How the plains differ in appearance. Ways to form plains

Plains– vast areas of the earth’s surface with small (up to 200 m) fluctuations in height and slight slopes.

Plains occupy 64% of the land area. Tectonically, they correspond to more or less stable platforms that did not show significant activity in modern times, regardless of their age - whether they are ancient or young. Most of the land's plains are located on ancient platforms (42%).

Based on the absolute height of the surface, plains are distinguished negative– lying below the level of the World Ocean (Caspian region), low-lying– from 0 to 200 m altitude (Amazonian, Black Sea, Indo-Gangetic lowlands, etc.), sublime– from 200 to 500 m (Central Russian, Valdai, Volga uplands, etc.). Plains also include plateau(high plains), which, as a rule, are located above 500 m and are separated from the adjacent plains by ledges (for example, the Great Plains in the USA, etc.). The depth and degree of dissection of them depends on the height of the plains and plateaus river valleys, gullies and ravines: the higher the plains, the more intensely they are dissected.

In terms of appearance, plains can be flat, wavy, hilly, stepped, and in terms of the general slope of the surface - horizontal, inclined, convex, concave.

The different appearance of the plains depends on their origin and internal structure, which largely depend on the direction of neotectonic movements. Based on this feature, all plains can be divided into two types - denudation and accumulation (see diagram 1). Within the former, the processes of denudation of loose material predominate; within the latter, its accumulation occurs.

It is clear that denudation surfaces have experienced upward tectonic movements for most of their history. It was thanks to them that the processes of destruction and demolition - denudation - prevailed here. However, the duration of denudation may vary, and this is also reflected in the morphology of such surfaces.

With continuous or almost continuous slow (epeirogenic) tectonic uplift, which continued throughout the entire existence of the territories, there were no conditions for the accumulation of sediments. There was only a denudation of the surface by various exogenous agents, and if thin continental or marine sediments accumulated for a short time, then during subsequent uplifts they were carried out of the territory. Therefore, in the structure of such plains, an ancient base comes to the surface - folds cut off by denudation, only slightly covered by a thin cover of Quaternary deposits. Such plains are called basement; It is easy to see that the basement plains tectonically correspond to the shields of ancient platforms and the protrusions of the folded foundation of young platforms. Basement plains on ancient platforms have a hilly topography, most often they are elevated. These are, for example, the plains of Fennoscandia - the Kola Peninsula and Karelia. Similar plains are located in northern Canada. Basement hills are widespread in Africa. As a rule, long-term denudation has cut off all the structural irregularities of the base, so such plains are astructural.

The plains on the “shields” of young platforms have a more “restless” hilly topography, with residual hill-type elevations, the formation of which is associated either with lithological features - harder stable rocks, or with structural conditions - former convex folds, microhorsts or exposed intrusions. Of course, they are all structurally determined. This is what, for example, the Kazakh small hills and part of the Gobi plains look like.

The plates of ancient and young platforms, experiencing a stable uplift only during the neotectonic stage of development, are composed of layers of sedimentary rocks of great thickness (hundreds of meters and a few kilometers) - limestones, dolomites, sandstones, siltstones, etc. Over millions of years, the sediments hardened, became rocky and acquired stability to erosion. These rocks lie more or less horizontally, as they were once deposited. Uplifts of territories during the neotectonic stage of development stimulated denudation on them, which did not allow young loose rocks to be deposited there. Plains on slabs of ancient and young platforms are called reservoir. From the surface, they are often covered with loose Quaternary continental sediments of low thickness, which practically do not affect their height and orographic features, but determine them appearance due to morphosculpture (East European, southern part of West Siberian, etc.).

Since strata plains are confined to platform plates, they are clearly structural - their macro- and even mesoforms of relief are determined by the geological structures of the cover: the nature of the bedding of rocks of varying hardness, their slope, etc.

During the Pliocene-Quaternary subsidence of territories, even relative ones, sediments carried away from surrounding areas began to accumulate on them. They filled in all the previous surface irregularities. This is how they were formed accumulative plains, composed of loose, Pliocene-Quaternary sediments. These are usually low-lying plains, sometimes even below sea level. According to the conditions of sedimentation, they are divided into marine and continental - alluvial, aeolian, etc. An example of accumulative plains are the Caspian, Black Sea, Kolyma, Yana-Indigirskaya lowlands composed of marine sediments, as well as the Pripyat, Leno-Vilyui, La Plata, etc. Accumulative Plains, as a rule, are confined to syneclises.

In large basins among the mountains and at their feet, accumulative plains have a surface inclined from the mountains, cut through by the valleys of many rivers flowing from the mountains and complicated by their alluvial cones. They are composed of loose continental sediments: alluvium, proluvium, colluvium, and lake sediments. For example, the Tarim Plain is composed of sands and loess, the Dzungarian Plain is composed of powerful sand accumulations brought from neighboring mountains. The ancient alluvial plain is the Karakum desert, composed of sands brought by rivers from southern mountains during the pluvial epochs of the Pleistocene.

The morphostructures of plains usually include ridges These are linearly elongated hills with rounded peaks, usually no more than 500 m high. They are composed of dislocated rocks of different ages. An indispensable feature of a ridge is the presence of a linear orientation, inherited from the structure of the folded region in which the ridge arose, for example, Timan, Donetsk, Yenisei.

It should be noted that all of the listed types of plains (basement, strata, accumulative), as well as plateaus, plateaus and ridges, according to I. P. Gerasimov and Yu. A. Meshcheryakov, are not morphographic concepts, but morphostructural ones, reflecting the relationship of relief with geological structure.

Plains on land form two latitudinal series corresponding to the platforms of Laurasia and Gondwana. Northern Plains Row formed within the relatively stable ancient North American and East European platforms in recent times and the young epi-Paleozoic West Siberian platform - a plate that experienced even slight subsidence and is expressed in relief as a predominantly low-lying plain.

The Central Siberian Plateau, and in the morphostructural sense these are high plains - plateaus, formed on the site of the ancient Siberian Platform, activated in recent times due to resonant movements from the east, from the active geosynclinal Western Pacific belt. The so-called Central Siberian Plateau includes volcanic plateaus(Putorana and Syverma), tuffaceous plateaus(Central Tunguska), trap plateaus(Tungusskoye, Vilyuiskoye), reservoir plateaus(Priangarskoye, Prilenskoye), etc.

The orographic and structural features of the northern plains are unique: low coastal accumulative plains predominate beyond the Arctic Circle; to the south, along the so-called active 62° parallel, there is a strip of basement hills and even plateaus on the shields of ancient platforms - Laurentian, Baltic, Anabar; in middle latitudes along 50° N. w. - again a strip of stratal and accumulative lowlands - North German, Polish, Polesie, Meshchera, Sredneobskaya, Vilyuiskaya.

On the East European Plain, Yu.A. Meshcheryakov also identified another pattern: the alternation of lowlands and hills. Since the movements on the East European Platform were wave-like in nature, and their source in the neotectonic stage was collisions of the Alpine belt, he established several alternating stripes of hills and lowlands, fanning out from the southwest to the east and taking an increasingly meridional direction as they move away from the Carpathians . The Carpathian strip of uplands (Volyn, Podolsk, Prydneprovskaya) is replaced by the Pripyat-Dnieper strip of lowlands (Pripyat, Prydneprovskaya), followed by the Central Russian strip of uplands (Belarusian, Smolensk-Moscow, Central Russian); the latter is successively replaced by the Upper Volga-Don strip of lowlands (Meshchera lowland, Oka-Don plain), then by the Volga upland, Trans-Volga lowland and, finally, by a strip of the Cis-Ural uplands.

In general, the plains of the northern series are inclined to the north, which is consistent with the flow of the rivers.

Southern Plains Row corresponds to the Gondwana platforms, which have experienced activation in recent times. Therefore, elevations predominate within its boundaries: stratum (in the Sahara) and basement (in southern Africa), as well as plateaus (Arabia, Hindustan). Only within the inherited troughs and syneclises did strata and accumulative plains form (Amazonian and La Plata lowlands, Congo depression, Central Lowland of Australia).

In general, the largest areas among the plains on the continents belong to strata plains, within which the primary plain surfaces are formed by horizontally lying layers of sedimentary rocks, and the basement and accumulative plains are of subordinate importance.

In conclusion, we emphasize once again that mountains and plains, as the main forms of relief on land, are created by internal processes: mountains gravitate towards mobile folded belts

Earth, and plains - to platforms (Table 14). Relatively small, relatively short-lived relief forms created by external exogenous processes superimpose on large ones and give them a unique appearance. They will be discussed below.

Plains are areas of the land surface, the bottom of oceans and seas, characterized by slight fluctuations in height (up to 200 m, slopes less than 5°). According to the structural principle, plains of platform and orogenic (mountain) regions are distinguished (mainly within intermountain and foothill troughs); according to the predominance of certain external processes - denudation, formed as a result of the destruction of elevated relief forms, and accumulative, resulting from the accumulation of layers of loose sediments. Collectively, the plains occupy most of the Earth's surface, 15-20% of the land. The largest plain in the world is the Amazon (over 5 million sq. km).

Numerous types of plains are distinguished by the nature and height of the surface, geological structure, origin and history of development. Depending on the appearance and size of the irregularities, they are distinguished: flat, wavy, ridged, stepped plains. Based on the shape of the surface, horizontal plains (the Great Chinese Plain), sloping plains (mainly foothills), and concave plains (in the intermountain depressions - the Tsaidam Basin) are distinguished.

The classification of plains by height relative to sea level is widespread. Negative plains are located below sea level, often in deserts, for example, the Qattara Depression or the lowest place on land - the Ghor Depression (up to 395 m below sea level). Low plains, or lowlands (altitudes from 0 to 200 m above sea level), include greatest plains world: Amazonian Lowland, East European Plain and West Siberian Plain. The surface of elevated plains, or hills, is located in the altitude range of 200-500 m (Central Russian Upland, Valdai Upland). Mountain plains rise above 500 m, for example, one of the largest in Central Asia- Gobi. The term plateau is often applied to both elevated and upland plains with a flat or undulating surface separated by slopes or ledges from lower neighboring areas.

The appearance of the plain depends largely on external processes. Based on the amount of influence of external processes, plains are divided into accumulative and denudative. Accumulative plains, formed by the accumulation of layers of loose sediments (accumulation), are river (alluvial), lake, sea, ash, glacial, and water-glacial. For example, the thickness of sediments, mainly fluvial and marine, in the Flanders Lowland (coast North Sea) reaches 600 m, and the thickness of silty rocks (loess) on the Loess Plateau is 250-300 m. Accumulative plains also include volcanic plateaus composed of solidified lavas and loose products of volcanic eruptions (Dariganga Plateau in Mongolia, Columbia Plateau in North America).

Denudation plains arose as a result of the destruction of ancient hills or mountains and the removal of the resulting material by water and wind (denudation). Depending on the predominant process due to which the ancient relief was destroyed and the surface leveled, erosion (with the predominance of the activity of flowing waters), abrasion (created by wave processes on the surface) are distinguished. sea ​​coasts), deflationary (wind-leveled) and other denudation plains. Many plains have a complex origin, as they were formed various processes. Depending on the mechanism of formation, denudation plains are divided into: peneplains - in this case, the removal and demolition of material occurred more or less evenly from the entire surface of ancient mountains, for example, the Kazakh small hills or the Tien Shan syrts; pediplains that arise from the destruction of previously elevated relief, which begins from the outskirts (many plains at the foot of the mountains, mainly deserts and savannas of Africa).

The participation of tectonic processes in the formation of plains can be either passive or active. With passive participation main role in the formation of structural plains, the rather even - horizontal or inclined (monoclinal) - occurrence of layers plays a role rocks(Turgai plateau). Many structural plains are simultaneously accumulative, for example, the Caspian Lowland, the North German Lowland. When denudation predominates in the formation of structural plains, stratified plains are distinguished (Swabian-Franconian Jura). What differs from them are the basement plains, developed in dislocated rocks (Lake Plateau in Finland). During intermittent tectonic uplifts, followed by a period of rest sufficient to destroy and level the relief, tiered plains are formed, for example, the Great Plains.

Platform plains are formed in areas of relatively quiet tectonic and magmatic activity. These include most of the plains, including the largest ones. The plains of orogenic regions (see orogen) are distinguished by intense activity of the earth's interior. These are the plains of intermountain basins (Fergana Valley) and foothill troughs (Podolsk Upland). Sometimes the plains are considered parts of the so-called lowland countries - vast spaces where there are small areas with highly dissected relief (for example, Zhiguli on the Russian Plain - a flat country).

• Lowland is a plain that rises no higher than 200 m above sea level.
• Highlands are flat areas of land with an altitude of 200 to 500 meters above sea level.
• A plateau is a plain with a flat or slightly undulating surface, elevated above sea level by more than 500 meters.

Accumulation

Seabed rise

Change of plains under the influence of water flows

Just like the mountains, the plains gradually change. Much work is done on them by water flows, both permanent (rivers) and temporary, which form on the slopes after heavy rains or during the spring snow melt.

Each tributary of the river digs out a valley through which it flows, each tributary erodes the banks and deepens, albeit slowly, its bed. The process of erosion occurs especially quickly on hills and plateaus, since the rivers originating from them have a more rapid flow.

Water flowing over the surface washes away the top, arable layer of soil from the fields along with nutrients, which are so necessary for plants. The washout occurs especially quickly on steep slopes not covered with vegetation; that's why steep slopes are not plowed. Slopes with a slight slope should only be plowed across. When plowing a slope transversely, the flowing water is retained by the furrows, absorbed into the ground and does not wash away the soil. Thus, millions of hectares of fertile soil are preserved from erosion. Material from the site

Changing plains under the influence of wind

The winds, sweeping over the plains, do great destructive work. It happens that hurricane-force winds blow over the plains for several days in a row, without ceasing. Begins dust storm. In one such storm, the wind can remove a layer of soil up to 25 cm thick, and previously fertile lands turn into barren wastelands.

Grass strips, which are created at certain intervals in the fields, as well as forest strips, reduce soil blowing.

Especially great job produces wind on plains covered with loose sand, not fastened by plant roots - dunes and dunes. Open space Sands are never level.

How the plains are depicted physical map? Tell us about a plain you know well.

1. Flat and hilly plains. Most of globe occupy the plains. Vast areas of flat or hilly surface of the Earth, individual sections of which vary in height, are called plains.
Imagine a flat, treeless steppe covered with grass. On such a plain, the horizon is visible from all sides and has a rectilinear outline of its boundaries. This is a flat plain.
Eurasia between the Yenisei and Lena rivers is located Central Siberian Plateau. Plateaus also occupy most of Africa.

The second type of plains is hilly plains. The relief of the hilly plains is very complex. There are separate hills and hills, ravines and depressions here.
The surface of plains usually slopes in one direction. The direction of river flow corresponds to this slope. The slope of the plain is clearly visible on the plan and map. Plains are most convenient for economic activity person. Most settlements are located on the plains. Flat terrain is convenient for agriculture, for the construction of transport routes, and industrial buildings. Therefore, people have been exploring lowland areas since ancient times. Currently, the vast majority of the peoples of the globe inhabit lowland areas.

2. Based on absolute height, three types of plains are distinguished (Fig. 43). Plains with an altitude of up to 200 m above sea level are called lowlands. On the physical map, lowlands are depicted green. Lowlands located near the coast of the sea are below its level. These include Caspian lowland in the west of our country. The largest lowland on the globe is the Amazon. South America.

Rice. 43. Differences in plains in height.

Plains with an absolute height of 200 m to 500 m are called hills (for example, hill Ustyurt between the Caspian and Aral seas). On physical maps, elevations are depicted in a yellowish color.
Plains with a height of more than 500 m are classified as plateaus. Plateaus are shown in brown on the map.

3. Formation of plains. Based on the method of formation, plains are divided into several types. Plains that are formed as a result of the exposure and uplift of the seabed are called primary plains. These plains include the Caspian Lowland.
There are plains around the globe formed from river sediments and sediments. On such plains, the thickness of sedimentary rocks, consisting of pebbles, sand, and clay, sometimes reaches several hundred meters. These plains include La Plata along the Parana River in South America, in Asia - Great Chinese Plain, Indo-Gangetic And Mesopotashian. At the same time, there are plains on the earth’s surface formed as a result of the long-term destruction of mountains. Such plains consist of folded layers of hard rocks. That's why they are hilly. Examples of rolling plains include East European Plain And Saryarka plain.
Some plains are formed by lava flows pouring onto the earth's surface. In this case, it is as if the existing irregularities are leveled. These plains include the following plateaus: Central Siberian, Western Australian, Deccan.

4.Change of plains. On the plains there are slow oscillatory movements caused by the influence of internal forces.
The plains are subject to various changes under the influence of external forces. Looking at a physical map, you will see how the surface of the earth is cut up by rivers and their tributaries. River water, washing away the banks and base, forms a valley. Because lowland rivers flow meanderingly, they form wide valleys. The greater the slope, the more river crash into the surface of the Earth and change its relief.
In spring, meltwater and rainwater create temporary surface currents (watercourses), forming ravines and ditches. Typically, gullies form on small hillsides that are not held together by plant roots. If measures are not taken in time ­ treading, the ravines branch out and grow. This can cause great damage to the farm: fields, arable land, gardens, roads, and various buildings. To stop the growth of ravines, they are covered with peat, crushed stone, and stones. The bottom and slopes are covered with peat, which creates conditions for the growth of vegetation.
A ditch, like a ravine, is an elongated depression. The only difference is that the ditch has gentle slopes. Its bottom and slopes are covered with grass and bushes.
The plains also change under the influence of the wind. Wind breaks down solid rocks and carries away particles. In deserts, steppes, arable lands and seashores, the effect of wind is very noticeable. On the coasts of the seas or large lakes you can see sand ridges formed by waves. The wind blowing from the sea surface easily carries dry sand from the shores. The grains of sand move with the wind until they encounter any obstacle (bush, stone, etc.). The sand, accumulating in this place, gradually takes the form of elongated mounds; on the side from which the wind blows, the slopes are gentle, and on the other, steeper. The two lower edges of the mound elongate and gradually decrease, so they acquire a crescent shape. These sandy hills are called dunes.
The height of the dunes, depending on the amount of sand and wind strength, reaches from 20-30 m to 50-100 m. The wind, blowing grains of sand from the slopes, shifts them towards the slope. Due to this, they are constantly moving forward.
Large dunes, moving from 1 m to 20 m per year, gradually change the terrain, and small dunes strong storm They move up to 2-3 m per day. Moving dunes cover forests, gardens, fields, and populated areas.
Sand hills in the desert are called dunes (Fig. 44). If dunes are formed by the accumulation of sand brought by the waters of oceans, seas and rivers, then dunes arise from sand during the weathering of local rocks. In our country, dunes are common in the Northern Aral Sea region, in the Kyzylkum desert, the Caspian lowland, and in the Southern Balkhash region. The height of the dunes usually reaches 15-20 m, and in the largest deserts of the globe - the Sahara, Central Asia, Australia - up to 100-120 m.

Rice. 44. Dunes.

Barchans, like dunes, are moved by the wind. Small dunes move up to 100-200 m per year, and large ones - up to 30-40 m per year. In most cases, the person himself contributes to the movement of sand. Sand hills are being transformed into wandering sands as a result of deforestation and overgrazing of pastures.
To stop the movement of dunes and dunes, drought-resistant shrubs and plants are planted on their gentle slopes. Trees are planted in the hollows between the hills.

1. What are called plains? What types of plains are there?

2. How do plains vary in elevation?

3. On the physical map, find all the plains named in the text.

4. If your area is flat, describe the topography of the land. Based on the height and relief, determine what type of plain it belongs to. Find out from adults how your area is used economically?

5. What forces and how do they influence changes in the relief of the plains? Justify your answer with specific examples.

6. Why can’t running water wash away the soil of the slopes with vegetation?

7*. In which parts of Kazakhstan is sandy terrain common and why?

The earth's topography is a collection of oceans and seas and land surface irregularities that vary in age, origin and size. It consists of shapes that combine with each other. The Earth's topography is quite diverse: gigantic ocean depressions and vast expanses of land, endless plains and mountains, high hills and deep gorges. Plains occupy the bulk of the Earth's surface. This article will give full description plains.

Mountains and plains

Various sciences study the reliefs of the Earth. The main landforms are mountains and plains. The question regarding what mountains and plains are can most fully be answered by geography. Plains are areas of land occupying 60% of the Earth's surface. Mountains occupy 40%. Definition of mountains and plains:

• Plains are fairly large areas of land with slight slopes and slight fluctuations in elevation.
• Mountains are vast, raised high above the plains and sharply dissected areas of land with significant differences in elevation. Mountain structure: folded or folded-block.

Based on absolute height, mountains are divided into:

• Low mountains. The height of such mountains is up to 1000m. They usually have gentle peaks, rounded slopes and relatively wide valleys. These include some mountains in northern Russia and Central Europe, for example the Khibiny Mountains on the Kola Peninsula.
• Srednegorye. Their height ranges from 1000m to 2000m. These include the Apennines and Pyrenees, the Carpathian and Crimean mountains and others.
• Highlands. These mountains have a height of more than 2000m. These are the Alps, Himalayas, Caucasus and others.

Plains classification

Plains are divided into types according to different characteristics, for example, by height, by surface type, by the history of their development and their structure. Types of plains by absolute height:

1. Plains lying below sea level. An example would be depressions such as Qattara, its height is 133 m below sea level, the Turfan depression, and the Caspian lowland.
2. Lowland plains. The height of such plains ranges from 0 to 200m. These include the largest plains in the world, the Amazon and La Plata lowlands.
3. The high plains range in height from 200m to 500m. An example is Great Desert Victoria.
4. Upland plateaus above 500m in height, such as the Ustyurt Plateau, Great Plains North America and others.

The surface of a plain can be inclined, horizontal, convex or concave. Plains are classified according to the type of surface: hilly, wavy, ridged, stepped. As a rule, the higher the plains, the more dissected they are. The types of plains also depend on the history of development and their structure:

• alluvial valleys, such as the Great Chinese Plain, Karakum Desert, etc.;
• glacial valleys;
• water-glacier, for example Polesie, the foothills of the Alps, the Caucasus and Altai;
• flat, low-lying sea plains. Such plains are a narrow strip along the coasts of seas and oceans. These are such plains as the Caspian and Black Sea.

There are plains that arose in place of the mountains after their destruction. They are composed of hard crystalline rocks and crumpled into folds. Such plains are called denudation plains. Examples of them are the Kazakh sandpiper, the plains of the Baltic and Canadian shields.

The climate of the plain depends on the climatic zone they are located and on what air masses they are influenced. This article systematized data on the main reliefs of the Earth and gave the concept of what mountains are and what a plain is.