The relief of the earth's surface.

I. Large features of the relief. On the earth's surface, one can distinguish, first of all, land (continents with islands) and oceanic depressions.

For a long time, geographers have paid attention to certain regularities that are observed in the outlines of the continents and in the arrangement of relief elements. So, to the north, the continents expand, to the south they sharpen (South America, Africa, India). The land is located in relation to the oceans, as they say, antipodal. The features now indicated were the reason for the creation of the "tetrahedral" theory of the shape of the earth. This hypothesis, which was pioneered by Green (1875), proceeds from the assumption that the earth, cooling, should tend to take the form of a tetrahedron, since the tetrahedron of all regular bodies with the same surface has the smallest volume. But at the same time, due to rotation, the earth tends to take on a spherical shape. As a result of both these influences, the earth has the shape of a pear. The edges of the "tetrahedron" correspond to the continents, and the planes to the oceans. Lapparan and Arldt developed Green's conjecture. According to their views, the top of the earth's "tetrahedron" coincides with the south pole, while the base is turned to the north; the corners of the base rest against the Archean massifs of Canada, Finland, and Siberia. This hypothesis is contradicted by the fact that the continents are located along the meridians only from the Tertiary time, while earlier, in the Mesozoic and Paleozoic times, the location of the continents was completely different - along the parallels.

The outlines of the western and eastern shores of the Atlantic Ocean are very remarkable: the convexity of the western coast of North Africa corresponds to the concavity between North and South America; the convexity of South America in the region of Cape San Roca corresponds to the concavity of the Gulf of Guinea. Surprisingly, these outlines, in general, correspond to the strike of the underwater Atlantic ridge. The similarity of the western and eastern shores of the Atlantic gave Pickering, in 1907, reason to suggest that Europe, Africa, and America were once one; subsequently, this single continent "broke", and the Atlantic Ocean formed at the site of the gap. The meteorologist A. Wegener came to the same idea independently in 1912, and precisely under the influence of the parallelism of the Atlantic Ocean coasts (A. Wegener, “Die Entstehung der Kontinente und Ozeane”, 2 Aufl., Braunschweig, 1920, p. VIII + 135 ; there is a Russian translation). According to Wegener, the earth's crust does not completely envelop the globe: at the bottom of the deep parts of the seas, magma comes out. Thus, the continents, or the lithosphere (see XI, 533), seem to float in the magma, or barysphere, like ice floes on water. As proof, the author cites the fact that the hypsographic curve, or the curve of the percentage distribution of areas of heights and depths on the earth's surface, shows two maxima, namely: 36% of the entire earth's area is occupied by depths from 4 to 5 km, and 22% - by heights between 0 and 1 km. Meanwhile, if the distribution of depths and heights were controlled by chance, then, according to Gauss's law, one would expect one maximum, namely, in the region of the so-called average level of the earth's crust (-2,300 m). Since the curve of heights and depths has two maxima, then, Wegener concludes, the undisturbed initial level should have consisted of two tiers: the continental level belongs to the lithosphere, the oceanic level to the barysphere.

This conclusion does not seem to us as indisputable as it does to Wegener. The presence of two maxima in the hypsometric curve indicates that the distribution of heights and depths on the earth's surface is not subject to chance, but depends on regularities - in this Wegener is right. But it is not clear why this pattern should be exactly the way Wegener suggests. The only thing that can be said, based on the consideration of the hypsometric curve, is that the causes that cause uneven terrain on land and on the ocean floor are different.

So, Wegener admits that in the open ocean magma directly composes the bottom. Like it or not, but, in any case, according to the current view, the lithosphere under the oceans is much thinner than under the continents, and the magma under the oceans is much closer to the surface of the earth than under the continents; Lukashevich (“Inorganic Life of the Earth”, I, 1908, p. 146), for example, takes the thickness of the lithosphere in the Himalayas to be 133 km, and in the deepest part of the ocean - only 79 km. According to Wegener, the lithosphere once covered the entire earth, and a boundless sea spread over it. For unknown reasons, this bark was torn in some places and folded in others. Wegener thinks that the aforementioned rupture was accompanied, on the one hand, by the formation of the Pacific Ocean, and, on the other hand, by the formation of folds in the gneiss massifs of Brazil, Africa, India, and Australia. Even during the Eocene, America, both North and South, adjoined Europe and Africa, and India with Ceylon - to Madagascar. But "inserting" North America into the outlines of Western Europe is not as easy as it seems. We have to make some risky assumptions. So, if we assume that Newfoundland was connected with Ireland, then things do not go well with Greenland and Labrador; Wegener therefore bends them to the northwest; such a bend "should" have occurred just before the Newfoundland-Ireland break.

From geology and geomorphology, Wegener extracts the following facts in favor of his theory. On the coast of northeastern Greenland, at 81° north latitude, there is a patch of undisplaced carboniferous deposits, to which exactly the same deposits correspond on the opposite coast of Svalbard. The Algonquian folds of the Hebrides and northern Scotland correspond to the same folds in Labrador and further south. These folds were considered to be the ends of the ridge, the middle part of which sank into the sea. But this submerged part should have a length of about 3,000 km. In Wegener's reconstruction, the American part is a direct continuation of the European one. Likewise, the Caledonian folds in Scandinavia and northern England are continued in Canada. Finally, the Armorican (Carboniferous) folds here and there form one system. As for the southern part of the Atlantic Ocean, Wegener finds similarities in the strike of dislocations in Brazil and West Africa (but since there are dislocations of various directions here and there, it is not difficult to find similar ones). Then, to the south of Buenos Aires, "Carboniferous" (in fact, Permian) dislocations were recently discovered, which in tectonics and geology correspond to the dislocations of the Cape Colony highlands.

So, Wegener accepts that even in the ice age Greenland adjoined North America, on the one hand, to northern Europe - on the other, the Atlantic Ocean reached north to New England and to northern Spain. South America separated from Africa in the Upper Eocene (now, however, Wegener is inclined to attribute the formation of the South Atlantic Ocean to the Cretaceous). In this regard, the following can be noted. If the northern and southern parts of the Atlantic Ocean were formed at different times, then it must be assumed that the formation of the Atlantic ridge occurred in the postglacial period; otherwise it is impossible to explain why the northern part of this ridge lies on the continuation of the southern one. We note that, according to Wegener's theory, it is completely inexplicable that underwater channels (Kongo, etc.) at the bottom of the Atlantic Ocean are indicative of large subsidence.

India, according to Wegener, was in conjunction with Madagascar until the beginning of the Tertiary. In front of the moving masses, according to Wegener, folded ridges arise, and the Himalayas began in a similar way in the Tertiary, simultaneously with the retreat of India north from Madagascar. If you smooth out the folds of the Himalayas, then Hindustan will come close to Madagascar. This conception of the formation of the Himalayas is completely unacceptable, in which even authors who generally sympathize with Wegener agree.

According to the theory of the spreading of the continents, the discontinuity of the locations of the Permian-Carboniferous glaciation is well explained: traces of it have been found in various places on the Gondwanan continent: in India, Australia, South America, and finally in Africa.

Wegener is trying to confirm his assumption about the separation of the New and Old Worlds with accurate digital data. If this process continues to the present, then the distance between Europe and North America must be increasing, and a comparison of old and new astronomical observations may reveal this. Indeed, the determinations of longitudes at Greenwich and Cambridge, Massachusetts, showed that between 1866 and 1892 the difference in longitudes increased by 0.23", or 4 meters per year. But later the reality of these data was not confirmed. Wegener now refers to the astronomical determinations of Koch (1907) in Greenland, which, compared with previous data, showed that Greenland "moved westward" by 1,190 m, that is, by 32 m during the period from 1870 to 1907. annually, and from 1823 to 1870 - by 9 m per year. To what extent these figures are real, the future must show.

If, relying on Wegener, we trace the movements of the continents in a geological perspective, it turns out that the continental masses tend to move: 1) from the poles towards the equator, 2) from east to west (note that, according to Lukashevich, in the lithosphere, on the contrary , movements with the nature of torsion are detected, namely, the slow movement from west to east of the polar regions relative to the equator (the reason is the slowing down of the earth's rotation from the tides and a decrease in the compression of the earth's spheroid).

In contrast to Wegener's theory, many authors both earlier (Dan) and now (Willis, Schuchert) adhere to the theory of the constancy of oceans and continents throughout the entire geological history of the earth. At the same time, they refer to the fact that although most of the land was covered by the sea more than once, all these seas were shallow, and there are no deep-water sediments anywhere on land. Kober (L. Kober, "Der Bau der Erde", 2 Aufl., Berlin, 1928) objects to this that there are no deep-sea sediments on land only in areas of ancient massifs or, as he calls them, cratogens, and in areas of geosynclines they are are available. Under the name cratogens, or archeids, Kober means areas that were subjected to folding processes in ancient times of the history of the earth, and then, as it were, frozen and remained unchanged until the present. In contrast to these areas, orogens are areas where mountain-building processes took place in later times; these include, for example, the Alps, the Caucasus, the Himalayas, the Verkhoyansk Range, and others. Examples of archeids can serve as: the Russian Plain, a significant part of Siberia, India, Australia, Brazil, Canada, etc. According to Kober, both orogen areas and and cratogens are constant in the history of the earth, but the continents and oceans are not constant. At the same time, orogens turn out to be geosynclines, under which the name Or (Haug; 1900) understands those places in the earth's crust in which marine sediments were first deposited; then these sediments were folded into folded mountain ranges; thus, geosynclines are plastic, mobile zones. It should only be noted that the areas occupied by the Kober orogens are much larger than the areas under the Og geosynclines; Thus, Kober considers the entire Atlantic Ocean to be a geosyncline or orogen. As we can see, it is difficult to combine the views of Og and Kober with Wegener's theory of the movement of continents.

II. Now let's move on to smaller landforms. Landforms can be classified from different points of view, but it is preferable to put the following three points in the basis: height (absolute and relative), geometric shape and origin.

A. Height classifications are well known and we do not dwell on them. According to the absolute height, lowlands and uplands are distinguished, according to the relative - lowlands and uplands.

B. Classification according to form. Landforms can be divided into three categories: 1) neutral: plains (and plateaus), slopes (and coasts); 2) positive, or hills: hills and mountains, mountain uplifts; 3) negative, or recesses: cracks, hollows and valleys, hollows, basins (seas, oceans), caves. These landforms are defined as follows.

1) Neutral forms. Plains (see) are such vast expanses of the earth's surface in which the height difference over the entire field of view is negligible, which is why the surface seems horizontal or almost horizontal. A plateau (plateau) is a plain dissected by deep valleys or rising in a ledge above neighboring lowlands. Plateaus should not be confused with highlands (highlands should be called vast uplands of considerable average height, where ridges and individual mountains alternate with vast lowlands; for example, the Pamirs). Slopes (cliffs, banks, coastal terraces) are inclined surfaces with a small vertical but significant horizontal extension.

2) Positive forms. Hills are small hills, no more than 200 m relative height. Mountains (see) are free-standing (isolated) hills, with a clearly defined foot and more than 200 m relative height. Mountain uplifts are vast elevations or systems of elevations over 200 m relative height.

3) Negative forms. Cracks are long, very narrow and relatively deep depressions that are not the result of the work of flowing water. Hollows - two slopes facing each other, but separated by a small area of ​​more or less flat surface. The trough type is a channel. If this surface, as a result of the work of flowing water, falls in one particular direction, we have a valley in front of us (q.v.). Hollows, or depressions, are closed or almost closed depressions, the slopes of which fall from all sides to one place (to the bottom). Type - funnel. Pools (see) - extensive recesses with slopes of irregular shape (that is, not like valleys and not like basins), for example, a river basin. Caves (see) - cavities in the earth's crust.

C. Classification by origin (genetic). Each of the above (item C) landforms can be classified by origin, bearing in mind that the forms of the surface of the earth's crust, generally speaking, may be due to:

1) movements of individual parts of the earth's crust by means of warehouses, faults, shifts, overlaps, uplifts and subsidences;

2) changes in the number of masses that make up a given section of the earth's crust. These changes can occur: a) by entrainment of mass due to the work of flowing water, sea surf, ice, wind, etc. - denudation forms; b) by bringing in mass due to the same reasons, as well as due to the activity of organisms, volcanoes, mud hills, etc. - accumulation forms or forms of accumulation;

3) the cumulative effect of all or part of the listed causes.

The classification of landforms was dealt with by: Richthofen (1886), Penk (1894, 1896), Passarge (1912,1926), Philippson (1924), Berg (1929).

Issues to consider:
1. Relief-forming factors. Types of tectonic movements.
2. Types of relief.
3. External processes that transform the surface of the Earth.

1. Relief-forming factors. Types of tectonic movements.
Relief -this is a set of irregularities of the earth's surface, differing in height above sea level, origin, etc., giving a unique look to our planet. The formation of the relief is influenced by both internal, tectonic, and external forces. Due to tectonic processes, mainly large surface irregularities arise - mountains, highlands, etc., and external forces are aimed at their destruction and the creation of smaller relief forms - river valleys, ravines, dunes, etc.

Tectonic factors

Tectonic factors include the movement of the earth's crust under the influence of the internal forces of the earth. Movements are divided into oscillatory, folding and discontinuous.

vibrationalmovements occur very slowly, accompanied by a gradual rise or fall of the earth's crust. You can trace them through the centuries. At present, Iceland, Greenland are rising in Europe; Holland, Southern England, Northern Italy are lowered. The sinking of the earth's crust is accompanied by the advance of the sea - transgression and the retreat due to the rise - regression. The sinking of land leads to the formation of bays, estuaries and bays. During the uplift, the West Siberian Plain, the Turanian, and the Amazonian were formed.

Folding movements are observed when forces move in a horizontal plane. At the same time, plastic rocks are crushed into masonry. The downward bend of the fold is called syncline, and up - anticline. Folds can form at depth and then be raised. This is how folded mountains are formed, for example, the Caucasus, the Alps, the Himalayas, the Andes.

Breaking movements are observed in rocks with low plasticity and vertical pressure force. Faults and displacements of rocks are formed. The sunken areas are called grabens, and those who have risen handfuls. Their alternation in the relief forms folded-blocky mountains, for example, Altai, Appalachians, Verkhoyansk Range. Grabens filled with water form tectonic lakes, for example, Baikal, Tanganyika.

External factorsLet's look at question 3.

- concave(hollows, river valleys, ravines, beams, etc.),

- convex(hills, mountain ranges, volcanic cones, etc.),

- just horizontal ,

- oblique surfaces.

Their size can be very diverse - from a few tens of centimeters to many hundreds and even thousands of kilometers.

Depending on the scale, allocate planetary, macro-, meso- and microforms of relief.

The planetary ones include the protrusions of the continents and the depressions of the oceans.

The depths of oceanic trenches fluctuate widely. The average depth is 3800 m, and the maximum, noted in the Mariana Trench of the Pacific Ocean, is 11022 m. The highest land point, Mount Everest (Chomolungma), reaches 8848 m. Thus, the height amplitude reaches almost 20 km.

The prevailing depths in the ocean are from 3000 to 6000 m, and the heights on land are less than 1000 m. High mountains and deep-sea depressions occupy only fractions of a percent of the Earth's surface.

The average height of the continents and their parts above sea level is also not the same: North America - 700 m, Africa - 640, South America - 580, Australia - 350, Antarctica - 2300, Eurasia - 635 m, and the height of Asia is 950 m, and Europe - only 320 m. Average land height 875 m.

In the relief of the ocean floor, there are: continental shelf, or shelf, - shallow part to a depth of 200 m, the width of which in some cases reaches many hundreds of kilometers; continental slope - rather steep ledge to a depth of 2500 m and ocean bed, which occupies most of the bottom with depths up to 6000 m.The greatest depths are noted in gutters, or ocean trenches, where they exceed the mark of 6000 m. The trenches usually stretch along the continents along the margins of the ocean.

In the central parts of the oceans, there are mid-ocean ridges (rifts): South Atlantic, Australian, Antarctic, etc.

The main elements of land relief are mountains and plains. They form the macrorelief of the Earth.

mountainthey call a hill that has a peak point, slopes, sole line, rising above the terrain above 200 m; an elevation up to 200 m high is called hill. Linearly elongated landforms with a ridge and slopes are mountain ranges. The ranges are separated by mountain ranges located between them. valleys. Connecting with each other, mountain ranges form mountain ranges. The collection of ridges, chains andvalleys are called mountain knot or mountain country, and in everyday life - mountains. For example, the Altai Mountains, the Ural Mountains.

Extensive areas of the earth's surface, consisting of mountain ranges, valleys and high plains, are called highlands. For example, the Iranian Highlands, the Armenian Highlands.

By origin, mountains are tectonic, volcanic and erosional.

tectonic mountains formed as a result of movements of the earth's crust. They can be folded, blocky and folded-blocky. All the highest mountains in the world - the Himalayas, the Hindu Kush, the Pamirs, the Cordillera, etc. - are folded. They are characterized by pointed peaks, narrow valleys (gorges), elongated ridges.

Block and fold-block mountains are formed as a result of the uplift and lowering of blocks of the earth's crust along fault planes. The relief of these mountains is characterized by flat tops and watersheds, wide, flat-bottomed valleys, for example, the Ural Mountains, Appalachians, Altai.

volcanic mountains formed as a result of the accumulation of products of volcanic activity.

Widespread on the surface of the earth erosional mountains (picture on the right), which are formed as a result of the dismemberment of high plains by external forces, primarily flowing waters.

By height, mountains are divided into low (up to 1000 m), medium-altitude (from 1000 to 2000 m), high (from 2000 to 5000 m) and highest (above 5 km) - they are indicated in brown on the scale of depths and heights (see map) .

The height of the mountains is easy to determine on a physical map. It can also be used to determine that most of the mountains belong to medium-high and high. Few peaks rise above 7000 m, and they are all in Asia. Only 12 mountain peaks located in the Karakorum mountains and the Himalayas have a height of more than 8000 m. The highest point of the planet is a mountain, or, more precisely, a mountain junction, Everest (Chomolungma) - 8848 m.

According to the nature of the surface, the plains are divided into flat, wavy And hilly, but on vast plains, such as Turan or West Siberian, one can meet areas with various forms of surface topography.

Depending on the height above sea level, the plains are divided into base(up to 200 m), sublime(up to 500 m) and high, or plateaus,(over 500 m). Elevated and high plains are always strongly dissected by water flows and have a hilly relief, while lowlands are often flat. Some plains are located below sea level. So, the Caspian lowland has a height of 28 m. Often on the plains there are closed basins of great depth. For example, the Karagis depression has a mark of 132 m, and the Dead Sea depression - 400 m.

Elevated plains bounded by steep ledges separating them from the surrounding area are called plateau. Such are the plateaus of Ustyurt, Putorana (Central Siberian Plateau), etc.

Plateau -flat-topped areas of the earth's surface, can have a significant height. So, for example, the Tibet plateau rises above 5000 m.

By origin, several types of plains are distinguished. Significant areas of land are occupied maritime, or primary, plains, formed as a result of marine regressions. These are, for example, the Turan, West Siberian, Great Chinese and a number of other plains. Almost all of them belong to the great plains of the planet. Most of them are lowlands, the relief is flat or slightly hilly.

Small spaces in river valleys are occupied alluvial, or alluvial, plains formed as a result of the leveling of the surface by river deposits - alluvium. This type includes the Indo-Gangetic, Mesopotamian, and Labrador plains. These plains are low, flat, and very fertile.

Plains are raised high above sea level - lava sheets(Central Siberian Plateau, Ethiopian and Iranian Highlands, Deccan Plateau). Some plains, such as the Kazakh uplands, were formed as a result of the destruction of mountains. They are callederosional.These plains are always elevated and hilly. These hills are composed of solid crystalline rocks and represent the remains of the mountains that once were here, their "roots".

Unlike internal ones, covering the entire thickness of the lithosphere, they act only on the surface of the Earth. The depth of their penetration into the earth's crust does not exceed a few meters (in caves - up to several hundred meters). The source of the origin of forces that cause external processes is thermal solar energy. A necessary condition for the action of external processes is the fork of gravity, in which all bodies tend to occupy the lowest position on Earth.

External processes are weathering of rocks, the work of wind, water and glaciers.

Weathering. It is divided into physical, chemical and organic.

When heated, the rock expands; when cooled, it contracts. Since the expansion coefficient of various minerals included in rock is not the same, the process of its destruction is intensified. At first, the rock breaks up into large blocks, which are crushed over time. The accelerated destruction of the rock is facilitated by water, which, penetrating into the cracks, freezes in them, expands and breaks the rock into separate parts. Physical weathering is most active where there is a sharp change in temperature, and solid igneous rocks come to the surface - granite, basalt, etc.

Chemical weathering - this is the impact on rocks of various aqueous solutions. In this case, unlike physical weathering, there is often a change in the chemical composition, and even the formation of new rocks. Chemical weathering operates everywhere, but it proceeds especially intensively in easily soluble rocks - limestone, gypsum, dolomite.

organic weathering is the process of destruction of rocks by living organisms - plants, animals and bacteria.

Lichens, for example, settling on rocks, wear away their surface with the released acid. Plant roots also secrete acid, and, in addition, the root system acts mechanically, as if tearing the rock. Earthworms, passing inorganic substances through themselves, transform the rock and improve the access of water and air to it.

The intensity of the weathering process depends on the constituent rocks and climate.

In the polar countries, frosty weathering is most actively manifested, in the temperate and humid tropics - chemical, in tropical deserts - mechanical.

Wind work. The wind can destroy rocks. Where rocky outcrops come to the surface of the earth, the wind bombards them with a grain of sand and, gradually erasing and destroying even the hardest rocks. Less resistant rocks are destroyed faster, specific, eolian landforms (figure on the right)- stone lace, aeolian mushrooms, pillars, towers.

dunes -these are crescent-shaped moving sandy hills. Their windward slope is always gentle (5-10°), and the leeward slope is steep - up to 35-40°. The formation of dunes is associated with the deceleration of the wind flow carrying sand, which occurs due to any obstacles - surface irregularities, stones, bushes, etc. The wind strength weakens, and sand deposition begins. The more constant the winds and the more sand, the faster the dune grows. The highest dunes - up to 120 m - were found in the deserts of the Arabian Peninsula.

The dunes move in the direction of the wind. The wind drives the grains of sand down a gentle slope. Having reached the ridge, the wind flow swirls, its speed decreases, the grains of sand fall out and roll down the steep leeward slope. This causes the movement of the entire dune at a speed of up to 50-60 m per year. Moving, dunes can fill up oases and even entire villages.

Dunesformed on sandy beaches . They stretch along the coast in the form of huge sandy ridges or hills up to 100 m or more high. Unlike dunes, they do not have a permanent shape, but can also move inland from the beach. In order to stop the movement of the dunes, trees and shrubs are planted, primarily pines.

The work of snow and ice. Snow has destructive power, especially in the mountains. Accumulating on the slopes, from time to time they break offslopes, forming snow avalanches. Such avalanches, moving at great speed, capture fragments of rocks and carry them down, sweeping away everything in their path.

The solid material that remains after the snow melts forms huge rocky mounds that block and fill intermountain depressions.

Doing even more work glaciers. They occupy vast areas on Earth - more than 16 million km 2, which is 11% of the land area.

There are continental, or integumentary, and mountain glaciers. Mainland ice covers vast areas in Antarctica, Greenland, and on many polar islands. The ice thickness of continental glaciers is not the same. For example, in Antarctica it reaches 4000 m. Under the influence of enormous gravity, the ice slides into the sea, breaks off, and forms icebergs- ice floating mountains.

At mountain glaciers are divided into two parts - areas of nutrition or accumulation of snow and melting. Snow is accumulating in the mountains above snow line. The height of this line is not the same in different latitudes: the closer to the equator, the higher the snow line. In Greenland, for example, it lies at an altitude of 500-600 m, and on the slopes of the Chimborazo volcano in the Andes - 4800 m.

Above the snow line, snow accumulates, compacts and gradually turns into ice. Ice has plastic properties and under the pressure of the overlying masses begins to slide down the slope. Depending on the mass of the glacier, its saturation with water and the steepness of the slope, the speed of movement varies from 0.1 to 8 m per day.

Moving along the slopes of the mountains, glaciers plow out potholes, smooth out rock ledges, and widen and deepen valleys. The detrital material that the glacier captures during its movement remains in place during the melting (retreat) of the glacier, forming a glacial moraine. Morena - these are piles of fragments of rocks, boulders, sand, clay left by the glacier. There are bottom, lateral, surface, middle and terminal moraines.

Mountain valleys, through which a glacier has ever passed, are easy to distinguish: in these valleys, the remains of moraines are always found, and their shape resembles a trough. Such valleys are called touches.

Work of flowing waters. Flowing waters include temporary rainfall and snowmelt, streams, rivers and groundwater. The work of flowing waters, taking into account the time factor, is grandiose. It can be said that the entire appearance of the earth's surface is to some extent created by flowing water. All flowing waters are united by the fact that they produce three types of work: destruction (erosion), transfer of products (transit) and them relation (accumulation). As a result, various irregularities are formed on the surface of the earth - ravines, furrows on slopes, cliffs, river valleys, sandy and pebble islands, etc., as well as voids in the thickness of rocks - caves.

As we already know, the earth's crust is mobile.

And this movement is determined by the movement of the substance of the mantle. As a result of such movement, mountains, oceanic depressions, and island arcs arise in the most mobile parts of the earth's crust. For stable areas of the earth's crust, flat surfaces are characteristic. All this we call the relief of the Earth.
Continents and oceans- the main, largest landforms of the Earth. Their formation is due to tectonic, cosmic and planetary processes.
The mainland (continent) is the largest massif of the earth's crust, which has a three-layer structure: a sedimentary layer, a "granite" layer and a "basalt" layer. The average thickness of the continental crust is 35-45 km. Most of the surface of the mainland protrudes above the level of the oceans. In the modern geological era, there are six continents: Eurasia, Africa, North America, South America, Australia, Antarctica.
The World Ocean is a continuous body of water surrounding the continents. The world ocean is divided by continents into four oceans: Pacific, Atlantic, Indian and Arctic. The share of land accounts for only 29% of the Earth's area. Everything else is the World Ocean.
Mountains and plains, as well as continents and oceans, are the main landforms of the Earth. Mountains are formed as a result of tectonic processes in zones of active tectonic activity, and plains - in areas that are little affected by mountain-forming processes.
Plains- large areas with a flat or hilly surface. They vary in height. An example of a lowland is the Amazonian lowland - the largest on Earth. It happens that the lowlands are located below sea level - these are depressions. The Caspian lowland is located 28 m below sea level. At an altitude of 200-500 m above sea level, there are uplands, for example, Central Russian, and above 500 m - plateaus. An example of such a plain is the Central Siberian Plateau.
Mountains- areas of the earth's surface elevated above sea level to a height of more than 500 m. Mountains are considered low if their height is from 500 to 1000 m; medium - from 1000 to 2000 m and high - over 2000 m. The highest mountain on Earth - Chomolungma (Everest) has a height of 8848 m. You can determine the height of the mountains on a physical map using the height scale.
Mountains differ not only in height, but also in shape. A linearly elongated group of mountains is called a mountain range. The mountains of the Caucasus have this shape.
There are also mountain belts (Andean belt), mountain systems (the system of mountains of Southern Siberia) and mountainous countries. Pamir is an example of a mountainous country.
Mountains and plains are located both on the continents and in the oceans. Mid-ocean ridges are an example of mountains in the ocean.
landform- the result of the struggle of internal and external forces. The internal forces of the Earth form large landforms: continents and oceans, mountains and plains. They not only form them, but also change and destroy them. External forces work constantly and slowly. They also destroy mountain ranges, fill deep depressions, form hills, valleys, gullies, ravines, form riverbeds, i.e., form smaller landforms.
The destruction and change of rocks under the influence of fluctuations in air temperature, moisture and living organisms is called weathering.
Here are some examples of weathering. In the mountains, these are landslides, landslides, mudflows, rockfalls, deep gorges cut by mountain rivers, and moraine deposits of glaciers. For plains, typical examples of weathering are ravines and river valleys.

They change quite quickly (a small ravine can appear in a few months), larger forms change slowly, over centuries. There are, however, factors (such as landslides) that can change the relief: mountains, clefts appear, and the direction of rivers changes. In the summer of 2007, one of these events did not happen: a landslide destroyed a unique geographical formation - a valley of geysers.

The relief changes under the influence of two types of factors: exogenous and endogenous. Endogenous (internal) factors: movements of the earth's crust, volcanic eruptions are discussed in detail in the relevant sections. Exogenous factors include: the destructive activity of wind and water, heat, flora and fauna.

Water has a serious impact on the relief. It erodes rocks, forming ravines, washing away entire hills, washing away rocks, which can then collapse. Rivers can become more full-flowing and lay a new course, or they can become shallow, and then land areas remain in place of the water. All of these are terrain changes. In addition, water interacts with rock materials, changing their composition and structure, which can lead to changes in topography.

The wind is especially active where there are no dense growths of plants. The wind blows away small particles of rock and brings them to other areas where they are deposited, lingering in water or plants.

Under the action of heat, many rocks are destroyed. Then, heating up, then, cooling back, they constantly expand and contract again. This leads to the destruction of the bonds between the molecules of the substance, the rocks crack.

Plants and animals also influence the formation of relief, some more strongly, others less. The roots of plants destroy dense rocks and at the same time strengthen looser ones. Microorganisms change the structure of the soil, which can also lead to a change in topography. Animals that build dams on rivers and streams, in particular, beavers, have a huge impact on the relief.

Basic landforms

1. Plains are flat or hilly areas of land that have a fairly large area. Plains differ in absolute height (above sea level):
2. Lowlands, the height does not exceed 200 m.
3. Elevations, height from 200 to 500 m.
4. Plateau, height over 500 m.
5. Plateau - a specific form of relief, having a flat top and steep edges, can reach 3 km.

Plains- more stable parts of the earth's surface, they are less likely, flat rivers are calmer, the relief changes much more slowly.

Mountains- land areas rising to a height of more than 500 m, with a certain peak and steep slopes.

Mountains can form ranges and highlands. Range - a group of mountains, obviously elongated in a certain direction and with a slight difference in height. famous mountain ranges.

Studying geography and topography, we are faced with such a concept as terrain. What is this term and what is it used for? In this article, we will deal with the meaning of this word, find out what types there are, and much more.

The concept of relief

So what does this term mean? The relief is a set of irregularities on the surface of our planet, which are composed of elementary forms. There is even a separate science that studies its origin, development history, dynamics and internal structure. It's called geomorphology. The relief consists of separate forms, that is, natural natural bodies, representing its individual parts and having their own dimensions.

Variety of forms

According to the morphological principle of classification, these can be either positive or negative. The first of them rise above the horizon line, representing an uplift of the surface. An example is a hillock, a hill, a plateau, a mountain, and so on. The latter, respectively, form a decrease relative to the horizon line. These can be valleys, beams, depressions, ravines, etc. As mentioned above, the relief form is composed of individual elements: surfaces (faces), points, lines (ribs), corners. According to the degree of complexity, complex and simple natural bodies are distinguished. Simple forms include mounds, hollows, hollows, etc. They are separate morphological elements, the combination of which forms a form. An example is a hillock. It is divided into such parts: sole, slope, top. A complex form consists of a number of simple ones. For example, the valley. It includes the channel, floodplain, slopes and so on.

According to the degree of slope, sub-horizontal surfaces (less than 20 degrees), inclined and slopes (more than 20 degrees) are distinguished. They can have a different shape - straight, convex, concave or stepped. According to the degree of strike, they are usually divided into closed and open.

Relief types

The combination of elementary forms that have a similar origin and extend over a certain space determines the type of relief. In large areas of our planet, it is possible to unite several separate species on the basis of a similar origin or difference. In such cases, it is customary to speak of groups of relief types. When the association is made on the basis of their formation, then one speaks of the genetic types of elementary forms. The most common types of land relief are flat and mountainous. In terms of height, the former are usually divided into depressions, uplands, lowlands, plateaus and plateaus. Among the latter, medium and low are distinguished.

flat relief

Which is characterized by insignificant (up to 200 meters) relative elevations, as well as a relatively small steepness of slopes (up to 5 degrees). The absolute heights here are small (only up to 500 meters). These areas (land, the bottom of the seas and oceans), depending on the absolute height, are low (up to 200 meters), elevated (200-500 meters), upland or high (over 500 meters). The relief of the plains depends primarily on the degree of ruggedness and soil and vegetation cover. It can be loamy, clayey, peaty, sandy loamy soils. They can be cut by riverbeds, gullies and ravines.

hilly terrain

This is a terrain that has a wavy character, forming irregularities with absolute heights up to 500 meters, relative elevations up to 200 meters and a steepness of not more than 5 degrees. The hills are often made of hard rocks, and the slopes and peaks are covered with a thick layer of loose rock. The lowlands between them are flat, wide or closed basins.

uplands

Mountain relief is a terrain that represents the surface of the planet, significantly elevated relative to the surrounding territory. It is characterized by absolute heights of 500 meters. Such a territory is distinguished by a diverse and complex relief, as well as specific natural and weather conditions. The main forms are mountain ranges with characteristic steep slopes, which often turn into cliffs and rocks, as well as gorges and hollows located between the ranges. The mountainous areas of the earth's surface are significantly elevated above the level of the ocean, while they have a common base that rises above the adjacent plains. They consist of many negative and positive landforms. According to the level of height, they are usually divided into low mountains (up to 800 meters), middle mountains (800-2000 meters) and high mountains (from 2000 meters).

relief formation

The age of elementary forms of the earth's surface can be relative and absolute. The first sets the formation of relief relative to some other surface (earlier or later). The second is determined by the relief is formed due to the constant interaction of exogenous and endogenous forces. So, endogenous processes are responsible for the formation of the main features of elementary forms, and exogenous, on the contrary, tend to equalize them. In relief formation, the main sources are the energy of the Earth and the Sun, and one should not forget about the influence of space. The formation of the earth's surface occurs under the influence of gravity. The main source of endogenous processes can be called the thermal energy of the planet, which is associated with radioactive decay occurring in its mantle. Thus, under the influence of these forces, the continental and oceanic crust was formed. Endogenous processes cause the formation of faults, folds, the movement of the lithosphere, volcanism and earthquakes.

Geological observations

Geomorphologists study the shape of the surface of our planet. Their main task is to study the geological structure and terrain of specific countries, continents, planets. When compiling the characteristics of a particular area, the observer is obliged to determine what caused the shape of the surface in front of him, to understand its origin. Of course, it will be difficult for a young geographer to understand these issues on his own, so it is better to turn to books or a teacher for help. Compiling a description of the relief, a group of geomorphologists must cross the study area. If you want to make a map only along the route of movement, then you should maximize the observation band. And in the process of research, periodically move away from the main path to the sides. This is especially important for poorly visible areas, where forests or hills obstruct the view.

Mapping

When recording information of a general nature (hilly, mountainous, rugged, etc.), it is also necessary to map and describe separately each relief element - a steep slope, ravine, ledge, river valley, etc. Determine the dimensions - depth, width, height, angles of inclination - often, as they say, by eye. Due to the fact that the relief depends on the geological structure of the area, when conducting observations, it is necessary to describe the geological structure, as well as the composition of the rocks that make up the studied surfaces, and not just their appearance. It is necessary to note in detail karst funnels, landslides, caves, etc. In addition to the description, schematic sketches of the study area should also be carried out.

According to this principle, you can explore the area near which your home is located, or you can describe the relief of the continents. The methodology is the same, only the scales are different, and it will take much more time to study the continent in detail. For example, in order to describe, you will need to create many research groups, and even then it will take more than one year. After all, the mainland mentioned is characterized by an abundance of mountains stretching along the entire continent, Amazonian virgin forests, Argentine pampas, etc., which creates additional difficulties.

Note to the young geomorphologist

When compiling a relief map of the area, it is recommended to ask local residents where you can observe the places where rock layers and groundwater come out. These data should be entered on the map of the area and described in detail and sketched. On the plains, rock is most often exposed in places where rivers or ravines have cut through the surface and formed coastal cliffs. Also, these layers can be observed in quarries or where a highway or railway passes through a cut-out recess. The young geologist will have to consider and describe each layer of the rock, it is necessary to start from the bottom. Using a tape measure, you can make the necessary measurements, which should also be entered in the field book. The description should indicate the dimensions and characteristics of each layer, their serial number and exact location.