As a result, the relief of the earth changes. Relief dependence on external geological processes

Rivers and their tributaries are the water arteries of our planet. They carry excess water from land to the ocean and play an active role in the ongoing transformation of the Earth's topography.

Amazon is the most deep river on the ground. She takes every second into Atlantic Ocean about 200 thousand m³ of water. It is fed by seventeen large tributaries, and the area of the drainage basin, which occupies almost the entire northern part South America, is approximately 7 million km². The length of the Amazon is about 7000 km, the width is often more than 10 km. The river is navigable for 1600 km from the mouth.

River of Records

The Amazon is the central artery, from which tributaries branch off, in themselves very large rivers. The origins of many of them are in the Andes (Rio Negro, Purus, Madeira). Others flow from the Brazilian plateau in the south (Tapajos, Xingu), and a smaller part from the north, from the Guiana plateau. When a river merges with one or more tributaries, such as the Rio Negro, the volume of water carried increases so much that a kind of inland sea is formed.

The Amazon flows on both sides of the equator, in a region with a humid, hot climate that receives between 1,500 and 3,000 mm of precipitation per year. Watercourses from the slopes of the Andes, fed by melting snow, are replenished by surface runoff water, since soils of rain equatorial forests unable to absorb the entire volume precipitation. Watercourses merge with small rivers, and they carry their waters into main artery. Flowing into the ocean, the Amazon reaches a width of 60 km at the mouth and forms an estuary with many islands.

Terrain change

Flowing waters not only carry excess water from land to sea. Along the way, they also change the terrain of the planet, restrained or violent, smooth or intermittent. This process involves huge volumes of transported rocks, reaching hundreds of millions of tons annually. Even the calmest-looking rivers never cease their activity for a moment, carrying dissolved substances, such as calcium bicarbonate, washed out from the decaying limestones.

Water carries loose, unconsolidated material: sand, clay and soil. As a result, rivers often take on a characteristic color. The water of some tributaries of the Amazon, such as the Rio Negro, seems dark due to the presence of iron and organic oxides in it. The waters of others abound in silt and appear whitish (Madeira). Downstream from the confluence with the Rio Negro, the waters of the Amazon flow for a long time in two immiscible multi-colored streams.

Hard way

lowland rivers equatorial belt they carry only small suspended particles and are not able to effectively destroy the strong bedrock lining their bottom. Therefore, the channels African rivers are replete with rapids and waterfalls, which form where the rocks are especially resistant to erosion.

Erosion processes are most noticeable in mountainous regions, where surface slopes are significant. riverbed mountain rivers often strewn with large fragments of rocks, which during periods high water move, slide, turn over and break up when rubbing against each other. When the watercourse enters the plain, all this clastic material is deposited in the form of fan-shaped accumulations - alluvial fans. When rivers flow into lakes, the same thing happens: a small delta is formed - the first stage in the formation of a lake basin.

large scale work

For many thousands of years, watercourses have carved incised valleys, gorges and canyons in the rocks. Steep-sided valleys usually form in hard rocks that water can only break down with the help of abrasive (abrasive) material - sand, gravel and pebbles. The rotational movement of water in whirlpools leads to the formation of natural depressions in the channel, called giant boilers.

In a similar way, rivers wash away steep banks and, by widening their course, create picturesque meanders. However, further expansion of river valleys requires the intervention of other mechanisms of the erosion process. Weathering, crushing and landslides gradually smooth out the forms created by the stream.

Captive or free

Rivers flowing through vast alluvial plains, freer in the choice of channel configuration than rivers locked in narrow gorges. Plain rivers often change their path, randomly meandering (wandering) within the main direction, such as the Okavango River in Botswana.

Sometimes rivers change course even more abruptly. As a result of the displacement of earth masses and changes in the water level, rivers capture neighboring watercourses and direct them into their own channel. Thus, the Moselle River in France, which once flowed into the Meuse, has now become a tributary of the Merte River.

Delta

River deltas are unstable structures, the ongoing reconstruction of which is based both on the accumulation of sediments carried by rivers and on their removal by the advancing sea. But luck in the battle between sea and land always favors the sea.

The area of the Nile delta in Egypt with an area of 24 thousand km2 is one of the most densely populated in the world, as is the delta of the legendary Ganges flowing in India. People have long settled in these low-lying, fertile regions. However, the boundary between the elements of water and land is changeable. Due to floods, rivers often change their course. Old channels, remaining higher, dry up, forming new lakes and swamps. Even where the sea has already receded, land areas are not protected from the intrusion of water.

The origin of the word "delta" is closely related to the Nile. This name was given to the lower reaches of the Nile by Herodotus in the 5th century BC. BC e., since the mouth of the river is similar in shape to an inverted capital letter D of the Greek alphabet. Since then, this term has been used to denote a lowland composed of river sediments at the mouth of a river flowing into a sea or lake. The Rhone even has two deltas: one, small, formed when the river flows into Lake Geneva, the other, much larger, in the Camargue, when it flows into the Mediterranean Sea.

Deltas may have different shape. Some rivers, such as the Mississippi, branch into several branches, so that their delta resembles a goose foot, others, such as the Ebro in Spain or the Po in Italy, form arcs. The variety of forms of the delta is determined both by the creative work of the river and by the opposition of the sea, the currents of which either prevent sedimentation or help wash sandbars, as happens in Venice. Yes, moving sea current deposits of the Po River led to the formation of a coastal rampart in the northern part of the delta, cutting off the Venetian lagoon from the sea. The study of displacements of the littoral zone shows that the shape of the coastline, riverbeds and their tributaries has been changing over the course of several millennia. Archival documents make it possible to trace the movements of the Rhone in the Camargue region and measure them in kilometers.

"Multiple" delta

A delta can be formed by several deltas located one behind the other, such as the Mississippi Delta. Having traveled a path of more than 6000 km, the river deposits Gulf of Mexico sediments, the annual volume of which is about 20 tons. No wonder the river transports so much material, because it collects water from more than a third of the United States and flows into such large rivers as the Missouri, Arkansas, Red River. In 5,000 years, six interlocking deltas formed at the mouth of the Mississippi, forming one in the shape of a goose foot.

Material quality

To win the battle with the sea and form a delta, the river must deposit a huge amount of alluvium. No less important is the nature of the transferred material. The Amazon basin is dominated by chemical weathering, so there is little sand and gravel. Although the annual solid flow of the river is about 1.3 million tons per day, it is dominated by fine particles, which are carried northward by the coastal current. That is why, when it flows into the Atlantic Ocean, the Amazon forms a huge estuary, and not a delta. However, active deforestation in the region leads to the destruction of the above ground cover and contributes to erosion. This can change the composition of the transported material, the direction of the channel, the speed of the current, and ultimately lead to the transformation of the estuary into a delta.

Although in other regions the amount and quality of sediment transported is sufficient to preserve the delta, the construction of dams and power plants on rivers and their tributaries can reduce sedimentation and lead to the victory of the sea.

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Geography is a science that studies the geographical shell of the earth, and it is also the science of the earth's relief. Relief is a constantly changing shape earth's surface or a set of irregularities in the earth's surface, differing in origin, size and age. Over millions of years of the history of the Earth, under the influence of various forces, where there were mountains, plains appeared, and where there were plains, high active volcanoes arose.

There is a direct relationship between the relief of the earth and the structure of the lithosphere. So mountains formed at the junctions of lithospheric plates, and plains in the centers of the plates.

Landforms or morphostructures

There are such large and small landforms as

continents- the largest forms; scientists believe that there was once only one continent, the gradual separation of which led to modern look Earth;
ocean trenches- also a large form of the earth's relief, which forms due to the movement of lithospheric plates; it is believed that once there were fewer oceans on earth, and in hundreds of thousands of years the situation will change again, perhaps some parts of the land will be flooded with water;
mountains- the most grandiose forms of the earth's relief, reaching grandiose heights, mountains can form chains of mountains;
highlands- free-standing mountains and range systems, such as the Pamirs or the Tien Shan;
shelves- land areas completely hidden under water;
plains- the most flat earth surface, best place for human life.

Fig 1. Relief of the Earth

Such forms have a specific name - morphostructures. Scientists distinguish between such types of morphostructures as planetary and regional, which were formed later. Tectonic movements participated in their development, and against their background there were movements of the upper horizons of the lithosphere.

Reasons for the transformation of the earth's surface

Changes in the relief of the Earth occur for various reasons. Transformation can occur under the influence of both internal and external forces.

External forces do not affect the earth's relief as much as internal ones.

internal forces

Relief age

Time elapsed since formation modern look The earth is called the age of the relief. It could be years, hundreds, thousands, millions of years. Age of large relief forms may be between 200 and 90 million years old. In addition to age, there are also numerical characteristics of the surface of the relief.

What have we learned?

The relief of the Earth is characterized by great diversity, complexity and incredible morphostructures. Why is the landform so diverse? There are large and small irregularities that occur under the influence of internal and external forces. Transformation and change happen slowly, gradually, one human life not enough to notice all the changes that have taken place. The earth's surface seems to breathe, then it falls, then it rises, and sometimes it simply bursts from the stresses that have arisen. Thus, the development of the Earth's relief is going on at the present time.

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Change in the Earth's relief

From the very beginning of the discussion of the problem of the formation of the globe, it was the mountains that confused scientists. Because if we assume that at first the Earth was a fiery, molten ball, then its surface after cooling should remain more or less smooth ... Well, maybe a little rough. Where did the high mountain ranges come from? deepest depressions in the oceans?

In the 19th century, the dominant idea was the idea that from time to time, for some reason, red-hot magma from the inside attacks the stone shell and then mountains swell and ridges rise in it. Rise? But why, then, are there so many regions on the surface where the ridges run in parallel folds, one next to the other? When inflated, each mountainous area it should have the shape of a dome or a bubble... It was not possible to explain the formation of folded mountains by the action of vertical forces coming from the depths. The folds required horizontal forces.

Now take an apple in your hand. Let it be a small, slightly wilted apple. Squeeze it in your hands. See how the skin has wrinkled, how it has become covered with small folds. And imagine that an apple is the size of the Earth. The folds will grow and turn into tall mountain ranges ... What forces could squeeze the earth so that it becomes covered with folds?

You know that every hot body shrinks when it cools. Perhaps this mechanism is also suitable for explaining the folded mountains on the globe? Imagine - the molten Earth has cooled down and covered with a crust. The crust or bark, like a stone dress, turned out to be "sewn" to a certain size. But the planet is cooling down further. And when it cools down, it shrinks. It is no wonder that over time the stone shirt turned out to be large, began to wrinkle, go in folds.

Such a process was proposed to explain the formation of the Earth's surface by the French scientist Elie de Beaumont. He called his hypothesis contraction from the word "contraction", which, translated from Latin, just meant - compression. One Swiss geologist tried to calculate what the size of the globe would be if all the folded mountains were smoothed out. It turned out to be a very impressive figure. In this case, the radius of our planet would increase by almost sixty kilometers!

The new hypothesis has gained many supporters. The most famous scientists supported her. They deepened and developed separate sections, turning the assumption of the French geologist into a single science of the development, movement and deformation of the earth's crust. In 1860, this science, which became the most important section of the complex of earth sciences, was proposed to be called geotectonics. We will continue to call this important section the same.

The hypothesis of contraction or compression of the Earth and wrinkling of its crust was especially strengthened when large "overthrusts" were discovered in the Alps and Appalachians. Geologists use this term to designate gaps in underlying rocks, when some of them are, as it were, pushed over others. The experts celebrated new hypothesis explained everything!

True, a small question arose: why were the folded mountains not distributed evenly over the entire surface of the earth, as on a wrinkled, shriveled apple, but were collected in mountain belts? And why were these belts located only along certain parallels and meridians? The question is trifling, but insidious. Because the contraction hypothesis could not answer it.

deep mountain roots

Around the middle of the 19th century, or rather in 1855, the English scientist D. Pratt conducted geodetic work on the territory of the "pearl of the British crown", that is, in India. He worked near the Himalayas. Every day, waking up in the morning, the Englishman admired the majestic spectacle of the grandiose mountainous region and involuntarily thought: how much can this colossal mountain range weigh? Its mass must certainly have a noticeable force of attraction. How would you know? Stop, but if so, then an impressive mass should deflect a light weight on a thread from the vertical. The vertical is the direction of the Earth's gravity, and the deviation is the direction of the Himalayas' gravity...

Pratt immediately estimated the total mass of the mountain range. It turned out to be a really decent amount. From it, using Newton's law, he calculated the expected deviation. Then, not far from the slopes of the mountains, he hung a weight on a thread and, using astronomical observations, measured its true deviation. Imagine the scientist's disappointment when, when comparing the results, it turned out that the theory differs from practice by more than five times. The calculated angle turned out to be larger than the measured one.

Pratt could not understand what his mistake was. He turned to the hypothesis put forward once by Leonardo da Vinci. The great Italian scientist and engineer suggested that the earth's crust and the molten subcrustal layer - the mantle are almost everywhere in balance. That is, blocks of bark float on a heavy melt, like ice floes on water. And since, in this case, part of the “floes”-blocks are immersed in the melt, in general, the blocks turn out to be lighter than those taken in the calculation. After all, who does not know that the iceberg has only a smaller part that protrudes above the water, and a large part is submerged ...

Pratt's compatriot J. Erie added his own considerations to his reasoning. “The density of rocks is about the same,” he said. - But higher and more powerful mountains stand, plunging deeper into the mantle. Less high mountains sit smaller. It turned out that the mountains seemed to have roots. Moreover, the root part turned out to be composed of less dense rocks, compared with the density of the mantle.

It's a good hypothesis. For a long time, scientists used it when measuring gravity in different parts of the Earth. Until such time as artificial satellites of the Earth flew over the planet - the most reliable pointers and recorders of the field of attraction. But they are still to be discussed.

At the end of the last century, the American geologist Dutton suggested that the highest and most powerful blocks of the earth's crust are eroded by rains and flowing waters more than the low ones, and therefore, they should become lighter and gradually “float”. Meanwhile, the lighter and lower blocks are subjected to precipitation from the tops of their higher neighbors, and they become heavier. And if they get heavy, then they sink. Is this process one of the possible causes earthquakes in the mountains and new mountain building?..

A lot of interesting hypotheses were put forward by scientists at the end of the last century. But perhaps the most fruitful of them was the creation of the doctrine of geosynclines and platforms.

Specialists call geosynclines rather extensive elongated sections of the earth's crust, where earthquakes and volcanic eruptions are especially often observed. The relief in these places is usually such that, as they say, "the devil himself will break his leg" - a fold on a fold.

Back in 1859, the American geologist J. Hall noticed that in mountainous folded areas the sediments are much thicker than in those places where the rocks lie in calm horizontal layers. Why is that? Perhaps, under the weight of the sediments accumulated here, washed away from the neighboring mountains, the earth's crust caved in? ..

I liked the suggestion. And a few years later, Hall's colleague James Dana developed the views of his predecessor. He called the elongated folds of the crust caused by lateral compression (at that time the contraction hypothesis was already dominant) geosynclines. The complex term comes from the combination of three Greek words: "ge" - earth, "sin" - together and "klino" - tilt.

Not all geologists immediately agreed with the opinion of the American specialist. Other pictures of the development of geosynclines have also been proposed. The dispute about them has not subsided to this day for more than a hundred years. Some believe that the heated subcortical substance is divided into heavy and light fractions. Heavy ones “sink”, squeezing lighter ones upwards. They rise, “float” and rip up, tearing apart the lithosphere. Then fragments of heavy plates slide off and crush the sedimentary layers...

Others propose a different mechanism. They believe that slow currents exist in the hot subcrustal substance of the Earth. They tighten, crush sedimentary rocks. And once in the depths, these rocks are melted down under the influence of pressure and high temperatures.

There are other concepts as well. According to one of them, for example, geosynclinal folds arise along the edges of continental platforms, floating like ice floes in the ocean, along the plastic subcrustal substance. Unfortunately, so far none of the existing proposals on this subject fully satisfies the laws observed in nature. And so the dispute, apparently, is far from over.

An outstanding Russian and Soviet geologist, public figure Alexander Petrovich Karpinsky was born in 1846 in the village of Turinskie mines in the Verkhotursky district in the Urals. Today it is the city that bears his name. His father was a forge / and engineer, and therefore it is not surprising that the young man, after graduating from the gymnasium, entered the famous Petersburg Mining Institute.

At thirty-one, Alexander Petrovich became a professor of geology. And nine years later he was elected a member of the Imperial Academy of Sciences.

He explores the structure and minerals of the Urals and compiles consolidated geological maps of the European part of Russia. Starting with petrography, the science of the composition and origin of rocks, Karpinsky deals with literally all sections of the science of the Earth and leaves a noticeable mark everywhere. He studies fossil organisms. He writes outstanding works on tectonics and on the geological past of the earth - on paleogeography.

The doctrine of geosynclines, despite the progressive ideas at its core, experienced many difficulties at the first stage. And at this time, Alexander Petrovich came to grips with the study of "quiet regions" of the earth's surface. Subsequently, they also received the name "platforms". In these works, Karpinsky summarized the huge material on the geology of Russia, accumulated by generations of Russian geologists. He showed how the outlines of the ancient seas that flooded these areas changed at different times. And he deduced two kinds of "wave-like oscillatory movements" of the earth's crust. One, more grandiose, forms oceanic depressions and continental uplifts. The other, not so majestic in scale, provides the appearance of depressions and bulges within the platform itself. So, for example, local fluctuations of the Russian platform, according to Karpinsky, occurred parallel to the Ural ridge in the meridional direction and parallel to the Caucasus - along the parallels.

After the work of Alexander Petrovich Karpinsky, it became clear that the platforms are not at all immovable and unchanging parts of the earth's surface. They develop and change over time. From time to time, mountainous areas join the edges of the platforms, which, freezing, increase their total area. Thus, the development of platforms turned out to be closely connected with the formation of geosynclines and emphasized the development of the entire Earth.

Alexander Petrovich based his conclusions on the principles of the contraction hypothesis, considering it "the happiest scientific achievement." And although the results of further research more and more clearly proved the inconsistency of this hypothesis, the theory of geosynclines and platforms continued to develop independently, becoming one of the most important provisions of geotectonics.

Expansion instead of compression

Perhaps it is precisely the new ideas about the initially cold earth buried the contraction hypothesis. There are new ideas. One of them was that our planet was formed from a denser substance than existing rocks. And the resulting globe was at first almost half the size of the present one. On such a dense cosmic body there were no special depressions and bulges - a continuous, fairly even shell. But gradually, warming up, the original planetary lump began to "swell". Its surface was cracked. Separate blocks of continents began to form, separated by deep depressions of the oceans.

However, the new hypothesis also had many vulnerabilities. And one of them again were folded mountains. After all, folds could only appear during compression.

To cope with such a contradiction, experts came to the conclusion that periods of expansion could be replaced by periods of contraction. Another “pulsation hypothesis” has appeared. It is still supported by a number of scientists today, believing that it is precisely in the alternate reduction and expansion of the earth's radius that the reasons for the movement of the continents may lie. After all, the epochs of folding in the history of our planet also followed each other.

The reasons for such pulsations are not very clear. The Russian scientist academician M. A. Usov connects them with cosmic factors - with the attraction of the Moon and the Sun, with the influence of other planets. Another scientist, Academician V. A. Obruchev, considered one of the possible reasons for the expansion of the Earth to be the transition of magma from a solid to a liquid state. At the same time, a lot of heat escapes from the depths. The Earth is cooling, and consequently, it is strongly compressed.

The pulsation hypothesis has quite a few supporters among modern scientists. They measured rock pressures at various points on our planet and concluded that in this moment The earth is going through a period of contraction. If so, then the number of earthquakes should be increasing...

I gave several examples so that you understand that the issues of the development of our planet are very complex. People have long been trying to penetrate the secret of the geological history of the Earth, but to this day there is no consensus on all issues among scientists.

Critical zones of the planet

Scientists have seen that various zones of the globe, its mountain systems, lowlands are confined to certain belts. Why not evenly over the entire surface?

For example, Alexander Petrovich Karpinsky noted mountain belts running in the meridional direction. And at the same time, Alexander Ivanovich Voeikov, an outstanding geographer and climatologist, as well as Russian geodesist and geographer Aleksey Andreevich Tillo, made very convincing arguments in favor of the latitudinal location of mountain systems.

Why, after all, special zones do not appear everywhere, but only in some critical areas?

Astronomers have long noticed that the course of the Earth's rotation is gradually slowing down. Our planet is slowed down mainly by tidal friction in its crust, arising from the attraction of the Sun and Moon. At the same time, the forces of the polar compression of the planet gradually decrease. This means that in high latitudes the lithosphere and hydrosphere will gradually rise, and in low latitudes at the equator - to fall. With such a process, the boundary strips that experience especially strong stresses, according to scientists, are the seventieth parallel, sixty-second and thirty-fifth, as well as the equator. It is in these belts that zones of tectonic disturbances are located. On land, these are mountainous regions, deep abysses and volcanoes. At sea - the "roaring forties" and other areas of countless dangerous adventures, more than once or twice ending tragically.

And look at the long Cordilleras of North and South America, the Appalachians, the Urals...

Find on the map West Siberian Plain, which passes into the lowland of the Turgai trough and into the Turan lowland.

Take a look at how the system of rift troughs goes, crossing the eastern part of Africa from north to south...

All of them are oriented along the meridians or close to them. The Soviet scientist G. N. Katterfeld considers the critical zones of the meridional direction of the belt, located between 105 - 75 °, 60 - 120 ° and 150 - 30 °.

These critical zones are very important for Earth researchers to know. They have a very large not only theoretical, but also practical value. Because it is in them that the enhanced magmatic activity of the subcrustal substance is observed. And along with magma, ore elements rise along cracks and faults into the upper zones of the crust, which create deposits of various metals. For example, even today geologists are well aware of the Pacific ore belt with large deposits of tin, silver and other metals. This belt encloses the greatest ocean of the earth in a huge ring. The Mediterranean ore belt is also known, containing copper and lead-zinc ores. From the Atlantic coast of southern Europe and North Africa it stretches through the Caucasus, the Tien Shan to the very Himalayas...

But what is the source of colossal energy, due to which grandiose tectonic processes are carried out in the earth's crust? On this occasion, even in our time, heated discussions do not stop. Some consider tectonics a property generally inherent in the self-development of any planet. They see the internal heat of the Earth as the source of her strength. Others prefer cosmic factors: the interaction of the Earth with the Sun, with the Moon, changes in solar activity, even the position of the Solar System relative to the center of the Galaxy...

There is no single point of view and no single opinion! Perhaps a few years will pass and a new hypothesis will appear, uniting the causes of planetary development on the basis of new factors already mined not only on the surface of the Earth, but also on other planets.

"Bomb" by Professor Wegener

Have you ever wondered, looking at a globe or a geographical map of the world, why the eastern coast of South America and West Coast Africans are so surprisingly similar? .. Take a closer look. The picture is amazing. The full impression is that once these separate pieces of land were a single huge blotch on the globe, one giant parent land.

Incidentally, this similarity was first noted back in 1620 by Bacon already known to us, as soon as more or less plausible maps with the New and Old Worlds had time to come out. And forty years later, the French abbot F. Place claimed that "before the Flood" both parts of the world were firmly, firmly connected to each other. True, the venerable father did not expand on the reason for their separation. But it is from this moment, if you wish, that you can begin the history of the development of the hypothesis of the movement of the continents, or the hypothesis of "mobilism", as it is called in science.

The real mobilism is associated with the name of Alfred Wegener, who revived the forgotten assumptions of Bacon and Place, putting them on "scientific feet". In general, the idea of the movement of the continents came to Wegener by chance. He looked at the map of the world and, just like you and me, was struck by the similarity of the coasts of the continents.

Who was Professor Wegener? He graduated from the university with a degree in astronomy. But it was, in his words, "too sedentary work" for his temperament. Having learned how to fly a balloon, he, along with his brother, took up atmospheric research and became interested in meteorology. A few years later he went to Greenland to conduct meteorological observations in its harsh climate.

When the founder of climatology, Corresponding Member of the St. Petersburg Academy of Sciences Alexander Ivanovich Voeikov read the young Wegener's book "Thermodynamics of the Atmosphere", he exclaimed: "A new star has risen in meteorology!"

And suddenly - Wegener and the structure and evolution of the Earth?

Like others of his contemporaries, Wegener imagined the earth as having come from a huge drop of molten matter. It gradually cooled down, covered with a crust, which rested on a heavy and liquid basalt mass.

While heading to Greenland, the scientist more than once drew attention to the mighty ice floes majestically floating on the cold water. Perhaps this image inspired him to imagine the blurring of the continents. But what forces could move them? But you have not forgotten that Wegener was an astronomer by education. And now, in his imagination, a clear picture arises of how the subcrustal layer is carried away by the rotation of the Earth, how the Moon excites giant tidal waves in the mantle that break open the fragile shell, and how pieces of the crust captured by tidal currents move and pile on top of each other, forming a single parent continent, christened Pangea by him. .

Pangea existed for many millions of years.

In the meantime, under the influence of the same external forces in its depths, all the tensions were accumulating and accumulating. And at one fine moment, the pro-continent could not stand it. Cracks ran along it, and it began to fall apart. The Americas broke away from Africa and Europe and sailed west. The Atlantic Ocean opened up between them. broke away from North America Greenland, and from Africa Hindustan. Antarctica split with Australia...

One day, almost by accident, at a meeting of the German Geological Society, Wegener without hesitation outlined his hypothesis to the audience. What has begun here!.. The venerable gentlemen, who had just dozed peacefully on their chairs, did not just wake up. They were furious. They shouted that Wegener's views were wrong and that his ideas were absurd and even ridiculous. And he himself is illiterate and... Let us recall that at that time the contraction hypothesis reigned supreme in the geological world. What kind of horizontal movement of the continents is possible with the general compression of the planet? No, the earth's crust can only rise and fall.

It is worth noting that such an approximate coincidence for many years was a strong argument for the opponents of mobilism - the hypothesis of the movement of the continents. Already in our time, when it was decided to reconstruct Pangea not along the coastline of the continents, but along the border of the continental slope, including the continents and shelves, the picture turned out to be completely different. In 1965, scientists used an electronic computer and picked up such a position of the continents, in which the mismatch zones turned out to be negligible. Isn't that proof? But back to Wegener.

Sharp criticism did not discourage the scientist. He only concluded that in order to prove a new idea, he needed to accumulate a lot of facts, a lot.

At that time, the scientist worked at the University of Marburg. He gave lectures to students, processed the materials of his trip to Greenland and thought. All his thoughts were captured by a new idea. He was looking for forces capable of moving the continents from their place, pulling them apart, looking for ways to move the continents.

Ultimately, Alfred Wegener was never able to find enough evidence to support his hypothesis. The forces of attraction of the Moon and the Sun were clearly not enough to move the lumps of the continents. And the idea of a continuous molten subcortical layer turned out to be untenable. The old school won.

The opinion that continents can move was, if not forgotten, then for a long time (in the understanding of our time - in fact, not for long at all) disappeared from the scene. And only in the fifties of the XX century the desecrated hypothesis was powerfully revived, replenished with new facts and took a leading role in modern Earth science.

Literature

1.#"#">Balandin R.K. Through the eyes of a geologist. - M., 1973

2.#"#">Gangnus A.A. The mystery of earthly catastrophes. - M., 1985

3. Ivanov V.L. Archipelago of two seas. - M., 2003

4. Katz Ya.G., Kozlov V.V., Makarova N.V. Geologists study the planet. - M., 1984

>>How and why the relief of Russia is changing

§ 14. How and why the relief of Russia is changing

Relief formation is influenced by various processes. They can be combined into two groups: internal (endogenous) and external (exogenous).

internal processes. Among them, the latest (neotectonic) crustal movements, volcanism and earthquakes. Thus, under the influence internal processes formed the largest, large and medium forms relief.

Neotectonic refers to the movements of the earth's crust that have occurred in it over the past 30 million years. They can be both vertical and horizontal. On the formation of relief greatest influence have vertical movements as a result of which the earth's crust rises and falls (Fig. 20).

Rice. 20. Recent tectonic movements.

The speed and height of vertical neotectonic movements in some areas were very significant. Most of modern mountains on the territory of Russia exist only thanks to the latest vertical uplifts, since even young, relatively recently formed mountains destroyed over several million years. The Caucasus Mountains, despite the destructive effect of external forces, were raised to a height of 4000 to 6000 m. The Urals by 200-600 m, Altai - by 1000-2000 m. in those places where the earth's crust sank, there were depressions of the seas and lakes, many lowlands.

According to fig. 20 determine what types of movements prevail on the territory of Russia.

Movements of the earth's crust are still taking place. The Greater Caucasus Range continues to rise at a rate of 8-14 mm per year. The Central Russian Upland grows somewhat more slowly - about 6 mm per year. And the territories of Tatarstan and the Vladimir region annually fall by 4-8 mm.

Along with slow movements of the earth's crust, earthquakes and volcanism play a certain role in the formation of large and medium landforms.

Earthquakes often lead to significant both vertical and horizontal displacements of rock layers, the occurrence of collapses and failures.

Volcanic eruptions form such specific landforms as volcanic cones, lava sheets and lava plateaus.

External processes, forming modern relief associated with the activities of the seas, flowing waters, glaciers, vefa. Under their influence, large landforms are destroyed and medium and small landforms are formed.

With the onset of the seas, sedimentary rocks are deposited in horizontal layers. Therefore, many coastal parts of the plains, from which the sea has receded relatively recently, have a flat relief. Thus, the Caspian and the north of the West Siberian lowland were formed.

flowing waters(rivers, streams, temporary water flows) erode the earth's surface. As a result of their destructive activity, relief forms are formed, called erosional. These are river valleys, beams, ravines.

valleys major rivers have a large width. For example, the Ob valley in its lower reaches is 160 km wide. Amur is slightly inferior to it - 150 km and Lena - 120 km. River valleys are a traditional place for people to settle, conduct special types of economy ( livestock farming in floodplain meadows, horticulture).

Ravines are a real disaster for Agriculture(Fig. 21). By breaking the fields into small sections, they make it difficult to process them. There are more than 400 thousand large ravines in Russia with a total area of 500 thousand hectares.

Glacier activity. IN Quaternary due to the cooling of the climate in many regions of the Earth, several ancient ice sheets arose. In some areas - the centers of glaciation - ice has been accumulating for thousands of years. In Eurasia, such centers were the tori of Scandinavia, the Polar Urals, the Putorana Plateau in the north of the Central Siberian Plateau, and the Byrranga Mountains on the Taimyr Peninsula (Fig. 22).

Using the population map in the atlas, compare the population density in the valleys of large Siberian rivers and in the surrounding territories.

The ice thickness in some of them reached 3000 m. Under the influence of its own weight, the glacier slid southward to the adjacent territories. Where the glacier passed, the earth's surface changed greatly. In places he smoothed it out. In some places, on the contrary, he plowed out depressions. Ice polished the rocks, leaving deep scratches on them. Accumulations of huge stones (boulders), sand, clay, and rubble moved along with the ice. This mixture of various rocks is called moraine. In the southern, warmer regions, the glacier melted. The moraine, which he carried with him, was deposited in the form of numerous hills, ridges, flat plains.

wind activity. The wind forms the relief mainly in arid regions and where sands lie on the surface. Under its influence, dunes, sand hills and ridges are formed. They are widespread in Caspian lowland, in the Kaliningrad region (Curonian Spit).

Fig.22. Borders ancient glaciation

Questions and tasks

1. What processes influence the formation of the Earth's relief at the present time? Describe them.
2. What glacial landforms are found in your area?
3. What landforms are called erosional? Give examples of erosional landforms in your area.
4. What modern relief-forming processes are typical for your area?

Geography of Russia: Nature. Population. Economy. 8 cells : studies. for 8 cells. general education institutions / V. P. Dronov, I. I. Barinova, V. Ya. Rom, A. A. Lobzhanidze; ed. V. P. Dronova. - 10th ed., stereotype. - M. : Bustard, 2009. - 271 p. : ill., maps.

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Weathering itself does not lead to the formation of landforms, but only turns solid rocks into loose ones and prepares the material for movement. The result of this movement are various landforms.

The action of gravity

Under the influence of gravity, rocks that are destroyed move but the surface of the Earth from elevated areas to lower ones. Stone blocks, crushed stone, sand often rush down from steep mountain slopes, giving rise to landslides and screes.

Under the influence of gravity, 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 water bodies, 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 along the lower, water-impervious layer. Heavy rains and rapid snowmelt 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 deaths.

Activity of flowing waters

The most important relief changer is moving water, which performs great destructive and creative work. Rivers cut wide river valleys in the plains, deep canyons and gorges in the mountains. Small water streams create a ravine-beam relief on the plains.

Flowing hearths not only create depressions on the surface, but also capture rock fragments, carry them and deposit them in depressions or in their own valleys. So flat plains are formed from river sediments along the rivers.

Karst

In areas where readily soluble rocks(limestone, gypsum, chalk, rock salt), amazing natural phenomena. Rivers and streams, dissolving rocks, disappear from the surface and rush into the depths of the earth's interior. Phenomena associated with the dissolution of surface rocks and are called karst. The dissolution of rocks leads to the formation of karst landforms: caves, abysses, mines, funnels, sometimes filled with water. The most beautiful stalactites (multi-meter lime "icicles") and stalagmites ("columns" of lime growths) form bizarre sculptures in the caves.

wind activity

In open treeless spaces, the wind moves giant accumulations of sand or clay particles, creating eolian landforms (Eolus is the patron god of the wind in ancient Greek mythology). Most of the sand dunes are covered with sandy hills. Sometimes they reach a height of 100 meters. From above, the dune looks like a sickle.

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

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

Glacier activity

human activity

Man plays an important role in changing the relief. The plains were especially strongly changed by his activity. People have long settled on the plains, they build houses and roads, fill up ravines, build embankments. A person changes the relief during mining: huge quarries are dug out, heaps of waste heaps are poured - heaps of waste rock.

The scale of human activity can be compared with natural processes. For example, rivers develop their valleys, carrying out rocks, and a person builds canals comparable in size.

Landforms created by man are called anthropogenic. Anthropogenic change in relief occurs with the help of modern technology and at a fairly fast pace.

Moving water and wind perform a huge destructive work, which is called (from the Latin word erosio corrosive). Land erosion is a natural process. However, it is enhanced by economic activity people: plowing slopes, deforestation, excessive grazing, laying roads. In the last hundred years alone, a third of all cultivated land in the world has been eroded. These processes reached the greatest extent in the large agricultural regions of Russia, China and the USA.

Formation of the Earth's relief

Features of the Earth's relief

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Process	Example	Manifestation in relief	Process essence
Weathering	Fig 2. Weathering	talus formation
wind force	Figure 3. Wind strength	formation of barkhans and dunes	transport of rocks and loose sediments
water power	Fig 4. The power of water	destruction of rocks	transport and erosion of rocks
Melting glaciers	Fig 5. Melting glaciers	changes in the shape of the continents	increase in the volume of water in the oceans