speaks of its purpose - to record the vibrations of the Earth.
Earthquakes can be of varying strengths. Scientists agreed to determine this force on an international 12-point scale, taking into account the degree of damage to buildings and changes in the Earth's topography. Here is a fragment of this scale (Table 5).
Table 5
Earthquakes are accompanied by tremors, following one after another. The place where the shock occurs in the depths of the earth's crust is called the hypocenter. The place on the earth's surface located above the hypocenter is called the epicenter of an earthquake.
Earthquakes cause the formation of cracks on the earth's surface, displacement, lowering or raising of individual blocks, landslides; cause damage to the economy and lead to the death of people.
Over time, it changes under the influence of various forces. Places where there were once great mountains become plains, and in some areas volcanoes arise. Scientists are trying to explain why this happens. And much is already known to modern science.
Reasons for transformation
The relief of the Earth is one of the most interesting mysteries of nature and even history. Because of the way the surface of our planet changed, the life of mankind also changed. Changes occur under the influence of internal and external forces.
Among all landforms, large and small ones stand out. The largest of them are continents. It is believed that hundreds of centuries ago, when there was no man yet, our planet had a completely different appearance. Perhaps there was only one continent, which over time was split into several parts. Then they separated again. And all those continents that exist now appeared.
Another major form was the oceanic trenches. It is believed that there were also fewer oceans before, but then there were more. Some scientists argue that hundreds of years later new ones will appear. Others say that the water will flood some areas of the land.
The relief of the planet has been changing over many centuries. Even though people sometimes greatly harm nature, their activities are not capable of significantly changing the relief. This requires such powerful forces that only nature has. However, man cannot not only radically transform the planet’s topography, but also stop the changes that nature itself produces. Despite the fact that science has made great strides forward, it is not yet possible to protect all people from earthquakes, volcanic eruptions and much more.
Basic information
The Earth's topography and major landforms attract the close attention of many scientists. The main varieties include mountains, highlands, shelves and plains.
The shelf is those areas of the earth's surface that are hidden under water. Very often they stretch along the banks. A shelf is a type of landform that is found only underwater.
Highlands are isolated valleys and even systems of ridges. Much of what is called mountains is actually highlands. For example, the Pamir is not a mountain, as many people believe. Also, the Tien Shan is a highland.
Mountains are the most ambitious landforms on the planet. They rise above the land by more than 600 meters. Their peaks are hidden behind the clouds. It happens that in warm countries you can see mountains whose peaks are covered with snow. The slopes are usually very steep, but some daredevils dare to climb them. Mountains can form chains.
The plains are stability. Residents of the plains are least likely to experience changes in relief. They hardly know what earthquakes are, which is why such places are considered the most favorable for life. A true plain is the flattest possible surface of the earth.
Internal and external forces
The influence of internal and external forces on the Earth's topography is enormous. If you study how the surface of the planet has changed over several centuries, you will notice how what seemed eternal disappears. It is being replaced by something new. External forces are not capable of changing the Earth's topography as much as internal ones. Both the first and second are divided into several types.
Inner forces
The internal forces that change the Earth's topography cannot be stopped. But in the modern world, scientists from different countries are trying to predict when and in what place there will be an earthquake, where a volcanic eruption will occur.
Internal forces include earthquakes, movements and volcanism.
As a result, all these processes lead to the appearance of new mountains and mountain ranges on land and on the ocean floor. In addition, geysers, hot springs, chains of volcanoes, ledges, cracks, depressions, landslides, volcanic cones and much more appear.
External forces
External forces are not capable of producing noticeable transformations. However, you should not lose sight of them. Those that shape the Earth's topography include the following: the work of wind and flowing water, weathering, melting glaciers and, of course, the work of people. Although man, as mentioned above, is not yet capable of greatly changing the appearance of the planet.
The work of external forces leads to the creation of hills and ravines, basins, dunes and dunes, river valleys, rubble, sand and much more. Water can very slowly destroy even a great mountain. And those stones that are now easily found on the shore may turn out to be part of a mountain that was once great.
Planet Earth is a grandiose creation in which everything is thought out to the smallest detail. It has changed over the centuries. Cardinal transformations of the relief have occurred, and all this is under the influence of internal and external forces. In order to better understand the processes occurring on the planet, it is imperative to know about the life it leads, not paying attention to humans.
Geological processes of relief formation
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.
2.5.1.1. 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 violent 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.
2.5.1.2. 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.
Until now, we have considered internal relief-forming factors, such as movements of the earth's crust, folding, etc. These processes are caused by the action of the internal energy of the Earth. As a result, large landforms such as mountains and plains are created. During the lesson you will learn how the relief was formed and continues to form under the influence of external geological processes.
Other forces are also working to destroy rocks - chemical. Seeping through cracks, water gradually dissolves rocks (see Fig. 3).
Rice. 3. Dissolution of rocks
The dissolving power of water increases with the content of various gases in it. Some rocks (granite, sandstone) do not dissolve with water, others (limestone, gypsum) dissolve very intensively. If water penetrates along cracks into layers of soluble rocks, then these cracks widen. In those places where water-soluble rocks are close to the surface, numerous dips, funnels and basins are observed on it. This karst landforms(see Fig. 4).
Rice. 4. Karst landforms
Karst is the process of dissolving rocks.
Karst landforms are developed in the East European Plain, the Urals, the Urals and the Caucasus.
Rocks can also be destroyed as a result of the vital activity of living organisms (saxifrage plants, etc.). This biological weathering.
Simultaneously with the processes of destruction, the products of destruction are transferred to low areas, thus the relief is smoothed out.
Let's consider how the Quaternary glaciation shaped the modern topography of our country. Glaciers have survived today only on the Arctic islands and on the highest peaks of Russia (see Fig. 5).
Rice. 5. Glaciers in the Caucasus Mountains ()
Going down steep slopes, glaciers form a special glacial landform. This type of relief is common in Russia and where there are no modern glaciers - in the northern parts of the East European and West Siberian Plains. This is the result of ancient glaciation that arose in the Quaternary era due to climate cooling (see Fig. 6).
Rice. 6. Territory of ancient glaciers
The largest centers of glaciation at that time were the Scandinavian Mountains, the Polar Urals, the Novaya Zemlya Islands, and the mountains of the Taimyr Peninsula. The ice thickness on the Scandinavian and Kola Peninsulas reached 3 kilometers.
Glaciation occurred more than once. It was approaching the territory of our plains in several waves. Scientists believe that there were approximately 3-4 glaciations, which were followed by interglacial eras. The last ice age ended about 10 thousand years ago. The most significant glaciation was on the East European Plain, where the southern edge of the glacier reached 48º-50º N. w.
To the south, the amount of precipitation decreased, so in Western Siberia glaciation reached only 60º C. sh., and east of the Yenisei due to the small amount of snow there was even less.
In the centers of glaciation, from where ancient glaciers moved, traces of activity in the form of special relief forms - Ram's foreheads - are widespread. These are rock protrusions with scratches and scars on the surface (slopes facing the movement of the glacier are gentle, and those opposite are steep) (see Fig. 7).
Rice. 7. Lamb forehead
Under the influence of their own weight, glaciers spread far from the center of their formation. Along their route, they smoothed out the terrain. A characteristic glacial relief is observed in Russia on the territory of the Kola Peninsula, the Timan Ridge, and the Republic of Karelia. The moving glacier scraped soft, loose rocks and even large, hard debris from the surface. Clay and hard rocks frozen into ice formed moraine(deposits of rock fragments formed by glaciers as they move and melt). These rocks were deposited in more southern areas where the glacier melted. As a result, moraine hills and even entire moraine plains were formed - Valdai, Smolensk-Moscow.
Rice. 8. Moraine formation
When the climate did not change for a long time, the glacier stopped in place and single moraines accumulated along its edge. In relief they are represented by curved rows tens or sometimes even hundreds of kilometers long, for example the Northern Uvaly on the East European Plain (see Fig. 8).
When glaciers melted, flows of meltwater formed, which washed over the moraine, therefore, in the areas of distribution of glacial hills and ridges, and especially along the edge of the glacier, water-glacial sediments accumulated. Sandy flat plains that arose along the outskirts of a melting glacier are called - outwash(from German “zandra” - sand). Examples of outwash plains are the Meshchera lowland, the Upper Volga, and the Vyatka-Kama lowlands. (see Fig. 9).
Rice. 9. Formation of outwash plains
Among the flat-low hills, water-glacial landforms are widespread, oz(from Swedish “oz” - ridge). These are narrow ridges, up to 30 meters high and up to several tens of kilometers long, shaped like railway embankments. They were formed as a result of the settling on the surface of loose sediment formed by rivers flowing along the surface of glaciers (see Fig. 10).
Rice. 10. Formation of eskers
All water flowing over land also forms a relief under the influence of gravity. Permanent watercourses - rivers - form river valleys. The formation of ravines is associated with temporary watercourses formed after heavy rains (see Fig. 11).
Rice. 11. Ravine
Overgrown, the ravine turns into a ravine. The slopes of the hills (Central Russian, Volga, etc.) have the most developed ravine-gully network. Well-developed river valleys are characteristic of rivers flowing outside the boundaries of the last glaciations. Flowing waters not only destroy rocks, but also accumulate river sediments - pebbles, gravel, sand and silt (see Fig. 12).
Rice. 12. Accumulation of river sediments
They consist of river floodplains, stretching in strips along river beds (see Fig. 13).
Rice. 13. River valley structure
Sometimes the latitude of floodplains ranges from 1.5 to 60 km (for example, near the Volga) and depends on the size of the rivers (see Fig. 14).
Rice. 14. Width of the Volga in various sections
Traditional places of human settlement are located along the river valleys and a special type of economic activity is being formed - livestock raising on floodplain meadows.
In lowlands experiencing slow tectonic subsidence, extensive river floods and wandering of their channels occur. As a result, plains are formed, built by river sediments. This type of relief is most common in the south of Western Siberia (see Fig. 15).
Rice. 15. Western Siberia
There are two types of erosion - lateral and bottom. Deep erosion is aimed at cutting streams into the depths and prevails in mountain rivers and rivers of plateaus, which is why deep river valleys with steep slopes are formed here. Lateral erosion is aimed at eroding the banks and is typical for lowland rivers. Speaking about the impact of water on the relief, we can also consider the impact of the sea. When seas advance on flooded land, sedimentary rocks accumulate in horizontal layers. The surface of the plains, from which the sea retreated long ago, has been greatly altered by flowing waters, wind, and glaciers. (see Fig. 16).
Rice. 16. Sea retreat
The plains, relatively recently abandoned by the sea, have a relatively flat topography. In Russia, this is the Caspian lowland, as well as many flat areas along the shores of the Arctic Ocean, part of the low-lying plains of the Ciscaucasia.
Wind activity also creates certain forms of relief, which are called aeolian. Aeolian landforms form in open spaces. In such conditions, the wind carries large amounts of sand and dust. Often a small bush is a sufficient barrier, the wind speed decreases and the sand falls to the ground. This is how small and then large sand hills are formed - barchans and dunes. In plan, the dune has the shape of a crescent, with its convex side facing the wind. As the wind direction changes, the orientation of the dune also changes. Landforms associated with wind are distributed mainly in the Caspian lowland (dunes), on the Baltic coast (dunes) (see Fig. 17).
Rice. 17. Formation of a dune
The wind blows a lot of small debris and sand from the bare mountain peaks. Many of the grains of sand it carries out hit the rocks again and contribute to their destruction. You can observe bizarre weathering figures - remnants(see Fig. 18).
Rice. 18. Remnants - bizarre landforms
The formation of special species - forests - is associated with the activity of wind. - this is a loose, porous, dusty rock (see Fig. 19).
Rice. 19. Forest
Forest covers large areas in the southern parts of the East European and West Siberian Plains, as well as in the Lena River basin, where there were no ancient glaciers (see Fig. 20).
Rice. 20. Territories of Russia covered with forest (shown in yellow)
It is believed that the formation of the forest is associated with the blowing of dust and strong winds. The most fertile soils form on the forest, but it is easily washed away by water and the deepest ravines appear in it.
- The formation of relief occurs under the influence of both external and internal forces.
- Internal forces create large landforms, and external forces destroy them, transforming them into smaller ones.
- Under the influence of external forces, both destructive and creative work is carried out.
Bibliography
- Geography of Russia. Nature. Population. 1 part 8th grade / V.P. Dronov, I.I. Barinova, V.Ya Rom, A.A. Lobzhanidze.
- V.B. Pyatunin, E.A. Customs. Geography of Russia. Nature. Population. 8th grade.
- Atlas. Geography of Russia. Population and economy. - M.: Bustard, 2012.
- V.P. Dronov, L.E. Savelyeva. UMK (educational and methodological set) “SPHERES”. Textbook “Russia: nature, population, economy. 8th grade". Atlas.
- The influence of internal and external processes on the formation of relief ().
- External forces that change the terrain. Weathering. ().
- Weathering().
- Glaciation on the territory of Russia ().
- Physics of dunes, or how sand waves are formed ().
Homework
- Is the statement true: “Weathering is the process of destruction of rocks under the influence of wind”?
- Under the influence of what forces (external or internal) did the peaks of the Caucasus Mountains and Altai acquire a pointed shape?
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 landforms, 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 relief forms 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 within 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 in 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 are dehydrated, recrystallized, and some minerals are replaced by 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 common 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 rupturing 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 wide 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.