Geography is a science that studies the geographical shell of the earth, and it is also the science of the earth's relief. Relief is a constantly changing form of the earth's surface or a set of irregularities of the earth's surface, differing in origin, size and age. Over millions of years of the history of the Earth, under the influence of various forces, where there were mountains, plains appeared, and where there were plains, high active volcanoes arose.

There is a direct relationship between the relief of the earth and the structure of the lithosphere. So mountains formed at the junctions of lithospheric plates, and plains in the centers of the plates.

Landforms or morphostructures

There are such large and small landforms as

• continents- the largest forms; scientists believe that there was once only one continent, the gradual separation of which led to the modern appearance of the Earth;
• ocean trenches- also a large form of the earth's relief, which forms due to the movement of lithospheric plates; it is believed that once there were fewer oceans on earth, and in hundreds of thousands of years the situation will change again, perhaps some parts of the land will be flooded with water;
• the mountains- the most grandiose forms of the earth's relief, reaching grandiose height, mountains can form chains of mountains;
• highlands- free-standing mountains and range systems, such as the Pamirs or the Tien Shan;
• shelves- land areas completely hidden under water;
• plains- the most flat earth's surface, the best place for human life.

Fig 1. Relief of the Earth

Such forms have a specific name - morphostructures. Scientists distinguish between such types of morphostructures as planetary and regional, which were formed later. Tectonic movements participated in their development, and against their background there were movements of the upper horizons of the lithosphere.

Reasons for the transformation of the earth's surface

Changes in the relief of the Earth occur for various reasons. Transformation can occur under the influence of both internal and external forces.

External forces do not affect the earth's relief as much as internal ones.

internal forces

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Internal forces include:

• earthquakes;
• movements of the earth's crust (tectonic movements);
• volcanism.

These processes lead to:

• mountains and mountain ranges (moreover, both on land and at the bottom of the seas and oceans);
• chains of volcanoes;
• geysers and hot springs;
• ledges;
• cracks;
• hollows and much more.

Outside forces

External forces include:

• weathering:
• the power of flowing water;
• underground water power
• melting glaciers;
• active transformational activity of people.

Naturally, external forces are not capable of producing global changes in the earth's relief. But long-term influence of this or that factor leads to transformation. Gradually appear

• hills, ravines, hollows, dunes and dunes, river valleys (all this refers to flat landforms);
• scree, gorges and rocks of bizarre outlines (all this refers to mountain forms of the earth's relief). Interestingly, external forces, acting gradually over a long period of time, are also capable of leading to global destruction. So water is quite capable of destroying a whole mountain.

It must be remembered that the relief is also influenced by such external processes as:

• circulation of water in the atmosphere;
• movement of air masses;
• change of vegetation cover;
• animal migration.

More detailed information is presented in the table of external forces that change the relief of the earth's surface (it can be used in geography lessons in grade 7).

Process	Example	Manifestation in relief	Process essence
Weathering	Fig 2. Weathering	talus formation
wind force	Figure 3. Wind strength	formation of barkhans and dunes	transfer rocks and loose deposits
water power	Fig 4. The power of water	destruction of rocks	transport and erosion of rocks
Melting glaciers	Fig 5. Melting glaciers	changes in the shape of the continents	increase in the volume of water in the oceans

Internal forces usually create various landforms, while external forces destroy them.

Relief age

The time that has elapsed since the formation of the modern appearance of the Earth is called the age of the relief. It could be years, hundreds, thousands, millions of years. The age of large relief forms can range from 200 to 90 million years. In addition to age, there are also numerical characteristics of the surface of the relief.

What have we learned?

The relief of the Earth is characterized by great diversity, complexity and incredible morphostructures. Why is the landform so diverse? There are large and small irregularities that occur under the influence of internal and external forces. Transformation and changes occur slowly, gradually, one human life is not enough to notice all the changes that have taken place. The earth's surface seems to breathe, then it falls, then it rises, and sometimes it simply bursts from the stresses that have arisen. Thus, the development of the Earth's relief is going on at the present time.

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Relief is a set of irregularities on the Earth's surface, characterized by different ages, history of development, nature of occurrence, outline, etc. The relief can be considered as part of the landscape. It refers to the geographical features that control climate, weather, and the nature of life on Earth. talking in simple words: Any shape on the surface of the Earth is known as landform.

Topographic relief map of the Earth

Origin of relief

The various forms of landforms that we have today have arisen due to natural processes: erosion, wind, rain, weather conditions, ice, chemical influences, etc. natural processes and natural disasters such as earthquakes and volcanic eruptions have created the various landforms we see today. Water and wind erosion can wear down land and form landforms such as valleys and canyons. Both processes take place over a long period of time, sometimes taking millions of years.

It took about 6 million years for the Colorado River to cut through the US state of Arizona. The Grand Canyon is 446 kilometers long.

The highest landform on Earth is Mount Everest in Nepal. Its peak is located at an altitude of 8,848 meters above sea level. This is part of the Himalayas, which is located in several Asian countries.

The deepest relief on Earth (almost 11,000 m) is the Mariana Trench (Marian Trench), which is located in the South Pacific Ocean.

The main landforms of the earth's crust

Mountains, hills, plateaus and plains are the four main landforms. Minor landforms include remnants, canyons, valleys, basins, basins, ridges, saddles, hollows, etc.

The mountains

A mountain is a large landform that extends above the surrounding land in a limited area, usually in the form of a peak or mountain system. The mountain is usually steeper and taller than the hill. Mountains are formed by tectonic forces or volcanism. These forces can locally lift the Earth's surface. Mountains are slowly being destroyed by the action of rivers, weather patterns and glaciers. Several mountains are individual peaks, but most of them are found on huge mountain ranges.

On the tops of high mountains, the climate is colder than at sea level. Weather conditions strongly influence: for different heights, a difference in flora and fauna is inherent. Due to the less favorable landscape and climate, mountains tend to be used less for Agriculture and more for and recreation such as mountain climbing.

The highest known mountain in solar system- Olympus Mons on Mars - 21171 m.

hills

Hills are a landform that protrudes above the surrounding area. Them distinctive feature, as a rule, is a rounded or oval top.

The distinction between hill and mountain is not clearly accepted throughout the world, and is largely subjective, but a hill is universally considered to be less high and less steep than a mountain. The Great Soviet Encyclopedia defines a hill as a hill with a relative height of up to 200 m.

Plateau

A plateau is a flat, elevated landform that rises abruptly from the surrounding terrain on at least one side. Plateaus are located on every continent and occupy a third of the land of our planet and are one of the main landforms of the Earth.

There are two types of plateaus: dissected and volcanic.

• A dissected plateau is formed as a result of an upward movement in the earth's crust. The uplift is caused by the slow collision of tectonic plates.

The Colorado Plateau, in the western United States, has been growing at about 0.3 centimeters per year for over 10 million years.

• The volcanic plateau is formed by numerous small volcanic eruptions that build up slowly over time, forming a plateau of lava flows.

The North Island Volcanic Plateau covers a large area of ​​the central North Island of New Zealand. There are still three active volcanoes on this volcanic plateau: Mount Tongariro, Mount Ngauruhoe, and Mount Ruapehu.

A valley is formed when river water cuts through a plateau. The Columbia Plateau, located between the Cascade and Rocky Mountains in the northwestern United States, is cut through by the Columbia River.

Erosion also forms a plateau. Sometimes it is so eroded that it breaks into smaller raised areas.

The largest plateau in the world is the Tibetan Plateau, located in Central Asia. It extends through Tibet, China and India, covering an area of ​​2.5 million km².

Plains

In geography, a plain is a flat, wide surface of the Earth, which usually does not change much in height (the fluctuation in height is not more than 200 meters, and the slope is less than 5 °). Plains occur as lowlands along mountain valleys, coastal plains, or small uplands.

The plain is one of the main landforms on our planet. They are present on every continent and cover more than one third of the world's land mass. Plains are usually grassland (temperate or subtropical), steppe (semi-arid), savannah (tropical), or tundra (polar) biomes. In some cases, deserts and rainforests can also be plains.

However, not all plains are meadows. Some of them, such as the Tabasco plain of Mexico, are covered with forests. The forest plains have different types trees, shrubs and other vegetation.

They can also be classified as plains. Part of the Sahara, the great desert in North Africa, has a flat relief.

In the Arctic, where the earth freezes, the plains are called. Despite the cold, many animals and plants survive here, including shrubs and moss.

relief elements

Land forms are classified according to characteristic physical features such as height, slope, orientation, rock exposure, and soil type. The terrain includes such elements as: berms, ridges, cliffs, valleys, rivers, islands, volcanoes and many other structural and dimensional (i.e. ponds and lakes, hills and mountains) elements, including different kinds inland and ocean water bodies, as well as subsurface objects.

The elements of individual landforms include: lines, points, surface angles, etc.

terrain levels

The relief can be classified as follows:

Relief of the first level

The entire lithosphere, consisting of continental and oceanic crust, is located under the relief of the first level.

The continental crust is less dense than the oceanic crust and is composed primarily of granitic rock, which includes silica and aluminium. While the oceanic crust is composed of basaltic rocks, silica and magnesium.

The relief of the first level mainly reflects the initial cooling and solidification of the earth's crust at the time of its formation.

Relief of the second level

This type of relief basically consists of all the endogenous forces that occur inside the earth's crust, in its bowels. Endogenous forces are responsible for the development of land surface variations.

Endogenous processes are classified as follows:

• Diastrophism - deformation of the earth's crust under the influence of the internal energy of our planet;
• Volcanism/Earthquakes.

The mountains - best example a product of endogenous processes on the continental crust, and in the oceanic crust - underwater ridges and trenches.

Relief of the third level

This type of relief is mainly composed of exogenous forces. Exogenous forces are those forces that arise on the surface of the Earth.

All exogenous forces are responsible for leveling the surface of the planet. The leveling process includes erosion, transport and sedimentation, resulting in the formation of valleys (due to erosion) and deltas (due to sedimentation). The following are the natural phenomena that carry out the entire alignment process:

• Running water (rivers);
• Wind;
• The groundwater;
• Glaciers;
• Sea waves.

Important note: all of the above phenomena do not work beyond the boundaries of the coastline. This means that the relief of the third level is limited only by the continental crust.

However, the continental margin (the area of ​​the ocean floor located between the deep sea and the coastline) may show signs of a third-level topography due to changes in mean sea level, climatic conditions, or region-specific processes.

Terrain height above sea level

The height of the area above sea level shows at what distance relative to the mean sea level (taken as zero) is the measured area (if it is a flat area) or a certain object.

Mean sea level is used as basic level to measure depth and height on Earth. Temperature, gravity, wind, currents, climate and other factors influence and change sea levels over time. For this and other reasons, recorded altitude measurements may differ from the actual altitude of a given location at that time.

On the territory of the CIS countries, the Baltic system of heights is used. The device for measuring the height of the Baltic Sea is called the Kronstadt footstock and is located at the mouth of the Blue Bridge, in the Kronstadt district of St. Petersburg.

Relief age

When it comes to measuring the age of a relief, the following terms are used in geomorphology:

• The absolute age of the relief is expressed in terms of time, as a rule, in years, during which the characteristic unevenness was formed.

• The relative age of the relief is a reflection of its development to a certain stage. In this case, the age of the relief can be determined by comparing it with other landforms.

Relief value

Understanding terrain features is critical for many reasons:

• The topography largely determines the suitability of an area for human settlement: flat, alluvial plains tend to have better soils suitable for agricultural activities than steep, rocky uplands.

• As for the quality environment, agriculture and hydrology, then understanding the terrain allows you to understand the boundaries of watersheds, drainage system, movement of water and influence on its quality. Integrated elevation data is used to predict river water quality.

• Understanding the terrain also supports soil conservation, especially in agriculture. Contour plowing is a common practice for sustainable farming on slopes; such plowing is characterized by tilling the soil along the lines of elevation rather than up and down the slope.

• Terrain is critical during military operations as it determines the ability of the military to capture and hold areas and move troops and materials. Understanding the terrain is fundamental to both defensive and offensive strategy.

• The terrain plays an important role in determining weather conditions. Two areas that are geographically close to each other can drastically differ in rainfall levels due to elevation differences or the "rain shadow" effect.

• Accurate knowledge of the terrain is vital in aviation, especially for low-flying routes and maneuvers, as well as airport altitudes. Terrain also affects the range and performance of radars and ground-based radio navigation systems. In addition, hilly or mountainous terrain can greatly influence the construction of a new airfield and the orientation of its runways.

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

The concept of relief

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

Variety of forms

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

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

Relief types

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

flat relief

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

hilly terrain

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

uplands

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

relief formation

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

Geological observations

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

Mapping

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

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

Note to the young geomorphologist

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

The "calm" life of the Earth's stone shell ends as soon as it comes into contact with water or gases. Then amazing transformations take place on the earth's surface and phenomena are observed that simply cannot arise in the deep bowels.

The relief of the Earth is a combination of various surface irregularities, both large and small, resulting from the activity of external and internal forces. An important role in the formation of relief is played by gravity, density and composition of rocks, activity and flowing waters. The formidable forces of nature, setting in motion the strongest rock massifs, both destroy them to the ground and create new mountains, gorges and valleys. Even on the vast plains appear, which eventually become covered with silt and large debris. This happens rather slowly, and the whole human life is not enough to notice changes in the surface. It seems to be breathing - it rises, then falls, waves run through it, it bursts from the stresses that have arisen.

On the surface of the planet, water circulates (from to land and further to), a change in vegetation cover and migration of animals, the movement of large debris and the smallest ache. Scientists consider all this to be a process of matter and energy exchange, which leads to the formation of loose sediments, and at the same time to the formation, i.e., to the process of morpholithogenesis. Even if a few grains of sand move a short distance or with water, a small hole or bump will appear on the surface. However, morpholithogenetic analysis reveals only a part of the relationships between the relief, atmosphere, and natural waters. The other part of the connections is shown by morphostructural analysis.

Morphostructures called the geological structures expressed in the modern relief. The largest morphostructures on Earth are. They belong to planetary morphostructures, within which there are mountain belts, plateaus and plains, underwater ridges and basins, differing in the structure of the earth's crust, type and speed, and the degree of participation of other factors in their formation. Thus, planetary morphostructures are composed of smaller regional morphostructures.

The relief of large regions was formed over many millions of years. On the sites of ancient platforms, a crystalline basement, composed of gneisses, granites, shales and sandstones, usually comes to the surface. Such a foundation serves as a base for the relief, a plinth, and those built by these rocks are called basement plains. In Russia, they can be found in, on, in the north of Siberia.

The analysis is used in the study of large landforms composed of various rocks; tectonic movements that caused the appearance of large landforms; discontinuous disturbances - faults that limit morphostructures.

If we talk about the age of the relief of large mountain belts, then it is obvious that their age is at least 200 million years; if, for example, we are talking about the age of the Caucasus Mountains, then it will be 80-90 million years. In both cases, to determine the age of the relief, it is necessary to know the beginning of the appearance of its largest and most characteristic forms. In mountainous areas, this is the formation of not only ridges, but also intermountain depressions. Often, to determine the time of the beginning of the division of the relief into hills and hills, mountains and depressions, the age of one of the ancient alignment surfaces is taken as the starting point of reference. This is the name of the wavy plain that existed in the past on many, slightly dissected by erosion.

The beginning of the division of the plain is the starting point for determining the age of the relief.

Relief age- the time that has elapsed since the formation of its modern appearance. It is measured in a single time - in years, hundreds, thousands, millions of years, although time ranges are often used, calling the relief Mesozoic, Neogene-Quaternary, Late Pleistocene, etc.

Formation of the Earth's relief

Features of the Earth's relief

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

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

Tectonic factors

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

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

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

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

External factorsLet's look at question 3.

2. Types of relief.
All landforms are divided into:

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

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

- just horizontal ,

- oblique surfaces.

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

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

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

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

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

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

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

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

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

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

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

By origin, mountains are tectonic, volcanic and erosional.

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

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

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

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

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

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

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

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

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

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

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

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

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

3. External processes that transform the surface of the Earth.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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