Volcano. What is Vulcan? geographical feature

Magmatism is a set of processes and phenomena associated with the activity of magma. Magma is a fiery-liquid natural usually silicate melt enriched in volatile components (H 2 O, CO 2 , CO, H 2 S, etc.). Low-silicate and non-silicate magmas are rare. Crystallization of magma leads to the formation of igneous (igneous) rocks.

The formation of magmatic melts occurs as a result of the melting of local areas of the mantle or the earth's crust. Most of the melting centers are located at relatively shallow depths in the range from 15 to 250 km.

There are several reasons for melting. The first reason is associated with the rapid rise of hot plastic deep matter from the region of high to the region of lower pressures. A decrease in pressure (in the absence of a significant change in temperature) leads to the onset of melting. The second reason is related to the increase in temperature (in the absence of a change in pressure). The reason for the heating of rocks is usually the intrusion of hot magmas and the fluid flow that accompanies them. The third reason is associated with the dehydration of minerals in the deep zones of the earth's crust. Water, released during the decomposition of minerals, sharply (by tens - hundreds of degrees) reduces the temperature of the beginning of the melting of rocks. Thus, melting begins due to the appearance of free water in the system.

The three considered mechanisms of melt generation are often combined: 1) the rise of asthenospheric matter into the area of ​​low pressure leads to the beginning of its melting - 2) the formed magma intrudes into the lithospheric mantle and lower crust, leading to partial melting of the rocks that make them up - 3) the rise of melts into less deep zones of the crust, where hydroxyl-containing minerals (micas, amphiboles) are present, leads, in turn, to the melting of rocks during the release of water.

Speaking about the mechanisms of melt generation, it should be noted that in most cases, not complete, but only partial melting of the substrate (rocks undergoing melting) occurs. The emerging melting center is a solid rock penetrated by capillaries filled with melt. The further evolution of the chamber is associated either with the squeezing out of this melt, or with an increase in its volume, leading to the formation of a "magmatic porridge" - magma saturated with refractory crystals. Upon reaching 30-40 volume% of the melt, this mixture acquires the properties of a liquid and is squeezed out into the region of lower pressures.

The mobility of magma is determined by its viscosity, which depends on the chemical composition and temperature. The lowest viscosity is possessed by deep mantle magmas, which have a high temperature (up to 1600-1800 0 C at the time of generation) and contain little silica (SiO 2). The highest viscosity is inherent in magmas that have arisen due to the melting of the material of the upper continental crust during the dehydration of minerals: they are formed at a temperature of 700-600 0 C and are maximally saturated with silica.

The melt squeezed out of the intergranular pores is filtered upward at a rate of several centimeters to several meters per year. If significant volumes of magma are introduced along cracks and faults, the rate of their rise is much higher. According to calculations, the rate of rise of some ultrabasic magmas (outpouring on the surface of which led to the formation of rare effusive ultrabasic rocks - komatiites) reached 1-10 m/s.

Patterns of magma evolution and formation of igneous rocks

The composition and features of rocks formed from magma are determined by a combination of the following factors: the initial composition of magma, the processes of its evolution, and the conditions of crystallization. All igneous rocks are divided into 6 orders according to silicic acidity:

Magmatic melts come from the mantle or are formed as a result of the melting of rocks in the earth's crust. As is known, the chemical composition of the mantle and crust are different, which primarily determines the differences in the composition of magmas. Magmas arising from the melting of mantle rocks, like these rocks themselves, are enriched in basic oxides - FeO, MgO, CaO, therefore, such magmas have an ultrabasic and basic composition. During their crystallization, ultrabasic and basic igneous rocks are formed, respectively. Magmas arising from the melting of crustal rocks depleted in basic oxides but sharply enriched in silica (a typical acidic oxide) have an acidic composition; during their crystallization, acidic rocks are formed.

However, primary magmas in the course of evolution often undergo significant compositional changes associated with the processes of crystallization differentiation, segregation, and hybridism, which gives rise to a variety of igneous rocks.

crystallization differentiation. As is known, according to the Bowen series, not all minerals crystallize simultaneously - olivines and pyroxenes are the first to separate from the melt. Having a density greater than the residual melt, if the viscosity of the magma is not too high, they settle to the bottom of the magma chamber, which prevents their further reaction with the melt. In this case, the residual melt will differ in chemical composition from the original (because some of the elements are included in the composition of minerals) and enriched in volatile components (they are not included in the minerals of early crystallization). Consequently, the minerals of early crystallization in this case form one rock, and the remaining magma will form other, different in composition, rocks. Processes of crystallization differentiation are typical for basic melts; The precipitation of femic minerals leads to layering in the magma chamber: its lower part acquires an ultramafic composition, while its upper part acquires a basic one. Under favorable conditions, differentiation can lead to the release of a small volume of felsic melt from the primary mafic magma (which has been studied on the example of frozen Alae lava lakes in the Hawaiian Islands and volcanoes in Iceland).

Segregation is a process of separation of magma with a decrease in temperature into two immiscible melts with different chemical composition (in the general view the course of this process can be represented as the process of separating water and oil from their mixture). Accordingly, rocks of different composition will crystallize from the separated magmas.

hybridism ("hybrida" - a mixture) is the process of mixing of magmas of different composition or assimilation of host rocks by magma. Interacting with host rocks of different composition, capturing and processing their fragments, the igneous melt is enriched with new components. The process of melting or complete assimilation of foreign material by magma is denoted by the term assimilation ("assimillato" - assimilation). For example, the interaction of mafic magmas with felsic wall rocks produces hybrid rocks of intermediate composition. Or, conversely, intrusion of silicic magmas into rocks rich in basic oxides can also lead to the formation of intermediate rocks.

It should also be taken into account that during the evolution of the melt, the above processes can be combined.

Moreover, magma of the same chemical composition can form different breeds . This is due to different conditions of magma crystallization and, above all, to depth.

According to the conditions of depth of formation (or on the basis of facies), igneous rocks are divided into intrusive, or deep, and effusive, or erupted, rocks. intrusive rocks are formed during the crystallization of magmatic melt at a depth in rock strata; Depending on the depth of formation, they are divided into two facies: 1) abyssal rocks formed at a considerable depth (several km), and 2) hypabyssal, which were formed at a relatively shallow depth (about 1-3 km). effusive rocks are formed as a result of the solidification of lava poured onto the surface or bottom of the oceans.

Thus, the following main facies are distinguished: abyssal, hypabyssal and effusive. In addition to the three named facies, there are also subvolcanic And vein breeds. The first of them are formed in near-surface conditions (up to a few hundred meters) and have a close resemblance to effusive rocks; the latter are close to hypabyssal. Effusive rocks are often accompanied by pyroclastic formations consisting of fragments of effusives, their minerals and volcanic glass.

Drawing - facies

Significant differences in the nature of the manifestation of magmatic processes in deep and surface conditions make it necessary to distinguish between intrusive and effusive processes.

Intrusive magmatism

Intrusive processes are associated with the formation and movement of magma below the Earth's surface. The magmatic melts formed in the depths of the Earth have a density lower than that of the surrounding solid rocks and, being mobile, penetrate into the overlying horizons. The process of magma intrusion is called intrusion (from "intrusio" - implementation). If magma solidifies before reaching the surface (among host rocks), then intrusive bodies are formed. In relation to the host rocks, intrusions are divided into consonants(concordant) and dissenters(discordant). The former lie in accordance with the host rocks, without crossing the boundaries of their layers; the latter have secant contacts. According to the shape, a number of varieties of intrusive bodies are distinguished.

Consonant forms of intrusives include sill, lopolith, laccolith, and other less common ones. Silla are conformable sheet-like intrusive bodies formed under the conditions of stretching of the earth's crust. Their thickness ranges from tens of cm to hundreds of meters. The intrusion of a large number of sills into the layered stratum forms something like a layer cake. At the same time, as a result of erosion, strong igneous rocks in the relief form “steps” ( English "sill" - threshold). Such multilevel sills composed of mafic rocks are widespread on the Siberian platform (as part of the Tunguska syneclise), on Hindustan (Dean), and other platforms. lopolites- These are large consonant intrusive saucer-shaped bodies. The thickness of the lopoliths reaches hundreds of meters, and the diameter is tens of kilometers. The largest is the Bushveld in South Africa. Formed under conditions of tectonic extension and subsidence. Laccoliths- a consonant intrusive body of a mushroom-like shape. The roof of the laccolith has a convex arched shape, the sole is usually horizontal. The Henry Mountains intrusions in North America are a classic example. They are formed under conditions of significant pressure of intruding magma on layered host rocks. They are shallow intrusions, since in deep horizons the pressure of magma cannot overcome the pressure of powerful strata of overlying rocks.

The most common unconformities include dikes, veins, stocks, and batholiths. Dike- a discontinuous intrusive body of a plate-like shape. They form in hypabyssal and subvolcanic conditions when magma is emplaced along faults and fissures. As a result of exogenous processes, the enclosing sedimentary dikes are destroyed faster than the dikes occurring in them, due to which, in the relief, the latter resemble destroyed walls ( name from English "dike", "dyke" - a barrier, a wall of stone). veins called small secant bodies irregular shape. Stock (from him. "Stock" - stick, trunk) is an unconformity intrusive columnar body. The largest intrusions are batholiths, they include intrusive bodies with an area of ​​more than 200 km 2 and a thickness of several km. Batholiths are composed of acidic abyssal rocks formed during the melting of the earth's crust in areas of mountain building. It is noteworthy that the granitoids that make up batholiths are formed both as a result of the melting of primary sedimentary "sialic" rocks (S-granites), and during the melting of primary magmatic, including basic "femic" rocks (I-granites). This is facilitated by the preliminary processing of the original rocks (substratum) by deep fluids, which introduce alkalis and silica into them. Magmas formed as a result of large-scale melting can crystallize at the place of their formation, creating autochthonous intrusions, or intrude into host rocks - allochthonous intrusions.

All large deep intrusive bodies (batholiths, stocks, lopolites, etc.) are often combined under the general term plutons. Their smaller branches are called apophyses.

Forms of occurrence of intrusive bodies

When interacting with the host rocks (“frame”), magma has a thermal and chemical effect on them. The zone of change in the near-contact part of the host rocks is being drilled exocontact. The thickness of such zones can vary from a few cm to tens of km, depending on the nature of the host rocks and the saturation of the magma with fluids. The intensity of changes can also vary significantly: from dehydration and slight compaction of rocks to complete replacement of the original composition by new mineral parageneses. On the other hand, the magma itself changes its composition. This occurs most intensively in the marginal parts of the intrusion. The zone of altered igneous rocks in the marginal part of the intrusion is called endocontact zone. Endocontact zones (facies) are characterized not only by changes in the chemical (and, as a result, mineral) composition of rocks, but also by differences in structural and textural features, sometimes saturation xenoliths(captured by magma inclusions) of host rocks. When studying and mapping territories within which several intrusive bodies are combined, the correct identification of phases and facies is of great importance. Each implementation phase are igneous bodies formed by the intrusion of one portion of magma. Bodies belonging to different penetration phases are separated by secant contacts. The diversity of facies can be associated not only with the presence of several phases, but also with the formation of endocontact zones. For endocontact facies, the presence of gradual transitions between rocks is characteristic (due to the decrease in the influence of host rocks with distance from the contact), rather than sharp boundaries.

Volcanic processes

Melts and gases released in the bowels of the planet can reach the surface, leading to volcanic eruption- the process of incandescent or hot solid, liquid and gaseous volcanic products entering the surface. The outlet openings through which volcanic products enter the surface of the planet are called volcanoes (Vulcan is the god of fire in Roman mythology.). Depending on the shape of the outlet, volcanoes are divided into fissure and central. Fissure volcanoes, or linear type have an outlet in the form of an extended crack (fault). The eruption occurs either along the entire crack, or in its individual sections. Such volcanoes are confined to expansion zones lithospheric plates, where as a result of stretching of the lithosphere, deep faults are formed, along which basalt melts are introduced. Active stretch zones are the areas of mid-ocean ridges. The volcanic islands of Iceland, which represent the exit of the Mid-Atlantic Ridge above the ocean surface, are one of the most volcanically active parts of the planet; typical fissure volcanoes are located here.

At volcanoes central type the eruption occurs through the supply pipe-like channel - mouth- passing from the volcanic chamber to the surface. The upper part of the vent that opens to the surface is called crater. Secondary outlet channels can branch off from the main vent along the fissures, giving rise to lateral craters. Volcanic products coming from the crater form volcanic structures. Often, the term "volcano" is understood as a hill with a crater on top, formed by the products of the eruption. The shape of volcanic structures depends on the nature of the eruptions. With calm outpourings of liquid basaltic lavas, flat shield volcanoes. In case of eruption of more viscous lavas and (or) ejections of solid products, volcanic cones are formed. The formation of a volcanic structure can occur as a result of a single eruption (such volcanoes are called monogenic), or as a result of multiple eruptions (volcanoes polygenic). Polygenic volcanoes built from alternating lava flows and loose volcanic material are called stratovolcanoes.

Another important criterion for classifying volcanoes is their level of activity. According to this criterion, volcanoes are divided into:

1. current- erupting or emitting hot gases and waters in the last 3500 years (historical period);
2. potentially active- Holocene volcanoes that erupted 3500-13500 years ago;
3. conditionally extinct volcanoes that did not show activity in the Holocene, but retained their external forms (younger than 100 thousand years old);
4. extinct- Volcanoes, significantly reworked by erosion, dilapidated, not active during the last 100 thousand years.

Schematic representations of the central (top) and shield (bottom) volcanoes (after Rast, 1982)

The products of volcanic eruptions are divided into liquid, solid and gaseous.

solid eruptions presented pyroclastic rocks (from the Greek "ryg" - fire and "klao" - I break, I break) - clastic rocks formed as a result of the accumulation of material ejected during volcanic eruptions. Divided into endoclastitis, formed during the spattering and solidification of lava, and exoclastites formed as a result of crushing of pre-coclastic rocks formed earlier. According to the size of the debris, they are divided into volcanic bombs, lapilli, volcanic sand and volcanic dust. Volcanic sand and volcanic dust are combined under the term volcanic ash.

Volcanic bombs are the largest among pyroclastic formations, their size can reach several meters in diameter. Formed from fragments of lava ejected from the crater. Depending on the viscosity, lavas have different shapes and surface sculptures. Spindle-shaped, drop-shaped, ribbon-shaped and ink-shaped bombs are formed during ejections of liquid (mainly basaltic) lavas. The spindly shape is due to the rapid rotation of low-viscosity lava during flight. The ink-shaped form occurs when ejections of liquid lava to a small height, not having time to harden, when they hit the ground, they are flattened. Tape bombs are formed by squeezing lava through narrow cracks, they are found in the form of fragments of tapes. Specific forms are formed during the flowing of basalt lavas. Thin streams of liquid lava are blown by the wind and harden into threads, such forms are called "Pele's hair" ( Pele - the goddess, according to legend, lives in one of the lava lakes in the Hawaiian Islands). Bombs formed by viscous lavas are characterized by polygonal outlines. Some bombs become covered in a chilled, hardened crust during flight, which is torn apart by gases released from the interior. Their surface takes the form of a "bread crust". Volcanic bombs can also be composed of exoclastic material, especially in explosions that destroy volcanic structures.

Lapilli (from lat. "lapillus" - pebble) are represented by rounded or angular volcanic ejecta, consisting of pieces of fresh lava frozen in flight, old lavas, and rocks alien to the volcano. The size of fragments corresponding to lapilli ranges from 2 to 50 mm.

The smallest pyroclastic material is volcanic ash. Most of the volcanic emissions are deposited near the volcano. As an illustration of this, it is enough to recall the cities of Herculaneum, Pompeii and Stabia covered with ashes during the eruption of Vesuvius in 79. During strong eruptions, volcanic dust can be thrown into the stratosphere and, in suspension, move in air currents for thousands of kilometers.

Originally loose volcanic products (called "tephra") are subsequently compacted and cemented, turning into volcanic tuffs. If fragments of pyroclastic rocks (bombs and lapilli) are cemented by lava, then lava breccias. Specific, deserving special consideration, formations are ignimbrites (from lat. "ignis" - fire and "imber" - downpour). Ignimbrites are rocks composed of sintered acidic pyroclastic material. Their formation is associated with the emergence scorching clouds(or ash flows) - streams of hot gas, lava drops and solid volcanic emissions resulting from intense pulsed gas release during an eruption.

Liquid products of eruptions are lavas. Lava (from ital. "lava" - I flood) is a liquid or viscous molten mass that comes to the surface during volcanic eruptions. Lava differs from magma by a low content of volatile components, which is associated with degassing of magma as it moves towards the surface. The nature of the flow of lava to the surface is determined by the intensity of gas release and the viscosity of the lava. There are three lava flow mechanisms - effusion, extrusion and explosion - and, accordingly, three main types of eruptions. Effusive eruptions are calm outpourings of lava from a volcano. Extrusion- type of eruption accompanied by extrusion viscous lava. Extrusive eruptions can be accompanied by explosive outgassing, leading to the formation of scorching clouds. explosive eruptions- These are eruptions of an explosive nature, due to the rapid release of gases.

Facies of volcanogenic rocks(Field geology, 1989)
1-dykes, 2-sills, laccoliths, 3-explosive subfacies, 4-lava flows (effusive subfacies), 5-domes and obelisks (extrusive subfacies), 6-vent facies, 7-hypabyssal intrusion

Lavas, like their intrusive counterparts, are primarily classified into ultrabasic, basic, intermediate, and felsic. Ultrabasic lavas in the Phanerozoic are very rare, although in the Precambrian (under conditions of a more intense influx of endogenous heat) they were much more widespread. Basic - basaltic - lavas are usually liquid, which is associated with a low content of silica and a high temperature at the exit to the surface (about 1000-1100 0 С and more). Due to their liquid state, they easily give off gases, which determines the effusive nature of eruptions, and the ability to spill over long distances in the form of streams, and in areas with a poorly dissected topography form extensive covers. The structural features of the surface of lava flows make it possible to distinguish two types among them, which are given Hawaiian names. The first type is called pahoehoe(or rope lavas) and forms on the surface of rapidly flowing lavas. The flowing lava is covered with a crust, which, under conditions of active movement, does not have time to acquire significant thickness and quickly wrinkles in waves. These "waves" with the further movement of the lava get off and look like ropes laid side by side.

Video illustrating the formation of a rope surface

The second type, called aa-lava, is characteristic of more viscous basaltic (or other composition) lavas. Due to the slower flow, the crust becomes thicker and breaks into angular fragments; the surface of aa lavas is an accumulation of acute-angled fragments with spike-like or needle-like protrusions.

Formation of AA lavas (Kilauea volcano)

As the silica content increases, the lavas become more viscous and solidify at a lower temperature. If basalt lavas remain mobile at temperatures of the order of 600-700 0 C, then andesitic (middle) lavas solidify already at 750 0 C or more. Usually the most viscous are felsic dacitic and liparitic lavas. Increased viscosity makes it difficult to separate gases, which can lead to explosive eruptions. If the viscosity of the lava is high and the pressure of the gases is relatively low, extrusion occurs. The structure of lava flows is also different. For viscous medium and acidic melts, the formation of blocky lavas is characteristic. blocky lavas outwardly similar to aa-lavas and differ from them in the absence of spiky and needle-shaped protrusions, as well as in the fact that the blocks on the surface have a more regular shape and a smooth surface. The movement of lava flows, the surface of which is covered with blocky lavas, leads to the formation of lava breccia horizons.

When liquid basalt lava is poured into water, the surface of the flows rapidly solidifies, which leads to the formation of peculiar "pipes" inside which the melt continues to move. Squeezing out from the edge of such a “pipe” into the water, a portion of lava acquires a drop-like shape. Since the cooling is uneven and the inner part continues to remain in a molten state for some time, the lava “drops” are flattened under the action of gravity and the weight of the following portions of lava. Heaps of such lavas are called pillow lavas or pillow lavas (from English. "pillow" - pillow).

Gaseous products of eruptions represented by water vapor, carbon dioxide, hydrogen, nitrogen, argon, sulfur oxides and other compounds (HCl, CH 4 , H 3 BO 3 , HF, etc.). The temperature of volcanic gases varies from a few tens of degrees to a thousand or more degrees. In general, high-temperature exhalations (HCl, CO 2 , O 2 , H 2 S, etc.) are associated with magma degassing, low-temperature ones (N 2 , CO 2 , H 2 , SO 2) are formed both by juvenile fluids and due to atmospheric gases and groundwater seeping into the volcano.

With the rapid release of gases from magma or the transformation of groundwater into steam, gas eruptions. During eruptions of this kind, there is a continuous or rhythmic release of gas from the vent, no emissions or very small amounts of ash. Powerful eruptions of gas and steam pierce a channel in the rocks, from which rock fragments are ejected, forming a shaft that borders the crater. Gas eruptions also occur through the vents of existing polygenic volcanoes (an example is the gas eruption of Vesuvius in 1906).

Types of volcanic eruptions

Depending on the nature of the eruptions, several types are distinguished among them. The basis of such a classification was laid by the French geologist Lacroix back in 1908. He identified 4 types, to which the author assigned the names of volcanoes: 1) Hawaiian, 2) Strombolian, 3) Vulcan and 4) Peleian. The proposed classification cannot include all known eruption mechanisms (subsequently, it was supplemented by new types - Icelandic, etc.), but, despite this, it has not lost its relevance today.

Hawaiian-type eruptions characterized by a calm effusive outpouring of very hot liquid basaltic magma under conditions of low gas pressure. Lava under pressure is thrown into the air in the form of lava fountains, from several tens to several hundred meters high (during the eruption of Kilauea in 1959, they reached a height of 450 m). The eruption usually occurs from fissure vents, especially in the early stages. It is accompanied by a small number of weak explosions that splatter lava. Liquid wisps of lava that fall at the base of the fountain in the form of spatter and blot-shaped bombs form spatter cones. Lava fountains, stretching along the crack, sometimes for several kilometers, form a shaft consisting of frozen lava splashes. Liquid lava drops can form Pele's hair. Hawaiian-type eruptions sometimes lead to the formation of lava lakes.
Examples are the eruptions of the volcanoes Kilauea, Hapemaumau in the Hawaiian Islands, Niragongo and Erta Ale in East Africa.

Very close to the described Hawaiian type Icelandic type; similarities are noted both in the nature of the eruptions and in the composition of the lavas. The difference lies in the following. During eruptions of the Hawaiian type, lava forms large dome-shaped massifs (shield volcanoes), and during eruptions of the Icelandic type, lava flows form flat sheets. The outpouring comes from cracks. In 1783, the famous eruption from the Laki fissure about 25 km long occurred in Iceland, as a result of which basalts created a plateau with an area of ​​600 km2. After the eruption, the fissure channel is filled with hardened lava, and a new fissure is formed next to it during the next eruption. As a result of the layering of many hundreds of mantles, extended lava plateaus (extensive ancient basalt plateaus of Siberia, India, Brazil and other regions of the planet) are formed above fissures that change their position in space.

Strombolian type eruptions. The name comes from the volcano Stromboli, located in the Tyrrhenian Sea off the coast of Italy. They are characterized by rhythmic (with interruptions from 1 to 10-12 min) ejections relative to liquid lava. Fragments of lava form volcanic bombs (pear-shaped, twisted, less often spindle-shaped, often flattened when falling) and lapilli; material of ashy dimension is almost absent. Ejections alternate with lava outpourings (compared to eruptions of Hawaiian-type volcanoes, the flows are shorter and thicker, which is associated with a higher viscosity of lavas). Another typical feature is the duration and continuity of development: the Stromboli volcano has been erupting since the 5th century BC. BC.

Volcanic eruptions. The name comes from the island of Vulcano in the group of Aeolian Islands off the coast of Italy. Associated with the eruption of viscous, usually andesitic or dacitic lava with a high content of gases from volcanoes of the central type. The viscous lava solidifies quickly, forming a plug that clogs the crater. The pressure of the gases released from the lava periodically “knocks out” the cork with an explosion. At the same time, a black cloud of pyroclastic material with bombs of the "breadcrust" type is thrown upwards, rounded, ellipsoidal and twisted bombs are practically absent. Sometimes explosions are accompanied by outpourings of lava in the form of short and powerful streams. Then the plug is formed again, and the cycle repeats.
Eruptions are separated by periods of complete rest. Eruptions of the Vulcan type are characteristic of the Avachinsky and Karymsky volcanoes in Kamchatka. The eruptions of Vesuvius are also close to this type.

Peleian-type eruptions. The name comes from the volcano Mont Pelee on the island of Martinique in the Caribbean. Occur when very viscous lava enters volcanoes of the central type, which brings it closer to the eruption of the Vulcan type. The lava solidifies in the vent and forms a powerful plug, which is squeezed out in the form of a monolithic obelisk (extrusion occurs). On the Mont Pele volcano, the obelisk has a height of 375 m and a diameter of 100 m. The hot volcanic gases accumulating in the vent sometimes escape through the frozen cork, leading to the formation of scorching clouds. The scorching cloud that arose during the eruption of Mont Pele on May 8, 1902 had a temperature of about 800 ° C and, moving down the slope of the volcano at a speed of 150 m / s, it destroyed the city of Saint-Pierre with 26,000 inhabitants.
A similar type of eruption was often observed near volcanoes on the island of Java, in particular near the Merapi volcano, and also in Kamchatka near the Bezymyanny volcano.

VOLCANISM, a set of endogenous processes associated with the formation and movement of magma in the bowels of the Earth and its eruption on the land surface, the bottom of the seas and oceans. It is an integral part of magmatism. In the process of volcanism, magma chambers are formed in the depths of the earth, the rocks around which can change under the influence of high temperature and the chemical action of magma. When the magmatic melt reaches the Earth's surface, the most spectacular manifestation of volcanism is observed - a volcanic eruption, which consists in the outpouring or gushing of liquid lava (effusion), squeezing out viscous lava (extrusion), destruction of the volcanic structure by an explosion and ejection of solid products of volcanic activity (explosion). As a result of eruptions different types and forces, volcanoes of various shapes and sizes are formed, volcanic rocks are formed. Volcanism is associated with phenomena that precede (harbingers), accompany and complete (post-volcanic phenomena) volcanic eruptions. Harbingers observed from several hours to several centuries before the eruption include some volcanic earthquakes, deformations of the earth's surface and volcanic structures, acoustic phenomena, changes in geophysical fields, composition and intensity of fumarolic gases (from active volcanoes), etc.

Phenomena observed during eruptions: volcanic explosions, associated shock waves, sharp jumps in atmospheric pressure, electrified eruptive (eruptive) clouds with Elmo fires, lightning, volcanic ashfalls and acid rains, the occurrence of lahars (mudstone flows), the formation of a tsunami - during falling into the water of huge volumes of landslide and explosive deposits. Volcanic phenomena also include a decrease in the level of solar radiation and temperature, the appearance of purple sunsets caused by clouding of the atmosphere by volcanic dust and aerosols during catastrophic explosive eruptions. After eruptions, post-volcanic phenomena are observed associated with the cooling of the magma chamber - outflows of volcanic gases (fumaroles) and thermal waters (thermal springs, geysers, etc.).

According to the place of manifestation, volcanism is distinguished terrestrial, underwater and subaerial (underwater-surface); according to the composition of the eruption products - sequentially differentiated basalt-andesite-rhyolite, contrast-differentiated basalt-rhyolite (bimodal), alkaline, alkaline-ultrabasic, basic, acidic and other volcanism is most characteristic of the convergent boundaries of lithospheric plates, where in the process of their counter interaction volcanic belts (island-arc and marginal-continental) are formed above the zone of subduction (subduction) of one plate under another or in the area of ​​collision (collision) of their continental parts. Volcanism is also widely manifested at the divergent boundaries of lithospheric plates, confined to mid-ocean ridges, where, as the plates move apart in the course of underwater volcanic activity, a new formation of the oceanic crust occurs. Volcanism is also characteristic of the inner parts of lithospheric plates - structures of hot spots, continental rift systems, trap provinces of continents, and intraoceanic basalt plateaus.

Volcanism began in the early stages of the Earth's development and became one of the main factors in the formation of the lithosphere, hydrosphere and atmosphere. The development of all three shells due to volcanism continues: the volume of rocks in the lithosphere increases annually by more than 5-10 km 3, and an average of 50-100 million tons of volcanic gases per year enter the atmosphere, some of which is spent on the transformation of the hydrosphere. Many deposits of metallic (gold, silver, non-ferrous metals, arsenic, etc.) and non-metallic (sulfur, borates, natural building materials, etc.) minerals, as well as geothermal resources, are genetically associated with volcanism.

Manifestations of volcanism have been identified on all planets of the terrestrial group. On Mercury, Mars, and the Moon, volcanism has probably already ended (or almost ended), and intensively continues only on Venus. At the end of the 20th - beginning of the 21st century, volcanic forms and ongoing volcanic activity were discovered on the satellites of Jupiter and Saturn - Europa, Io, Callisto, Ganymede, Titan. On Europa and Io, a specific type of volcanism is noted - cryovolcanism (eruption of ice and gas).

Lit .: Melekestsev IV Volcanism and relief formation. M., 1980; Rast H. Volcanoes and vulcanism. M., 1982; Vlodavets V. I. Handbook of volcanology. M., 1984; Markhinin E.K. Volcanism. M., 1985.

INTRODUCTION

The phenomena of volcanic eruptions accompany the entire history of the Earth. It is likely that they influenced the climate and biota of the Earth. Currently, volcanoes are present on all continents, and some of them are active and represent not only a spectacular sight, but also formidable dangerous phenomena.

The volcanoes of the Mediterranean were associated with the deity of fire on Etna and the volcanoes of the islands of Vulcano and Santorini. It was believed that the Cyclopes worked in the underground workshops.

Aristotle considered them to be the result of the action of compressed air in the voids of the Earth. Empedocles believed that the cause of the action of volcanoes is the material melted in the depths of the Earth. In the 18th century, a hypothesis arose that a thermal layer exists inside the Earth, and as a result of folding phenomena, this heated material is sometimes brought to the surface. In the 20th century, factual material is first accumulated, and then ideas arise. They have become most productive since the emergence of the theory of lithospheric plate tectonics. Satellite studies have shown that volcanism is a cosmic phenomenon: traces of volcanism were found on the surface of the Moon and Venus, and active volcanoes were found on the surface of Jupiter's moon Io.

It is also important to consider volcanism from the point of view of the global impact on the geographic envelope in the process of its evolution.

The purpose of the work is to study the processes of volcanism on Earth and its geographical consequences.

In accordance with the goal, the following tasks are solved in the work:

1) Definitions are given: volcanism, volcano, volcano structure, types of volcanic eruptions;

2) The main volcanic belts of the Earth are being studied;

3) Post-volcanic phenomena are being studied;

4) The role of volcanism in the transformation of the relief and climate of the Earth is characterized.

The work used educational materials, scientific publications, Internet resources.

CHAPTER 1. GENERAL CONCEPTS ABOUT VOLCANISM

1.1 The concept of the process of volcanism

A volcano is a place where magma or mud comes to the surface from a vent. In addition, it is possible for magma to erupt along cracks and gases to escape after an eruption outside the volcano. A volcano is also called a form of relief that arose during the accumulation of volcanic material.

Volcanism is a set of processes associated with the appearance of magma on the surface of the Earth. If magma appears on the surface, then this is an effusive eruption, and if it remains at a depth, this is an intrusive process.

If magmatic melts burst to the surface, then volcanic eruptions occurred, which were mostly calm in nature. This type of magmatism is called effusive.

Often, volcanic eruptions are explosive in nature, in which magma does not erupt, but explodes, and cooled melt products, including frozen droplets of volcanic glass, fall onto the earth's surface. Such eruptions are called explosive.

Magma is a melt of silicates located in the deep zones of a sphere or mantle. It is formed at certain pressures and temperatures and, from a chemical point of view, is a melt that contains silica (Si), oxygen (O 2) and volatile substances present in the form of gas (bubbles) or solution and melt.

The viscosity of magmas depends on the composition, pressure, temperature, gas and moisture saturation.

According to the composition, 4 groups of magmas are distinguished - acidic, basic, alkaline and alkaline earth.

According to the depth of formation, 3 types of magmas are distinguished: pyromagma (deep melt rich in gas with T ~ 1200°C, very mobile, speed on slopes up to 60 km/h), hypomagma (at large P, insufficiently saturated and inactive, T = 800-1000 °С, as a rule, acidic), epimagma (degassed and not erupted).

Magma generation is a consequence of fractional melting of mantle rocks under the influence of heat input, decompaction, and an increase in water content in certain zones of the upper mantle (water can reduce melting). This occurs: 1) in rifts, 2) in subduction zones, 3) above hot spots, 4) in transform fault zones.

Magma types determine the nature of the eruption. It is necessary to distinguish between primary and secondary magmas. Primary ones occur at different depths of the earth's crust and upper mantle and, as a rule, have a homogeneous composition. However, moving into the upper levels of the earth's crust, where the thermodynamic conditions are different, primary magmas change their composition, turning into secondary ones and forming different magmatic series. This process is called magmatic differentiation.

If a liquid magmatic melt reaches the earth's surface, it erupts. The nature of the eruption is determined by: the composition of the melt; temperature; pressure; the concentration of volatile components; water saturation. One of the most important causes of magma eruptions is its degassing. It is the gases contained in the melt that serve as the "engine" that causes the eruption.

1.2 Structure of volcanoes

Magma chambers below volcanoes are usually roughly circular in plan, but it is not always possible to determine whether their three-dimensional shape approaches spherical or is elongated and flattened. Some active volcanoes have been intensively studied using seismometers to determine the sources of vibration caused by the movement of magma or gas bubbles, as well as to measure the deceleration of artificially generated seismic waves passing through the magma chamber. In some cases, the existence of several magma chambers at different depths has been established.

In classically shaped volcanoes (a cone-shaped mountain), the magma chamber closest to the surface is usually associated with a vertical cylindrical passage (several meters to tens of meters in diameter), which is called a supply channel. Magma erupted from volcanoes of this shape usually has a basaltic or andesitic composition. The place where the supply channel reaches the surface is called a vent and is usually located at the bottom of a depression on top of a volcano called a crater. Volcanic craters are the result of a combination of several processes. A powerful eruption can expand the vent and turn it into a crater due to the crushing and ejection of surrounding rocks, and the bottom of the crater can sink due to voids left by the eruption and magma leakage. In addition, the height of the rims of the crater may increase as a result of the accumulation of material ejected during explosive eruptions. Volcano vents are not always exposed to the sky, but are often blocked by debris or solidified lava, or hidden under lake waters or accumulated rainwater.

A large, shallow magma chamber containing rhyolitic magma is often connected to the surface by a ring fault rather than a cylindrical conduit. Such a fault allows the overlying rocks to move up or down, depending on the change in the volume of magma within the chamber. A depression formed as a result of a decrease in the volume of magma below (for example, after an eruption), volcanologists call a caldera. The same term is used for any volcanic crater larger than 1 km in diameter, since craters of this size are formed more by subsidence of the earth's surface than by explosive ejection of rocks.

Rice. 1.1. The structure of the volcano 1 - volcanic bomb; 2 - canonical volcano; 3 - layer of ash and lava; 4 - dike; 5 - the mouth of the volcano; 6 - strength; 7 – magma chamber; 8 - shield volcano.

1.3 Types of volcanic eruptions

volcanism climate relief magma

Liquid, solid and gaseous volcanic products, as well as forms of volcanic structures, are formed as a result of eruptions of various types, due to the chemical composition of magma, its gas saturation, temperature and viscosity. There are different classifications of volcanic eruptions, among them there are common types for all.

The Hawaiian type of eruptions is characterized by ejections of very liquid, highly mobile basaltic lava, which form huge flat shield volcanoes (Fig. 1.2.). Pyroclastic material is practically absent, often lava lakes are formed, which, gushing to a height of hundreds of meters, throw out liquid pieces of lava such as cakes, creating shafts and spatter cones. Lava flows of small thickness spread over tens of kilometers.

Sometimes changes occur along faults in a series of small cones (Figure 1.3).

Rice. 1.2. Eruption of liquid basaltic lava. Volcano Kilauea

Strombolian type(from Stromboli volcano in the Aeolian Islands north of Sicily) eruptions are associated with more viscous basic lava, which is ejected by explosions of different strength from the vent, forming relatively short and more powerful flows (Fig. 1.3).

Rice. 1.3. Strombolian type eruption

Explosions form cinder cones and plumes of twisted volcanic bombs. Stromboli Volcano regularly ejects a "charge" of bombs and pieces of red-hot slag into the air.

plinian type(volcanic, Vesuvian) got its name from the Roman scientist Pliny the Elder, who died during the eruption of Vesuvius in 79 AD. (3 large cities were destroyed - Herculaneum, Stabia and Pompeii). characteristic feature eruptions of this type are powerful, often sudden explosions, accompanied by emissions of huge amounts of tephra, forming ash and pumice flows. It was under the high-temperature tephra that Pompeii Stabia was buried, and Herculaneum was littered with mud-stone flows - lahars. As a result of powerful explosions, the near-surface magma chamber emptied the summit part of Vesuvius, collapsed and formed a caldera, into which, 100 years later, a new volcanic cone grew - modern Vesuvius. Plinian eruptions are very dangerous and occur suddenly, often without any prior preparation. The grandiose explosion in 1883 of the Krakatoa volcano in the Sunda Strait between the islands of Sumatra and Java belongs to the same type, the sound from which was heard at a distance of up to 5000 km, volcanic ash reached almost 100 km height. The eruption was accompanied by the emergence of huge (25-40 m) waves in the tsunami ocean, in which about 40 thousand people died in coastal areas. A giant caldera formed on the site of the Krakatau group of islands.

T.I.FROLOV
Volcanic rocks are products of a deep process - volcanism. According to the definition of the famous volcanologist A. Jaggar, volcanism is a set of phenomena occurring in the earth's crust and under it, leading to a breakthrough of molten masses through the solid crust. Volcanism is associated with the flow of hot deep gases - fluids from the bowels of the Earth. Fluids contribute to the decompaction and local rise of deep matter, which, as a result of a decrease in pressure (decompression), begins to partially melt, forming deep diapirs - sources of magmatic melts. Depending on the intensity of heating, the formation of melts occurs at different levels of the mantle and the earth's crust, starting from depths of 300 - 400 km.

Volcanology is the science of volcanoes and their products (volcanic rocks), the causes of volcanism due to geodynamic, tectonic and physico-chemical processes occurring in the bowels of the Earth. In addition to the actual geological sciences: historical geology, geotectonics, petrography, mineralogy, lithology, geochemistry and geophysics, volcanology uses data from geography, geomorphology, physical chemistry, and partly from astronomy, since volcanism is a planetary phenomenon. Being products of deep (endogenous) processes, volcanoes that form on the Earth's surface affect environment, atmosphere and hydrosphere, precipitation formation. Volcanology, as it were, focuses the problems linking the processes of internal and external energy of the Earth.

The general classification of all igneous rocks, including volcanic ones, is based on their chemical composition and, first of all, on the content and ratio of silica and alkalis in the rocks (Fig. 1). According to the content of silica, the most common oxide in igneous rocks, the latter are divided into four groups: ultrabasic (30 - 44% SiO2), basic (44 - 53%), medium (53 - 64%), acidic (64 - 78%). Another important feature of the classification is the alkalinity of rocks, which is estimated by the sum of the contents of Na2O + K2O. On this basis, rocks of normal alkalinity and alkaline are distinguished.

The most widely distributed among the volcanic rocks of the Earth are the main rocks - basalts, which are derivatives of the mantle substance and are found both in the oceans and on the continents. They can be compared with the "blood" of our planet, which appears in any violation of the earth's crust. Depending on the geological position, basalts differ in composition. Most of them belong to rocks of normal alkalinity. These are lime-rich low-alkaline (tholeiitic) and calc-alkaline basalts. Less common are alkaline basalts undersaturated with silica. During differentiation, basaltic magmas give rise to a series of rocks (tholeiitic, calc-alkaline, and alkaline), united by origin from a single magma, retaining common features with parental basaltic magmas, up to extremely acidic ones. Among the intrusive rocks, granites are the most common. They belong to the group of silicic rocks, in the formation of which the substance of the earth's crust plays a significant role. The rocks of average composition, which are represented mainly by volcanic andesites, are less common and only in the mobile belts of the Earth. At the same time, the average composition of the earth's crust corresponds to andesites, and not to basalts or granites, corresponding to a mixture of these latter in a ratio of 2: 1.

HOW VOLCANISM EVOLVED IN THE HISTORY OF THE EARTH

The earliest processes of volcanism are synchronous with the formation of the Earth as a planet. In all likelihood, already at the stage of accretion (the concentration of planetary matter due to gas-dust nebulae and the collision of solid cosmic debris - planetosimals) its heating took place. The release of energy due to accretion and gravitational contraction turned out to be sufficient for its initial, partial or complete melting, with the subsequent differentiation of the Earth into shells. A little later, these sources of heating were joined by the release of heat by radioactive elements. The concentration of the iron-stony mass of the Earth, as well as on other planets solar system, was accompanied by the separation of a gaseous, predominantly hydrogen, shell, which it later lost during the period of maximum solar activity, in contrast to the large, distant planets of the Jupiter group. This is evidenced by the impoverishment of modern earth's atmosphere rare inert gases - neon and xenon in comparison with cosmic matter.

According to A.A. Marakushev, the differentiation of the iron-stony mass of the Earth, similar in composition to meteorites - chondrites and completely melted under high pressure of a hydrogen gas shell, led to a high concentration of essentially hydrogen fluids (volatile components in the supercritical state) in the metallic (iron-nickel) core that began to separate. Thus, the Earth acquired a large fluid reserve in its bowels, which determined its subsequent, unique in its duration, in comparison with other planets, endogenous activity. As the Earth consolidated in the direction from its outer shells to the center, the internal fluid pressure increased and periodic degassing occurred, accompanied by the formation of magmatic melts that came to the surface when the frozen crust cracked. Thus, the earliest volcanism, which was characterized by an explosive, highly explosive nature, was associated with the beginning of the cooling of the Earth and was accompanied by the formation of the atmosphere. According to other ideas, the primary atmosphere, formed at the stage of accretion, was subsequently preserved, gradually evolving in its composition. One way or another, approximately 3.8 - 3.9 billion years ago, when the temperature on the Earth's surface and in the adjacent parts of the atmosphere dropped below the boiling point of water, the hydrosphere was formed. The presence of the atmosphere and hydrosphere made possible the further development of life on Earth. At first, the atmosphere was poor in oxygen until the simplest forms of life that produced it appeared, which happened about 3 billion years ago (Fig. 2).

The composition of the earliest volcanic rocks of the Earth, now completely reworked by subsequent processes, can be judged by comparing it with other terrestrial planets, in particular with our relatively well-studied satellite, the Moon. The Moon is a planet of more primitive development, which has used up its fluid reserves early and, as a result, has lost its endogenous activity. It is currently a "dead" planet. The absence of a metallic core in it indicates that the processes of its differentiation into shells stopped early, and a negligibly weak magnetic field indicates the complete solidification of its interior. At the same time, the presence of fluids in the early stages of the development of the Moon is evidenced by gas bubbles in lunar volcanic rocks, which consist mainly of hydrogen, which indicates their high reduction.

The most ancient, currently known rocks of the Moon, developed on the surface of the lunar crust on the so-called lunar continents, have an age of 4.4 - 4.6 billion years, which is close to the estimated age of the formation of the Earth. They are crystallized at shallow depths or on the surface, rich in high-calcium feldspar - anorthite - light-colored basic rocks, which are commonly called anorthosites. The rocks of the lunar continents were subjected to intense meteorite bombardment with the formation of fragments, partially melted down and mixed with meteorite matter. As a result, numerous impact craters coexisting with craters of volcanic origin were formed. It is assumed that the lower parts of the lunar crust are composed of rocks of a more basic, low-silica composition, close to stony meteorites, and anorthosites are directly underlain by anorthite gabbro (eucrites). On Earth, the association of anorthosites and eucrites is known in the so-called layered mafic intrusions and is the result of differentiation of basaltic magma. Since the physical and chemical laws that determine differentiation are the same throughout the Universe, it is logical to assume that on the Moon the most ancient crust of lunar meteorites was formed as a result of early melting and subsequent differentiation of the magmatic melt that formed the upper shell of the Moon in the form of the so-called "lunar ocean of magma". The differences in the processes of differentiation of lunar magmas from terrestrial ones lie in the fact that on the Moon it extremely rarely reaches the formation of high-silica felsic rocks.

Later, large depressions formed on the Moon, called lunar seas, filled with younger (3.2 - 4 billion years) basalts. On the whole, these basalts are close in composition to the basalts of the Earth. They are distinguished by a low content of alkalis, especially sodium, and the absence of iron oxides and minerals containing the OH hydroxyl group, which confirms the loss of volatile components by the melt and the reducing environment of volcanism. Feldspar-free rocks known on the Moon - pyroxenites and dunites, probably compose the lunar mantle, being either a remnant from the melting of basalt rocks (the so-called restite), or their heavy differentiate (cumulate). The early crust of Mars and Mercury is similar to the cratered crust of the lunar continents. On Mars, moreover, later basaltic volcanism is widely developed. There is also a basaltic crust on Venus, but data on this planet is still very limited.

The use of data from comparative planetology allows us to state that the formation of the early crust of the terrestrial planets occurred as a result of the crystallization of magmatic melts that underwent greater or lesser differentiation. The cracking of this frozen proto-crust with the formation of depressions was later accompanied by basaltic volcanism.

Unlike other planets, Earth did not have the earliest crust. More or less reliably, the history of the Earth's volcanism can be traced only from the Early Archean. The oldest known age dates belong to Archean gneisses (3.8 - 4 billion years) and grains of the mineral zircon (4.2 - 4.3 billion years) in metamorphosed quartzites. These dates are 0.5 billion years younger than the formation of the Earth. It can be assumed that all this time the Earth developed similarly to other planets of the terrestrial group. From about 4 billion years ago, a continental proto-crust was formed on the Earth, consisting of gneisses, predominantly of igneous origin, differing from granites in lower silica and potassium contents and called "gray gneisses" or the TTG association, after the name of the three main igneous rocks corresponding to the composition of these gneisses : tonalites, trondhjemites and granodiorites, subsequently subjected to intense metamorphism. However, "gray gneisses" hardly represented the primary crust of the Earth. It is also unknown how widespread they were. In contrast to the much less silicate rocks of the lunar continents (anorthosites), such large volumes of felsic rocks cannot be obtained by differentiation of basalts. The formation of "gray gneisses" of igneous origin is theoretically possible only during the remelting of rocks of basalt or komatite-basalt composition, which, due to their gravity, have sunk to the deep levels of the planet. Thus, we come to the conclusion about the basaltic composition of the crust, which is earlier than the "gray-gneiss" known to us. The presence of an early basaltic crust is confirmed by finds in Archean "gray" gneisses of older metamorphosed mafic blocks. It is not known whether the parent magma of the basalts that formed the early crust of the Earth underwent differentiation to form lunar-like anorthosites, although this is theoretically quite possible. Intensive multi-stage differentiation of planetary matter, which led to the formation of acid granitoid rocks, became possible due to the water regime established on Earth due to the large fluid reserve in its interior. Water promotes differentiation and is very important for the formation of acidic rocks.

Thus, during the earliest (Katarchean) and Archean time, mainly as a result of magmatism processes, which were joined by sedimentation after the formation of the hydrosphere, the earth's crust was formed. It began to be intensively processed by the products of active degassing of the early Earth with the addition of silica and alkalis. Degassing was due to the formation of the solid inner core of the Earth. It caused the processes of metamorphism up to melting with a general acidification of the composition of the crust. So, already in the Archean, the Earth had all the hard shells inherent in it - the crust, the mantle and the core.

The growing differences in the degree of permeability of the crust and upper mantle, which were due to differences in their thermal and geodynamic regimes, led to the heterogeneity of the composition of the crust and to the formation of its different types. In areas of compression, where degassing and rising to the surface of emerging melts was difficult, the latter experienced intense differentiation, and the previously formed basic volcanic rocks, being compacted, sank to a depth and were remelted. A protocontinental two-layer crust was formed, which had a contrasting composition: its upper part was composed mainly of acid volcanic and intrusive rocks, processed by metamorphic processes into gneisses and granulites, the lower part was composed of basic rocks, basalts, komatites and gabbroids. Such a crust was characteristic of protocontinents. The proto-oceanic crust, which had a predominantly basaltic composition, formed in the extension areas. Along the breaks in the protocontinental crust and in the zones of its junction with the protooceanic, the first mobile belts of the Earth (protogeosynclines) were formed, characterized by increased endogenous activity. Even then, they had a complex structure and consisted of less mobile uplifted zones that had undergone intense high-temperature metamorphism, and zones of intense extension and subsidence. The latter were called greenstone belts, since the rocks composing them acquired green color as a result of processes of low-temperature metamorphism. The extensional setting of the early stages of the formation of mobile belts was replaced with the prevailing compressional setting in the course of evolution, which led to the appearance of felsic rocks and the first rocks of the calc-alkaline series with andesites (see Fig. 1). The mobile belts, which had completed their development, attached themselves to the areas of development of the continental crust and increased its area. According to modern concepts, from 60 to 85% of the modern continental crust was formed in the Archaean, and its thickness was close to modern, that is, it was about 35 - 40 km.

At the turn of the Archean and Proterozoic (2700 - 2500 million years) a new stage began in the development of volcanism on Earth. Melting processes became possible in the thick crust formed by that time, and more acidic rocks appeared. Their composition has changed significantly, primarily due to an increase in the content of silica and potassium. Real potassium granites, which were smelted from the bark, were widely used. Intense differentiation of mantle basaltic melts under the action of fluids in mobile belts, accompanied by interaction with the crustal material, led to an increase in the volume of andesites (see Fig. 1). Thus, in addition to mantle volcanism, crustal and mixed mantle-crustal volcanism became increasingly important. At the same time, due to the weakening of the processes of degassing of the Earth and the heat flow associated with them, such high degrees of melting in the mantle, which could lead to the formation of ultrabasic komatite melts (see Fig. 1), turned out to be impossible, and if they did occur, then rarely rose to the surface due to their high density compared to the earth's crust. They underwent differentiation in intermediate chambers and their derivatives, less dense basalts, fell to the surface. The processes of high-temperature metamorphism and granitization also became less intense, which acquired not an areal, but a local character. In all likelihood, two types of the earth's crust were finally formed at that time (Fig. 3), corresponding to continents and oceans. However, the time of formation of the oceans has not yet been finally determined.

In the subsequent stage of the development of the Earth, which began 570 million years ago and is called the Phanerozoic, those trends that appeared in the Proterozoic were further developed. Volcanism is becoming more and more diverse, acquiring clear distinctions in oceanic and continental segments. In extension zones in the oceans (mid-ocean rift ridges), tholeiitic basalts erupt, and in similar extension zones on the continents (continental rifts), they are joined by and often dominated by alkaline volcanic rocks. Mobile belts of the Earth, called geosynclinal, are magmatically active for tens and hundreds of millions of years, starting from early tholeiite-basalt volcanism, which together with ultrabasic intrusive rocks form ophiolite associations under extensional conditions. Later, as extension changes into compression, they give way to contrasting basalt-rhyolite and calc-alkaline andesitic volcanism, which flourished in the Phanerozoic. After folding, the formation of granites and orogeny (growth of mountains), volcanism in the mobile belts becomes alkaline. Such volcanism usually ends their endogenous activity.

The evolution of volcanism in the Phanerozoic mobile belts repeats that in the development of the Earth: from homogeneous basalt and contrasting basalt-rhyolite associations that prevailed in the Archaean, to continuous silicic acidity with large volumes of andesites, and, finally, to alkaline associations, which are practically absent in the Archaean. This evolution, both in individual belts and on the Earth as a whole, reflects a general decrease in permeability and an increase in the rigidity of the earth's crust, which determines a higher degree of differentiation of mantle magmatic melts and their interaction with the material of the earth's crust, a deepening of the level of magma formation and a decrease in the degree of melting. The foregoing is connected with the change in the internal parameters of the planet, in particular with the general decrease in the global heat flux from its interior, which is estimated to be 3–4 times less than in the early stages of the Earth's development. Correspondingly, local upward flows of fluids resulting from periodic degassing of the subsoil also decrease. It is they that cause the heating of individual areas (movable belts, rifts, etc.) and their magmatic activity. These flows are formed in connection with the accumulation of light components at the crystallization front of the outer liquid core in separate protrusions-traps that float up, forming convective jets.

Endogenous activity is periodic. It caused the presence of large pulsations of the Earth with alternating predominance of basic and ultrabasic magmatism, fixing extension, and calc-alkaline volcanism, granite formation and metamorphism, fixing the predominance of compression. This periodicity determines the presence of magmatic and tectonic cycles, which, as it were, are superimposed on the irreversible development of the Earth.

WHERE DO VOLCANO EVENTS OCCUR IN CENOSIOIC?

The geological structures where volcanic rocks are formed in the youngest, Cenozoic, stage of the Earth's development, which began 67 million years ago, are located both within the oceanic and continental segments of the Earth. The former include mid-ocean ridges and numerous volcanoes on the ocean floor, the largest of which form oceanic islands (Iceland, Hawaii, etc.). All of them are characterized by an environment of high permeability of the earth's crust (Fig. 4). On the continents, in a similar setting, volcanoes erupt, associated with large extension zones - continental rifts (East African, Baikal, etc.). In conditions of predominant compression, volcanism occurs in mountain structures, which are currently active intracontinental mobile belts (Caucasus, Carpathians, etc.). The mobile belts on the margins of the continents (the so-called active margins) are peculiar. They are developed mainly along the periphery of the Pacific Ocean, and in its western margin, as in the ancient mobile belts, they combine zones of predominant compression - island arcs (Kurilo-Kamchatka, Tonga, Aleutian, etc.) and zones of intense extension - rear marginal seas (Japanese, Philippine, Coral, etc.). In the mobile belts of the eastern margin of the Pacific Ocean, the extension is less significant. On the edge of the American continent there are mountain ranges (Andes, Cordillera), which are analogues of island arcs, in the rear of which there are continental depressions - analogues of marginal seas, where the stretching situation prevails. Under conditions of high permeability, as always in the history of the Earth, mantle melts erupt, and in oceanic structures they have predominantly normal alkalinity, while in continental structures they have increased and high. In settings of predominant compression on the continental crust, in addition to mantle rocks, rocks of mixed mantle-crustal (andesites) and crustal (some felsic volcanics and granites) origin are widespread (Fig. 5).

If we take into account the features of the modern stage of the Earth's development, which include the high intensity of the ocean formation process and the widespread development of rift zones on the continents, it becomes clear that in the Cenozoic stage of development, extension predominates and, as a result, the associated mantle, mainly basalt volcanism, is widespread. , especially intense in the oceans.

HOW VOLCANISM IS TRANSFORMING THE EARTH'S CRUST

Even at the beginning of the last century, it was noticed that rocks form regularly repeating associations, called geological formations, more closely related to geological structures than individual rocks. Rows of formations that replace each other in time are called temporary, and those that replace each other in space are called lateral formation rows. Together, they make it possible to decipher the main stages in the development of geological structures and are important indicators in the restoration of geological settings of the past. Volcanic formations, including volcanic rocks, products of their washing and redeposition, and often sedimentary rocks, are more convenient to use for these purposes than intrusive ones, since they are members of layered sections, which makes it possible to accurately determine the time of their formation.

There are two types of series of volcanogenic formations. The first, called homodromous, begins with basic rocks - basalts, giving way to formations with gradually increasing volumes of medium and acidic rocks. The second series is antidromic, beginning with formations of predominantly felsic composition with an increase in the role of basic volcanism towards the end of the series. The first, therefore, is associated with mantle volcanism and high permeability of the crust, and only as the permeability decreases and the crust is heated by deep heat, the latter begins to participate in magma formation. The antidromic series is characteristic of geological structures with thick, poorly permeable continental crust, when direct penetration of mantle melts to the surface is difficult. They interact with the material of the earth's crust the more intensely, the more it warms up. Basalt formations appear only later, when the crust cracks under the pressure of mantle magmas.

Homodromic series of volcanic formations are characteristic of the oceans and geosynclinal mobile belts and reflect, respectively, the formation of the oceanic and continental crust. Antidromic series are characteristic of structures that are laid down on the continental crust heated after the previous cycle of magmatism. Typical examples are marginal seas and continental rifts that appear immediately after orogeny (epiorogenic rifts). From the beginning of magmatic cycles, mantle-crustal and crustal rocks of intermediate and acidic composition appear in them, giving way to basic ones as the continental crust is destroyed (destruction). If this process goes far enough, as, for example, in marginal seas, then the continental crust, as a result of a complex set of processes, including extension, is replaced by the oceanic one.

The processes of transformation of the crust in long-term developing mobile belts of the geosynclinal type, which are very heterogeneous in their structures, are the most diverse and multidirectional. They contain structures with both an extension regime and a compression regime, and the type of crustal transformation depends on the predominance of certain processes. However, as a rule, the processes of formation of a new continental crust dominate, which attaches to the previously formed one, increasing its area. But this does not always happen, since, despite the vast areas occupied by mobile belts of different ages, the vast majority of the continental crust is of Archean age. Consequently, the destruction of the already formed continental crust also took place within the mobile belts. This is also evidenced by the cutting of the structures of the margins of the continents by the oceanic crust.

Volcanism reflects the evolution of the Earth during its geological history. The irreversibility of the development of the Earth is expressed in the disappearance or sharp decrease in the volume of some types of rocks (for example, comatites) along with the appearance or increase in the volume of others (for example, alkaline rocks). The general trend of evolution indicates a gradual attenuation of the deep (endogenous) activity of the Earth and an increase in the processes of processing of the continental crust during magma formation.

Volcanism is an indicator of the geodynamic conditions of extension and prevailing compression that exist on Earth. Typomorphic for the former is mantle volcanism, for the latter, mantle-crustal and crustal.

Volcanism reflects the presence of cyclicity against the background of the general irreversible development of the Earth. Cyclicity determines the repeatability of formation series in one separately taken and in different time, but the same type of geological structures.

The evolution of volcanism in the geostructures of the Earth is an indicator of the formation of the earth's crust and its destruction (destruction). These two processes continuously transform the earth's crust, carrying out the exchange of matter between the solid shells of the earth - the crust and mantle.

* * *
Tatyana Ivanovna Frolova - Professor of the Department of Petrology, Faculty of Geology, Lomonosov Moscow State University M.V. Lomonosov, Honored Professor of Moscow State University, full member of the Academy of Natural Sciences (RANS) and the International Academy of Sciences of Higher Education; specialist in the field of volcanism of the mobile belts of the Earth - ancient (Urals) and modern (West Pacific active margin); author of monographs: "Geosynclinal volcanism" (1977), "Origin of volcanic series of island arcs" (1987), "Magmatism and transformation of the earth's crust of active margins" (1989), etc.

VOLCANISM ON THE EARTH AND ITS GEOGRAPHICAL CONSEQUENCES

The course work was completed by a student of the 1st year of the 1st group Bobkov Stepan

Ministry of Education of the Republic of Belarus

Belarusian State University

Faculty of Geography

Department of General Geography

ANNOTATION

Volcanism, types of volcanic eruptions, composition of lavas, effusive, extrusive process.

Types are being studied: volcanoes, volcanic eruptions. Their geographical distribution is considered. The role of volcanism in the formation of the earth's surface.

Bibliography 5 titles, Fig. 3, p. 21

ANATACY

Babkov S.U. Volcanism on the earth and yago geographic findings (cursive work).-Mn., 2003.-21s.

Volcanism, types of volcanic extrusion, natural lava, effusive, extrusive processes.

Pravodzіtstsa dasledvanne typaў: volcanic, volcanic vyarzhennyaў razglyadetstsa іh geographic size of the cavalry. The role of volcanism in the pharmaceutical preparation of the earth's surface.

Bibliyagr.5 titles, small.3, old.21

Bobkov S.V. Volcanism on the Earth and main of it in the geography sphere. (cours paper).-Minsk, 2003. -21 p.

Volcanism , types of volcanism effusion, contest of lavs, effusion , extrusive edifice.

The tips of volcanous and effusion have been researched. Role of volcanism in forming of earth’s surface.

The bibliograthy 5 references, pictures 3, pages 21.

INTRODUCTION

Volcanic activity, which is one of the most formidable natural phenomena, often brings great disasters to people and the national economy. Therefore, it must be borne in mind that although not all active volcanoes cause misfortunes, nevertheless, each of them can be a source of negative events to one degree or another, volcanic eruptions are of varying strength, but only those accompanied by death are catastrophic. and material values.

It is also important to consider volcanism from the point of view of the global impact on the geographic envelope in the process of its evolution.

The goal is to study volcanism as the most important manifestation of endogenous processes, geographical distribution.

You also need to follow:

1) classification of eruptions.

2) types of volcanoes.

3) composition of erupting lavas.

4) The consequences of the activity of volcanism for the geographic envelope.

I, as the author of this term paper, want to draw the attention of others on this issue, to show the global nature of this process, the causes and consequences of the impact of volcanism on the geographic envelope. It's no secret that each of us would like to be close to an erupting volcano. At least once to feel our microscopicity compared to the natural forces of the Earth. Moreover, for each geographer, expeditions and research should remain the main source of knowledge, and not study the entire diversity of the Earth only from books and pictures.

CHAPTER 1. GENERAL CONCEPTS ABOUT VOLCANISM.

“Volcanism is a phenomenon due to which, during the course of geological history, the outer shells of the Earth were formed - the crust, hydrosphere and atmosphere, that is, the habitat of living organisms - the biosphere.”

This opinion is expressed by most volcanologists, but this is by no means the only idea about the development of the geographic envelope.

Volcanism covers all phenomena associated with the eruption of magma to the surface. When magma is deep in the earth's crust under high pressure, all of its gaseous components remain in a dissolved state. As the magma moves towards the surface, the pressure decreases, gases begin to be released, as a result, the magma pouring onto the surface differs significantly from the original one. To emphasize this difference, magma erupted on the surface is called lava. The process of eruption is called eruptive activity.

Volcanic eruptions proceed differently, depending on the composition of the products of the eruption. In some cases, eruptions proceed quietly, gases are released without large explosions, and liquid lava flows freely to the surface. In other cases, eruptions are very violent, accompanied by powerful gas explosions and squeezing or outpouring of relatively viscous lava. The eruptions of some volcanoes consist only in grandiose gas explosions, as a result of which colossal clouds of gas and water vapor saturated with lava are formed, rising to great heights.

According to modern concepts, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the bowels of the Earth to its surface. At a depth of 50 to 350 km, in the thickness of our planet, pockets of molten matter - magma - are formed. In areas of crushing and fractures of the earth's crust, magma rises and pours out to the surface in the form of lava (it differs from magma in that it contains almost no volatile components, which, when the pressure drops, are separated from the magma and go into the atmosphere.

In places of eruption, lava covers, flows, volcanoes-mountains, composed of lavas and their pulverized particles - pyroclasts, arise. According to the content of the main component - silicon oxide of the magma and the volcanic rocks formed by them - volcanics are divided into ultrabasic (silicon oxide less than 40%), basic (40-52%), medium (52-65%), acidic (65-75%). The most common basic, or basaltic, magma.

CHAPTER 2. TYPES OF VOLCANOES, COMPOSITION OF LAVA. CLASSIFICATION ACCORDING TO THE NATURE OF THE ERUPTION.

The classification of volcanoes is based mainly on the nature of their eruptions and on the structure of volcanic apparatuses. And the nature of the eruption, in turn, is determined by the composition of the lava, the degree of its viscosity and mobility, temperature, and the amount of gases contained in it. Three processes are manifested in volcanic eruptions: 1) effusive - the outpouring of lava and its spreading over the earth's surface; 2) explosive (explosive) - an explosion and the release of a large amount of pyroclastic material (solid eruption products); 3) extrusive - squeezing out, or squeezing out, magmatic matter onto the surface in a liquid or solid state. In a number of cases, mutual transitions of these processes and their complex combination with each other are observed. As a result, many volcanoes are characterized by a mixed type of eruption - explosive-effusive, extrusive-explosive, and sometimes one type of eruption is replaced by another in time. Depending on the nature of the eruption, the complexity and diversity of volcanic structures and forms of occurrence of volcanic material is noted.

Among volcanic eruptions, the following are distinguished: 1) eruptions of the central type, 2) fissures and 3) areal.

Volcanoes of the central type.

They have a shape close to round in plan, and are represented by cones, shields, and domes. At the top there is usually a bowl-shaped or funnel-shaped depression, called a crater (Greek 'crater'-bowl). From the crater into the depths of the earth's crust there is a magma-supplying channel, or a volcano vent, which has a tubular shape, along which magma from a deep chamber rises to the surface. Among volcanoes of the central type, polygenic ones, formed as a result of repeated eruptions, and monogenic ones, which manifested their activity once, stand out.

polygenic volcanoes.

These include most of the known volcanoes in the world. There is no unified and generally accepted classification of polygenic volcanoes. Different types of eruptions are most often referred to by the names of known volcanoes, in which one or another process manifests itself most characteristically.

Effusive, or lava, volcanoes.

The predominant process in these volcanoes is effusion, or the outpouring of lava to the surface and its movement in the form of flows along the slopes of a volcanic mountain. Volcanoes of the Hawaiian Islands, Samoa, Iceland, etc. can be cited as examples of this nature of the eruption.

Hawaiian type.

Hawaii is formed by the merged peaks of five volcanoes, of which four were active in historical time. The activity of two volcanoes has been especially well studied: Mauna Loa, which rises almost 4200 meters above the level of the Pacific Ocean, and Kilauea with a height of more than 1200 meters.

The lava in these volcanoes is mainly basaltic, easily mobile, and high-temperature (about 12,000). In the crater lake, lava is bubbling all the time, its level either decreases or rises. During eruptions, lava rises, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are released relatively quietly, forming bursts above the crater, lava fountains rising in height from several to hundreds of meters (rarely). Lava foamed by gases splatters and solidifies in the form of thin glass threads ‘Pele’s hair’. Then the crater lake overflows and lava begins to overflow over its edges and flow down the slopes of the volcano in the form of large flows.

Effusive underwater.

Eruptions are the most numerous and least studied. They are also associated with rift structures and are distinguished by the predominance of basaltic lavas. At the bottom of the ocean, at a depth of 2 km or more, the water pressure is so great that explosions do not occur, which means that pyroclasts do not occur. Under water pressure, even liquid basaltic lava does not spread far, forming short dome-shaped bodies or narrow and long flows covered from the surface with a glassy crust. A distinctive feature of submarine volcanoes located at great depths is the abundant release of fluids containing high amounts of copper, lead, zinc and other non-ferrous metals.

Mixed explosive-effusive (gas-explosive-lava) volcanoes.

Examples of such volcanoes are the volcanoes of Italy: Etna - the highest volcano in Europe (more than 3263 m), located on the island of Sicily; Vesuvius (about 1200 m high), located near Naples; Stromboli and Vulcano from the group of Aeolian Islands in the Strait of Messina. This category includes many volcanoes of Kamchatka, the Kuril and Japanese islands, and the western part of the Cordillera mobile belt. The lavas of these volcanoes are different - from basic (basalt), andesite-basalt, andesitic to acidic (liparitic). Among them, several types are conditionally distinguished.

Strombolian type.

It is characteristic of the Stromboli volcano, which rises in the Mediterranean Sea to a height of 900 m. The lava of this volcano is mainly of basalt composition, but lower temperature (1000-1100) than the lava of the volcanoes of the Hawaiian Islands, therefore it is less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from a few minutes to an hour. Gas explosions eject hot lava to a relatively small height, which then falls onto the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly pieces of lava). Characteristically, very little ash is emitted. The cone-shaped volcanic apparatus consists of layers of slag and solidified lava. Such a famous volcano as Izalco belongs to the same type.

Ethno-Vesuvian (Vulcan) type.

Volcanoes are explosive (gas-explosive) and extrusive-explosive.

This category includes many volcanoes, in which large gas-explosive processes with the release of a large amount of solid eruption products, almost without lava outpouring (or in limited sizes) are predominant. This nature of the eruption is associated with the composition of the lavas, their viscosity, relatively low mobility and high saturation with gases. In a number of volcanoes, gas-explosive and extrusive processes are simultaneously observed, expressed in the squeezing out of viscous lava and the formation of domes and obelisks towering above the crater.

Peleian type.

Especially clearly manifested in the volcano Mont Pele on about. Martinique is part of the Lesser Antilles. The lava of this volcano is predominantly medium, andesitic, highly viscous and saturated with gases. As it solidifies, it forms a solid plug in the crater of the volcano, which prevents the free exit of gas, which, accumulating under it, creates very high pressures. Lava is squeezed out in the form of obelisks, domes. Eruptions occur as violent explosions. There are huge clouds of gases, supersaturated with lava. These hot (with temperatures over 700-800) gas-ash avalanches do not rise high, but roll down the slopes of the volcano at high speed and destroy all life on their way.

Krakatau type.

It is distinguished by the name of the volcano Krakatau, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The oldest of them, Rakata, is composed of basalts, and the other two, younger ones, are andesites. These three merged volcanoes are located in an ancient vast underwater caldera, formed in prehistoric times. Until 1883, for 20 years, Krakatoa did not show active activity. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate strength in May, after some interruptions they resumed again in June, July, August with a gradual increase in intensity. On August 26, there were two large explosions. On the morning of August 27, there was a giant explosion that was heard in Australia and on the islands in the western Indian Ocean at a distance of 4000-5000 km. An incandescent gas-ash cloud rose to a height of about 80 km. Huge waves up to 30 m high, which arose from the explosion and shaking of the Earth, called tsunamis, caused great destruction on the adjacent islands of Indonesia, they were washed away from the shores of Java and Sumatra about 36 thousand people. In some places, destruction and human casualties were associated with a blast wave of enormous power.

Katmai type.

It is distinguished by the name of one of the large volcanoes in Alaska, near the base of which in 1912 a large gas-explosive eruption and a directed ejection of avalanches, or flows, of a hot gas-pyroclastic mixture occurred. The pyroclastic material had an acidic, rhyolitic or andesite-rhyolite composition. This hot gas-ash mixture filled a deep valley located northwest of the foot of Mount Katmai for 23 km. In place of the former valley, a flat plain about 4 km wide was formed. From the flow that filled it, mass releases of high-temperature fumaroles were observed for many years, which served as the basis for calling it the “Valley of Ten Thousand Smokes”.

monogenic volcanoes.

Maar type.

This type combines only once erupted volcanoes, now extinct explosive volcanoes. In relief, they are represented by flat saucer-shaped basins framed by low ramparts. The swells contain both volcanic cinders and fragments of nonvolcanic rocks that make up this territory. In a vertical section, the crater has the form of a funnel, which in the lower part is connected to a tubular vent, or explosion tube. These include volcanoes of the central type, formed during a single eruption. These are gas-explosive eruptions, sometimes accompanied by effusive or extrusive processes. As a result, small slag or slag-lava cones (from tens to a few hundred meters high) with a saucer-shaped or bowl-shaped crater depression are formed on the surface. Such numerous monogenic volcanoes are observed in large numbers on the slopes or at the foot of large polygenic volcanoes. Monogenic forms also include gas-explosive funnels with an inlet pipe-like channel (vent). They are formed by a single gas explosion of great force. Diamond pipes belong to a special category. Explosion pipes in South Africa are widely known as diatremes (Greek “dia” - through, “trema” - hole, hole). Their diameter ranges from 25 to 800 meters, they are filled with a kind of brecciated volcanic rock called kimberlite (according to the city of Kimberley in South Africa). This rock contains ultramafic rocks - garnet-bearing peridotites (pyrope is a satellite of diamond), characteristic of the Earth's upper mantle. This indicates the formation of magma under the surface and its rapid rise to the surface, accompanied by gas explosions.

Fissure eruptions.

They are confined to large faults and cracks in the earth's crust, which play the role of magma channels. The eruption, especially in the early phases, can occur along the entire fissure or separate sections of its sections. Subsequently, groups of contiguous volcanic centers appear along the fault line or crack. The erupted main lava, after solidification, forms basalt covers of various sizes with an almost horizontal surface. In historical times, such powerful fissure eruptions of basaltic lava were observed in Iceland. Fissure eruptions are widespread on the slopes of large volcanoes. O lower, apparently, are widely developed within the faults of the East Pacific Rise and in other mobile zones of the World Ocean. Particularly significant fissure eruptions were in past geological periods, when powerful lava covers were formed.

Areal type of eruption.

This type includes massive eruptions from numerous closely spaced volcanoes of the central type. They are often confined to small fissures, or nodes of their intersection. In the process of eruption, some centers die off, while others arise. The areal type of eruption sometimes captures vast areas where the products of the eruption merge, forming continuous covers.

CHAPTER 3. GEOGRAPHICAL DISTRIBUTION OF VOLCANOES.

At present, there are several thousand extinct and active volcanoes on the globe, and among the extinct volcanoes, many ceased their activity tens and hundreds of thousands of years, and in some cases millions of years ago (in the Neogene and Quaternary periods), some relatively recently. According to V.I. Vlodavets, the total number of active volcanoes (since 1500 BC) is 817, including volcanoes of the solfataric stage (201) .

In the geographical distribution of volcanoes, a certain regularity is outlined, associated with recent history development of the earth's crust. On the continents, volcanoes are located mainly in their marginal parts, on the coasts of the oceans and seas, within the limits of young tectonically mobile mountain structures. Volcanoes are especially widely developed in the transition zones from the continents to the oceans - within the island arcs bordering deep-sea trenches. In the oceans, many volcanoes are confined to mid-ocean underwater ridges. Thus, the main regularity of the distribution of volcanoes is their confinement only to mobile zones of the earth's crust. The location of volcanoes within these zones is closely related to deep faults reaching the subcrustal region. Thus, in island arcs (Japanese, Kurile-Kamchatka, Aleutian, etc.), volcanoes are distributed in chains along fault lines, mainly longitudinal and transverse faults. Some of the volcanoes are also found in older massifs, rejuvenated in newest stage folding by the formation of young deep faults.

The Pacific zone is characterized greatest development modern volcanism. Within its boundaries, two subzones are distinguished: the subzone of the marginal parts of the continents and island arcs, represented by a ring of volcanoes surrounding the Pacific Ocean, and the subzone of the Pacific proper with volcanoes at the bottom of the Pacific Ocean. At the same time, mainly andesitic lava is erupted in the first subzone, and basaltic lava is erupted in the second.

The first subzone passes through Kamchatka, where about 129 volcanoes are concentrated, of which 28 exhibit modern activities. Among them, the largest are Klyuchevskoy, Karymsky Shiveluch, Bezymyanny, Tolbachik, Avachinsky, etc. From Kamchatka, this strip of volcanoes stretches to the Kuril Islands, where 40 active volcanoes are known, including the mighty Alaid. South of the Kuril Islands are the Japanese Islands, where there are about 184 volcanoes, of which more than 55 were active in historical time. Among them are Bandai and the majestic Fujiyama. Further, the volcanic subzone goes through the islands of Taiwan, New Britain, the Solomons, the New Hebrides, New Zealand and then goes to Antarctica, where on about. Ross is dominated by four young volcanoes. Of these, the most famous are Erebus, which operated in 1841 and 1968, and Terror with side craters.

The described strip of volcanoes passes further to the South Antilles underwater ridge (submerged continuation of the Andes), elongated to the east and accompanied by a chain of islands: South Shetland, South Orkney, South Sandwich, South Georgia. It then continues along the coast. South America. High young mountains rise along the western coast - the Andes, to which numerous volcanoes are confined, arranged linearly along deep faults. In total, there are several hundred volcanoes within the Andes, of which many are currently active or were active in the recent past, and some reach enormous heights (Aconcagua -7035 m, Tupungata-6700 m.).

The most intense volcanic activity is observed within the young structures of Central America (Mexico, Guatemala, El Salvador, Honduras, Costa Rica, Panama). The greatest young volcanoes are known here: Popocatepel, Orizaba, as well as Izalco, called the lighthouse of the Pacific Ocean due to continuous eruptions. This active volcanic zone is adjacent to the Lesser Antilles volcanic arc. Atlantic Ocean, where, in particular, is the famous volcano Mont Pele (on the island of Martinique).

There are not so many volcanoes currently active within the Cordillera of North America (about 12). However, the presence of powerful lava flows and covers, as well as destroyed cones, testifies to the previous active volcanic activity. The Pacific ring is closed by the volcanoes of Alaska with the famous Katmai volcano and numerous volcanoes of the Aleutian Islands.

The second subzone is the Pacific region proper. Behind last years underwater ridges have been discovered at the bottom of the Pacific Ocean and big number deep faults, with which numerous volcanoes are associated, sometimes protruding in the form of islands, sometimes located below the ocean level. Most of the Pacific islands owe their origin to volcanoes. Among them, the volcanoes of the Hawaiian Islands are the most studied. According to G. Menard, there are about 10 thousand underwater volcanoes at the bottom of the Pacific Ocean, towering 1 km above it. and more.

Mediterranean-Indonesian zone

This zone of active modern volcanism is also divided into two subzones: Mediterranean, Indonesian.

The Indonesian subzone is characterized by much greater volcanic activity. These are typical island arcs, similar to the Japanese, Kuril, and Aleutian arcs, limited by faults and deep-water depressions. A very large number of active, damped and extinct volcanoes are concentrated here. Only on about. Java and the four islands located to the east, there are 90 volcanoes, and dozens of volcanoes are extinct or are in the process of fading. It is to this zone that the described Krakatoa volcano is confined, the eruptions of which are distinguished by unusually grandiose explosions. In the east, the Indonesian subzone merges with the Pacific.

Between the active Mediterranean and Indonesian volcanic subzones, there are a number of extinct volcanoes in inland mountain structures. These include the extinct volcanoes of Asia Minor, the largest of them are Erjiyes and others; to the south, within Turkey, rises Big and Small Ararat, in the Caucasus - the two-headed Elbrus, Kazbek, around which there are hot springs. Further, in the Elbrus ridge, there is a volcano called Damavend and others.

.Atlantic zone.

Within the Atlantic Ocean, modern volcanic activity, with the exception of the above Antilles island arcs and the Gulf of Guinea region, does not affect the continents. Volcanoes are confined mainly to the Mid-Atlantic Ridge and its lateral branches. Some of the large islands within them are volcanic. A number of volcanoes of the Atlantic Ocean begins in the north from about. Jan Mayen. South is located about. Iceland, which has a large number of active volcanoes and where fissure eruptions of the main lava occurred relatively recently. In 1973, a major eruption of Helgafel took place over the course of six months, as a result of which a thick layer of volcanic ash covered the streets and houses of Vestmannaeyjar. To the south are the volcanoes of the Azores, the Ascension Islands, Asuncien, Tristan da Cunha, Gough and about. Bouvet.

Standing apart are the volcanic islands of the Canaries, Cape Verde, St. Helena, located in the eastern part of the Atlantic Ocean, outside the median ridge, near the coast of Africa. There is a high intensity of volcanic processes in the Canary Islands. At the bottom of the Atlantic Ocean there are also many underwater volcanic mountains and hills.

Indian Ocean zone.

IN Indian Ocean underwater ridges and deep faults are also developed. There are many extinct volcanoes, indicating relatively recent volcanic activity. Many of the islands scattered around Antarctica also appear to be of volcanic origin. Modern active volcanoes are located near Madagascar, on the Comoros, about. Mauritius and Reunion. To the south, volcanoes are known on the islands of Kerguelen, Crozet. Recently extinct volcanic cones are found in Madagascar.

Volcanoes of the central parts of the continents

They are relatively rare. The most striking manifestation of modern volcanism was in Africa. In the area adjacent to the Gulf of Guinea, a large stratovolcano Kamerun rises, its last eruption was in 1959. In the Sahara, on the Tibesti volcanic highlands, there are volcanoes with huge calderas (13-14 km.), In which there are several cones and outlets of volcanic gases and hot springs. In East Africa, there is a well-known system of deep faults (rift structure), stretching for 3.5 thousand km from the mouth of the Zambezi in the south to Somalia in the north, with which volcanic activity is associated. Among the numerous extinct volcanoes there are active volcanoes in the Virunga mountains (Lake Kivu region). Volcanoes in Tanzania and Kenya are especially famous. Here are the active large volcanoes of Africa: Meru with a caldera and somma; Kilimanjaro, whose cone reaches a height of 5895 m (the highest point in Africa); Kenya to the east of the lake. Victoria. A number of active volcanoes are located parallel to the Red Sea and directly in the sea itself. As for the sea itself, basalt lava comes to the surface in its faults, which is a sign of the already oceanic crust that has already formed here.

There are no active volcanoes within Western Europe. There are extinct volcanoes in many countries of Western Europe - in France, in the Rhine region of Germany and other countries. In some cases, mineral springs are associated with them.

CHAPTER 4. POST-VOLCANIC PHENOMENA

During the attenuation of volcanic activity, a number of characteristic phenomena are observed for a long time, indicating active processes continuing in depth. These include the release of gases (fumaroles), geysers, mud volcanoes, thermal baths.

Fumaroles (volcanic gases).

After volcanic eruptions, gaseous products are emitted for a long time from the craters themselves, from various cracks, from hot tuff-lava flows and cones. The composition of post-volcanic gases contains the same gases of the group of halides, sulfur, carbon, water vapor and others that are released during volcanic eruptions. However, it is impossible to outline a single scheme for the composition of gases for all volcanoes. So, in Alaska, thousands of gas jets with a temperature of 600-650, which include a large amount of halides (HCl and HF), boric acid, hydrogen sulfide and carbon dioxide . A somewhat different picture is observed in the region of the famous Phlegrean Fields in Italy, west of Naples, where there are many volcanic craters and small cones for thousands of years characterized exclusively by solfataric activity. In other cases, carbon dioxide dominates.

Geysers.

Geysers are periodically operating steam-water fountains. They got their fame and name in Iceland, where they were observed for the first time. In addition to Iceland, geysers are widely developed in the Yellowstone Park in the USA, in New Zealand, and in Kamchatka. Each geyser is usually associated with a round hole, or griffin. Griffins come in a variety of sizes. In depth, this channel, apparently, passes into tectonic cracks. The entire channel is filled with superheated underground water. Its temperature in the griffin can be 90-98 degrees, while in the depths of the channel it is much higher and reaches 125-150 degrees. and more. At a certain moment, intense vaporization begins in the depths, as a result, the column of water in the griffin rises. In this case, each particle of water finds itself in a zone of lower pressure, boiling and eruption of water and steam begin. After the eruption, the channel is gradually filled with underground water, partly with water ejected during the eruption and flowing back into the gryphon; for some time, an equilibrium is established, the violation of which leads to a new steam-water eruption. The height of the fountain depends on the size of the geyser. In one of the large geysers in Yellowstone Park, the height of the fountain of water and steam reached 40 m.

Mud volcanoes (salses).

They are sometimes found in the same areas as geysers (Kamchatka, Java, Sicily, etc.). Hot water vapor and gases break through cracks to the surface, are ejected and form small outlet holes with a diameter of tens of centimeters to one meter or more. These holes are filled with mud, which is a mixture of gas vapors with groundwater and loose volcanic products and is characterized by a high temperature (up to 80-90 0). This is how mud volcanoes arise. The density, or consistency, of mud determines the nature of their activity and structure. With relatively liquid mud, vapor and gas emissions cause splashes in it, the mud spreads freely and, at the same time, a cone with a crater at the top of no more than 1-1.5 m, consisting entirely of mud. In mud volcanoes of volcanic regions, in addition to water vapor, carbon dioxide and hydrogen sulfide are released.

“Depending on the causes of occurrence, mud volcanoes can be divided into: 1) associated with the release of combustible gases; 2) confined to areas of magmatic volcanism and caused by emissions of magmatic gases.” . These include the Apsheron and Taman mud volcanoes.

CONCLUSION.

Modern active volcanoes are a vivid manifestation of endogenous processes accessible to direct observation, which played a huge role in the development of geographical science. However, the study of volcanism is not only of cognitive importance. Active volcanoes, along with earthquakes, pose a formidable danger to nearby settlements. The moments of their eruptions often bring irreparable natural disasters, expressed not only in huge material damage, but sometimes in mass death of the population. Well, for example, the eruption of Vesuvius in 79 AD is well known, which destroyed the cities of Herculaneum, Pompeii and Stabia, as well as a number of villages located on the slopes and at the foot of the volcano. Several thousand people died as a result of this eruption.

So modern active volcanoes, characterized by intense cycles of vigorous eruptive activity and representing, unlike their ancient and extinct counterparts, objects for research volcanic observations, are the most favorable, although far from safe.

In order not to give the impression that volcanic activity brings only disasters, one should cite such brief information about some useful aspects.

Huge ejected masses of volcanic ash renew the soil and make it more fertile.

Water vapor and gases released in volcanic areas, steam-water mixtures and hot springs have become sources of geothermal energy.

Many mineral springs are associated with volcanic activity and are used for balneological purposes.

Products of direct volcanic activity - individual lavas, pumice, perlite, etc. are used in the construction and chemical industries. The formation of some minerals, such as sulfur, cinnabar, and a number of others, is associated with fumarole and hydrothermal activity. Volcanic products of underwater eruptions are sources of accumulation of minerals such as iron, manganese, phosphorus, etc.

And I would also like to say that volcanism as a process has not been fully studied and that humanity still has many unsolved mysteries besides volcanism, and someone needs to solve them.

And the study of modern volcanic activity is of great theoretical importance, as it helps to understand the processes and phenomena that took place on Earth in ancient times.

Bibliography

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