p> 2 The boundary areas between the lithospheric plates, in which volcanic eruptions and earthquakes occur, are:
1.platforms; 2. seismic belts;
3. mountains; 4. oceanic plains.
3. What forms of relief are formed mainly under the influence of external forces?
1. protrusions of the continents; 2. vast plains;
3. deep water troughs; 4. river valleys.
4. Determine the type of climate for this characteristic:
"The temperature in summer and winter is + 25º ... + 28 ° С, the annual precipitation is more than 2000 - 3000 mm."
5. At what latitudes do the ascending air currents prevail and low pressure belts are formed?
1.in equatorial and polar; 3. in temperate and equatorial;
2. in polar and tropical; 4. in tropical and equatorial.
6. Cold currents include:
1. Peruvian and Gulf Stream; 2. Peruvian and Californian;
3. California and Brazilian.
7. The names of the natural areas are given by nature:
1. animal world; 2. vegetation;
3. economic activity person.
8. What natural complex formed as a result of human activity?
1. river valley; 2. mountain system;
3. irrigation canal; 4. high-altitude belt.
9. Determine which natural area is referred to:
«… low temperatures all year round, precipitation is rare, mainly in the form of snow, dwarf vegetation, lemmings, arctic foxes are found ... ”.
10.90% of all living organisms harvested by humans in the ocean are:
1. shrimp, crabs; 2. molluscs;
3. algae; 4. fish.
11. By map natural areas world and soil map, determine which soils prevail in Africa in the zone of humid equatorial forests:
1. red ferralitic seasonal wet forests and high-mountain savannas;
2.Red-yellow ferralite evergreen forests;
3.Red-brown savannah;
4. reddish-brown deserted savannah.
12. What are the coordinates of the westernmost point in Africa?
1.14 ° N .; 15 ° W; 2.14 ° S .; 17 ° W;
3.17 ° N; 26 ° W; 4.11 ° N; 3 ° East
13.In North Africa more than in the South:
1.diamonds; 2. gold;
3. oil; 4. copper.
14. Which lake in Africa is the largest in area?
1.Victoria; 2.Nyasa;
3. Tanganyika; 4. Chad.
15. The shortest people on Earth living in Africa:
1.bushmen; 2. pygmies;
3. Ethiopians; 4. Berbers.
16. What is called screaming in Australia?
1. underground artesian waters; 3. temporary drying up rivers;
2. light eucalyptus forests; 4. fenced pastures for livestock.
17. The bitch devil is found:
1.in Northern Australia; 2. in Eastern Australia;
3.on the island New Guinea; 4. on the island of Tasmania.
18. Which islands are located in the Caribbean Sea north of South America:
1. Tierra del Fuego; 2. Falkland Islands;
3. Lesser Antilles; 4. Galapagos.
19. Descendants from marriages of blacks and whites are called:
1. mestizo; 2. sambo;
3. mulattoes; 4. Indians.
20. Who Discovered Antarctica?
1. J. Cook; 2. MP Lazarev and FF Bellingshausen;
3. R. Amundsen; 4. R. Scott.
21. On which river is the national park " Grand canyon»?
1. p. Colombia; 2.p. Colorado;
3. p. Niagara; 4. p. St. Lawrence.
22.The lowest territory of Eurasia is:
1. Caspian lowland; 3. Dead Sea;
2. Mesopotamian lowland; 4. Lake Geneva.
23. “This country is the homeland of Charles Dickens, W. Shakespeare, Walter Scott. In its capital, you can visit the Tower, watch the changing of the royal guard at Buckingham Palace. " What country are we talking about?
1.France; 2.Spain;
3.Italy; 4. Great Britain.
24. Relate the rivers of the world:
river mainland
1.Congo; A. Eurasia;
2. Mississippi; B. South America;
3.Mekong; B. Australia;
4. Darling G. North America;
7. Amazing phenomena- spreading and subduction
These phenomena are illustrated in the figure on p. 74. Let's start with spreading. It occurs along the mid-ocean ridges - the boundaries of the separating plates (these boundaries always run along the ocean floor). In our figure, the mid-ocean ridge separates lithospheric plates A and B. These can be, for example, the Pacific plate and the Nazca plate, respectively. The lines with arrows in the figure show the directions of movement of the magmatic masses of the asthenosphere. It is easy to see that the asthenosphere tends to pull plate A to the left, and plate B to the right, and thereby pushes these plates apart. The spreading of the plates is also facilitated by the flow of magma from the asthenosphere, directed from bottom to top directly to the interface between the plates; it acts like a kind of wedge. So, plates A and B move slightly apart, a crevice (rift) is formed between them. The pressure of the rocks in this place drops and a chamber of molten magma appears there. An underwater volcanic eruption occurs, molten basalt pours out through a crevice and solidifies, forming basalt lava. This is how the edges of the sliding plates A and B build up. So, the build-up occurs due to the magmatic mass that has risen from the asthenosphere and spread along the slopes of the mid-ocean ridge. Hence the English term "spreading", which means "expansion", "spreading".
Keep in mind that spreading occurs continuously. A&V slabs are growing all the time. This is exactly how the movement of these plates is carried out in different sides... Let us emphasize: the movement of lithospheric plates is not the movement of an object in space (from one place to another); it has nothing to do with the movement of, say, an ice floe on the surface of the water. The movement of the lithospheric plate occurs due to the fact that in some place (where the mid-ocean ridge is located) new and new parts of the plate are constantly growing, as a result of which the previously formed parts of the plate are constantly moving away from the mentioned place. So this movement should be perceived not as movement, but as growth (one might say: expansion).
Well, when it grows, of course, the question arises: what to do with the "extra" parts of the plate? Here plate B has grown so much that it has reached plate C. If in our case plate B is the Nazca plate, then plate C can be the South American plate.
Note that there is a continent on plate C; it is a more massive plate compared to oceanic plate B. So, plate B has reached plate C. What next? The answer is known: plate B will bend downward, dive (move) under plate C and continue to grow in the depths of the asthenosphere under plate C, gradually turning into the substance of the asthenosphere. This phenomenon is called subduction. This term comes from the words "sub" and "duction". In Latin, they mean "under" and "lead", respectively. So "subduction" is bringing under something. In our case, plate B turned out to be brought under plate C.
The figure clearly shows that, due to the bowing of plate B, the depth of the ocean near the edge of the continental plate C increases - a deep-sea trench is formed here. Chains usually appear near the gutters active volcanoes... They are formed above the place where the "diving" lithospheric plate, obliquely sinking into the depths, begins to partially melt. Melting occurs due to the fact that the temperature has increased with depth (up to 1000-1200 ° C), and the pressure of the rocks has not yet increased very much.
Now you are introducing the essence of the concept of global plate tectonics. The Earth's lithosphere is a collection of plates that float on the surface of the viscous asthenosphere. Under the influence of the asthenosphere, oceanic lithospheric plates move away from the mid-ocean ridges, the craters of which provide a constant growth of the oceanic lithosphere (this is the phenomenon of stredding). Oceanic plates are moving towards deep sea trenches; there they go deeper and are ultimately absorbed by the asthenosphere (this is a subduction phenomenon). In the spreading zones, the earth's crust is "fed" by the matter of the asthenosphere, and in the zones of subduction, it returns the "excess" of matter to the asthenosphere. These processes occur due to the thermal energy of the earth's interior. Spreading zones and subduction zones are the most active tectonically. They account for the bulk (more than 90%) of earthquake and volcanic foci on the globe.
Let us add two remarks to the described picture. First, there are boundaries between the slabs moving roughly parallel to each other. At such boundaries, one slab (or part of a slab) is displaced relative to the other vertically. These are the so-called transform faults. An example is the large Pacific rifts running parallel to each other. The second remark is that subduction can be accompanied by crushing and formation of mountain folds at the edge of the continental crust. This is how the Andes were formed in South America. The formation of the Tibetan Plateau and the Himalayas deserves a special discussion. We will talk about this in the next paragraph.
The earth's crust is the uppermost layer of the earth, and then it is studied best of all. In its depths lie rocks and minerals that are very valuable for humans, which he learned to use in the economy. Figure 1. Structure of the Earth Top layer crust consists of fairly soft rocks. They are formed as a result of the destruction of solid rocks (for example, sand), the deposition of animal remains (chalk) or ...
Two tectonic regimes are distinguished: platform and orogenic, which correspond to second-order megastructures - platforms and orogens. On the platforms, the relief of plains of different heights of various genesis develops, in the areas of mountain building - mountainous countries. Platform plains Platform plains develop on platforms of different ages and are the main megaform of the continental relief ...
And sometimes even gaps can form. These forms are widespread in the Central Asian regions. Karst and karst landforms. Limestone, gypsum and other related rocks almost always have a large number of cracks. Rain and snow waters go deep into the earth along these cracks. At the same time, they gradually dissolve limestones and expand cracks. As a result, the entire layer of limestone ...
High point throughout Ukraine, Mount Hoverla (2,061 m) in the Ukrainian Carpathians. Lowlands, hills and mountains of Ukraine are confined to various tectonic structures that influenced the development of modern relief, on the surface of certain parts of the territory. Lowlands. In the north of Ukraine there is the Polesye lowland, which slopes towards the Pripyat and Dnieper rivers. Its heights do not exceed 200 m, only ...
geomorphology relief vegetation meadow
The relief of any part of the earth's surface is composed of multiple and alternating individual relief forms, each of which consists of relief elements.
Landforms can be closed (moraine hill, moraine depression) or open (ravine, ravine), simple or complex, positive or negative. The positive ones include the forms protruding relative to a certain sub-horizontal level, while the negative forms are deepened relative to this level.
Landforms can be very different in size, origin and age.
Thus, several relief classifications have been developed.
Morphological classification is due to the geometric dimensions of the relief forms.
Planetary forms are continents, mobile belts, ocean floor and mid-ocean ridges;
Megaforms are parts of planetary forms, i.e. plains and mountains;
Macroforms are parts of megaforms: mountain ranges, large valleys and depressions;
Mesoforms are medium-sized forms: beams, ravines;
Microforms are irregularities that complicate the surface of mesoforms: sinkholes, gullies;
Nanoforms are very small irregularities that complicate meso- and microforms: bumps, ripples on the slopes of dunes, etc.
Genetic classification.
There are two classes:
Forms formed as a result of the activity of internal, endogenous forces.
Forms formed due to exogenous, external forces.
The first class includes three subclasses.
1) Forms associated with tectonic movements.
Tectonic movements in the earth's crust are constantly manifested. In some cases, they are slow, hardly noticeable to the human eye (epochs of rest), in others - in the form of intense stormy processes (tectonic revolutions).
2) forms associated with volcanic activity.
Volcanoes are geological formations on the surface of the earth's crust that spew lava, volcanic gases, rocks (volcanic bombs), and pyroclastic flows to the surface.
3) landforms caused by earthquakes
Like other endogenous factors, earthquakes have a significant relief-forming significance. The geomorphological role of earthquakes is expressed in the formation of cracks, in the displacement of blocks of the earth's crust along cracks in the vertical and horizontal directions, sometimes in folded deformations.
Let's designate some types of relief forms formed by external forces.
1) Fluvial forms - landforms created by the activity of water streams.
2) Aeolian forms - landforms that arise under the influence of the wind;
3) glacial forms - landforms caused by the activity of ice and snow
Morphogenetic classification.
It was first proposed at the beginning of the 20th century by Engelny. He identified three categories of relief:
1. Geotecture - the largest landforms on Earth: planetary and megaforms. They are created by cosmic and planetary forces .;
2. Morphostructures - large forms of the earth's surface, which are created under the influence of endogenous and exogenous processes, but with the leading and active role of tectonic movements .;
3. Morphosculptures are medium and small forms of relief (meso-, micro and nanoforms), created with the participation of endo- and exogenous forces, but with the leading and active role of exogenous forces ..
This classification was improved by the Russian geomorphologists I.P. Gerasimov and Yu.A. Meshcheryakov. It takes into account the fact that the dimensions of the relief bear the imprint of origin.
At the same time, the following stand out:
Geotectures are the largest landforms on Earth: planetary and megaforms. They are created by cosmic and planetary forces.
Morphostructures are large forms of the earth's surface, which are created under the influence of endogenous and exogenous processes, but with the leading and active role of tectonic movements.
Morphosculptures are medium and small forms of relief (meso-, micro and nanoforms), created with the participation of endo- and exogenous forces, but with the leading and active role of exogenous forces.
Relief classification by age.
The development of the relief of any territory, as shown by the American geomorphologist W. Davis, occurs in stages. The age of a relief can be understood to mean certain stages of its development. For example, the formation of a river valley after the retreat of a glacier: at first, the river cuts into the underlying rocks, there are many irregularities in the longitudinal profile, and there is no floodplain. This is the youthful stage of the river valley. Then a normal profile is formed, the river floodplain is formed. This is the maturity stage of the valley. Due to lateral erosion, the floodplain expands, the course of the river slows down, and the channel becomes meandering. Coming to the stages of old age in the development of the river valley.
W. Davis took into account the complex of morphological and dynamic characteristics and identified three stages: youth, maturity and old age of the relief.
A little earlier in the section "classification by genetic characteristics" the main relief-forming factors have already been noted, they can be divided into two large groups:
Endogenous
Exogenous
Endogenous factors.
The relief is formed under the influence of the internal energy of the Earth. The processes taking place inside the globe, leave their mark on the outer shell in the form different forms relief. Endogenous factors are divided into three main types: tectonic, volcanic and earthquakes.
Mountain building, earthquakes, volcanism are associated with tectonic movements in the earth's crust. The form, nature and intensity of destruction of the earth's surface, sedimentation, and the distribution of land and sea also depend on these movements.
Summing up modern views about tectogenesis, according to the predominance of direction, two types of tectonic movements can be distinguished - vertical (radial) and horizontal (tangential). Both types of movements can occur both independently and in interaction with each other (often one type of movement gives rise to another) and are manifested 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 discontinuous faults of various scales.
Thus, ascending flows of the heated material of the upper mantle lead to the formation of large positive landforms such as the East Pacific Rise.
Horizontal displacements of lithospheric plates towards each other lead to their collision (collision), pushing of some plates under others (subduction) or pushing one plate over another (obduction). All these processes determine the formation of deep-sea trenches and the island arcs bordering them, grandiose mountain structures. This example illustrates the transition of horizontal movements to vertical ones.
There are 3 types of volcanic landforms: Volcanic mountains, negative landforms of volcanic formations, pseudovolcanic landforms.
Volcanic mountains.
The most common form of volcanic mountains are volcanic cones. depending on the type of lava and the nature of the eruptions, the cones may have steeper or more gentle slopes. In those cases when the cone is composed mainly of solid or loose volcanic products ejected by the volcano, the cone is called bulk. In those cases, when, along with solid products of eruption, the volcano periodically pours out lava, a peculiar layered structure of the cone is obtained. It should be noted that layered cones are the most common. Classic examples of such cones are Klyuchevskaya Sopka, Kronotskaya Sopka, Fujiyama and many others. The steepness of slope-filled and layered cones reaches 30-35 °.
The first and most characteristic negative form is the crater. The shape and size of the crater depend primarily on the materials that make up the cone, and then on the degree of destruction of the volcano. The sizes of the craters are very different and, as already mentioned, little depends on the size of the volcano. For example, the Fossa volcano (on Vulcano Island) 386 m high has a crater over 500 m in diameter, and Etna volcano 3297 m high has a crater 227 m in diameter. At the same time, the crater of the Mauna Loa volcano (in the Hawaiian Islands) has a crater 2438 m wide. Big sizes the last crater, as we already know, is primarily due to the nature of the lava.
Pseudovolcanic landforms.
In addition to the eruption of deep-seated magmatic products, the phenomena of eruption of mud or water are observed in nature. This is the so-called pseudovolcanism; it includes mud volcanoes and geysers. Mud volcanoes are very similar to real volcanoes, only they consist of other products. The cones of mud volcanoes are up to 300-400 meters high; at the top is a crater filled with water or mud. Mud volcanoes are quite common. In some cases, they are confined to areas of modern volcanism and owe their origin to post-volcanic phenomena. In other cases, mud volcanoes are associated with oil deposits, namely with oil gases released along the zones of tectonic structures and faults. Finally, there is a third case of mud eruptions associated with the release of gases as a result of the decomposition of organic masses in the deltaic sediments of large rivers (Indus, Mississippi, etc.).
Often, as a result of earthquakes, structures of the graben type are formed, respectively, expressed in the relief in the form of negative forms.
Occasionally, during earthquakes, specific positive landforms can occur. Thus, during the earthquake in northern Mexico (1887), mounds up to 7 meters high were formed between the two faults, and during the Assaam earthquake in India, a number of islands moved into the sea, for one of them 150 m and a width of 25 m. In some cases, along cracks formed during earthquakes, water rose, carrying sand and clay to the surface. The result is small bulk cones. Sometimes, during earthquakes, deformations such as folded disturbances are formed. Due to the fact that many forms of relief that arise during earthquakes have a relatively small size, they are quickly destroyed under the influence of exogenous processes.
An important relief-forming role is played by some processes caused by earthquakes and accompanying them. During earthquakes, as a result of strong tremors on steep mountain slopes, river and sea banks, landslides, talus, wasps, landslides and avalanches appear and become more active. The activity of all these phenomena changes the relief and hydro-regime of the territory.
A certain relief-forming role is played by earthquakes, the centers of which are located in the sea (seaquakes). Under their influence, there is a movement of huge masses of loose and water-saturated bottom sediments on the gentle slopes of the seabed. Seaquakes form tsunamis that hit the coast and have a significant impact on the morphology of sea coasts.
Exogenous factors.
Relief formation under the influence of water.
The movement of water across the earth's surface is called runoff. Off-channel and channel runoff are distinguished and water streams are also named accordingly. The process of deepening its channel by a watercourse and expanding it to the sides is called erosion. The erosion process consists in the fact that solid debris, moved by water in the channel of a watercourse, scratches its bottom and walls and thus opens up soil particles.
Erosion carries out both the vertical incision of the watercourse into the rock mass (deep erosion) and the expansion of the channel by erosion of the banks (lateral erosion). Deep erosion depends mainly on the magnitude of the fall (slope) of the watercourse bottom.
Simultaneously with the process of erosion, the process of accumulation of debris carried by water and the remains of the vital activity of plants and animals proceeds. So, for example, if in the upper course a watercourse performs erosional work, then downstream, where the speed of the water flow decreases, it accumulates erosion materials.
As a result of the combined action of erosion and accumulation, the earth's surface is gradually leveled: the hills are lowered, and the depressions are filled with erosion materials. The significance of this process on the earth's surface is extremely great. Calculations show that all the rivers of the world in just a year carry out to the seas and oceans about 2.7 billion tons of dissolved rocks, i.e. about 26 tons from each square kilometer of land, and rivers carry out at least 16 billion tons of debris. . T.
The initial form of erosion is gullies. Ravines represent the first stage in the development of a ravine. They concentrate streams of melt and rainwater, which contributes to their further development and transformation into a ravine.
Each water stream tends to impart a slope to its channel in which neither erosion nor accumulation occurs. This slope is the smaller, the finer the sediment and the greater the flow rate of water in a given flow. Under these conditions, the longitudinal profile of the channel is characterized by a uniform increase in slope from the mouth to the upper reaches and has the shape of a concave curve, called the “normal” dip curve.
The hydrosphere is not only rivers and lakes, it is primarily seas and oceans. Coastal marine processes also affect relief formation. Before talking about the coastal marine process and the landforms created by them, we will introduce some definitions.
Coastline (shoreline) - the line along which the horizontal water surface the sea is crossed by land. Since the level of water bodies is not constant, the coastline is a conditional concept applied in relation to some average long-term position of the water body level.
Coast - a strip of land adjacent to the coastline, the relief of which is formed by the sea at a given average water level.
An underwater coastal slope is a coastal strip of the seabed, within which waves are capable of active work.
The coastal zone includes the coast and the underwater coastal slope.
Water, under the influence of currents or wind, carries out the transfer of loose rocks within the coastal zone, and thereby affects the relief of the coast and underwater coastal slopes.
Also, under the influence of gravity at the bottom of the world's oceans, the movement of rocks occurs, which changes the underwater relief.
Relief formation under the influence of wind.
For the emergence of these forms, it is necessary: frequent and strong winds; insignificant amount atmospheric precipitation; intense physical weathering of rocks; absence or sparseness of vegetation cover.
Such conditions are found in tropical deserts as well as in temperate deserts. The manifestation of aeolian processes is associated, apparently, with climatic conditions. Regardless of these conditions, the accumulation of loose sand and the formation of aeolian forms occurs on the sea shores, as well as in river valleys.
The following types of aeolian processes are distinguished:
1. Deflation - blowing loose soil;
2. Corrosion - that is, turning and grinding hard rocks;
3. Transfer of soil by wind;
4. Accumulation of material.
Relief formation under the influence of ice and snow.
The movement of glaciers in many cases is characterized by unevenness. This is explained by the fact that the speed of ice movement depends on many factors, including temperature, the amount of water entering the glacier, atmospheric precipitation, etc. As a result of the activity of glaciers, glacial landforms are formed, and perennial snowfields form nival landforms.
Glaciers, moving along the slopes, sometimes form rather deep potholes and hollows, often smooth out, bedrock protrusions, expand and deepen the existing depressions. They move the resulting debris in the direction of their movement and deposit it at the edge of the glacial tongue. This material carried by the glacier is called the moving moraine. Moving moraines can be bottom, surface and internal.
All glaciers have bottom moraines. They are formed when the glacier breaks down its bed and are located in the lower part of the ice mass. Moving with the glacier, the clastic material of the bottom moraine in some places grinds the bed of the glacier, and in others it scratches and splits off pieces of rock from it, while the material of the moraine itself is gradually crushed from friction: boulders turn into crushed stone, gravel, sand and clay particles.
Surface moraines are products of destruction (large fragments and rubble) of mountain slopes, accumulating on the surface of the glacier in the form of ridges sometimes up to 20-30 m high and moving with it. The material of the surface moraines does not undergo such a strong processing as the material of the bottom moraines; therefore, the fragments that make it up mostly retain their angular shape and sharp edges.
Internal moraines are formed in the body of a glacier when debris fills in cracks in the ice mass, as well as as a result of some part of the bottom moraine material freezing into the ice.
In addition to moving glaciers, permafrost plays an important role in the formation of the earth's surface relief. The formation of permafrost landforms is due to cryogenic processes associated with freezing and thawing of rocks. Cryogenic processes include heaving, icing, cryogenic weathering, frost sorting, cryogenic creep, frost cracking, thermokarst.
Relief formation due to karsts.
Karst (from German Karst, after the name of the Kras limestone plateau in Slovenia) is a set of processes and phenomena associated with the activity of water and expressed in the dissolution of rocks and the formation of voids in them, as well as peculiar forms of relief that arise in areas composed of relatively easily soluble in water rocks - gypsum, limestone, marble, dolomite and rock salt.
Karst landforms are widespread on the surface of the continents. The term "karst" comes from the name of the mountain plateau Karst, located on the eastern coast of the Adriatic Sea, southeast of the city of Trieste (Croatia), where this landscape is most represented. There is no surface hydrographic network and no vegetation, and the surface is covered with cracks, pits, potholes and craters.
Karst usually develops in areas with a horizontal or slightly wavy surface, provided enough precipitation. Very important condition karst development is the permeability of soluble rocks, which is explained by fracturing or porosity of rocks. In mountainous areas, it is more often observed on gentle slopes and at the bottom of wide valleys. Karst develops especially fully in areas where the thickness of soluble, permeable rocks is significant, and the surface is high above the surrounding area, which is necessary for the circulation of groundwater. In limestones, forms of open karst are noted (in the regions of the Mountainous Crimea and the Caucasus). In the areas of open karst development, the following relief forms are found: saucer-shaped depressions, cone-shaped karst sinkholes, karst wells, natural mines, etc.
Karst, developing in a temperate climate, typical for most regions of Russia and Western Europe, with rainfall of a non-torrential nature, evenly distributed throughout the year, is called covered. Rains only partially wash away the products of destruction from the surface of limestone or other rocks and do not prevent the formation of a soil layer and vegetation on it. The karst of temperate latitudes is characterized by negative forms of relief.
Karst sinkholes are often observed. They are found in isolation, but they can be located so densely, the shape of the funnels is very diverse: round, elliptical, oblong, irregular. Usually there is a hole at the bottom of the funnel that absorbs water - ponor.
Karst regions are also characterized by large underground cavities - caves and grottoes. They are found in mountainous areas and reach a depth of more than 500 m. Underground rivers with a sandy or pebble bottom often flow along the bottom of the caves.
Biogenic factor of relief formation.
Any living creature on the planet is a transformer. As a result of its vital activity, each living organism transforms its habitat. Most living beings live directly on the earth or in it and, accordingly, one way or another transforms the surface of the earth. Many living things affect the relief to one degree or another.
Biogenic relief is a set of forms of the earth's surface, formed as a result of the vital activity of organisms. Biota as an agent of relief formation is a combination of extremely diverse organisms - microbes, plants, fungi, animals, the impact of which on the earth's surface is diverse. In other words, biogenic relief formation is a complex of processes that transform the Earth's relief from creating irregularities of various scales - from nano to macroforms. The biogenic factor of relief formation acts almost everywhere on the earth's surface and plays a huge role in relief formation.
Biota affects the relief of the earth's surface both directly and indirectly, changing the rates of biogenic geomorphological processes, up to blocking or, on the contrary, initiation. Moreover, in many cases, the indirect impact is the most significant for relief formation. So, quite often changes in the vegetation cover of a territory can lead to a change in the rates of processes by two or three orders of magnitude, or to a change in the spectrum of the main geomorphological processes.
The biogenic factor affected the relief of the earth's surface directly or indirectly for at least 4 billion years, i.e. practically throughout the entire geological history of the Earth, while the role of the biogenic factor increased during the evolution of the biota.
At present, biogenic landforms from nano-microforms to macroforms are almost ubiquitous on land. Their total number reaches, apparently, the first billion pieces. Their density is hundreds of pieces / ha. Biogenic relief formation is the leading geomorphological process on at least 15% of the land.
The overwhelming majority of biogenic forms are relatively small in size - at the level of nano- and microforms, but there are also very large forms.
Global relief- a set of irregularities in the land, the bottom of the oceans and seas throughout the entire globe. The global topography includes the largest forms of the earth's surface: continents (continental protrusions) and oceans (oceanic troughs). There are six continents, they are located in the Northern and Southern Hemispheres (Australia, Africa, Antarctica, Eurasia, South America, North America). Four oceans (Pacific, Atlantic, Indian, Arctic) form the World Ocean.
Some scientists also identify the fifth Southern Ocean, washing Antarctica. Its northern border lies within the parallels from 57 to 48 ° S. NS.
The geographic patterns of the relief of the Earth as part of the geographic envelope are expressed in the peculiar location of the continents and oceans on the planet. The globe clearly shows the features of the Earth's relief: the Northern Hemisphere stands out as a continental one, and the Southern Hemisphere as an oceanic one. The Eastern Hemisphere is mostly land, while the Western Hemisphere is mostly bodies of water. Most of the continents are wedge-shaped, tapering to the south.
A. Wegener's hypothesis
There are several hypotheses and theories about the formation of the Earth's relief, including the development of its largest forms - continents and oceans. German scientist A. Wegener put forward a hypothesis (scientific assumption) of continental drift. It consisted in the fact that on Earth in the geological past there was a single supercontinent Pangea, surrounded by the waters of the Panthalassa ocean. About 200 million years ago Pangea split into two continents - Laurasia (from which most of Eurasia, North America, Greenland were formed) and Gondwana (South America, Africa, Antarctica, Australia, the Hindustan and Arabian peninsulas were formed), separated by the Tethys Ocean (Fig. 3). The continents gradually diverged in different directions and took on modern outlines.
Lithospheric plate theory
Later, scientists found out that A. Wegener's hypothesis justified itself only partially. She was unable to explain the mechanism and reasons for vertical movements in the lithosphere. New views on the origin of continents and oceans arose and developed. In the early 60s of the XX century, with the emergence of new data on the structure of the oceans, scientists came to the conclusion about the existence of lithospheric plates, which are involved in movement. Lithospheric plates are stable blocks of the earth's crust, separated by mobile regions and giant faults, slowly moving along the plastic layer in the upper mantle. Lithospheric plates include oceanic and continental crust and the most upper part robes.
The largest lithospheric plates are the Eurasian, Indo-Australian, North American, South American, African, Antarctic, Pacific. Mid-ocean ridges and deep-sea trenches are the boundaries of lithospheric plates and large landforms of the Earth.
The plates lie on the asthenosphere and slide along it. Asthenosphere- a plastic layer of the upper mantle of low hardness, strength and viscosity (under the continents at a depth of 100-150 km, under the oceans - about 50 km).
The forces that cause the plates to slide along the asthenosphere are formed under the action of internal forces arising in the outer core of the Earth, and during the rotation of the Earth around its axis. The most important reason for sliding is the accumulation of heat in the bowels of the Earth during the decay of radioactive elements.
The most significant are the horizontal movements of the lithospheric plates. Plates move on average at a speed of up to 5 cm per year: they collide, diverge or slide against one another.
In the place of collision of lithospheric plates, global folded belts are formed, which are a system of mountain formations between two platforms.
If two lithospheric plates come closer to the continental crust, then their edges, together with the sedimentary rocks accumulated on them, are crumpled into folds and mountains are formed. For example, the Alpine-Himalayan mountain belt arose at the junction of the Indo-Australian and Eurasian lithospheric plates (Fig. 4a).
If the lithospheric plates, one of which has a more powerful continental crust, and the other less powerful oceanic crust, approach each other, then the oceanic plate seems to "dive" under the continental one. This is because the oceanic plate is more dense, and how heavier it is, it sinks. In the deep layers of the mantle, the oceanic plate melts again. In this case, deep-sea trenches appear, and on land - mountains (see Fig. 4b).
Almost everything happens in these places. natural disasters associated with the internal forces of the Earth. Off the coast of South America are the deep-water Peruvian and Chilean trenches, and the highlands of the Andes, stretching along the coast, are replete with active and extinct volcanoes.
In the case of thrusting of the oceanic crust onto another oceanic crust, the edge of one plate rises somewhat, forming an island arc, while the other sinks, forming troughs. So in the Pacific Ocean the Aleutian Islands and the trench framing them were formed, the Kuril Islands and the Kuril-Kamchatka Trench, the Japanese Islands, the Mariana Islands and the Trench, in the Atlantic - the Antilles and the Puerto Rico Trench.
In places where the plates diverge, faults arise in the lithosphere, forming deep depressions in the relief - rifts. There is a rise of molten magma, the outpouring of lava along cracks-faults and its gradual cooling (see Fig. 4c). In places of breaks on the ocean floor, the earth's crust grows and renews itself. An example is the mid-ocean ridge - an area of divergence of lithospheric plates located at the bottom of the Atlantic Ocean.
The rift separates the North American and Eurasian plates in the North Atlantic Ocean and the African plate from the South American plate in the South. In the zone of axial mid-oceanic ridges, the rifts are large linear tectonic structures of the earth's crust hundreds and thousands in length, tens and hundreds of kilometers wide. Due to the movement of the plates, the outlines of the continents and the distances between them change.
The data from the International Space Orbital Station make it possible to calculate the location of the divergence of the lithospheric plates. It helps to predict earthquakes and volcanic eruptions, other phenomena and processes on Earth.
On Earth, the global fold belts, formed over a long time, continue to develop - the Pacific and Alpine-Himalayan. The first one encircles the Pacific Ocean, forming the Pacific "ring of fire". It includes the mountain ranges of the Cordilleras, Andes, mountain systems Malay Archipelago, Japanese, Kuril Islands, Kamchatka Peninsula, Aleutian Islands.
The Alpine-Himalayan belt in Eurasia stretches from the Pyrenees in the west to the Malay archipelago in the east (Pyrenees, Alps, Caucasus, Himalayas, etc.). Active mountain-building processes continue here, accompanied by volcanic eruptions.
The Alpine-Himalayan and Pacific fold belts are young mountains that have not been completely formed and did not have time to collapse. They are mainly composed of young sedimentary rocks of marine origin, covering the ancient crystalline cores of the folds. Volcanic rocks overlap sedimentary rocks or are embedded in their thickness. Deposits of iron and polymetallic ores, tin and tungsten are confined to the folded belts.
The global relief of the Earth includes the largest forms of the earth's surface: continents (continental protrusions) and oceans (oceanic troughs). The northern hemisphere of the Earth stands out as a continental one, and the southern hemisphere is predominantly oceanic, the eastern hemisphere is mostly land, and the western hemisphere is mainly water.
Hello dear readers! Today I would like to talk about what are the main forms of relief. So shall we begin?
Relief(French relief, from Latin relevo - I raise) is a set of irregularities of the land, the bottom of the seas and oceans, different in contours, sizes, origin, age and development history.
Consists of positive (convex) and negative (concave) shapes. The relief is formed mainly due to the long-term simultaneous influence of endogenous (internal) and exogenous (external) processes on the earth's surface.
The main structure of the earth's relief is created by forces that are hidden deep in the bowels of the Earth. Day in and day out she is influenced by external processes, relentlessly modifying, cutting deep valleys and smoothing mountains.
Geomorphology - it is the science of changes in terrestrial relief. Geologists know that the old epithet "eternal mountains" is far from the truth.
Mountains (you can learn more about mountains and their types) are not at all eternal, even though the geological time of their formation and destruction can be measured in hundreds of millions of years.
The industrial revolution began in the mid-1700s. And from that moment on, human activities have played an important role in the transformation of the face of the Earth, which sometimes leads to unexpected results.
The continents acquired their present place on the planet and their appearance as a result of tectonics, that is, the movement of geological plates that form the solid outer shell of the Earth.
The movements, which are the most recent in time, have occurred within the last 200 million years - this can include the connection of India with the rest of Asia (more about this part of the world) and the formation of the Atlantic Ocean depression.
Our planet has undergone many other changes throughout its history. The result of all these convergence and divergence of huge masses, displacements have become numerous folds and faults of the earth's crust (more detailed information about the earth's crust), as well as powerful piles of rocks from which mountain systems were formed.
I will give you 3 striking examples of recent mountain building or orogeny, as geologists call it. As a result of the collision of the European plate with the African plate, the Alps arose. When Asia collided with India, the Himalayas soared to the skies.
The Andes pushed upward a shift of the Antarctic Plate and the Nazca Plate, which together form part of the Pacific Trench, beneath the plate on which South America rests.
These mountain systems are all relatively young. Their sharp outlines did not manage to soften those chemical and physical processes that continue to change the earth's appearance even today.
Earthquakes wreak havoc and rarely have long lasting effects. But on the other hand, volcanic activity injects fresh rocks into the earth's crust from the depths of the mantle, often significantly changing the usual appearance of the mountains.
The main forms of relief.
Within the land, the earth's crust consists of a variety of tectonic structures, which are more or less separated from one another, and differ from adjacent areas geological structure, composition, origin and age of rocks.
Each tectonic structure is characterized by a certain history of the movements of the earth's crust, its intensity, regime, accumulation, manifestations of volcanism and other features.
The nature of the relief of the Earth's surface is closely related to these tectonic structures, and with the composition of the rocks that form them.
Therefore, the most important areas of the Earth with a homogeneous relief and a close history of their development - the so-called morphostructural regions - directly reflect the main tectonic structural elements the earth's crust.
Processes on the earth's surface that affect the main landforms formed by internal, that is, endogenous processes are also closely related to geological structures.
Individual details of large landforms form external, or exogenous, processes, weakening or intensifying the action of endogenous forces.
These details of large morphostructures are called morphosculptures. By the range of tectonic movements, by their nature and activity, two groups of geological structures are distinguished: moving orogenic belts and persistent platforms.
They also differ in the thickness of the earth's crust, its structure and the history of geological development. Their relief is also not the same - these are different morphostructures.
Plains of various types with low relief amplitudes are characteristic of platforms. The plains are distinguished by high (Brazilian - 400-1000 m absolute, that is, altitudes above sea level, African) and low (Russian Plain - 100-200 m absolute, West Siberian Plain).
More than half of the entire land area is occupied by the morphostructure of platform plains. Such plains are characterized by a complex relief, the forms of which were formed in the course of the destruction of heights and the redeposition of materials of their destruction.
In large open spaces of the plains, as a rule, the same layers of rocks are exposed, and this determines the appearance of a homogeneous relief.
Among the platform plains, young and ancient sites are distinguished. Young platforms can bend and are more mobile. Ancient platforms are characterized by rigidity: they rise or fall as a single larger block.
Four-fifths of the surface of all land plains falls on a part of such platforms. On the plains endogenous processes manifest themselves as weak vertical tectonic movements. The variety of their relief is associated with surface processes.
Tectonic movements also affect the nakh: denudation or destruction processes prevail in the ascending areas, and accumulation or accumulation prevails in the areas that decrease.
WITH climatic features localities are closely related external, or exogenous, processes - the work of the wind (aeolian processes), erosion by flowing waters (erosion), dissolving action of groundwater (more about groundwater) (karst), washing away by rainwater (deluvial processes) and others.
The relief of mountainous countries corresponds to orogenic belts. Mountainous countries occupy more than a third of the land area. As a rule, the relief of these countries is complex, highly dissected and with large amplitudes of heights.
Various types mountainous terrain depend on the rocks that make them up, on the height of the mountains, on the modern features of the nature of the area and on the geological history.
In mountainous countries with complex relief, separate ridges, mountain ranges and various intermontane depressions are distinguished. The mountains are formed by bent and inclined layers of rocks.
Strongly bent into folds, crumpled rocks alternate with igneous crystalline rocks, in which there is no lamination (basalt, liparite, granite, andesite, etc.).
Mountains arose in places of the earth's surface that have undergone intense tectonic uplift. This process was accompanied by collapse of sedimentary layers. They were torn, cracked, bent, compacted.
From the bowels of the Earth, magma rose through the breaks, which cooled down at depth or poured out onto the surface. Earthquakes have occurred several times.
The formation of large landforms - lowlands, plains, mountain ranges - is primarily associated with deep geological processes that have shaped the earth's surface throughout geological history.
During various exogenous processes, numerical and various sculptural or small forms of relief are formed - terraces, river valleys, karst abysses, etc.
For practical activities study of large forms of relief of the Earth, their dynamics and various processes that change the surface of the Earth.
Weathering of rocks.
The earth's crust is composed of rocks. Softer substances, called soils, are also formed from them.
A process called weathering is the main process that changes the appearance of rocks. It occurs under the influence of atmospheric processes.
There are 2 forms of weathering: chemical, in which it decomposes, and mechanical, in which it crumbles into pieces.
Formation of rocks occurs under high pressure. As a result of cooling, deep in the bowels of the Earth, molten magma, volcanic rocks are formed. And at the bottom of the seas, sedimentary rocks are formed from rock debris, organic remains and silt deposits.
Impact of weather.
Often in rocks there are multilayer horizontal strata and cracks. They eventually rise to the surface of the earth, where the pressure is much lower. The stone expands as the pressure decreases, and all cracks in it accordingly.
The stone is easily exposed to weather factors due to naturally formed cracks, strata and joints. For example, water that has frozen in a crack expands, pushing its edges apart. This process is called frost wedging.
The action of plant roots that grow in crevices and, like wedges, push them apart, can be called mechanical weathering.
Chemical weathering occurs through the mediation of water. Water, flowing over the surface or absorbing into the rock, carries chemicals into it. For example, the oxygen in water reacts with the iron in the rock.
Carbon dioxide absorbed from the air is present in rainwater. It forms carbonic acid. This weak acid dissolves limestone. With its help, a characteristic karst relief is formed, which got its name from the area in Yugoslavia, as well as huge labyrinths of underground caves.
Many minerals dissolve with the help of water. And minerals, in turn, react with rocks and decompose them. Atmospheric salts and acids also play an important role in this process.
Erosion.
Erosion is the destruction of rocks by ice, sea, water currents or wind. Of all the processes that change the earth's appearance, we know it best of all.
River erosion is a combination of chemical and mechanical processes. Water not only moves rocks, and even huge boulders, but, as we have seen, dissolves their chemical components.
Rivers (more about rivers) erode floodplains, carrying soil far into the ocean. There it settles at the bottom, eventually turning into sedimentary rocks. The sea (about what such a sea can be) is constantly and tirelessly working on the alteration of the coastline. In some places it builds up something, and in others it cuts something off.
The wind carries small particles like sand over incredibly long distances. For example, in southern England the wind brings, from time to time, sand from the Sahara, covering the roofs of houses and cars with a thin layer of reddish dust.
The effect of gravity.
The gravity of landslides causes solid rocks to slide downhill, altering the terrain. As a result of weathering, fragments of rocks are formed, which make up the bulk of the landslide. Water acts as a lubricant, reducing friction between particles.
Landslides sometimes move slowly, but sometimes, they rush at a speed of 100 m / s and more. The creep is the slowest landslide. Such a landslide crawls only a few centimeters in a year. And only after a few years, when trees, fences and walls bend under the pressure of the bearing earth, it will be possible to notice it.
Mudflow or mud flow can cause oversaturation of clay or soil (more about soil) with water. It happens that for years the earth holds firmly in place, but a small earthquake is enough to bring it down the slope.
In a number of recent disasters, such as the June 1991 eruption of Mount Pinatubo in the Philippines, the main reason The victims and destruction were mud streams, which flooded many houses to the very roof.
As a result of avalanches (stone, snow, or both), similar disasters occur. Landslide or mudslide is the most common form of landslide.
On the steep bank, which is washed away by the river, where a layer of soil has broken off from the base, sometimes traces of a landslide can be seen. A large landslide can lead to significant changes in the relief.
Rockfalls are not uncommon on steep rocky slopes, in deep gorges or mountains, especially in places where destroyed or soft rocks predominate.
The mass that slid down forms a gentle slope at the foot of the mountain. Long tongues Many mountain slopes are covered with rubble talus.
Ice ages.
The centuries-old climatic fluctuations also led to significant changes in the terrestrial topography.
In the polar ice caps, during the last ice age, huge masses of water were bound. The northern cap extended far south in North America and the European continent.
Ice covered about 30% of the land on Earth (for comparison, today it is only 10%). The sea level during the ice age (for more information on the ice age) was about 80 meters lower than today.
The ice was melting, and this led to colossal changes in the topography of the Earth's surface. For example, to these: the Bering Strait appeared between Alaska and Siberia, Great Britain and Ireland turned out to be islands that were separated from all of Europe in flocks, the land area between New Guinea and Australia went under water.
Glaciers.
In the ice-covered polar regions and in the high mountain regions of the planet, there are glaciers (more about glaciers) - ice rivers. The glaciers of Antarctica and Greenland annually dump huge masses of ice into the ocean (what the ocean is), forming icebergs that pose a danger to navigation.
During the Ice Age, glaciers played a major role in giving the relief of the northern regions of the Earth a familiar look to us.
Crawling with a giant plane on the earth's surface, they hewed out the depressions of the valleys and cut mountains.
Under the weight of glaciers, old mountains, such as the mountains in the north of Scotland, have lost their sharpness and former height.
Glaciers in many places have cut away completely multi-meter layers of rocks that have accumulated over millions of years.
The glacier, as it moves, captures, in the so-called accumulation area, a lot of rock fragments.
Not only stones get there, but also water in the form of snow, which turns into ice and forms the body of the glacier.
Glacial deposits.
Having passed the border of the snow cover on the slope of the mountain, the glacier moves into the ablation zone, that is, gradual melting and erosion. The glacier, towards the end of this zone, begins to leave dragged sediments of rocks on the ground. They are called moraines.
The place where the glacier finally melts and turns into an ordinary river is often designated as the terminal moraine.
Those places where long-disappeared glaciers ended their existence can be found on such moraines.
Glaciers, like rivers, have a main channel and tributaries. The glacial tributary flows into the main channel from a lateral valley that it has paved.
Usually its bottom is located above the bottom of the main channel. The glaciers, which have completely melted, leave behind a main U-shaped valley, as well as several side ones, from where picturesque waterfalls rush down.
Such landscapes can often be found in the Alps. The key to the driving force of the glacier lies in the presence of so-called erratic boulders. These are separate fragments of rock, different from the rocks of the glacial bed.
Lakes (for more information on lakes) are, from a geological point of view, short-lived landforms. Over time, they are filled with sediment of rivers that flow into them, their banks are destroyed and the water leaves.
Glaciers have formed countless lakes in North America, Europe (you can learn more about this part of the world) and Asia, carving out hollows in rocks, or blocking the valleys with terminal moraines. There are many glacial lakes in Finland and Canada.
For example, other lakes, such as Crater Lake in Oregon (USA) (more about this country), form in the craters of extinct volcanoes as they fill with water.
Siberian Baikal and the Dead Sea, between Jordan and Israel, originated in deep cracks in the earth's crust that were formed by prehistoric earthquakes.
Anthropogenic landforms.
New relief forms are being created by the labor of builders and engineers. The Netherlands is a great example of this. The Dutch proudly say that with my own hands created their country.
They were able to recapture about 40% of the territory from the sea, thanks to the powerful system of dams and canals. The need for hydropower and fresh water forced people to build a considerable number of artificial lakes or reservoirs.
In the state of Nevada (USA) there is Lake Mead, it was formed as a result of the blocking of the Hoover Dam, the Colorado River.
After the construction of the Aswan High Dam on the Nile, Lake Nasser arose in 1968 (near the border of Sudan with Egypt).
The main task of this dam was to provide water for agriculture on a regular basis and to regulate annual floods.
Egypt has suffered from eternal floods in the Nile, and it was decided that a dam would help solve this age-old problem.
But on the other hand.
But the Aswan Dam is a shining example of the fact that jokes with nature are bad: she will not tolerate rash actions.
The whole problem is that this dam blocks off the annual deposits of fresh silt that fertilized the agricultural land, and in fact, that formed the Delta.
Silt is now accumulating behind the wall of the Aswan Dam, threatening the existence of Lake Nasser. Significant changes can be expected in the Egyptian relief.
Man-made railways and highways, with their clipped slopes and embankments, as well as mine waste heaps, which have long disfigured the landscape in some industrialized countries, give the Earth a new look.
Erosion is caused by the cutting down of trees and other plants (their root system holds movable soils).
It was these ill-considered human actions that led, in the mid-1930s, to the emergence of the Dust Cauldron in the Great Plains, and today they threaten the Amazon basin in South America.
Well, dear friends, that's all for now. But wait for new articles soon 😉 I hope that this article helped you to understand what forms of relief are.