Mountains differ not only in their height, landscape diversity, size, but also in origin. There are three main types of mountains: block, folded and domed mountains.

How blocky mountains are formed

The earth's crust does not stand still, but is in constant motion. When cracks or faults of tectonic plates appear in it, huge masses of rock begin to move not in the longitudinal, but in the vertical direction. Part of the rock can fall in this case, and the other part, adjacent to the fault, rise. An example of the formation of blocky mountains is the Teton mountain range. This ridge is located in Wyoming. On the eastern side of the ridge, sheer rocks are visible, which have risen during the fracture of the earth's crust. On the other side of the Teton ridge, there is a valley that sank down.

How folded mountains are formed

The parallel movement of the earth's crust leads to the appearance of folded mountains. The appearance of folded mountains is best seen in the famous Alps. The Alps arose as a result of the collision of the lithospheric plate of the continent of Africa and the lithospheric plate of the continent of Eurasia. Over the course of several million years, these plates have been in contact with each other with tremendous pressure. As a result, the edges of the lithospheric plates crumpled, forming giant folds, which over time were covered with faults. This is how one of the most magnificent mountain ranges in the world was formed.

How domed mountains form

Hot magma is found inside the earth's crust. Magma, breaking up under tremendous pressure, lifts the rocks that lie higher. Thus, a dome-shaped bend of the earth's crust is obtained. Over time, wind erosion exposes igneous rock. An example of domed mountains is the Drakensberg Mountains in South Africa. More than a thousand meters high, weathered igneous rock is clearly visible in it.

Mountains folded, blocky, folded-blocky

Folded mountains are elevations of the earth's surface that arise in the mobile zones of the earth's crust. They are most typical for young geosynclinal zones. In them, the thickness of rocks is crumpled into folds of various sizes and steepness, raised to a certain height. First, the relief of folded mountains corresponds to tectonic structures: ridges - anticlines, valleys - synclines; subsequently, this correspondence is violated.

Blocky mountains are elevations of the earth's surface, separated by tectonic faults. Blocky mountains are characterized by massiveness, steep slopes, relatively insignificant dissection. Occur in territories that previously had mountainous relief and leveled by denudation, as well as in flat areas.

Folded-block mountains are elevations of the earth's surface caused by complex deformations of the earth's crust - plastic and discontinuous.

Fold-block mountains arise mainly during deformation and uplift of rock strata, crumpled into folds and have lost their plasticity. They are widespread in young geosynclinal zones. Examples of folded-block mountains are the mountains of the Tien Shan, Altai, mountains of a significant part of the Balkan Peninsula.

River valley concept

River valleys are relatively narrow, long hollows formed by rivers that slope, in accordance with their course, from upper to lower reaches. The valleys are winding and rectilinear. The components of a young river valley are the bottom and slopes, in a later period of development - the channel and bed of the river, floodplains, terraces, and the root bank. The depth, width, and the number of terraces in the river valley depend on the age and thickness of the river, the geological structure of the area, the position of the base of erosion, and general changes in physical and geographical conditions. The origin of the river valley is mainly erosional, but many of them, especially large ones, have a tectonic structure. River valleys produced from heterogeneous rocks, and those that reflect the peculiarities of the geological structure of the area, are called structural river valleys. The main structural types of valleys include: synclinal valleys (folds of rocks are convex downward) anticlinal valleys (successively layered convex bend, the core of which is composed of ancient layers of rocks, and the upper part is younger) monoclinal valley (longitudinal, of course, asymmetric valley produced in rocks , lying with a slope of layers to one side) valley-graben (formed in places of rupture of rocks and subsidence of the central blocks, the lateral ones remain at the same level or rise).

Plain areas are often inclined to the channel, and the systems of degrees in river valleys, created by the erosion and accumulative work of the river, form river terraces. They are subdivided: by height above the bottom of the valley - into floodplain and above floodplain terraces; behind the morphological character and structure - on the enclosed and superimposed terraces.

The floodplain is a part of a river valley dotted with vegetation and is only inundated during floods. The floodplain has many depressions. They alternate with ridges. The riverbed floodplain is the highest, with alluvium; the central floodplain is lower, with less silt; near-terraced - the most lowered, swampy, adjacent to the high bank and composed of silt. Floodplains up to 40 km wide are characteristic of large flat rivers with uneven flow. The soils of the floodplain, which are replenished with organic silt, are very fertile.

The value of the relief in economic activity human

The relief of the earth's surface leads to many features of a particular territory, and therefore, in any construction, prospecting for minerals, in agriculture and in military affairs, it is always necessary to take into account its specifics.

The relief depends on the location and configuration of agricultural land, the use of this or that technique, the nature of reclamation work, the placement of crops.

The slope of the surface affects the conditions of water flow, moisture content, the intensity of soil washout and the formation of ravines. Ravines reduce the area of ​​arable land, cut roads.

The angle of incidence of sunlight on the earth's surface depends on the steepness of the slope of the terrain. The southern slope is warm, the western and eastern slopes are intermediate. Therefore, the duration of the frost-free period on convex landforms is slightly longer than in hollows.

Depending on the nature of the relief, the rivers are divided into flat and mountain ones. Plain rivers are in total used for timber rafting and river transport, and mountainous ones are rich in hydro resources and they build hydroelectric power stations.

The terrain affects the amount of excavation during road construction. With a slight steepness of the slope and rough terrain, the volume of excavation and construction costs increases. When choosing routes for automobiles and railways and their construction takes into account the possibility of karst phenomena, landslides, etc.

To design industrial facilities, settlements, you need to know well the relief of the surrounding area and the processes that create this relief.

Some parts of the earth's crust are very swampy, although they are quite suitable for agricultural use. When carrying out work on the drainage of swamps (reclamation) there, ditches and canals are dug through which swamp waters flow into rivers. However, before digging these ditches and canals, the slope of the terrain must be determined. To do this, use the exact topographic maps and special geodetic techniques called leveling. Leveling determines the heights of neighboring terrain points, that is, they establish the excess of one terrain point over another.

Without knowing the relief and without taking into account its features, it is impossible to use the territory for the economy with maximum efficiency.

Folded-block or simply block mountains, geologists call orographic structures that formed and rose in the most ancient geological eras, but much later rejuvenated and split into separate blocks or blocks during the repeated uplift of the territory. Most mountain systems on the planet are folded-block, because folded structures are rare. With the rejuvenation of ancient mountains, the formation of folds is necessarily accompanied by the occurrence of faults and the formation of block formations.

Folded-block mountain systems appear in the majority on the site of ancient mountainous countries already destroyed by erosion. With the activation of tectonic processes in the places of the oldest orographic structures that have become peneplains, new uplifts of the earth's crust and vertical displacements of individual block structures that have arisen during faults occur. That is why, rising above the surrounding territory mountain ranges have little dissection and steep slopes.

In the structure of folded-block structures, specialists distinguish horst-like uplifts, when a separate block of the earth's crust rises above the surrounding territory to a considerable height. The Vosges and Besalitsa, the Sierra Nevada, the Black Forest and the Harz are striking examples of mountain-like mountains. Another element of blocky mountains is graben-like depressions of the earth's crust, when a single block sinks to a considerable depth relative to the surrounding territory. Most often, deep steep slopes are often grabens in the relief of blocky mountains.

A characteristic feature of folded-block orographic structures are flat tops, vast watersheds and wide flat-bottomed intermontane valleys, which appeared as a result of faults in the earth's crust. These structures in the relief are formed with the loss of plasticity of ancient rocks, their inability to crumple into folds, the appearance of deep tectonic faults during the rejuvenation and revival of mountain systems.

Ural

The lithospheric folds at the base of the Urals were formed in the redistribution of the Ural-Mongolian geosynclinal region into the Paleozoic Hercynian folding. Paleozoic structures in the Urals were formed in the Late Cambrian in a geosynclinal depression, which was gradually filled with continental crust and subsequently subjected to strong compression during strong volcanism.

Later, for a long time during the Mesozoic and Paleogene, the processes of strong destruction and leveling of Hercynian structures took place in the Urals. Gradually, the mountain system turned into an ancient peneplain or a very hilly hill. In the Neogene and Quaternary periods, active mountain-building processes and intensive rejuvenation of the territory began in the Urals. The old mountains rose again and split into separate blocks, which rose and fell to different heights. The uneven uplift of lithospheric blocks led to large differences in the external shape and height of individual ridges.

Altai

The complex folded system within the Ural-Mongolian geosynclinal area was formed by Precambrian and Paleozoic rocks strongly dislocated and crumpled into folds in the Caledonian and Hercynian times of tectogenesis. In subsequent geological periods, after the Paleozoic, the mountainous country was severely destroyed and practically turned into a denudation plain or an ancient peneplain.

In the Neogene and the subsequent Quaternary geological period, Altai, which had been heavily destroyed by that time, again underwent uplift and rejuvenation. With the general tectonic uplift of the territory, the ancient rocks of the mountainous country that lost their plasticity were split into huge blocks under the influence of deep tectonic faults. This process was accompanied by powerful continental glaciation and strong erosional dissection of the mountainous country.

Sayan

A typical example of folded-block mountains is the Sayan Mountains, which formed partly within the Ural-Mongolian folding system during the ancient Baikal folding, partly during the Caledonian orogeny. After a long intensive mountain building in the Sayan Mountains, a period of relative tectonic calm began, which continued in the Mesozoic and Paleogene. The mountains that rose up collapsed and turned into a vast denudation plain, often called peneplain by geologists.

But in the Neogene and later in the Quaternary, they experienced again the strongest rejuvenating tectonic movements. This process was accompanied by the widespread outpouring of basalts and the formation of numerous volcanoes. The territory has split into separate tectonic blocks, constantly shifting relative to others. This process went with glaciation. high mountains mountain peaks and strong erosional dissection of the entire territory.

Tien Shan

The powerful and geologically heterogeneous mountain system of the Tien Shan is an excellent example of an extensive blocky structure. It was formed on the territory of the Ural-Mongolian geosyncline in the northern part during the Caledonian orogeny, and in the southern part during the Hercynian time. These parts, different in geology and geomorphology, are separated by a deep tectonic seam, which experts call the “Nikolaev line”.

After an active and prolonged mountain-building process, the Tien Shan was destroyed for a long time and turned into a highly dissected denudation plain. At the end of the Paleogene in the Oligocene, a powerful mountain-building process began again throughout the Tien Shan, which split the mountainous country into separate blocks and created the modern alpine relief... Powerful tectonic movements led to the formation of stepped relief forms, the development of deep erosional river valleys and the appearance of continental glaciation.

Chersky ridge

An example of a folded-block structure of a mountain system is the ID Chersky ridge. It was formed and rose significantly in the Mesozoic, when, in the powerful process of mountain building, new tectonic structures were joining to the northeastern part of the Siberian platform. Then, for a long time, at the border of the Mesozoic and Cenozoic period, the ridge was in a stable state, collapsed and actively peneplained.

In the era of the latest Alpine orogeny, the ridge underwent powerful rejuvenation and widespread uplift, split into separate block blocks. Some blocks immediately rose into horst-like elevated Mountain peaks, others sank into the graben-like depressions of the intermontane valleys. Therefore, the relief of the ridge is highly dissected, it alternates between high and medium mountain ranges covered with continental glaciation, vast intermontane valleys, remnant stone ridges and stepped relief forms.

Back ridge

In Transbaikalia, the Stanovoy Ridge is a typical example of a blocky structure of the territory. It was formed back in the Precambrian from Archean and Early Proterozoic rocks cut through by intrusions of ancient porphyrites and coarse-grained multi-colored granites in the south of the Siberian platform. The oldest Archean and Proterozoic rocks on the planet are overlain here by deposits of the Late Jurassic and Early Cretaceous.

In the later, long period of denudation and erosional destruction, the territory of the ridge leveled off and strongly peneplained. In the Pliocene-Quaternary geological time, the territory of the ridge rose again, split into separate tectonic blocks, large ruptures, faults and young intrusions appeared here.

Appalachian

The Caledonian-Hercynian, the oldest folded-block structure of the Appalachian mountains, underwent strong mountain-building tectonic shifts in the Paleozoic. Mountains under intense volcanic processes high peaks rose and crumpled into large folds. The subsequent Late Paleozoic prolonged erosional denudation smoothed mountain peaks, exposed ancient folds, and greatly dissected the relief.

In the Meso-Cenozoic rejuvenating slow uplift of the Appalachian territory, the appearance of the modern mid-mountainous relief gradually took shape, in which the so-called "inversion of the relief" is observed, where there is no clear correspondence of its forms to the most ancient folded structures. The amplitude of tectonic uplifts and the movement of blocks formed at deep faults were different in certain parts of the mountainous country.

The modern appearance of the mountains is very heterogeneous, high mountain ranges are adjacent here with vast and flat-bottomed intermountain valleys, erosion-remnant forms, deep gorges and foothill plateaus. In areas affected by continental glaciation, there are end-moraine ridges, river valleys with a trough profile, alpine glacial lakes and many waterfalls on rivers flowing along the hanging valleys in the relief.

Sierra nevada

The formation of the American Californian high "snow-capped mountains" of the Sierra Nevada began in the Jurassic "Nevada orogeny", typical of folded mountains, by the movement of the Pacific tectonic plate under the North American plate. The deep magma of the melting oceanic plate created extensive granite intrusions in the cores of the future ridge. Later, a period of prolonged relative calm and severe destruction began in the Sierra Nevada mountains.

In the Oligocene and the subsequent Neogene, a new period of orogenesis began in the Sierra Nevada mountain system, which markedly raised the territory, split into blocks, carved deep V-shaped canyons with glaciers, exposed the famous local "batholiths" located on intrusive bodies in the depths of the earth's crust. The growth of the Sierra Nevada is still taking place, it causes large earthquakes of up to 8 points here.

Mountains can be classified according to different criteria: 1) geographical location and age, taking into account their morphology; 2) features of the structure, taking into account the geological structure. In the first case, mountains are subdivided into cordillera, mountain systems, ridges, groups, chains, and single mountains.

The name "cordillera" comes from the Spanish word for "chain" or "rope". The Cordillera include ridges, mountain groups and mountain systems of different ages. Cordillera area in the west North America includes Coast Ranges, Cascade Mountains, Sierra Nevada, Rocky and many small ranges between the Rocky Mountains and Sierra Nevada in the states of Utah and Nevada. The Cordilleras of Central Asia include, for example, the Himalayas, Kunlun and Tien Shan.

Mountain systems are made up of ranges and groups of mountains that are similar in age and origin (for example, the Appalachians). The ridges consist of mountains stretched out in a long narrow strip. The Sangre de Cristo Mountains, which stretch in the states of Colorado and New Mexico for 240 km, usually no more than 24 km wide, with many peaks reaching 4000–4300 m, are a typical ridge. The group consists of genetically closely related mountains without the distinct linear structure characteristic of the ridge. The Henry Mountains in Utah and the Bear Poe Mountains in Montana are typical examples of mountain groups. In many parts of the world there are solitary mountains, usually of volcanic origin. These are, for example, Mount Hood in Oregon and Mount Rainier in Washington, which are volcanic cones.

The second classification of mountains is based on taking into account the endogenous processes of relief formation. Volcanic mountains are formed by the accumulation of masses of igneous rocks during volcanic eruptions. Mountains can also arise as a result of uneven development of erosion-denudation processes within a vast territory that has experienced tectonic uplift. Mountains can also form directly as a result of tectonic movements themselves, for example, during arched uplifts of sections of the earth's surface, during disjunctive dislocations of blocks of the earth's crust, or during intense folding and uplift of relatively narrow zones. The latter situation is typical for many large mountain systems of the globe, where orogenesis continues to this day. Such mountains are called folded mountains, although during the long history of development after the initial folding, they were also influenced by other mountain building processes.

Folded mountains.

Initially, many large mountain systems were folded, but in the course of subsequent development, their structure became very complicated. The zones of initial folding are limited by geosynclinal belts - huge troughs in which sediments accumulated, mainly in shallow oceanic settings. Before the beginning of folding, their thickness reached 15,000 m and more. The confinement of folded mountains to geosynclines seems paradoxical; however, it is likely that the same processes that contributed to the formation of geosynclines subsequently ensured crushing of sediments into folds and the formation of mountain systems. At the final stage, folding is localized within the geosyncline, since, due to the high thickness of sedimentary strata, the least stable zones of the earth's crust arise there.

A classic example of folded mountains is the Appalachians in eastern North America. The geosyncline in which they formed had a much greater extent compared to modern mountains. For about 250 million years, sedimentation took place in a slowly sinking basin. The maximum sediment thickness exceeded 7600 m. Then the geosyncline underwent lateral compression, as a result of which it narrowed to about 160 km. Sedimentary strata accumulated in the geosyncline were strongly crumpled into folds and broken by faults, along which disjunctive dislocations occurred. During the stage of folding, the territory experienced intense uplift, the rate of which exceeded the rate of impact of erosion-denudation processes. Over time, these processes led to the destruction of the mountains and a decrease in their surface. The Appalachians were repeatedly uplifted and subsequently denudated. However, not all areas of the initial folding zone experienced re-uplift.

Primary deformations during the formation of folded mountains are usually accompanied by significant volcanic activity. Volcanic eruptions occur during or shortly after folding, and large masses of molten magma are poured into the folded mountains to compose batholiths. They are often exposed during deep erosional dissection of folded structures.

Many folded mountain systems are dissected by huge thrusts with faults, along which rock covers tens and hundreds of meters thick were displaced for many kilometers. In the folded mountains, both rather simple folded structures (for example, in the Jura mountains) and very complex ones (as in the Alps) can be represented. In some cases, the folding process develops more intensively along the periphery of geosynclines, and, as a result, on transverse profile there are two marginal folded ridges and the central uplifted part of the mountains with a lesser development of folding. Thrusts extend from the marginal ridges towards the central massif. The massifs of older and more stable rocks that limit the geosynclinal trough are called forelands. Such a simplified structure diagram does not always correspond to reality. For example, in the mountain belt located between Central Asia and Hindustan, there are sublatitudinally oriented Kunlun mountains at its northern border, the Himalayas at the southern, and between them the Tibetan plateau. In relation to this mountain belt, the Tarim Basin in the north and the Indian subcontinent in the south are forelands.

Erosion-denudation processes in folded mountains lead to the formation of characteristic landscapes. As a result of erosional dissection of folded layers of sedimentary rocks, a series of elongated ridges and valleys is formed. The ridges correspond to outcrops of more stable rocks, while the valleys are worked out in less stable rocks. Landscapes of this type are found in western Pennsylvania. With deep erosional dissection of a folded mountainous country, the sedimentary stratum can be completely destroyed, and the core, composed of igneous or metamorphic rocks, can be exposed.

Blocky mountains.

Many large mountain ranges were formed as a result of tectonic uplifts that occurred along faults in the earth's crust. The Sierra Nevada Mountains in California are a huge horst with a length of approx. 640 km and a width of 80 to 120 km. The most elevated was the eastern edge of this horst, where the height of Mount Whitney reaches 418 m above sea level. The structure of this horst is dominated by granites that make up the core of the giant batholith; however, sedimentary strata accumulated in the geosynclinal trough, in which the folded mountains of the Sierra Nevada were formed, also survived.

The modern appearance of the Appalachians was largely formed as a result of several processes: the primary folded mountains experienced the effects of erosion and denudation, and then were uplifted along the faults. However, the Appalachians are not your typical blocky mountains.

A series of blocky mountain ranges are found in the Great Basin between the Rocky Mountains to the east and the Sierra Nevada to the west. These ridges were lifted as horsts along the boundary faults, and the final appearance was formed under the influence of erosion-denudation processes. Most of the ridges stretch in the submeridional direction and are 30 to 80 km wide. As a result of uneven uplift, some slopes turned out to be steeper than others. Long narrow valleys run between the ridges, partially filled with sediments carried from the adjacent blocky mountains. Such valleys, as a rule, are confined to immersion zones - grabens. There is an assumption that the blocky mountains Great Basin formed in the zone of stretching of the earth's crust, since tensile stresses are characteristic for most of the faults.

Arched mountains.

In many areas, areas of land that have experienced tectonic uplift have acquired a mountainous appearance under the influence of erosion processes. Where the uplift took place over a relatively small area and had an arched character, arched mountains were formed, a striking example of which is the Black Hills in South Dakota, which are approx. 160 km. This area experienced a crestal uplift, and most of the sedimentary cover was removed by subsequent erosion and denudation. As a result, the central core was exposed, composed of igneous and metamorphic rocks. It is flanked by ridges of more stable sedimentary rocks, while the valleys between the ridges are mined in less persistent rocks.

Where laccoliths (lenticular bodies of intrusive igneous rocks) penetrated into the thickness of sedimentary rocks, the cover sediments could also experience arched uplifts. An illustrative example of eroded arched uplifts is Mount Henry, Utah.

In the Lake District in the west of England, there was also a crestal uplift, but of slightly lesser amplitude than in the Black Hills.

Remaining plateaus.

Due to the action of erosion-denudation processes, mountain landscapes are formed in the place of any elevated territory. Their severity depends on the initial height. With the destruction of high plateaus, such as Colorado (in the southwestern United States), a highly dissected mountainous relief is formed. The Colorado Plateau, hundreds of kilometers wide, was raised to a height of approx. 3000 m.The erosion-denudation processes have not yet completely transformed it into a mountainous landscape, however, within some large canyons, for example The grand canyon R. Colorado, mountains several hundred meters high arose. These are erosional remnants that have not yet been denuded. With the further development of erosion processes, the plateau will acquire an increasingly pronounced mountainous appearance.

In the absence of repeated uplifts, any area will eventually be leveled and turned into a low monotonous plain. Even there, however, isolated hills of more resilient rocks will remain. These remnants are called monadnocks after Mount Monadnock in New Hampshire (USA).

Volcanic mountains

are of different types. Volcanic cones, widespread in almost all regions of the globe, are formed due to accumulations of lava and rock fragments erupted through long cylindrical vents by forces acting deep in the bowels of the Earth. Illustrative examples of volcanic cones are Mayon Mountains in the Philippines, Fujiyama in Japan, Popocatepetl in Mexico, Misty in Peru, Shasta in California, etc. Ash cones have a similar structure, but not so high and are composed mainly of volcanic slag - porous volcanic rock, like ashes. Such cones are found near Lassen Peak in California and in northeastern New Mexico.

Shield volcanoes form with repeated outpourings of lava. They are usually not as tall and not as symmetrical as volcanic cones. There are many shield volcanoes in the Hawaiian and Aleutian Islands. In some areas, the foci of volcanic eruptions were so close together that the igneous rocks formed entire ridges that connected the initially isolated volcanoes. This type includes the Absaroka Ridge in the eastern part of Yellowstone Park in Wyoming.

Volcano chains occur in long, narrow zones. Probably the most famous example is the volcanic Hawaiian chain of islands stretching over 1,600 km. All of these islands were formed as a result of the outpouring of lava and eruptions of debris from craters located on the ocean floor. If we count from the surface of this bottom, where the depths are approx. 5500 m, then some of the peaks of the Hawaiian Islands will be among the highest mountains in the world.

Thick strata of volcanic deposits can be dissected by rivers or glaciers and become isolated mountains or groups of mountains. A typical example is the San Juan Mountains in Colorado. Intense volcanic activity here manifested itself during the formation of the Rocky Mountains. Lavas of various types and volcanic breccias in this area cover an area of ​​more than 15.5 thousand square meters. km, and the maximum thickness of volcanic deposits exceeds 1830 m. Under the influence of glacial and water erosion, volcanic rock massifs were deeply dissected and turned into high mountains. Volcanic rocks are currently preserved only on the tops of the mountains. Thick strata of sedimentary and metamorphic rocks are exposed below. Mountains of this type are found on areas of lava plateaus prepared by erosion, in particular the Columbian plateau, located between the Rocky and Cascade mountains.

Distribution and age of mountains.

Mountains are found on all continents and many large islands- in Greenland, Madagascar, Taiwan, New Zealand, British, etc. The mountains of Antarctica are largely buried under the ice sheet, but there are individual volcanic mountains, such as the Erebus volcano, and mountain ranges, including the mountains of the Queen Maud Land and Mary Byrd lands are high and well defined in relief. Australia has fewer mountains than any other mainland. In the Americas, Europe, Asia and Africa, there are cordillera, mountain systems, ridges, mountain groups, and solitary mountains. The Himalayas, located in the south of Central Asia, are the tallest and youngest mountain range in the world. The longest mountain system is the Andes in South America, stretching 7,560 km from Cape Horn to Caribbean... They are older than the Himalayas and, apparently, had a more complex history of development. The mountains of Brazil are lower and much older than the Andes.

In North America, mountains are very diverse in age, structure, structure, origin and degree of dissection. The Laurentian Upland, which covers the area from Lake Superior to Nova Scotia, is a relic of highly eroded high mountains that formed in the Archean more than 570 million years ago. In many places, only the structural roots of these ancient mountains have survived. The Appalachians are intermediate in age. For the first time they experienced uplift in the Late Paleozoic c. 280 million years ago and were much higher than now. Then they underwent significant destruction, and in the Paleogene approx. 60 million years ago, they were re-raised to modern heights. The Sierra Nevada Mountains are younger than the Appalachians. They, too, have passed the stage of significant destruction and re-uplift. The Rocky Mountain system of the United States and Canada is younger than the Sierra Nevada, but older than the Himalayas. The Rocky Mountains formed in the Late Cretaceous and Paleogene. They survived two major stages of uplift, the last one in the Pliocene, only 2–3 million years ago. It is unlikely that the Rocky Mountains have ever been higher than they are today. The Cascade Mountains and Ridges in the western United States and most of Alaska's mountains are younger than the Rocky Mountains. The coastal ranges of California are currently experiencing very slow uplift.

The variety of the structure and structure of the mountains.

The mountains are very diverse not only in age, but also in structure. The Alps in Europe have the most complex structure. The rock strata there were exposed to unusually powerful forces, which was reflected in the intrusion of large batholiths of igneous rocks and in the formation of extremely diverse overturned folds and faults with huge displacement amplitudes. In contrast, the Black Hills have a very simple structure.

The geological structure of mountains is as diverse as their structures. For example, rocks that are folded Northern part The rocky mountains in the provinces of Alberta and British Columbia are mostly Paleozoic limestones and shales. In Wyoming and Colorado, most of the mountains have cores of granites and other ancient igneous rocks overlain by strata of Paleozoic and Mesozoic sedimentary rocks. In addition, a variety of volcanic rocks are widely represented in the central and southern parts of the Rocky Mountains, but in the north of these mountains there are practically no volcanic rocks. Such differences are found in other mountains of the world.

Although, in principle, there are no two completely identical mountains, young volcanic mountains are often very similar in size and shape, as evidenced by the example of Fujiyama in Japan and Mayon in the Philippines, which have regular conical shapes. Note, however, that many of Japan's volcanoes are composed of andesites (igneous rock of intermediate composition), while the volcanic mountains in the Philippines are composed of basalts (a heavier black rock containing a lot of iron). The volcanoes of the Cascade Mountains in Oregon are mainly composed of rhyolite (rock containing more silica and less iron than basalts and andesites).

ORIGIN OF THE MOUNTAINS

No one can explain with certainty how the mountains were formed, but the lack of reliable knowledge about orogeny (mountain building) should not hinder and does not hinder the attempts by scientists to explain this process. The main hypotheses of the formation of mountains are considered below.

Submersion of oceanic trenches.

This hypothesis was based on the fact that many mountain ranges are confined to the periphery of the continents. The rocks that make up the bottom of the oceans are somewhat heavier than the rocks that lie at the base of the continents. When large-scale movements occur in the bowels of the Earth, oceanic troughs tend to sink, squeezing the continents upward, and folded mountains are formed at the edges of the continents. This hypothesis not only does not explain, but also does not recognize the existence of geosynclinal troughs (depressions of the earth's crust) at the stage preceding mountain building. Nor does she explain the origin of mountain systems such as the Rocky Mountains or the Himalayas, which are remote from the continental margins.

Kober's hypothesis.

Austrian scientist Leopold Kober studied in detail geological structure Alps. Developing his concept of mountain building, he tried to explain the origin of large thrusts, or tectonic sheets, which are found in both the northern and southern parts of the Alps. They are composed of thick strata of sedimentary rocks that have undergone significant lateral pressure, as a result of which recumbent or overturned folds have formed. In some places, boreholes in the mountains cut through the same sedimentary layers three times or more. To explain the formation of overturned folds and associated thrusts, Kober suggested that the central and southern parts of Europe were once occupied by a huge geosyncline. Thick strata of Early Paleozoic sediments accumulated in it in the conditions of epicontinental sea ​​basin that filled the geosynclinal trough. Northern Europe and North Africa were very stable forelands. When orogeny began, these forelands began to converge, squeezing fragile young sediments upward. With the development of this process, which was likened to a slowly shrinking vice, the raised sedimentary rocks crumpled, formed overturned folds, or advanced on approaching forelands. Kober tried (without much success) to apply these concepts to explain the development of other mountain areas. The very idea of ​​lateral displacement of land masses seems to quite satisfactorily explain the orogeny of the Alps, but it turned out to be inapplicable to other mountains and therefore was rejected as a whole.

Continental drift hypothesis

proceeds from the fact that most of the mountains are located on the continental outskirts, and the continents themselves are constantly moving in a horizontal direction (drifting). In the course of this drift, mountains are formed on the outskirts of the advancing continent. Thus, the Andes were formed during the migration of South America to the west, and the Atlas Mountains - as a result of the movement of Africa to the north.

In connection with the interpretation of mountain building, this hypothesis meets with many objections. It does not explain the formation of wide, symmetrical folds that occur in the Appalachians and Jura. In addition, on its basis, it is impossible to substantiate the existence of a geosynclinal trough that preceded mountain building, as well as the presence of such generally recognized stages of orogenesis as the replacement of the initial folding by the development of vertical faults and the resumption of uplift. Nevertheless, in recent years, much evidence has been found for the continental drift hypothesis, and it has gained many supporters.

Hypotheses of convection (subcrustal) currents.

For more than a hundred years, the development of hypotheses about the possibility of the existence of convection currents in the interior of the Earth, causing deformations of the earth's surface, continued. From 1933 to 1938 alone, at least six hypotheses were put forward about the participation of convection currents in mountain building. However, they are all based on such unknown parameters as the temperature of the earth's interior, fluidity, viscosity, crystal structure of rocks, compressive strength of different rocks, etc.

As an example, consider the Griggs conjecture. It assumes that the Earth is divided into convection cells, extending from the base of the earth's crust to the outer core, located at a depth of approx. 2900 km below sea level. These meshes are the size of the mainland, but their outer surface is usually 7,700 to 9,700 km in diameter. At the beginning of the convection cycle, the masses of rocks enclosing the core are very hot, while on the surface of the cell they are relatively cold. If the amount of heat supplied from the earth's core to the base of the cell exceeds the amount of heat that can pass through the cell, convection flow occurs. As the heated rocks rise upward, the cold rocks from the surface of the cell sink. It is estimated that it takes approx. 30 million years. During this time, long downward movements occur in the earth's crust along the periphery of the cell. The subsidence of geosynclines is accompanied by the accumulation of sediment strata hundreds of meters thick. In general, the stage of subsidence and filling of geosynclines lasts approx. 25 million years. Under the influence of lateral compression along the edges of the geosynclinal trough, caused by convection currents, the sediments of the weakened zone of the geosyncline are crumpled into folds and complicated by faults. These deformations occur without significant uplift of the folded strata disturbed by faults for about 5–10 Ma. When, finally, the convection currents die out, the compressive forces weaken, subsidence slows down, and the sedimentary rocks that filled the geosyncline rise. The estimated duration of this final stage of mountain building is approx. 25 million years.

The Griggs hypothesis explains the origin of geosynclines and their filling with sediments. It also reinforces the opinion of many geologists that folds and thrusts in many mountain systems proceeded without significant uplift, which occurred later. However, she leaves a number of questions unanswered. Do convection currents actually exist? The seismograms of earthquakes indicate the relative homogeneity of the mantle - the layer located between the earth's crust and the core. Is the division of the Earth's interior into convection cells justified? If convection currents and cells exist, mountains must appear simultaneously along the boundaries of each cell. How true is this?

The Rocky Mountain system in Canada and the United States is roughly the same age throughout its entire length. Its uplift began in the Late Cretaceous and continued intermittently during the Paleogene and Neogene, but the mountains in Canada are confined to the geosyncline, which began to sag in the Cambrian, while the mountains in Colorado, to the geosyncline, which began to form only in the Early Cretaceous. How does the hypothesis of convection currents explain such a discrepancy in the age of geosynclines exceeding 300 million years?

Swelling hypothesis, or geotumor.

The heat released during the decay of radioactive substances has long attracted the attention of scientists interested in the processes taking place in the bowels of the Earth. The release of enormous amounts of heat from the explosion of the atomic bombs dropped on Japan in 1945 stimulated the study of radioactive substances and their possible role in mountain building. As a result of these studies, the J.L. Rich hypothesis emerged. Rich assumed that somehow large quantities of radioactive substances were locally concentrated in the earth's crust. When they decay, heat is released, under the influence of which the surrounding rocks melt and expand, which leads to swelling of the earth's crust (geotumor). When the land rises between the geotumor zone and the surrounding area not affected by endogenous processes, geosynclines are formed. They accumulate precipitation, and the troughs themselves deepen both due to the continuing geotumor and under the weight of precipitation. The thickness and strength of rocks in the upper part of the earth's crust in the region of the geotumor decreases. Finally, the earth's crust in the geotumor zone turns out to be so high up that part of its crust slides over steep surfaces, forming thrust faults, crushing sedimentary rocks into folds and uplifting them in the form of mountains. This kind of movement can be repeated until magma begins to pour out from under the crust in the form of huge lava flows. When they cool, the dome settles, and the period of orogeny ends.

The bloating hypothesis has not received widespread acceptance. None of the known geological processes can explain how the accumulation of masses of radioactive materials can lead to the formation of geotumors with a length of 3200–4800 km and a width of several hundred kilometers; comparable to the Appalachian and Rocky Mountain systems. Seismic data obtained in all regions of the globe do not confirm the presence of such large geotumors of molten rock in the earth's crust.

Contractional, or contraction of the Earth, hypothesis

is based on the assumption that throughout the history of the existence of the Earth as a separate planet, its volume has been constantly decreasing due to compression. The contraction of the inner part of the planet is accompanied by changes in the earth's solid crust. Stresses accumulate intermittently and lead to the development of powerful lateral compression and deformations of the cortex. Downward movements lead to the formation of geosynclines, which can be flooded by epicontinental seas, and then filled with sediments. Thus, at the final stage of development and filling of the geosyncline, a long, relatively narrow wedge-shaped geological body of young unstable rocks is created, resting on the weakened base of the geosyncline and bordered by older and much more stable rocks. With the resumption of lateral compression in this weakened zone, folded mountains are formed, complicated by thrusts.

This hypothesis seems to explain both the contraction of the earth's crust, expressed in many folded mountain systems, and the reason for the emergence of mountains on the site of ancient geosynclines. Since in many cases the compression occurs deep within the Earth's interior, the hypothesis also provides an explanation for the volcanic activity that often accompanies mountain building. However, a number of geologists reject this hypothesis on the grounds that the heat loss and subsequent compression were not large enough to provide for the folds and faults that are found in modern and ancient mountain regions of the world. Another objection to this hypothesis is the assumption that the Earth does not lose, but accumulates heat. If this is true, then the value of the hypothesis is reduced to zero. Further, if the core and the mantle of the Earth contain a significant amount of radioactive substances that emit more heat than can be removed, then the core and the mantle, respectively, expand. As a result, tensile stresses will arise in the earth's crust, and by no means compression, and the entire Earth will turn into a red-hot melt of rocks.

MOUNTAINS AS A HUMAN ENVIRONMENT

Influence of altitude on climate.

Consider some of the climatic features of mountainous areas. Temperatures in the mountains drop by about 0.6 ° C with a rise for every 100 m of altitude. The disappearance of the vegetation cover and the deterioration of living conditions high in the mountains are explained by such a rapid decrease in temperature.

With altitude, atmospheric pressure decreases. Normal atmospheric pressure at sea level is 1034 g / cm 2. At an altitude of 8800 m, which roughly corresponds to the height of Chomolungma (Everest), the pressure drops to 668 g / cm 2. At higher altitudes, more heat from direct solar radiation reaches the surface, since the layer of air that reflects and absorbs radiation is thinner there. However, this layer retains less heat reflected by the earth's surface into the atmosphere. This heat loss explains the low temperatures at high altitudes. Cold winds, clouds and hurricanes also contribute to lower temperatures. Low atmospheric pressure at high altitudes has a different effect on living conditions in the mountains. The boiling point of water at sea level is 100 ° C, and at an altitude of 4300 m above sea level, due to lower pressure, it is only 86 ° C.

The upper border of the forest and the snow line.

Two terms are often used in mountain descriptions: "upper forest boundary" and "snow line". The upper border of the forest is the level above which trees do not grow or hardly grow. Its position depends on the average annual temperatures, precipitation, slope exposure and latitude. In general, the forest boundary in low latitudes is located higher than in high latitudes. In the Rocky Mountains in Colorado and Wyoming, it runs at altitudes of 3400–3500 m, in Alberta and British Columbia - it drops to 2700–2900 m, and in Alaska it is even lower. Above the border of the forest, in conditions of low temperatures and scarce vegetation, quite a few people live. Small groups of nomads move across northern Tibet, and only a few Indian tribes live in the highlands of Ecuador and Peru. In the Andes, in the territories of Bolivia, Chile and Peru, there are higher pastures, i.e. at altitudes over 4000 m, there are rich deposits of copper, gold, tin, tungsten and many other metals. All foodstuffs and everything necessary for the construction of settlements and the development of deposits have to be imported from the regions below.

The snow line is the level below which snow does not remain on the surface all year round. The position of this line varies with annual solid precipitation, slope exposure, elevation and latitude. At the equator in Ecuador, the snow line runs at an altitude of approx. 5500 m. In Antarctica, Greenland and Alaska, it is raised only a few meters above sea level. In the Rocky Mountains of Colorado, the height of the snow line is approximately 3700 m. This does not mean at all that snowfields are widespread above this level, and below them there are not. In fact, snowfields often occupy protected areas above 3,700 m, but they can also be found at lower altitudes in deep gorges and on the northern slopes. Since the snowfields, growing every year, may eventually become a source of food for the glaciers, the position of the snow line in the mountains is of interest to geologists and glaciologists. In many parts of the world, where regular observations of the position of the snow line were carried out at meteorological stations, it was found that in the first half of the 20th century. its level increased, and, accordingly, the size of snowfields and glaciers decreased. There is now overwhelming evidence that this trend has reversed. It is difficult to judge how stable it is, but if it persists for many years, it can lead to the development of extensive glaciation, similar to the Pleistocene, which ended ca. 10,000 years ago.

In general, the amount of liquid and solid precipitation in the mountains is much higher than in the adjacent plains. This can be both beneficial and negative for the inhabitants of the mountains. Atmospheric precipitation can fully meet the needs for water for domestic and industrial needs, but in case of excess it can lead to devastating floods, and heavy snowfalls can completely isolate mountain settlements for several days or even weeks. Strong winds create snow drifts that block roads and railways.

Mountains as barriers.

Mountains around the world have long served as barriers to communication and some activities. For centuries, the only route from Central Asia to South Asia ran through the Khyber Pass on the border of modern Afghanistan and Pakistan. Countless caravans of camels and foot carriers carrying heavy loads of goods traversed this wilderness in the mountains. Famous Alpine passes such as Saint Gotthard and Simplon have been used for many years to travel between Italy and Switzerland. Today, the tunnels under the passes maintain heavy rail traffic all year round. In winter, when the passes are covered with snow, everyone transport connection carried out through the tunnels.

Roads.

Due to the high altitudes and rugged terrain, the construction of roads and railways in the mountains is much more expensive than in the plains. Automotive and railway transport there it wears out faster, and the rails fail under the same load in a shorter period of time than on the plains. Where the valley floor is wide enough, the track is usually placed along rivers. However, mountain rivers often overflow their banks and can destroy large sections of roads and railways. If the width of the valley floor is insufficient, the roadbed has to be laid along the sides of the valley.

Human activities in the mountains.

In the Rocky Mountains, in connection with the construction of roads and the provision of modern household amenities (for example, the use of butane for lighting and heating houses, etc.), human living conditions at altitudes up to 3050 m are steadily improving. Here, in many settlements located at altitudes from 2150 to 2750 m, the number of summer houses significantly exceeds the number of houses of permanent residents.

The mountains save you from the summer heat. A prime example of such a refuge is the city of Baguio, the summer capital of the Philippines, which is dubbed "the city on a thousand hills." It is located just 209 km north of Manila at an altitude of approx. 1460 m.At the beginning of the 20th century. the Philippine government built government buildings, employee residences and a hospital there, as in Manila itself, it was difficult to establish an effective government apparatus in the summer due extreme heat and high humidity. The experiment of creating a summer capital in Baguio has been very successful.

Agriculture.

In general, such features of the relief as steep slopes and narrow valleys limit the possibilities for the development of agriculture in the mountains of the temperate zone of North America. There, small farms mainly grow corn, beans, barley, potatoes and, in some places, tobacco, as well as apples, pears, peaches, cherries and berry bushes. In very warm climates, bananas, figs, coffee, olives, almonds and pecans are added to this list. In the north of the temperate zone of the Northern Hemisphere and in the south of the southern temperate zone, the growing season is too short for most crops to mature, and late spring and early autumn frosts are common.

In the mountains, grazing is widespread. Where summer rainfall is abundant, grasses grow beautifully. In the Swiss Alps in the summer, entire families move with their small herds of cows or goats to the high valleys, where they are engaged in cheese making and butter making. In the Rocky Mountains of the United States, large herds of cows and sheep are driven from the plains to the mountains every summer, where they fatten their weight in fertile meadows.

Logging

- one of the most important sectors of the economy in the mountainous regions of the world, ranking second after grazing livestock. Some mountains are devoid of vegetation due to lack of rainfall, but in temperate and tropical zones, most mountains are covered (or were previously covered) with dense forests. The variety of tree species is very great. Tropical mountain forests provide valuable deciduous wood (mahogany, pink and ebony, teak).

Mining industry.

The mining of metal ores is an important branch of the economy in many mountainous regions. Thanks to the development of deposits of copper, tin and tungsten in Chile, Peru and Bolivia, mining settlements arose at an altitude of 3,700-4,600 m, where, due to the cold, strong winds and hurricanes create the most difficult living conditions. The labor productivity of the miners there is very low and the value of the products of the mining industry is prohibitively high.

Population density.

Due to the peculiarities of the climate and relief, mountainous areas often cannot be populated as densely as flat ones. For example, in the mountainous country of Bhutan, located in the Himalayas, the population density is 39 people per 1 sq. km, while at a short distance from it on the low Bengal Plain in Bangladesh, it is more than 900 people per 1 sq. km. Similar differences in population density in the mountains and plains exist in Scotland.

Table: Mountain peaks

MOUNTAIN PEAKS
	Absolute height, m		Absolute height, m
EUROPE		NORTH AMERICA
Elbrus, Russia	5642	McKinley, Alaska	6194
Dykhtau, Russia	5203	Logan, Canada	5959
Kazbek, Russia - Georgia	5033	Orizaba, Mexico	5610
Mont Blanc, France	4807	Saint Elijah, Alaska - Canada	5489
Ushba, Georgia	4695	Popocatepetl, Mexico	5452
Dufour, Switzerland - Italy	4634	Foraker, Alaska	5304
Weisshorn, Switzerland	4506	Istaxihuatl, Mexico	5286
Matterhorn, Switzerland	4478	Lucania, Canada	5226
Bazarduzu, Russia - Azerbaijan	4466	Bona, Alaska	5005
Finsterahorn, Switzerland	4274	Blackburn, Alaska	4996
Jungfrau, Switzerland	4158	Sanford, Alaska	4949
Dombay-Ulgen (Dombay-Elgen), Russia - Georgia	4046	Wood, Canada	4842
		Vancouver, Alaska	4785
ASIA		Churchill, Alaska	4766
Chomolungma (Everest), China - Nepal	8848	Fairweather, Alaska	4663
Chogori (K-2, Godwin-Austen), China	8611	Baer, ​​Alaska	4520
		Hunter, Alaska	4444
Kanchenjunga, Nepal - India	8598	Whitney, California	4418
Lhotse, Nepal - China	8501	Elbert, Colorado	4399
Makalu, China - Nepal	8481	Massif, Colorado	4396
Dhaulagiri, Nepal	8172	Harvard, Colorado	4395
Manaslu, Nepal	8156	Rainier, Washington	4392
Chopu, China	8153	Nevado de Toluca, Mexico	4392
Nangaparbat, Kashmir	8126	Williamson, California	4381
Annapurna, Nepal	8078	Blanca Peak, Colorado	4372
Gasherbrum, Kashmir	8068	La Plata, Colorado	4370
Shishabangma, China	8012	Ancompagre Peak, Colorado	4361
Nandadevi, India	7817	Creston Peak, Colorado	4357
Rakaposhi, Kashmir	7788	Lincoln, Colorado	4354
Kamet, India	7756	Grace Peak, Colorado	4349
Namchabarwa, China	7756	Antero, Colorado	4349
Gurla Mandhata, China	7728	Evans, Colorado	4348
Ulugmuztag, China	7723	Longs Peak, Colorado	4345
Kongur, China	7719	White Mountain Peak, California	4342
Tirichmir, Pakistan	7690	North Palisade, California	4341
Gungashan (Minyak-Gankar), China	7556	Wrangel, Alaska	4317
Kula Kangri, China - Bhutan	7554	Shasta, California	4317
Muztagata, China	7546	Sill, California	4317
Communism peak, Tajikistan	7495	Pikes Peak, Colorado	4301
Victory peak, Kyrgyzstan - China	7439	Russell, California	4293
Jomolhari, Bhutan	7314	Split Mountain, California	4285
Lenin peak, Tajikistan - Kyrgyzstan	7134	Middle Palisade, California	4279
Korzhenevskoy peak, Tajikistan	7105	SOUTH AMERICA
Khan Tengri peak, Kyrgyzstan	6995	Aconcagua, Argentina	6959
Kangrinboche (Kailash), China	6714	Ojos del Salado, Argentina	6893
Khakaborazi, Myanmar	5881	Bonete, Argentina	6872
Demavend, Iran	5604	Bonete Chico, Argentina	6850
Bogdo-Ula, China	5445	Mercedario, Argentina	6770
Ararat, Turkey	5137	Huascaran, Peru	6746
Jaya, Indonesia	5030	Llullaillaco, Argentina - Chile	6739
Mandala, Indonesia	4760	Erupaha, Peru	6634
Klyuchevskaya Sopka, Russia	4750	Galan, Argentina	6600
Tricor, Indonesia	4750	Tupungato, Argentina - Chile	6570
Belukha, Russia	4506	Sahama, Bolivia	6542
Munhe-Khairkhan-Uul, Mongolia	4362	Koropuna, Peru	6425
AFRICA		Ilyampu, Bolivia	6421
Kilimanjaro, Tanzania	5895	Ilimani, Bolivia	6322
Kenya, Kenya	5199	Las Tortolas, Argentina - Chile	6320
Rwenzori, Congo (DRC) - Uganda	5109	Chimborazo, Ecuador	6310
Ras Dashen, Ethiopia	4620	Belgrano, Argentina	6250
Elgon, Kenya - Uganda	4321	Toroni, Bolivia	5982
Toubkal, Morocco	4165	Tutupaca, Chile	5980
Cameroon, Cameroon	4100	San Pedro, Chile	5974
AUSTRALIA AND OCEANIA		ANTARCTICA
Wilhelm, Papua New Guinea	4509	Vinson array	5140
Giluwe, Papua New Guinea	4368	Kerkpatrick	4528
Mauna Kea, about. Hawaii	4205	Markham	4351
Mauna Loa, about. Hawaii	4169	Jackson	4191
Victoria, Papua New Guinea	4035	Sidley	4181
Capella, Papua New Guinea	3993	Minto	4163
Albert Edward, Papua New Guinea	3990	Wörtherkaka	3630
Kostsyushko, Australia	2228	Menzies	3313



It is a sharp rise among the rest of the territory, with significant differences in altitude - up to several kilometers. Sometimes the mountains have a fairly clear line of the sole at the slope, but more often the foothills.

It is very easy to find folded mountains on the map, because mountains as such are everywhere, on absolutely all continents and even on every island. Somewhere there are more of them, somewhere - less, as, for example, in Australia. In Antarctica, they are hidden by an ice layer. The highest (and youngest) mountain system is the Himalayas, the longest is the Andes, which stretch across the entire South America seven and a half thousand kilometers.

How old are the mountains

Mountains are like people, they can also be young, mature and old. But if people are younger, the smoother, then in the mountains the opposite is true: a sharp relief and high heights indicate a young age.

The old mountains and the relief are worn out, smoothed, and the heights are not with such large differences. For example, the Pamirs are young mountains, and the Ural mountains are old, any map will show that.

Relief characteristics

Folded mountains have an integral structure, but for the most detailed inspection you need to know the principles by which the general characteristics of the relief are compiled. This applies not only but also literally meter deviations from the state of flat lands - this is the so-called mountain microrelief. The ability to classify correctly depends on the exact knowledge of what kind of mountains there are.

Here it is necessary to consider such elements as foothills, valleys, slopes, moraines, passes, ridges, peaks, glaciers and many others, since a wide variety of mountains, including folded mountains, are found on earth.

Mountain classification by height

The height can be classified very simply - there are only three groups:

• Low mountains with a height of no more than a kilometer. Most often these are old mountains, destroyed by time, or very young, gradually growing. They have rounded tops, gentle slopes, on which trees grow. There are such mountains on every continent.
• Middle mountains in height from one thousand to three thousand meters. Here is another, changing landscape, depending on the height - the so-called altitudinal zonation. Such mountains are in Siberia and Far East, on the Apennine, on the Iberian Peninsulas, Scandinavian, Appalachian and many others.
• Highlands- more than three thousand meters. These are always young mountains, subject to weathering, the effects of temperature changes and the growth of glaciers. Characteristic features: troughs - trough-like valleys, carlings - sharp peaks, glacial circuses - bowl-like depressions on the slopes. Here, the altitude is marked by belts - a forest at the foothills, icy deserts closer to the peaks. The term summarizing these characteristics is "alpine landscape". The Alps are a very young mountain system, like the Himalayas, Karakorum, Andes, Rocky and other folded mountains.

Classification of mountains by geographic location

The geographical position divides the relief into systems, mountain groups, mountain ranges and single mountains. Of the largest formations - mountain belts: Alpine-Himalayan - across the whole of Eurasia, Andean-Cordillera - across both Americas.

A little smaller is a mountainous country, that is, many united mountain systems. In turn, the mountain system consists of groups of mountains and ridges of the same age, most often these are folded mountains. Examples: Appalachian Mountains, Sangre de Cristo.

A group of mountains differs from a ridge in that it does not build its peaks in a narrow long strip. Solitary mountains are most often of volcanic origin. In appearance, the peaks are divided into peak-like, plateau-like, domed and some others. Seamounts can form islands with their tops.

Mountain formation

Orogenesis is the most complex of the processes, as a result of which rocks are crumpled into folds. Scientists know for certain what folded mountains are, but only hypotheses are considered how they appeared.

• The first hypothesis is oceanic troughs. The map clearly shows that all mountain systems are located on the outskirts of the continents. This means that the continental rocks are lighter than the bottom rocks of the ocean. Movements inside the Earth seem to squeeze the continent out of its insides, and folded mountains are bottom surfaces that have come out onto land. This theory has many opponents. For example, folded mountains are the Himalayas, which are clearly not bottom, as they are located on the mainland itself. And according to this hypothesis, it is impossible to explain the existence of depressions - geosynclinal troughs.
• Leopold Kober hypothesis, who studied the Alps dear to him. These young mountains have not yet undergone destructive processes. It turned out that tectonic large thrusts were formed by huge strata of sedimentary rocks. Alpine mountains clarified their origin, but this path is absolutely not similar to the emergence of other mountains, it was not possible to apply this theory anywhere else.
• Continental drift- a very popular theory, also criticized as not explaining the entire process of orogenesis.
• Subcortical currents in the bowels of the Earth they cause deformation of the surface and form mountains. However, this hypothesis has not been proven either. On the contrary, humanity is not yet aware of even such parameters as the temperature of the earth's interior, and even more so - the viscosity, fluidity and crystal structure of deep rocks, compressive strength, and so on.
• Earth compression hypothesis- with its own advantages and disadvantages. We do not know whether the planet accumulates heat or loses it, if it loses it - this theory is consistent, if it accumulates it - no.

What are the mountains

All kinds of sedimentary rocks accumulated in the troughs of the earth's crust, which then crumpled and, with the help of volcanic activity, folded mountains were formed. Examples: Appalachian east coast North America, Zagros Mountains in Turkey.

Blocky mountains appeared due to tectonic uplifts along faults in the earth's crust. As, for example, California - Sierra Levada. But sometimes the already formed folded ones suddenly begin to rise along the fault. This is how folded-block mountains are formed. The most typical are the Appalachians.

Those mountains that were formed as folded strata of rocks, but were broken by young faults into blocks and rose to different heights, are also folded-block. The Tien Shan mountains, for example, as well as the Altai mountains.

The Vaulted Mountains are a domed tectonic uplift plus erosion processes over a small area. These are the mountains of the Lake District in England, as well as the Black Hills, located in South Dakota.

Volcanic ones were formed under the influence of lava. There are two types of them: volcanic cones (Fujiyama and others like them) and shield volcanoes (less tall and not so symmetrical).

Mountain climate

The mountainous climate is fundamentally different from the climate of any other territories. Temperatures drop by more than half a degree for every hundred meters of altitude. The wind is also usually very cold, which is facilitated by cloudiness. Frequent hurricanes.

With the climb, the atmospheric pressure also decreases. On Everest, for example, up to 250 millimeters of mercury. Water boils at eighty-six degrees.

The higher, the less vegetation cover, until it is completely absent, and in the glaciers and on the snow caps, life is almost completely absent.

Linear zones

Thanks to fault-tectonic analysis, it was possible to compile a definition of what fold mountains are, as a result of which they were formed and how dependent on deep planetary faults. All - both ancient and modern - mountain areas are included in certain linear zones, which were formed in only two directions - northwest and northeast, repeating the direction of deep faults.

These belts are bordered by platforms. There is a dependence: the platform changes the position and shape, and the external forms and orientation in the space of the folded belts change. During the formation of mountains, everything is decided by fault tectonics (blocks) of the crystalline base. The vertical movements of the foundation blocks form folded mountains.

Examples of the Carpathians or Verkhoyansk-Chukotka region show Various types tectonic movements during the formation of mountain folds. The Zagros Mountains also emerged in the same way.

Geological structure

Everything in the mountains is diverse - from structure to structure. for example, the same Rocky Mountains change along their entire length. In the northern part - Paleozoic shales and limestones, further - closer to Colorado - granites, igneous rocks with Mesozoic sediments. Even further, in the central part, there are volcanic rocks, which are absent in the northern areas. The same picture will appear if we consider the geological structure of many other mountain ranges.

They say that no two mountains are alike, but volcanic massifs, for example, often have a number of similar features. The correctness of the outlines of the Japanese cone, etc. But if we start a detailed geological analysis now, we will see that the saying is quite right. Many volcanoes in Japan are composed of andesites (magma), and the Philippine rocks are basaltic, which is much heavier due to the high iron content. And the Oregon Cascade Mountains folded their volcanoes with rhyolite (silica).

The time of the formation of folded mountains

The formation of mountains in the entire process occurred due to the development of geosynclines in different geological periods, even in the era of folding up to the Cambrian. But only young (comparatively, of course) - Cenozoic uplifts belong to the modern mountains. The older mountains were leveled long ago and were raised again by new tectonic movements in the form of blocks and arches.

The vaulted block mountains are most often revived. They are as common as the younger, folded ones. Today's is neotectonics. It is possible to study the folding that formed tectonic structures if we consider the difference in the age of the mountains, and not the relief created by it. If the Cenozoic is recent, then it is difficult to think about the age of the very first mountain formations.

And only volcanic mountains can grow right before our eyes - during the entire eruption. Eruptions most often occur in the same place, so each portion of lava builds up the mountain. In the center of the mainland, a volcano is a rarity. They tend to form entire underwater islands, often forming arcs several thousand kilometers long.

How mountains die

The mountains could stand forever. But they are being killed, albeit slowly when compared to human life. This is, first of all, frosts, splitting the rock into small pieces. This is how taluses are formed, which are then carried down by snow or ice, building moraine ridges. This is water - rain, snow, hail - which makes its way even through such indestructible walls. The water is collected in the rivers, which make themselves winding between the mountain spurs of the valley. The history of the destruction of unshakable mountains, of course, is long, but inevitable. And the glaciers! Whole spurs, it happens, are cleanly cut off by them.

Such erosion gradually lowers the mountains, turning them into a plain: somewhere green, with deep rivers, somewhere deserted, sanding all the remaining hills with sand. This surface of the Earth is called "peneplain" - almost a plain. And, I must say, this stage occurs extremely rarely. The mountains are reborn! The earth's crust begins to move again, the terrain rises, starting a new phase in the development of the relief.