Relief happens. Relief of Russia: characteristics, map, landscape, forms and mountain systems

RELIEF FORMS AND THEIR CLASSIFICATION

Under relief , as an object of study of geomorphology, is understood as the totality of all forms of the lithosphere surface (convexities, concavities and plains) of different geological structure and origin, located at different stages of development, in complex combinations with each other and in complex interactions with the environment.

It is now necessary to establish what are called its forms and elements, how forms can be classified and how they are formed.

DIFFERENT PRINCIPLES OF RELIEF CLASSIFICATION

Landforms can be subdividedAndt:

1) by external signs;

2) by complexity;

3) by size;

4) by origin (genesis).

The first three are of auxiliary importance, the last is the main one used in geomorphological studies.

1. Classification of landforms according to external features

    positive

    negative

    transitional, for example flat (horizontal).

In each group there are closed And open forms

the positive form represents a convexity; negative form – concavity.

Closed landforms those that are limited on all sides by slopes or lines (plantar, edge, watershed) are considered.

Examples. A mountain that has bounding slopes and a distinct plantar ridge.

A karst sinkhole, often clearly defined by a closed edge line.

Unclosed landforms usually lack slopes on one or even both sides.

Example. A ravine bounded on three sides by slopes with distinct edge lines.

Lines limiting landforms , are not always clearly visible on the ground.

Example. River valleys with gentle slopes of bedrock banks, gradually turning into interfluve spaces.

The slopes themselves are in this case elements of the river valley. Without clearly defined edges, they can be separated from watershed spaces through careful geomorphological studies.

2. Classification of landforms by complexity

Simple forms differ small in size, do not include other forms. Examples: mounds, gullies, etc.

Complex landforms can be various sizes and consist of various combinations of simple forms, often of different origins.

Example. Valleys of large rivers. Negative, open, complex landform. Includes a variety of simple forms and their complexes. Such forms are riverbed levees, river terraces (bedrock and alluvial), gullies and ravines on slopes, etc.

It is important to establish common concepts and terminology necessary when studying and describing the relief.

Below is a brief description of some positive and negative landforms most commonly found in nature*.

Positive landforms

Mound - an isolated hill with a sharply defined bottom line and a relative height of up to 50 m. Mounds are closed landforms built by humans.

Hill - an isolated dome-shaped, less often conical, hill with gentle slopes and a weakly defined plantar line. The tops of the hills are sharp, rounded and flat. The relative height of the hills is up to 200 m.

Hillock - an isolated dome-shaped hill with a clearly defined base line and a relative height of up to 100 m. In some cases, the shape of the mounds can be conical. The slopes of the mounds have a steepness of up to 25°, the tops are usually flat or slightly convex.

hummocks - small positive relief forms, similar to mounds, but having a height of no more than 1.0-1.5 m.

Uval - an elongated hill of considerable length (up to 10-15 km) with gentle slopes, flat or convex, and with a weakly defined plantar line. The apical surfaces of the ridges are flat or slightly convex. Ridges are closed relief forms, simple or complex, and have a relative height of up to 200 m.

Ridge - often a narrow, elongated hill with a slope steepness of 20° or more. The ridges have flat or rounded apical surfaces and sharply defined bottom lines. The relative height of the ridges is no more than 200 m. Ridges are closed relief forms, simple and complex.

Plateau - elevated plain, limited by well-defined slopes, often steep or complex in shape; it represents a complex, closed relief form. Usually the plateau is folded in horizontal layers. The surface of the plateau can be flat, wavy, hilly and often significantly dissected by negative relief forms.

Mountain - an isolated positive landform with a relative height of more than 200 m, mostly with steep slopes various shapes and a pronounced plantar line.

The summit surfaces of mountains can be

  • domed,

    pyramidal,

    conical, etc.

A mountain, which is a closed landform, can be

    simple and

    often complex.

One should distinguish from mountains “peaks” and “peaks,” which are the highest points in mountain ranges and highlands.

mountain range - an elongated hill of considerable length, with a relative height of more than 200 m and steep slopes. A sharply defined apical (surface) is called a ridge. Being a complex form of relief, the mountain range is often complicated by rocky outcrops on the ridge and slopes.

mountain ridge - a low mountain range with gentle slopes and a flat or slightly convex summit surface. Ridges often consist of several ridges, distinguished by denudation (Timansky Ridge, Donetsk Ridge).

Highlands - a very complex form of relief, highly elevated above sea level and adjacent spaces, includes complex systems of mountain ranges, peaks, etc. forms of mountain relief (Armenian, Philippine highlands).

Negative landforms

Hollow or drainage basin - an elongated depression with gentle slopes on three sides, usually covered with vegetation, open towards the general slope of the terrain. The edges of the hollows are usually unclear. The hollow is a simple, open form of relief and has a shallow depth (up to several meters) and insignificant length (up to 200-500 m).

Gulch - an elongated depression having a small depth (from 0.1 to 1-2 m) and width (from 0.3 to 4-5 m) and open towards the general slope of the area. The length of the ravine is insignificant (from 2-4 to 10-20 m); at the upper end the ravine closes. The slopes of the ravine are steep, bare and have a sharp edge. A ravine is one of the simplest landforms.

Ravine - an elongated depression, open, gradually expanding and sloping towards the general slope of the area. The slopes of the ravines are steep, vertical in places, devoid of vegetation and have a clearly defined edge. The depth of the ravines is up to 50 m, the length can reach several kilometers.

Beam - an elongated depression with gentle slopes covered with vegetation, open towards the general slope of the area. The bottom of the beam has a gentle slope, a gently concave transverse profile and is secured by vegetation. The edge of the slopes is clearly expressed. The length of the beams can reach several kilometers. The depth and width are different. Large beams represent complex landforms.

Valley - elongated, not closed (except in certain cases), with a slope in one direction - a complex form of relief. The slopes of the valleys have varying steepness and are often complicated by terraces, ravines, landslides and gullies. The bottom of the valleys can have different widths and is often complicated by ramparts, ridges, etc. The length of the valleys can reach hundreds and thousands of kilometers. When they meet, the valleys do not intersect, but merge into one common one. Valleys through which rivers flow are called river valleys, and those without rivers are called dry.

Basin or depression - a depression closed on all sides and having slopes of different steepness and shape. The shape and size of the basins can be different; Positive and negative relief forms often form on the bottom and slopes. Small basins with insignificant depth, gentle slopes and a flat or very slightly concave bottom are called saucers, or depressions.

Depressions and depressions can reach enormous sizes. The term “trench of the Atlantic (or Pacific, Indian) Ocean” was repeatedly used above. In this case, the basin will represent a part of the depression, isolated by underwater rises or groups of islands (North Pacific Basin, Somali Basin).

Gutters (deep-sea trenches) - narrow, highly elongated and deep depressions in the bottom of seas and oceans, which are usually places of greatest depth (Mariana, Philippine, Java and other trenches).

The above classification of landforms is called morphographic. It is based on the characteristics of the external features of relief forms, which are studied and described as completely as possible. However, from the above description of a number of forms it can be seen that often the same name is applied to forms of different sizes and origins. This is especially clearly seen in the example of basins and depressions, but can also be extended to other forms (for example, valleys and ridges). Thus, a more distinct division of landforms by size is necessary. The study of landforms in terms of their size is called morphometry.

The above morphographic classification partially contains morphometric data (for individual landforms, their approximate sizes are indicated), but they are random in nature and do not have a unified system. Considering the need for morphometric classification, a division of landforms by size is given as a possible option (with an attempt to link this division with relatively established terminology).

3. Classification of landforms by size

It is based on the morphometric principle.

    P planetary landforms .

    Horizontal dimensions are determined by millions of square kilometers.

    Vertically, the average difference in elevations between positive and negative landforms reaches 2500 - 6500 m, and the maximum is almost 20,000 m.

    Positive landforms are continents, negative landforms are ocean basins.

    It is advisable to identify transitional forms, which should include the continental shelf, shelf and continental slope.

2. Mega landforms .

    Horizontal dimensions are determined by tens and hundreds of thousands of square kilometers.

    The vertical difference in elevations between positive and negative relief forms reaches 500-4000 m, the maximum does not go beyond 11,000 m.

    Positive forms of relief - highlands, mountainous countries, underwater “swells” (Mid-Atlantic ridge, Hawaiian underwater ridge), extensive uplands (Volga region), etc.

    Negative: landforms - extensive depressions (Brazilian, Argentinean) and basins on the ocean floor, the Caspian lowland, etc.

    It is advisable to identify transitional forms - areas of continental shallows (for example, off the northern coasts of Asia and North America).

These landforms are clearly shown on small-scale maps.

3. m acroforms of relief .

    Horizontal dimensions are determined by tens, hundreds and thousands of square kilometers.

    Vertically, the difference in elevations between positive and negative landforms can reach 200-2000 m.

    Positive forms of relief are mountain ranges (Trialetsky, Chatkal), mountain nodes, peaks, individual mountains, etc.

    Negative - large valleys, depressions such as a lake depression. Baikal, some underwater trenches, etc.

4. m relief forms .

    Horizontal dimensions are determined by hundreds and thousands (less often hundreds of thousands) square meters.

    The relative height difference is up to 200-300 m, but is usually measured in meters and tens of meters.

    Positive forms of relief are hills, terraces in the valleys of large rivers and mountainous ones, etc.

    Negative forms of relief - fields and large karst sinkholes, ravines, ravines, basins of small lakes, etc.

These landforms are satisfactorily depicted on maps at a scale of 1:50,000; details can only be conveyed on larger scale maps.

5. Microforms of relief .

    The horizontal dimensions of these landforms are defined by square meters and hundreds of square meters.

    The relative height difference is measured in meters and less often in tens of meters.

    Positive landforms are small mounds, riverbed banks, mounds, road embankments, alluvial cones, etc.

    Negative forms - gullies, small ravines, karst sinkholes small sizes, road cuts, etc.

For accurate representation on maps, a scale of 1:10,000 and even 1:5000 is required.

6. Nanoforms of relief .

    Horizontal dimensions are determined by square decimeters and meters.

    The relative height is determined in decimeters, but can reach 1-2 m.

    On large-scale maps they are conveyed by conventional symbols and only in special cases can they be conveyed (individual forms) by contour lines of an additional section (1-0.5-0.25 m).

These forms of relief include hummocks, bite braids, potholes, small gullies, etc.

7. The smallest forms of relief (topographic roughness ) .

    Horizontal dimensions are determined by square centimeters and decimeters; for highly elongated forms they can reach square meters.

    The relative excess is measured in centimeters and sometimes decimeters.

They are not depicted on maps, but are noticeable during precise geodetic work. An example of such landforms is sand ripples, furrows in fields, etc.

If further, more fractional subdivision is necessary, the above classification of seven groups can be subdivided into more fractional parts (for example, average relief forms of the first, second, third, etc. order).

The above classifications of landforms clearly show that morphography and morphometry cannot provide a complete description of landforms, which is necessary for a geomorphologist.

Example. Depressions that have the same elements (deep point and faces - concave in profile and plan) and dimensions can be a karst sinkhole or the crater of a small volcano.

When characterizing depressions only in terms of shape, the same terminology can be used, and when depicting on a map, the same methods of representation can be used.

It is absolutely clear that this approach to depicting a karst sinkhole and volcanic crater is completely wrong, since it makes it possible to convey only the form, but does not reflect the origin, relationships with surrounding forms, geological structure, developing geological processes in a given territory, and the possible further development of the depicted forms relief. If we compare geological structure faces and bottom of the karst funnel with the faces and bottom of the crater, we will find fundamental differences in them.

A sinkhole forms in a layer of soluble rock. limestones, gypsum, etc.).

In the structure of the crater, on the contrary, rocks of igneous origin are observed, ejected during a volcanic eruption.

The origin of a sinkhole and a volcanic crater is also completely different.

A karst sinkhole was formed as a result of the chemical action of water on soluble rocks,

And the volcanic crater is the result of a violent manifestation internal energy the globe - an explosion of vapors and gases that had a high temperature and were under enormous pressure, etc.

From point of view relationships with other forms There are also certain differences between the sinkhole and the crater.

Karst sinkholes are usually located in groups, together with other karst landforms (fields, pits, caves, etc.),

And volcanic craters are found together with volcanic landforms (for example, lava flows) and various manifestations of the internal energy of the Earth (hot springs, geysers, etc.).

Minerals :

Having encountered a karst sinkhole, we can make the assumption that the area contains rocks that can be used as building materials (gypsum, limestone), but we do not receive any indication of the possible presence of other minerals.

In the area of ​​the volcano crater, you can count on finding deposits of volcanic tuffs, stone materials suitable for road construction, and some relatively valuable materials (agate, sulfur, sulfur compounds of various metals, etc.).

Soils and vegetation, developed on limestones and on volcanic rocks, will also be different.

Thus, outwardly identical landforms, but having different genesis, will indicate great differences in the natural situation in the area surrounding them. Such comparisons can be made for many relief forms, similar in outline, but different in genesis and internal structure.

Two terraces in a valley, rivers may have very similar external contours, but one of them may be structural and the other alluvial. The first one, composed of bedrock developed in the area, can serve as a place for extracting stones. building materials, and the second is to have large reserves of sand and pebbles.

The differences can be just as great between remnant and accumulative hills, etc.

The above comparisons clearly show that the external shape does not determine all the features of the relief.

When depicting a relief on a map and interpreting it on aerial photographs, it is important to clearly identify the shape so that the genesis of the relief can be determined to establish its main features and practical use.

Thus, To fully characterize the relief and correctly depict its forms on the map, you need to have a good knowledge of the processes of its formation and development.

Therefore, in addition to the examples already given above of classifying landforms according to external features (shape and size), it is necessary to analyze classification of landforms by genesis (origin), which has the most important practical and scientific significance.

4. Genetic classification of relief

The most common genetic classification is the division of forms earth's surface into three categories (I.P. Gerasimov).

When studying the relief in more detail, what comes to the fore is genetic classification, which is complemented morphographic features relief and the age of its forms. Based on their origin, landforms are divided into two large groups:

1) caused by the activity of internal (endogenous) forces;

2) caused by the activity of external (exogenous) forces.

The first, in turn, can be divided into:

a) landforms caused by movements earth's crust(mountain-forming, oscillatory);

b) landforms caused by magmatic (volcanic) processes.

The latter can be divided into relief forms caused by:

a) weathering processes;

b) the activity of flowing waters;

c) activities of groundwater;

d) sea activities;

e) activity of snow and ice;

f) wind activity;

g) development of permafrost;

h) the activities of organisms;

i) human activity.

IN general scheme in this classification the following are distinguished:

In each of these groups, relief forms created by certain exogenous processes are distinguished:

    erosive,

    glacial,

    gravitational,

    alluvial,

    proluvial.

With the combined influence of a number of processes, denudation relief is distinguished complex denudation landforms.

In relief analysis, the division into groups of denudation and accumulative forms is of particular importance.

Denudation surfaces in the Earth's topography, these are areas where demolition and denudation predominate. Their dominance is typical for areas of uplift of the earth's crust.

A cumulative surfaces typical for sagging or neutral areas.

Leveling surfaces are formed when hills are cut off by denudation and depressions are filled with destruction products. Typical in stable areas, in conditions of very weak, slow uplifts .

Denudation-accumulative forms are formed during the secondary occurrence of denudation in areas of accumulative relief (for example, alluvial fans strongly dissected by erosion).

Most relief-forming agents are characterized by destructive, transporting (carrying) and accumulative activities.

Hence, under the influence of the same geological agent, relief forms may arise due to the destruction and ablation of rocks, and relief forms due to the accumulation of the brought substance.

The destruction and transfer of matter composing the surface of the lithosphere, carried out by the entire set of external geological agents, means general term- denudation, and the relief forms caused by this process are called denudation.

These relief forms are further divided into forms caused by the destructive activity of water flows (rivers), and are called erosive.

forms caused by the destructive activity of the sea - abrasive etc.

Landforms resulting from the accumulation of matter are called accumulative and are divided into glacial, aeolian, etc.

Genetic, morphographic and morphometric classifications may be partly interrelated.

Determining the type of relief

Terrain type - certain combinations of relief forms that are regularly repeated over vast areas of the lithosphere surface and have a similar origin, geological structure and development history.

In this determination of the type of relief, the need arises combine types into larger units, For example into groups of relief types(group of types of mountainous relief, flat relief). Such a combination can be made according to various characteristics (for example, a group of glacial relief types).

Groups of relief types can be combined into units of a larger order(continental relief complex and ocean bottom relief complex, etc.).

When identifying and studying large relief complexes, it should be taken into account that one will have to operate with two unequal quantities. This is explained by the fact that the relief of land has been studied incomparably better than the relief of the bottom of the World Ocean.

When separating the relief of continents and the relief of the ocean floor into special complexes, the equivalent transitional relief complex, since the relief of the continents and the ocean floor is connected by a number of transitions, represented by the relief of the coasts, islands, peninsulas, the bottom of the seas located on the continental shallows, the relief of the shelf, the continental slope, the Mediterranean seas, etc.

Despite the wide variety of unevenness of the earth's surface, the main forms of relief can be distinguished: mountain, basin, ridge, hollow, saddle.

The top of the mountain, the bottom of the basin, and the saddle point are characteristic points of the relief; the watershed line of a ridge, the drainage line of a ravine, the line of the base of a mountain or ridge, the edge line of a basin or ravine are characteristic lines of the relief.

Classification

Landforms vary:

Planetary landforms

  • Geosynclinal belts
  • Mid-ocean ridges

Mega landforms

Macro relief forms

Individual ridges and depressions of a mountainous country Examples: Main Caucasus Range, Bzyb Range (Abkhazia)...

Mesoforms of relief

Microforms of relief

Nanoforms of relief

Examples: meadow tussock, surchin, small erosion grooves, ripple marks on the surface of aeolian forms or on the seabed.

Methods of depicting relief

The method of depicting the relief should provide a good spatial understanding of the terrain, reliable determination of the directions and steepness of slopes and marks of individual points, and the solution of various engineering problems.

During the existence of geodesy, several methods of depicting the relief on topographic maps. Let's list some of them:

  1. A promising way.
  2. Washing method. This method is used on small-scale maps. The surface of the Earth is shown brown: The more marks, the thicker the color. Sea depths are shown in blue or green: The greater the depth, the thicker the color.
  3. Hatching method.
  4. Marking method. With this method, marks of individual terrain points are marked on the map.
  5. Contour method.

Currently, on topographic maps, the method of contours is used in combination with the method of marks, and on one square decimeter of the map, as a rule, at least five point marks are labeled.

Notes


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Landforms of the Earth

Under relief refers to various irregularities or a set of forms of horizontal and vertical division of the earth's surface. Relief plays a huge role in the formation of landscapes. The nature of the flow, microclimate, distribution of soil and vegetation cover, and so on depend on the relief. In turn, the relief changes under the influence of these factors. Any form of relief, from a single hummock to a mountain range, does not remain unchanged. They are created and destroyed by the diverse and continuous processes operating on Earth.

Diverse landforms are classified in two directions: according to morphological and genetic characteristics.

By morphological classification takes into account the external features and dimensions of landforms without assessing their origin and relationship.

This classification is used in topography and cartography because topographic maps primarily show the external outlines and dimensions of various landforms. Morphological classification is used when first becoming acquainted with landforms in elementary school.

Genetic classification of landforms is made based on taking into account their genesis (origin), age, relationship and dynamics. This classification makes it possible to consider landforms, generalizing them into genetic series. Related forms may not be similar in appearance, but they represent links in the same chain, although they are at different stages of their development. For example, a small ravine, a ravine and clouds are very different in appearance and size, but they are all different stages of the development of a form caused by the water-erosion process.

Neither the morphological nor the genetic principle of classification can be completely “independent”. Any form of relief is associated with a variety of processes. When they talk, for example, about karst or glacial landforms, they only emphasize the predominant role of some factor. Any form of relief is the result of the combined activity of many natural processes.

According to morphological characteristics, the most elementary is the division of the land surface into mountains and plains. Inside both of them there are micro-, meso- and macroforms, as well as positive (convex) and negative (hollow) forms.

The most important positive forms are a hill, a mountain, a ridge, a highland, a plateau, and a plateau.

The most important negative forms are hollows, gullies, ravines, various valleys and depressions, canyons and others.

A relief that depends entirely on geological structure– on the composition of rocks, the forms of occurrence of their layers – is called structural. IN last years Humans begin to play a huge role in the formation of relief. For example, coal mining open method leads to the formation of ravines, the creation of communication routes in the mountains leads to a change in the appearance of mountainous countries. All this contributes to the formation of anthropogenic relief.

The solid earth's surface has irregularities of various orders. The greatest (planetary) landforms are oceanic trenches and continents. They are the main elements of the relief of the earth's surface, arising in the process of formation and uneven development of the earth's crust, and correspond to the continental oceanic types of its structure. Planetary relief elements are divided into second-order relief forms - megaforms. These include mountain structures and large plains. Within mega relief forms, macro relief forms are distinguished. These are mountain ranges, mountain valleys, depressions of large lakes, etc. On the surface of macroforms there are mesoforms - forms average size(hills, ravines) and microforms - small relief forms with height fluctuations of several meters or less (small dunes, gullies).

In order to depict the terrain on a plan or map, it is necessary to measure the height of various parts of our Earth. Absolute height called the elevation of a point on the earth's surface along a plumb line above sea level. In the Republic of Belarus, as in Russian Federation, absolute height is measured from the level of the Baltic Sea, taken as 0 meters. In the city of Kronstadt, located on one of the islands in the Baltic Sea, there is a footstock - a rail with divisions. The absolute height is measured from the zero of this foot rod. This height can be positive or negative. If a point lies above sea level, then its height is considered positive (hills, heights, mountains), and if below it is considered negative (ocean depressions). Points on land (Caspian Lowland) can also have a negative absolute height. On plans and maps, absolute height is indicated by a point, around which the number of meters is marked. This designation is called height mark. The difference in the absolute heights of the points shows relative height, that is, the elevation of one point on the earth's surface relative to another.

In different parts of the World Ocean, although they are all connected like communicating vessels, the levels are not the same. Thus, the ocean level near Kronstadt is 1.8 meters higher than the level of the Pacific Ocean near Vladivostok. There are several reasons for this; one of them is related to the processes occurring during the ebb and flow of the tides. For practical purposes, the average long-term level is used, which is taken as the initial level.

Main forms of mountainous landforms
Parts of the earth's surface that are highly elevated above the plains and strongly dissected are called mountains. They are delimited from the adjacent plains by a clear line of the base or have foothills - a transitional strip with lower altitudes than the mountains.

The mountains are very diverse. Most often they form mountainous countries, in which you can find peaks - individual mountains, noticeably rising above the general level of the mountainous country. For example, Elbrus in the Caucasus, Chomolungma in the Himalayas, Belukha in Altai. In the Sayan Mountains, Transbaikalia, on Far East mountains are often conical in shape with a flattened or rocky top. Such mountains are called hills. Special mountains formed as a result of long-term destruction are called small hills and are found, for example, in Central Kazakhstan. It is characterized by randomly scattered hills and small ridges of various shapes, sometimes with slightly pointed peaks and a wide base, with a relative height of 50 - 100 meters. They are separated by wide flat pits, often occupied by lakes, or valleys.

Typical for the relief of mountainous countries mountain ranges – mountain structures stretched over long distances with a well-defined axis in the form of a single watershed line, along which the highest altitudes are grouped. The mountain range has two slopes, they are often asymmetrical, often of different steepness. For example, in the Ural Mountains the eastern slope is steep and the western slope is gentle, which is explained historical development this mountainous country. The top part of the ridge is called mountain ridge. Depending on the age of the mountainous country and its geological structure, it varies: the peaks of young mountains are most often pointed, covered with glaciers, while those of old ones are rounded and plateau-like. Wide depressions with gentle slopes are called mountain passes. If a mountain range is not high and has soft, rounded peaks, then it is called a mountain ridge. Usually these are the remains of destroyed ancient mountains. For example, the Timan Ridge, the Yenisei Ridge and others.

A weakly dissected mountain uplift with a clearly defined base, approximately equally elongated in length and width, is called mountain range. For example, the Putorana plateau in Eastern Siberia. The area where two or more mountain ranges intersect is called mountain node. Usually the mountains in mountain nodes are high and difficult to access. An example is the Tabyn-Bogdo-Ola mountain junction in Altai. Mountain ranges, of the same origin, located in a single order, make up mountain systems. The lower edges of such mountain systems are called foothills. Many of Africa's mountains have flat tops and steep or stepped slopes. Such mountains are called table mountains. They most often arise when flowing waters dissect stratified plains; the peaks of such mountains are formed by durable sediments. The permanent covering of mountain tops with snow is called proteins(Altai), and the bare peaks located above the limits of vegetation are chars, which usually have a dome-shaped shape.

Mountains are divided into three groups according to their height:

Low mountains, or low mountains. Their absolute height is approximately 800–1000 meters. Such mountains usually have soft, rounded outlines and their altitudinal zonation is poorly defined. These are, for example, the Kazakh small hills, the Northern Urals, spurs of the Tien Shan, and individual ridges of Transcaucasia.

Medium-high, mountains or mid-mountain. They have an absolute height of up to 2000 meters. These mountains also, as a rule, have gentle outlines and rounded peaks. They are often densely covered with forests, have gentle slopes, and are covered with loose sediments - products of weathering. Such mountains rise above the snow line, so their peaks are rarely covered with snow. It is extremely rare that these mountains have pointed peaks, narrow and jagged ridges (Urals, Khibiny, Novaya Zemlya mountains).

High mountains, or highlands. The absolute height of these mountains is more than 2000 meters above sea level. Such mountains often rise above the snow line, and therefore their peaks are often covered with snow and glaciers. They have steep slopes and are bare in the upper parts, that is, not covered with loose sediments and devoid of vegetation. Their peaks are rocky, with many sharp ridges and peaks (Pamir, Himalayas, Andes, Cordillera, Pyrenees, Alps, Caucasus Mountains, Tien Shan and others).

Based on their origin, mountains can be divided into tectonic and volcanic. Tectonic mountains arose as a result of the movement of the earth's crust. In mobile zones of the earth's crust, most often at the edges lithospheric plates, rocks as a result of tectonic movements are crushed into folds of various sizes and steepness. This is how they are formed folded mountains. On land, folded mountains are a rare phenomenon, since when they rise above sea level, the folds of rocks lose their plasticity and begin to break, producing cracks with fold displacements. Typical mountains of this type have been preserved only in isolated areas in the Himalayas, which arose during the era of Alpine folding.

With repeated tectonic movements, when folds of rocks that have lost their plasticity and hardened undergo fractures into large blocks of the earth’s crust that rise or fall, folded - block mountains. This type is typical for old mountains. Thus, the folded mountains of Altai, which arose during the Baikal and Caledonian eras of mountain building, were again subject to tectonic movements during the Hercynian and Mesozoic eras of folding. During the Alpine folding, they turned into folded - block mountains, like many other mountain structures.

Volcanic mountains are composed of products of volcanic eruptions; they have a characteristic conical shape. They are located, as a rule, near fault lines or the boundaries of lithospheric plates, where active volcanism occurs.

Volcanic mountains form unique shapes when destroyed by external agents. Here, as in other mountains, powerful accumulations of rocks and stones are formed, and “stone streams” descend along the rocks. The difference is that the “rock flows” descend not only along the outer slopes of the cone, but also along the inner slopes of the crater. Below the snow line, the main destroyer is rainfall. They cut through potholes and ravines radiating from the edges of the crater along the internal (crater) and external slopes. These potholes are called barrancos. At first, the barrancos are numerous and shallow, but then their depth increases. As a result of the growth of the outer and inner barrancos, the crater expands, the volcano gradually lowers and takes the shape of a saucer surrounded by a more or less raised rampart. After the eruption, the volcanic cone rises again and takes on sharper shapes.

Erosion mountains can arise as a result of the dissection of plateaus and flat hills by rivers. An example of such mountains is the many interfluve mountains of the Central Siberian Plateau (Vilyuisky, Tungussky, Ilimsky and others). They are characterized by table shapes and box-shaped and sometimes canyon-shaped valleys. Much more often, mountains of erosion origin are observed within the middle mountains. But these are no longer independent mountain systems, but parts of mountain ranges that arose as a result of the dissection of these ranges by mountain streams and rivers.

The main factors that affect mountains that rise above the snow line are frost weathering and the work of snow and ice. The presence of steep slopes helps weathering products quickly roll down and expose the surface of rocks for further weathering. Winds play a major role in the destruction of high mountains, the speed of which greatly increases with height. Therefore, the winds here are capable of blowing away not only small particles, but also larger debris.

The variety of rocks that make up the mountains leads to uneven weathering. As a result, areas composed of stronger rocks turn out to be highly elevated above areas composed of less durable rocks. With further weathering, highly elevated areas take the form of sharp peaks, peaks and rocks. Highland landforms were first studied in the Alps. Therefore, all high mountains with sharp peaks, peaks, sharp jagged ridges, snow, ravines and glaciers began to be called alpine-type mountains.

In mountains of medium altitude, frost weathering plays a very small role. True, chemical and organic weathering occurs more intensely here, but the areas of distribution of this weathering are relatively small, since the slopes of the mountains are sloping - the weathering products remain in place and delay further weathering. Here the main destroyers are flowing waters. Mountains are characterized by a large number of rivers and all kinds of watercourses. Even in desert countries, mountains are always rich in water, because the amount of precipitation usually increases with height. Mountain rivers are usually distinguished by a large slope of their channels, rapid flows, and an abundance of rapids, cascades and waterfalls, which determines their great destructive power. This leads to the fact that the mountain slopes are cut through by a large number of transverse valleys. The upper reaches of mountain streams, cutting into the slopes, reach watershed ridges and meet the upper reaches of rivers on the opposite slope. Their valleys little by little connect and cut the ridges into pieces. As the rivers continue to flow, the mountain ranges break up into separate mountains, which in turn fall apart. In the end, instead of mountain ranges, as a result of the work of flowing waters alone, hilly countries can appear. The lower the mountains become, the more sedimentary their slopes become, and the rivers flowing from the slopes reduce their destructive power. However, they continue their work, depositing destruction products at the bottom of valleys and washing away slopes. Ultimately, mountains can be destroyed to the ground, and in their place a leveled, slightly hilly surface remains. Only rare isolated mountains, which are called remnant mountains or witnesses, can remind of the mountainous country that was once here.

The process of destruction occurs so quickly that if the mountains had not risen, they would have been destroyed to the ground within one or two geological periods. But this does not happen, since the growth of mountains under the influence of the internal forces of the Earth continues for a long time. For example, if the Ural Mountains, which arose as a high mountainous country at the end Paleozoic era, did not experience further uplifts, they would have disappeared long ago. When mountains are destroyed, it is possible that the rise of the mountains occurs more slowly than their destruction. Under these conditions, the height of the mountains will decrease. When the uplift of mountains occurs faster than destruction, then the mountains rise.

Plains
The word “plain” or the expression “flat place” is well known to everyone. Everyone knows that there are no absolutely flat places, that plains can have a slope, hills, and so on. In geography, flat areas mean vast spaces in which the heights of neighboring areas differ little from each other. An example of one of the most perfect plains is the West Siberian Lowland and especially its southern part. In the northern part, the West Siberian Lowland is hilly; here there are rises reaching 200 meters in absolute height. But not all plains have a table-level surface. For example, within the East European (Russian) Plain there are elevations of up to 300 meters or more in absolute height and depressions, the absolute height of which is below ocean level (Caspian Lowland). The same can be said about other large lowlands (Amazonian, Mississippian, Laplata and others).

The flat regions include not only lowlands, but also many plateaus: Central Siberian, Arabian, Deccan, Laplat and others. Due to the high absolute height, their surface is quite dissected by flowing waters. So far we have talked about fairly large plains. But besides them there are many smaller plains, located mainly along the banks of rivers, lakes, and the sea. The plains are not the same in character, structure and origin. Therefore, they are divided into groups according to certain characteristics. If we take absolute height as a basis, then the plains are divided into lowlands (from 0 to 200 meters), hills (up to 300 - 500 meters) and plateaus (over 500 meters). Depending on the relief, plains are classified as flat, sloping, bowl-shaped, wavy and others. However, the shape, character and many other features of the plain are determined by its origin. Therefore, when considering the plains of the globe, they are divided into groups based on genetic principles.

Vast plains emerging from sea level are called primary plains. They are composed predominantly of horizontally lying layers, which determine the basic shape of the surface of these plains, which gives grounds to call the primary plains structural. The most typical example of a young primary plain is the Caspian Lowland, which became land only at the end of the Quaternary period. Its surface is almost not dissected by rivers. Examples of more ancient primary plains are the East European Plain and the Central Siberian Plateau. They were formed in Mesozoic and even Paleozoic times. These plains have been greatly modified by subsequent processes. For example, the surface of the Central Siberian Plateau is strongly dissected by rivers, the valleys of which are strongly incised to a depth of 250 - 300 meters. Individual sections of the plateau dissected by rivers, depending on their size, have different names. Vast areas with a more or less flat surface are called plateaus. Smaller areas, depending on the height, are called mesas or mesas. The flat top surface of mesas is usually due to the more resistant rock of the upper strata (quartzite, lava sheets, etc.).

In addition to the primary plains, there are plains of other origins. Typically these plains have a significantly smaller area. Plains formed by sediments and deposits of river waters are collectively called alluvial plains. Alluvial plains are divided into river and delta plains. Plains are formed by deposits of loose materials. Brought by melted glacial waters, they are called fluvioglacial. If plains arise on the site of former lakes, then they are called lacustrine. These plains are flat lake bottoms that have disappeared as a result of rivers draining them or filling lake basins with sediment. Lowland cavities often form along the coasts of the seas. In some cases, these plains are obtained as a result of the accumulation of sediments (accumulative plains), in others they are caused by the abrasive activity of the sea (abrasion plains).

The erupted mafic lavas can form large, flat spaces called lava plateaus. Lava plateaus are difficult to destroy. The river valleys here have a canyon-like character. Subsequently, the plains expand, and the plateau is divided into table mountains. On vertical slopes you can often see the columnar structure of basalts. As a result of long-term destruction of mountains, leveled, slightly hilly surfaces, known collectively as leveled surfaces or peneplains, can form. Unlike plains formed by accumulation, these plains are composed of hard rocks, the occurrence of which can be very diverse. Low areas among the mountains are places where destruction products accumulate. As a result, vast elevated plains are formed, which are called highland plateaus (Gobi, Tibet and others).

At first glance, it may seem that groundwater cannot greatly influence the earth's surface. However, groundwater produces significant geological work. They dissolve salts, carry away small particles, and in some cases create underground channels. Although the activity of groundwater proceeds slowly, its results significantly affect the nature of the earth's surface.

Landslides and landslide relief. Sometimes landslide phenomena manifest themselves very clearly. For example, in 1839, the village of Fedorovka, located not far from Saratov, completely slipped towards the Volga. In 1884, in Saratov, part of the bank slid down to the river, and buildings located along the slope collapsed. Similar cases are often observed in other places, mainly along river banks. They are called landslides. The examples given refer to cases where sliding sections of the banks led to the destruction of buildings. In fact, landslides of banks and slopes are observed much more often. Traces of landslides can be observed on almost every river with high banks, especially if the banks are composed of clay. Landslide banks are uneven, stepped and, as it were, pitted with depressions of various sizes and shapes. In the depressions you can see springs, swamps and small lakes.

Landslides are most often caused by groundwater. If the rock layers that make up high banks or slopes have a certain slope, then groundwater will flow towards the slope. For large quantities groundwater(in rainy years) and in the presence of impermeable layers composed of clays, the overlying layers can break off and slide down the smooth, abundantly wetted clay surface. Precipitation also accelerates this process by saturating the soil with water and increasing its weight and mobility. When there is heavy rain, landslides can also occur in horizontally lying clayey rocks. Clay masses saturated with water slide easily due to their increased weight. A landslide usually has the shape of a semicircle, the open side of which faces the valley. The edges of the landslide protrude, and the bottom of the landslide usually declines toward the slopes. The bottom microrelief is usually very complex. The width of the semicircle (from cape to cape) can be very different - from several meters to a few kilometers. If landslide processes are very developed, then neighboring circuses merge, and a so-called landslide terrace is formed, which is characterized by the unevenness of its surface. Landslide phenomena make the construction of various structures very difficult.

Collapse forms. In thick layers of loose sediments (especially loess), with insignificant moisture, local soil subsidence can form. Melted snow waters here collect in depressions and slowly seep through the ground. At the same time, water dissolves salts and carries away small particles of water. As a result of this process, significant depressions are formed on the surface. The most common of them are pods or sedate “saucers”, which have a rounded shape with very gentle slopes. Their depth usually does not exceed 5–7 meters, and their width is 50–100 meters. Occasionally, steppe saucers up to several kilometers wide are found. Pods are widespread in Western Siberia, on the loess plains of Ukraine, in the Perekop steppe and other areas. If a river cuts through loess strata, then the underground waters that feed it work especially vigorously. As a result, chains of sinkholes appear on the surface along underground streams, and sometimes even failures can form. These forms are widespread in Central Asian regions.

Karst and karst landforms. Limestones, gypsum and other related rocks almost always have a large number of cracks. Rain and snow waters go deep into the earth through these cracks. At the same time, they gradually dissolve limestones and widen the cracks. As a result, the entire thickness of limestone rocks is penetrated by a large number of different passages.

Here, funnel-shaped depressions, natural wells and shafts, elongated but closed depressions of various sizes and shapes are striking. Such areas are called karst areas or simply karst. Karst areas are characterized by the absence surface waters, which causes poor vegetation development. In karst areas, underground rivers, powerful springs, small but deep lakes with clean water, and so on are widespread.

The main forms of relief characteristic of karst areas are: karsts, sinkholes, karst wells and mines, elongated closed basins (blind valleys) and caves.

Small streams of atmospheric water, flowing along the inclined surface of limestone, wash away weathering products and simultaneously dissolve the rock. As a result, narrow grooves are formed on the surface of the limestone, the depth of which varies from several centimeters to one to two meters. Areas covered with these grooves are called karrs, and large areas of karrs are called kar fields. Subsequently, the carr furrows deepen, the ridges separating the furrows break up into separate blocks. A similar “ruin” surface of limestone is characteristic of most karst areas of the globe.

Relief of the ocean floor
The main way to study the topography of the bottom of seas and oceans is to measure depths. The depths of shallow water basins are known to be measured using a simple lot. However, great depths of seas and oceans cannot be measured with such a lot, since the weight of the cable will be significantly more weight cargo The simplest instrument for measuring sea depths is Brook's lot. It consists of an iron tube onto which a weight is placed. As soon as the tube touches the bottom, the weight is automatically released and the tube floats, or is brought to the surface. Currently, the steel string on which the lot is attached is lowered using a special device called a depth gauge. The depth gauge will allow you to mechanically measure the length of the cable. The moment the lot touches the bottom, the meter automatically turns off and shows the depth. The lot tube captures the soil sample. At the same time, a thermometer placed in the tube records the bottom temperature of the water. The main disadvantage of measuring depth using lots is the length of the operation. For example, it takes about one hour to lower a lot to a depth of four kilometers, and about two hours to lower it to a depth of six kilometers. The lifting of the lot is done even more slowly, and each measurement requires the vessel to stand for a long time. Therefore, the method of measuring depths using an echo sounder is used. As you know, sound travels in water at a speed of about 1500 meters per second. If a strong sound is made on the surface of the water, then the sound wave, having reached the bottom, will be reflected and at the same speed will go to the surface of the water. By noting exactly the moment of sound occurrence and the moment of return of the reflected wave, it is easy to calculate the depth of a given place. This method of measuring depths requires very little time and measurements can be carried out without stopping the vessel. Currently, ultrasonic waves with a frequency of about 200,000 vibrations per second are used to measure depth. Ultrasonic waves are sent and captured using special instruments that automatically draw a detailed profile of the bottom along the ship's route. The echogram also makes it possible to get an idea of ​​the nature of the soil at the bottom of the sea. If the bottom is composed of silty soil, the lines of the echogram are wide, if the soil is hard, they are narrow.

List of used literature
1. A.A. Polovinkin “Physical Geography” State educational and pedagogical publishing house of the Ministry of Education of the RSFSR. Moscow - 1959;
2. N.S. Ratobylsky, P.A. Lyarsky “General geography and local history” Minsk “Higher School” - 1987.

Classifications of landforms

There are several classifications of landforms of the Earth, having different bases. According to one of them, two groups of relief forms are distinguished:

  • positive - convex in relation to the horizon plane (continents, mountains, hills, hills, etc.);
  • negative - concave (oceans, basins, river valleys, ravines, gullies, etc.).

The classification of landforms of the Earth by size is presented in Table. 1 and in Fig. 1.

Table 1. Landforms of the Earth by size

Rice. 1. Classification of the largest landforms

Let us separately consider the relief forms characteristic of the land and the bottom of the World Ocean.

Relief of the Earth on the World Map

Landforms of the ocean floor

The bottom of the World Ocean is divided by depth into the following components: continental shallows (shelf), continental (coastal) slope, bed, deep-sea (abyssal) basins (trenches) (Fig. 2).

Mainland Shoal- the coastal part of the seas and lying between the coast and the continental slope. This former coastal plain is expressed in the topography of the ocean floor as a shallow, slightly hilly plain. Its formation is mainly associated with the subsidence of individual land areas. This is confirmed by the presence within the continental shallows of underwater valleys, coastal terraces, fossil ice, permafrost, remains of terrestrial organisms, etc. Continental shallows are usually distinguished by a slight bottom slope, which is practically horizontal. On average, they decrease from 0 to 200 m, but within their limits there can be depths of over 500 m. The relief of the continental shallows is closely related to the relief of the adjacent land. On mountainous coasts, as a rule, the continental shelf is narrow, and on flat coasts it is wide. The continental shelf reaches its greatest width off the coast of North America - 1400 km, in the Barents and South China Seas - 1200-1300 km. Typically, the shelf is covered with clastic rocks brought by rivers from land or formed during the destruction of coastlines.

Rice. 2. Relief forms of the ocean floor

Continental slope - inclined surface the bottom of the seas and oceans, connecting the outer edge of the continental shallows with the ocean bed, extending to a depth of 2-3 thousand m. It has fairly large angles of inclination (on average 4-7°). The average width of the continental slope is 65 km. Off the coast of coral and volcanic islands, these angles reach 20-40°, and near the coral islands there are angles of greater magnitude, almost vertical slopes - cliffs. Steep continental slopes lead to the fact that in areas of maximum bottom inclination, masses of loose sediments slide to the depths under the influence of gravity. In these areas, a bare slope or muddy bottom may be found.

The relief of the continental slope is complex. Often the bottom of the continental slope is cut by narrow deep gorges-canyons. They are often found near steep rocky shores. But there are no canyons on continental slopes with a gentle slope of the bottom, and also where outside On the mainland shallows there are stumps of islands or underwater reefs. The tops of many canyons are adjacent to the mouths of existing or ancient rivers. Therefore, canyons are considered as an underwater continuation of flooded river beds.

Another characteristic element of the relief of the continental slope is underwater terraces. These are the underwater terraces of the Sea of ​​Japan, located at depths from 700 to 1200 m.

ocean bed- the main space of the bottom of the World Ocean with prevailing depths of more than 3000 m, extending from the underwater edge of the continent into the depths of the ocean. The area of ​​the ocean floor is about 255 million km 2, i.e., more than 50% of the bottom of the World Ocean. The stock has slight angles of inclination, on average they are 20-40°.

The relief of the ocean floor is no less complex than the relief of the land. The most important elements of its relief are abyssal plains, oceanic basins, deep-sea ridges, mid-ocean ridges, hills and submarine plateaus.

IN central parts oceans are located mid-ocean ridges, rising to a height of 1-2 km and forming a continuous ring of uplifts in the Southern Hemisphere at 40-60° S. w. Three ridges extending northward from it extend meridianally in each ocean: the Mid-Atlantic, Mid-Indian and East Pacific. The total length of the mid-ocean ridges is more than 60 thousand km.

Between the mid-ocean ridges there are deep-sea (abyssal) plains.

Abyssal plains- flat surfaces of the bottom of the World Ocean, which lie at depths of 2.5-5.5 km. It is the abyssal plains that occupy approximately 40% of the ocean floor area. Some of them are flat, others are undulating with a height range of up to 1000 m. One plain is separated from the other by ridges.

Some of the single mountains located on the abyssal plains protrude above the surface of the water in the form of islands. Most of these mountains are extinct or active volcanoes.

Chains of volcanic islands above a subduction zone, occurring where one oceanic plate subducts beneath another, are called island arcs.

In shallow waters in tropical seas (mainly in the Pacific and Indian oceans), coral reefs form - calcareous geological structures formed by colonial coral polyps and certain types of algae that can extract lime from sea water.

About 2% of the ocean floor is occupied deep-sea (over 6000m) depressions - trenches. They are located where oceanic crust subducts beneath continents. These are the deepest parts of the oceans. Over 22 deep-sea depressions are known, of which 17 are located in the Pacific Ocean.

Landforms

The main landforms on land are mountains and plains.

Mountains - isolated peaks, massifs, ridges (usually more than 500 m above sea level) of various origins.

In total, 24% of the earth's surface is mountainous.

The highest point of the mountain is called mountain peak. The highest mountain peak on Earth is Mount Chomolungma - 8848 m.

Depending on the height, mountains are low, medium, high and highest (Fig. 3).

Rice. 3. Classification of mountains by height

The highest mountains of our planet are the Himalayas, examples of high mountains are the Cordillera, Andes, Caucasus, Pamir, middle ones are the Scandinavian Mountains and the Carpathians, low ones are the Ural Mountains.

In addition to the mountains mentioned, there are many others on the globe. You can get acquainted with them from the atlas maps.

According to the method of formation, the following types of mountains are distinguished:

  • folded - formed as a result of the folding of a thick layer of sedimentary rocks (mainly formed during the Alpine era of mountain building, which is why they are called young mountains) (Fig. 4);
  • blocky - formed as a result of the rise of hard blocks of the earth's crust to a great height; characteristic of ancient platforms: the internal forces of the Earth split the rigid foundation of the platforms into separate blocks and raise them to a considerable height; as a rule, ancient or revived) (Fig. 5);
  • folded-block mountains are old folded mountains that were largely destroyed, and then, in new periods of mountain building, individual blocks of them were again raised to great heights (Fig. 6).

Rice. 4. Formation of folded mountains

Rice. 5. Formation of old (block) mountains

Based on their location, epigeosynclinal and epiplatform mountains are distinguished.

Based on their origin, mountains are divided into tectonic, erosional, and volcanic.

Rice. 6. Formation of folded-block renewed mountains

Tectonic mountains- these are mountains that were formed as a result of complex tectonic disturbances of the earth’s crust (folds, thrusts and various types of faults).

Erosion mountains - highly elevated plateau-like regions of the earth's surface with a horizontal geological structure, strongly and deeply dissected by erosion valleys.

Volcanic mountains - These are volcanic cones, lava flows and tuff sheets, distributed over a large area and usually superimposed on a tectonic base (on a young mountainous country or on ancient platform structures, such as the volcanoes of Africa). Volcanic cones are formed by accumulations of lava and rock fragments erupted through long cylindrical vents. These are the Maoin mountains in the Philippines, Mount Fuji in Japan, Popocatepetl in Mexico, Misti in Peru, Shasta in California, etc. Heat cones They have a structure similar to volcanic cones, but are not so high and are composed mainly of volcanic scoria - porous volcanic rock that looks like ash.

Depending on the areas occupied by mountains, their structure and age, mountain belts, mountain systems, mountainous countries, mountain ranges, mountain ranges and uplifts of a smaller rank are distinguished.

mountain range called a linearly elongated positive form of relief, formed by large folds and having a significant extent, mostly in the form of a single watershed line, along which the most
significant heights, with clearly defined ridges and slopes facing in opposite directions.

Mountain chain- a long mountain range, elongated in the direction of the general strike of the folds and separated from adjacent parallel chains by longitudinal valleys.

Mountain system- a collection of mountain ranges, chains, formed during one geotectonic epoch and having spatial unity and a similar structure, uplands(extensive mountain uplifts, which are a combination of high plains, mountain ranges and massifs, sometimes alternating with wide intermountain basins) and intermountain depressions.

Mountain country- a set of mountain systems formed in one geotectonic era, but having different structure and appearance.

Mountain belt- the largest unit in the classification of mountainous relief, corresponding to the largest mountain structures, united spatially and according to the history of development. Usually the mountain belt extends for many thousands of kilometers. An example is the Alpine-Himalayan mountain belt.

Plain- one of essential elements relief of the surface of the land, the bottom of the seas and oceans, characterized by small fluctuations in heights and slight slopes.

The formation diagram of the plains is shown in Fig. 7.

Rice. 7. Formation of plains

Depending on the height among the plains, the land is divided into:

  • lowlands - having an absolute height from 0 to 200 m;
  • elevations - no higher than 500 m;
  • plateaus.

Plateau- a vast area of ​​relief with a height of 500 to 1000 m or more with a predominance of flat or slightly undulating watershed surfaces, sometimes separated by narrow, deeply incised valleys.

The surface of the plains can be horizontal or inclined. Depending on the nature of the mesorelief complicating the surface of the plain, flat, stepped, terraced, wavy, ridged, hilly, hilly and other plains are distinguished.

Based on the principle of the predominance of existing exogenous processes, the plains are divided into denudation, formed as a result of the destruction and demolition of pre-existing terrain irregularities, and accumulative, resulting from the accumulation of thick layers of loose sediments.

Denudation plains, the surface of which is close to the structural surfaces of a slightly disturbed cover, are called reservoir.

Accumulative plains are usually divided into volcanic, marine, alluvial, lacustrine, glacial, etc. Accumulative plains of complex origin are also common: lacustrine-alluvial, deltaic-sea, alluvial-proluvial.

The general features of the relief of planet Earth are the following:

Land occupies only 29% of the Earth's surface, which is 149 million km 2. The bulk of the landmass is concentrated in the Northern Hemisphere.

The average height of the Earth's land is 970 m.

On land, plains and low mountains up to 1000 m high predominate. Mountain elevations above 4000 m occupy an insignificant area.

The average depth of the ocean is 3704 m. The topography of the bottom of the World Ocean is dominated by plains. Deep-sea trenches and trenches account for only about 1.5% of the ocean's area.

The totality of the irregularities of the earth's surface form it relief. Landforms vary in size, origin, and development history. The relief of the earth, or more correctly, the earth's surface, is the result of a complex interaction of internal and external forces. Internal forces, the energy of which is provided by the internal energy of the Earth itself, create large irregularities. External forces smooth out these irregularities, creating smaller irregularities.

The largest landforms of the Earth- ridges of continents and depressions of oceans. Their distribution is determined by the structure of the earth's crust - the presence or absence of a granite layer. There are currently six continents on Earth. Land on the Earth's surface is distributed unevenly. We can distinguish two conventional hemispheres on the planet - oceanic and continental. In the center of the first is located Pacific Ocean, in the center of the second is Africa. The prevailing heights within the land are about 800 m, the average depths of the ocean are about 3500 m. The surface of the land and the ocean bottom is complicated by lower-order irregularities.

The main landforms are mountains and plains. About 60% of the land surface is occupied plains. These are vast areas of the earth's surface with small fluctuations in heights (about 200 m), relatively low elevated above sea level. According to absolute height, the plains are divided on lowlands (height from 0 to 200 m), hills (200-500 m) and plateaus (above 500 m). By the nature of the surface- flat, hilly and stepped. Lowland areas are the most populated and developed by people. Most cities and transport routes and the main tracts of cultivated land are concentrated on them.

They call them mountains distinct elevations on the earth's surface with heights of more than 200 m, with well-defined slopes and bases. Mountainous regions occupy about 40% of the land surface. Most of the mountains on Earth stretch in mutually perpendicular directions, close to sublatitudinal or submeridional. By height, mountains are divided into low (with altitudes up to 1000 m), medium altitude (1000-2000 m) and high (over 2000 m). According to the structure of mountains there are folded, folded - blocky and blocky. According to geomorphological age, they distinguish young, rejuvenated and reborn mountains. Mountains of tectonic origin predominate on land, while mountains of volcanic origin predominate in the oceans.

Within the land, the distribution of mountainous and lowland areas is determined by the structure of the earth's crust. On the platforms, due to the horizontal occurrence of rocks, there are plains. In folded areas, rocks occur in the form of folds, and in the relief they correspond to mountains.

The structure of the earth's crust determines not only the relief, but also the placement of mineral resources. Minerals of sedimentary origin (oil, gas, coal, salts) are concentrated in the sedimentary rocks of the platform cover. Minerals of igneous origin - in folded areas and crystalline platform basements. The greatest variety of minerals is characteristic of ancient platforms.

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