At first glance, the ground under your feet seems absolutely motionless, but in reality it is not so. The earth has a mobile structure that makes movements of various kinds. The movement of the earth's crust, volcanism, in most cases can carry a colossal destructive force, but there are other movements that are too slow and invisible to the naked human eye.

The concept of movement of the earth's crust

The earth's crust consists of several large tectonic plates, each of which moves under the influence of internal processes of the Earth. The movement of the earth's crust is a very slow, one might say, secular phenomenon that is not perceptible by human senses, and yet this process plays a huge role in our lives. Noticeable manifestations of the movement of tectonic layers are the formation of mountain ranges accompanied by earthquakes.

Causes of tectonic movements

The solid component of our planet - the lithosphere - consists of three layers: the core (the deepest), the mantle (the intermediate layer) and the earth's crust (the surface part). In the core and mantle, too high a temperature causes solid matter to change into a fluid state, forming gases and increasing pressure. Since the mantle is limited by the earth's crust, and the mantle material cannot increase in volume, the result is a steam boiler effect when processes occurring in the bowels of the earth activate the movement of the earth's crust. At the same time, the movement of tectonic plates is stronger in areas with the highest temperature and pressure of the mantle on the upper layers of the lithosphere.

History of the study

The possible displacement of layers was suspected long before our era. Thus, history knows the first assumptions of the ancient Greek scientist - geographer Strabo. He hypothesized that some rise and fall periodically. Later, the Russian encyclopedist Lomonosov wrote that tectonic movements of the earth's crust are earthquakes invisible to humans. The inhabitants of medieval Scandinavia also guessed about the movement of the earth's surface, who noticed that their villages, once founded in the coastal zone, after centuries found themselves far from the sea coast.

Nevertheless, the movement of the earth’s crust and volcanism began to be studied purposefully and on a large scale during the active development of scientific and technological progress, which took place in the 19th century. The research was carried out by both our Russian geologists (Belousov, Kosygin, Tetyaev, etc.) and foreign scientists (A. Wegener, J. Wilson, Gilbert).

Classification of types of crustal movement

There are two types of movement patterns:

• Horizontal.
• Vertical movements of tectonic plates.

Both of these types of tectonics are self-sufficient, independent of each other and can occur simultaneously. Both the first and second play a fundamental role in shaping the topography of our planet. In addition, types of movement of the earth's crust are the primary object of study for geologists, because they:

• Are the direct cause of creation and transformation modern relief, as well as transgression and regression of some areas of marine territories.
• They destroy primary relief structures of folded, inclined and discontinuous types, creating new ones in their place.
• They ensure the exchange of substances between the mantle and the earth's crust, and also ensure the release of magmatic matter through channels to the surface.

Horizontal tectonic movements of the earth's crust

As mentioned above, the surface of our planet consists of tectonic plates on which continents and oceans are located. Moreover, many geologists of our time believe that the formation of the current image of the continents occurred due to the horizontal displacement of these very huge layers of the earth's crust. When a tectonic plate shifts, the continent that sits on it shifts along with it. Thus, horizontal and at the same time very slow movements of the earth’s crust led to the fact that the geographical map was transformed over many millions of years, the same continents moved away from each other.

The tectonics of the last three centuries has been most accurately studied. The movement of the earth's crust at the present stage is studied using high-precision equipment, thanks to which it was possible to find out that horizontal tectonic displacements of the earth's surface are exclusively unidirectional in nature and overcome only a few cm annually.

As tectonic plates shift, they converge in some places and diverge in others. Mountains form in plate collision zones, and cracks (faults) form in plate divergence zones. A striking example of the divergence of lithospheric plates observed at the present time are the so-called Great African Rifts. They are distinguished not only by the greatest length of cracks in the earth's crust (more than 6000 km), but also by their extreme activity. The breakup of the African continent is happening so quickly that probably in the not too distant future the eastern part of the continent will separate and a new ocean will form.

Vertical movement of the earth's crust

Vertical movements of the lithosphere, also called radial, unlike horizontal ones, have a dual direction, that is, land can rise and fall after some time. The consequence of vertical movements of the lithosphere is also the rise (transgression) and fall (regression) of sea level. The centuries-old movements of the earth's crust up and down, which occurred many centuries ago, can be traced by the traces left behind, namely: the Naples temple, built back in the 4th century AD, is currently located at an altitude of more than 5 m above sea level, however its columns are strewn with mollusk shells. This is clear evidence that the temple was under water for a long time, which means that this section of soil systematically moved in a vertical direction, either along an ascending axis, or along a descending one. This cycle of movements is known as oscillatory movements of the earth's crust.

Regression of the sea leads to the fact that the once seabed becomes dry land and plains are formed, among which are the North and West Siberian plains, the Amazon, Turan, etc. Currently, land uplift is observed in Europe (Scandinavian Peninsula, Iceland, Ukraine, Sweden) and subsidence (Holland, southern England, northern Italy).

Earthquakes and volcanism as a consequence of the movement of the lithosphere

The horizontal movement of the earth's crust leads to a collision or fracture of tectonic plates, which is manifested by earthquakes of varying strength, which is measured on the Richter scale. Seismic waves up to 3 points on this scale are not perceptible to humans; ground vibrations with magnitudes from 6 to 9 can already lead to significant destruction and loss of life.

Due to the horizontal and vertical movement of the lithosphere, channels are formed at the boundaries of tectonic plates through which mantle material under pressure erupts onto the earth's surface. This process is called volcanism, we can observe it in the form of volcanoes, geysers and warm springs. There are many volcanoes on Earth, some of which are still active. they can be both on land and under water. Together with magmatic deposits, they spew hundreds of tons of smoke, gas and ash into the atmosphere. Underwater volcanoes are the main ones in terms of the force of the eruption; they exceed those on land. Currently, the vast majority of volcanic formations on the seafloor are inactive.

The importance of tectonics for humans

In the life of mankind, movements of the earth's crust play a huge role. And this applies not only to the formation of rocks, the gradual influence on the climate, but also to the very life of entire cities.

For example, the annual transgression of Venice threatens the city with the fact that in the near future it will be under water. Similar cases are repeated in history; many ancient settlements went under water, and through certain time again found themselves above sea level.

The earth's crust is characterized by tectonic processes that determine its constant restructuring and development. The driving force behind these processes is mainly the internal energy of the Earth. Tectonic processes cause movements in the earth's crust - tectonic movements.

Tectonic processes in the earth's crust are studied by the geological science of geotectonics. The following applies according to modern ideas global geotectonics to intraplate tectonics, while the very movement of continents and the earth’s crust under the oceans is caused by the movement of lithospheric plates, such as, for example,

Pacific or Eurasian. The formation of geosynclinal zones is confined to zones of subduction (undergoing) or obduction (creeping) of one such lithospheric plate onto another, as in the case of the Japanese Islands. Due to the fact that construction is still focused primarily on land, i.e., on continents located on lithospheric plates, the concepts of intraplate tectonics are very important for engineering geology.

Tectonic movements. In the earth's crust they manifest themselves in different ways, both in time and space. In time, movements manifest themselves in the form of slow (epeirogenic) and fast (orogenic - mountain-building) movements. According to their position in space (in the predominant direction), tectonic movements are radial (along the radii of the Earth), acting vertically up and down, and tangential, directed horizontally. The different nature of movements is associated with the horizontal structure of the earth's crust, i.e., with its basic structures.

Basic structures of the earth's crust. The horizontal structure of the earth's crust is very complex, but to understand tectonic movements it can be simplified if we take as a basis the position that the earth's crust consists of two main structures - platforms and geosynclines.

Platforms are the largest structures of the earth's crust. These are continents and ocean basins. These are stable, rigid, inactive structures. They are characterized by leveled forms of relief of the earth's surface (such as a plain). Quiet, slow movements of a vertical nature (epeirogenic) are typical for platforms.

Geosynclines are sections of the earth's crust that are mobile articulations of platforms. They are characterized by a variety of tectonic movements, among which strong, abrupt, unpredictable in time and space predominate; volcanism and seismic phenomena are associated with them. Faults in the earth's crust occur in geosynclines, and intensive accumulation of thick layers of sedimentary rocks occurs. Tectonic forces move layers of sedimentary rocks out of a horizontal position and give them the shape of folds. Geosynclines include: 1) a latitudinal belt, which covers the Mediterranean, the Caucasus, Western Asia and up to Indonesia; The belt includes Altai, the Sayan Mountains, the Baikal region, 2) the annular Pacific belt - North and South America, Japan, Sakhalin, the Kuril Islands, Kamchatka, the south of Primorye.

Platform movements. These territories are characterized by slow vertical oscillatory movements (epeirogenic). They are expressed in the fact that certain areas of the earth's crust have been uplifted for many centuries, while other areas are subsiding. The movements are slow, long-term, but a lot depends on them: the position of the boundaries between land and seas, shallowing or increased erosive activity of rivers, the formation of the Earth's topography, increasing levels of reservoirs, the movement of water in gravity channels, the position of coastal areas in relation to sea level and much more.

It is interesting to note that platforms (continents) tend to move horizontally. Thus, based on data obtained from artificial Earth satellites, it was established that in just five years Australia “swimmed” to the Japanese Islands by 38 cm (76 mm per year), Europe - by 19 cm, North America - by 11, the Hawaiian Islands - by 39 cm (78 mm per year). Scientists have calculated that if this rate of movement continues, then the closest neighbor to Japan, the Hawaiian Islands, will merge with the Japanese Islands in 100 million years.

For engineering geology, modern vertical oscillatory movements of platforms are of particular interest, causing change heights of the earth's surface in a particular area. The rate of their manifestation is assessed by high-precision geodetic work. Annual rate of modern oscillatory movements platforms is most often equal to several millimeters, but there are areas where the rate is 1-2 cm/year or even more. The numbers are small, but over a long period of time they grow to significant values. For example, Scandinavia has risen by 19 cm in just the last 50 years. For many centuries, areas of the Netherlands have been intensively sinking (40-60 mm/year).

Oscillatory movements can also be traced in Russia. The Central Russian Upland rises by 1.5-2 cm/year, the Kursk region - up to 3.6 mm/year. A number of territories are experiencing subsidence of the Earth's surface: Moscow (3.7 mm/year), St. Petersburg (3.6 mm/year), Eastern Ciscaucasia (5-7 mm/year). There are areas where the rise of the Earth's surface occurs more intensely. So, in the second half of the 20th century. The level of the Caspian Sea began to rise by 14-15 cm/year, which led to the flooding of many coastal areas of the Astrakhan region. By 2000, the overall rise in sea level exceeded 2 m. Apparently, this is due to tectonic movements of the earth's crust in the Caspian Sea region.

Modern fluctuations of the Earth's surface are taken into account during the construction of various objects: large reservoirs, high dams, reclamation systems, but especially during the construction of airfields and spaceports.

Rice. 4.

Volcanism. Volcanoes are mountains or cone-shaped hills that are created by magma reaching the surface of the Earth (Fig. 4). Magma comes out of the volcano and spreads along its slopes and the surrounding area. In these cases, the magma is called lava.

Volcanoes are divided into active ones, which periodically erupt magma, and extinct ones, which are currently inactive. But history knows cases when extinct volcanoes resumed their activity, as was the case with the Vesuvius volcano (Italy), the unexpected eruption of which occurred in 79 AD. e., which led to the destruction of three cities. The now extinct Kazbek volcano (Caucasus) was still active at the beginning of the Quaternary period, and its lavas lie in many places on the Georgian Military Highway.

Volcanoes are confined to moving areas of the earth's crust, i.e., geosynclines. Today, more than 850 active volcanoes are known, 76 of which are located on the ocean floor. On the territory of Russia, volcanoes are located in Kamchatka (28 active) and in Kuril Islands(10 active). The largest volcanoes are Klyuchevskaya Sopka (the height of the mountain cone is 4850 m), Avachinsky, Karymsky, Bezymyanny.

Volcanic eruptions occur in different ways - in the form of explosions and violent outpouring of lava, or calmly, without explosions, when lava slowly spreads around the volcanic cone. The volcanoes of Kamchatka and the Kuril Islands are among the most dangerous, i.e. explosive. The eruption of such volcanoes begins with tremors (earthquakes, sometimes up to magnitude 5), followed by explosions with the release of lava, gases and water vapor.

Lavas form flows, the width and length of which depend on the slopes of the mountain cones and the surrounding terrain. There is a known case (Iceland) when the length of a lava flow reached 80 km with a thickness of 10-50 m. The speed of the flows varies, depends on the type of magma and ranges from 5-7 to 30 km/h. When volcanoes explode, solid material in the form of fragments flies out of their craters simultaneously with lava. different sizes: 1) blocks (bombs) weighing several tons; 2) pieces called lapilli (1-3 cm in diameter) and 3) particles in the form of sand and dust. The dust particles are called volcanic ash. All these debris are scattered over various distances and create multi-meter sediments. Volcanic ash is carried the farthest (hundreds and even thousands of kilometers).

At the same time as lava and rocks, volcanoes emit gases. In most cases, the gases are poisonous. No less dangerous are water vapors, which quickly condense, leading to the formation of enormous mud flows (mudflows) on the slopes and at the foot of the cones. They have great destructive power and create multi-meter sediments.

The above confirms that roads and, especially, airfields should be built at a certain distance from active volcanoes.

The distance is usually determined based on many years of construction experience in each specific area and taking into account the characteristics of the eruptions of a particular volcano.

An interesting case is when people tried to fight the elements. The eruption of Mount Etna (Sicily) lasted 130 days. 300 tons of cement blocks tied with heavy steel chains were thrown into the lava flows. This changed the direction of the main flow.

Seismic phenomena

Seismic(from Greek Be^toz - shaking) phenomena- elastic vibrations of the earth's crust, occurring due to the fact that stresses arise in its depths (or in the upper mantle), which ultimately, under the influence of tectonic forces, find outlet in the deformation of compressed rocks, in the formation of ruptures, which manifests itself in the form of tremors. Thus, seismic tremors are a purely mechanical phenomenon. When shocks occur, elastic waves arise that propagate in all directions from the rupture sites. These waves are called seismic.

If most of the rocks that make up the earth's crust are considered as an elastic medium, then seismic waves transmit deformations that occur in rocks over considerable distances and at high speed. These waves are divided into longitudinal and transverse according to the type of deformation.

Longitudinal waves (or compression-tension waves) cause rock particles to vibrate in a direction coinciding with the movement of the wave. Transverse waves (or "shear waves") propagate in a direction perpendicular to the direction of motion of the longitudinal waves. The speed and energy of these waves are 1.7 times less than that of longitudinal waves.

When underground elastic waves meet the surface of the earth, a new look oscillatory movement - the so-called superficial waves. These are ordinary gravity waves that lead to deformations of the earth's surface (Fig. 5).

The place where a seismic shock occurs, lying deep in the earth's crust, is called the hypocenter. The depth of the hypocenter can be 1 - 10 km - surface seismic phenomena;

Rice. 5. Scheme of propagation of seismic waves on the earth's surface (G) And

in the earth's crust (2):

G - hypocenter; E - epicenter. Seismic waves: / - longitudinal; 2- transverse; 3- superficial

Rice. 6. Consequences of earthquakes: A- in a city block; b- on a mountain plateau in Iran

30-50 km are crustal and 100-700 km are deep. The most destructive are surface seismic phenomena.

The projection of the hypocenter onto the daylight surface is called the epicenter. The impact force of the longitudinal wave at the epicenter is maximum.

An analysis of cases of seismic phenomena has shown that in seismically active regions of the Earth, up to 70% of hypocenters are located to a depth of 60 km.

The duration of seismic waves is usually limited to a few seconds, sometimes minutes, but there are cases of longer exposure. For example, in 1923 in Kamchatka, the seismic phenomenon lasted from February to April (195 tremors).

Shakes of the earth's crust of seismic origin occur very often and, as a natural disaster, after hurricanes and typhoons, they occupy the second place in terms of material damage caused to humanity (Fig. 6). Every year about 100 thousand seismic phenomena are recorded on the globe, of which about 100

R and s 6. Continuation

lead to destruction, and in some cases to disasters, as, for example, in Tokyo (1923), San Francisco (1906), in Chile and on the island of Sicily (1968). An exceptionally strong seismic phenomenon occurred in Mongolia (1956). One of the mountain peaks split in half, part of a mountain 400 m high collapsed into a gorge, forming a fault depression up to 18 km long and about 800 m wide, on

• 5 m or more
• 0.5...1.0 m

Rice. 7.

Cracks up to 20 m wide appeared on the surface of the earth, the main one stretching for 250 km.

Seismic phenomena occur both on land and at the bottom of the oceans. In this regard, they distinguish between seaquakes and earthquakes.

Seaquakes occur in the oceanic depressions of the Pacific and, less commonly, the Indian and Atlantic oceans. The rapid rise and fall of the bottom generates gentle waves (tsunamis) on its surface with a distance between crests of several kilometers and a height of many meters (Fig. 7). When approaching the shores, along with the rise of the bottom, the wave height increases to 15-20 m or more. A unique case occurred in 1964 in Alaska, where the wave height reached 66 m at a speed of 585 km/h.

Tsunamis travel over distances of hundreds and even thousands of kilometers at a speed of 500-800 km/h or more.

In Russia, tsunamis occur in the Pacific Ocean off the coast of Kamchatka and the Kuril Islands. One of these tsunamis occurred in 1952. Before the wave arrived, the sea retreated 500 m, and 40 minutes later the wave hit the shore with terrible force, destroyed all buildings and roads, and covered the coastal area with sand, silt and rock fragments. After some time, after the first, a second wave 10-15 m high came, which completed the destruction of the coast below the ten-meter mark.

Tsunamis occur less frequently than earthquakes. So, over the last 200 years in Kamchatka and the Kuril Islands there have been only 14 of them, four of which were catastrophic. The last global catastrophic tsunami occurred in Indian Ocean at the end of December 2004, when, according to general estimates, more than 200 thousand people died in Indonesia and the countries of Indochina.

The construction of roads and airfields on shores where a tsunami may approach requires the implementation of protective measures. In Russia, as in the neighboring countries of the Pacific region, there is an observation service that promptly notifies of the approach of a tsunami. This allows people to be protected from danger. Highways placed on a high part of the relief, if necessary, cover the banks with reinforced concrete piers, install wave walls, and create protective earthen embankments.

Earthquakes are seismic phenomena on land. In Russia, earthquakes occur in the Caucasus, Altai, Sayan Mountains, Baikal region, Sakhalin, Kuril Islands and Kamchatka. All these territories are located in the geosynclinal belt. Until now, only these areas were considered seismic, but already in the second half of the 20th century. It became obvious that earthquakes, under certain conditions, can also occur on platforms, although they, unlike tectonic earthquakes, have a different origin.

Based on the origin of land earthquakes, it is proposed to distinguish four types of earthquakes:

• 1. Tectonic, caused by tectonic forces of the earth's crust and making up the vast majority of earthquakes. They are characterized by wide areas and great strength or, in other words, high score.
• 2. Volcanic, associated with volcanic eruptions and having a local distribution, but sometimes of great force.
• 3. Denudation (landslides and collapses), generated by the fall of large masses of rocks from slopes or falling into failures as a result of karst formation. Such earthquakes are also local in nature and relatively small in strength.
• 4. Technogenic, associated with human production activities.

Today it is quite obvious that human production activities can influence the seismic situation even at the global level. These are so-called induced earthquakes. They can be caused by the filling of vast reservoirs, pumping of oil, gas, interstratal groundwater, nuclear explosions, massive military bombings, etc. The above list shows that a person can have a certain impact on geological space through his activities

Rice. 8.

capable of creating incentives for negative tectonic events, known as natural-man-made disasters.

Estimation of earthquake strength. Humanity has been observing and recording earthquakes around the globe for many centuries. Nowadays, special equipment is widely used, in particular, seismographs, which make it possible to qualitatively determine where an earthquake occurred and evaluate its strength. The instruments automatically record the Earth's vibrations and draw a seismogram (Fig. 8).

At present, the dependence of earthquakes on the structure, composition and state of the earth's crust has been revealed. It looks like this.

• 1. In dense rocks, the speed of propagation of a seismic shock is greater than in loose cohesive and incoherent sedimentary rocks, however, the strength of the earthquake (its intensity), on the contrary, increases in the latter.
• 2. Water content, water saturation, and high groundwater levels increase the intensity of earthquakes. Territories composed of quicksand, silt, swampy and water-logged sedimentary rocks are areas of increased earthquake intensity.
• 3. Geological structures and tectonic faults located across the movement of seismic waves can reduce the intensity of earthquakes.
• 4. Isolated and sharply defined forms of land surface relief (hills, steep mountain slopes and ravines) can increase the seismicity of the territory.

Every earthquake is necessarily accompanied by a number of physical phenomena. These are sounds, light effects, waves on solid media, landslides, slides, cracks and holes in the ground, destruction of houses, roads and bridges. Sounds in the form of an “underground hum” are very characteristic.

The intensity of earthquakes on the earth's surface (surface shaking) is estimated by seismic scales. In Russia, a scale consisting of 12 points is used to assess the strength of earthquakes (Table 1). Each point corresponds to a certain value of seismic acceleration - A, mm/s 2, calculated by the formula

a = 4p 2 A/T 2,

Where L- vibration amplitude, mm; T - period of oscillation of a seismic wave, s. By size A determine the seismicity coefficient, which is necessary to assess the strength and stability of structures:

Ks = A/&

where # is the acceleration of gravity, mm/s 2 .

Table 1

Seismic 12 point scale

In addition to the 12-point scale, which is used in many countries around the world, the Richter scale (magnitude scale - M). Magnitudes are calculated values. Maximum magnitude values M- 8,5-9.

Construction of roads and airfields. An important place is occupied by seismic zoning of territories and forecast of manifestations. possible earthquakes. Seismic zoning is expressed in the compilation seismic maps, which can be used to determine the value of the maximum score for a given territory (Fig. 9). It's a difficult task. IN recent years the maps are periodically updated, as the seismicity of the earth’s crust in a number of areas increases. In most cases, new cards increase point values. The elements are treacherous. This can be seen in the following example. In 1976 earthquake

Rice. 9. Seismic zoning map. Seismic point lines:

I - from 1 to 5; II - from 5 to 7; III - up to 8

in Uzbekistan (8 points) destroyed the village of Gazli. The village was rebuilt, but in 1984 the earthquake repeated, but with a magnitude of 9.00 and it was destroyed again.

In recent years, Russia has created a Map of the general seismic zoning of the country's territory (meaning the Map of tectonic earthquakes). From this map it is clear that if previously Sakhalin, Kamchatka, and the Kuril Islands were considered especially dangerous in terms of seismicity, now these territories include Eastern Siberia and the adjacent Baikal region and Transbaikalia, including the Altai Mountains. For these territories, earthquakes of 9 points are possible (on the Richter scale - L / up to 8.5). For the first time, zones of magnitude 10 earthquakes (Sakhalin, Kamchatka, Kuril Islands) appeared on the Map. Previously, there were no such areas in Russia. The territory of the North Caucasus has been transferred from a 6-7 point rating to a 9 point rating.

Earthquake forecast. Earthquakes cannot be prevented. The forecast requires answers to three questions - where, what strength and when the earthquake will occur. Science is working in this direction, but precise reliable answers are not yet available.

Construction under the forecast of earthquakes of 6 points or more is carried out in accordance with Construction Norms and Rules (SNiP). The score is determined from the Map and adjusted depending on the relief, geology and hydrogeology of the area. Points can only be adjusted upward.

In seismic areas, it is recommended to build roads and airfields away from steep mountain slopes and cliffs; the slopes of excavations and subgrades over 4 m are made more flat; with 6 points or more, the height of embankments and the depth of excavations should not exceed 15-20 m; water-saturated soils under embankments should be drained by drainage; special attention is paid to increasing the stability of bridges, which are dangerous to build on tectonic faults.

The position of the earth's crust between the mantle and the outer shells - the atmosphere, hydrosphere and biosphere - determines the influence of external and internal forces of the Earth on it.

The structure of the earth's crust is heterogeneous (Fig. 19). The upper layer, whose thickness varies from 0 to 20 km, is complex sedimentary rocks– sand, clay, limestone, etc. This is confirmed by data obtained from studying outcrops and drill hole cores, as well as the results of seismic studies: these rocks are loose, the speed of seismic waves is low.

Rice. 19. Structure of the earth's crust

Below, under the continents, is located granite layer, composed of rocks whose density corresponds to the density of granite. The speed of seismic waves in this layer, as in granites, is 5.5–6 km/s.

Under the oceans there is no granite layer, but on the continents in some places it comes out to the surface.

Even lower is a layer in which seismic waves propagate at a speed of 6.5 km/s. This speed is typical for basalts, therefore, despite the fact that the layer is complex different breeds, they call him basalt.

The boundary between granite and basalt layers is called Conrad surface. This section corresponds to a jump in the speed of seismic waves from 6 to 6.5 km/s.

Depending on the structure and thickness, two types of bark are distinguished - mainland And oceanic. Under the continents, the crust contains all three layers - sedimentary, granite and basalt. Its thickness on the plains reaches 15 km, and in the mountains it increases to 80 km, forming “mountain roots”. Under the oceans, the granite layer is completely absent in many places, and the basalts are covered with a thin cover of sedimentary rocks. In the deep-sea parts of the ocean, the thickness of the crust does not exceed 3–5 km, and the upper mantle lies below.

Mantle. This is an intermediate shell located between the lithosphere and the Earth's core. Its lower boundary supposedly lies at a depth of 2900 km. The mantle accounts for more than half of the Earth's volume. The mantle material is in a superheated state and experiences enormous pressure from the overlying lithosphere. The mantle has a great influence on the processes occurring on Earth. Magma chambers arise in the upper mantle, and ores, diamonds and other minerals are formed. This is where internal heat comes to the surface of the Earth. The material of the upper mantle constantly and actively moves, causing the movement of the lithosphere and the earth's crust.

Core. There are two parts in the core: the outer, to a depth of 5 thousand km, and the inner, to the center of the Earth. The outer core is liquid, since transverse waves do not pass through it, while the inner core is solid. The substance of the core, especially the inner one, is highly compacted and its density corresponds to metals, which is why it is called metallic.

§ 17. Physical properties and chemical composition of the Earth

TO physical properties Earth includes temperature (internal heat), density and pressure.

Internal heat of the Earth. According to modern ideas, the Earth after its formation was a cold body. Then the decay of radioactive elements gradually warmed it up. However, as a result of the radiation of heat from the surface into the near-Earth space, it cooled. A relatively cold lithosphere and crust were formed. Temperatures are still high at great depths today. An increase in temperatures with depth can be observed directly in deep mines and boreholes, during volcanic eruptions. Thus, pouring volcanic lava has a temperature of 1200–1300 °C.

On the Earth's surface, the temperature is constantly changing and depends on the influx of solar heat. Daily temperature fluctuations extend to a depth of 1–1.5 m, seasonal fluctuations up to 30 m. Below this layer lies a zone of constant temperatures, where they always remain unchanged and correspond to the average annual temperatures of a given area on the Earth’s surface.

The depth of the constant temperature zone is not the same in different places and depends on the climate and thermal conductivity of rocks. Below this zone, temperatures begin to rise, on average by 30 °C every 100 m. However, this value is not constant and depends on the composition of rocks, the presence of volcanoes, and the activity of thermal radiation from the bowels of the Earth. Thus, in Russia it ranges from 1.4 m in Pyatigorsk to 180 m on the Kola Peninsula.

Knowing the radius of the Earth, it can be calculated that in the center its temperature should reach 200,000 °C. However, at this temperature the Earth would turn into hot gas. It is generally accepted that a gradual increase in temperatures occurs only in the lithosphere, and the source of internal heat of the Earth is the upper mantle. Below, the temperature increase slows down, and in the center of the Earth it does not exceed 50,000 °C.

Density of the Earth. The denser the body, the greater the mass per unit volume. The standard of density is considered to be water, 1 cm 3 of which weighs 1 g, i.e., the density of water is 1 g/s 3 . The density of other bodies is determined by the ratio of their mass to the mass of water of the same volume. From this it is clear that all bodies with a density greater than 1 sink, and those with less density float.

The density of the Earth is not the same in different places. Sedimentary rocks have a density of 1.5–2 g/cm3, and basalts have a density of more than 2 g/cm3. The average density of the Earth is 5.52 g/cm 3 - this is more than 2 times the density of granite. In the center of the Earth, the density of the rocks composing it increases and amounts to 15–17 g/cm3.

Pressure inside the Earth. The rocks located in the center of the Earth experience enormous pressure from the overlying layers. It is calculated that at a depth of only 1 km the pressure is 10 4 hPa, and in the upper mantle it exceeds 6 * 10 4 hPa. Laboratory experiments show that at this pressure, solids, such as marble, bend and can even flow, that is, they acquire properties intermediate between a solid and a liquid. This state of substances is called plastic. This experiment suggests that in the deep interior of the Earth, matter is in a plastic state.

Chemical composition of the Earth. In the Earth you can find all the chemical elements of D.I. Mendeleev’s table. However, their number is not the same, they are distributed extremely unevenly. For example, in the earth's crust, oxygen (O) makes up more than 50%, iron (Fe) less than 5% of its mass. It is estimated that the basalt and granite layers consist mainly of oxygen, silicon and aluminum, with an increasing proportion of silicon, magnesium and iron in the mantle. In general, it is generally accepted that 8 elements (oxygen, silicon, aluminum, iron, calcium, magnesium, sodium, hydrogen) account for 99.5% of the composition of the earth’s crust, and all others – 0.5%. Data on the composition of the mantle and core are speculative.

§ 18. Movement of the earth's crust

The earth's crust only seems motionless, absolutely stable. In fact, she makes continuous and varied movements. Some of them occur very slowly and are not perceived by the human senses, others, such as earthquakes, are landslide and destructive. What titanic forces set the earth's crust in motion?

Internal forces of the Earth, the source of their origin. It is known that at the boundary of the mantle and lithosphere the temperature exceeds 1500 °C. At this temperature, matter must either melt or turn into gas. When solids transform into a liquid or gaseous state, their volume must increase. However, this does not happen, since the overheated rocks are under pressure from the overlying layers of the lithosphere. A “steam boiler” effect occurs when matter, seeking to expand, presses on the lithosphere, causing it to move along with the earth’s crust. Moreover, the higher the temperature, the stronger the pressure and the more active the lithosphere moves. Particularly strong pressure centers arise in those places in the upper mantle where radioactive elements, the decay of which heats the constituent rocks to even higher temperatures. Movements of the earth's crust under the influence of the internal forces of the Earth are called tectonic. These movements are divided into oscillatory, folding and bursting.

Oscillatory movements. These movements occur very slowly, imperceptibly for humans, which is why they are also called centuries-old or epeirogenic. In some places the earth's crust rises, in others it falls. In this case, the rise is often replaced by a fall, and vice versa. These movements can be traced only by the “traces” that remain after them on the earth’s surface. For example, on the coast Mediterranean Sea, near Naples, there are the ruins of the temple of Serapis, the columns of which were worn away by sea mollusks at an altitude of up to 5.5 m above modern sea level. This serves as absolute proof that the temple, built in the 4th century, was at the bottom of the sea, and then it was raised. Now this area of ​​land is sinking again. Often on the coasts of seas above their current level there are steps - sea terraces, once created by the surf. On the platforms of these steps you can find the remains marine organisms. This indicates that the terrace areas were once the bottom of the sea, and then the shore rose and the sea retreated.

The descent of the earth's crust below 0 m above sea level is accompanied by the advance of the sea - transgression, and the rise - by his retreat - regression. Currently in Europe, uplifts occur in Iceland, Greenland, and the Scandinavian Peninsula. Observations have established that the region of the Gulf of Bothnia is rising at a rate of 2 cm per year, i.e. 2 m per century. At the same time, the territory of Holland, southern England, northern Italy, the Black Sea lowland, and the coast of the Kara Sea is subsiding. A sign of the subsidence of sea coasts is the formation of sea bays in the estuaries of rivers - estuaries (lips) and estuaries.

When the earth's crust rises and the sea retreats, the seabed, composed of sedimentary rocks, turns out to be dry land. This is how extensive marine (primary) plains: for example, West Siberian, Turanian, North Siberian, Amazonian (Fig. 20).

Rice. 20. The structure of primary, or marine, strata plains

Folding movements. In cases where rock layers are sufficiently plastic, under the influence of internal forces they collapse into folds. When the pressure is directed vertically, the rocks are displaced, and if in the horizontal plane, they are compressed into folds. The shape of the folds can be very diverse. When the bend of the fold is directed downward, it is called a syncline, upward - an anticline (Fig. 21). Folds form at great depths, i.e. when high temperatures and great pressure, and then under the influence of internal forces they can be lifted. This is how they arise fold mountains Caucasian, Alps, Himalayas, Andes, etc. (Fig. 22). In such mountains, folds are easy to observe where they are exposed and come to the surface.

Rice. 21. Synclinal (1) and anticlinal (2) folds

Rice. 22. fold mountains

Breaking movements. If the rocks are not strong enough to withstand the action of internal forces, cracks (faults) form in the earth's crust and vertical displacement of the rocks occurs. The sunken areas are called grabens, and those who rose - handfuls(Fig. 23). The alternation of horsts and grabens creates block (revived) mountains. Examples of such mountains are: Altai, Sayan, Verkhoyansk Range, Appalachians in North America and many others. Revived mountains differ from folded ones both in internal structure and in appearance - morphology. The slopes of these mountains are often steep, the valleys, like the watersheds, are wide and flat. Rock layers are always displaced relative to each other.

Rice. 23. Revived fold-block mountains

The sunken areas in these mountains, grabens, sometimes fill with water, and then deep lakes are formed: for example, Baikal and Teletskoye in Russia, Tanganyika and Nyasa in Africa.

§ 19. Volcanoes and earthquakes

With a further increase in temperature in the bowels of the Earth, rocks, despite high pressure, melt, forming magma. This releases a lot of gases. This further increases both the volume of the melt and its pressure on the surrounding rocks. As a result, very dense, gas-rich magma tends to go where the pressure is lower. It fills cracks in the earth's crust, breaks and lifts the layers of its constituent rocks. Part of the magma, before reaching the earth's surface, solidifies in the thickness of the earth's crust, forming magma veins and laccoliths. Sometimes magma breaks out to the surface and erupts in the form of lava, gases, volcanic ash, rock fragments and frozen lava clots.

Volcanoes. Each volcano has a channel through which lava erupts (Fig. 24). This vent, which always ends in a funnel-shaped expansion - crater. The diameter of the craters ranges from several hundred meters to many kilometers. For example, the diameter of the Vesuvius crater is 568 m. Very large craters are called calderas. For example, the caldera of the Uzon volcano in Kamchatka, which is filled by Lake Kronotskoye, reaches 30 km in diameter.

The shape and height of volcanoes depend on the viscosity of the lava. Liquid lava spreads quickly and easily and does not form a cone-shaped mountain. An example is the Kilauza volcano on Hawaiian Islands. The crater of this volcano is a round lake with a diameter of about 1 km, filled with bubbling liquid lava. The level of lava, like water in the bowl of a spring, then falls, then rises, splashing out over the edge of the crater.

Rice. 24. Volcanic cone in section

More widespread are volcanoes with viscous lava, which, when cooled, forms a volcanic cone. The cone always has a layered structure, which indicates that eruptions occurred many times, and the volcano grew gradually, from eruption to eruption.

The height of volcanic cones ranges from several tens of meters to several kilometers. For example, the Aconcagua volcano in the Andes has a height of 6960 m.

There are about 1,500 volcano mountains, active and extinct. Among them are such giants as Elbrus in the Caucasus, Klyuchevskaya Sopka in Kamchatka, Fuji in Japan, Kilimanjaro in Africa and many others.

Most active volcanoes are located around the Pacific Ocean, forming the Pacific Ring of Fire, and in the Mediterranean-Indonesian belt. In Kamchatka alone, 28 active volcanoes are known, and in total there are more than 600. The distribution of active volcanoes is natural - they are all confined to mobile zones of the earth’s crust (Fig. 25).

Rice. 25. Zones of volcanism and earthquakes

In the Earth's geological past, volcanism was more active than it is now. In addition to the usual (central) eruptions, fissure eruptions occurred. From giant cracks (faults) in the earth's crust, stretching for tens and hundreds of kilometers, lava erupted onto the earth's surface. Continuous or patchy lava covers were created, leveling the terrain. The thickness of the lava reached 1.5–2 km. This is how they were formed lava plains. Examples of such plains are certain sections of the Central Siberian Plateau, the central part of the Deccan Plateau in India, the Armenian Highlands, and the Columbia Plateau.

Earthquakes. The causes of earthquakes are different: volcanic eruptions, mountain collapses. But the most powerful of them arise as a result of movements of the earth's crust. Such earthquakes are called tectonic. They usually originate at great depths, at the boundary of the mantle and lithosphere. The origin of an earthquake is called hypocenter or hearth. On the surface of the Earth, above the hypocenter, is epicenter earthquakes (Fig. 26). Here the strength of the earthquake is greatest, and as it moves away from the epicenter it weakens.

Rice. 26. Hypocenter and epicenter of earthquake

The earth's crust shakes continuously. Over 10,000 earthquakes are observed throughout the year, but most of them are so weak that they are not felt by humans and are recorded only by instruments.

The strength of earthquakes is measured in points - from 1 to 12. Powerful 12-point earthquakes are rare and are catastrophic in nature. During such earthquakes, deformations occur in the earth's crust, cracks, shifts, faults, landslides in the mountains and failures in the plains form. If they occur in densely populated areas, then great destruction and numerous casualties occur. The largest earthquakes in history are Messina (1908), Tokyo (1923), Tashkent (1966), Chilean (1976) and Spitak (1988). In each of these earthquakes, tens, hundreds and thousands of people died, and cities were destroyed almost to the ground.

Often the hypocenter is located under the ocean. Then a destructive ocean wave arises - tsunami.

§ 20. External processes transforming the surface of the Earth

Simultaneously with internal, tectonic processes, external processes operate on Earth. Unlike internal ones, which cover the entire thickness of the lithosphere, they act only on the Earth’s surface. The depth of their penetration into the earth's crust does not exceed several meters and only in caves - up to several hundred meters. The source of the forces causing external processes is thermal solar energy.

External processes are very diverse. These include the weathering of rocks, the work of wind, water and glaciers.

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

Physical weathering- This is mechanical crushing, grinding of rocks.

It occurs when there is a sudden change in temperature. When heated, rock expands; when cooled, it contracts. Since the expansion coefficient of different minerals included in the rock is not the same, the process of its destruction intensifies. Initially, the rock breaks up into large blocks, which are crushed over time. Accelerated destruction of the rock is facilitated by water, which, penetrating into cracks, freezes in them, expands and tears the rock into separate parts. Physical weathering is most active where it occurs abrupt change temperatures, and hard igneous rocks come to the surface - granite, basalt, syenites, etc.

Chemical weathering- this is a chemical effect on rocks of various aqueous solutions.

In this case, in contrast to physical weathering, various chemical reactions, and as a result, a change in the chemical composition and, possibly, the formation of new rocks. Chemical weathering occurs everywhere, but is especially intense in easily soluble rocks - limestone, gypsum, dolomite.

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

Lichens, for example, settling on rocks, wear away their surface with secreted acid. Plant roots also secrete acid, and in addition, the root system acts mechanically, as if tearing the rock. Earthworms, passing through themselves, do not organic matter, transform the rock and improve access to water and air.

Weathering and climate. All types of weathering occur simultaneously, but act with different intensities. This depends not only on the constituent rocks, but also mainly on the climate.

Frost weathering is most active in polar countries, chemical weathering in temperate countries, mechanical weathering in tropical deserts, and chemical weathering in the humid tropics.

The work of the wind. Wind is capable of destroying rocks and transporting and depositing solid particles. The stronger the wind and the more often it blows, the great job he is capable of producing. Where rocky outcrops emerge on the Earth's surface, the wind bombards them with grains of sand, gradually erasing and destroying even the hardest rocks. Less stable rocks are destroyed faster, and specific, aeolian landforms– stone laces, aeolian mushrooms, pillars, towers.

In sandy deserts and along the shores of seas and large lakes, the wind creates specific relief forms - barchans and dunes.

Dunes- These are moving sandy hills of a crescent shape. Their windward slope is always gentle (5-10°), and the leeward slope is steep – up to 35–40° (Fig. 27). The formation of dunes is associated with the inhibition of the wind flow carrying sand, which occurs due to any obstacles - uneven surfaces, stones, bushes, etc. The force of the wind weakens, and sand deposition begins. The more constant the winds and the more sand, the faster the dune grows. The highest dunes - up to 120 m - were found in the deserts of the Arabian Peninsula.

Rice. 27. The structure of the dune (the arrow shows the direction of the wind)

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

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

Snow and ice work. Snow, especially in the mountains, does a lot of work. Huge masses of snow accumulate on the mountain slopes. From time to time they fall from the slopes, forming snow avalanches. Such avalanches, moving at tremendous speed, capture rock fragments and carry them down, sweeping away everything in their path. Due to the terrible danger that avalanches pose, they are called “white death”.

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

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

There are continental, or cover, and mountain glaciers. Continental ice occupy vast areas in Antarctica, Greenland, and many polar islands. The ice thickness of continental glaciers varies. For example, in Antarctica it reaches 4000 m. Under the influence of enormous gravity, the ice slides into the sea, breaks off, and icebergs– ice floating mountains.

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

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

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

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

Work of flowing waters. Flowing waters include temporary rainfall and snowmelt water, streams, rivers and groundwater. The work of flowing waters, taking into account the time factor, is enormous. We can say that the entire appearance of the earth's surface is, to one degree or another, created by flowing water. All flowing waters are united by the fact that they perform three types of work:

– destruction (erosion);

– transfer of products (transit);

– relation (accumulation).

As a result, various irregularities are formed on the surface of the Earth - ravines, furrows on slopes, cliffs, river valleys, sand and pebble islands, etc., as well as voids in the thickness of rocks - caves.

The action of gravity. All bodies - liquid, solid, gaseous, located on the Earth - are attracted to it.

The force with which a body is attracted to the Earth is called gravity.

Under the influence of this force, all bodies tend to occupy the lowest position on the earth's surface. As a result, water flows arise in rivers, rainwater seeps into the thickness of the earth's crust, snow avalanches collapse, glaciers move, and rock fragments move down the slopes. Gravity – necessary condition actions of external processes. Otherwise, the weathering products would remain at the site of their formation, covering the underlying rocks like a cloak.

§ 21. Minerals and rocks

As you already know, the Earth consists of many chemical elements - oxygen, nitrogen, silicon, iron, etc. By combining with each other, chemical elements form minerals.

Minerals. Most minerals are composed of two or more chemical elements. You can find out how many elements are contained in a mineral by its chemical formula. For example, halite (table salt) is composed of sodium and chlorine and has the formula NCl; magnetite (magnetic iron ore) - from three molecules of iron and two oxygen (F 3 O 2), etc. Some minerals are formed by one chemical element, for example: sulfur, gold, platinum, diamond, etc. Such minerals are called native. About 40 native elements are known in nature, accounting for 0.1% of the mass of the earth’s crust.

Minerals can be not only solid, but also liquid (water, mercury, oil), and gaseous (hydrogen sulfide, carbon dioxide).

Most minerals have a crystalline structure. The crystal shape for a given mineral is always constant. For example, quartz crystals have the shape of a prism, halite crystals have the shape of a cube, etc. If table salt dissolved in water and then crystallized, the newly formed minerals will take on a cubic shape. Many minerals have the ability to grow. Their sizes range from microscopic to gigantic. For example, a beryl crystal 8 m long and 3 m in diameter was found on the island of Madagascar. Its weight is almost 400 tons.

According to their formation, all minerals are divided into several groups. Some of them (feldspar, quartz, mica) are released from the magma during its slow cooling at great depths; others (sulfur) - when lava cools quickly; third (garnet, jasper, diamond) - at high temperatures and pressure at great depths; the fourth (garnets, rubies, amethysts) are released from hot aqueous solutions in underground veins; fifths (gypsum, salts, brown iron ore) are formed during chemical weathering.

In total, there are more than 2,500 minerals in nature. To identify and study them great value have physical properties, which include luster, color, the color of the trait, i.e., the trace left by the mineral, transparency, hardness, cleavage, fracture, and specific gravity. For example, quartz has a prismatic crystal shape, glassy luster, no cleavage, conchoidal fracture, hardness 7, specific gravity 2.65 g/cm 3 , has no features; Halite has a cubic crystal shape, hardness 2.2, specific gravity 2.1 g/cm3, glass luster, white color, perfect cleavage, salty taste, etc.

Of the minerals, the most famous and widespread are 40–50, which are called rock-forming minerals (feldspar, quartz, halite, etc.).

Rocks. These rocks are an accumulation of one or more minerals. Marble, limestone, and gypsum consist of one mineral, while granite and basalt consist of several. In total, there are about 1000 rocks in nature. Depending on their origin - genesis - rocks are divided into three main groups: igneous, sedimentary and metamorphic.

Igneous rocks. Formed when magma cools; crystalline structure, do not have layering; do not contain animal or plant remains. Among igneous rocks, a distinction is made between deep-seated and eruptive. Deep rocks formed deep in the earth's crust, where magma is under high pressure and its cooling occurs very slowly. An example of a plutonic rock is granite, the most common crystalline rock composed primarily of three minerals: quartz, feldspar, and mica. The color of granites depends on the color of the feldspar. Most often they are gray or pink.

When magma erupts onto the surface, it forms erupted rocks. They are either a sintered mass, reminiscent of slag, or glassy, ​​in which case they are called volcanic glass. IN in some cases a fine-crystalline rock such as basalt is formed.

Sedimentary rocks. Cover approximately 80% of the entire surface of the Earth. They are characterized by layering and porosity. As a rule, sedimentary rocks are the result of the accumulation in the seas and oceans of the remains of dead organisms or particles of destroyed solid rocks carried from land. The accumulation process occurs unevenly, so layers of different thicknesses are formed. Fossils or imprints of animals and plants are found in many sedimentary rocks.

Depending on the place of formation, sedimentary rocks are divided into continental and marine. TO continental breeds include, for example, clays. Clay is a crushed product of the destruction of hard rocks. They consist of tiny scaly particles and have the ability to absorb water. Clays are plastic and waterproof. Their colors vary - from white to blue and even black. White clays are used to produce porcelain.

Loess is a rock of continental origin and widespread. It is a fine-grained, non-laminated, yellowish rock consisting of a mixture of quartz, clay particles, lime carbonate and iron oxide hydrates. Easily allows water to pass through.

Marine rocks usually form on the ocean floor. These include some clays, sands, and gravels.

Large group of sedimentary biogenic rocks formed from the remains of dead animals and plants. These include limestones, dolomites and some combustible minerals (peat, coal, oil shale).

Limestone, consisting of calcium carbonate, is especially widespread in the earth's crust. In its fragments one can easily see accumulations of small shells and even skeletons of small animals. The color of limestones varies, most often gray.

Chalk is also formed from the smallest shells - inhabitants of the sea. Huge reserves of this rock are located in the Belgorod region, where along the steep banks of rivers you can see outcrops of thick layers of chalk, distinguished by its whiteness.

Limestones that contain an admixture of magnesium carbonate are called dolomites. Limestones have wide application in construction. They are used to make lime for plastering and cement. The best cement is made from marl.

In those seas where animals with flint shells previously lived and algae containing flint grew, the tripoli rock formed. This is a light, dense, usually yellowish or light gray rock that is used as a building material.

Sedimentary rocks also include rocks formed by precipitation from aqueous solutions(gypsum, rock salt, potassium salt, brown iron ore, etc.).

Metamorphic rocks. This group of rocks was formed from sedimentary and igneous rocks under the influence of high temperatures, pressure, and chemical changes. Thus, when temperature and pressure act on clay, shales are formed, on sand - dense sandstones, and on limestone - marble. Changes, i.e. metamorphoses, occur not only with sedimentary rocks, but also with igneous rocks. Under the influence of high temperatures and pressure, granite acquires a layered structure and a new rock is formed - gneiss.

High temperature and pressure promote recrystallization of rocks. Sandstones form a very strong crystalline rock - quartzite.

§ 22. Development of the earth's crust

Science has established that more than 2.5 billion years ago, planet Earth was completely covered by ocean. Then, under the influence of internal forces, the uplift of individual sections of the earth's crust began. The uplift process was accompanied by violent volcanism, earthquakes, and mountain building. This is how the first land masses arose - the ancient cores of modern continents. Academician V. A. Obruchev called them "the ancient crown of the Earth."

As soon as the land rose above the ocean, external processes began to act on its surface. Rocks were destroyed, the products of destruction were carried into the ocean and accumulated along its outskirts in the form of sedimentary rocks. The thickness of the sediments reached several kilometers, and under its pressure the ocean floor began to bend. Such giant troughs of the earth's crust under the oceans are called geosynclines. The formation of geosynclines in the history of the Earth has been continuous from ancient times to the present. There are several stages in the life of geosynclines:

– embryonic– deflection of the earth’s crust and accumulation of sediments (Fig. 28, A);

– maturation– filling of the trough with sediments, when their thickness reaches 15–18 km and radial and lateral pressure arises;

– folding– the formation of folded mountains under the pressure of the internal forces of the Earth (this process is accompanied by violent volcanism and earthquakes) (Fig. 28, B);

– attenuation– destruction of the emerging mountains by external processes and the formation in their place of a residual hilly plain (Fig. 28).

Rice. 28. Scheme of the structure of the plain formed as a result of the destruction of mountains (the dotted line shows the reconstruction of the former mountainous country)

Since sedimentary rocks in the geosyncline area are plastic, as a result of the resulting pressure they are crushed into folds. Fold mountains are formed, such as the Alps, Caucasus, Himalayas, Andes, etc.

The periods when active formation of folded mountains occurs in geosynclines are called eras of folding. Several such eras are known in the history of the Earth: Baikal, Caledonian, Hercynian, Mesozoic and Alpine.

The process of mountain building in a geosyncline can also cover non-geosynclinal areas - areas of former, now destroyed mountains. Since the rocks here are hard and lack plasticity, they do not fold into folds, but are broken by faults. Some areas rise, others fall - revived block and folded block mountains appear. For example, during the Alpine era of folding, the folded Pamir mountains were formed and the Altai and Sayan mountains were revived. Therefore, the age of mountains is determined not by the time of their formation, but by the age of the folded base, which is always indicated on tectonic maps.

Geosynclines at different stages of development still exist today. Thus, along the Asian coast of the Pacific Ocean, in the Mediterranean Sea there is a modern geosyncline, which is going through a maturation stage, and in the Caucasus, in the Andes and other folded mountains the process of mountain formation is completing; Kazakh small hills are peneplain, rolling plain, formed on the site of the destroyed mountains of the Caledonian and Hercynian folds. The base of ancient mountains comes to the surface here - small hills - “witness mountains”, composed of durable igneous and metamorphic rocks.

Vast areas of the earth's crust with relatively low mobility and flat topography are called platforms. At the base of the platforms, in their foundations, lie strong igneous and metamorphic rocks, indicating the processes of mountain building that once took place here. Usually the foundation is covered by a thick layer of sedimentary rock. Sometimes basement rocks come to the surface, forming shields. The age of the platform corresponds to the age of the foundation. Ancient (Precambrian) platforms include the East European, Siberian, Brazilian, etc.

The platforms are mostly plains. They experience predominantly oscillatory movements. However, in some cases, the formation of revived block mountains is possible on them. Thus, as a result of the emergence of the Great African Rifts, individual sections of the ancient African platform rose and fell and blocky mountains and highlands were formed East Africa, volcano mountains Kenya and Kilimanjaro.

Lithospheric plates and their movement. The doctrine of geosynclines and platforms is called in science "fixism" since, according to this theory, large blocks of bark are fixed in one place. In the second half of the 20th century. many scientists supported theory of mobilism, which is based on the idea of ​​horizontal movements of the lithosphere. According to this theory, the entire lithosphere is divided into giant blocks - lithospheric plates - by deep faults reaching the upper mantle. Boundaries between plates can occur both on land and on the ocean floor. In the oceans, these boundaries are usually mid-ocean ridges. In these areas it was recorded large number faults - rifts, along which the material of the upper mantle flows to the bottom of the ocean, spreading over it. In those areas where the boundaries between plates pass, mountain building processes are often activated - in the Himalayas, Andes, Cordillera, Alps, etc. The base of the plates is in the asthenosphere, and along its plastic substrate the lithospheric plates, like giant icebergs, slowly move into different directions(Fig. 29). The movement of the plates is recorded by precise measurements from space. Thus, the African and Arabian shores of the Red Sea are slowly moving away from each other, which has allowed some scientists to call this sea the “embryo” of the future ocean. Space images also make it possible to trace the direction of deep faults in the earth's crust.

Rice. 29. Movement of lithospheric plates

The theory of mobilism convincingly explains the formation of mountains, since their formation requires not only radial, but also lateral pressure. Where two plates collide, one of them plunges under the other, and “hummocks”, i.e. mountains, are formed along the collision boundary. This process is accompanied by earthquakes and volcanism.

§ 23. Relief of the globe

Relief- this is a set of irregularities of the earth’s surface, differing in height above sea level, origin, etc.

These irregularities give our planet a unique appearance. The formation of relief is influenced by both internal, tectonic, and external forces. Thanks to tectonic processes, mainly large surface irregularities arise - mountains, highlands, etc., and external forces are aimed at their destruction and the creation of smaller relief forms - river valleys, ravines, dunes, etc.

All relief forms are divided into concave (depressions, river valleys, ravines, gullies, etc.), convex (hills, mountain ranges, volcanic cones, etc.), simply horizontal and inclined surfaces. Their size can be very diverse - from several tens of centimeters to many hundreds and even thousands of kilometers.

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

Planetary objects include continental protrusions and ocean depressions. Continents and oceans are often antipodes. Thus, Antarctica lies against the Arctic Ocean, North America - against the Indian Ocean, Australia - against the Atlantic, and only South America– against Southeast Asia.

The depths of oceanic depressions vary widely. The average depth is 3800 m, and the maximum recorded in Mariana Trench Pacific Ocean - 11,022 m. The highest point of land - Mount Everest (Qomolungma) reaches 8848 m. Thus, the amplitude of heights reaches almost 20 km.

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

The average height of the continents and their parts above ocean level is also different: North America - 700 m, Africa - 640, South America - 580, Australia - 350, Antarctica - 2300, Eurasia - 635 m, with the height of Asia 950 m, and Europe - only 320 m. Average land height 875 m.

Relief of the ocean floor. On the ocean floor, as on land, there are various landforms - mountains, plains, depressions, trenches, etc. They usually have softer outlines than similar landforms, since external processes proceed more calmly here.

The relief of the ocean floor includes:

– continental shelf, or shelf (shelf), – shallow part up to a depth of 200 m, the width of which in some cases reaches many hundreds of kilometers;

– continental slope– a rather steep ledge to a depth of 2500 m;

– ocean bed, which occupies most of the bottom with depths up to 6000 m.

The greatest depths were noted in gutters, or oceanic depressions, where they exceed 6000 m. The trenches usually stretch along continents along the margins of the ocean.

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

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

Mountain called a hill that has a summit point, slopes, and a bottom line rising above the terrain above 200 m; an elevation up to 200 m high is called hill. Linearly elongated landforms with a ridge and slopes are mountain ranges. The ridges are separated by those located between them mountain valleys. Connecting with each other, mountain ranges form mountain ranges. A set of ridges, chains and valleys is called mountain node, or mountainous country, and in everyday life - mountains. For example, the Altai Mountains, the Ural Mountains, etc.

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

The origin of mountains is tectonic, volcanic and erosive.

Tectonic mountains formed as a result of movements of the earth's crust, they consist of one or many folds raised to a considerable height. All highest mountains world - the Himalayas, Hindu Kush, Pamir, Cordillera, etc. - folded. They are characterized by pointed peaks, narrow valleys (gorges), and elongated ridges.

Blocky And fold-block mountains are formed as a result of the rise and fall of blocks (blocks) of the earth's crust along fault planes. The relief of these mountains is characterized by flat peaks and watersheds, wide, flat-bottomed valleys. These are, for example, the Ural Mountains, Appalachians, Altai, etc.

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

Quite widespread on the Earth's surface eroded mountains, which are formed as a result of the dismemberment of high plains by external forces, primarily flowing waters.

By height, mountains are divided into low (up to 1000 m), medium-high (from 1000 to 2000 m), high (from 2000 to 5000 m) and highest (above 5 km).

The height of mountains can be easily determined from a physical map. It can also be used to determine that most of the mountains belong to the mid-altitude and high range. Few peaks rise above 7000 m, and all of them are in Asia. Only 12 mountain peaks, located in the Karakoram mountains and the Himalayas, have a height of more than 8000 m. Highest point planet is a mountain, or, more precisely, a mountain node, Everest (Qomolungma) - 8848 m.

Most of the land surface is occupied by flat areas. Plains- these are areas of the earth's surface that have a flat or slightly hilly topography. Most often the plains are slightly sloping.

Based on the nature of the surface, plains are divided into flat, wavy And hilly, but on vast plains, for example Turan or West Siberian, one can find areas with various forms of surface relief.

Depending on the height above sea level, the plains are divided into low-lying(up to 200 m), sublime(up to 500 m) and high (plateaus)(over 500 m). Elevated and high plains are always heavily dissected by water flows and have a hilly topography, while low-lying ones are often flat. Some plains are located below sea level. Thus, the Caspian lowland has a height of 28 m. Closed basins of great depth are often found on the plains. For example, the Karagis depression has an elevation of 132 m, and the Dead Sea depression has an elevation of 400 m.

Elevated plains bounded by steep escarpments separating them from the surrounding area are called plateau. These are the plateaus of Ustyurt, Putorana, etc.

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

Based on their origin, there are several types of plains. Significant land areas are occupied by marine (primary) plains, formed as a result of marine regressions. These are, for example, the Turanian, West Siberian, Great Chinese and a number of other plains. Almost all of them belong to the great plains of the planet. Most of them are lowlands, the terrain is flat or slightly hilly.

Stratified plains- These are flat areas of ancient platforms with almost horizontal occurrence of layers of sedimentary rocks. Such plains include, for example, the East European. These plains mostly have hilly terrain.

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

The plains are raised high above sea level - lava sheets(Central Siberian Plateau, Ethiopian and Iranian Plateaus, Deccan Plateau). Some plains, for example the Kazakh small hills, were formed as a result of the destruction of mountains. They are called erosive. These plains are always elevated and hilly. These hills are composed of durable crystalline rocks and represent the remains of the mountains that were once here, their “roots”.

§ 24. Soil

Soil– this is the upper fertile layer of the lithosphere, which has a number of properties inherent in living and inanimate nature.

The formation and existence of this natural body cannot be imagined without living beings. The surface layers of rock are only the initial substrate from which, under the influence of plants, microorganisms and animals, they are formed various types soil

The founder of soil science, Russian scientist V.V. Dokuchaev, showed that

soil is an independent natural body formed on the surface of rocks under the influence of living organisms, climate, water, relief, and also humans.

This natural formation has been created over thousands of years. The process of soil formation begins with the settlement of microorganisms on bare rocks and stones. Feeding on carbon dioxide, nitrogen and water vapor from the atmosphere, using mineral salts of rock, microorganisms release organic acids as a result of their vital activity. These substances gradually change the chemical composition of rocks, making them less durable and ultimately loosening the surface layer. Then lichens settle on such rock. Unpretentious to water and nutrients, they continue the process of destruction, while simultaneously enriching the rock with organic matter. As a result of the activity of microorganisms and lichens, the rock gradually turns into a substrate suitable for colonization by plants and animals. The final transformation of the original rock into soil occurs due to the vital activity of these organisms.

Plants absorb carbon dioxide from the atmosphere and water and minerals from the soil, creating organic compounds. As plants die, they enrich the soil with these compounds. Animals feed on plants and their remains. The products of their vital activity are excrement, and after death their corpses also end up in the soil. The entire mass of dead organic matter accumulated as a result of the vital activity of plants and animals serves as a food supply and habitat for microorganisms and fungi. They destroy organic substances and mineralize them. As a result of the activity of microorganisms, complex organic substances are formed that make up soil humus.

Soil humus is a mixture of stable organic compounds formed during the decomposition of plant and animal residues and their metabolic products with the participation of microorganisms.

In the soil, primary minerals decompose and clay secondary minerals form. Thus, the cycle of substances occurs in the soil.

Moisture capacity is the soil's ability to hold water.

Soil with a lot of sand does not retain water well and has low moisture holding capacity. Clay soil, on the other hand, holds a lot of water and has a high moisture holding capacity. In case of heavy rainfall, water fills all the pores in such soil, preventing air from passing deeper. Loose, lumpy soils retain moisture better than dense soils.

Moisture permeability- This is the ability of the soil to pass water.

The soil is permeated with tiny pores - capillaries. Through capillaries, water can move not only downwards, but also in all directions, including from bottom to top. The higher the capillarity of the soil, the higher its moisture permeability, the faster water penetrates the soil and rises upward from deeper layers. Water “sticks” to the walls of the capillaries and seems to creep upward. The thinner the capillaries, the higher the water rises through them. When the capillaries reach the surface, the water evaporates. Sandy soils have high moisture permeability, while clay soils have low permeability. If, after rain or watering, a crust (with many capillaries) has formed on the surface of the soil, the water evaporates very quickly. When loosening the soil, capillaries are destroyed, which reduces water evaporation. It’s not for nothing that loosening the soil is called dry watering.

Soils can have a different structure, that is, they can consist of lumps of different shapes and sizes into which soil particles are glued. The best soils, such as chernozems, have a fine-lumpy or granular structure. According to the chemical composition, soils can be rich or poor in nutrients. An indicator of soil fertility is the amount of humus, since it contains all the basic elements of plant nutrition. For example, chernozem soils contain up to 30% humus. Soils can be acidic, neutral and alkaline. Neutral soils are most favorable for plants. To reduce acidity, they are limed, and gypsum is added to the soil to reduce alkalinity.

Mechanical composition of soils. Based on their mechanical composition, soils are divided into clayey, sandy, loamy and sandy loam.

Clay soils have high moisture capacity and are best provided with batteries.

Sandy soils low moisture capacity, well permeable to moisture, but poor in humus.

Loamy– the most favorable in their physical properties for agriculture, with average moisture capacity and moisture permeability, well provided with humus.

Sandy loam– structureless soils, poor in humus, well permeable to water and air. To use such soils, it is necessary to improve their composition and apply fertilizers.

Soil types. The most common soil types in our country are: tundra, podzolic, sod-podzolic, chernozem, chestnut, gray soil, red soil and yellow soil.

Tundra soils are located in the Far North in the permafrost zone. They are waterlogged and extremely poor in humus.

Podzolic soils common in the taiga under coniferous trees, and sod-podzolic– under coniferous-deciduous forests. Broadleaf forests grow on gray forest soils. All these soils contain enough humus and are well structured.

In the forest-steppe and steppe zones there are chernozem soils. They were formed under steppe and grassy vegetation and are rich in humus. Humus gives the soil a black color. They have a strong structure and high fertility.

Chestnut soils located further south, they form in drier conditions. They are characterized by a lack of moisture.

Serozem soils characteristic of deserts and semi-deserts. They are rich in nutrients, but poor in nitrogen, and there is not enough water.

Krasnozems And zheltozems are formed in the subtropics in humid and warm climates. They are well structured, quite moisture-absorbing, but have a lower humus content, so fertilizers are added to these soils to increase fertility.

To increase soil fertility, it is necessary to regulate not only the content of nutrients, but also the presence of moisture and aeration. The topsoil should always be loose to provide air access to the roots of the plants.

Consolidated cargo: cargo transportation from Moscow, road transport of goods marstrans.ru.

Tectonic movements are movements of the earth's crust associated with internal forces in the earth's crust and mantle.Branch of Geology, which studies these movements, as well as the modern structure and development of structural elements of the earth's crust is called tectonics.

The largest structural elements of the earth's crust are platforms, geosynclines and oceanic plates.

Platforms are huge, relatively stationary, stable sections of the earth's crust. The platforms are characterized by a two-tier structure. The lower, more ancient tier (crystalline basement) is composed of sedimentary rocks, crushed into folds, or igneous rocks subjected to metamorphism. The upper tier (platform cover) consists almost entirely of horizontally occurring sedimentary rocks.

Classic examples of platform areas are the East European (Russian) platform, West Siberian, Turanian and Siberian, which occupy vast spaces. The North African, Indian and other platforms are also known in the world.

The thickness of the upper tier of the platforms reaches 1.5-2.0 km or more. The section of the earth's crust where the upper layer is absent and the crystalline foundation extends directly to the outer surface is called shields (Baltic, Voronezh, Ukrainian, etc.).

Within platforms, tectonic movements are expressed in the form of slow vertical oscillatory movements of the earth's crust. Volcanism and seismic movements (earthquakes) are poorly developed or completely absent. The relief of the platforms is closely related to the deep structure of the earth's crust and is expressed mainly in the form of vast plains (lowlands).

Geosynclines are the most mobile, linearly elongated sections of the earth's crust, framing platforms. On early stages In their development, they are characterized by intense dives, and in the final stages – by impulsive rises.

Geosynclinal regions are the Alps, Carpathians, Crimea, Caucasus, Pamirs, Himalayas, the Pacific coastline and other folded mountain structures. All these areas are characterized by active tectonic movements, high seismicity and volcanism. In these same areas, powerful magmatic processes are actively developing with the formation of effusive lava covers and flows and intrusive bodies (stocks, etc.). In Northern Eurasia, the most mobile and seismically active region is the Kuril-Kamchatka zone.

Oceanic plates are the largest tectonic structures in the earth's crust and form the basis of the ocean floors. Unlike continents, oceanic plates have not been studied enough, which is associated with significant difficulties in obtaining geological information about their structure and composition of matter.

The following main tectonic movements of the earth's crust are distinguished:

- oscillatory;

- folded;

- explosive.

Oscillatory tectonic movements manifest themselves in the form of slow uneven uplifts and lowerings of individual sections of the earth's crust. The oscillatory nature of their movement lies in the change in its sign: uplift in some geological epochs is replaced by lowering in others. Tectonic movements of this type occur continuously and everywhere. There are no tectonically stationary sections of the earth's crust on the earth's surface - some rise, others fall.

According to the time of their manifestation, oscillatory movements are divided into modern (last 5-7 thousand years), newest (Neogene and Quaternary periods) and movements of past geological periods.

Modern oscillatory movements are studied at special testing sites using repeated geodetic observations using the method of high-precision leveling. More ancient oscillatory movements are judged by the alternation of marine and continental sediments and a number of other features.

The rate of rise or fall of individual sections of the earth's crust varies widely and can reach 10-20 mm per year or more. For example, south coast The North Sea in Holland drops by 5-7 mm per year. Holland is saved from the invasion of the sea onto land (transgression) by dams up to 15 m high, which are constantly being built up. At the same time, in nearby areas in Northern Sweden in the coastal zone, modern uplifts of the earth's crust of up to 10-12 mm per year are observed. In these areas, part of the port facilities turned out to be remote from the sea due to its retreat from the coast (regression).

Geodetic observations carried out in the areas of the Black, Caspian and Azov Seas showed that the Caspian Lowland, the eastern coast of the Akhzov Sea, the depressions at the mouths of the Terek and Kuban rivers, and the northwestern coast of the Black Sea are sinking at a rate of 2-4 mm per year. As a consequence, transgression is observed in these areas, i.e. advance of the sea onto land. On the contrary, slow uplifts are experienced by land areas on the coast of the Baltic Sea, as well as, for example, the areas of Kursk, the mountain regions of Altai, Sayan, New land etc. Other areas continue to sink: Moscow (3.7 mm/year), St. Petersburg (3.6 mm/year), etc.

The greatest intensity of oscillatory movements of the earth's crust is observed in geosynclinal areas, and the lowest in platform areas.

The geological significance of oscillatory movements is enormous. They determine the conditions of sedimentation, the position of the boundaries between land and sea, shallowing or increased erosive activity of rivers. Oscillatory movements that occurred in recent times (Neogene-Quaternary period) had a decisive influence on the formation of the modern topography of the Earth.

Oscillatory (modern) movements must be taken into account when constructing hydraulic structures such as reservoirs, dams, shipping canals, cities by the sea, etc.

Fold tectonic movements. In geosynclinal areas, tectonic movements can significantly disrupt the original form of rock formation. Disturbances in the forms of the primary occurrence of rocks caused by the tectonic movement of the earth's crust are called dislocations. They are divided into folded and discontinuous.

Folded dislocations can be in the form of elongated linear folds or expressed in a general tilt of the layers in one direction.

An anticline is an elongated linear fold, convexly facing upward. In the core (center) of the anticline there are more ancient layers, on the wings of the folds there are younger ones.

A syncline is a fold similar to an anticline, but convexly directed downwards. The core of the syncline contains younger layers than those on the wings.

Monocline - is a thickness of rock layers inclined in one direction at the same angle.

Flexure is a knee-shaped fold with a stepwise bending of layers.

The orientation of layers in a monoclinal occurrence is characterized using the strike line, dip line and dip angle.

Rupture tectonic movements. They lead to disruption of the continuity of rocks and their rupture along any surface. Fractures in rocks occur when stresses in the earth's crust exceed the tensile strength of rocks.

Fault dislocations include normal faults, reverse faults, thrusts, strike-slip faults, grabens and horsts.

Reset– is formed as a result of the lowering of one part of the thickness relative to another.

Reverse fault - formed when one part of the strata rises relative to another.

Thrust – displacement of rock blocks along an inclined fault surface.

Shear is the displacement of rock blocks in the horizontal direction.

A graben is a section of the earth’s crust bounded by tectonic faults (faults) and descended along them relative to adjacent sections.

An example of large grabens is the depression of Lake Baikal and the valley of the Rhine River.

Horst is an elevated section of the earth's crust, bounded by faults or reverse faults.

Disruptive tectonic movements are often accompanied by the formation of various tectonic cracks, which are characterized by their capture of thick rock strata, consistency of orientation, the presence of traces of displacement and other signs.

A special type of discontinuous tectonic faults are deep faults that divide the earth's crust into separate large blocks. Deep faults have a length of hundreds and thousands of kilometers and a depth of more than 300 km. Modern intense earthquakes and active volcanic activity (for example, faults of the Kuril-Kamchatka zone) are confined to the zones of their development.

Tectonic movements that cause the formation of folds and ruptures are called mountain-building.

The significance of tectonic conditions for construction. The tectonic features of the area very significantly influence the choice of location of various buildings and structures, their layout, construction conditions and operation of construction projects.

Areas with horizontal, undisturbed layers are favorable for construction. The presence of dislocations and a developed system of tectonic cracks significantly worsens the engineering and geological conditions of the construction area. In particular, during the construction development of a territory with active tectonic activity, it is necessary to take into account the intense fracturing and fragmentation of rocks, which reduces their strength and stability, a sharp increase in seismic activity in places where fault dislocations develop, and other features.

The intensity of oscillatory movements of the earth's crust must be taken into account when constructing protective dams, as well as linear structures of considerable length (canals, railways, etc.).

Movement of the earth's crust

The earth's crust only seems motionless, absolutely stable. In fact, she makes continuous and varied movements. Some of them occur very slowly and are not perceived by the human senses, others, such as earthquakes, are landslide and destructive. What titanic forces set the earth's crust in motion?

Internal forces of the Earth, the source of their origin. It is known that at the boundary of the mantle and lithosphere the temperature exceeds 1500 °C. At this temperature, matter must either melt or turn into gas. When solids transform into a liquid or gaseous state, their volume must increase. However, this does not happen, since the overheated rocks are under pressure from the overlying layers of the lithosphere. A “steam boiler” effect occurs when matter, seeking to expand, presses on the lithosphere, causing it to move along with the earth’s crust. Moreover, the higher the temperature, the stronger the pressure and the more active the lithosphere moves. Particularly strong pressure centers arise in those places in the upper mantle where radioactive elements are concentrated, the decay of which heats the constituent rocks to even higher temperatures. Movements of the earth's crust under the influence of the internal forces of the Earth are called tectonic. These movements are divided into oscillatory, folding and bursting.

Oscillatory movements. These movements occur very slowly, imperceptibly for humans, which is why they are also called centuries-old or epeirogenic. In some places the earth's crust rises, in others it falls. In this case, the rise is often replaced by a fall, and vice versa. These movements can be traced only by the “traces” that remain after them on the earth’s surface. For example, on the Mediterranean coast, near Naples, there are the ruins of the Temple of Serapis, the columns of which were worn away by sea mollusks at an altitude of up to 5.5 m above modern sea level. This serves as absolute proof that the temple, built in the 4th century, was at the bottom of the sea, and then it was raised. Now this area of ​​land is sinking again. Often on the coasts of seas above their current level there are steps - sea terraces, once created by the surf. On the platforms of these steps you can find the remains of marine organisms. This indicates that the terrace areas were once the bottom of the sea, and then the shore rose and the sea retreated.

The descent of the earth's crust below 0 m above sea level is accompanied by the advance of the sea - transgression, and the rise - by his retreat - regression. Currently in Europe, uplifts occur in Iceland, Greenland, and the Scandinavian Peninsula. Observations have established that the region of the Gulf of Bothnia is rising at a rate of 2 cm per year, i.e. 2 m per century. At the same time, the territory of Holland, southern England, northern Italy, the Black Sea lowland, and the coast of the Kara Sea is subsiding. A sign of the subsidence of sea coasts is the formation of sea bays in the estuaries of rivers - estuaries (lips) and estuaries.

When the earth's crust rises and the sea retreats, the seabed, composed of sedimentary rocks, turns out to be dry land. This is how extensive marine (primary) plains: for example, West Siberian, Turanian, North Siberian, Amazonian (Fig. 20).

Rice. 20. The structure of primary, or marine, strata plains

Folding movements. In cases where rock layers are sufficiently plastic, under the influence of internal forces they collapse into folds. When the pressure is directed vertically, the rocks are displaced, and if in the horizontal plane, they are compressed into folds. The shape of the folds can be very diverse. When the bend of the fold is directed downward, it is called a syncline, upward - an anticline (Fig. 21). Folds form at great depths, i.e. at high temperatures and high pressure, and then under the influence of internal forces they can be lifted. This is how they arise fold mountains Caucasian, Alps, Himalayas, Andes, etc. (Fig. 22). In such mountains, folds are easy to observe where they are exposed and come to the surface.

Rice. 21. Synclinal (1) and anticlinal (2) folds

Rice. 22. fold mountains

Breaking movements. If the rocks are not strong enough to withstand the action of internal forces, cracks (faults) form in the earth's crust and vertical displacement of the rocks occurs. The sunken areas are called grabens, and those who rose - handfuls(Fig. 23). The alternation of horsts and grabens creates block (revived) mountains. Examples of such mountains are: Altai, Sayan, Verkhoyansk Range, Appalachians in North America and many others. Revived mountains differ from folded ones both in internal structure and in appearance - morphology. The slopes of these mountains are often steep, the valleys, like the watersheds, are wide and flat. Rock layers are always displaced relative to each other.

Rice. 23. Revived fold-block mountains

The sunken areas in these mountains, grabens, sometimes fill with water, and then deep lakes are formed: for example, Baikal and Teletskoye in Russia, Tanganyika and Nyasa in Africa.