The state of rest is unknown to our planet. This applies not only to external, but also to internal processes that occur in the bowels of the Earth: its lithospheric plates are constantly moving. True, some sections of the lithosphere are quite stable, while others, especially those located at the junctions of tectonic plates, are extremely mobile and constantly shudder.

Naturally, people could not leave such a phenomenon unattended, and therefore, throughout their history, they studied and explained it. For example, in Myanmar, the legend is still preserved that our planet is entwined with a huge ring of snakes, and when they begin to move, the earth begins to tremble. Such stories could not satisfy inquisitive human minds for a long time, and in order to find out the truth, the most curious drilled the earth, drew maps, made hypotheses and put forward assumptions.

The concept of the lithosphere contains the solid shell of the Earth, consisting of the earth's crust and a layer of softened rocks that make up the upper mantle, the asthenosphere (its plastic composition makes it possible for the plates that make up the earth's crust to move along it at a speed of 2 to 16 cm in year). It is interesting that the upper layer of the lithosphere is elastic, and the lower layer is plastic, which makes it possible for the plates to maintain balance when moving, despite constant shaking.

During numerous studies, scientists came to the conclusion that the lithosphere has a heterogeneous thickness, and largely depends on the terrain under which it is located. So, on land, its thickness ranges from 25 to 200 km (the older the platform, the larger it is, and the thinnest is under the young mountain ranges).

But the thinnest layer of the earth's crust is under the oceans: its average thickness ranges from 7 to 10 km, and in some regions of the Pacific Ocean it even reaches five. The thickest layer of the crust is located along the edges of the oceans, the thinnest - under the mid-ocean ridges. Interestingly, the lithosphere has not yet fully formed, and this process continues to this day (mainly under the ocean floor).

What is the earth's crust made of

The structure of the lithosphere under the oceans and continents is different in that there is no granite layer under the ocean floor, since the oceanic crust has undergone melting processes many times during its formation. Common to the oceanic and continental crust are such layers of the lithosphere as basalt and sedimentary.

Thus, the earth's crust consists mainly of rocks that are formed during the cooling and crystallization of magma, which penetrates into the lithosphere through cracks. If at the same time the magma could not seep to the surface, then it formed such coarse-grained rocks as granite, gabbro, diorite, due to its slow cooling and crystallization.

But the magma that managed to get out, due to rapid cooling, formed small crystals - basalt, liparite, andesite.

As for sedimentary rocks, they were formed in the Earth's lithosphere in different ways: clastic rocks appeared as a result of the destruction of sand, sandstones and clay, chemical rocks were formed due to various chemical reactions in aqueous solutions - these are gypsum, salt, phosphorites. Organic were formed by plant and lime residues - chalk, peat, limestone, coal.

Interestingly, some rocks appeared due to a complete or partial change in their composition: granite was transformed into gneiss, sandstone into quartzite, limestone into marble. According to scientific research, scientists were able to establish that the lithosphere consists of:

• Oxygen - 49%;
• Silicon - 26%;
• Aluminum - 7%;
• Iron - 5%;
• Calcium - 4%
• The composition of the lithosphere includes many minerals, the most common are feldspar and quartz.

As for the structure of the lithosphere, stable and mobile zones are distinguished here (in other words, platforms and folded belts). On tectonic maps, you can always see the marked boundaries of both stable and dangerous territories. First of all, this is the Pacific Ring of Fire (located along the edges of the Pacific Ocean), as well as part of the Alpine-Himalayan seismic belt (Southern Europe and the Caucasus).

Description of platforms

The platform is practically immovable parts of the earth's crust that have gone through a very long stage of geological formation. Their age is determined by the stage of formation of the crystalline basement (granite and basalt layers). Ancient or Precambrian platforms on the map are always located in the center of the continent, young ones are either on the edge of the mainland, or between the Precambrian platforms.

Mountain-fold area

The mountain-folded region was formed during the collision of tectonic plates, which are located on the mainland. If the mountain ranges were formed recently, increased seismic activity is recorded near them, and all of them are located along the edges of the lithospheric plates (the younger massifs belong to the Alpine and Cimmerian stages of formation). Older areas related to the ancient, Paleozoic folding, can be located both on the edge of the mainland, for example, in North America and Australia, and in the center - in Eurasia.

It is interesting that scientists determine the age of mountain-folded areas according to the youngest folds. Since mountain building is ongoing, this makes it possible to determine only the time frame of the stages of development of our Earth. For example, the presence of a mountain range in the middle of a tectonic plate indicates that the border once passed here.

Lithospheric plates

Despite the fact that ninety percent of the lithosphere consists of fourteen lithospheric plates, many do not agree with this statement and draw their own tectonic maps, saying that there are seven large and about ten small ones. This division is rather arbitrary, because with the development of science, scientists either identify new plates, or recognize certain boundaries as non-existent, especially when it comes to small plates.

It is worth noting that the largest tectonic plates are very clearly visible on the map and they are:

• The Pacific is the largest plate on the planet, along the boundaries of which constant collisions of tectonic plates occur and faults form - this is the reason for its constant decrease;
• Eurasian - covers almost the entire territory of Eurasia (except Hindustan and the Arabian Peninsula) and contains the largest part of the continental crust;
• Indo-Australian - consists of the Australian continent and the Indian subcontinent. Due to constant collisions with the Eurasian plate, it is in the process of breaking;
• South American - consists of the South American mainland and part of the Atlantic Ocean;
• North American - consists of the North American continent, part of northeastern Siberia, the northwestern part of the Atlantic and half of the Arctic Oceans;
• African - consists of the African mainland and the oceanic crust of the Atlantic and Indian oceans. It is interesting that the plates adjacent to it move in the opposite direction from it, therefore the largest fault of our planet is located here;
• The Antarctic Plate is made up of the mainland Antarctica and the nearby oceanic crust. Due to the fact that the plate is surrounded by mid-ocean ridges, the rest of the continents are constantly moving away from it.

Movement of tectonic plates

Lithospheric plates, connecting and separating, change their outlines all the time. This allows scientists to put forward the theory that about 200 million years ago the lithosphere had only Pangea - a single continent, which subsequently split into parts, which began to gradually move away from each other at a very low speed (on average, about seven centimeters per year ).

There is an assumption that due to the movement of the lithosphere, in 250 million years a new continent will form on our planet due to the union of moving continents.

When there is a collision of the oceanic and continental plates, the edge of the oceanic crust sinks under the continental one, while on the other side of the oceanic plate its boundary diverges from the plate adjacent to it. The boundary along which the movement of the lithospheres occurs is called the subduction zone, where the upper and plunging edges of the plate are distinguished. It is interesting that the plate, plunging into the mantle, begins to melt when the upper part of the earth's crust is squeezed, as a result of which mountains are formed, and if magma also erupts, then volcanoes.

In places where tectonic plates come into contact with each other, there are zones of maximum volcanic and seismic activity: during the movement and collision of the lithosphere, the earth's crust collapses, and when they diverge, faults and depressions form (the lithosphere and the Earth's relief are connected with each other). This is the reason why the largest landforms of the Earth are located along the edges of the tectonic plates - mountain ranges with active volcanoes and deep-sea trenches.

Relief

It is not surprising that the movement of the lithospheres directly affects the appearance of our planet, and the diversity of the Earth's relief is amazing (the relief is a set of irregularities on the earth's surface that are above sea level at different heights, and therefore the main forms of the Earth's relief are conditionally divided into convex (continents , mountains) and concave - oceans, river valleys, gorges).

It is worth noting that the land occupies only 29% of our planet (149 million km2), and the lithosphere and the Earth's topography consist mainly of plains, mountains and low mountains. As for the ocean, its average depth is a little less than four kilometers, and the lithosphere and the relief of the Earth in the ocean consist of a continental shelf, a coastal slope, an oceanic bed, and abyssal or deep-sea trenches. Most of the ocean has a complex and varied relief: there are plains, basins, plateaus, hills, and ridges up to 2 km high.

Problems of the lithosphere

The intensive development of industry has led to the fact that man and the lithosphere have recently become extremely difficult to get along with each other: pollution of the lithosphere is acquiring catastrophic proportions. This happened due to the increase in industrial waste in combination with household waste and fertilizers and pesticides used in agriculture, which negatively affects the chemical composition of the soil and living organisms. Scientists have calculated that about one ton of garbage falls per person per year, including 50 kg of hardly decomposable waste.

Today, pollution of the lithosphere has become an urgent problem, since nature is not able to cope with it on its own: the self-purification of the earth's crust is very slow, and therefore harmful substances gradually accumulate and eventually negatively affect the main culprit of the problem - man.

Theme "Lithosphere"

in 7th grade

K.S. LAZAREVICH

How to conduct literate,
interesting and meaningful lessons
on upcoming topics

The boundaries of the lithosphere

The course of geography in the 7th grade begins with the fact that students return to topics that seemed to be studied in the 6th grade - the lithosphere, atmosphere, hydrosphere. This beginning of the course already shows how unreliable, unsteady the knowledge gained in the first year of geography. And for the 7th grade, these topics are quite complicated, but there is no need to talk about the 6th grade. We will try to analyze the difficulties that are encountered in the first topics of the 7th grade. At the same time, we will return to the textbooks of the previous year of study, clarify and correct some of the provisions found there.

Term lithosphere has been used in science for a long time - probably since the middle of the 19th century. But it acquired its modern significance less than half a century ago. Even in the geological dictionary of the 1955 edition it is said:
LITHOSPHERE - the same as Earth's crust.
In the dictionary of the 1973 edition and in subsequent ones we already read:
The LITHOSPHERE ... in the modern sense includes the earth's crust ... and the rigid upper part of the Earth's upper mantle.

We draw the reader's attention to the wording: the upper part of the upper mantle. Meanwhile, in one of the textbooks in the figure it is indicated: "The lithosphere (the earth's crust and upper mantle)", and according to the figure it turns out that the entire mantle, which is not part of the lithosphere, is lower (Krylova 6, p. 50, fig. 30 ). By the way, in the same textbook in the text (p. 49) and in the textbook for the 7th grade (Krylova 7, p. 9) everything is correct: it is said about the upper part of the mantle. Upper mantle is a geological term for a very large layer; the upper mantle has a thickness (thickness) of up to 500, according to some classifications - over 900 km, and the lithosphere includes only the upper ones from several tens to two hundred kilometers. All this is difficult not only for students, but also for teachers. It would be better to abandon the term at school altogether lithosphere, limiting itself to mentioning the earth's crust; but here lithospheric plates arise, and there is no way without the lithosphere. Perhaps rice will help. 1, it is easy to redraw it in an enlarged form. Speaking of the lithosphere, one must firmly remember that it includes the earth's crust and the upper, relatively thin layer of the mantle, but not the upper mantle- the last term is much broader.

Layers of the lithosphere

The earth's crust, with tenacity worthy of a better application, is continued in all textbooks to be divided into three layers - sedimentary, granite and basalt. And it's time to change the record.
Most of the information about the deep structure of the Earth was obtained from indirect, geophysical data - from the propagation velocities of seismic waves, from changes in the magnitude and direction of gravity (insignificant, perceptible only by very accurate instruments), from magnetic properties and the magnitude of the electrical conductivity of rocks. The mass of dense rocks in the same volume is greater than less dense rocks, they create an increased gravitational field. In dense rocks, shock waves travel faster (recall that sound travels noticeably faster in water than in air). Passing through rocks with different physical properties, waves are reflected, refracted, and absorbed. Waves are transverse and longitudinal, the speed of their propagation is different. Explore the passage of natural shock waves during earthquakes, create these waves artificially, producing explosions.
From all these data, a picture of the distribution over the area and in depth of rocks with different physical properties is formed. On its basis, a model of the structure of the Earth's interior is created: rocks are selected whose physical properties more or less coincide with the properties determined using indirect methods, and these rocks are mentally placed at the appropriate depth. When it is possible to drill a well to a depth previously inaccessible, or to obtain some other reliable data, this model is confirmed in whole or in part. It happens that it is not confirmed at all, you have to build a new one. After all, it is by no means excluded that rocks lie at depth that we do not meet on the surface at all, or that at depth, at high temperature and pressure, the properties of rocks well known to us will change beyond recognition.
In 1909, the Serbian geophysicist Andrei Mohoro'vich noticed that at a depth of 54 km, the velocities of seismic waves increase sharply, abruptly. Subsequently, this jump was traced throughout the globe at depths from 5 to 90 km and is now known as the Mohorovichich boundary (or surface), in short, the Moho boundary, even shorter, the M boundary. The M surface is considered the lower boundary of the earth's crust. An important feature of this surface is that, in general terms, it is like a mirror image of the relief of the earth's surface: it is higher under the oceans, lower under the continental plains, lower than everything under the highest mountains (these are the so-called mountain roots).
This feature of the earth's crust, probably, will not be difficult to explain to schoolchildren by letting several pieces of wood of different shapes, preferably heavy, so that they go into the water by 2 / 3 - 3 / 4, float in a transparent vessel with water; those of them that protrude above the water will also be deeper submerged (Fig. 2).

According to the traditional concept of the structure of the earth's crust, which can be read in any textbook, it is customary to distinguish three main layers in the composition of the earth's crust. The upper of them is composed mainly of sedimentary rocks and is called sedimentary. The two lower layers are called "granite" and "basalt". Accordingly, two types of the earth's crust are distinguished. continental crust contains all three layers and has a thickness of 35-50 km, under the mountains up to 90 km. In the oceanic crust, the sedimentary layer has a much smaller thickness, and the middle, "granite" layer is absent; the thickness of the oceanic crust is 5–10 km (Fig. 3). Between the "granite" and "basalt" layers lies the Konrad boundary, named after the Austrian geophysicist who discovered it; it is not mentioned in school textbooks.

But research over the past two decades has shown that this well-proportioned, easy-to-remember scheme does not fit well with reality. "Granite" and "basalt" layers consist mainly of igneous and metamorphic rocks. At the Konrad boundary, there is an abrupt increase in seismic wave velocities. Such an increase in velocities can be expected during the transition of waves from rocks with a density of 2.7 to rocks with a density of 3 g/cm 3 , which approximately corresponds to the densities of granite and basalt. Therefore, the overlying layer was called "granite", and the underlying "basalt". But note: these names are in quotation marks everywhere. Geophysicists did not consider these layers to be composed of granite and basalt, they only talked about some analogy. However, even many geologists could not resist the temptation to believe that the "granite" layer is really from granite, and the "basalt" layer is from basalt. What can we say about the authors of school textbooks!
Korinskaya, p. 20, fig. 8. Signatures to the conventional signs: “A layer of sedimentary rocks. layer of granite. Basalt layer.
Petrova, p. 47-48. “We are entering the granite layer of the Earth. Granite ... was formed from magma in the thickness of the earth's crust ... We are entering a layer of basalt - a rock of deep origin. (By the way, this is not true: basalt is not deep, but outflowing rock.)
Finarov, p. 15 and Krylova 7, p. 10, fig. 1 - the granite and basalt layers are named without quotes, and the student clearly sees that they consist of these rocks.
The necessary reservation is made only in one textbook, but is it sufficient to draw attention to it?
“In the mainland [crust] lies a layer called granite. It is composed of igneous and metamorphic rocks, similar in composition and density to granites ... The lower layer of the earth's crust is a layer conventionally called basalt; it ... consists of rocks whose density is close to that of basalts” (Krylova, Gerasimova, p. 10).
One of the tasks of the Kola superdeep well was to reach the Konrad boundary, which, according to geophysical data, lies in this place at a depth of 7-8 km. And perhaps the most important geological result of drilling was the proof of the absence of the Konrad boundary in its geological understanding: in which rocks the well went above the boundary established by geophysicists, in the same rocks it passed several kilometers below it.

And the geophysical fate at the Konrad boundary turned out to be not as glorious as that at the Mohorovichich boundary. In some places it was singled out confidently, in other places - less confidently (whether she was alone, or not alone), somewhere they were not found at all. There was a need to abandon the terms "granite layer" and "basalt layer", even if in quotation marks, and to recognize that the Konrad boundary does not exist. The modern model of the structure of the earth's crust looks much more complicated than the classical three-layer model (Fig. 4). It still has continental and oceanic crust. Characteristic features of the continental crust can be considered a significant (tens of kilometers) thickness, an increase in density from top to bottom - gradual or spasmodic; the sedimentary layer within the continental crust is usually thicker than within the oceanic. The oceanic crust is much thinner, more homogeneous in composition; in relation to it, one can speak of a basalt layer without quotes, since the ocean floor is composed mainly of basalts.

For more details see: I.N. Galkin. Into the ocean behind the bark//Geography, No. 42/97, p. 6-7, 13.
** For more details see: T.S. Mints, M.V. Mints. Kola Superdeep//Geography, No. 33/99, p. 1-4.

Theory of lithospheric plates

This theory is usually very attractive to students. She is elegant and seemingly explains everything. Many of the perplexities that arise among scientists in connection with it relate to issues so complex that it’s not even worth talking about them in school (for example, which non-specialist will be able to assess the legitimacy of the doubts that arise in connection with the redistribution of heat flow from the bowels of the Earth to the surface? ). But students must be told that there are unresolved problems in this theory, which, perhaps, will force them to reconsider it - most likely not entirely, but in some details.
According to the texts of textbooks, schoolchildren can conclude that plate tectonics is a refinement of Alfred Wegener's hypothesis, which peacefully replaced it. Actually it is not. Wegener has continents composed of a relatively light substance, which he called sial(silicium-aluminum), as if floating on the surface of a heavier substance - sima(silicium-magnesium). At first, the hypothesis captivated almost everyone, it was accepted with enthusiasm. But after 2-3 decades, it turned out that the physical properties of the rocks do not allow such navigation, and a fat cross was put on the theory of continental drift. And as often happens, the baby was thrown out with the water: the theory is bad, which means that the continents cannot move at all. Only by the 60s, that is, only 40-45 years ago, when the global system of mid-ocean ridges had already been discovered, they built an almost new theory, in which only a change in the relative position of the continents remained from Wegener's hypothesis, in particular, an explanation of the similarity of the outlines of the continents on both sides of the Atlantic.
The most important difference between modern plate tectonics and Wegener's hypothesis is that Wegener continents moved along the substance that made up the ocean floor, in the modern theory plates are involved in the movement, which include areas of both land and the ocean floor; The boundaries between plates can run along the bottom of the ocean, and on land, and along the boundaries of continents and oceans.
The movement of lithospheric plates occurs along the asthenosphere - a layer of the upper mantle that underlies the lithosphere and has viscosity and plasticity. Mention of the asthenosphere in the texts of textbooks could not be found, but in one textbook, not only the asthenosphere, but also “the layer of the mantle above the asthenosphere” is signed on the figure (Finarov, p. 16, Fig. 4). It is not worth mentioning the asthenosphere in the lessons, the structure of the upper layers of the Earth is already quite complicated.
The textbooks explain that along the axes of the mid-ocean ridges, the areas of lithospheric plates gradually increase. This process has been named spreading(English spreading expansion, distribution). But the surface of the globe cannot increase. The emergence of new sections of the earth's crust on the sides of the mid-ocean ridges must be compensated for by its disappearance somewhere. If we believe that lithospheric plates are sufficiently stable, it is natural to assume that the disappearance of the crust, as well as the formation of a new one, should occur at the boundaries of approaching plates. In this case, there can be three different cases:
- two parts of the oceanic crust are approaching;
- a section of the continental crust is approaching a section of the oceanic;
- two sections of the continental crust are approaching.
The process that occurs when parts of the oceanic crust approach each other can be schematically described as follows: the edge of one plate rises somewhat, forming an island arc; the other goes under it, here the level of the upper surface of the lithosphere decreases, and a deep-water oceanic trench is formed. Such are the Aleutian Islands and the Aleutian Trench framing them, the Kuril Islands and the Kuril-Kamchatka Trench, the Japanese Islands and the Japanese Trench, the Mariana Islands and the Mariana Trench, etc.; All this in the Pacific Ocean. In the Atlantic - the Antilles and the Puerto Rico Trench, the South Sandwich Islands and the South Sandwich Trench. The movement of plates relative to each other is accompanied by significant mechanical stresses, therefore, in all these places, high seismicity and intense volcanic activity are observed. The sources of earthquakes are located mainly on the surface of contact between two plates and can be at great depths. The edge of the plate, which has gone deep, plunges into the mantle, where it gradually turns into mantle matter. The subducting plate is heated, and magma is melted out of it, which erupts in island arc volcanoes (Fig. 5).

The process of submerging one plate under another is called subduction(literally - pushing). This Latin term, like the English word "spreading" above, is widely used, both appear in popular literature, so teachers need to know them, but it hardly makes sense to introduce them in a school course.
When sections of the continental and oceanic crust move towards each other, the process proceeds approximately in the same way as in the case of a meeting of two sections of the oceanic crust, only instead of an island arc, a powerful chain of mountains is formed along the coast of the mainland. The oceanic crust is also submerged under the continental edge of the plate, forming deep-sea trenches, volcanic and seismic processes are just as intense. Magma that does not reach the earth's surface crystallizes, forming granitic batholiths (Fig. 6). A typical example is the Cordillera of Central and South America and the system of trenches running along the coast - Central American, Peruvian and Chilean.

When two sections of the continental crust approach each other, the edge of each of them experiences folding, faults, mountains are formed, and seismic processes are intense. Volcanism is also observed, but less than in the first two cases, since the earth's crust in such places is very thick (Fig. 7). This is how the Alpine-Himalayan mountain belt was formed, stretching from North Africa and the western tip of Europe through all of Eurasia to Indochina; it includes the highest mountains on Earth, high seismicity is observed along its entire length, and there are active volcanoes in the west of the belt.
Several textbooks contain diagrams of the position of the continents so many millions of years ago.

In one book (Krylova 7, p. 21, fig. 12) the location of the continents after 50 million years is given. If this textbook is used, it would be worth commenting on the scheme, saying beforehand that this is only a forecast, a very approximate one, which will be justified only if the general direction of movement of the plates is maintained, and no major restructuring of them occurs. According to the forecast, the Atlantic Ocean, the East African Rifts (they will be filled with the waters of the World Ocean) and the Red Sea will expand significantly, which will directly connect the Mediterranean Sea with the Indian Ocean.

Thus, when checking whether schoolchildren remember well the topic “Lithosphere” in the 6th grade, it is necessary to simultaneously dispel some misconceptions that could arise. If you want to give students the basics of knowledge at the modern level, you will have to, while explaining new, more complex material, abandon the presentation of outdated information given in textbooks.
Here are the main theses that need to be stated and explained.
1. The lithosphere includes the earth's crust and the upper, relatively small part of the mantle.
2. The earth's crust is of two types - continental and oceanic.
3. The continental crust has a significant (tens of kilometers) thickness, its density increases downwards. The crust consists of sedimentary rocks (usually at the top), below are igneous and metamorphic rocks of various compositions.
4. The thickness of the oceanic crust is 5-10 km, it is composed mainly of basalts.
(When explaining the structure of the continental and oceanic crust, the "granite" and "basalt" layers, and even more so the Konrad boundary, should not be mentioned.)
5. The theory of plate tectonics came to replace Wegener's hypothesis only after the hypothesis was completely rejected.
6. According to Wegener's hypothesis, the continents moved along the denser matter that makes up the ocean floor.
7. According to the theory of lithospheric plates, large areas of the lithosphere with continental crust, or oceanic, or both, are involved in the movement.
Different types of interaction of lithospheric plates with different types of the earth's crust may or may not be considered by the teacher, depending on the degree of preparedness of the class. These examples are interesting, they can be illustrated on the physical map of the world, but they are not included in the compulsory program.

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Korinskaya - V.A. Korinskaya, I.V. Dushina, V.A. Shchenev. Geography of continents and oceans: Proc. for 7 cells. avg. school - M.: Enlightenment, 1993. - 287 p.
Krylova 6 - O.V. Krylov. Physical Geography: Beginning. course: Proc. for 6 cells. general education institutions. - M.: Enlightenment, 1999 (and subsequent editions). - 192 p.
Krylova 7 - O.V. Krylov. Continents and oceans: Proc. for 7 cells. general education institutions. Moscow: Education, 1999 (and subsequent editions). - 304 p.
Krylova, Gerasimova - O.V. Krylova, T.P. Gerasimov. Geography of continents and oceans: Prob. textbook for 7 cells. general education institutions. - M.: Enlightenment, 1995. - 318 p.
Petrova - N.N. Petrov. Geography. Initial course. Grade 6: Proc. for general education textbook establishments. - M.: Bustard; DiK, 1997. - 256 p.
Finarov - D.P. Finarov, S.V. Vasiliev, Z.I. Shipunova, E.Ya. Chernikhov. Geography of continents and oceans: Proc. for 7 cells. general education institutions. - M.: Enlightenment, 1996. - 302 p.

Relief and geological processes.

1. The concept of relief, its classification. Relief formation factors.

2. Morphosculptural mesorelief.

Coastal relief.

3. The relief of the bottom of the oceans

The lithosphere is a solid shell of the Earth, including the earth's crust and the upper layer of the mantle to the asthenosphere.

Until the 60s. 20th century the concepts of "lithosphere" and "earth's crust" were considered identical. At present, the view of the lithosphere has changed.

The lithosphere is studied by geology (the material composition of the lithosphere, its structure, origin, development) and physical geography (or general geography), or rather, geomorphology, the science of the genesis (emergence and development) of relief. Geomorphology as a science of the relief of the earth's surface arose at the beginning of the 20th century. abroad (in France), and then in Russia. The foundations of geomorphology in Russia were laid by V.V. Dokuchaev, P.N. Kropotkin, I.D. Chersky, V.A. Obruchev, P.P. Semenov-Tyan-Shansky, A.A. Borzov, I.S. Shchukin.

Relief and geological processes

The relief is a combination of all the irregularities of the surface of the globe (from the protrusions of the continents and the depressions of the oceans up to swampy bumps and molehills). The word "relief" was borrowed from the French language, in which it goes back to the Latin "raise".

A relief is a three-dimensional body that occupies a volume in the earth's crust. The relief can take the following forms:

- positive (above the surrounding surface - mountains, hills, hills, etc.);

- negative (below the surrounding surface - depressions, ravines, lowlands, etc.);

- neutral.

The whole variety of landforms on Earth has been created geological processes . Geological processes are processes that change the earth's crust. These include processes endogenous occurring inside the earth's crust (i.e. internal processes - differentiation of matter in the bowels of the Earth, the transition of solid matter to liquid, radioactive decay, etc.), and exogenous occurring on the surface of the earth's crust (i.e. external processes - they are associated with the activities of the Sun, water, wind, ice, living organisms).

Endogenous processes tend to create predominantly large landforms: mountain ranges, intermountain depressions, etc.; under their influence, volcanic eruptions and earthquakes occur. Endogenous processes create the so-called morphostructures - mountains, mountain systems, vast and deep depressions, etc. Exogenous processes tend to smooth out, even out the relief created by endogenous processes. Exogenous processes create the so-called morphosculptures - ravines, hills, river valleys, etc. Thus, endogenous and exogenous processes develop simultaneously, interconnectedly and in different directions. This manifests the dialectical law of unity and struggle of opposites.

To endogenous processes include magmatism, metamorphism, tectonic movements.

Magmatism. It is customary to distinguish intrusive magmatism - the intrusion of magma into the earth's crust (plutonism) - and effusive magmatism - an eruption, an outpouring of magma on the surface of the Earth. Effusive magmatism is also called volcanism. The erupting and solidified magma is called lava . During a volcanic eruption, solid, liquid and gaseous products of volcanic activity are ejected to the surface. Depending on the ways in which lava flows, volcanoes are divided into volcanoes of the central type - they have a cone-shaped shape (Klyuchevskaya Sopka in Kamchatka, Vesuvius, Etna in the Mediterranean, etc.) - and fissure-type volcanoes (there are many of them in Iceland, New Zealand, and in the past such volcanoes were on the Dekan plateau, in the middle part of Siberia and some other places).

Currently, there are more than 700 active volcanoes on land, and there are even more at the bottom of the ocean. Volcanic activity is confined to tectonically active zones of the globe, to seismic belts (seismic belts are longer than volcanic zones). There are four zones of volcanism:

1. The Pacific "ring of fire" - it accounts for ¾ of all active volcanoes (Klyuchevskaya Sopka, Fujiyama, San Pedro, Chimborazo, Orizaba, Erebus, etc.).

2. Mediterranean-Indonesian belt, including Vesuvius, Etna, Elbrus, Krakatoa, etc.

3. Mid-Atlantic belt, including the island of Iceland, the Azores and the Canary Islands, the island of St. Helena.

4. East African belt, including Kilimanjaro and others.

One of the manifestations of the late stages of volcanism is geysers - hot springs, periodically ejecting fountains of hot water and steam to a height of several meters.

Metamorphism . Metamorphism is understood as a change in rocks under the influence of temperature, pressure, chemically active substances released from the bowels of the Earth. In this case, for example, limestone turns into marble, sandstone into quartzite, marl into amphibolite, etc.

Tectonic movements (processes) are divided into oscillatory (epeirogenic - from the Greek "epeirogenesis" - the birth of continents) and mountain-forming (orogenic - from the Greek "oros" - mountain) - these are folding and discontinuous movements.

To exogenous processes weathering, geological activity of the wind, surface and ground waters, glaciers, wave and wind activity.

Weathering - it is the process of rock destruction. It can be: 1) physical - thermal and permafrost, 2) chemical - dissolution of substances with water, i.e. karst, oxidation, hydrolysis, 3) biological - the activity of living organisms. The residual products of weathering are called eluvium (weathering crust).

physical weathering . The main factors of physical weathering are: temperature fluctuations during the day, freezing water, crystal growth in rock cracks. Physical weathering does not lead to the formation of new minerals, and its main result is the physical destruction of rocks into fragments. Distinguish between permafrost and thermal weathering. Permafrost (frosty) weathering proceeds with the participation of water, periodically freezing in the cracks of rocks. The resulting ice, due to the increase in volume, exerts enormous pressure on the walls of the cracks. At the same time, the cracks expand, and the rocks gradually disintegrate into fragments. Permafrost weathering manifests itself especially in the polar, subpolar and high-mountain regions. Thermal weathering occurs on land constantly and almost everywhere under the influence of temperature fluctuations during the day. Thermal weathering is most active in deserts, where the daily temperature range is especially large. As a result, rocky and gravelly deserts are formed.

chemical weathering . The main agents (factors) of chemical weathering are oxygen, water, carbon dioxide. Chemical weathering leads to the formation of new rocks and minerals. There are the following types of chemical weathering: oxidation, hydration, dissolution and hydrolysis. Oxidation reactions occur within the upper part of the earth's crust, located above groundwater. Atmospheric water can contain up to 3% (by volume of water) of dissolved air. The air dissolved in water contains more oxygen (up to 35%) than atmospheric air. Therefore, atmospheric waters circulating in the upper part of the earth's crust have a greater oxidizing effect on minerals than atmospheric air. Hydration is the process of combining minerals with water, leading to the formation of new compounds resistant to weathering (for example, the transition of anhydrite to gypsum). Dissolution and hydrolysis occur under the combined action of water and carbon dioxide on rocks and minerals. As a result of hydrolysis, complex processes of decomposition of minerals occur with the removal of some elements (mainly in the form of salts of carbonic acid).

biological weathering - these are the processes of destruction of rocks under the influence of organisms: bacteria, plants and animals. Plant roots can mechanically destroy and chemically alter the rock. The role of organisms in the loosening of rocks is great. But the main role in biological weathering belongs to microorganisms.

In fact, it is under the influence of microorganisms that the rock turns into soil.

The processes associated with the activity of the wind are called eolian . The destructive work of the wind is deflation (blowing) and corrosion (turning). The wind also transports and accumulates (accumulates) matter. The creative activity of the wind consists in the accumulation of matter. In this case, dunes and dunes are formed - in deserts, on the coasts of the seas.

The processes associated with the activity of water are called fluvial .

The geological activity of surface waters (rivers, rains, melt waters) also consists in erosion (destruction), transportation and accumulation. Rain and melt water produce planar washout of loose sedimentary material. Deposits of such material are called deluvium . In mountainous areas, temporary streams (rain showers, melting of a glacier) can form cones of material when they enter the foothill plain. Such deposits are called proluvium .

Permanent streams (rivers) also perform various geological work (destruction, transportation, accumulation). The destructive activity of rivers consists in deep (bottom) and lateral erosion, the creative activity in the accumulation alluvium . Alluvial deposits differ from eluvium and deluvium in their good sorting.

The destructive activity of groundwater consists in the formation of karst, landslides; creative - in the formation of stalactites (calcite icicles) and stalagmites (rock outgrowths directed upwards).

The processes associated with the activity of ice are called glacial . In the geological activity of ice, one should distinguish between the activities of seasonal ice, permafrost, and glaciers (mountains and continents). Physical permafrost weathering is associated with seasonal ice. Phenomena associated with permafrost solifluction (slow flow, sliding of thawing soils) and thermokarst (subsidence of soil as a result of thawing permafrost). Mountain glaciers are formed in the mountains and are characterized by small size. Often they stretch along the valley in the form of an icy river. Such valleys usually have a specific trough-like shape and are called touches . The speed of movement of mountain glaciers is usually from 0.1 to 7 meters per day. Continental glaciers reach very large sizes. So, on the territory of Antarctica, the ice cover occupies about 13 million km 2, on the territory of Greenland - about 1.9 million km 2. A characteristic feature of this type of glaciers is the spreading of ice in all directions from the feeding area.

The destructive work of a glacier is called exaration . When the glacier moves, curly rocks, sheep foreheads, troughs, etc. are formed. The creative work of the glacier is to accumulate moraines . Moraine deposits are detrital material formed as a result of glacier activity. The creative work of glaciers also includes the accumulation of fluvioglacial deposits that arise when a glacier melts and have a flow direction (i.e. flow out from under the glacier). When the glacier melts, cover deposits are also formed - deposits of shallow near-glacial, melt water spills. They are well sorted and named outwash fields .

The geological activity of swamps consists in the accumulation of peat.

The destructive work of waves is called abrasion (destruction of the coast). The creative work of this process is in the accumulation of sediments and their redistribution.