What is relief? Let's define the concept. What is relief - definition

RELIEF (French relief, from Latin relevo - I raise), a set of forms of the earth's surface, differing in shape, size, origin, history of development. The relief is formed mainly as a result of a long-term simultaneous impact on the earth's surface of tectonic, volcanic and other processes, the activity of water, wind, sun, glaciers, etc. The development and formation of the relief is studied by geomorphology.

Modern Encyclopedia. 2000 .

See what "RELIEF" is in other dictionaries:

relief- a, m. relief m. 1. Convex image on a plane. BAS 1. The hall of four tiers is decorated with bulges (reliefs) from the best dramatic contents. 1821. Sumarokov Walk 2 40. I admired the Chinese furniture.. with reliefs and wooden… … Historical Dictionary of Gallicisms of the Russian Language

- (French relief, from Latin relevo I raise), a sculptural image on a plane. Inseparable connection with the plane, which is physical basis and the background of the image, is specific feature relief as a type of sculpture. Art Encyclopedia

- (fr. relief, from lat. relevare to raise, elevate). Convex image; sculptural works, more or less convex. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. RELIEF 1) convex sculptural images ... ... Dictionary of foreign words of the Russian language

- (French relief, from Latin relevo I raise), a set of irregularities of the earth's surface, different in shape, size, origin, age and history of development. It is composed of positive forms that form elevations, and negative ones, ... ... Ecological dictionary

- (French relief from Latin relevo I raise), a set of uneven land, the bottom of the oceans and seas, various in shape, size, origin, age and history of development. It is composed of positive (convex) and negative (concave) forms ... Big Encyclopedic Dictionary

RELIEF, relief, male. (French relief). 1. Convex image on a plane (special). Reliefs are weakly convex bas-reliefs and strongly convex high reliefs. 2. The structure of the earth's surface (geographic, geol.). Rugged terrain. Mountain ... ... Dictionary Ushakov

- [fr. relief bulge] the totality of all forms of the earth's surface for each specific area and the Earth as a whole. It is formed as a result of mutual influence on the earth's crust endogenous and exogenous processes. There are R. of different orders, ... ... Geological Encyclopedia

Panel, topography, landscape, bas-relief, mascaron, high relief Dictionary of Russian synonyms. relief n., number of synonyms: 19 bas-relief (2) ... Synonym dictionary

A set of irregularities on the surface of the land, the bottom of the oceans and seas, diverse in shape, size, origin, age and history of development. It is one of the main elements of the terrain that determines its tactical properties. Relief ... ... Marine Dictionary

relief- RELIEF, a, m. Figure, forms (about the body). Swing (or work on) relief to build muscle. from sports... Dictionary of Russian Argo

Books

• , Krasnov A.N.. Relief, vegetation and soils of Kharkov province Geotectonics and relief of Kharkov vegetation, surface morphology, soils, vegetation (including weeds) are considered.…
• Relief, vegetation and soils of the Kharkov province, Krasnov A.N. This book will be produced in accordance with your order using Print-on-Demand technology. Relief, vegetation and soils of the Kharkov province The geotectonics and relief of the Kharkov ...

The totality of uneven dry and hard surfaces of the earth is commonly called relief. The word relief, which is French in origin, in Latin sounds like "relevo", which means "raise" in translation. What is relief? Consider this concept in a geographical definition.

The relief consists of relief forms, which have a variety of sizes in relation to the horizontal plane and are divided into positive and negative. Elevations above the horizon line are considered positive forms of relief, for example: hills, mountains, mounds, plateaus. Negative forms form depressions of a solid surface, for example: depressions, valleys and ravines.

Origin of relief

There is a concept of "relief formation agents", which describes the processes that affect the formation of relief. These processes form and develop the relief, affecting the surface of the Earth for a long time, both from the inside and from the outside. Internal impact(endogenous) is due to the energy of heat emanating from the bowels of the Earth and affecting the movement of the crust, as a result of which faults and magmatisms, folds and movement of blocks of the earth's crust are formed. Exogenous impact or external is due to the energy of the Sun.

Radiant energy on the Earth's surface is converted into the energy of water, air and other substances of the lithosphere. In fact, the external processes of relief formation are influenced by many various factors, such as the impact of the water masses of the oceans, lakes, seas, reservoirs and flowing streams, gusts strong wind, dissolution of ice blocks and other rocks, as well as economic activity people or animals. The formation of bulges and depressions of various shapes and sizes on the earth's surface directly depends on all these processes.

Relief categories

Sharp and gradual changes in the surface of the Earth, such as high mountain ranges, small hills and valleys, as well as deep depressions on the bottom of the oceans and seas, imply the presence of different categories of relief:

• Mega-reliefs. They differ in their globality. This is the ocean floor and protrusions of the continents, which even at first glance show us sharp and rather large-scale changes in the surface of the earth's crust.
• Macroreliefs. They do not differ in significance, but are slightly inferior in size to mega-reliefs and represent strong depressions or elevations in relation to the horizon line.
• Mesoreliefs. They differ in the scale of surface drops and occupy an intermediate step between macrorelief and microrelief.
• microreliefs- is relatively small relief surfaces such as canyons, valleys, gorges, steppe fields and plains. Even the smallest changes in the Earth's surface affect the formation of relief. The concept of nanorelief characterizes such minor differences in the surface as anthills or minks of various sizes.

Geomorphology is a science that studies all the internal and external processes of the Earth that affect the formation, formation and modification of the relief.

How terrain affects human life

Much depends on the relief, for example, climate, air temperature, the presence of water and vegetation (mountains, deserts, oases). It is with theoretical knowledge about the nature of the relief that people can find out all the necessary information about a particular continent or country. Also, knowledge about all the features of the relief helps people choose a place for settlement, build factories, factories, houses, build entire cities and build highways.

How does a person influence the formation of relief

Human activity is truly limitless and very large-scale. Thus, using specialized equipment and special equipment, people began to independently change the relief. The process of extracting minerals from the bowels of the Earth, pumping out gas, sand, water, construction and filling artificial reservoirs and reservoirs not only greatly change hard surfaces, but also adversely affect natural reliefs. As a result of such actions, individual layers of the Earth die, and earthquakes occur, which sometimes have a strong destructive effect on all living things.

And so, the definition of what a relief is can be described as a modification of the earth's surface in one direction or another, that is, a set of depressions and protrusions (irregularities) in relation to the horizon line, differing in principle of origin, size, shape and age.

Relief - this is a set of irregularities of the land surface and the bottom of the World Ocean, diverse in shape, shape, size, origin, age, etc.

Relief classification according to size :

1. Megarelief is planetary forms: continental protrusions, ocean beds, mountain systems, flat areas of platforms, mid-ocean ridges.

2. Macrorelief - these are mountain ranges, intermountain depressions, individual mountains, uplands, lowlands.

3. Mesorelief - these are medium landforms: ravines, hills, river valleys, dunes, dunes, hollows, hollows.

4. Microrelief - these are karst funnels, steppe saucers, channels of medium and small rivers, mounds, erosion furrows.

5. Nanorelief - these are the smallest depressions, depressions, swampy bumps, anthills, burrows of digging animals.

By genesis (origin) the following types of relief can be distinguished:

1. Geotecture - these are landforms created by endogenous processes (protrusions of the continents, depressions of the oceans, mountain structures, plains).

2. Morphostructure - these are landforms that have formed during the interaction of endogenous and exogenous processes, but with the leading role of endogenous ones (mountain ranges, intermountain depressions, uplands, lowlands).

3. Morphosculpture - these are landforms formed by exogenous processes (river valleys, karst sinkholes, ridges of moraine deposits, etc.).

Relief formation factors :

1. Space:

a) mountain building cycles associated with the position solar system in the galaxy;

b) high and low tides associated with the gravity of the Sun and the Moon (in the ocean, water rises by 1 m, near the coast up to a maximum of 18 m, land rises by 0.5 m).

2. Terrestrial endogenous (as a rule, they create ascending landforms):

a) land fluctuations;

b) mountain-building movements (fold-forming and discontinuous);

c) volcanism;

d) earthquakes;

e) movement of lithospheric plates.

3. Terrestrial exogenous (create mainly descending landforms):

a) weathering - physical, chemical, biological;

c) flowing waters - underground, surface;

d) glaciers.

4. Anthropogenic - landforms created with the participation of man (road embankments, waste heaps, waste rock dumps, quarries, etc. - up to the appearance of ravines as a result of economic activity).

Planetary relief of the Earth. The total area of ​​the continents is 2.4 times less than the area of ​​the World Ocean, and about the same number of times the specific gravity of their rocks is greater than the specific gravity of oceanic waters. Continents and water on Earth are antipodes. The planetary relief is formed under the action of endogenous forces. It should also be taken into account that this is the relief of a rotating body. An increase or decrease in the speed of the Earth's rotation affects the movement of lithospheric plates and, ultimately, the emerging relief. The speed of the Earth's axial rotation does not remain constant. Compression of the Earth and reduction of its volume, as a consequence of this compression, accelerates the rotation of the planet, and tidal friction slows it down. But the action of tidal friction turns out to be predominant, and therefore the speed of axial rotation, in general, becomes less. At the same time, the northern hemisphere rotates more slowly than the southern one. This explains the difference in the distribution of continents and oceans over the hemispheres: in the northern hemisphere, land prevails, in the southern - water; in addition, the southern continents are displaced in relation to the northern ones to the east (meridian skew).

The study of the planetary relief leads to the conclusion that there is a regular relationship between the areas of the continents (oceans) and their average height (depth), as well as the thickness of the crust and the energy of tectonic activity. The larger the area of ​​the mainland, the higher it is and the more powerful the crust. Thus, the area of ​​the largest continent - Eurasia - is about 54 million km 2, the average height is almost 700 m, the maximum height is 8848 m; the area of ​​​​the smallest continent - Australia - 9 million km 2, the average height is 400 m, the maximum is 2234 m.

Similarly: than more ocean, the deeper it is and the thinner the bark under it. The average land height is 870 m, and the ocean depth is 3800 m.

If we build a generalized profile of the Earth - a hypsographic curve, then there will be 2 steps on the globe: continental and oceanic. These steps include:

The largest area on Earth is occupied by the "ocean bed" stage - 204 million km 2 (and the entire ocean has an area of ​​361 million km 2).

The two steps of the curve correspond to two types of crust: continental and oceanic. Geotectures of the 1st order are the continents and the ocean basins.

The maximum thickness of the crust under the mountains is 60-70 km, the minimum is 5-15 km under the ocean, and the average is 30-40 km under the plains. The observed pattern is explained by isostasy (the same weight), i.e. the desire of the earth's crust to balance in spite of the processes that violate it. An excess of mass on the surface corresponds to a lack of it at some depth, and vice versa. The mountains have a more powerful crust, composed of light rocks, the oceanic crust is heavier (the mantle comes close here).

The destruction of the mountains upsets the balance. Under the destroyed mountains, the mantle begins to rise, press on the earth's crust, and balance is restored. The formation of a powerful ice cover leads to the deflection of the earth's crust, and its melting leads to straightening and uplift. Under Antarctica, the earth's crust has sunk by about 700 m, and in the central parts it is bent below the level of the World Ocean (approximately the same is observed in Greenland). The fact that the release from the ice cover is accompanied by uplift is convinced by an example: the Scandinavian Peninsula is rising at a rate of 1 cm/year, and just after the glacier melted it was 30 cm/year. The Scandinavian peninsula should rise about 100 m more until full equilibrium. The Baltic Sea and Hudson Bay are the remnants of a trough caused by the weight of the glacier (in a few tens of thousands of years they should probably disappear).

Thus, the average height of the continent and the average depth of the oceans are evidence of a certain thickness of the crust and its “floating” or “immersion” into the substance of the upper mantle. Under existing conditions, the average thickness of the crust should not be more than 50 km, and that of the ocean should not be thinner than 5 km. Isostatic equilibrium is carried out in the asthenosphere (in the mantle), because the asthenosphere has the lowest viscosity of all the earth's layers.

Land relief (morphostructural macrorelief). The main elements of land relief are mountains and plains. Mountains occupy about 40% of the land, and plains about 60%. Mountains and plains on the surface of the continents correspond to the main structural elements of the continental (continental) crust: mobile (orogenic) belts and relatively stable parts of it - platforms. Orogenic belts and platforms are geotectures of the second order (after the protrusions of the continents and the depressions of the oceans).

Mountains are vast, highly elevated above the ocean level and highly dissected areas of the earth's surface. Plains are vast areas of the earth's surface with small elevation fluctuations and slight slopes.

The mountains. The term "mountains" (from the Greek "oros" - mountain - "orogens") is synonymous with "mountain country", "mountain system". Mountains are one of the landforms. From the point of view of the genesis of the relief, mountains belong to the categories of geotecture (mountainous countries, structures) and morphostructures (mountain ranges, individual mountains, intermountain depressions, etc.).

A mountain is a positive landform that rises in isolation above a relatively flat area by at least 200 m. (A positive landform with a relative height of less than 200 m is called a hill).

Mountains are characterized by the following elements: peak - the highest part of the mountain; sole - the line of transition from the slope of the mountain to the plain; mountain range - a linearly elongated positive landform; the crest of the ridge is the highest part of it; the lowest sections of the mountain range are called mountain passes (wide passes are called saddles, and deeply incised - mountain passes). Crossing, mountain ranges form mountain nodes (for example, Pamir). A mountainous country, consisting of mountain ranges and relatively flat areas of the earth's surface located high above sea level, is called highlands.

Height dependent mountains can be distinguished:

1) low - up to 1000 m (Urals, Appalachians, Crimea, Khibiny, Timan Ridge, etc.);

2) medium-altitude - from 1000 to 2000 m (Carpathians, Scandinavian ridge Chersky, Verkhoyansky ridge, Bolshoy Vodorazdelny, etc.);

3) high - above 2000 m (Cordillera, Andes, Alps, Caucasus, Pamir, Tien Shan, Himalayas, Kun-Lun, etc.).

Mountain-building processes took place on the Earth unevenly: either subsided, then intensified. In the geological history of the Earth, there are 5 mountain building cycles (or folding):

1) Baikal (pre-Paleozoic) - occurred at the end of the Proterozoic - the mountain systems of the Baikal, Transbaikalia, Sayan, Timan Ridge;

2) Caledonian - flowed in the early Paleozoic - the Northern Tien Shan, the mountains of Southern Transbaikalia, the Kazakh hills, the Brazilian Highlands;

3) Hercynian - in the late Paleozoic - the Southern Tien Shan, the Urals, the Appalachians, the mountains of Central Europe;

4) Mesozoic (Cimmerian) - in the Mesozoic - the mountains of Northeastern Siberia, the Far East, Indochina, the Cordillera;

5) Alpine (Cenozoic) - in the Cenozoic - the Carpathians, Crimea, Caucasus, Kopetdag, Pamir, the mountains of Kamchatka, the Himalayas, the Alps, the Pyrenees, the Andes.

Classification of mountains by genesis. By origin, mountains are divided into tectonic, volcanic, erosional. The most common are tectonic mountains, which are divided into folded and blocky.

1. Fold mountains consist of one or more folds. They tend to be tall and have pointed tops. The folded mountains are young in age; they were formed in the Cenozoic during the Alpine folding. These are primary orogens that arose at the site of geosynclines, and therefore they are called post-geosynclinal or epigeosynclinal (from the Greek epi - “after”). Folded mountains include all mountains of alpine folding.

2. blocky (fault) mountains formed on the site of folded mountains that arose before the Cenozoic. Mountains are not eternal. The mountains that arose in distant epochs (in the Proterozoic, Paleozoic, Mesozoic) collapsed, smoothed out and turned into a peneplain (plain) or low mountains. When a new Alpine orogenic cycle began in the Cenozoic, folds did not form in the place of these mountains, but blocky mountains arose. Horsts (protrusions) and grabens (depressions) were formed as a result of uplift and subsidence of blocks of the earth's crust. The tops of these mountains are gentle, not pointed. These mountains vary in height. The blocky mountains are old in age; they were formed a very long time ago: in the Baikal, Caledonian, Hercynian, Mesozoic folding and were completely or partially destroyed by the beginning of the Cenozoic. In the Cenozoic, they rose again, therefore they are called secondary orogens that arose on the site of the peneplain (or low mountains), therefore they are also called epiplatform.

Blocky mountains are subdivided into folded-blocky and blocky-folded. Folded-blocky arose during repeated mountain building on the site of destroyed mountains in the areas of the Baikal, Caledonian and Hercynian foldings. These mountains were reborn (from peneplain) by raising blocks on different height. They are called reborn. They can also be tall. The fold-block (reborn) mountains include: Tien Shan, Altai, Sayans, mountains of the Baikal and Transbaikalia, Greater Khingan, Nan Shan, Kunlun, mountains of central Europe, etc.

blocky-folded mountains arose on the site of partially destroyed mountains in areas of Mesozoic folding. These mountains have risen where there were lowlands. Their height is different. The blocky-folded mountains are generally less high. They are called rejuvenated. The blocky-folded (rejuvenated) mountains include: the Chersky, Verkhoyansk, Rocky Mountains, the ridges of the Tibet highlands, the mountains of Indochina, etc.

3. erosion mountains - these are mountains formed with the leading role of exogenous processes. Initially, they could be of both tectonic and volcanic origin. Under the influence of water, wind, ice, these mountains have changed their appearance. Erosion mountains, as a rule, are low, and their tops are flat, although they are young in age: the Crimea, the Carpathians, etc.

In the location of mountain ranges and the valleys separating them, the following types of dismemberment can be distinguished:

1) radial - the ridges radiate in all directions from the highest central part - the mountain junction (Pamir);

2) pinnate (transverse) - side ridges depart from the main water-dividing ridge in a direction approximately perpendicular to the main ridge (Greater Caucasus);

3) rocker - the ridges depart from the main one on one side and at an acute angle (the ridges of western Sakhalin);

4) branched - fan-shaped arrangement of ridges from one center (Pamir-Alai);

5) lattice - parallel mountain ranges are separated by short transverse valleys (Southern Urals), mountains of East Asia.

Morphostructure of volcanic regions. (Mountains and plains of volcanic origin). There are several thousand volcanoes on the globe, of which more than 700 are active on land, and even more in the ocean. There are tens of thousands of extinct volcanoes. An extinct volcano is one that has never erupted in human memory.

The relief created by volcanic processes is characterized by great originality. It depends on the type of eruption and can be either flat or mountainous.

Volcanism - this is a set of processes associated with the penetration into the earth's crust and outpouring on the surface of the earth of a molten and gas-saturated mass - magma. During volcanic eruptions, loose and solid products - ash and stones - also come to the Earth's surface.

There are 3 types of volcanic eruptions.

1. Areal - with this type of eruption, magma, melting the crust, pours out onto its surface in colossal masses over vast spaces. Such eruptions occurred in the early stages of the formation of the earth's crust and are not observed now.

2. Fissure (linear) - during such eruptions, a large mass of liquid lava is poured out, which, spreading widely, forms huge lava covers. In the past, they were widespread in Eastern Siberia, Transcaucasia, Hindustan, South America (Patagonia), Australia, Colombia, etc., and are now rarely observed (in Iceland, New Zealand, the Azores, Canaries, Hawaiian Islands). Lava plateaus look like undulating plains.

3. Central - magma rises to the earth's surface through a relatively narrow channel - a vent. This type of volcanoes includes Klyuchevskaya Sopka in Kamchatka, Fujiyama in Japan, Elbrus in the Caucasus and many other volcanoes.

Plains. Plains are a morphostructural element of the continental crust, corresponding to platforms, with small height fluctuations at close distances. Plains are areas of considerable extent, where the fluctuation in altitude does not exceed 200 m.

Depending on the height, the plains are distinguished: negative (lie below sea level, for example, the Caspian plain); low - lowlands - from 0 to 200 m (Amazonian, West Siberian); medium-altitude - elevations - from 200 to 500 m (Great Plains, Central Russian); high - plateaus and plateaus - above 500 m (Central Siberian, Ustyurt).

Extensive, relatively flat, but folded into folded layers of rocks, areas on the site of the destroyed mountains are called plateaus . Smooth, wavy or slightly dissected, elevated and ledge-limited surface areas are assigned plateau (for example, Ustyurt, Putorana, etc.).

By morphology (in appearance) it is customary to distinguish plains:

1) according to the shape of the surface -

a) horizontal - these are most often young sea plains (for example, the Caspian) or alluvial (river sediments);

b) inclined - these are the plains of the foothills (the plains of the Ciscaucasia);

c) concave - their surface goes down to the center of the plain (for example, the Turan lowland);

d) convex - their surface is inclined from the center to the outskirts (plain of Karelia);

2) by the nature of the relief -

a) flat - plains with a uniform surface;

b) hilly - plains, characterized by different directions and steepness of the fall of the surface;

c) wavy (maned) - plains, characterized by the fall of the surface in one direction or the other;

d) stepped.

Now let's focus on the classification of plains by genesis (origin).

1. Reservoir (primary) plains. These plains are the most common on the continents (64%). They are composed of layers of sedimentary cover, below which is a crystalline basement. Sedimentary layers most often accumulate at the bottom of the sea when the foundation of the platform has sunk below sea level. Then the platform rose again, and the seabed became land (hence the name "primary" - that is, formed after the sea). Thus, the Russian Plain (East European), West Siberian, Amazonian and others are composed of layers of marine and lagoon-continental origin. In the Meso-Cenozoic time, their foundations experienced repeated tectonic movements. Some sections of the foundation were lower, others higher. They formed ledges - anteclises (for example, the Volga-Kama anteclise) and depressions - syneclises (for example, the Moscow syneclise). The ledges of the East European basement correspond to the uplands (Volga, Central Russian, Northern ridges, the Donetsk Ridge, etc.), the depressions correspond to the lowlands (Pecherskaya, Oka-Donskaya, Volga-Vetluzhskaya, etc.).

2. Denudation (basement) - these are plains that arose as a result of the destruction of mountainous countries and the removal of destruction products (denudation) from the remaining base of the mountains - the base (there are about 20% of such plains). Denudation plains are also widespread on the continents. In the tectonic structure of the platforms, the socle plains correspond to the shields. They take large areas in Africa, Australia; these are also the plains of Hindustan and Arabia, these are the Brazilian and Guiana highlands (i.e., the relief of the Gondwanan continents). Socle plains are also common on the Laura-Asian continents. These are well-known physical and geographical countries (shields): Baltic, Ukrainian, Anabar, Aldan, Canadian and others.

Basement plains are ancient leveling surfaces, or peneplains. The denudation process (leveling process) cannot lead to the formation of a perfectly leveled surface, because. demolition of loose material stops at a slope of 3 o. The shields may contain tectonic fissures, which in the relief correspond to river valleys, grabens (which are often lacustrine basins), etc.

3. accumulative - these are plains formed by leveling the surface during the accumulation (accumulation) of material (they account for 16%). In structure, they are close to reservoir. Their main difference is that the sedimentary cover is composed of young deposits (of the Quaternary period).

Accumulative plains are heterogeneous:

a) alluvial - composed of river pumps (Hungarian lowland, Mesopotamian, Caspian, Indo-Gangetic lowlands, etc.);

b) fluvioglacial - formed due to the activity of melted glacial waters (Zander plains in Central Europe and North America); North Polish, North German, Trans-Volga, Polissya, Meshchera;

c) lacustrine - these are flat bottoms of former lakes, they are composed of layered lacustrine sediments (comparatively small in size);

d) volcanic - occur when a huge mass of magma pours out through cracks in the earth's crust (Columbian Plateau, Deccan Plateau).

Morphosculptural mesorelief

Mesorelief is a relief consisting of medium-sized forms: small plains, river valleys, gorges, small hills, ravines, beams, hills, canyons, dunes, dunes, sinkholes, etc.

Morphosculptural relief is a relief created by exogenous (external) processes. Thus, morphosculptural mesorelief are medium landforms created by exogenous processes. Most often, the morphosculptural mesorelief is characteristic of the plains, but it can also occur in the mountains.

Morphosculptural mesorelief is divided into the following types:

1. fluvial - relief created by flowing water:

a) fluvial-accumulative (water-accumulative) - river plains (alluvial), deltas, floodplains, terraces);

b) fluvial-erosion (water-sculptural) - ravines, dry channels, river valleys, karst, etc.).

2. Glacial (glacial) and nival (snowy) reliefs:

a) glacial-accumulative - moraine hills, drumlins, kams, lakes;

b) glacial-erosive - sheep's foreheads, curly rocks, punishments, carlings, troughs;

c) fluvio-glacial (water-glacial) - sanders.

3. cryogenic (permafrost): solifluction terraces, thermokarst, etc.

4. eolian :

a) eolian relief of arid (arid) areas: (dunes);

b) eolian relief of sea coasts: (dunes).

5. Abrasion-accumulative (shore relief).

The mesorelief can be incised (during erosion processes) and superimposed (during accumulative processes).

fluvial relief. Fluvial landforms are the most common on Earth. They occupy more than half of the land area (59%). Flowing water does its work everywhere (even in tropical deserts), except for the polar ice zones.

Fluvial (water) relief can be both erosive and accumulative. There are 6 types of fluvial relief:

Ravine-beam relief. ravines - steep-walled ruts of large sizes, formed as a result of the eroding activity of storm and melt water. From the main ravine depart side, called otvershki. This is how a complex system of large and small ravines and erosion potholes arises.

The formation and growth of ravines is facilitated by the elevated relief, storm type of precipitation, rapid snow melting, loose rocks, as well as anthropogenic factors: deforestation, plowing of slopes, etc.

The length of the ravines can reach several kilometers, the depth is on average 10-12 m (maximum - up to 80 m). Over time, the steepness of the slopes decreases, and the ravine turns into a beam - the final stage of the development of the ravine. Beam - this is a dry or with temporary watercourses (in spring or after heavy rains) depression in the relief, the slopes of which are covered with turf. The varieties of the beam are: a log - a wide and deep depression with soft outlines and gentle sod slopes - and a dry valley - a large beam with a wide and flat bottom, gentle slopes, at the bottom of which there is a temporary stream in the spring and in the flood.

Ravine-beam landforms are most common in forest-steppes and steppes, but may also be present in other zones.

Syrt relief - this is a relief that forms under the same conditions as the ravine, but in the presence of not loose rocks, but clayey ones. Syrt relief is a wavy hills. It is common in the steppes, dry steppes and semi-deserts (for example, the upland of the General Syrt).

Dry streams. This relief is characteristic of an arid climate, where precipitation falls randomly and channels of temporary streams form after rain. Dry channels are characteristic of deserts. In Africa they are called wadi, in Australia they are called screams, in Central Asia- Uzbeks.

Landslide relief. The formation of this type of relief is associated with the activity of not surface, but groundwater(ground). Landslides are sliding downward displacement of rock masses under the influence of gravity. Landslides occur in mountainous areas (on the slopes of mountains), along the banks of rivers, lakes, seas, ravines - where there is an alternation of clay water-resistant and sandy-gravel layers. Landslides take place on the banks of the Volga, Dnieper, Kama, etc. The landslide relief is typical for the coast of the Black and Azov Seas.

Suffusion relief also formed under the action of groundwater. Suffusion - this is the removal of the smallest particles of rock and dissolved substances by groundwater. This leads to the landing of the surface and the formation of such forms as steppe saucers (pods) - shallow closed depressions (or depressions) with a depth of 1 to 3 m and a diameter of 10 to 100 m. Sometimes such depressions are filled with water (lakes).

In some cases, suffocated funnels and dips are formed. And the combination of these landforms forms suffusion fields. The suffosion relief is widespread in the steppe zones, especially on forest-like rocks.

Karst relief - this is a relief formed under the influence of surface and, mainly, groundwater. Karst - this is the relief of easily soluble rocks that have arisen as a result of the dissolving activity of water - limestone, dolomite, less often gypsum, salts, chalk. The word "karst" comes from its own name - the Karst plateau, located on the Balkan Peninsula. The main conditions for the emergence of karst relief are: 1) the presence of soluble rocks with cracks in them; 2) sufficient (but not excessive) amount of water; 3) a sufficiently low level of groundwater, etc.

Distinguish:

1. Open, surface karst ( Mediterranean ) - if karst-forming rocks protrude onto the day surface. Forms of open karst are carr - deep furrows on the surface devoid of vegetation (their depth is up to 2 m). Their combination forms carr fields, which are difficult to pass. Sinkholes are considered to be a widespread form of surface karst (they are also typical for covered karst). Karst funnels are cone-shaped depressions with steep slopes (up to 45 o), at the bottom of which there is a ponor - a hole that serves to pass the water flowing into the funnel. The diameter of karst funnels can reach 100 m. Funnels of even larger diameter are called sinkholes. They arise at the site of the failure of the roof of the underground karst caves. With a large thickness of karst-forming rocks and where deep water seepage is possible, funnels take the form of karst wells and karst mines (deep - up to several tens of meters - cylindrical failures).

2. Covered karst ( Central European ) - if karst-forming rocks lie at a certain depth and are covered from above by a layer of insoluble rocks (sands, clays, etc.). Forms of covered or underground karst are karst caves. They arise in the thickness of limestones and other readily soluble rocks under the action of groundwater. If water seeps from above, then sinter formations appear: from the ceiling - stalactites, from the bottom - stalagmites. Merging, stalactites and stalagmites form columns. (If the air is humid, no streaks will form). Caves can be cold or warm. At the bottom of some caves there are lakes and even underground rivers can flow. The length of the caves sometimes reaches several kilometers (for example, in the Alps there are caves longer than 70 km). Covered karst, as well as surface karst, is characterized by sinkholes and sinkholes. In some cases, sinkholes and sinkholes can fill with water, forming lakes.

Karst relief is a widespread form of relief on Earth, because. karst rocks occupy vast areas on land - about 34%; these are limestones, dolomites, gypsums, salts, chalk and others.

Karst phenomena can be present at different latitudes. Karst (open and covered) is widely developed in the Mediterranean, on the coasts of the Adriatic, Black and other seas of this region. In the Alps, where the longest cave in the world is located - Helloch (in Switzerland), in North America (Mammoth Cave on the western slope of the Appalachians - its length is 71 km; in Cuba; in the interior of Florida), in Northern Australia, China and Indochina, in Central Asia, Central Europe; in Russia, karst takes place on the Russian Plain, in particular, in the Right Bank of the Nizhny Novgorod region. There is karst in the Urals (the icy Kungur cave), in many regions of Siberia and the Far East (Sikhote-Alin, etc.).

river valleys (fluvial-erosive relief). River valleys belong to the fluvial variety, i.e. water, relief, which is created by surface waters collected in channels (permanent water flows - rivers).

A river valley is a negative (incised) landform, linearly elongated, with one-sided dip and open at the mouth.

The main elements of the valley relief are: the bottom, slopes, bedrock banks, terraces, floodplain and channel.

The bottom of the river valley (or bottom) is the lowest part of it, along which the river flows. For undeveloped valleys, usually mountainous, the bottom may coincide with the channel. channel is a depression at the bottom of a valley through which water flows.

The slopes of the valley can be simple and stepped, steep and gentle, high and low. floodplain - part of the river valley, regularly flooded in high water (or flood). The width of the floodplain varies from a few meters to 30-40 or more kilometers (near the Ob, in the lower reaches of the Volga and other major rivers). The floodplain is usually composed of alluvium (deposition of the river) and covered with vegetation (usually meadow), but sometimes the floodplain is cut into bedrock, and alluvium is almost absent - such a floodplain is called indigenous. Outwardly, the floodplain seems to be flat and even, but there are differences in the microrelief of the floodplain, therefore, a river floodplain, a river bank, and a central floodplain (a slightly lowered part) are distinguished.

In the floodplain there may be oxbow lakes formed from the old riverbed. In some places, the floodplain is swampy.

If the river stops flooding the floodplain for any reason, the floodplain turns into a terrace.

Terraces - horizontal or slightly inclined surfaces, which are the remnants of former floodplains; they are stretched along the slope of the valley. Appearance terraces - step-down relief to the river.

We can name the following reasons that turn the floodplain into a terrace:

1) self-development of the river - the river, eroding the bottom and crashing into the rock, leaves a staircase of terraces - former floodplains;

2) climatic fluctuations - aridization, glaciation, etc.;

3) tectonic fluctuations of the earth's crust - the rise of the source or the lowering of the mouth;

4) increase or decrease in the basis of erosion.

The lowest river terrace is the floodplain (floodplain terrace), therefore, all other terraces are called above the floodplain. They are counted from the bottom up from the river. Large rivers have 2-3 floodplain terraces (for example, the Volga has 3, because the Volga ran into its deposits three times). According to their structure, terraces are of 3 types:

1) erosional or primary (erosion terraces) - the result of a river cutting into rocks;

2) accumulative or alluvial (accumulation terraces) - associated with the accumulation of river sediments (alluvium) in the valley and with the subsequent incision of the river into them;

3) socle or mixed (erosion-accumulative terraces) - these are terraces with a root base covered with alluvium, i.e. Bottom part– the socle is composed of bedrock, and the upper one is composed of alluvium.

The relief of the valleys is determined by the morphostructure into which the valley is cut (valleys can coincide in direction with the axes of folds, with fault lines, they can be associated with grabens, etc.); as well as the position of the base of erosion (this is a horizontal surface at the level of which the water flow loses its strength and below which it cannot deepen its channel). Erosion basis is the level of the reservoir into which the river flows. The ultimate basis of erosion for all rivers globe is the surface of the oceans.

Crashing into rocks, the river flow tends to develop an equilibrium profile, in which the optimal ratio is established between erosion, material transfer and its accumulation. A river can develop an equilibrium profile only under conditions of prolonged tectonic quiescence and an unchanged position of the erosion basis. The undeveloped longitudinal profile of the rivers has many irregularities - rapids, waterfalls. Waterfall - the fall of the river flow from a pronounced ledge in the riverbed, composed of solid rocks. There are two types of waterfalls:

1) Niagara - the width of such a waterfall is greater than its height (for example, Niagara Falls in North America; it consists of two parts: Canadian, left, about 40 m high, more than 90% of the total mass of water of the Niagara River falls through it; right, American, about 45 m high. The waterfall washes away the base of the ledge and slowly recedes up the river, at a rate of about 1 m per year. Victoria Falls in Africa, more than 100 m high, belongs to the same type of waterfalls.

2) Yosemite - the height of such a waterfall is greater than its width (for example, a waterfall on the Merced River in the western United States - a narrow stream of water falls from a height of almost 700 m; the highest Angel Falls on the Churun ​​River is about 1000 m - in the Orinoco River basin).

thresholds - a phenomenon similar to waterfalls, but having a lower ledge height. They can be placed at the site of a waterfall when its ledge collapses.

According to morphology, the following are distinguished river valley types :

1. Gorge - a valley created almost exclusively by deep erosion of the flow. The slopes of such a valley are steep and may even overhang. The whole bottom is occupied by the river. Most often, valleys of this type are characteristic of mountainous regions.

2. Canyon (gorge) - a valley with almost steep slopes, with a narrow bottom. Valleys of this type are typical for plateaus and plateaus (the Grand Canyon of Colorado, its depth is 1800 m; there are such valleys in Africa on the Abyssinian Highlands, on the volcanic plateaus of India, Brazil, on the Central Siberian Plateau and in other parts of the world).

3. V -shaped – the slopes of these valleys are more gentle than those of the canyon. They can be dissected by small erosional forms; there are also ledges on them.

The three types of river valleys mentioned above are undeveloped valleys.

4. U - figurative (floodplain) - such valleys have a wide flat bottom; the channel occupies only part of the bottom, the lowest; the rest of the valley is a floodplain (that is, it is regularly flooded with water during floods).

5. Decorated - valleys, which have not only a floodplain, but also terraces above the floodplain.

Each river during its life goes through a geographical cycle of its development, in which 3 stages are distinguished: youth, maturity and old age. In youth, the river has a very large difference in the absolute heights of the mouth and source. At this stage, bottom erosion (deep) prevails near the river; the river is trying to develop an equilibrium profile between the source and the mouth - the bottom of the channel is being washed out. The bottom erosion limit is the erosion basis. At this stage, the river has valleys of an undeveloped type (V-shaped, canyon, gorge). The channel is almost straight, it occupies the entire bottom of the valley.

At maturity, the river widens the valley. At this stage, the river is dominated by lateral erosion (bank erosion). The channel becomes winding, the bottom is wide, the river begins to meander (from the name of the Meander River in Asia Minor, which has many meanders, a similar name for river bends comes from). Meandering occurs under the influence of lateral erosion as a result of turbulent flow. Concave shores begin to erode more strongly, and a depression forms near the concave shore - a stretch. At the convex banks, the opposite is true - mineral material (sand, etc.) begins to be deposited, and then a shoal is formed. A relatively straight section of the channel between two reaches is called a rift. The rift is distinguished by a relatively small depth (unlike the reaches). The line connecting the deepest places along the channel is called the fairway. As the tortuosity increases, the meandering process intensifies, and at a certain moment (more often during floods) the isthmus can break, and the channel straightens, and the meander turns into an oxbow lake.

At maturity, the river has a U-shaped valley and forms a floodplain. In old age, the river fully develops an equilibrium profile. Lateral and bottom erosion fade. The river valley becomes wide, sometimes swampy. If tectonic processes or global climate changes occur (for example, a decrease in the erosion base or an uplift of any part of the river valley), then bottom erosion resumes, as a result of which the river deepens the channel, and a ledge is formed - a terrace above the floodplain. The river valley becomes shaped.

Most river valleys are characterized by an asymmetrical structure: as a rule, the right slopes are steeper than the left ones. The asymmetry of the slopes is explained by the following reasons:

1) the Coriolis force resulting from the rotation of the Earth;

2) climatic factors - the slopes of the southern exposure are steeper;

3) primary slope of the surface;

4) monoclinic occurrence of layers of different hardness.

Alluvial plains and deltas (fluvial-accumulative relief). As a result of the geological activity of the rivers, accumulation processes take place simultaneously with erosion. For the Earth as a whole, the volume of deposited material is equal to the volume of washed out, but the continents are characterized by a negative balance, because. a significant part of the products of denudation (demolition) is deposited in the sea. The alluvial plains include: the Great Chinese Plain, Indo-Ganga, Mesopotamian, Hungarian, Ussuri, Zeya-Bureya, Yano-Indigirskaya, Vilyuisskaya, the central part of the West Siberian, Turan, lowlands of Central Asia and others.

A special place among the forms of fluvial-accumulative relief is occupied by deltas - alluvial fans of rivers. The formation of deltas is explained by the following reasons:

1) a sufficiently significant solid runoff of the river;

2) weak movement of water in the reservoir into which the river flows;

3) the underwater slope on which river sediments are deposited should be gentle;

4) the river must reach the erosion base.

The rate of growth of deltas averages from a few meters to 100 m per year. The most extensive deltas have rivers: the Nile, the Amazon, the Mississippi, the Volga, the Tigris, the Lena, the Ganges, the Syr Darya and some others.

By location, the deltas are divided into filling deltas (located in bays) and protrusion deltas (protruded into the sea).

The shape of the delta is arched (for example, the deltas of the Volga, Lena, Nile), lobed (Mississippi delta) and beak-shaped (Tiger delta).

The surface of the deltas is usually flat, slightly undulating, dissected by many old channels. Over time, the old channels turn into deltaic lakes.

Glacial (glacial) and nival (snow) relief.

Glacial and nival processes are important factors in the formation of relief in mountains and plains.

Ice and snow (especially ice) perform destructive geological work (exaration and nivation), transport work (movement of clastic material, etc.) and creative geological work (accumulation or accumulation of loose material). Exaration and nivation lead to the emergence of glacial-erosion landforms: car, carling, sheep foreheads, troughs. The transporting and creative work of ice (glacier) leads to the creation of glacial-accumulative landforms: moraine deposits - kam, oz, drumlin. As a kind of glacial-accumulative relief, fluvioglacial (water-glacial) relief - outwash fields (outhands) can be considered.

Modern glacial and nival processes of relief formation can be observed above the snow line in the mountains and even below it (the snow line is the boundary above which snow in the mountains remains even in summer) and in high (polar) latitudes - in Antarctica and on the Arctic islands.

Glacial and nival processes proceeded very intensively in the Quaternary period. More precisely - in the Pleistocene. There were several glaciations during the Pleistocene. At that time, there were 3 major ice sheets on Earth:

1) North America with Greenland - ice originated here in three centers: in the north of the Cordilleras, on the Labrador Peninsula and in the north of Hudson Bay, the southern border of the glacier reached 37.5 o N, and the area covered with ice was about 13, 7 million km 2;

2) Eurasia - there were also 3 glaciation centers here: the Scandinavian Peninsula, the Northern Urals and the Taimyr Peninsula; the southern border of the glacier reached 48 o N. in Europe and much less in Western Siberia (in Eastern Siberia, glaciation was only mountainous); the area covered with ice was equal to 5.5 million km 2;

3) Antarctica - the maximum northern border of the glacier reached Tierra del Fuego; the glaciation area was larger than the modern one - more than 15 million km 2.

Mountain glaciers at that time occupied a much larger area than now, and the snow line descended below the modern one. In general, the ancient glaciation (Pleistocene) covered about 26% of the land - this is 2.5 times more than the modern one, and in the northern hemisphere it was more extensive than in the southern.

The climate at the beginning of the Quarvertic period was very unstable. Periods of cooling were replaced by periods of warming, so the glacial epochs were replaced by interglacial ones. The question of the number of ice ages has not been finally resolved. So, it is believed that glaciation was 3 or 4 times on the Russian Plain: the glacier advanced and retreated, reaching in turn as much as possible to the territory of the modern Dnieper, Moscow, Valdai.

Forms of nival and glacial relief:

1. Forms of destruction (glacial-erosive relief): karlings, carlings, troughs, sheep foreheads, curly rocks, skerries.

Kara and carlings- these are typical forms of nival mountain relief. Their origin is connected with the activity of snow. Kara are niche-like depressions on the slopes of mountains. The formation of a car begins with the appearance of accumulations of snow on the slope. When it melts, the rocks are moistened, and at negative temperatures, the wet rocks freeze, which leads to their cracking and destruction. Kar grows mainly deep into the slope. Quite often, karlings, located next to each other, grow and merge into single fields, above which rise sharp pyramidal peaks - carlings. Carlings are gradually destroyed and eventually disappear - a wavy surface remains.

With the destructive activity of ice, the emergence of such landforms as troughs is associated. trogs- these are trough-shaped valleys, transformed by a glacier, with a wide gently concave bottom and steep slopes. At a certain height above the bottom, gentle areas are formed - the shoulders of the troughs (the bottom of the more ancient troughs), above the steep slope again continues. The troughs can be plowed by both mountain and continental glaciers. Moving glaciers (mountain or continental) smooth, level the surface, soft rocks are cut off, hard rocks are polished. Scratches or furrows (glacial shading) may remain on solid rocks - they are formed from stones frozen into the ice and moving with it. The moving glacier cuts and polishes outcroppings of hard crystalline rocks, which take on streamlined shapes. This is how sheep's foreheads arise. The accumulation of sheep foreheads forms a peculiar relief of curly rocks. They are common in Karelia, in the uplands of Canada, in Taimyr. Curly rocks located in the sea or lake form countless small stone islands called skerries.

2. Accumulative forms (glacial-accumulative relief): moraines, moraine ridges and hills (kams, eskers, drumlins) and outwash fields.

When the glacier slows down its movement and stops, moraine material, brought from crystalline massifs, is deposited at the edge of the glacier, and local ekrasation products are added to it. When a glacier melts, the material melts, and in this case, melt waters acquire a decisive role in the formation of the relief. In areas of moraine relief, kams are common - small hills (5-4 m high) of irregular shape, with an uneven surface. Kamas are formed as a result of projecting onto the surface of sediments of lakes located in an ancient glacier or in glacier grottoes.

Oz- long and narrow ridges, similar to embankments. Their length reaches 3-40 km, width - tens of meters, and height - from 5 to 8 m. Their slopes are steep. The formation of oz is not completely clear. It is believed that they were formed from the sediments of rivers flowing in the inside - or subglacial tunnels, washed out in the glaciers that stopped moving.

Drumlins- elongated hills, elongated with long axes parallel to the movement of the glacier (their dimensions are about 200 m, width - 5-40 m). At the base of each drumlin is a core of bedrock, which is topped with moraine. The outcroppings of the bedrock caused the formation of cracks in the ice, into which the detrital material of the moraine fell. After the ice melted, this material formed a moraine hill - drumlin.

Kams, lakes, drumlins, as a rule, are the result of ancient glaciation. In mountainous areas, moraine deposits are currently formed in the form of moraine ridges (terminal moraine, lateral, median).

With activity ancient glacier, or rather, with melted glacial waters, the formation of zanders (zander fields) is associated - vast sand and pebble plains (from the German sand - sand). Streams of melt water came out from under the glacier, which carried a lot of sand and even pebbles. These flows rushed into the lowlands and deposited sediments there, called fluvio-glacial (water-glacial). This is how sands (or lacustrine-alluvial plains) were formed.

Glacial-accumulative landforms are widespread in the north of North America, in the northwest and north of Europe, in the north of Western Siberia. Further south, on the northern continents, loess deposits take place. Loess- yellow-brown or gray-brown, silty loose loam. There are many hypotheses about the origin of loess. One of them is associated with a glacier. According to this hypothesis, loess was formed from sediments that were blown off the ice sheet by the wind and carried away from the glacier (eolian hypothesis). According to another hypothesis, loess was formed from deposits of melted glacial waters, i.e. like outwash sands. But loess is the smallest, dusty fraction of water-glacial sediments. This is the water-glacial hypothesis. There are other hypotheses (for example, eolian arid climate).

Loess rocks are generally distributed south of outwash fields in the Central Russian Upland, Podolsk Upland, in the south of the East European Plain, in the basin of the Yellow River, etc.

Cryogenic (permafrost) relief.

Cryogenic landforms are associated with seasonal and permafrost. Permafrost soils are impermeable, which leads to waterlogging. The permafrost delays the deep erosion of rivers, but leads to the expansion of river valleys and floodplains. The slopes of the ravines are asymmetric, because the northern slope thaws more strongly. Permafrost is characterized by solifluction landforms - swells, tongues, ridges, solifluction terraces. Solifluction- this is a process of slow sliding down the slope of heavily waterlogged soils and loose soil. The upper layers lying on the permafrost are saturated with rain and melt water, become heavy and slowly slide (flow) down the slope under the influence of gravity, even if the slope is 3-5 o. Solifluction can be associated not only with permafrost, but also with seasonal (also happens in spring). The most common type of solifluction forms is an undulating relief on slopes. Thermokarst forms are also common on permafrost. They arise as a result of thawing of permafrost soils. The thawed soil sags, and thermokarst funnels, dips, and hollows are formed. The formation of thermokarst can be caused by a violation of the thermal regime in the upper part of the soil - deforestation, plowing, fire, etc.

When thawing buried ice large flat depressions (hollows) - alasses are formed. Polygonal formations are widespread on permafrost. They are associated with the phenomenon of heaving of the soil. As a result of the development of seasonal permafrost, the active layer is sandwiched between seasonal permafrost and permafrost. In this case, swelling of the upper layer with turf occurs. There are gaps, and the clay mass is poured onto the surface: clay spots (spotted tundra).

Areas with permafrost are also characterized by icy formations - icing. They are of two types: river ice, which occurs when the river freezes to the bottom - when water breaks through the ice or goes to the side of the channel. Freezing, it forms ice. And the second type is groundwater ice. They appear when they freeze ground water. This leads to the formation of hillocks (convex, rounded landforms) and the outpouring of water onto the surface, followed by its freezing. Perennial heaving mounds are called hydrolacoliths. Inside such mounds there is an ice core, and on top lies a layer of mineral soil and peat. Such hills can be up to 40 m high and up to 200 m wide.

The cryogenic relief is widespread in the north of North America, in the north of the European part of Russia, in the north of Western Siberia, in Eastern and Northeast Siberia, in Transbaikalia and in the mountains.

Eolian relief.

Aeolian relief is relief created by the wind. It is typical for arid (desert) areas and coasts of the seas, lakes, large rivers. The main conditions for the formation of the aeolian relief are: constantly blowing winds of sufficient intensity, the presence of loose, light, portable material (sand), the absence of vegetation cover or its weak development.

Eolian relief of desert regions. Deserts are widespread on the globe. They are found in both tropical and temperate latitudes. In the northern hemisphere, deserts are located in Africa - the Sahara, the Libyan Desert; in Arabia - Rub al-Khali, Great Nefud; in India - Tar; in Central Asia - the Karakum and Kyzyl Kum; in Central Asia - Gobi; in North America, the Great Basin. Deserts of the southern hemisphere: in Africa - Kalahari, Namib; in Australia - Victoria, Great Sandy, Gibson Desert; in South America- Atacama.

Depending on the rocks that make up the surface of the desert, there are: stony deserts (hamads), sandy (ergs, nefuds, kums), clayey (takyrs), saline deserts (shors).

The main factors of relief formation in deserts are physical weathering and wind activity. Under the influence of a temperature difference, the rocks are destroyed, which leads to the formation of a large amount of detrital, loose material. The wind produces destructive work: deflation (blowing) and corrosion (turning); transporting - transfer of loose material; creative - the deposition of loose material. As a result of the destructive work of the wind (deflation and corrosion), such forms of relief arise as blowing niches, stone mushrooms, towers, columns. A lot of clastic material accumulates on the surface at the foot of these landforms. Such a relief takes place in stony deserts. During the transporting and creative work of the wind dunes, dune chains, hilly sands are formed.

dunes- These are sandy hills that have the shape of a crescent. The slopes facing the wind are gentle (5-10 o), and from the side of the wind shadow are steep (up to 30 o). The average height of the dune is 5-10 m (in the Sahara - several tens of meters). Single dunes are rare. More often, a whole set of dunes is formed - dune chains.

An even more common relief is hilly sands - large sandy massifs fixed by vegetation. They have irregular shape and reach a height of up to 5 m. There are no hilly sands in tropical deserts. Dunes, dune chains and hilly sands are characteristic of sandy deserts.

Eolian relief of the coasts of seas and lakes. On the sandy coasts of the seas, lakes, in the valleys of large rivers, on outwash plains, sandy hills - dunes can be found. They occur under favorable wind conditions and in the presence of large masses sand. Dunes occur on the coast of the Baltic Sea (from the German-Polish lowland to the Gulf of Finland), on the shores of the White Sea, along the coast of the English Channel and the Pas de Calais. Dune relief is found along the shores of some lakes: the Caspian, Aral, Ladoga, Onega, as well as on the sandy terraces of large rivers (for example, the Volga, Oka, etc.). The height of the dunes is 5-50 m.

The study of the origin of the relief, the history of its development, internal structure and the speakers are engaged geomorphology(from Greek ge - Earth, morphe - form, logos - teaching).

The relief consists of landforms- natural bodies, which are parts of the relief and have a certain size. Among the landforms, positive and negative are distinguished (the morphographic principle of classification). positive forms rise above horizontal line, representing the elevation of the surface. Their examples are hillock, hill, mountain, plateau, etc. Negative forms relief in relation to the horizontal plane form depressions. These are valleys, ravines, beams, depressions.

Landforms are made up of landforms. relief elements- separate parts of landforms: surfaces (faces), lines (edges), points, angles in the aggregate forming landforms. To the number external signs landforms belongs to the degree of their complexity. On this basis, one distinguishes simple and complex forms. simple shapes(hill, hollow, hollow, etc.) consist of separate morphological elements, the combination of which forms the form. For example, at a hillock, a sole, slopes and top are distinguished. complex shapes consist of a number of simple An example is a valley, which includes slopes, a floodplain, a channel, etc.

According to the slope, the surfaces are divided into sub-horizontal ones with a slope of less than 2 0 and inclined surfaces (slopes) with large slopes. slopes may be different shape and be straight, concave, convex, stepped. Surfaces can be smooth, convex and concave. Along strike - closed and open. According to the degree of dissection of the surface, flat and mountainous territories are distinguished.

The combination of relief forms that have a similar origin and regularly repeat in a certain space forms relief type. On larger expanses of the earth's surface, it is possible to combine individual types of relief on the basis of their similar origin or difference. In this case, one speaks of relief type groups. Since the association of relief types is carried out on the basis of their origin, one speaks of genetic relief types.

The two most common types of land relief are mountainous and flat. According to the height, the plains are divided into depressions, lowlands, uplands, plateaus and plateaus, and the mountains are divided into low, medium, high and highest.

By size, landforms are divided into planetary forms, with an area of ​​millions of km 2 with a range of heights of 2.5-6 thousand m - these are the continents, geosynclinal belts, the ocean floor, SOHs. Megaforms- an area of ​​​​hundreds and thousands of km 2 with a range of heights of 500-4000 m - these are parts of planetary forms - plains and mountainous countries. macroforms- an area of ​​​​hundreds of km 2 with a range of heights of 200-2000 m. - these are large ridges, large valleys and depressions. Mesoforms- with an area of ​​​​up to 100 km 2 with a height span of 200-1000 m - these are, for example, large beam systems. Microforms with an area of ​​up to 100 m 2 and a height span of up to 10 m - these are gullies, karst funnels, suffusion saucers, dunes, etc.). Nanoforms with an area of ​​​​up to 1 m 2 and a height span of up to 2 m - these are marmots, the smallest depressions, bumps, etc.).

According to the morphogenetic classification, all landforms are divided into geotectures- irregularities formed under the influence of endogenous forces - ledges of the continents and depressions of the oceans, morphostructures- irregularities formed under the influence of endogenous and exogenous forces, and the leading ones are endogenous - these are plains and mountainous countries, morphosculptures- landforms formed by exogenous forces - small irregularities complicating the surfaces of mountains and plains.

Plains- these are areas of the land surface, the bottom of the seas and oceans, which are characterized by: slight fluctuations in altitude (up to 200 m) and a slight slope of the terrain (up to 5 °). Depending on the absolute heights, there are: low-lying (up to 200 m); elevated (200-500 m); upland or high (more than 500 m) plains.

A mountain is a positive landform that rises above a relatively flat area by at least 200 m. The mountain is bounded by slopes on all sides. The transition from slopes to plains is the bottom of the mountain. The highest part of the mountain is its vertex.

With very gentle slopes, a positive landform with a height of more than 200 m is called - hill.

The mountains – these are highly dissected areas of the earth's surface, raised high above the level of the Ocean. At the same time, the mountains have a single base, rising above the adjacent plains, and consists of many positive and negative landforms. In terms of height, low mountains up to 800 m are distinguished, middle mountains - 800-2000 and high mountains - more than 2000 m.

The age of the relief can be: absolute - determined by the geochronological scale; relative - the formation of a relief is established earlier or later than any other form or surface.

The relief is formed as a result of the constant interaction of endogenous and exogenous forces. Endogenous processes mainly create the main features of the relief, while exogenous processes try to level it. The sources of energy in relief formation are: the internal energy of the Earth, the energy of the Sun and the influence of space. Relief formation occurs under the influence of gravity. The energy source of endogenous processes is thermal energy Earth associated with radioactive decay in the mantle. Due to endogenous forces, the earth's crust was separated from the mantle with the formation of its two types: continental and oceanic. Endogenous forces cause movements of the lithosphere, the formation of folds, faults, earthquakes and volcanism.

Movements of the lithosphere are characterized by different directions and intensity in time and space. In the direction relative to the surface of the Earth, vertical and horizontal movements are distinguished; by direction - reversible (oscillatory) and irreversible; according to the speed of manifestation - fast (earthquakes) and slow (secular).

Horizontal movements of the lithosphere are manifested in the slow movement of huge lithospheric plates along with continents and oceans along the plastic asthenosphere. Deep faults (rifts) separating the plates are usually located at the bottom of the oceans, where the earth's crust is the thinnest (5-7 km). Magma rises along the faults and, solidifying, builds up the edges of the plates, forming the Mid-Ocean ridges. As a result, the plates move apart, moving away from each other at a rate of 1-12 cm/year. Their separation leads to a collision with neighboring plates, or to immersion (diving) under them. At the same time, the edges of neighboring plates rise, which leads to the emergence of mountain-building processes and mobile belts, which are characterized by high volcanism and seismicity. Example: Far East. Changes in the planetary relief of the Earth are associated with a decrease in the speed of its rotation as a result of the decelerating effect of the Moon. The stresses that arise in the body of the Earth in this case cause deformation of the earth's crust and movement of the plates of the lithosphere.

The vertical movements of the lithospheric plates are caused by the fact that the mountains, composed of lighter rocks, have a more powerful earth's crust, and under the Ocean it is thin and covered with water. The mantle here comes close to the surface, which compensates for the lack of mass. Additional loading, for example, the formation of an ice cover, leads to the "pressing" of the earth's crust into the mantle. So Antarctica sank 700 m, and in its central parts the land was below the Ocean. The same thing happened in Greenland. The release of the glacier is causing the earth's crust to rise: the Scandinavian Peninsula is now rising at a rate of 1 cm/year. The vertical movements of smaller blocks are always reflected in the relief. Particularly visible are the forms created by modern (neotectonic) movements. For example, in the Central Chernozem region, the area of ​​the Central Russian Upland rises by 4-6 mm/year, while the area of ​​the Oka-Don Lowland falls by 2 mm/year.

Vertical and horizontal movements of the earth's crust lead to deformation of rock layers, leading to two types of dislocations: folded - bending of the layers without violating their integrity, and discontinuous, where, as a rule, the crust blocks move in vertical and horizontal directions. Both types of dislocations are characteristic of the mobile belts of the Earth, where mountains are formed. However, folded dislocations are practically absent in the platform cover. Dislocations in mountains are accompanied by magmatism and earthquakes.

Exogenous processes are associated with the arrival on Earth solar energy, but they flow with the participation of gravity. In this case, the weathering of rocks and the movement of material under the action of gravity occur: landslides, landslides, screes, material transfer by water and wind. Weathering is a set of processes of mechanical destruction and chemical change of rocks. The general effect of the processes of destruction and transport of rocks is called denudation, which leads to the leveling of the surface of the lithosphere. If there were no endogenous processes on Earth, then our planet would have had a completely flat surface. This imaginary surface is called the main level of denudation. In reality, there are many temporal levels of denudation at which equalization processes may fade for some time. The intensity of manifestation of denudation processes depends on the composition of rocks and climate. Highest value at the same time, it has the height of the terrain above sea level, or the basis of erosion.

Exogenous processes, smoothing out large irregularities of the earth's surface, form a smaller relief - denudation and accumulative morphosculpture. The variety of exogenous processes, as well as denudation and accumulative landforms resulting from their manifestation, can be combined into the following types:

1. activity of surface waters (temporary streams and rivers) - fluvial relief;
2. groundwater - karst, suffusion and landslide relief;
3. glaciers and melted glacial waters - glacial (glacial) and water-glacial relief;
4. changes under the influence of various processes in permafrost rocks - permafrost (cryogenic) relief;
5. wind activity - eolian relief;
6. coastal marine processes - the relief of sea coasts;
7. living organisms - biogenic relief;
8. man - anthropogenic relief.

As can be seen, the relief of the surface of the lithosphere is the result of the counteraction of endogenous and exogenous processes. The former create uneven terrain, while the latter smooth them out. Relief formation can be dominated by endo- or exogenous forces. In the first case, the height of the relief increases - this is an upward development of the relief. In the second, positive landforms are destroyed and depressions are filled. This is a downward development.

Relief

Layout with terrain

The main landforms are mountains, hollows, ridges, and hollows.

On large-scale topographic and sports maps, the relief is depicted by isohypses - horizontal lines, numerical marks and additional conventional signs. On small-scale topographic and physical maps, relief is indicated by color (hypsometric coloration with clear or blurred steps) and hillshade.

Denudation plains arise on the site of destroyed mountains. Accumulative plains are formed during the long-term accumulation of strata of loose sedimentary rocks at the site of extensive subsidence of the earth's surface.

Folded mountains - uplifts of the earth's surface that occur in mobile zones of the earth's crust, most often at the edges of lithospheric plates. Blocky mountains arise as a result of the formation of horsts, grabens and the movement of sections of the earth's crust along faults. Folded-blocky mountains appeared on the site of sections of the earth's crust that in the past underwent mountain building, transformation into a denudation plain and repeated mountain building. Volcanic mountains are formed during volcanic eruptions.

see also

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See what "Relief" is in other dictionaries:

relief- a, m. relief m. 1. Convex image on a plane. BAS 1. The hall of four tiers is decorated with bulges (reliefs) from the best dramatic contents. 1821. Sumarokov Walk 2 40. I admired the Chinese furniture .. with reliefs and wooden ... ... Historical Dictionary of Gallicisms of the Russian Language

Relief- (French relief, from Latin relevo I raise), a sculptural image on a plane. The inextricable connection with the plane, which is the physical basis and background of the image, is a specific feature of the relief as a type of sculpture. ... ... Art Encyclopedia

RELIEF- (fr. relief, from lat. relevare to raise, elevate). Convex image; sculptural works, more or less convex. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. RELIEF 1) convex sculptural images ... ... Dictionary of foreign words of the Russian language

RELIEF- (French relief, from Latin relevo I raise), a set of irregularities of the earth's surface, different in shape, size, origin, age and history of development. It is composed of positive forms that form elevations, and negative ones, ... ... Ecological dictionary

RELIEF- (French relief from Latin relevo I raise), a set of uneven land, the bottom of the oceans and seas, various in shape, size, origin, age and history of development. It is composed of positive (convex) and negative (concave) forms ... Big Encyclopedic Dictionary

RELIEF- RELIEF, relief, male. (French relief). 1. Convex image on a plane (special). Reliefs are weakly convex bas-reliefs and strongly convex high reliefs. 2. The structure of the earth's surface (geographic, geol.). Rugged terrain. Mountain ... ... Explanatory Dictionary of Ushakov

RELIEF- (French relief, from Latin relevo I raise), a set of forms of the earth's surface, differing in shape, size, origin, history of development. The relief is formed mainly as a result of a long simultaneous ... ... Modern Encyclopedia

Relief- [fr. relief bulge] the totality of all forms of the earth's surface for each specific area and the Earth as a whole. It is formed as a result of mutual influence of endogenous and exogenous processes on the earth's crust. There are R. of different orders, ... ... Geological Encyclopedia

relief- panels, topography, landscape, bas-relief, mascaron, high relief Dictionary of Russian synonyms. relief n., number of synonyms: 19 bas-relief (2) ... Synonym dictionary

Relief- a set of irregularities on the surface of the land, the bottom of the oceans and seas, diverse in shape, size, origin, age and history of development. It is one of the main elements of the terrain that determines its tactical properties. Relief ... ... Marine Dictionary

relief- RELIEF, a, m. Figure, forms (about the body). Swing (or work on) relief to build muscle. from sports... Dictionary of Russian Argo

Books

• Relief, vegetation and soils of Kharkov province, Krasnov A.N.