Volcanism as the most important manifestation of endogenous processes. Volcanoes

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They have in plan a form close to round, and are represented by cones, shields, domes. At the top is usually a cup-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 supply channel, or a vent of a volcano, which has a tubular shape through which magma from the deep hearth rises to the surface. Among the volcanoes of the central type, there are polygenic, formed as a result of multiple eruptions, and monogenic - once manifested their activities. Polygenic volcanoes. These include the majority of known volcanoes   of the world. There is no single and generally accepted classification of polygenic volcanoes. Various types of eruptions are most often designated by the name of known volcanoes, in which one or the other process is most characteristic.

Effusive, or lava, volcanoes. The predominant process in these volcanoes is effusion, or the outflow 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 type of eruption.

Hawaiian type .. Hawaii are formed by the merged peaks of five volcanoes, of which four acted in historical time. The activity of two volcanoes is especially well studied: Mauna Loa, which rises almost 4,200 meters above the Pacific Ocean level, and Kilauea, which is over 1,200 meters high. The lava in these volcanoes is basic basaltic, readily mobile, high-temperature (about 12,000). In the crater lake the lava is constantly bubbling, its level is then lowered, then it rises. When eruptions, the lava ascends, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are relatively calm, forming bursts above the crater, lava fountains rising from a few to hundreds of meters (rarely). The lava blown by gases is sprayed and frozen in the form of thin glass filaments with `Pele hair. '" Then the crater lake overflows and the lava begins to pour over its edges and flow down the slopes of the volcano in the form of large streams.

Effusive underwater. Eruptions are the most numerous and least studied. They are also confined to rift structures, distinguished by the dominance of basaltic lavas. At the bottom of the ocean at a depth of 2 km or more, the water pressure is so great that no explosions occur, and so pyroclasts do not arise. Under the pressure of water, even liquid basaltic lava does not spread, it forms short domed bodies or narrow and long streams covered with a glassy crust from the surface. A distinctive feature of underwater volcanoes at great depths is abundant release of fluids containing a high amount 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   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 the Aeolian Islands in the Strait of Messina. The same category includes many volcanoes of Kamchatka, the Kurile Islands and the Japanese Islands and the western part of the Cordillera mobile belt. The lavas of these volcanoes are different - from the basic (basaltic), andesite-basaltic, andesite to acid (liparite). Among them, several types are conventionally distinguished.

Strombolian type. Characteristic for the volcano Stromboli, rising in the Mediterranean to a height of 900 m. The lava of this volcano is mainly basaltic, but more low-temperature (1000-1100) than the lava of Hawaiian volcanoes, therefore less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from a few minutes to an hour. Gas explosions throw out a heated lava at a relatively low height, which then falls on the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly lava pieces). It is characteristic that very little ash is emitted. The volcanic apparatus of the cone-shaped form consists of layers of slag and solidified lava. The same type of known volcano as Isalco belongs to this type.

Explosive volcanoes (gas-explosive) extrusive-explosive. This category includes many volcanoes, in which the major gas-explosive processes with the release of a large amount of solid erupt products, predominantly without lava outflow or in limited sizes, are of major importance. This type of eruption is associated with the composition of lavas, their viscosity, relatively low mobility and high gas saturation. In a number of volcanoes, gas-explosive and extrusive processes are simultaneously observed, expressing the squeezing of viscous lava and the formation of domes and obelisks that rise above the crater.

Peleic type. Especially vividly manifested in the volcano Mont Pelay on. Martinique, part of the group of Lesser Antilles. The lava of this volcano is predominantly average, andesitic, it has a high viscosity and is saturated with gases. Frozen, it forms a solid plug in the vent of the volcano, preventing the free flow of gas, which, accumulating under it, creates a very large pressure. Lava is squeezed out in the form of obelisks, domes. Eruptions occur as violent explosions. There are huge clouds of gases, oversaturated with lava. These hot (with a temperature above 700-800) gas ash ash avalanches do not rise high, but roll down at high speed along the slopes of the volcano and destroy all living things on their way.

Krakatau type. Dedicated to the name of the volcano Krakatau, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The most ancient of them, Rakata, is composed of basalts, and two other, more young, andesites. These three fused volcanoes are located in an ancient vast underwater caldera, formed in prehistoric times. Until 1883, for 20 years, Krakatoa was not active. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate strength in May, after several interruptions, they resumed in June, July, August with a gradual increase in intensity. August 26, there were two big explosions. On the morning of August 27, there was a giant explosion that was heard in Australia and on islands in the western Indian Ocean at a distance of 4000-5000 km. At a height of about 80 km a red-hot gas-ash cloud rose. Huge waves up to 30 m in height, caused by the explosion and earthquakes, called tsunamis, caused great destruction on the adjacent islands of Indonesia, they were washed from the coast of Java and Sumatra about 36 thousand people. Places of destruction and human sacrifices were associated with an explosive wave of immense power

The Kathmai type. It is distinguished by the name of one of the large volcanoes   Alaska, near the base, which in 1912 there was a large gas-explosive eruption and directed emission of avalanches or streams, a hot gas-pyroclastic mixture. The pyroclastic material had an acidic, rhyolite or andesite-rhyolite composition. This incandescent gas-ash mixture filled a deep valley for 23 km, located to the north-west of the foot of Mount Kathmai. In place of the former valley, a flat plain of about 4 km in width was formed. From the stream that filled it for many years, there were massive releases of high-temperature fumaroles, which served as the basis for calling it "Valley of ten thousand fumes."

Monogenic volcanoes. Maarsky type. This type unites only once erupted volcanoes, now extinct explosive volcanoes. In the relief they are represented by flat saucer-shaped basins, framed by low valleys. In the composition of the shafts there are both volcanic slags and fragments of non-volcanic rocks composing this territory. In the vertical section, the crater has the form of a funnel, which in the lower part is connected to a pipe-shaped vent or to an 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 (height from tens to the first hundreds of meters) with a saucer-shaped or bowl-shaped crater 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 a leading duct-like channel (jug). They are formed by a single gas explosion of great strength. Diamond-bearing tubes belong to a special category. The explosion tubes 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 (in Kimberley, South Africa). In the composition of this breed there are ultrabasic rocks - garnet containing peridotites (pyrope-satellite of diamond), characteristic for the upper mantle of the Earth. This indicates the undermining of magma and its rapid rise to the surface, accompanied by gas explosions.

The shape of the volcano depends on the composition of the erupting lava.

Shield Volcano

From the central vents and lateral craters, streams of liquid basaltic lava erupt and spread out for a long time. Gradually from these layers a wide "shield" with flat edges is formed. A typical example of such a volcano is Mauna Loa in Hawaii. Its height from the foot of the ocean floor is about ten kilometers.

Stratovolcano

Viscous and dense lava quickly freezes. Stratovolcanoes are composed of many layers of lava and pyroclastic material - a hot mixture of gases, debris and ash. They have a sharp cone with concave slopes, the lava also flows out of the cracks, solidifying in the form of ribbed corridors that serve as a support for the volcano. Examples of stratovolcanoes are Etna, Vesuvius, Fujiyama.

Slag cone

During the eruption, large fragments of porous slag are heaped around the crater in the form of a cone. Small - form sloping slopes at the foot. This is the most common type of volcanoes on land. In height, they are not more than a few hundred meters and erupt only once. An example is Flat Tolbachik in Kamchatka, which exploded in December 2012.

Dome of the Volcano

Granite viscous magma, rising from the depths of the volcano, can not flow down the slopes and freezes at the top, forming a dome. She clogs his throat, like a cork, which over time blows out the gases accumulated inside. This dome is now forming over the crater of the St. Helens volcano in the northwest of the United States, formed during the 1980 eruption.

In brief

1) Without the volcanoes, Earth would not have an atmosphere

All gases in the air, with the exception of oxygen, are of volcanic origin.

2) It is impossible to prevent eruption

You can only warn people of the impending danger, to give them time to prepare for the inevitable.

3) There are 1,500 volcanoes in the world

The overwhelming majority is located along the zones, where one plate of the earth's crust is moved under the other, plunging into the semi-molten layer of the mantle.

Where are volcanoes born?

In the zone of divergence of lithospheric plates

When the continental plates disagree through the formed ruptures in the earth's crust, a red-hot rock from the mantle rises and, melting into magma, causes eruptions.

In the zone of collision of lithospheric plates

When the ocean plate falls under the continental, water gets into the hot mantle, reducing the melting temperature of its upper layers. As a result, magma is formed, which breaks through the continental plate.

Above the "hot spots"

In some areas, the "plumes" from the Earth's mantle are rising hot streams of solid matter. If the pressure in the upper layers of the plume is weakened, it melts and forms a magma. The plume is motionless, and the tectonic plates above it move. Where they pass over the "hot spot", new volcanoes emerge.

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Introduction ...................................................................................................... 2

ChapterI.   General ideas about volcanism ............ ... .. .................................... ... 4

ChapterII. Types of volcanoes, composition of lavas. Types of volcanic eruptions ..................... ... 5

2.1. Volcanoes of central type ...................................................... ... ...... .. 5

2.1.1. Polygenic volcanoes ... .. ...................................................... ... ....... .... 6th

2.1.2. Monogenic volcanoes ....... ............. ........................... .. ....... ............... 15

2.2. Fracture type of eruption ....................................... .. ...................... 15

2.3. The actual type of eruption ............................................. .. ............... .. 16

ChapterIII. Geographical distribution of volcanoes .................................................................. 16

3.1. The Mediterranean-Indonesian zone ........................................ ......... .. 18

3.2. Atlantic zone ................................................. ......................... 19

3.3. The Indian Ocean Zone .................................................................. 19

3.4. Volcanoes of the central parts of the continents ..................................... .... ..... 20

3.5. Active volcanoes of the earth ........................... ... .... ......................... ... 20

3.6. Volcanic products ......................................................... .. ...... ... 22

ChapterIV. Potpolcanic phenomena .......................................... .. ................... 29

4.1. Fumaroles (volcanic gases) ............................ ........................ ...... 29

4.2. Geysers .. ................................................. ............................ ...... .. .... thirty

4.3. Mud volcanoes .......................................................... ............ .. ... ... 32

Conclusion ............................................................................ .... ............ ... .... 34

List of used literature ................................................................................................. .. 35

INTRODUCTION

Relevance of the topic:

Volcanic activity, which belongs to a number of the most formidable phenomena of nature, often brings huge disasters to people and the national economy. Therefore, it must be borne in mind that although not all active volcanoes cause unhappiness, nevertheless, each of them may be, to some extent, a source of negative events.

Purpose of study:

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

It is necessary to trace:

Classification of eruptions.

Types of volcanoes.

Composition of erupting lavas.

The effects of volcanism on the geographic environment.

Location of a certain sequence:

To study volcanic activity, it is necessary to trace and study the types of volcanoes, the classification of eruptions, the composition of erupting lavas, the effects of volcanism on the geographic shell.

The theoretical side of the work:

Is the study of volcanism as the most important manifestation of endogenous processes, geographical distribution.

The practical side of the work:

To attract 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 geographical envelope. It's no secret that each of us would like to visit not far from the erupting volcano. At times we feel our microscopy in comparison with the natural forces of the Earth. And even more so for every geographer, the main source of knowledge should remain expeditions and research, and not study the entire diversity of the Earth only from books and pictures.

Course work structure:

The work consists of: Introduction, one table, two diagrams, 15 figures, conclusion, list of used literature, statement in 35 pages

CHAPTER I. GENERAL PRESENTATIONS OF VOLCANISM.

"Volcanism is a phenomenon through which during the geological history the outer shells of the Earth-the crust, the hydrosphere and the atmosphere, ie the habitat of living organisms-the biosphere, have formed."

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

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

Volcanic eruptions occur unequally, depending on the composition of the products of the eruption. In some cases, eruptions proceed calmly, gases are released without large explosions and liquid lava flows freely onto the surface. In other cases, eruptions are very violent, accompanied by powerful gas explosions and squeezing or pouring out relatively viscous lava. Eruptions of some volcanoes consist only in grandiose gas explosions, resulting in the formation of huge clouds of gas and water vapor saturated with lava, rising to a huge height.

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, foci of molten matter - magma - form in the thickness of our planet. In the areas of crushing and faults of the earth's crust, magma rises and pours to the surface in the form of lava (differs from magma in that it almost does not contain volatile components, which, when pressure falls, separate from magma and escape into the atmosphere.

In places of eruption, lava covers, streams, volcanoes-mountains formed by lavas and their dispersed particles-pyroclasts appear. According to the content of the main constituent - silicon oxide, magmas and volcanic rocks formed by them - volcanites 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.

CHAPTERII. TYPES OF VOLCANOES, COMPOSITION OF LOVE.

CLASSIFICATION BY THE CHARACTER OF 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, the temperature, the amount of gases contained in it. In the volcanic eruptions are three processes:

1) effusive - outpouring of lava and spreading it over the earth's surface;

2) Explosive (explosive) - explosion and ejection of a large amount of pyroclastic material (solid eruption products);

3) extrusive - squeezing, or extruding, magmatic substance on the surface in a liquid or solid state. In a number of cases, there are mutual transitions of these processes and a complex combination of these processes. As a result, many volcanoes are characterized by a mixed type of eruption - explosive-effusive, extrusive-excusive, and sometimes one type of eruption is replaced by another in time. Depending on the nature of the eruption, the complexity and variety of volcanic structures and forms of occurrence of volcanic material are noted.

Among the volcanic eruptions are the following:

1) central-type eruptions

2) cracked

3) Areal.

2.1. Central type volcanoes.

They have in plan a form close to round, and are represented by cones, shields, domes. At the top there is usually a cup-shaped or funnel-shaped depression, called a crater (Greek crater-bowl). From the crater to the depth of the earth's crust, there is a magma-supply channel, or a vent of a volcano, with a tubular shape through which magma rises to the surface from a deep hearth. Among the volcanoes of the central type, there are polygenic, formed as a result of multiple eruptions, and monogenic - once manifested their activities.

2.1.1.Poligennye volcanoes.

These include most of the world's most famous volcanoes. There is no single and generally accepted classification of polygenic volcanoes. Various types of eruptions are most often designated by the name of known volcanoes, in which one or the other process is most characteristic.

Effusive, or lava, volcanoes.

The predominant process in these volcanoes is effusion, or the outflow 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 type of eruption.

Hawaiian type.

Hawaii is formed by the merging peaks of five volcanoes, of which four operated in historical time. The activity of two volcanoes is particularly well studied; Mauna Loa, towering almost 4,200 meters above the Pacific Ocean level, and Kilauea over 1,200 meters high.

Lava in these volcanoes is the basaltic basin, easily mobile, high-temperature (about 1200 0). In the crater lake the lava is constantly bubbling, its level is then lowered, then it rises. When eruptions, the lava ascends, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are relatively calm, forming bursts above the crater, lava fountains rising from a few to hundreds of meters (rarely). Glowed with lava, the lava splashes and solidifies in the form of thin glass filaments with Pele's hair. Then the crater lake overflows and the lava begins to pour over its edges and flow down the slopes of the volcano in the form of large streams.

Fig.1 Hawaiian type (www.criazon.com)

Effusive underwater.

Eruptions are the most numerous and least studied. They are also confined to rift structures, distinguished by the dominance of basaltic lavas. At the bottom of the ocean at a depth of 2 km or more, the water pressure is so great that no explosions occur, and so pyroclasts do not arise. Under the pressure of water, even liquid basaltic lava does not spread, it forms short domed bodies or narrow and long streams covered with a glassy crust from the surface. A distinctive feature of underwater volcanoes at great depths is abundant release of fluids containing a high amount 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 of 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 the Aeolian Islands in the Strait of Messina. The same category includes many volcanoes of Kamchatka, the Kurile Islands and the Japanese Islands and the western part of the Cordillera mobile belt. The lavas of these volcanoes are different - from the basic (basaltic), andesite-basaltic, andesite to acid (liparite). Among them, there are several types.

Strombolian type.

Characteristic for the volcano Stromboli, rising in the Mediterranean to a height of 900 m. The lava of this volcano is mainly basaltic, but more low-temperature (1000-1100) than the lava of Hawaiian volcanoes, therefore less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from a few minutes to an hour. Gas explosions throw out the heated lava at a relatively low height, which then falls on the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly lava pieces). It is characteristic that ashes are emitted very little. The volcanic apparatus of the cone-shaped form consists of layers of slag and solidified lava. The same type of known volcano as Isalco belongs to this type.

Fig.2 Strombolian type ( www. criazon. com)

Fig. 3 Strombolian type (www.criazon.com)

Ethno-Vesuvian (Vulcan) type.

Fig.4. The volcano of Etna (www.criazon.com) Fig. 5 The main crater (www.criazon.com)

Fig.6 The eruption of the volcano Vesuvius (www.criazon.com)

Explosive volcanoes (gas-explosive) and

extrusion-explosive.

This category includes many volcanoes, in which the major gas-explosive processes with the emission of a large amount of solid erupt products are predominant, with almost no outflow of lavas (or in limited sizes). This type of eruption is associated with the composition of lavas, their viscosity, relatively low mobility and high gas saturation. In a number of volcanoes, gas-explosive and extrusive processes are simultaneously observed, expressing the squeezing of viscous lava and the formation of domes and obelisks that rise above the crater.

Peleic type.

Especially vividly manifested in the volcano Mont Pelay on. Martinique, part of the group of Lesser Antilles. The lava of this volcano is predominantly average, andesitic, it has a high viscosity and is saturated with gases. Frozen, it forms in the vole of the volcano a solid stopper, 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, oversaturated with lava. These hot (with a temperature above 700-800) gas ash ash avalanches do not rise high, but roll down at high speed along the slopes of the volcano and destroy all living things on their way.

Fig. 7 The eruption of the Mon-pele volcano

Fig. 7 The eruption of the volcano Mont Pele (www.criazon.com)

Krakatau type.

Dedicated to the name of the volcano Krakatau, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The most ancient of them, Rakata, is composed of basalts, and two other, more young ones, andesites. These three fused volcanoes are located in an ancient vast underwater caldera, formed in prehistoric times. Until 1883, for 20 years, Krakatoa was not active. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate strength in May, after several interruptions, they resumed in June, July, August with a gradual increase in intensity. August 26, there were two big explosions. On the morning of August 27, there was a giant explosion that was heard in Australia and on islands in the western Indian Ocean at a distance of 4000-5000 km. At a height of about 80 km a red-hot gas-ash cloud rose. Huge waves up to 30 m in height, caused by the explosion and earthquakes, called tsunamis, caused great destruction on the adjacent islands of Indonesia, they were washed from the coast of Java and Sumatra about 36 thousand people. Places of destruction and

human victims were associated with an explosive wave of enormous power.

Fig. Volcano Krakatau early XIX century. (www.criazon.com)

Fig. 9 The volcano of Krakatoa. View from space ( www. criazon. com)

The Kathmai type.

It is distinguished by the name of one of the large volcanoes of Alaska, near the base of which in 1912 there was a large gas-explosive eruption and directed emission of avalanches or streams, a hot gas-pyroclastic mixture. The pyroclastic material had an acidic, rhyolite or andesite-rhyolite composition. This incandescent gas-ash mixture filled a deep valley for 23 km, located to the north-west of the foot of Mount Kathmai. In place of the former valley, a flat plain of about 4 km in width was formed. From the stream that filled it for many years, there were massive releases of high-temperature fumaroles, which served as the basis for calling it "Valley of ten thousand fumes."

Fig. 10 Crater Lake Katmai ( www. criazon. com)

2.1.2. Monogenic volcanoes.

Maarsky type.

This type unites only once erupted volcanoes, now extinct explosive volcanoes. In the relief they are represented by flat saucer-shaped basins, framed by low valleys. In the composition of the shafts there are both volcanic slags and fragments of non-volcanic rocks composing this territory. In the vertical section, the crater has the form of a funnel, which in the lower part is connected to a pipe-shaped vent or to an explosion tube. These include volcanoes of the central type, formed during a single eruption. These are gas-explosive eruptions, sometimes accompanied by effusive or erosive processes. As a result, small slag or slag-lava cones (height from tens to the first hundreds of meters) with a saucer-shaped or bowl-shaped crater 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 a leading duct-like channel (jug). They are formed by a single gas explosion of great strength. Diamond-bearing tubes belong to a special category. The explosion tubes in South Africa are widely known as diatremes (Greek "dia" through, "trum" hole, hole). Their diameter ranges from 25 to 800 meters, they are filled with a kind of brecciated volcanic rock, called kimberlite (in Kimberley, South Africa). In the composition of this breed there are ultrabasic rocks - garnet-bearing peridotites (pyrope-satellite of diamond), characteristic for the upper mantle of the Earth. This indicates the undercover formation of magma and its rapid rise to the surface, accompanied by gas explosions.

2.2.Trashchannye eruptions.

They are confined to large faults and cracks in the earth's crust, playing the role of magma-channel channels. The eruption, especially in the early phases, can occur along the entire gaze or parts of its sections. Subsequently, groups of proximate volcanic centers arise along the fault or crack line. Outpoured main lava after hardening forms basalt covers of various sizes with an almost horizontal surface. In historical times, such powerful fractured outpourings of basalt lava were observed in Iceland. Fissure outpourings are widespread on the slopes of large volcanoes. Neither, apparently, are widely developed within the faults of the East Pacific Rise and in other mobile zones of the World Ocean. Especially significant fissure outpourings were in the past geological periods, when powerful lava sheets formed.

2.3.Areal type of eruption.

This type includes mass eruptions from numerous closely located volcanoes of the central type. They are often confined to small cracks, or nodes of their intersection. During the eruption, some centers die off, and others arise. The real type of eruption sometimes captures vast areas in which the products of the eruption merge, forming continuous covers.

CHAPTERIII.

GEOGRAPHICAL DISTRIBUTION OF VOLCANOES.

At present, there are several thousand extinct and active volcanoes on the globe, and among extinct volcanoes, many ceased their activities 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. The total number of active volcanoes (from 1500 BC) is 817, including volcanoes of the solfataric stage (201).

In the geographical distribution of volcanoes, a definite regularity is associated with the recent history of the 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. Especially widely developed volcanoes in the transition zones from the continents to the oceans-within the island arcs bordering deep-sea gutters. In the oceans, many volcanoes are confined to the mid-oceanic underwater ridges. Thus, the main regularity of the distribution of volcanoes is their confinement only to the mobile zones of the earth's crust. The location of volcanoes within these zones is closely related to deep faults reaching the subcrustal area. Thus, in island arcs (Japanese, Kuril-Kamchatka, Aleut, etc.), volcanoes are spread by chains along fault lines, mainly longitudinal faults transverse and oblique. Some of the volcanoes also occur in older massifs, rejuvenated in the newest stage of folding by the formation of young deep faults.

The Pacific zone is characterized by the greatest development of modern volcanism. Within its limits, two subzones are distinguished: the subzone of the marginal parts of the continents and island arcs represented by the ring of volcanoes surrounding the Pacific Ocean and the Pacific proper subzone with volcanoes on the bottom of the Pacific Ocean. In the first subzone, andesitic lava is erupted predominantly, and basaltic lava in the second.

The first subzone passes through Kamchatka, where about 129 volcanoes are concentrated, of which 28 exhibit modern activity. Among them, the largest are Klyuchevskoy, Karymsky Shiveluch, Bezymyanny, Tolbachik, Avachinsky, and others. This strip of volcanoes stretches from the Kamchatka Peninsula to the Kuril Islands, where 40 active volcanoes, including the mighty Alaid, are known. South of the Kuril Islands are the Japanese islands, where about 184 volcanoes, of which over 55 operated in historical time. Among them, Bandai and the majestic Fujiyama. Further volcanic subzone goes through the islands of Taiwan, New Britain, Solomon, New Hebrides, New Zealand and then goes to Antarctica, where on. Ross is four young volcanoes. The most known of them are Erebus, operating in 1841 and 1968, and Terror with side craters.

The described strip of volcanoes goes further to the South Antillian underwater range (the submerged continuation of the Andes), stretched to the east and accompanied by a chain of islands: South Shetland, South Orkney, South Sandwich, South Georgia. Further it continues along the coast of South America. Along the western shore, the high and young mountains, the Andes, rise, to which are associated numerous volcanoes, located linearly, along deep faults. Altogether within the Andes there are several hundred volcanoes, many of which are currently operating or operating in the recent past, and some reach huge 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). Here are known the greatest young volcanoes: Popocatepel, Orizaba, and also Isalco, called the lighthouse of the Pacific Ocean due to continuous eruptions. To this active volcanic zone adjoins the Maloantil volcanic arc of the Atlantic Ocean, where, in particular, is located the famous volcano   Mont-Pele (on the island of Martinique).

Within the Cordillera of North America, currently operating volcanoes are not so many (about 12). However, the presence of powerful lava flows and covers, as well as destroyed cones, indicates a previous active volcanic activity. The Pacific Ring is closed by volcanoes of Alaska with the famous volcano Kathmai and numerous volcanoes of the Aleutian Islands.

The second subzone is actually the Pacific Region. In recent years, underwater ridges and a large number of deep faults have been found on the bottom of the Pacific Ocean, with which numerous volcanoes are connected, then they act as islands, then below the ocean level. The predominant part of the islands of the Pacific owes its origin to volcanoes. Among them, the most studied volcanoes of the Hawaiian Islands. According to G. Menard, at the bottom of the Pacific Ocean there are about 10 thousand underwater volcanoes, towering over it at 1 km. and more.

3.1. The Mediterranean-Indonesian zone

This zone of active modern volcanism also divides into two sub-zones: Mediterranean, Indonesian.

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

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

3.2. Atlantic zone.

Within the Atlantic Ocean, modern volcanic activity, with the exception of the above-mentioned Antilles island arcs and the Gulf of Guinea, does not affect the continents. Volcanoes are confined mainly to the Mid-Atlantic ridge and its lateral branches. Part of the large islands within them is volcanic. A number of volcanoes of the Atlantic Ocean begin in the north with Fr. Jan Mayen. South of is located about. Iceland, which has a large number of active volcanoes and where recently there have been fissures outpouring of the main lava. In 1973, within six months, a major eruption of Helgafel occurred, as a result of which a powerful layer of volcanic ash covered the streets and houses of Westmanaeyar. To the south are the volcanoes of the Azores, Ascension, Asunciens, Tristan da Cunha, Gough and Fr. Bouvet.

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

3.3.Indoceanic zone.

The Indian Ocean also has underwater ridges and deep faults. There are a lot of extinct volcanoes, indicative of a relatively recent volcanic activity. Many of the islands scattered around Antarctica, apparently, also of volcanic origin. Current active volcanoes are located near Madagascar, on the Comoros, on. Mauritius and Reunion. To the south, volcanoes are known on the islands of Kerguelen, Crozet. In Madagascar there are recently extinct volcanic cones.

3.4.The volcanoes of the central parts of the continents

They are a relatively rare phenomenon. The most vivid manifestation of modern volcanism was in Africa. In the area adjacent to the Gulf of Guinea, stands a large stratovolcano of Cameroon, its last eruption was in 1959. In the Sahara, volcanos with huge calderas (13-14 km) are located in the volcanic highlands of Tibesti, in which there are several cones and volcanic gas outcrops and hot springs. In East Africa, there is a well-known system of deep faults (a rift structure) stretching 3,500 km from the mouth of the Zambezi in the south to Somalia in the north, from which volcanic activity is associated. Among the numerous extinct volcanoes there are active volcanoes in the Virunga Mountains (Lake Kivu area). Volcanoes in Tanzania and Kenya are especially famous. Here there are active large volcanoes in Africa: Meru with caldera and somma; Kilimanjaro, whose cone reaches a height of 5895 m. (The highest point of Africa); Kenya to the east of the lake. Victoria. A number of active volcanoes are located parallel to the Red Sea and directly to the sea. As for the sea itself, basalt lava comes to its surface in its faults, which is a sign of the already oceanic crust that has already formed there.

There are no active volcanoes within Western Europe. Extinct volcanoes are found in many countries of Western Europe - in France, in the Prirainsky region of Germany and other countries. In some cases, they are connected with the exits of mineral springs.

3.5. Active volcanoes of the earth

A volcano erupting in historical time is considered to be active. A total of about 2,500 eruptions of 500 such volcanoes are known. On the map are some of the most famous, as well as the volcanoes mentioned in the text.

Fig.11    Main types of volcanoes

Extrusive (lava) dome (on the left) has a rounded shape and steep slopes, cut deep furrows. In the crater of the volcano, a cork of frozen lava can form, which prevents the release of gases, which subsequently leads to explosion and destruction of the dome. The steeply pyroclastic cone (right) is composed of alternating interbeds of ash and slags.

3.6 Volcanic products

Lava- this is magma, poured onto the earth's surface during eruptions, and then hardening. Lava outpouring can occur from the main vertex crater, a lateral crater on the slope of the volcano or from cracks associated with the volcanic focus. It flows down the slope in the form of a lava flow. In some cases, lava flows out in rift zones of enormous length. For example, in Iceland in 1783 within the chain of Lucky craters, stretched along a tectonic fault for a distance of approx. 20 km, there was an outflow of ~ 12.5 km 3 of lava spreading over an area of ​​~ 570 km 2.

Composition of lava. Solid rocks formed during the cooling of lava contain mainly silica, alumina, iron, magnesium, calcium, sodium, potassium, titanium and water. Usually in lavas the content of each of these components exceeds one percent, and many other elements are present in less quantity.

TABLE 1

(Chebotar Lyudmila)

There are many types of volcanic rocks, differing in chemical composition. The most common types are found in the content of the silica: basalts - 48-53%, andesite - 54-62%, dacite - 63-70%, rhyolite - 70-76% (see table). Breeds in which the amount of silicon dioxide is less contain magnesium and iron in large amounts. When the lava cools, a considerable part of the melt forms a volcanic glass, in the mass of which there are individual microscopic crystals. The exceptions are the so-called. phenocrysts  large crystals formed in magma yet in the bowels of the Earth and brought to the surface by a stream of liquid lava. Most often phenocrysts are represented by feldspars, olivine, pyroxene and quartz. Species containing phenocrysts are usually called porphyrites. The color of the volcanic glass depends on the amount of iron present in it: the more iron, the darker it is. Thus, even without chemical analyzes, one can guess that the light colored rock is rhyolite or dacite, dark-colored  basalt, gray  andesite. According to the minerals that are distinguishable in the rock, its type is determined. For example, olivine, a mineral containing iron and magnesium, is characteristic of basalts, quartz  for rhyolites.

As magma is raised to the surface, the released gases form tiny bubbles with a diameter of more often up to 1.5 mm, rarely up to 2.5 cm. They are stored in the frozen rock. This is how bubble lava is formed. Depending on the chemical composition, the lavas differ in viscosity, or in fluidity. With a high content of silicon dioxide (silica), lava is characterized by a high viscosity. The viscosity of magma and lava largely determines the nature of the eruption and the type of volcanic products. Liquid basaltic lavas with a low silica content form extended lava flows over 100 km in length (for example, it is known that one of the lava flows in Iceland stretches for 145 km). The thickness of lava flows is usually from 3 to 15 m. More liquid lavas form more delicate streams. Flows 35 m thick are usual in Hawaii. When solidification begins on the surface of the basalt stream, its internal part can remain in the liquid state, continuing to flow and leaving behind it an elongated cavity or lava tunnel. For example, on the island of Lanzarot (Canary Islands), a large lava tunnel can be traced for 5 km. The surface of the lava flow is even and undulating (in Hawaii such a lava is called pahoecho) or uneven. Hot lava, which has high fluidity, can move at a speed of more than 35 km / h, but more often its speed does not exceed several meters per hour. In a slowly moving stream, pieces of the frozen upper crust may fall off and overlap with lava; As a result, a zone enriched with debris is formed in the bottom part. When the lava hardens, columnar separations are sometimes formed (polyhedral vertical columns from a few centimeters to 3 m in diameter) or a fracture perpendicular to the cooling surface. When lava flows into a crater or caldera, a lava lake forms, which eventually cools down. For example, such a lake was formed in one of the craters of the Kilauea volcano on the island of Hawaii during the eruptions 1967-1968, when lava entered this crater at a rate of 1.1-10 6 m 3 / h (partially lava subsequently returned to the volcano's mouth). In neighboring craters for 6 months the thickness of the crust of frozen lava on lava lakes reached 6.4 m.

Domes, maars and tuff rings. Very dense lava (most often of dacite composition) during eruptions through the main crater or lateral cracks forms not streams, but a dome with a diameter of up to 1.5 km and a height of up to 600 m. For example, such a dome formed in the crater of St. Helens volcano (USA) after exclusively a strong eruption   in May 1980. The pressure under the dome may increase, and after a few weeks, months or years, it can be destroyed at the next eruption. In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks  lumps or stalks of frozen lava, often tens of hundreds and hundreds of meters high, protrude above its surface. After the catastrophic eruption in 1902 of the Montagne-Pele volcano on the island of Martinique, a lava spire emerged in the crater, which in a day grew by 9 m and as a result reached a height of 250 m, and a year later collapsed. On the Usu volcano on Hokkaido (Japan) in 1942, during the first three months after the eruption, the lava dome of the Syowa-Shinzan rose 200 m. The lava that formed it made its way through the thickness of previously formed sediments.

Maar is a volcanic crater formed during an explosive eruption (most often with high humidity of rocks) without the outpouring of lava. The ring shaft from the clastic rocks thrown out by the explosion is not formed, in contrast to the tuff rings  also craters of explosions, which are usually surrounded by rings of detrital products.

Clastic materialemitted into the air during an eruption, is called tephra, or pyroclastic debris. The deposits formed by them are also called. The fragments of pyroclastic rocks are of different sizes. The largest of them are volcanic lumps. If the products at the time of ejection are so liquefied that they freeze and form in the air, then so-called volcanic bombs. Material of less than 0.4 cm is referred to ash, and fragments from pea size to walnut  to lapilli. Hardened deposits, consisting of lapilli, are called lapillium tuff. There are several types of tephra, differing in color and porosity. Light-colored, porous, not drowning in water tephra is called pumice stone. The dark bubble tephra, consisting of separate lapillian dimensions, is called volcanic slag. Pieces of liquid lava, which are briefly in the air and do not have time to fully harden, form splashes, often forming small spray cones near the outlets of lava flows. If these sprays are caking, the emerging pyroclastic deposits are called agglutinates.

An air-weighted mixture of very fine pyroclastic material and heated gas, ejected from an eruption from the crater or cracks and moving above the soil surface at a speed of ~ 100 km / h, forms ash streams. They extend to many kilometers, sometimes overcoming water spaces and elevations. These formations are also known under the name of scorching clouds; they are so hot that they shine at night. In ash streams, large debris can also be present, incl. and pieces of rock torn from the walls of the volcano's mouth. Most often, scorching clouds are formed when a column of ash and gases is thrown out of the vents vertically. Under the action of gravity, counteracting the pressure of the erupting gases, the marginal parts of the column begin to settle and descend along the slope of the volcano in the form of a hot avalanche. In some cases, scorching clouds appear along the periphery of the volcanic dome or at the base of the volcanic obelisk. It is also possible to eject them from annular cracks around the caldera. Deposits of ash streams form the volcanic rock ignimbrite. These streams transport both small and large fragments of pumice. If the ignimbrites are deposited with a sufficiently thick layer, the inner horizons can be so hot that the pumice fragments melt, forming a caked ignimbrite, or a caked tuff. As the rock cools down in its internal parts, a columnar separation can be formed, with a less distinct shape and larger structure than similar structures in lava flows.

Directed volcanic explosions are a rather rare phenomenon. The deposits created by them can easily be confused with sediments of detrital rocks, with which they often coexist. For example, during the eruption of St. Helens volcano just before the directed explosion, an avalanche of crushed stone occurred.

Underwater volcanic eruptions. If there is a reservoir above the volcanic focus, during the eruption the pyroclastic material is saturated with water and spreads around the hearth. Deposits of this type, first described in the Philippines, formed as a result of the eruption in 1968 of the Taal volcano, located at the bottom of the lake; they are often represented by thin wavy layers of pumice.

Seli volcanic eruptions may be associated with mudslides, or mud flows. Sometimes they are called lahars (originally described in Indonesia). The formation of lakhars is not part of the volcanic process, but represents one of its consequences. On the slopes of active volcanoes, a loose material (ash, lapilli, volcanic debris) is accumulated in abundance, emitted from volcanoes or falling out of scorching clouds. This material is easily involved in the movement of water after rain, with the melting of ice and snow on the slopes of volcanoes or breakthroughs of crater lakes. Mud flows flow with great speed down the riverbeds of watercourses. During the eruption of the Ruiz volcano in Colombia in November 1985, more than 40 million m 3 of clastic material was sown at a speed above 40 km / h to the piedmont plain. At the same time, the city of Armero was destroyed and about. 20 thousand people. Most often, such villages descend during eruptions or immediately after it. This is due to the fact that during eruptions accompanied by the release of thermal energy melting of snow and ice, the breakthrough and descent of crater lakes and violation of the stability of the slopes.

Gasesthe gases emitted from the magma, the gases before and after the eruption, are in the form of white jets of water vapor. When tephra is mixed with them during the eruption, the outflows become gray or black. Weak emission of gases in volcanic areas can last for years. Such outlets of hot gases and vapors through the holes at the bottom of the crater or slopes of the volcano, as well as on the surface of lava or ash streams are called fumaroles. To specific types of fumarole include solfatary, containing sulfur compounds, and mofety, in which carbon dioxide predominates. The temperature of the fumarolic gases is close to the temperature of the magma and can reach 800 ° C, but it can also drop to the boiling point of water (~ 100 ° C), whose pairs are the main constituent of fumaroles. Fumarolic gases are generated both in shallow near-surface horizons, and at great depths in incandescent rocks. In 1912, as a result of the eruption of the volcano Novarupta in Alaska, the famous Valley of ten thousand fumes was formed, where on the surface of volcanic emissions an area of ​​approx. 120 km 2 there were many high-temperature fumaroles. Currently in the Valley there are only a few fumaroles with a fairly low temperature. Sometimes white vapor streams rise from the surface of the still lava flow that has not cooled down; most often it is rainwater, heated by contact with a hot stream of lava.

Chemical composition of volcanic gases. The gas released from volcanoes is 50-85% composed of water vapor. More than 10% accounted for carbon dioxide, ca. 5% is sulfur dioxide, 25%  hydrogen chloride and 0.02-0.05%  hydrogen fluoride. Hydrogen sulfide and gaseous sulfur are usually contained in small amounts. Sometimes there are hydrogen, methane and carbon monoxide, as well as a small admixture of various metals. In gas emissions from the surface of the lava flow covered with vegetation, ammonia was detected.

Tsunami   huge sea waves, associated mainly with underwater earthquakes, but sometimes occur during volcanic eruptions on the ocean floor, which can cause the formation of several waves, which occur at intervals of several minutes to several hours. The eruption of the volcano Krakatau on August 26, 1883 and the subsequent collapse of its caldera was accompanied by a tsunami of more than 30 m in height, resulting in numerous human casualties on the coasts of Java and Sumatra.

CHAPTERIV.

THE SUBSTANTIVE PECULIARITIES

With the attenuation of volcanic activity, a number of characteristic phenomena are observed for a long time, indicating active processes that continue in depth. These include the emission of gases (fumaroles), geysers, mud volcanoes, thermae.

4.1. Fumaroles (volcanic gases).

After the eruption of volcanoes, gaseous products from the craters themselves, various cracks, from hot tuffolovo flows and cones are released for a long time. In the composition of volcanic gases there are the same gases of the group of halides, sulfur, carbon, water vapor and others that are released during volcanic eruptions. However, one can not outline a unified scheme for the composition of gases for all volcanoes. Thus, in Alaska, thousands of gas jets with a temperature of 600-650 are separated from tufogenic lava products from the Katmai volcano eruption (1912) over the next years, in which a large number of halides (HCl and HF), boric acid, hydrogen sulphide and carbon dioxide . A somewhat different picture is observed in the area of ​​the famous Phlegrean fields in Italy, west of Naples, where many volcanic craters and small cones have been characterized for thousands of years by exclusively solfataric activity. In other cases, carbon dioxide prevails.

Fig.13 The largest fumarole of the volcano Avachinsky Sopka   (www.criazon.com)

Fig.14 Sulfuric   deposits around fumaroles (www.criazon.com)

4.2. Geysers.

Geysers are periodically operating steam-water fountains. Their fame and name they received in Iceland, where they were observed for the first time. In addition to Iceland, geysers are widely developed in the Yellowstone Park of the USA, in New Zealand, in Kamchatka. Each geyser is usually confined to a rounded hole, or griffin. Griffins come in various sizes. In the depth of this channel, apparently, passes into tectonic fissures. The entire canal is filled with overheated underground water. Its temperature in the griffin can be 90-98 degrees, while in the depth of the channel it is much higher and reaches 125-150 gr. and more. At some point in the depths of intense vaporization begins, as a result, the column of water in the griffin is raised. Thus each particle of water appears in a zone of smaller pressure, boiling begins and eruption of water and steam. After the eruption, the canal gradually fills up with underground water, partly with water thrown out by the eruption and draining back into the griffin; 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 of Yellowstone Park the height of the fountain of water and steam reached 40 m.

Fig. 15. Scheme of action of the geyser. (www.criazon.com)

The water under hydrostatic pressure in underground voids is gradually heated above 100 °. When the critical temperature is reached, it boils. The resulting vapor   fromnoise is thrown out of the geyser, carrying with it boiling water .

Mud volcanoes (salsa).

They are sometimes found in the same areas as the geysers (Kamchatka, Java, Sicily, etc.). Hot water vapor and gases break through to the surface through cracks, are ejected and form small outlets 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 characterized by high temperatures (up to 80-90 0). So there are mud volcanoes. Density, or consistency, of dirt determines the nature of their activity and structure. With relatively liquid dirt, the release of vapors and gases causes splashes in it, the mud spreads freely and the cone with the crater at the top is 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 the mud volcanoes can be divided into: 1) associated with the release of combustible gases;

2) confined to the areas of magmatic volcanism and caused by the release of magmatic gases. " . These include Absheron, Taman mud volcanoes.

Fig.16 Mud volcano. surroundings Pirikiškul. Azerbaijan   (www.criazon.com)

Fig.17 Mud volcano near Salton Sea (www.criazon.com)

CONCLUSION.

Current active volcanoes are a vivid manifestation of endogenous processes accessible to direct observation, which played a huge role in the development of geographic science. However, the study of volcanism has not only cognitive significance. Operating volcanoes, along with earthquakes, pose a formidable danger to nearby settlements. Moments of their eruptions are often irreparable natural disasters, expressed not only in the huge material damage, but sometimes in the mass death of the population. Well, for example, we know the eruption of Vesuvius in 79 AD, which destroyed the cities of Herculaneum, Pompeii and Stabia, as well as a number of villages on the slopes and at the foot of the volcano. As a result of this eruption, several thousand people died.

Thus, the current active volcanoes, characterized by intensive cycles of energetic eruptive activity and representing, in contrast to their ancient and extinct counterparts, objects for scientific research volcanic observations, are most favorable, although far from being safe.

To avoid the impression that volcanic activity brings only disasters, it is necessary to give such brief information about some useful aspects.

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

The vapors of water and gases released in the volcanic regions, steam-water mixtures and hot springs became sources of geothermal energy.

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

Products of direct volcanic activity - individual lavas, pumice, perlite, etc. find application in the building and chemical industries. With fumarolic and hydrothermal activity, the formation of certain minerals, such as sulfur, cinnabar, and several others, is associated. 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 there are still many unresolved mysteries in front of mankind besides volcanism and they have to be solved by someone.

And the study of modern volcanic activity has an important theoretical significance, since it helps to understand the processes and phenomena that occurred on Earth in ancient times.

BIBLIOGRAPHY.

1.   Aprodov VA Volcanoes .- M.: Thought, 1982.-361 p.

2.   Wlodavets V.I. Volcanoes of the Earth .- M .: Nauka, 1973.-168 p.

3.   Markhinin E.K. Volcanoes and life. -M.: Thought, 1980-196 p.

4.   Yakushko OF Fundamentals of geomorphology // Relief-forming role of volcanic processes .- Mn .: BSU, 1997.- from 46-53.

5.   Yakushova A.F. Geology with the fundamentals of geomorphology // Magmatizm. Moscow: Izd-vo Mosk. University, 1983.- from 236-266.

They bring to the surface an average of at least 5-6 km 3 of volcanic material per year, about 80% of which erupt underwater volcanoes and only 20% - terrestrial. The most intensive removal of volcanic material (about 4 km 3 per year) occurs along the rift zones of the mid-oceanic ridges. Volcanism here is manifested in the form of calm lava fissures at a depth of 3-4 km and is practically inaccessible to direct observation. Terrestrial volcanoes are usually individual cone-shaped mountains (volcanic cones) with a central crater, built up by products of eruptions. The dimensions of the volcanoes depend on their hypsometric position. The maximum relative height (cone top over the base) of active volcanoes reaches 9 km in the oceans, 6 km in island arcs, and 3 km in mountain structures. The average height of the active volcanoes of the Earth is 1.75 km, the volume is 85 km 3.

Classification.   Volcanoes are divided into active, potentially active, conditionally extinct and extinct. The active ones include volcanoes erupting or exhibiting solfatar activity (release of hot gases and water) over the last 3500 years of the historical period. Their total number is 947 (1980). The Holocene volcanoes that erupted 3500-13500 years ago are potentially active. The total number of known volcanoes is 1343. Volcanoes, which did not show activity in the Holocene, but retained their outer forms (under the age of 100 thousand years), are considered conditionally extinct. Volcanoes, substantially reworked by erosion, dilapidated, not showing activity during the last 100 thousand years, are called extinct.

Depending on the shape of the feed channels, volcanoes are divided into central and fissured. In the depth of magmatic foci, volcanoes of mantle (30-70 km and more), crustal (5-45 km) and mixed feeding are distinguished. The products of the eruptions of the first are represented, the second is predominantly, and, thirdly, all types of volcanic rocks. In the oceans only volcanoes of mantle nutrition are known (Kilauea in the Hawaiian Islands, Teide on the island of Tenerife, etc.), and on the island arcs and continental - mantle, crustal and mixed Klyuchevskaya Sopka, Shiveluch and Karymskaya Sopka in Kamchatka, Kilimanjaro in Africa, Vesuvius in Italy, etc.), in the mountainous structures - only the chickens (Elbrus in the Caucasus, Lassen Peak in North America, etc.).

Volcanic phenomena.   Eruptions are long (for several years, decades and centuries) and short-term (measured by a clock). Volcanic earthquakes, acoustic phenomena, changes in the magnetic field and composition of fumarolic gases, and other phenomena are among the precursors of the eruption. The eruption of volcanoes of the central type usually begins with an increase in the emission of gases first together with the dark cold debris of the lavas, and then with the hot flashes. In some cases, these outbursts are accompanied by outpourings of lava. The height of the rise of gases, water vapor, saturated with ash and wreckage fragments, depending on the strength of the explosions, usually ranges from 1 to 5 km (during the eruption of the Bezymyanny volcano on Kamchatka in 1956 it reached 45 km). The discarded material is transferred to distances from several kilometers to tens of thousands of kilometers. The volume of ejected detrital material sometimes reaches several km 3.

The eruption of volcanoes of the central type is an alternation of weak and strong explosions and eruptions of lavas. Explosions of maximum force are called culminating paroxysms. After them, the force of explosions decreases and the eruptions gradually stop. The volumes of the lava spread over a dozen km 3. Fracture eruption proceeds differently: there is a quiet outflow of lavas from the cracks with the formation along them one or a number of small volcanoes (slag cones); the formation of lava covers is characteristic. Examples of fissure eruptions are Lucky volcanoes in Iceland (in 1783) and Tolbachik in Kamchatka (1975-76).

Types of eruptions. Depending on the quantitative ratio of erupting volcanic products (gaseous, liquid and solid) and viscosity of lavas, four main types of eruptions are identified: effusive, mixed, extrusive and explosive, or, as they are often called, Hawaiian Strombolian, Dome and Vulcan respectively.

Hawaiian type of eruption, which often creates thyroid volcanoes, differs relatively quiet outpouring of liquid (basaltic) lava, forming in the craters fiery-liquid lakes and lava flows. Gases contained in a small amount form fountains, throwing lumps and drops of liquid lava, which are stretched in flight into thin glass filaments (Kilauea on the island of Hawaii).

In the Strombolian type of eruptions, which usually create stratovolcanoes, along with sufficiently abundant effusions of liquid basaltic and andesite-basalt lavas (sometimes very long streams form), small explosions predominate that throw out slag pieces and various twisted and spindle-shaped bombs (stromboli in the Aeolian Islands, Mihara in Japan, some eruptions of Klyuchevskaya Sopka).

For the dome type, squeezing and pushing out a viscous (andesite, dacite or rhyolite) lava with a strong pressure from the channel of volcanoes and the formation of domes (Puy de Dome in Auvergne, France, Central Semyachik in Kamchatka), cryptocopoles (Syowa-Shinzan on the island of Hokkaido, Japan) and obelisks (Shiveluch in Kamchatka).

In the Vulcan type, gases play an important role, producing explosions and ejections of huge clouds, crowded with large amounts of debris of rocks, lavas and ashes. Lavas are viscous (andesite, dacite or rhyolite), form small flows (Vulcano in the Aeolian Islands, Avachinskaya Sopka   and Karymskaya Sopka in Kamchatka).

Each of the main types of eruptions is divided into several subtypes. Of these, Peleic and Kathmai, which are intermediate between the dome and Vulcan types, stand out. A characteristic feature of the former is the formation of domes and directed explosions of very hot clouds, overflowing with self-explosive in flight and with the debris and lumps of lavas rolling down the slope of the volcanoes (Montagne-Pele to Martinique Island). The eruptions of the Katmai subtype are distinguished by the ejection of a very hot, highly mobile sand flow (Katmai in Alaska). Dome-forming eruptions are sometimes accompanied by hot or sufficiently cooled avalanches, as well as mud flows. The ultravulcan subtype is expressed in very strong explosions with the release of a huge amount of debris lavas and rocks of the canal walls.

Eruptions of underwater volcanoes, located at great depths, are usually invisible, because large water pressure prevents explosive eruptions. At lower depths, eruptions are manifested by explosions (releases) of huge amounts of vapor and gases, overflowing with lava pieces. Explosive eruptions continue until the erupting material forms an island rising above sea level. After that, explosions alternate with outpourings of lava.

Products of the eruption   volcanoes are gaseous (see), liquid (see) and solid (see). Depending on the nature of the eruptions and the composition of the magma, structures of various shapes and heights are formed on the surface. They are volcanic apparatuses consisting of a pipe-shaped or fissured channel, a vent (the uppermost part of the channel) surrounding the channel from different sides of the powerful accumulations of lavas and volcanic clastic products and the crater (the cup-shaped depression located on top of the structure).

Placement of active volcanoes on the Earth's surface.   Modern volcanoes are known in all major geological-structural elements and geographic regions of the Earth (Table). However, they are very unevenly distributed. There is a direct correlation between their quantity and tectonic activity of the area: the largest number   active volcanoes per unit area are accounted for by island arcs (Kamchatka, Kuril Islands, Indonesia, etc.) and mountain structures (South and North America). The most concentrated active volcanoes   world, characterized by the highest frequency of eruptions.

The lowest density of volcanoes is characteristic for oceans and continental platforms; here they are connected mainly with rift zones - narrow and extended areas of splits and subsidence of the earth's crust. These are, for example, the East African rift system (Nyiragongo and others) and the Mid-Atlantic ridge with splits in the axial zone (Iceland).

The causes of volcanoes.   The geographical location of volcanoes indicates a close connection between the belts of volcanic activity and the dislocated mobile zones of the earth's crust. The ascent of magma through the asthenosphere and the lithosphere to the earth's surface occurs through cracks and pipe-like channels, apparently under the influence of hydrostatic forces. When magmatic melts reach the upper horizons of the earth's crust and the Earth's surface, the explosive release of volcanic gases also becomes the driving force of the eruption process.

Since volcanoes are a potential hazard, systematic observations of their behavior are conducted to predict the upcoming eruptions. The study of the nature of volcanoes includes the recording and analysis of movements of the earth's crust, earthquakes, changes in the composition of gases, electromagnetic anomalies.