What are the components in a volcano. Volcanoes

An average of at least 5-6 km 3 of volcanic material is brought to the surface per year, about 80% of which is erupted by underwater volcanoes and only 20% by terrestrial ones. The most intense outflow of volcanic material (about 4 km 3 per year) occurs along the rift zones of the mid-ocean ridges. Volcanism here manifests itself in the form of calm lava fissure eruptions at a depth of 3-4 km and is practically inaccessible to direct observation. Ground volcanoes are usually individual cone-shaped mountains (volcanic cones) with a central crater, composed of eruption products. The size of volcanoes depends on their hypsometric position. The maximum relative height (elevation of the top of the cone 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 subdivided into active, potentially active, conditionally extinct and extinct. Active volcanoes are those that have erupted or have shown solfatara activity (release of hot gases and water) over the past 3500 years of the historical period. Their total number is 947 (1980). Potentially active are Holocene volcanoes that erupted 3500-13500 years ago. Total amount famous volcanoes is 1343. Volcanoes that did not show activity in the Holocene, but retained their external forms (less than 100 thousand years old) are considered conditionally extinct. Volcanoes, significantly reworked by erosion, dilapidated, not showing activity for the last 100 thousand years, are called extinct.

Depending on the shape of the supply channels, volcanoes are divided into central and fissure. Volcanoes of mantle (30–70 km and more), crustal (5–45 km) and mixed feeding differ in the depth of magma chambers. The products of the eruption of the first are presented, of the second - mainly, and, of the third - all types volcanic mountains rocks. In the oceans, only volcanoes of mantle feeding are known (Kilauea on the Hawaiian Islands, Teide on Tenerife, etc.), and on island arcs and continental arcs - of mantle, crustal and mixed ( Klyuchevskaya Sopka, Shiveluch and Karymskaya Sopka in Kamchatka, Kilimanjaro in Africa, Vesuvius in Italy, etc.), in mountain structures - only chickens (Elbrus in the Caucasus, Lassen Peak in North America, etc.).

Volcanic phenomena. Eruptions are long-term (over several years, decades and centuries) and short-term (measured in hours). The precursors of an eruption include volcanic earthquakes, acoustic phenomena, changes magnetic field and composition of fumarole gases and other phenomena. Volcanic eruption central type usually begins with an increase in gas emissions, first together with dark cold lava fragments, and then with red-hot ones. These outbursts are in some cases accompanied by the outpouring of lava. The height of the rise of gases, water vapor, saturated with ash and lava fragments, depending on the strength of the explosions, usually ranges from 1 to 5 km (during the eruption of the Bezymyanny volcano in Kamchatka in 1956, it reached 45 km). The ejected material is transported over distances from several kilometers to tens of thousands of kilometers. The volume of the ejected debris sometimes reaches several km 3.

The eruption of volcanoes of the central type is an alternation of weak and strong explosions and eruptions of lava. Explosions of maximum force are called climactic paroxysm. After them, there is a decrease in the force of explosions and a gradual cessation of eruptions. The volume of the erupted lava is over ten km 3. A fissure eruption proceeds differently: there is a quiet outpouring of lava from cracks with the formation of one or a series of small volcanoes (cinder cones) along them; the formation of lava sheets is characteristic. Examples fissure eruption are the volcanoes Laki in Iceland (in 1783) and the Tolbachik volcano in Kamchatka (1975–76).

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

The Hawaiian type of eruption, which most often creates shield volcanoes, is distinguished by a relatively calm outpouring of liquid (basaltic) lava, which forms fiery liquid lakes and lava flows in craters. Small amounts of gases form fountains, throwing out lumps and drops of liquid lava, which are drawn in flight into thin glass filaments (Kilauea on the island of Hawaii).

In the Strombolian type of eruptions, which usually create stratovolcanoes, along with fairly abundant outpourings of liquid basaltic and basaltic andesite lavas (sometimes they form very long flows), small explosions predominate, which throw out pieces of slag and various twisted and spindle-shaped bombs (stromboli, Mihipara in Japan, some eruptions of Klyuchevskaya Sopka).

The dome type is characterized by the squeezing and ejection of viscous (andesitic, dacitic or rhyolite) lava by strong pressure from the channel of volcanoes and the formation of domes (Puy de Dom in Auvergne, France; Central Semyachik in Kamchatka), crypto domes (Showa-Shinzan on the island of Hokkaido, Japan) and obelisks (Shiveluch in Kamchatka).

In the Vulcan type, gases play an important role, producing explosions and emissions of huge clouds overflowing with large amounts of rock debris, lava and ash. Viscous lavas (andesitic, dacitic or rhyolitic), form small flows (Vulcano on the Aeolian Islands, Avachinskaya Sopka and Karymskaya Sopka in Kamchatka).

Each of the main types of eruptions is divided into several subtypes. Of these, the Pelei and Katmai types stand out, intermediate between the dome and Vulcan types. A characteristic feature of the first is the formation of domes and directional explosions of very hot clouds overflowing with debris and lava blocks that explode in flight and when rolling down the slope of volcanoes (Montagne Pele to Martinique Island). Eruptions of the Katmai subtype are distinguished by the ejection of a very hot, highly mobile sandy stream (Katmai in Alaska). Dome-forming eruptions are sometimes accompanied by incandescent or sufficiently cooled avalanches, as well as mud streams. The Ultravolcanic subtype is expressed in very strong explosions with the release of a huge amount of lava fragments and rocks from the channel walls.

Eruptions of underwater volcanoes located at great depths are usually invisible, because great pressure water prevents explosive eruptions. At shallower depths, eruptions are manifested by explosions (emissions) of huge amounts of steam and gases overflowing with lava pieces. Explosive eruptions continue until the erupted material forms an island that rises above sea level. Then the explosions alternate with the outpouring of lava.

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

Placement of active volcanoes on the surface of the Earth. Modern volcanoes are known in all large geological and structural elements and geographic regions of the Earth (table). However, they are distributed extremely unevenly. There is a direct relationship between their number and the tectonic activity of the region: the largest number of active volcanoes per unit area falls on island arcs (Kamchatka, Kuril Islands, Indonesia, etc.) and mountain structures (South and North America). Here are also concentrated the most active volcanoes the world characterized by the highest frequency of eruption.

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

The reasons for the activity of volcanoes. The geographical location of the volcanoes indicates a close connection between the belts volcanic activity and dislocated mobile zones of the earth's crust. The rise of magma through the asthenosphere and 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 surface of the Earth driving force the eruption process also becomes a violent release of volcanic gases.

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

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Home> Abstract> Geography

Introduction ……………………………………………………………………………………… 2

ChapterI. General ideas about vulcanism …………… .. ……………………………… ... 4

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

2.1. Volcanoes of the central type …………………………………………… ... …… .. 5

2.1.1. Polygenic volcanoes… .. …………………………………………… ... …….…. 6

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

2.2. Fissure type of eruption ………………………………… .. …………………. 15

2.3. Areal type of eruption …………………………………… .. …………… .. 16

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

3.1. Mediterranean-Indonesian zone …………………………………. ……… .. 18

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

3.3. Indian Ocean zone ………………………………………. ………………… ....…. 19

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

3.5. Active volcanoes land ……………………… ...…. …………………….… 20

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

ChapterIV... Postvolcanic 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, one of the most formidable natural phenomena, often brings enormous disasters to people and the national economy. Therefore, it must be borne in mind that although not all active volcanoes cause misfortune, nevertheless, each of them can be, to one degree or another, a source of negative events.

Purpose of the study:

The aim is to study volcanism as the most important manifestation endogenous processes, and their geographic distribution.

It is necessary to trace:

Classification of eruptions.

Types of volcanoes.

Composition of erupting lava.

Consequences of volcanic activity for the geographic envelope.

The location of a specific 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 consequences of volcanic activity on the geographic envelope.

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 globality of this process, the causes and consequences of the impact of volcanism on the geographic shell. It is no secret that each of us would like to be near an erupting volcano, at least once to feel our microscopic character in comparison with the natural forces of the Earth. And even more so for every 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.

The structure of the course work:

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

CHAPTER I. GENERAL CONCEPTS ABOUT VOLCANISM.

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

This opinion is expressed by the majority of volcanologists, but this is far from the only idea of ​​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 gas components remain in a dissolved state. As the magma moves to the surface, the pressure decreases, gases begin to evolve, as a result, the magma poured onto the surface is significantly different from the original. To emphasize this difference, the magma that poured out to the surface is called lava. The eruption process is called eruptive activity.

Volcanic eruptions are not the same, depending on the composition of the eruption products. 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 out 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, rise 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 interior of the Earth to its surface. At a depth of 50 to 350 km, in the thickness of our planet, foci of molten matter - magma are formed. Along the sites of crushing and fractures of the earth's crust, magma rises and pours out to the surface in the form of lava (differs from magma in that it contains almost no volatile components, which are separated from magma when pressure drops and go into the atmosphere.

In places of eruption, lava sheets, flows, volcanoes-mountains, composed of lavas and their dispersed particles - pyroclasts appear. According to the content of the main component - magma silicon oxide 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 abundant is basic, or basaltic, magma.

CHAPTERII... TYPES OF VOLCANOES, COMPOSITION OF LAVA.

CLASSIFICATION BY THE NATURE OF THE Eruption.

The classification of volcanoes is based mainly on the nature of their eruptions and on the structure of volcanic apparatus. 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) - explosion and release a large number pyroclastic material (solid products of eruption);

3) extrusive - squeezing, or squeezing, 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 variety of volcanic edifices and forms of occurrence of volcanic material are noted.

Among volcanic eruptions, the following stand out:

1) eruptions of the central type

2) fractured

3) areal.

2.1 Volcanoes of the central type.

They have a shape close to rounded in plan, and are represented by cones, shields, 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 supply channel, or a volcano crater, which has a pipe-like shape, along which magma from a deep chamber rises to the surface. Among the volcanoes of the central type, polygenic, formed as a result of repeated eruptions, and monogenic, which once manifested their activity, stand out.

2.1.1 Polygenic volcanoes.

These include most of the known volcanoes in the world. There is no unified and generally accepted classification of polygenic volcanoes. Various types of eruptions are most often designated by the name of the famous volcanoes in which this or that process manifests itself most characteristically.

Effusive, or lava, volcanoes.

The predominant process in these volcanoes is effusion, or the outpouring of lava onto the surface and its movement in the form of flows along the slopes of the volcanic mountain. The 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 merging peaks of five volcanoes, of which four were active in historical time. The activity of two volcanoes is especially well studied; Mauna Loa, which rises almost 4200 meters above the Pacific Ocean, and Kilauea is over 1200 meters high.

The lava in these volcanoes is basic basaltic, easily mobile, high-temperature (about 1200 0). In the crater lake, lava boils all the time, its level goes down and up. During eruptions, lava rises, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are released relatively calmly, forming splashes above the crater, lava fountains rising in height from several to hundreds of meters (rarely). The gas-foamed lava is sprayed and solidified in the form of thin glass filaments ‘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.

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

Effusive underwater.

Eruptions are the most numerous and least studied. They are also confined to rift structures and are 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, which means that no pyroclasts appear. Under water pressure, even liquid basaltic lava does not spread far, it forms short domed bodies or narrow and long streams covered from the surface with a glassy crust. Distinctive feature submarine volcanoes located at great depths are 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 (over 3263 m), located on the island of Sicily; Vesuvius (about 1200 m high), located near Naples; Stromboli and Vulcano from the Aeolian Islands group in the Strait of Messina. Many volcanoes of Kamchatka, the Kuril and Japanese islands and the western part of the Cordillera mobile belt belong to the same category. The lavas of these volcanoes are different - from basic (basaltic), andesite-basaltic, andesite to acidic (liparite). Several types are conventionally distinguished among them.

Strombolian type.

It is characteristic of the Stromboli volcano, which rises in the Mediterranean Sea to an altitude of 900 m. The lava of this volcano is mainly of basalt composition, but it has a lower temperature (1000-1100) than the lava of the volcanoes of the Hawaiian islands, therefore it is less mobile and saturated with gases. The eruptions occur rhythmically at regular intervals, from a few minutes to an hour. Gas explosions throw hot lava to a relatively small height, which then falls on the slopes of the volcano in the form of spirally wound bombs and slag (porous, bubbly lava lumps). It is characteristic that very little ash is thrown out. A cone-shaped volcanic apparatus consists of layers of slag and solidified lava. Such a well-known volcano as Isalco belongs to the same type.

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

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

Ethno-Vesuvian (Vulcan) type.

Fig. 4 Etna volcano (www.criazon.com) Fig. 5 Main crater (www.criazon.com)

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

Explosive volcanoes (gas explosive) and

extrusive-explosive.

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

Peleus type.

It was especially clearly manifested in the Mont Pele volcano on the island. Martinique, part of the Lesser Antilles group. The lava of this volcano is predominantly medium, andesitic, highly viscous and gas-rich. When solidified, it forms a solid plug in the volcano's vent, which prevents the free escape 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. Huge clouds of gases are formed, oversaturated with lava. These incandescent (with temperatures over 700-800) gas-ash avalanches do not rise high, but slide down the slopes of the volcano at high speed and destroy all living things on their way.

Rice. 7 The eruption of the Mont Pele volcano

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

Krakatoa type.

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

human casualties were associated with a blast wave of enormous force.

Rice. 8 Krakatoa volcano, early 19th century. (www.criazon.com)

Rice. 9 Volcano Krakatoa. View from space ( www. criazon. com)

Katmay type.

It is distinguished by the name of one of the large volcanoes in Alaska, near the base of which in 1912 there was a large gas-explosive eruption and a directed release of avalanches, or streams, of a hot gas-pyroclastic mixture. The pyroclastic material had an acidic, rhyolite or andesite-rhyolite composition. This incandescent ash-gas mixture filled a 23 km deep valley located northwest of the foot of Mount Katmai. In place of the former valley, a flat plain about 4 km wide was formed. For many years, from the stream that filled it, massive emissions of high-temperature fumaroles were observed, which served as the basis for calling it the "Valley of Ten Thousand Smokes".

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

2.1.2. Monogenic volcanoes.

Maar type.

This type unites only once erupted volcanoes, now extinct explosive volcanoes. In relief, they are represented by flat saucer-shaped hollows framed by low ramparts. The shafts contain both volcanic slags and debris volcanic rocks that make up the given territory. In vertical section, the crater looks like a funnel, which in the lower part is connected to a pipe-like 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 in height) 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 a supply pipe-like channel (throat). They are formed by one gas explosion of great strength. Diamond pipes belong to a special category. Explosion tubes in South Africa are widely known as diatremes (Greek "dia" - through, "tram" - hole, hole). Their diameter ranges from 25 to 800 meters, they are filled with a kind of brecciated volcanic rock called kimberlite (after the city of Kimberley in South Africa). This rock contains ultrabasic rocks - garnet-bearing peridotites (pyrope is a diamond companion), characteristic of top mantle Earth. This indicates the undercurrent formation of magma and its rapid rise to the surface, accompanied by gas explosions.

2.2 Fracture eruptions.

They are confined to large faults and cracks in the earth's crust, which play the role of magma conduits. The eruption, especially in the early phases, can occur along the entire mother-in-law or in certain areas of her sections. Subsequently, along the fault line or cracks, groups of close volcanic centers arise. The poured out main lava, after solidification, forms basalt covers of various sizes with an almost horizontal surface. In historical time, similar powerful fissure outpourings of basaltic lava were observed in Iceland. Fissure effusions are widespread on slopes large volcanoes... They are apparently widespread within the faults of the East Pacific Rise and in other mobile zones of the World Ocean. Especially significant fissure eruptions were in the past geological periods, when thick lava sheets were formed.

2.3. Areal type of eruption.

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

CHAPTERIII.

GEOGRAPHICAL DISTRIBUTION OF VOLCANOES.

Currently, there are several thousand extinct and active volcanoes on the globe, and among the extinct volcanoes, many ceased their activity for tens and hundreds of thousands of years, and in some cases even 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 solfatara stage (201).

In the geographical distribution of volcanoes, a certain pattern is outlined, 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. Volcanoes are especially widespread in transition zones from continents to oceans — within island arcs bordering on deep-sea trenches. In the oceans, many volcanoes are confined to the mid-oceanic underwater ridges. Thus, the main regularity in 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 region. So, in island arcs (Japanese, Kuril-Kamchatka, Aleutian, etc.) volcanoes are distributed in chains along fault lines, mainly longitudinal transverse and oblique faults. Some of the volcanoes are also found in older massifs, rejuvenated in the latest 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 subzone proper of the Pacific Ocean with volcanoes at the bottom of the Pacific Ocean. At the same time, mainly andesite lava is erupted in the first subzone, and basaltic lava in the second.

The first subzone passes through Kamchatka, where about 129 volcanoes are concentrated, of which 28 exhibit modern activity. The largest of them 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, Solomon, New Hebrides, New Zealand and then passes to Antarctica, where on about. Rossa is dominated by four young volcanoes. Of these, the most famous are Erebus, which operated in 1841 and 1968, and the Terror with side craters.

The described strip of volcanoes passes further on to the South Antilles submarine 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. Then it continues along the coast of South America. Along the western coast there are high young mountains - the Andes, to which numerous volcanoes are confined, located linearly along the deep faults. In total, there are several hundred volcanoes within the Andes, many of which are currently active or have operated 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, and Isalco, called the lighthouse of the Pacific Ocean because of the continuous eruptions. This active volcanic zone is adjoined by the Maloantil volcanic arc of the Atlantic Ocean, where, in particular, there is famous volcano Mont Pele (on the island of Martinique).

There are not so many active volcanoes within the Cordilleras 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 itself. Per last years at the bottom of the Pacific Ocean, underwater ridges and big number deep faults, which are associated with numerous volcanoes, now protruding in the form of islands, then located below ocean level. The overwhelming majority of the islands in the Pacific Ocean owe their origin to volcanoes. Among them, the most studied are the volcanoes of the Hawaiian Islands. 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.

3.1 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, Aleutian, bounded by faults and deep-water depressions. A very large number of active, dying 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 attenuation stage. 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 joins 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 which are Erdzhiyas and others; to the south, within Turkey, the Big and Small Ararat rises, in the Caucasus - the two-headed Elbrus, Kazbek, around which there are hot springs. Further, in the Elbrus ridge, there is the Demavend volcano and others.

3.2 Atlantic area.

Within the Atlantic Ocean, contemporary volcanic activity, with the exception of the above-mentioned Antilles island arcs and the Gulf of Guinea region, does not affect the continents. Volcanoes are mainly confined to the Mid-Atlantic Ridge and its lateral branches. Some of the large islands within them are volcanic. A number of volcanoes in the Atlantic Ocean begins in the north from about. Jan Mayen. To the south is about. Iceland, where there are a large number of active volcanoes and where fissure outpourings of the main lava took place relatively recently. In 1973, a major eruption of Helgafel took place for 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, Ascension Islands, Asuncienne, Tristan da Cunha, Gough and about. Bouvet.

The volcanic islands of the Canary Islands, 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 Canary Islands... There are also many volcanic seamounts and highlands at the bottom of the Atlantic Ocean.

3.3. Indian Ocean zone.

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

3.4 Volcanoes of the central parts of the continents

They are relatively rare. The most striking manifestation of modern volcanism is in Africa. In the area adjacent to the Gulf of Guinea, a large stratovolcano Cameroon rises, its last eruption was in 1959. In the Sahara, on the volcanic highlands of Tibesti, 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. There are active large volcanoes in Africa: Meru with 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 oceanic crust that has already formed here.

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

3.5. Active volcanoes of the earth

A volcano that erupted in historical time is considered to be active. In total, approximately 2500 eruptions of 500 such volcanoes are known. Some of the most famous volcanoes, as well as those mentioned in the text, are marked on the map.

Fig. 11 The main types of volcanoes

The extrusive (lava) dome (left) has a rounded shape and steep slopes cut by deep grooves. In the crater of the volcano, a plug of solidified lava can form, which prevents the release of gases, which subsequently leads to an explosion and destruction of the dome. The steeply sloping pyroclastic cone (right) is composed of alternating layers of ash and slag.

3.6 Volcanic products

Lava- This is magma that pours out onto the earth's surface during eruptions, and then solidifies. Lava outpouring can come from a main summit crater, a side crater on the side of a volcano, or from cracks associated with a volcanic chamber. It flows down the slope in the form of a lava flow. In some cases, there is an outpouring of lava in rift zones of enormous extent. For example, in Iceland in 1783 within the Lucky crater chain, which stretched along a tectonic fault for a distance of approx. 20 km, there was an outpouring of ~ 12.5 km 3 of lava, which was distributed over an area of ​​~ 570 km 2.

Lava composition... Hard rocks formed during the cooling of lava contain mainly silicon dioxide, oxides of aluminum, iron, magnesium, calcium, sodium, potassium, titanium and water. Usually, lavas contain more than one percent of each of these components, and many other elements are present in smaller amounts.

TABLE 1

THE AVERAGE CHEMICAL COMPOSITION OF SOME LAVA (in weight percent)
Oxides	Nepheline basalt	Basalt	Andesite	Dacite	Phonolite	Trachyte	Rhyolite

(Chebotar Ludmila)

There are many types of volcanic rocks that differ in chemical composition. Most often, there are four types, belonging to which is established by the content of silicon dioxide in the rock: basalt - 48-53%, andesite - 54-62%, dacite - 63-70%, rhyolite - 70-76% (see table). Rocks in which the amount of silicon dioxide is less, contain a large amount of magnesium and iron. When lava cools, a significant part of the melt forms volcanic glass, in the mass of which individual microscopic crystals are found. The exception is the so-called. phenocrysts  large crystals formed in magma in the interior of the Earth and carried to the surface by a flow of liquid lava. Most often, phenocrysts are represented by feldspars, olivine, pyroxene, and quartz. Rocks containing phenocrysts are commonly referred to as porphyrites. The color of 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. The type of mineral is determined by the minerals distinguishable in the rock. So, for example, olivine, a mineral containing iron and magnesium, is typical for basalts, quartz - for rhyolites.

As the magma rises to the surface, the evolved gases form tiny bubbles, often up to 1.5 mm in diameter, less often up to 2.5 cm. They remain in the solidified rock. This is how bubble lavas are formed. Depending on the chemical composition, lavas differ in viscosity, or fluidity. With a high content of silicon dioxide (silica), lava is characterized by 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 long (for example, it is known that one of the lava flows in Iceland stretches for 145 km). The thickness of lava flows usually ranges from 3 to 15 m. Thinner lavas form thinner lavas. In Hawaii, flows 3–5 m thick are common. When solidification begins on the surface of a basalt flow, its interior can remain in a liquid state, continuing to flow and leaving behind an elongated cavity, or lava tunnel. For example, on Lanzarote Island (Canary Islands), a large lava tunnel can be traced for 5 km. The surface of a lava flow is flat and wavy (in Hawaii, this lava is called pahoehoe) or uneven. Hot lava, which has a 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, chunks of the solidified upper crust can fall off and be overlapped by lava; As a result, a debris-enriched zone is formed in the bottom part. When lava solidifies, sometimes columnar units (multifaceted vertical columns with a diameter of several centimeters to 3 m) or fractures perpendicular to the cooling surface are formed. When lava flows into a crater or caldera, a lava lake is formed, which cools over time. For example, such a lake was formed in one of the craters of the Kilauea volcano on Hawaii during the 1967-1968 eruptions, when lava entered this crater at a rate of 1.110 6 m 3 / h (partly lava subsequently returned to the volcano's mouth). In the neighboring craters for 6 months, the thickness of the solidified lava crust on lava lakes reached 6.4 m.

Domes, maars and tuff rings. Very viscous lava (most often of dacite composition) during eruptions through the main crater or side cracks forms not flows, 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 was formed in the crater of St. Helens volcano (USA) after exclusively violent eruption in May 1980. The pressure under the dome can increase, and after a few weeks, months or years, it can be destroyed by the next eruption. In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks blocks or spiers of solidified lava, often tens and hundreds of meters high, protrude above its surface. After the catastrophic eruption in 1902 of the Montagne Pele volcano on Martinique Island, a lava spire formed in the crater, which grew by 9 m per day and as a result reached a height of 250 m, and collapsed a year later. On Usu volcano on Hokkaido Island (Japan) in 1942, during the first three months after the eruption, the Showa-Shinzan lava dome rose by 200 m. The viscous lava that formed it broke through the thickness of the 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. An annular wall of debris ejected by the explosion is not formed, in contrast to tuff rings, also explosion craters, which are usually surrounded by rings of debris.

Debris thrown into the air during an eruption is called tephra, or pyroclastic debris. The deposits formed by them are also called. Fragments of pyroclastic rocks are different sizes... The largest of them are volcanic boulders. If the products at the time of release are so liquid that they freeze and take shape while still in the air, then the so-called. volcanic bombs. Material less than 0.4 cm in size is classified as ash, and fragments ranging in size from a pea to walnut to lapilli. The hardened deposits of lapilli are called lapilli tuff. Several types of tephra are distinguished, differing in color and porosity. Light-colored, porous, water-resistant tephra is called pumice. The dark bubbly tephra, made up of lapillian particles, is called volcanic slag. Pieces of liquid lava, which are briefly in the air and do not have time to completely solidify, form splashes, often forming small spray cones near the places where lava flows emerge. If these splashes are sintered, the pyroclastic deposits that form are called agglutinates.

A mixture of very fine pyroclastic material and heated gas suspended in air, ejected from a crater or cracks during an eruption and moving above the ground at a speed of ~ 100 km / h, forms ash flows. They spread over many kilometers, sometimes overcoming bodies of water and hills. These formations are also known as scorching clouds; they are so hot that they glow at night. Ash streams may also contain large debris, incl. and pieces of rock torn from the walls of the volcano's vent. Most often, scorching clouds are formed when a column of ash and gases collapses, ejected vertically from the vent. Under the influence of gravity, opposing the pressure of the erupted gases, the edge parts of the pillar begin to settle and descend along the slope of the volcano in the form of an incandescent avalanche. In some cases, scorching clouds appear around the periphery of a volcanic dome or at the base of a volcanic obelisk. They may also be ejected from ring fissures around the caldera. Deposits ash flows form ignimbrite volcanic rock. These streams transport both small and large pieces of pumice. If ignimbrite is deposited in a sufficiently thick layer, the inner horizons can be so hot that pumice debris melts to form caked ignimbrite, or caked tuff. As the rock cools down, a columnar jointing may form in its inner parts, which is less distinct in shape and larger than similar structures in lava flows.

Directional volcanic explosions are rare. The deposits they create are easily confused with the clastic deposits with which they often coexist. For example, during the eruption of Mount St. Helens immediately before the directed explosion, an avalanche of rubble occurred.

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

Sat down volcanic eruptions can be associated with mudflows, or mud-stone flows. They are sometimes called lahars (originally described in Indonesia). The formation of lahars is not part of the volcanic process, but is one of its consequences. On the slopes of active volcanoes, loose material (ash, lapilli, volcanic debris) accumulates in abundance, ejected from volcanoes or falling out of scorching clouds. This material is easily involved in movement by water after rains, when ice and snow melts on the slopes of volcanoes or breaks through the sides of crater lakes. Mud streams rush down the stream beds with great speed. During the eruption of the Ruiz volcano in Colombia in November 1985, mudflows moving at a speed of more than 40 km / h carried more than 40 million m3 of debris to the foothill plain. At the same time, the city of Armero was destroyed and approx. 20 thousand people. Most often, such mudflows disappear during the eruption 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, breakthrough and descent of crater lakes and disturbance of the stability of slopes occur.

Gases gases released from magma before and after the eruption have the form of white jets of water vapor. When tephra is mixed with them during the eruption, the emissions turn gray or black. Low gas evolution in volcanic areas can last for years. Such outflows of hot gases and vapors through holes on the bottom of a crater or on the slopes of a volcano, as well as on the surface of lava or ash flows, are called fumaroles. Special types of fumaroles include solfatars, containing sulfur compounds, and mofets, in which carbon dioxide predominates. The temperature of fumarole gases is close to the temperature of magma and can reach 800C, but it can also decrease to the boiling point of water (~ 100C), the vapors of which are the main constituent of fumaroles. Fumarole gases originate both in shallow near-surface horizons and at great depths in hot rocks. In 1912, as a result of the eruption of the Novarupta volcano in Alaska, the famous Valley of Ten Thousand Smokes was formed, where on the surface of volcanic emissions with an area of ​​approx. 120 km 2, a lot of high-temperature fumaroles arose. Currently, only a few fumaroles with rather low temperatures are active in the Valley. Sometimes white streams of steam rise from the surface of the still uncooled lava flow; most often it is rainwater, heated in contact with a hot lava flow.

Chemical composition of volcanic gases. The gas released from volcanoes is 50–85% water vapor. Over 10% is accounted for by carbon dioxide, approx. 5% is sulfur dioxide, 2 - 5% is hydrogen chloride and 0.02-0.05% is hydrogen fluoride. Hydrogen sulfide and gaseous sulfur are usually found in small amounts. Sometimes hydrogen, methane and carbon monoxide are present, as well as a small admixture of various metals. Ammonia was found in gas emissions from the surface of a lava flow covered with vegetation.

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

CHAPTERIV.

POSTULCANIC PHENOMENA

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

4.1 Fumaroles (volcanic gases).

After volcanic eruptions, for a long time, gaseous products are emitted from the craters themselves, various cracks, from hot tuff-lava flows and cones. The composition of postvolcanic gases contains the same gases of the group of halogens, 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 are emitted from the tuffaceous-lava products of the Katmai volcano (1912) over the next years, which contain a large amount of halogens (HCl and HF), boric acid, hydrogen sulfide and carbon dioxide ... A somewhat different picture is observed in the area 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 solfatara activity. In other cases, carbon dioxide predominates.

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

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

4.2 Geysers.

Geysers are periodically operating steam-water fountains. They received 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 of the USA, New Zealand, and Kamchatka. Each geyser is usually confined to a rounded hole, or griffin. Griffins come in a variety of sizes. In depth, this channel, apparently, turns into tectonic cracks. The entire channel is filled with overheated underground water. Its temperature in a griffin can be 90-98 degrees, while in the depth 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 is in a zone of lower pressure, boiling and eruption of water and steam begins. After the eruption, the channel is gradually filled with underground water, partly with water thrown out during the eruption and flowing back into the griffin; for some time, equilibrium is established, the violation of which leads to a new steam-water eruption. The gushing height 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.

Rice. 15. Scheme of the geyser. (www.criazon.com)

The water under hydrostatic pressure in underground cavities gradually heats up above 100 °. When the critical temperature is reached, it boils. Steam generated with noise is thrown out of the geyser, carrying boiling water with it .

4.3 Mud volcanoes (salsa).

They are sometimes found in the same areas as geysers (Kamchatka, Java, Sicily, etc.). Hot water vapors and gases break through to the surface through cracks, are thrown out and form small outlets with diameters ranging from 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). mud volcanoes... The density, or consistency, of the mud determines the nature of their activity and structure. With relatively liquid mud, the release of vapors and gases causes bursts 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 the 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 flammable gases;

2) confined to areas of magmatic volcanism and caused by outbursts of magmatic gases ”. ... These include Apsheron, Taman mud volcanoes.

Fig. 16 Mud volcano. the vicinity of Pirikishkul. Azerbaijan(www.criazon.com)

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

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 cognitive. Active volcanoes, along with earthquakes, pose a formidable danger to closely located settlements. The moments of their eruptions often bring irreparable natural disasters, which are expressed not only in enormous material damage, but sometimes in mass deaths of the population. For example, the eruption of Vesuvius in 79 AD is well known, which destroyed the cities of Herculaneum, Pompeia and Stabia, as well as a number of villages located on the slopes and at the foot of the volcano. As a result of this eruption, several thousand people died.

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

In order not to get the impression that volcanic activity brings only disasters, such a brief information about some of the useful aspects should be given.

Huge masses of volcanic ash thrown out 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, which are used for balneological purposes.

The products of direct volcanic activity - individual lavas, pumice, perlite, and others - 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 fumarolic 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 before mankind there are still many unsolved mysteries besides volcanism, and they need someone to unravel 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.

1. Aprodov V.A. Volcanoes.- M.: Mysl, 1982.-361 p.

2. Vlodavets V.I. Volcanoes of the Earth.- Moscow: Nauka, 1973.-168 p.

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

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

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