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.
Relief-forming processes
It would be incorrect to believe that the topography of our planet was formed in those ancient geological eras under the influence of internal (endogenous) forces. Even in such stable forms of the earth's surface as platforms, changes occur under the influence of external factors. All relief-forming processes can be divided into two large groups: internal (endogenous) and external (exogenous).
The main exogenous processes that change the topography of our country include weathering, glaciation, the activity of flowing waters and wind processes (see Fig. 1).
Rice. 1. External relief-forming factors
Weathering
Weathering is the process of destruction and change of rocks under the influence of mechanical and chemical influences of the atmosphere, ground and surface waters and organisms.
Rocks are destroyed by temperature changes due to the fact that the minerals from which they are composed have different coefficients of thermal expansion. Over time, cracks appear in the once monolithic rock. Water penetrates into them, which freezes at subzero temperatures and, turning into ice, literally “tears” the rocks. They are destroyed, and at the same time the relief forms are “smoothed out”. Such processes are called physical weathering. They occur most intensely in the mountains, where solid monolithic rocks come to the surface. The rate of physical weathering processes (about 1 mm per year), it would seem, is not very high. However, over millions of years the mountains will decrease by 1 kilometer. Thus, it would take 10 million years for the Earth's highest mountains, the Himalayas, to be completely destroyed. By geological standards, this is a very short time period (see Fig. 2).
Rice. 2. Physical weathering
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.
Glaciation
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 sediments formed by rivers flowing along the surface of glaciers (see Fig. 10).
Rice. 10. Formation of eskers
Activity of flowing waters
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 that form 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
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. Wind-related landforms are distributed mainly in the Caspian lowland (dunes) and 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
Forests cover 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.
Let's sum it up
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. The 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?
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?
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 at the surface of the earth, where there are more grains of sand.
As a result of wind activity, dense deposits of dust particles can accumulate.
Such homogeneous, porous, grayish-yellow rocks are called loess.
Glacier activity
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
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.
Remember
- Due to what source of energy do external forces act that change the surface of the Earth? What happens to solid rocks when heated and then cooled? How do tree roots and burrowing animals affect rocks?
How external forces affect the terrain. You already know that internal forces make the Earth's surface vary in height. External forces act in the opposite direction. They destroy large elevations of the relief, transport rock fragments and fill depressions with them. Thus, external forces smooth and level the surface. However, external processes are not only destroyers, but also creators of relief. By destroying its large forms, they create medium and small irregularities.
The main external forces are weathering, the work of flowing waters, wind, glaciers, and the sea. Human economic activity has also become a significant external force.
Weathering. Weathering occurs due to the effect on the surface of temperature fluctuations, water with substances dissolved in it, and living organisms. The work of the wind has nothing to do with weathering.
Weathering is the destruction and change of rocks on the land surface under the influence of natural environmental conditions.
During weathering, physical, chemical, and biological processes operate simultaneously throughout the land surface. However, under different natural conditions, one or another of these processes may predominate. Therefore, physical, chemical and biological weathering are distinguished.
Rice. 60. Placers of stones at the foot of the mountains
main reason physical weathering- temperature fluctuations. During the day, rocks heat up and expand; at night, they cool and contract. Because of this, monolithic rocks crack and break up into fragments. This is how placers of blocks, crushed stone and sand are formed (Fig. 60). Physical weathering is typical for areas with large and sharp temperature changes and dry air: deserts, mountain peaks not covered with snow (Fig. 61).
Chemical weathering- this is the dissolution, decomposition of some minerals and the formation of other minerals and rocks in their place. It occurs under the influence of oxygen in the air, water and substances dissolved in it. In humid and hot climates, chemical weathering occurs more actively than in cold and dry climates. The main result of chemical weathering is the formation of clay from hard and durable rocks: granites, basalts, gneisses, etc.
Biological weathering occurs under the influence of plant and animal organisms. The roots of trees growing on rocks, like wedges, push the cracks apart. Animals, especially burrowing rodents, also contribute to the destruction of rocks. But the main effect of living organisms is different. They supply organic matter to the soil, which helps decompose minerals. Therefore, where lush vegetation grows, biological weathering is especially active.
Rice. 61. Bizarre landforms formed by weathering
Strength varies among different breeds. Some collapse faster, others slower. Therefore, when rocks of different strengths weather, bizarre relief forms appear: pillars, columns, balls, gates.
Even microorganisms, lichens, and mosses have an impact on rocks. If you remove moss from a stone, you will find small depressions underneath it filled with loose matter. This is the result of the destruction of solid rock by organic acids secreted by mosses.
Physical, chemical and biological weathering occurs everywhere and constantly. Under its influence, even the most durable rocks turn into loose material - debris and clay. Loose material is transported by water flows, wind, and glaciers over vast distances. When it enters lakes, seas and oceans, it accumulates clastic and clay sediments.
Questions and tasks
- How do external forces acting on the earth's surface change?
- What is weathering? How does it affect rocks?
- What types does a single weathering process consist of?
- How do living organisms affect rocks?
- How do animals and plants participate in physical and chemical weathering?