How mountains are divided by origin. What types of mountains are there? Volcanic mountains, folded mountains, blocky, dome-shaped mountains. Antarctica - Mount Vinson

Mountains are different: old and young, rocky and flat, domed and peaked. Some of them are covered with dense forests, others with lifeless stone deposits. But in this article we will talk about their height. Which mountains are medium and which are considered high?

Mountain as a landform

First of all, it is worth answering the question of whether this is a positive form of relief, characterized by a sharp and isolated elevation of the terrain. In any mountain, three main elements are clearly visible:

• vertex;
• foot;
• slope.

Any mountain system on the planet is nothing more than a complex system of valleys (depressions) and ridges, consisting of dozens of individual peaks. All of them are external manifestations of the internal (endogenous) forces of the Earth - tectonic movements of the earth's crust and volcanism.

Mountains create the most beautiful and unique landscapes on the surface of our planet. They are distinguished by their unique soil cover, unique flora and fauna. But people settle in the mountains extremely reluctantly. According to statistics, about 50% of the earth's population lives at altitudes not exceeding 200 meters above sea level.

Classification of mountains in geomorphology. Mountains are medium, low and high

In geomorphological science, mountains are usually classified according to a number of characteristics: age, height, geographical location, genesis, shape of peaks, etc.

By their origin they can be tectonic, denudation or volcanic, and by age - old or young. Moreover, a mountain system whose formation time does not exceed 50 million years is considered young. By geological standards, this is a very small age.

Depending on the shape of their peak, mountains are:

• peaked;
• domed;
• plateau-shaped (“table”).

Geographers distinguish mountains based on their altitude above sea level:

• low;
• average;
• tall.

Sometimes in the literature you can find intermediate altitude types, for example, medium-high or medium-low mountains. It is immediately worth noting that mountains of medium height can be found in any part of the world. However, most of them are in Europe and Asia.

Middle Mountains: examples and height

8848 meters - this is the height reached by the highest peak in the world - Chomolungma, or Everest. The absolute height of the middle mountains is much more modest: from 1 to 3 km above sea level.

The most famous examples of such mountain systems are the Carpathians, Appalachians, Tatras, Apennines, Pyrenees, Scandinavian and Drakensberg Mountains, Australian Alps, Stara Planina. There are medium mountains also within Russia. These are the Ural Mountains, Eastern Sayan, Sikhote-Alin (pictured below) and others.

An important feature of the middle mountains is the presence of altitudinal zones. That is, the vegetation and landscapes here change with altitude.

Carpathians

The Carpathians are the largest mountain system in Europe, spanning eight countries. Linguists, explaining the origin of its name, came to the conclusion that this toponym has Proto-Indo-European roots and is translated as “stone”, “rock”.

The Carpathians stretch in an arc of one and a half thousand kilometers, from the Czech Republic to Serbia. And the highest point of this mountain system is located on the territory of Slovakia (Mount Gerlachovsky Štit, 2654 m). An interesting fact: between the Alps and the extreme eastern spurs of the Carpathians there are only 15 kilometers.

The Carpathians are young mountains. They formed in the Cenozoic. However, their outlines are smooth and gentle, which is more typical of older geological structures. This can be explained by the fact that the Carpathians are predominantly composed of soft rocks (chalk, limestone and clay).

The mountain system is divided into three conventional parts: Western, Eastern (or Ukrainian) and Southern Carpathians. It also includes the Transylvanian Plateau. are characterized by fairly high seismicity. Here is the so-called Vrancea zone, which “produces” earthquakes with a magnitude of 7-8.

Appalachia

Geomorphologists often call the Appalachians the identical twin of the Carpathians. In appearance they are not much different from each other. The Appalachian Mountains are located in the eastern part of North America, within two states (USA and Canada). They stretch from to the Gulf of Mexico in the south. The total length of the mountain system is about 2500 kilometers.

If the European Carpathians are young mountains, then the American Appalachians are a product of earlier Hercynian and Caledonian folds. They formed about 200-400 million years ago.

The Appalachian Mountains are rich in a variety of mineral resources. Coal, asbestos, oil, and iron ore are mined here. In this regard, this mountainous region is also very often called the historical “industrial belt” of the United States.

Australian Alps

It turns out that the Alps are not only in Europe. Residents of the smallest and driest continent can also go hiking in the real Alps. But only in Australia!

This mountain system is located in the southern part of the continent. It is here that the highest point in all of Australia is located - Mount Kosciuszko (2228 m). And on the slopes of these mountains, the longest river of the mainland, the Murray, originates.

The Australian Alps are stunningly diverse in landscape terms. In these mountains you can find snow-capped peaks, deep green valleys, and lakes with clear water. The mountain slopes are decorated with bizarre-looking rocks. The Australian Alps are home to several picturesque national parks and excellent ski resorts.

Finally

Now you know which mountains are medium and which are high. Geomorphologists distinguish three types of mountain systems based on height. The middle mountains have an altitude of 1000 to 3000 meters above sea level. The Carpathians, Appalachians, and Australian Alps are the most striking examples of such mountain systems in the world.

Mountains

Mountains

a collection of closely spaced individual mountains, mountain ranges, mountain spurs, ridges, highlands, as well as the canyons, valleys, and depressions separating them, occupying a certain territory, more or less clearly separated from the surrounding plains. Compared to plains, mountains are characterized by much larger abs. and relative heights, steeper slopes of their constituent forms, increased intensity of exogenous processes occurring in them; in other words, mountains are characterized by a special relief, which is called mountainous. Therefore, the term “mountains” also refers to one of the two main. (along with plains) morphological types of relief of the earth's surface. Between the mountains and plains there is often a strip of hilly foothills, the relief of which is intermediate (between mountainous and flat) in nature. Ch. Endogenous processes play a role in the formation of mountains, so most mountains tectonic: folded, blocky, transitional between them, etc. In addition to those indicated, the type volcanic mountains, which are large accumulations of active or extinct volcanoes, lava massifs and other forms associated with volcanism, as well as the type intrusive mountains resulting from the introduction of large volumes magma(intrusions) into the upper layers of the earth's crust, which leads to an uplift of the earth's surface. The term "mountains" is sometimes used as a synonym for the terms "mountain country" and "mountain system".

Geography. Modern illustrated encyclopedia. - M.: Rosman. Edited by prof. A. P. Gorkina. 2006 .

elevated areas of the earth's surface, rising steeply above the surrounding area. Unlike plateaus, peaks in mountains occupy a small area.
Mountains can be classified according to different criteria: 1) geographical location and age, taking into account their morphology; 2) structural features, taking into account the geological structure. In the first case, mountains are divided into cordilleras, mountain systems, ridges, groups, chains and single mountains.
The name "cordillera" comes from the Spanish word meaning "chain" or "rope". The cordillera includes ranges, groups of mountains and mountain systems of different ages. The Cordillera region of western North America includes the Coast Ranges, Cascade Mountains, Sierra Nevada Mountains, Rocky Mountains, 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 consist 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 extend over 240 km in Colorado and New Mexico, are usually no more than 24 km wide, with many peaks reaching heights of 4000–4300 m, are a typical range. The group consists of genetically closely related mountains in the absence of a clearly defined linear structure characteristic of a ridge. Mount Henry in Utah and Mount Bear Paw in Montana are typical examples of mountain groups. In many areas of the globe there are single mountains, usually of volcanic origin. Such 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 endogenous processes of relief formation. Volcanic mountains are formed due to the accumulation of masses of igneous rocks during volcanic eruptions. Mountains can also arise as a result of the uneven development of erosion-denudation processes within a vast territory that has experienced tectonic uplift. Mountains can also be formed 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 intensive 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, although during the long history of development after the initial folding they were influenced by other mountain-building processes.
Fold mountains. Initially, many large mountain systems were folded, but during subsequent development their structure became very significantly more complex. Zones of initial folding are limited by geosynclinal belts - huge troughs in which sediments accumulated, mainly in shallow oceanic environments. Before folding began, their thickness reached 15,000 m or more. The association of folded mountains with geosynclines seems paradoxical, however, it is likely that the same processes that contributed to the formation of geosynclines subsequently ensured the collapse of sediments into folds and the formation of mountain systems. At the final stage, folding is localized within the geosyncline, since due to the large thickness of sedimentary strata, the least stable zones of the earth's crust arise there.
A classic example of fold mountains is the Appalachians in eastern North America. The geosyncline in which they formed had a much greater extent compared to modern mountains. Over the course of approximately 250 million years, sedimentation occurred in a slowly subsiding basin. The maximum sediment thickness exceeded 7600 m. Then the geosyncline underwent lateral compression, as a result of which it narrowed to approximately 160 km. The sedimentary strata accumulated in the geosyncline were strongly folded and broken by faults along which disjunctive dislocations occurred. During the stage of folding, the territory experienced intense uplift, the speed of which exceeded the rate of impact of erosion-denudation processes. Over time, these processes led to the destruction of the mountains and the reduction of their surface. The Appalachians have been repeatedly uplifted and subsequently denuded. However, not all areas of the original folding zone experienced re-uplift.
Primary deformations during the formation of folded mountains are usually accompanied by significant volcanic activity. Volcanic eruptions occur during folding or shortly after its completion, and large masses of molten magma flow into the folded mountains to form batholiths. They often open up 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 have shifted for many kilometers. Fold mountains can contain both fairly simple folded structures (for example, in the Jura Mountains) and very complex ones (as in the Alps). In some cases, the process of folding develops more intensively along the periphery of geosynclines, and as a result, two marginal folded ridges and a central elevated part of the mountains with less development of folding are distinguished on the transverse profile. Thrusts extend from the marginal ridges towards the central massif. Massifs of older and more stable rocks that bound a 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 the sublatitudinal Kunlun Mountains at its northern border, the Himalayas at the southern border, and the Tibetan Plateau between them. In relation to this mountain belt, the Tarim Basin in the north and the Hindustan Peninsula 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 resistant rocks, while the valleys are carved out of less resistant rocks. Landscapes of this type are found in western Pennsylvania. With deep erosional dissection of a folded mountainous country, the sedimentary layer can be completely destroyed, and the core, composed of igneous or metamorphic rocks, can be exposed.
Block 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 of approx. 640 km and width from 80 to 120 km. The eastern edge of this horst was raised most highly, where the height of Mount Whitney reaches 418 m above sea level. The structure of this horst is dominated by granites, which form the core of the giant batholith, but sedimentary strata that accumulated in the geosynclinal trough in which the folded Sierra Nevada mountains were formed were also preserved.
The modern appearance of the Appalachians was largely formed as a result of several processes: the primary fold mountains were exposed to erosion and denudation, and then were uplifted along faults. However, the Appalachians are not typical block 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 raised as horsts along the faults that bound them, and their final appearance was formed under the influence of erosion-denudation processes. Most of the ridges extend in the submeridional direction and have a width of 30 to 80 km. As a result of uneven uplift, some slopes were steeper than others. Between the ridges lie long narrow valleys, partially filled with sediments carried down from the adjacent blocky mountains. Such valleys, as a rule, are confined to subsidence zones - grabens. It is assumed that the block mountains of the Great Basin were formed in a zone of extension of the earth's crust, since most faults here are characterized by tensile stresses.
Arch Mountains. In many areas, land areas that experienced tectonic uplift acquired a mountainous appearance under the influence of erosion processes. Where the uplift occurred over a relatively small area and was arched in nature, arched mountains were formed, a striking example of which is the Black Hills Mountains in South Dakota, which are approx. 160 km. The area experienced arch uplift and most of the sedimentary cover was removed by subsequent erosion and denudation. As a result, a central core composed of igneous and metamorphic rocks was exposed. It is framed by ridges consisting of more resistant sedimentary rocks, while the valleys between the ridges are worked out in less resistant rocks.
Where laccoliths (lenticular bodies of intrusive igneous rocks) were intruded into the sedimentary rocks, the underlying sediments could also experience arching uplifts. A good example of eroded arched uplifts is Mount Henry in Utah.
The Lake District in western England also experienced arching, but of somewhat less amplitude than in the Black Hills.
Remnant plateaus. Due to the action of erosion-denudation processes, mountain landscapes are formed on the site of any elevated territory. The degree of their severity depends on the initial height. When high plateaus, such as Colorado (in the southwestern United States), are destroyed, highly dissected mountainous terrain is formed. The Colorado Plateau, hundreds of kilometers wide, was raised to a height of approx. 3000 m. Erosion-denudation processes have not yet had time to completely transform it into a mountain landscape, however, within some large canyons, for example the Grand Canyon of the river. Colorado, mountains several hundred meters high arose. These are erosional remains that have not yet been denuded. With the further development of erosion processes, the plateau will acquire an increasingly pronounced mountain appearance.
In the absence of repeated uplifts, any territory will eventually be leveled and turn into a low, monotonous plain. Nevertheless, even there, isolated hills composed of more resistant rocks will remain. Such remnants are called monadnocks after Mount Monadnock in New Hampshire (USA).
Volcanic mountains There are different types. Common in almost every region of the globe, volcanic cones are formed by accumulations of lava and rock fragments erupted through long cylindrical vents by forces operating deep within the Earth. Illustrative examples of volcanic cones are Mount Mayon in the Philippines, Mount Fuji in Japan, Popocatepetl in Mexico, Misti in Peru, Shasta in California, etc. Ash cones have a similar structure, but are not so high and are composed mainly of volcanic scoria - porous volcanic rock, externally like ash. Such cones are found near Lassen Peak in California and northeastern New Mexico.
Shield volcanoes are formed by repeated outpourings of lava. They are usually not as tall and have a less symmetrical structure than volcanic cones. There are many shield volcanoes on the Hawaiian and Aleutian Islands. In some areas, the foci of volcanic eruptions were so close that the igneous rocks formed entire ridges that connected the initially isolated volcanoes. This type includes the Absaroka Range in the eastern part of Yellowstone Park in Wyoming.
Chains of volcanoes occur in long, narrow zones. Probably the most famous example is the chain of volcanic Hawaiian Islands, which extends over 1,600 km. All of these islands were formed as a result of lava outpourings and eruptions of debris from craters located on the ocean floor. If you 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 layers of volcanic deposits can be cut away by rivers or glaciers and turn into isolated mountains or groups of mountains. A typical example is the San Juan Mountains in Colorado. Intense volcanic activity occurred here during the formation of the Rocky Mountains. Lavas of various types and volcanic breccias in this area occupy 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, the volcanic rock masses were deeply dissected and turned into high mountains. Volcanic rocks are currently preserved only on the mountain tops. Below, thick strata of sedimentary and metamorphic rocks are exposed. Mountains of this type are found on areas of lava plateaus prepared by erosion, in particular the Columbia, located between the Rocky and Cascade Mountains.
Distribution and age of mountains. There are mountains on all continents and many large islands - in Greenland, Madagascar, Taiwan, New Zealand, British, etc. The mountains of Antarctica are largely buried under ice cover, but there are individual volcanic mountains, for example Mount Erebus, and mountain ranges , including the mountains of Queen Maud Land and Mary Baird Land - high and well defined in relief. Australia has fewer mountains than any other continent. In North and South America, Europe, Asia and Africa there are cordilleras, mountain systems, ranges, groups of mountains and single mountains. The Himalayas, located in the south of Central Asia, are the highest and youngest mountain systems in the world. The longest mountain system is the Andes in South America, stretching 7560 km from Cape Horn to the Caribbean Sea. They are older than the Himalayas and apparently had a more complex history of development. The mountains of Brazil are lower and significantly older than the Andes.
In North America, the mountains show very great diversity in age, structure, structure, origin and degree of dissection. The Laurentian Upland, which occupies the territory from Lake Superior to Nova Scotia, is a relic of heavily 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 remain. Appalachians are intermediate in age. They first 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 were re-raised to modern heights. The Sierra Nevada Mountains are younger than the Appalachians. They also went through a stage of significant destruction and re-raising. 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 during 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 now. The Cascade Mountains and Coast Ranges of the western United States and most of the Alaskan mountains are younger than the Rocky Mountains. The California Coast Ranges are still experiencing very slow uplift.
Diversity of structure and structure of 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 subjected to unusually powerful forces, which were reflected in the emplacement of large batholiths of igneous rocks and in the formation of an extremely diverse range of overturned folds and faults with enormous amplitudes of displacement. In contrast, the Black Hills have a very simple structure.
The geological structure of the mountains is as diverse as their structures. For example, the rocks that make up the northern part of the Rocky Mountains in the provinces of Alberta and British Columbia are mainly Paleozoic limestones and shales. In Wyoming and Colorado, most of the mountains have cores of granite and other ancient igneous rocks overlain by layers 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 occur in other mountains of the world.
Although in principle no two mountains are exactly alike, young volcanic mountains are often quite similar in size and shape, as evidenced by the regular cone shapes of Fuji in Japan and Mayon in the Philippines. However, note that many of Japan's volcanoes are composed of andesites (a medium-composition igneous rock), while the volcanic mountains in the Philippines are composed of basalts (a heavier, black-colored rock containing a lot of iron). The volcanoes of the Cascade Mountains in Oregon are composed primarily of rhyolite (a rock containing more silica and less iron compared to basalts and andesites).
ORIGIN OF MOUNTAINS
No one can explain with certainty how mountains were formed, but the lack of reliable knowledge about orogenesis (mountain building) should not and does not hinder scientists' attempts to explain this process. The main hypotheses for the formation of mountains are discussed below.
Submergence of oceanic trenches. This hypothesis was based on the fact that many mountain ranges are confined to the periphery of 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 trenches tend to sink, squeezing 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. It also does not explain the origin of such mountain systems as the Rocky Mountains or the Himalayas, which are remote from the continental margins.
Kober's hypothesis. The Austrian scientist Leopold Kober studied in detail the geological structure of the Alps. In developing his concept of mountain building, he attempted to explain the origin of the large thrust faults, or tectonic nappes, that occur in both the northern and southern parts of the Alps. They are composed of thick strata of sedimentary rocks that have been subjected to significant lateral pressure, resulting in the formation of recumbent or overturned folds. In some places, boreholes in the mountains penetrate the same layers of sedimentary rocks three or more times. To explain the formation of overturned folds and associated thrust faults, Kober proposed that central and southern Europe were once occupied by a huge geosyncline. Thick strata of Early Paleozoic sediments accumulated in it under the conditions of an epicontinental sea basin, which filled a geosynclinal trough. Northern Europe and North Africa were forelands composed of very stable rocks. When orogenesis began, these forelands began to move closer together, squeezing upward the fragile young sediments. With the development of this process, which was likened to a slowly tightening vice, the uplifted sedimentary rocks were crushed, formed overturned folds, or were pushed onto the approaching forelands. Kober tried (without much success) to apply these ideas to explain the development of other mountainous areas. In itself, the idea of ​​lateral movement of land masses seems to explain the orogenesis of the Alps quite satisfactorily, but it turned out to be inapplicable to other mountains and therefore was rejected as a whole.
Continental drift hypothesis comes from the fact that most mountains are located on the continental margins, and the continents themselves are constantly moving in the horizontal direction (drifting). During this drift, mountains form on the edge 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 formation, this hypothesis encounters many objections. It does not explain the formation of the broad, symmetrical folds that occur in the Appalachians and the 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 accepted stages of orogenesis as the replacement of initial folding by the development of vertical faults and the resumption of uplift. However, in recent years, much evidence has been discovered for the continental drift hypothesis, and it has gained many supporters.
Hypotheses of convection (subcrustal) flows. 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, has continued. From 1933 to 1938 alone, no less than six hypotheses were put forward about the participation of convection currents in mountain formation. However, all of them are based on unknown parameters such as temperatures of the earth’s interior, fluidity, viscosity, crystal structure of rocks, compressive strength of different rocks, etc.
As an example, consider the Griggs hypothesis. It suggests 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 ca. 2900 km below sea level. These cells are the size of a continent, but usually their outer surface diameter is from 7700 to 9700 km. At the beginning of the convection cycle, the rock masses surrounding the core are highly heated, while at the surface of the cell they are relatively cold. If the amount of heat flowing from the earth's core to the base of the cell exceeds the amount of heat that can pass through the cell, a convection current occurs. As the heated rocks rise upward, the cold rocks from the surface of the cell sink. It is estimated that for matter from the surface of the core to reach the surface of the convection cell, it takes approx. 30 million years. During this time, long-term downward movements occur in the earth's crust along the periphery of the cell. The subsidence of geosynclines is accompanied by the accumulation of sediments hundreds of meters thick. In general, the stage of subsidence and filling of geosynclines continues for ca. 25 million years. Under the influence of lateral compression along the edges of the geosynclinal trough caused by convection currents, the deposits of the weakened zone of the geosyncline are crushed into folds and complicated by faults. These deformations occur without significant uplift of the faulted folded strata over a period of approximately 5–10 million years. When the convection currents finally die out, the compression forces are weakened, the subsidence slows down, and the thickness of the sedimentary rocks that filled the geosyncline rises. The estimated duration of this final stage of mountain building is ca. 25 million years.
Griggs' hypothesis explains the origin of geosynclines and their filling with sediments. It also reinforces the opinion of many geologists that the formation of folds and thrusts in many mountain systems occurred without significant uplift, which occurred later. However, it leaves a number of questions unanswered. Do convection currents really exist? Seismograms of earthquakes indicate the relative homogeneity of the mantle - the layer located between the earth's crust and core. Is the division of the Earth's interior into convection cells justified? If convection currents and cells exist, mountains should arise simultaneously along the boundaries of each cell. How true is this?
The Rocky Mountain systems in Canada and the United States are approximately the same age throughout their entire length. Its uplift began in the Late Cretaceous and continued intermittently throughout the Paleogene and Neogene, but the mountains in Canada are confined to a geosyncline that began to sag in the Cambrian, while the mountains in Colorado are associated with a geosyncline that 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?
Hypothesis of swelling, or geotumor. The heat released during the decay of radioactive substances has long attracted the attention of scientists interested in the processes occurring in the bowels of the Earth. The release of enormous amounts of heat from the explosion of atomic bombs dropped on Japan in 1945 stimulated the study of radioactive substances and their possible role in mountain building processes. As a result of these studies, J.L. Rich's hypothesis appeared. Rich assumed that somehow large amounts 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 territory not affected by endogenous processes, geosynclines are formed. Sediment accumulates in them, and the troughs themselves deepen both due to ongoing geotumor and under the weight of precipitation. The thickness and strength of rocks in the upper part of the earth's crust in the geotumor region decreases. Finally, the earth's crust in the geotumor zone turns out to be so high that part of its crust slides along steep surfaces, forming thrusts, 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 orogenesis ends.
The swelling hypothesis is not widely accepted. None of the known geological processes allows us to explain how the accumulation of masses of radioactive materials can lead to the formation of geotumours with a length of 3200–4800 km and a width of several hundred kilometers, i.e. 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.
Contraction, or compression of the Earth, hypothesis is based on the assumption that throughout the entire history of the existence of the Earth as a separate planet, its volume has constantly decreased due to compression. The compression of the planet's interior is accompanied by changes in the solid crust. Stresses accumulate intermittently and lead to the development of powerful lateral compression and deformation of the crust. Downward movements lead to the formation of geosynclines, which can be flooded by epicontinental seas and then filled with sediment. Thus, at the final stage of development and filling of the geosyncline, a long, relatively narrow wedge-shaped geological body is created from young unstable rocks, resting on the weakened base of the geosyncline and bordered by older and much more stable rocks. When lateral compression resumes, folded mountains complicated by thrust faults form in this weakened zone.
This hypothesis seems to explain both the reduction of the earth's crust, expressed in many folded mountain systems, and the reason for the emergence of mountains in place of ancient geosynclines. Since in many cases compression occurs deep within the Earth, 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 heat loss and subsequent compression were not great enough to produce the folds and faults that are found in modern and ancient mountainous areas of the world. Another objection to this hypothesis is the assumption that the Earth does not lose, but accumulates heat. If this is indeed the case, then the value of the hypothesis is reduced to zero. Further, if the Earth's core and mantle contain a significant amount of radioactive substances that release more heat than can be removed, then the core and mantle expand accordingly. As a result, tensile stresses will arise in the earth's crust, and not compression, and the entire Earth will turn into a hot melt of rocks.
MOUNTAINS AS HUMAN HABITAT
The influence of altitude on climate. Let's consider some climatic features of mountain areas. Temperatures in the mountains decrease by about 0.6° C for every 100 m of elevation. The disappearance of vegetation cover and the deterioration of living conditions high in the mountains are explained by such a rapid drop in temperature.
Atmospheric pressure decreases with altitude. Normal atmospheric pressure at sea level is 1034 g/cm2. At an altitude of 8800 m, which approximately corresponds to the height of Chomolungma (Everest), the pressure drops to 668 g/cm2. At higher altitudes, more heat from direct solar radiation reaches the surface because the layer of air that reflects and absorbs the radiation is thinner there. However, this layer retains less heat reflected by the earth's surface into the atmosphere. Such heat losses explain 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 often used in descriptions of mountains are “tree top” and “snow line.” The upper limit of the forest is the level above which trees do not grow or hardly grow. Its position depends on average annual temperatures, precipitation, slope exposure and latitude. In general, the forest line is higher at low latitudes than at high latitudes. In the Rocky Mountains of Colorado and Wyoming it occurs at altitudes of 3400–3500 m, in Alberta and British Columbia it drops to 2700–2900 m, and in Alaska it is located even lower. Quite a few people live above the forest line in conditions of low temperatures and sparse vegetation. Small groups of nomads move throughout 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 above 4000 m, there are rich deposits of copper, gold, tin, tungsten and many other metals. All food products and everything necessary for the construction of settlements and mining have to be imported from the lower regions.
The snow line is the level below which snow does not remain on the surface all year round. The position of this line varies depending on the annual amount of solid precipitation, slope exposure, altitude and latitude. Near the equator in Ecuador, the snow line passes at an altitude of approx. 5500 m. In Antarctica, Greenland and Alaska it is raised only a few meters above sea level. In the Colorado Rockies, the height of the snow line is approximately 3,700 m. This does not mean that snowfields are widespread above this level and not below them. 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 northern-facing slopes. Since snowfields, growing every year, can eventually become a source of food for glaciers, the position of the snow line in the mountains is of interest to geologists and glaciologists. In many areas 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 indisputable evidence that this trend has been reversed. It is difficult to judge how stable it is, but if it persists for many years, it could lead to the development of an 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 greater than on the adjacent plains. This can be both a favorable and a negative factor for mountain residents. Atmospheric precipitation can fully meet the water needs for domestic and industrial needs, but in case of excess it can lead to destructive floods, and heavy snowfalls can completely isolate mountain settlements for several days or even weeks. Strong winds form snow drifts that block roads and railways.
Mountains are like 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 porters with heavy loads of goods crossed this wild place in the mountains. Famous Alpine passes such as St. Gotthard and Simplon have been used for many years for communication between Italy and Switzerland. Nowadays, the tunnels built under the passes support heavy rail traffic all year round. In winter, when the passes are filled with snow, all transport communications are carried out through tunnels.
Roads. Due to the high altitudes and rugged terrain, the construction of roads and railways in the mountains is much more expensive than on the plains. Road and rail transport wears out faster there, and rails with the same load fail in a shorter time than on the plains. Where the valley floor is wide enough, the railway track is usually placed along the rivers. However, mountain rivers often overflow their banks and can destroy large sections of roads and railways. If the width of the valley bottom is not sufficient, the roadbed has to be laid along the sides of the valley.
Human activity in the mountains. In the Rocky Mountains, due to the construction of highways and the provision of modern household amenities (for example, the use of butane for lighting and heating homes, 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 good example of such a refuge is the city of Baguio, the summer capital of the Philippines, which is called the “city of 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, housing for employees and a hospital there, since in Manila itself it was difficult to establish effective government work in the summer due to the intense heat and high humidity. The experiment of creating a summer capital in Baguio was very successful.
Agriculture. In general, terrain features such as steep slopes and narrow valleys limit the development of agriculture in the temperate mountains 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 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 ripen and late spring and early autumn frosts are common.
Pasture farming is widespread in the mountains. Where summer rainfall is abundant, grass grows well. In the Swiss Alps, in the summer, entire families move with their small herds of cows or goats to the high mountain valleys, where they practice cheese making and make butter. In the Rocky Mountains of the United States, large herds of cows and sheep are driven each summer from the plains to the mountains, where they gain weight in the rich meadows.
Logging- one of the most important sectors of the economy in the mountainous regions of the globe, ranking second after pasture livestock farming. Some mountains are bare of vegetation due to lack of rainfall, but in temperate and tropical zones most mountains are (or were formerly) covered with dense forests. The variety of tree species is very large. Tropical mountain forests produce valuable deciduous wood (red, rosewood, ebony, teak).
Mining industry. Mining of metal ores is an important sector 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 altitudes of 3700–4600 m, where the cold, strong winds and hurricanes create the most difficult living conditions. The productivity of miners there is very low, and the cost of mining products is prohibitively high.
Population density . Due to the peculiarities of climate and topography, mountainous areas often cannot be as densely populated as lowland 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 between the highlands and the lowlands exist in Scotland.
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 Elias,

So, according to the origin of mountains, there are tectonic, volcanic and erosional (denudation):

Tectonic mountains are formed as a result of the collision of moving parts of the earth's crust - lithospheric plates. This collision causes folds to form on the surface of the earth. This is how folded mountains arise. When interacting with air, water and under the influence of glaciers, the rock layers that form folded mountains lose their plasticity, which leads to the formation of cracks and faults. Currently, folded mountains have been preserved in their original form only in certain parts of the young mountains - the Himalayas, formed during the era of Alpine folding.

With repeated movements of the earth's crust, hardened folds of rock are broken into large blocks, which, under the influence of tectonic forces, rise or fall. This is how folded block mountains arise. This type of mountains is typical for old (ancient) mountains. An example is the Altai mountains. The emergence of these mountains occurred during the Baikal and Caledonian eras of mountain building; in the Hercynian and Mesozoic eras they were subject to repeated movements of the earth's crust. The type of folded-block mountains was finally adopted during the Alpine folding.

Volcanic mountains are formed during the process of volcanic eruptions. They are usually located along fault lines in the earth's crust or at the boundaries of lithospheric plates.

Volcanic There are two types of mountains:

Volcanic cones. These mountains acquired their cone-shaped appearance as a result of the eruption of magma through long cylindrical vents. This type of mountain is widespread throughout the world. These are Fuji in Japan, Mount Mayon in the Philippines, Popocatepetl in Mexico, Misti in Peru, Shasta in California, etc.
Shield volcanoes. Formed by repeated outpouring of lava. They differ from volcanic cones in their asymmetrical shape and small size.

In areas of the globe where active volcanic activity occurs, entire chains of volcanoes can form. The most famous is the chain of Hawaiian Islands of volcanic origin, more than 1600 km long. These islands are the tops of underwater volcanoes, whose height from the surface of the ocean floor is more than 5500 meters.

Erosion (denudation) mountains.

Erosion Mountains arose as a result of intensive dissection of stratified plains, plateaus and plateaus by flowing waters. Most mountains of this type are characterized by a table shape and the presence of box-shaped and sometimes canyon-type valleys between them. The last type of valley occurs most often when a lava plateau is dissected.

Examples of erosional (denudation) mountains are the mountains of the Central Siberian Plateau (Vilyuisky, Tungussky, Ilimsky, etc.). Most often, erosion mountains can be found not in the form of separate mountain systems, but within mountain ranges, where they are formed by the dissection of rock layers by mountain rivers.

Mountain systems occupy about forty percent of the surface of our planet: they can be seen on every continent, on many islands and on the ocean floor. The fewest ranges are found on the Australian continent, and almost all the mountain ranges of Antarctica are reliably hidden under ice.

Mountains are parts of the earth's crust that, as a result of the movement of tectonic plates, volcanic eruptions, or other processes occurring within the planet, have risen to a significant height and began to rise above the plains. The height of some hills is small and amounts to about three hundred meters, others rise more than eight thousand meters above sea level. The type of mountains is extremely diverse: it can be a single peak, or it can be a long mountain range, which includes hundreds and even thousands of cones.

Considering that the structure of the mountains is ten percent sedimentary, and ninety percent igneous and metamorphic rocks (appearing as a result of changes in the structure of sedimentary and volcanic rocks), geologists often discover mineral deposits inside them and under the mountain.

The mountain relief consists of several parts:

• Mountain (hill) – a low or high cone-shaped mountain, consisting of a peak, slopes and a base (the place where the slopes merge with the surrounding territory);
• Ridges are strongly elongated mountain heights, the slopes of which, on the one hand, are often gentle, and on the other, steep. They are also watersheds because they direct river water flowing downhill from different sides of the slopes in opposite directions. For example, the Rocky Mountains extend from the north to the southeast, and their length is about five thousand kilometers, due to which the Rocky Mountains are a watershed between the basins of the Pacific and Atlantic oceans;

• A saddle is a depression of relief between two hills located near each other, usually the beginning of two valleys that go downhill in different directions;
• A hollow is an open, slightly inclined, downhill depression in the relief, which below, when the slopes merge, forms a drainage line;
• Basin - located below sea level, a cone-shaped depression, which is characterized by a bottom, slopes and an edge line - the place where the slopes meet the surface.

Formation theory

Throughout the history of their development, people have put forward a variety of theories about how exactly the mountains of the world were formed. At first these were myths, legends and tales, then the versions began to be more substantiated. For example, it has been suggested that mountain systems arose due to the movement of matter under the ocean floor, causing the arching of its surface, which causes the heaving of the earth's crust along the margins of the ocean.

This hypothesis did not explain in any way the presence of mountain systems inside the continent. Then they considered the version that the Earth is constantly decreasing in volume, and this happens in leaps and bounds and leads to deformation of the surface, where folds are formed, some of which rise above the surface, and the other goes downhill.

Later, the idea emerged that the mountain system was formed during continental drift. The idea was not bad, but it did not explain the reason for the movement of the continents, so it was forgotten. Instead, another hypothesis arose, suggesting that there are currents inside the Earth that cause the rise and fall (going downhill) of the earth's crust, affecting the topography of the planet. Despite the fact that many people liked the idea, no scientific evidence was found to support it.

The modern hypothesis of the formation of mountains arose in the middle of the last century, when the movement of lithospheric plates was proven, during the collision of which a thinner plate goes under the neighboring one, forming hills on the earth's surface. This theory was combined with previous versions, it explained a lot and was accepted as the main one.

Age of the mountains

Based on the theory of the movement of tectonic plates and soil analyses, it was found that each mountain system was formed at one time. The age of young ranges ranges from 50 to 80 million years, while old mountain systems appeared more than a hundred million years ago (for comparison, the age of our planet is about four and a half billion years).

Young mountain ranges (Rocky Mountains, Himalayas) are interesting because their internal processes are still developing.

For example, due to the constant collision of the Indian and Asian plates, the high mountains of the Himalayas grow by five centimeters per year. This process is always accompanied by earthquakes, and in some cases – volcanic eruptions. A young, growing mountain system is easily recognizable by its sharply defined relief, consisting of alternating peaks and protrusions, the sharp shape of the peaks, and the presence of very steep and high slopes that complicate both the ascent and descent from the mountain.

The ancient mountain system differs from the younger one in that all processes inside it have long ceased, while external processes that cause erosion continue to affect the surface of the Earth. An interesting fact: geologists have discovered more than one area on the plains where there was previously a mountain system, from which only roots remained, securely hidden under a thick layer of sedimentary rocks. The most ancient hills of the Earth were recognized as the remains of mountains that are located in the Hudson Bay area: they appeared almost simultaneously with our planet.

As for the ancient mountains, which time has not erased from the face of the Earth (for example, the Ural or Scandinavian), they can be recognized primarily by their height, not exceeding one and a half thousand meters, gentle slopes, and also by severe erosion. If in young mountains water streams flow in narrow gorges, then the rivers of an old mountain flow along a well-defined wide river valley.

It is not uncommon for older mountain ranges to include younger formations. For example, the Rocky Mountains, which appeared as a result of a tectonic shift from 80 to 50 million years ago, are a young part of the Western Cordillera, which began to form more than 120 million years ago. It should be noted that the Rocky Mountains are still growing, so earthquakes and post-volcanic phenomena are common in the region where they are located.

Types of mountains

The answer to the question of what kinds of mountains there are is not as simple as it seems: mountain ranges differ not only in age, but also in structure, origin, shape, location, height:

1. In terms of altitude, low mountains are characterized by heights of up to 800 meters, middle mountains – up to 3 thousand meters and high mountains – more than 3 thousand meters. The height of mountains in some cases can reach incredible proportions. For example, the height of Everest, which for a long period was listed in reference books as the highest mountain in the world, is almost nine kilometers. Recently, this primacy was called into question when a large mountain was discovered at the bottom of the Pacific Ocean, exceeding the size of Chomolungma: the height of the inactive Mauna Kea volcano from its base to its summit exceeds ten kilometers.
2. By origin - volcanic, tectonic or erosional (erosion of plains by strong river flows, for example, canyons and mesas consisting of limestone, basalt, sandstone).
3. At the top, a young high mountain usually has a peak-shaped, pointed shape. The top of the mountain can have a plateau-shaped, dome-shaped or rounded shape, which is typical both for old, heavily destroyed volcanoes and for areas where a large mountain has arisen as a result of the collision of plates.

Zoning

If the hill itself is not high, then the nature of the mountain at its base and at the top is not particularly different. True, this largely depends on which altitudinal group it belongs to. For example, the characteristic of continental-type mountains implies a complete absence of forests.

But when describing the low and middle elevations of the coastal type, one cannot fail to mention the presence of a forest landscape and meadows. If we are talking about a mountain with a height of more than three thousand meters, it is worth considering: in order to climb to its peak, you need to overcome absolutely all the belts of our planet. Therefore, the weather in the mountains differs significantly from the climate of the adjacent plains.

This is explained by the fact that the temperature drops by six degrees with each kilometer traveled. In addition, atmospheric pressure decreases, the level of solar radiation increases and the amount of precipitation changes. Accordingly, such weather in the mountains also affects nature.

Exactly how many zones a high mountain will have depends largely on what climatic zone it is in (mountain ranges near the equator have the largest number of zonal zones). It is also important at what height these zones will be located, how the slopes are located: on the sunny side they are usually lower. Geologists divide altitudinal zones into several parts.

Nival altitude belt

Only a high mountain can boast of having a nival belt: in the tropics it begins at an altitude exceeding 6.5 km above sea level. m., the further north it is, the lower it is located (ascent and descent from the mountain is quite difficult and often fraught with death).

This zone is characterized by the presence of glaciers and eternal snow (the Rocky Mountains or the Himalayas, which include the highest mountain in the world, Everest), while the surface not covered with snow is subject to severe erosion, primarily weathering. The vegetation here is extremely sparse - lichens and a few herbs. There are also few animals: sometimes predators wander here, rodents are found, birds fly in and some types of insects can be seen.

Mountain-tundra altitudinal belt

Winter in the mountain-tundra zone is long, summer is short and cold. Average temperatures do not exceed +9°C. A strong wind constantly blows here, and the soil often freezes (only lichens, mosses, and low shrubs grow). This belt is not typical for all mountains: in warm latitudes it is absent; instead, an alpine or subalpine belt is located at this level.

Alpine altitudinal zone

The alpine belt is typical for mountains of the coastal type, and is almost never found in sharply continental latitudes. In the Himalayas it is located at an altitude exceeding 3.6 kilometers, in the Alps and Andes - 2.2 kilometers. During the short summer period, the meadows bloom profusely here, but winter is long and the slopes are completely covered with snow.

Desert-steppe belt

Characteristic of mountains that are located in desert and semi-desert areas of tropical latitudes and temperate zones. In drier areas it is located above the subalpine zone, in more humid areas it is located above the mountain forest zone. The landscape of this zone is first characterized by the presence of steppe, then semi-desert and desert.

Subalpine altitudinal zone

In this zone, meadows are mixed with small areas of forests. Sometimes geologists combine this zone with the alpine zone and call it the mountain-meadow belt.

Mountain-forest altitudinal belt

The mountain-forest belt is characterized by the presence of forest landscapes, while there is an extremely large amount of vegetation here and all its types largely depend on the latitude where the mountain is located. This belt goes downhill.

Human life in the mountains

Despite the fact that people settle mainly in the lowlands, at the base of the mountain, they long ago learned to benefit from almost the entire mountain surface and learn to make the most of relatively small spaces. For example, in the Alps (the highest mountain is Mont Blanc, 4810 m high), at the foot you can often see vineyards and garden plots, the middle part is sown with agricultural crops, and cattle are grazed in the alpine meadows.

In these same mountains, thanks to a large amount of minerals, salt and precious metals, the mining industry is developed, paper and pulp are harvested from the forest, and hydroelectric power stations were built on the banks of the rivers.

People also actively use the mountains located on the American continent. A striking example is the Rocky Mountains (the largest mountain in the range is Elbert, 4.4 km high). The Rocky Mountains hide in their depths huge reserves of coal, lead, zinc, silver, shale, oil and natural gas. Despite the fact that relatively few people live here (four people per square kilometer, and the population of only a few cities exceeds fifty thousand),

The Rocky Mountains have extremely developed agriculture and forestry industries. Americans and Canadians successfully use mountain lands for grazing livestock and growing crops.

The Rocky Mountains are now an extremely popular destination among tourists: there are a huge number of national parks here, including Yellowstone, famous for its geysers and geothermal springs.

General concept. A mountain is usually called any pronounced rise, the base, slopes and top of which can be relatively easily distinguished. Free-standing mountains are extremely rare. Most often, mountains are united into large groups, and their bases closely merge, forming a common skeleton, or the base of the mountains, clearly rising above the neighboring plain regions.

Based on the location of the mountains in the plan, isolated mountains, mountain ranges and mountain ranges are distinguished. The first, that is, free-standing mountains, as already mentioned, are relatively rare and are either volcanoes or the remains of ancient destroyed mountains. The second, i.e. mountain ranges, are the most common type of mountainous areas.

Mountain ranges usually consist not of one, but of many rows of mountains, sometimes located very closely. As an example, we can point to the Main Caucasus Range, along the northern slope of which at least four more or less clearly defined rows of mountains are distinguished. Other mountain ranges have a similar character.

Mountain ranges They are vast mountain uplifts, equally developed in both length and width.

Large mountain ranges are rare. Most often they form separate sections of mountain ranges. An example of a large, highly dissected massif is the Khan Tengri mountain range.

The height of mountains is always measured vertically from the base to the top or from ocean level and also to the top. The height from the bottom to the top is called relative. The height from ocean level to the top is absolute. Absolute height makes it possible to compare the heights of mountains regardless of where they are located. In geography, absolute heights are almost always given.

Depending on their height, mountains are divided into low(below 1 thousand), average(from 1 to 2 thousand. m) And high(above 2 thousand m). When it comes to mountain ranges or mountainous areas, they usually include: small mountains, middle mountains And highlands. Examples of small mountains are the Timan Ridge, the Salair Ridge, as well as the foothills of many mountainous countries. Examples of middle mountains in the USSR are the Urals, the mountains of Transbaikalia, Sikhote-Alin and many others.

Types of mountains, identified on the basis of their height, are also characterized by relief features. For example, the highlands are characterized by sharp peaks, jagged ridges and deeply incised valleys (Fig. 235, 1). The highlands are also characterized by snowy peaks and glaciers. Mountains of medium height (or medium altitude) usually have rounded and seemingly smoothed shapes of the peaks and soft outlines of the ridges (Fig. 235, 2). The same, only even more smoothed forms are characteristic of small mountains. But here relative height becomes of great importance. If individual mountains of small mountains do not rise above the total surface above 200 m, then they are no longer called mountains, but hills.

Finally, mountains are also divided according to their origin. This division by origin is especially important for us, because it largely determines the character, structure, and location of the mountains. Depending on the origin (genesis) there are:

1) tectonic mountains,

2) volcanic mountains,

3) mountains are erosive.

We will analyze each of these types of mountains separately. Tectonic mountains, in turn, are divided into folded, folded-block and table-block.

Fold mountains. Let us recall that we call folded mountains those mountains in which folding clearly predominates. Fold mountains are found on all continents and many islands and are perhaps the most common, and fold mountains are the highest in height.

Mountains consisting of one fold (anticline) are relatively very rare. Much more often, mountain ranges consist of many parallel folds. In addition, the folds are usually much shorter in length than the ridges, due to which there may be several folds along the line of one ridge.

The very shape of the fold (in plan) largely determines the elongated shape of the ridges of folded mountains. Indeed, most of the folded mountains have a characteristic shape (Urals, Greater Caucasus, Cordillera).

Fold mountains usually consist of a series of parallel mountain ranges. In most cases, mountain ranges are located very close to one another, and, merging at their bases, form a wide and powerful mountain range. Mountain ranges stretch for hundreds and sometimes thousands of kilometers (the Caucasus Range is about 1 thousand. km, Ural over 2 thousand km). Most often, large ridges (in plan) have an arcuate shape and less often a rectilinear one.

Examples of arcuate ridges are the Alps, Carpathians, and Himalayas; examples of rectilinear ones are the Pyrenees, the Main Caucasus Range, the Urals, the southern part of the Andes, etc.

There are often cases when mountain ranges branch and even diverge like a fan. Examples of branching ridges are the mountains of the Pamir-Alai, Southern Urals and many others. Instead of the word branching, many authors use the word virgation. In cases where the branches of the ridges extend at a very acute angle or are located parallel to each other, the term “echelon” arrangement of the ridges is sometimes used.

Folds that appear on the surface of the Earth, under the influence of weathering, the work of flowing waters, the work of ice and the activity of other agents, immediately begin to collapse. Anticlines, as the most elevated parts of folded mountains, are destroyed first. The rapid destruction of anticlines is partly facilitated by the fracturing characteristic of bends. Therefore, when folds are severely destroyed, valleys often appear in place of anticlines. (anticlinal valleys), and in place of synclines there are mountain ranges. And the steeper the folds, the more intense the destruction of anticlines. As a result, the observed forms of mountains do not always correspond to structural forms, that is, forms determined by anticlines and synclines.

In cases where mountains, chains and ridges arise on the site of the wings of an anticline, the dip of the strata usually occurs only in one direction. The structure of such mountain chains is called monoclinal. The ridges or chains of mountains that arose on the site of the wings of a destroyed anticline are called cuestas, cuesta ridges, or cuesta chains. Asymmetry of slopes is typical for cuestas. The cuesta terrain is wide; distributed on all continents. An example is the northern foothills of the Caucasus.

Mesa Mountains are relatively rare. They arise on the site of lowland countries broken by faults, most often composed of horizontal strata. Elevated areas form mountains, usually table-type. The degree of elevation of areas can be different (from tens of meters to thousands of meters). It is difficult to notice any pattern in the distribution of rises and falls here. A typical example of table-block mountains is part of the Jura Mountains (Table Jura), as well as the Black Forest, Vosges, and some parts of the Armenian Highlands. An example of raising table forms to a lower height is Samarskaya Luka. There are many very high table rises in southern Africa.

Much more widespread fold-block mountains. The history of the formation of folded block mountains is quite complex. Let us consider, as an example, the main stages of the development of Altai. First, on the site of modern Altai (at the end of the Paleozoic), a high folded mountainous country arose. Then the mountains gradually collapsed and the country became a hilly plain. During the Tertiary period, this leveled section of the earth's crust, under the influence of the internal forces of the Earth, broke into pieces, with some parts rising and others falling. The result was a complex mountainous country, the ridges of which were located in a variety of directions. Examples of folded-block mountains in the USSR are the Tien Shan, Transbaikalia, Bureinsky Mountains and many others.

Volcanic mountains we are already quite familiar. Let us only note the special nature of the destruction of volcanic mountains under the influence of external agents.

The summits of high volcanoes, like the summits of other high mountains, are subject to vigorous processes of physical weathering. Here, as in other mountains, under the influence of sharp temperature fluctuations, powerful accumulations of rocks, stones and boulders are formed. Just like in other mountains, “stone streams” descend down the slopes. The only difference is that the “stone flows” descend not only along the outer slopes of the cone, but also along the inner slopes of the crater. On higher volcanic mountains glaciers develop, the destructive work of which is already known to us.

Below the snow line, the main destroyers are rainfall. They cut through potholes and ravines radiating from the edges of the crater along the internal (crater) and external slopes (Fig. 236). These erosion grooves on the outer and inner slopes of the volcano are called Barrancos. At first, the barrancos are numerous and shallow, but then their depth increases. As a result of the growth of the outer and inner barrancos, the crater expands, the volcano gradually lowers and takes the shape of a saucer surrounded by a more or less raised rampart.

As for laccoliths, they first lose their outer cover, consisting of sedimentary rocks. First, this cover is destroyed at the top, then on the slopes; at the base, the remains of the cover, together with deluvial cloaks, last much longer. Laccoliths freed from the cover of uplifted sedimentary rocks are called opened(or prepared) laccoliths.

Erosion mountains. By the name erosion mountains we mean mountains that have arisen mainly as a result of the erosive activity of flowing waters. Such mountains can arise as a result of the dissection of plateaus and flat hills by rivers. An example of such mountains is the many interfluve mountains of the Central Siberian Plateau (Vilyuisky, Tungussky, Ilimsky, etc.). They are characterized by table shapes and box-shaped valleys, and in some cases even canyon-shaped ones. The latter are especially characteristic of a dissected lava plateau.

Much more often, mountains of erosion origin are observed within the middle mountains. But these are no longer independent mountain systems, but parts of mountain ranges that arose as a result of the dissection of these ranges by mountain streams and rivers.

Vertical zonation of landforms in the mountains. Each ridge, each mountain range often differs from each other in its relief forms. It is enough to compare, for example, the shapes of peaks and ridges with the highlands of the middle mountains. The former are distinguished by sharp peaks and jagged ridges, the latter, on the contrary, have soft, calm outlines of both peaks and ridges (Fig. 235).

This striking difference is due to many reasons, but the most important of them is their altitude above sea level, or, more precisely, the climatic conditions that exist at different altitudes. In the mountain zone located above the snow line, water is predominantly in a solid state (i.e., in the state of snow and ice). It is clear that there can be no streams or rivers there, and therefore, the erosive activity of flowing waters will be absent. But there are snow and ice there, which carry out tireless and highly peculiar work.

The situation is completely different in the lower zones, where the main agents are flowing waters. It is clear that the forms of relief of high mountains that arise under certain conditions will differ sharply from the forms of mountains that arise under other conditions.

As you rise upward, the physical-geographical conditions do not change immediately, but more or less gradually. It is clear that relief forms, determined by various physical and geographical conditions, will also change gradually. Let us dwell on the relief forms of the three most typical zones: high mountains, middle mountains and low mountains.

Landforms of high mountains. Frosty weathering, the work of snow and ice - these are the main factors that most affect mountains that rise above the snow line. The thin, clear air favors the heating of steep slopes devoid of snow cover. Clouds that temporarily cover the sun lead to rapid cooling. Thus, here at high altitudes, the rocks that make up the mountains are subject to not only daily, but also more frequent temperature fluctuations. The latter creates extremely favorable conditions for frost weathering, and the presence of steep slopes helps weathering products quickly roll down and expose the surface of rocks for further weathering.

Frost weathering in the mountains is greatly aided by winds, the speed of which, as is known, increases significantly with altitude. Therefore, the winds here are capable of blowing away (and blowing out of cracks) not only small dust particles, but also larger debris.

The variety of rocks that make up the mountains leads to uneven weathering. As a result, areas composed of stronger rocks turn out to be highly elevated above the general level of areas composed of less durable rocks. With further frost weathering, highly elevated areas take the form of sharp peaks, peaks and ridges, which gives the ridges of mountain ranges a jagged shape.

In cases where the rocks are homogeneous, the pointed peaks eventually round out and become flat. On their surface, as a result of the same frost weathering, entire “seas” of rocks and stones accumulate. On slopes, and especially on steep ones, the products of frost weathering slide down in huge “rock flows”, forming colossal screes; Screes below the snow line are washed away by flowing waters. Talus that descends into glacier feeding areas and onto the edges of glaciers is carried away by glaciers. This is how the steep slopes of high mountains are unloaded from frost weathering products.

In high mountains, in addition to frost weathering, as already mentioned, snow and ice carry out enormous destructive work.

We have already talked enough about what forms of relief arise as a result of glacial and steam-forming activity. These forms will be dominant within the highlands. Above the modern snow line, sharp peaks, peaks and jagged ridges with cirques and glacial cirques usually catch the eye. Near the snow line there are glacial valleys with moraines and cirques. Even lower are traces of ancient glaciers and pits, at the bottom of which there are lakes or swamps or simply a drainage funnel.

Highland landforms were first studied in the Alps. Hence, all high mountains with sharp peaks, peaks, sharp jagged ridges, ravines, snow and glaciers began to be called mountains alpine type. Along with this, all forms characteristic of high mountains are often called alpine forms.

Landforms of low and middle mountains. Let us now turn to the lower sections of the mountains, which, based on their heights and dominant forms, can be classified as small and medium mountains. There are no longer eternal snows or glaciers here.

Sometimes, however, there may be traces of ancient glaciations, more or less modified by the work of flowing waters and other agents. These are usually dilapidated troughs, carts and circuses, along the bottom of which there are lakes and rivers. In some places, the remains of moraines, smoothed rocks and typical glacial boulders have been preserved.

In mountains of medium height, frost weathering is much less pronounced, occurring only during the cold periods of the year. True, chemical and organic weathering occurs more intensely here, but the area of ​​distribution of this weathering is much smaller. This happens because the slopes of the mountains we characterize are more sloping, due to which weathering products more often remain in place and delay further weathering. In the same areas where rocks come to the surface, they quickly weather and take on various, sometimes very characteristic, shapes.

If above the snow line the main destroyers were frost weathering, snow and ice, then here the main destroyers are flowing waters.

Mountains are generally characterized by a large number of rivers and all kinds of watercourses. Even in desert countries, mountains are always rich in water, because the amount of precipitation usually increases with height. The Tien Shan and Pamir-Alai mountains in Central Asia, from where such powerful rivers as the Syr-Darya and Amu-Darya receive their food, can be very indicative in this regard.

Mountain rivers are distinguished by a large slope of their channels, rapid currents, and an abundance of rapids, cascades and waterfalls, which determines their enormous destructive power. Finally, it should be noted that mountain rivers, fed by meltwater from snow and glaciers, have a large rise in water levels every day in the summer, which also increases their destructive power. All this taken together leads to the fact that the mountain slopes are cut through by a large number of transverse valleys. The latter often have the character of gorges. Depending on the strength of the rocks composing their slopes, gorges can be very deep and narrow. But, no matter how strong the rocks are, the steep slopes of the gorges are still gradually destroyed, become sloping and the gorges turn into ordinary wide valleys.

If the height of the mountains does not exceed the height of the snow line, then all the main work of destroying the mountains is done by rivers. The upper reaches of mountain streams, cutting into the slopes, reach watershed ridges. Here they meet the headwaters of rivers on the opposite slope, and their valleys little by little unite and cut the mountain ranges into pieces. As the rivers continue to flow, the mountain ranges break up into separate mountains, which in turn fall apart. Thus, in place of mountain ranges, as a result of the work of flowing waters alone, hilly countries can appear. The lower the mountains become, the more sedimentary their slopes become, and the rivers flowing from the slopes can no longer have the same destructive power. Nevertheless, the rivers continue their work. They deposit destruction products at the bottom of valleys, fill basins and erode slopes. Ultimately, the mountains can be destroyed to the ground, and in their place a leveled, slightly hilly surface will remain. Only rare preserved, isolated mountains still remind one of the mountainous country that was once here. These remaining isolated mountains are called outliers mountains, or witness mountains(Fig. 237 a, b, c). The leveled, slightly hilly surface that remains in place of the mountains is called peneplain, or simply a leveled surface.

If areas of low and medium mountains find themselves in dry climate conditions (in deserts and semi-deserts), then wind becomes of great importance in the formation of small forms. The wind, as already mentioned, helps weathering, carrying away particles of the resulting loose rocks. In addition, in desert countries the wind often carries sand. Under the impact of grains of sand, resistant rocks are polished, while less resistant rocks are destroyed.

The process of destruction of mountains occurs so quickly that if the mountains stopped uplifting, they would all be destroyed to the ground within one or two geological periods. But this does not happen, because under the influence of the internal forces of the Earth, the growth of mountains (uplift) usually continues for a very long time. So, for example, if the Ural Mountains, which arose as a high mountainous country at the end of the Paleozoic era, had not experienced further uplifts, they would have disappeared long ago. But thanks to repeated uplifts, despite continuous destruction, these mountains continue to exist.

When mountains are destroyed, two cases are possible. The first case: the rise of mountains proceeds more slowly than their destruction. Under these conditions, the height cannot increase, but can only decrease. When the uplift of mountains occurs faster than destruction, then the mountains rise.

To understand the nature of each mountain we study, it is necessary to pay special attention to the following points:

1. For folded mountains - the time of formation of the first folds and the time of formation of the last folds. For blocky ones - the state of a given mountainous country before the onset of faults and the time of the first and last movements of layers of the earth's crust along cracks.

2. The state of the mountains at the beginning of the Ice Age and during the glaciation period.

3. The state and life of mountains in post-glacial times.

The first, in addition to the age of the mountains, gives us an idea of ​​the main large forms and location of the ridges themselves. In addition, here we learn about the nature of rocks and the way they are deposited, which is of great importance in the further formation of mountains.

The second, i.e., the state of the mountains at the beginning of the Ice Age and during the glaciation period, is especially important for those mountains that were subject to glaciation. Glaciers, depending on their nature (continental ice, valley glaciers, etc.), can greatly change even large forms of mountain relief.

The state of the mountains in post-glacial times largely determines the nature of the details of the forms. Climate is of greatest importance in this case. For example, in cold climates, frost weathering and the work of snow and ice can occur at all altitudes. Therefore, here not only high mountains, but also mountains of medium height have alpine shapes (Anadyrsky, Koryaksky ridges, etc.).

By age, mountains are distinguished between young and ancient. However, one should distinguish between the geological and geomorphological ages of mountains. Geological age is the time when a folded structure first formed. Geomorphological age is the time of the last formation of mountainous relief. In nature there are mountains that formed as folded structures in the Caledonian era, but their relief was formed in Quaternary time under the influence of new orogenic movements. Geomorphologically ancient mountains have been subject to destruction for a long time. In relief, they most often appear as peneplains, or outlier mountains. The relief forms of ancient mountains are soft, with gentle slopes.

The slopes in a fairly humid climate are covered with a thick cloak of colluvial-elluvial formations. The river valleys are well developed. Young mountains have a great height, a highly dissected surface, and a large range of heights. Valleys often have the character of gorges and gorges. As a rule, modern glaciers develop on them. The relief of young mountains is characterized by sharp, steep shapes. An example of such mountains is the Caucasus Mountains.

- Source-

Polovinkin, A.A. Fundamentals of general geoscience/ A.A. Polovinkin. - M.: State educational and pedagogical publishing house of the Ministry of Education of the RSFSR, 1958. - 482 p.

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