At the word “volcano,” most people recall Vesuvius, Fuji, or volcanoes in Kamchatka — elegant cone-shaped mountains.
In fact, there are other types of volcanoes, not at all similar to our usual ones. We have already spoken about it.
Now consider another type of volcanism - fissure.

Volcanic eruption Plosky Tolbachik (photo from your-kamchatka.com)

The role of volcanoes in the development of life on Earth is significant. According to some hypotheses, the first living organisms originated around underwater volcanoes; volcanoes were able to melt the frozen Earth and cause the spring of life 700 million years ago; volcanoes in Siberia "helped" to start the era of dinosaurs, and volcanoes in India - to finish it. A volcano in Indonesia almost destroyed the human race, and a volcano in Yellowstone several times covered with ashes half of the modern territory of the United States.
1

How is a typical volcano formed? Many of them are in the area of ​​collision of tectonic plates. Examples are volcanoes in the “ring of fire” around the Pacific Ocean: in Kamchatka, in Japan, Indonesia, New Zealand, on the Pacific coast of North and South America.
When an oceanic tectonic plate collides with a continental plate, the oceanic plate goes down as it is denser and heavier due to its chemical composition. At the same time, the impurities contained in the oceanic plate (in particular, water) are heated and begin to leak up through the mantle under the continental plate. Oddly enough, this causes the melting of the solid matter of the upper layer of the mantle and its transformation into magma. This happens for the same reason that snow melts when it is sprinkled with salt: contamination of solids with impurities lowers the melting point. Due to the large amount of gases dissolved in magma and under high pressure, magma rises and causes a volcanic eruption.

Volcanoes are also formed at the place of plate divergence, for example, along the Great Rift Valley on the border of the African and Arabian tectonic plates.
2



Volcano Erta Ale in Ethiopia. (photo - Mikhail Korostelev)

As a result of this discrepancy, in a few million years the modern territory of Somalia, Tanzania and Mozambique in eastern Africa will separate from the continent and a new ocean will emerge in the middle of Africa.
3

Kilimanjaro - volcano in northeastern Tanzania, the highest peak in Africa

At the same time, most of the plate divergence points are located not on the continent, but under water, along the mid-ocean ridges. It was in these places that one of the main biological discoveries of the twentieth century was made — ecological systems of hydrothermal sources.
In the 1990s, the German scientist Günter Wachterschauser proposed the hypothesis of the origin of life around hydrothermal springs, which was called the “world of iron and sulfur”. According to this hypothesis, life on Earth was generated not by the Sun, but by the energy of volcanoes, and at the initial stage, before the appearance of proteins and DNA, used hydrogen sulfide, hydrogen cyanide, iron, nickel and carbon monoxide.
4

Eruption of underwater volcano

After a couple of billion years, volcanoes have helped life on Earth once again. In 1950-1960, geologists Sir Douglas Mawson and Brian Harland discovered the fossil trails of a glacier that covered tropical latitudes between 850 and 630 million years ago. The researchers suggested that the earth had passed through a period when it was completely covered with ice. This hypothesis is called Snowball Earth ("Earth-snow"). Mawson and Harland were objected by the Russian climatologist Mikhail Budyko, who made the calculations and showed that there would be no one to freeze the frozen Earth, since the ice would reflect the sun's rays into space and the Earth would remain a “snowball” forever. Only in 1992, American Joseph Lynn Kirshvink substantiated the assumption that the Earth was defrosted by the greenhouse effect of gases emitted into the atmosphere by volcanoes. After that, the real spring came on Earth: large multicellular animals of the Ediacarian and Cambrian periods appeared.

Magmatism   (Magmatism) - geological processes associated with the formation of magma, its movement in the earth's crust and its outpouring to the surface, including the activity of volcanoes (volcanism).

Volcanism   (Volcanism; Vulcanism; Vulcanicity) - a set of processes and phenomena caused by the movement of magma in the upper mantle, the crust and its penetration from the depths of the Earth to the earth's surface. A typical manifestation of volcanism is the formation of magmatic geological bodies during the introduction of magma and its solidification in sedimentary rocks, as well as the outpouring of magma (lava) on the surface with the formation of specific relief forms (volcanoes).
5

Karymsky Volcano - one of the most active volcanoes in Kamchatka

“Volcanism is a phenomenon due to which the outer envelopes of the Earth — the crust, hydrosphere, and atmosphere, ie, the living environment — the biosphere — formed during geological history,” most volcanologists express this view, but this is by no means the only idea of ​​geographical development shell.
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 350km, in the thickness of our planet, pockets of molten matter — magma — are formed. In the crushing and crusting areas of the crust, magma rises and pours out onto the surface in the form of lava (differs from magma in that it contains almost no volatile components, which, when the pressure drops, are separated from the magma and escape to the atmosphere. volcanoes.
6

Fujiyama - the highest mountain peak (3776 m) of Japan. It is a volcano with a crater with a diameter of about 500 meters and a depth of 200 meters. The most devastating eruptions occurred in 800, 864 and 1707.

Currently, over 4 thousand have been identified on the globe. volcanoes.
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From here

TO acting   include volcanoes erupting and showing solfatarnaya activity (release of hot gases and water) for the last 3,500 years of the historical period. In 1980, they numbered 947.

TO potentially acting   Holocene volcanoes erupt 3500-13500 years ago. They are about 1343 pieces.
8

Mount Ararat is a volcano that is considered extinct. In fact, it, like the other volcanoes of the Caucasus that showed volcanic activity in the Late Quaternary time: Ararat, Aragats, Kazbek, Kabardzhin, Elbrus, etc., is potentially active. In the central sector of the North Caucasus, eruptions of the Elbrus volcano in the Late Pleistocene and Holocene were repeatedly observed.

TO   conditionally extinct   Volcanoes are not active in the Holocene, but retain their outer forms (older than 100 thousand years).
9

SHASTA (Shasta) is an extinct volcano in the southern part of the Cascade Mountains, in the USA.

Extinct volcanoes   substantially processed by erosion, dilapidated, not showing activity during the last 100 thousand. years old.

Fissure volcanoes are manifested in the outpouring of lava on the earth's surface through large cracks or splits. In separate periods of time, mainly at the prehistoric stage, this type of volcanism reached a fairly large scale, with the result that a huge amount of volcanic material - lava - was carried to the Earth’s surface. Powerful fields are known in India on the Deccan Plateau, where they covered an area of ​​5.105 km2 with an average thickness of 1 to 3 km. Also known in the northwestern United States, in Siberia. At that time, basaltic rocks of fissure effusions were depleted of silica (about 50%) and enriched with ferrous iron (8-12%). Lava mobile, liquid, and therefore traced for tens of kilometers from the place of their outpouring. The power of individual streams was 5-15m. In the United States, as well as in India, many kilometers of strata accumulated, this happened gradually, layer by layer, over many years. Such flat lava formations with a characteristic step-like relief form are called platobasalts or traps.
12

Trapp basalts in the upper reaches of the Colorado River.

Siberian traps - one of the largest trap provinces located on the East-Siberian platform. Siberian traps poured at the boundary of the Paleozoic and Mesozoic, Permian and Triassic periods. Simultaneously with them, the largest (Permo-Triassic) extinction of species of the Earth's history occurred. They are developed on an area of ​​about 4 million km², the volume of erupted melts was about 2 million km³ of effusive and intrusive rocks.
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The Putoran Plateau is composed of trapp basalt. Waterfall on the Putorana plateau. (Author - Sergey Gorshkov)

250 million years ago, on the border of the Paleozoic and Mesozoic Era, massive lava eruptions took place on the territory of a volcanic province called the Siberian Traps, with the center in the area of ​​modern Norilsk. For several hundred thousand years, 2 million cubic kilometers of lava spread over about 4 million square kilometers. At the same time, the greatest extinction occurred in the history of the Earth, which destroyed 96% of marine and about 70% of terrestrial animal species. According to one theory, mass extinction was associated with the "volcanic winter." At first, volcanic dust polluted the atmosphere, causing global cooling and a lack of light for plants. At the same time, sulfurous volcanic gases caused acid rain from sulfuric acid, which destroyed land-based plants and mollusks into the sea. Then global warming occurred due to carbon dioxide emitted and the greenhouse effect.

After each major extinction, new species flourish. After the extinction of the Paleozoic species, dinosaurs became favorites. In turn, dinosaurs became extinct 65 million years ago. For a long time, the extinction of dinosaurs was explained by the collision of the Earth with an asteroid that fell in the area of ​​the Yucatan Peninsula in southern Mexico. But according to new researches by Gerta Keller from Princeton and Thierry Adatte from Switzerland, the main cause of dinosaur death was the Dekan Trapps - volcanoes, which covered half of the territory of modern India for 30 thousand years and also caused the “volcanic winter”.
14

Dean Plateau (Plateau Dean or South Plateau), which covers almost the entire South India

Plateau Dean is a large trap province located in Hindustan and makes up the Deccan Plateau. The total basalt power of the center of the province is more than 2,000 meters; they are developed on an area of ​​1.5 million km². The volume of basalts is estimated at 512,000 km3. The Dekan traps began to pour out on the border of the Cretaceous and Paleogene, and they are also associated with the Cretaceous-Paleogene extinction, as a result of which dinosaurs and many other species disappeared.
Scientists knew that a series of eruptions that created the Dean Trap Province, occurred near the chalk-Paleogene border, when mass extinction occurred. Now, after studying the rocks in India and the marine sediments of this era, they claim that for the first time they were able to clearly link volcanism on the Dean plateau and the death of dinosaurs.
The most powerful phase of the period of volcanism on Dean ended when the mass extinction had already begun. At the same time, carbon dioxide and sulfur dioxide, which change the climate, from these volcanoes (the lava from which spread over many hundreds of kilometers, forming layers of two-kilometer-thick basalt) were ejected 10 times more than during the impact of the asteroid on Yucatan.
Scientists were also able to explain the delay in the sharp rise of the development of sea creatures (which can be clearly seen in marine minerals after the Cretaceous-Paleogene border). The fact is that the last surge of volcanism on the Deccan occurred 280 thousand years after extinction. This delayed in time the restoration of the number of microorganisms in the seas.

Currently, fissure volcanism is common in Iceland (Laki volcano), on Kamchatka (Tolbachinsky volcano), and on one of the islands of New Zealand. The largest eruption of lava on the island of Iceland along the giant cracked lacquer, 30 km long, occurred in 1783, when lava came to the day surface for two months. During this time, 12 km 3 of basaltic lava has poured out, which flooded almost 915 km2 of the adjacent lowland with a 170 m thick layer. A similar eruption was observed in 1886. on one of the islands of New Zealand. Within two hours, 12 small craters with a diameter of several hundred meters acted on a 30 km stretch. The eruption was accompanied by explosions and ejection of ash, which covered an area of ​​10 thousand km2, the thickness of the cover reached 75m near the crack. The explosive effect was enhanced by the powerful release of vapors from the lake basins adjacent to the crack. Such explosions, due to the presence of water, are called phreatic. After the eruption in place of the lakes, a graben-shaped depression was formed with a length of 5 km and a width of 1.5-3 km.
15

The total volume of the erupted pyroclasts was 1 km3, lava - 1.2 km3, total - 2.2 km3. It was the largest basaltic eruption in the Kuril-Kamchatka volcanic belt in historical time, one of the fifteen eruptions of the 20th century, whose products exceeded 1 million cubic meters. km., one of six large fissure eruptions observed in the world in historical time. Thanks to enhanced systematic research, the Great Tolbachinsky fissure eruption is currently one of the three most studied large volcanic eruptions.

The lavas that have caused such large-scale events in the past are represented by the most common type on Earth - basalt. Their name indicates that they later turned into black and heavy rock - basalt.
The vast basaltic fields (traps) hundreds of millions of years old hide in themselves still very unusual forms. Where the ancient traps come to the surface, such as, for example, on the cliffs of Siberian rivers, one can find rows of vertical 5- and 6-sided prisms. This is a columnar separation, which is formed during the slow cooling of a large mass of a homogeneous melt. Basalt gradually decreases in volume and cracks along strictly defined planes. Sounds familiar, doesn't it?
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Israel. River Zavitan. Pools of prisms. (and this is mine)

The Golan Heights (Ramat Ha-Golan) are part of a basaltic plateau of volcanic origin, the total area of ​​which is 35,000 sq. Km. Geologists believe that the age of the Golan is about one and a half million years.

Bordering in the west with the Jordan depression in the east, the Golan Plateau reaches the Nakhal-Rakkad canyon (a tributary of the Yarmuk river) and a chain of high hills (Hermon spurs), dropping from the north to the south from 1000 m to 350 m above sea level. Several dozens of extinct volcanoes (including Avital, Warda and Hermonite, over 1200 m above sea level), some with whole and deformed craters, covered the plateau and adjacent areas with lava in the recent geological epoch, creating a characteristic landscape with black basalt rocks and brown tuff (volcanic emissions), lying on top of sedimentary chalk and limestone rocks. Mainly heading west and densely covered with bushes along the coast, the streams washed deep ravines in the soil, often with waterfalls on the ledges.
And the basaltic plateau spilled on top of other rocks, and ledges, and waterfalls. and prisms in rivers - well, very suitable for fissure volcanism. P.S.All photos illustrating the text are found on the web. Where she knew - indicated the exact authorship.

Course work in geology:

"Volcanism"

Introduction:

Volcanic sediments, ash clouds over the continent, significant climate change and the terrain of the Earth ... all these are the consequences of a volcanic eruption. I chose this exchange rate topic because the recent effects of the Eyjafjallajökull volcano eruption shook the world and made many people think about our environment.

K.P. Bryullov

The Last Day of Pompeii, 1830-33

2. Volcanoes, a general concept:

What are volcanoes? Volcanoes are geological formations on the surface of the earth's crust or the crust of another planet, where magma comes to the surface, forming lava, volcanic gases, stones (volcanic bombs) and pyroclastic flows.

Depending on the degree of volcanic activity, volcanoes are divided into active, dormant and extinct. An active volcano is considered to be a volcano that erupted in a historical period of time or in the Holocene. The concept of active is quite inaccurate, as the volcano, which has active fumaroles, some scientists refer to active, and some to extinct. Inactive dormant volcanoes are considered as sleeping, where eruptions are possible, and extinct volcanoes are considered unlikely.

However, among volcanologists there is no consensus on how to identify an active volcano. The period of activity of a volcano can last from several months to several million years. Many volcanoes showed volcanic activity several tens of thousands of years ago, but at the present time are not considered active.

3. Areas of volcanic activity

The main areas of volcanic activity are South America, Central America, Java, Melanesia, the Japanese Islands, the Kuril Islands, the Kamchatka Peninsula, the northwestern part of the United States, Alaska, the Hawaiian Islands, the Aleutian Islands, Iceland, the Atlantic Ocean.

As you can see, volcanoes operate across the entire area of ​​the globe, and until now, scientists can not pinpoint exactly which areas are potentially dangerous.

Name of the volcano

Location

Height, m

Lulaillaicoo

Chilean Andes

South America

San pedro

Central Andes

South America

Cotopaxi

Equatorial Andes

South America

Kilimanjaro

masai Plateau

Central Andes

South America

Mexican highlands

Popocatepetl

Mexican highlands

North and Central America

Equatorial Andes

South America

Northwest Andes

South America

Klyuchevskaya Sopka

kamchatka Peninsula

Cordilleras

North and Central America

Tahumulko

Central America

North and Central America

Mauna loa

Hawaiian Islands

Australia and Oceania

massif cameroon

Anatolian

plateau about. Sumatra

Canary Islands

about. Sumatra

Antarctica

Ichinskaya Sopka

kamchatka Peninsula

Kronotskaya Sopka

kamchatka Peninsula

Koryak Sopka

kamchatka Peninsula

about. Sicily

kamchatka Peninsula

Lassen peak

Cordilleras

North and Central America

Southern Andes

South America

Manchu-Korean mountains

New Zealand

Australia and Oceania

Pactusan

Korean peninsula

Avachinskaya Sopka

kamchatka Peninsula

Kuril Islands

alaska Peninsula

North and Central America

Kuril Islands

about. Iceland

Montagne pele

about. Martinique

North and Central America

Apennine Peninsula

Stromboli

Aeolian Islands

Krakatau

Sunda Strait

Anatolian plateau about. Sumatra

This is a short list of volcanoes known to scientists, but there are even more unexplored volcanoes in the world and some of them still exist today.

4. Types of volcanic structures, the classification of volcanoes in shape.

In general, the volcanoes are divided into linear and central, however, this division is arbitrary, since most of the volcanoes are confined to linear tectonic disturbances (faults) in the earth's crust.

Linear volcanoes or fissure-type volcanoes have extended supply channels associated with a deep cleavage of the crust. As a rule, basalt liquid magma is poured out of such cracks, which, spreading to the sides, forms large lava covers. Along the cracks, gentle spatter shafts, wide flat cones, lava fields arise. If magma has a more acidic composition (higher content of silicon dioxide in the melt), linear extrusive shafts and arrays are formed. When explosive eruptions occur, explosive ditches tens of kilometers in length may occur.

The shapes of volcanoes of the central type depend on the composition and viscosity of the magma. Hot and lightly mobile basaltic magmas create vast and flat shield volcanoes (Mauna Loa, Hawaiian Islands). If the volcano periodically erupts the lava, then the pyroclastic material, there is a cone-shaped layered structure, stratovolcano. The slopes of such a volcano are usually covered with deep radial ravines - barrancos. Volcanos of the central type can be purely lava, or formed only by volcanic products - volcanic slags, tuffs, etc., formations, or be mixed - stratovolcanoes.

There are monogenic and polygenic volcanoes. The first occurred as a result of a single eruption, the second - multiple eruptions. Viscous, acidic in composition, low-temperature magma, squeezing out of the vent, forms extrusive domes

Needle of Mont-Pele, 1902

In addition to calderas, there are large negative forms of relief associated with the deflection caused by the weight of the erupted volcanic material and the lack of pressure at depth that occurred during the unloading of the magma chamber. Such structures are called volcanotectonic depressions, depressions. Vulkanotectonic depressions are very widespread and often accompany the formation of powerful ignimbrites — volcanic rocks of an acidic composition, having a different genesis. They are lava or formed by caked or boiled tuffs. They are characterized by lenticular detachments of volcanic glass, pumice, lava, called fiamme and tuff or tofovidnaya structure of the main mass. As a rule, large volumes of ignimbrites are associated with shallow magmatic chambers formed due to melting and replacement of enclosing rocks. Negative landforms associated with volcanoes of the central type are represented by calderas, large rounded dips, several kilometers in diameter.

5. Volcanic eruption.

Volcanic eruptions are geological emergencies that can lead to natural disasters. The eruption process can last from several hours to many years. Among the various classifications are common types of eruptions:

Hawaiian type - liquid basaltic lava emissions, often formed by lava lakes. should resemble scorching clouds or hot avalanches.

Hawaiian Eruption Type: 1: Ash Trail, 2: Lava Fountain, 3: Crater, 4: Lava Lake, 5: Fumaroles, 6: Lava Flow, 7: Layers of Lava and Ash, 8: Layer of Rock, 9: Sill, 10: Magma channel, 11: Magma chamber, 12: Dyke

The Plinian type (volcanic, Vesuvian) of eruptions was named after the Roman scientist Pliny the Elder, who died during the eruption of Vesuvius in 79 AD e., destroyed three large cities of Herculaneum, Stabiae and Pompeii.

A characteristic feature of this type of eruption is powerful, often sudden explosions, accompanied by the release of huge amounts of tephra, forming pumice and ash streams. Plinian eruptions are dangerous, as they occur suddenly, often without preliminary foreshadowing events. Large Plinian-type eruptions, such as the eruptions of St. Helens volcano on May 18, 1980 or the Pinatubo eruption in the Philippines on June 15, 1991, can emit ash and volcanic gases tens of kilometers into the atmosphere. In the Plinian type of eruption, fast-moving pyroclastic flows often occur.

Plinian type of eruption: 1: Ash plume, 2: Magmatic channel, 3: Rain of volcanic ash, 4: Layers of lava and ash, 5: Layer of rock, 6: Magmatic chamber

Hydroexplosive type - eruptions occurring in the shallow conditions of the oceans and seas, are characterized by the formation of a large amount of steam that occurs when hot red magma and seawater come into contact.

Classification of volcanoes in the form:

Thyroid volcanoes are formed as a result of repeated emissions of liquid lava. This form is typical for volcanoes spewing low viscosity basalt lava: it flows both from the central crater and from the slopes of the volcano. Lava spreads evenly for miles. Like, for example, on the volcano Mauna Loa in the Hawaiian Islands where it flows directly into the ocean.

Slag cones eject only loose substances such as stones and ash from their vents: the largest fragments accumulate in layers around the crater. Because of this, the volcano with each eruption is getting higher. Light particles fly off for a longer distance, which makes the slopes gently sloping.

Stratovolcanoes, or “layered volcanoes,” periodically erupt lava and pyroclastic matter — a mixture of hot gas, ash, and hot stones. Therefore, the deposits on their cone alternate. On the slopes of stratovolcanoes ribbed corridors of frozen lava form, which serve as a support for the volcano.

Domed volcanoes form when granite, viscous magma rises above the edges of a volcanic crater and only a small amount percolates.

outward, flowing down the slopes. Magma clogs the mouth of a volcano, like a cork, which the gases accumulated under the dome literally knock out of the mouth.

^ 6. Significance of volcanic eruptions for the planet and humanity

For a long time, it was believed that some types of volcanoes that exist on our planet, for example, small mud and giant igneous ones, which emit hot magma from huge depths, have no genetic affinity. However, studying for a number of years a variety of volcanoes, their distribution areas, periods when they erupt, we came to the conclusion that the “work” of all volcanoes is associated with a single global geodynamic process - the movement of huge lithospheric plates. When analyzing the spread of volcanoes in the world, it turned out that they (as well as, incidentally, the areas where earthquakes occur) are most often located on the borders of lithospheric plates - in narrow zones of tectonic activation. There are several types of borders. One of them is in subduction zones, where the lithospheric plate is immersed in the upper mantle. These zones, which are characterized by deep (deep-focus) earthquakes, received another name - Zavaritsky-Benioff zones. They are found in many areas of the Earth - in the South American Andes, on the islands of Tonga, New Hebrides, in the Sea of ​​Japan, Indonesia, on the Antilles, etc. Large magmatic volcanoes, whose roots penetrate the depths of the Earth tens of kilometers, are often found here. . The second type of boundaries between the plates is the spreading zone, where the ocean floor spreads and a narrow, extended depression (rift) forms, in which a new crust occurs.

Literature:

1. 
   Obruchev V.A. Fundamentals of Geology. State edition of geological literature. M.-L. 1947
2. 
   Fundamentals of Geology, N.V.Koronovsky, A.F. Yakusheva. - M .: Higher school, 1991. - p. 225-232.
3. 
   Yampolsky M. The Observer. M., 2000, p. 95-110
4. 
   //dic.academic.ru/dic.nsf/ruwiki/640658
5. 
   //geopriroda.ru/vulcans/

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- (from the Latin. Vulcanus) - cone-shaped or dome-shaped elevations above the channels, explosion tubes and cracks in the earth's crust, which erupt from the depths, magma, gaseous products, ash, fragments of rocks. The process of release to the surface of these substances is called a volcanic eruption. Volcanic eruption occurs due to magma degassing. Magma, in a magma chamber, is under pressure, when pressure reaches a critical point, magma spills out through cracks in the earth's crust. Rising upward, magma loses gases and water vapors and turns into lava - magma depleted in gases.
Products of volcanic eruptions:
1. Liquid
This is exactly lava, the temperature of these eruptions in the range of 600-1200 seconds. The viscosity of lava is due to its chemical composition and depends on the amount of silica or silicon dioxide.
2. Gaseous - fumarole and sofion, during the crystallization of magma it is the released gases cause explosions and throw lava to the surface.
3. Solid - volcanic bombs (pieces of hardened lava), lapilli (small fragments of lava), ash, volcanic sand. When a volcano erupts, they fly out at a speed of 500-600 m / s.
Types of Volcanoes
1. Area volcanoes
Currently, such volcanoes are not found, since these volcanoes are confined to the emergence of a large amount of lava on the surface of a large area, i.e. such volcanoes existed in the early stages of the earth’s development, when the crust was quite thin.
2. Cracked volcanoes
These volcanoes are characterized by the eruption of magma on the earth's surface through large cracks or splits.
3. Central type
The most common type of volcanoes, implies the formation of cone-shaped vents. Vent ends with expansion crater. Volcanos of the central type may have side craters, which are located on its slopes.
Varieties of volcanoes in shape
1. Thyroid Volcano
This form is typical for volcanoes spewing low viscosity basalt lava: it flows for a long time both from the central mouth and from the side craters of the volcano. Lava spreads evenly for miles; gradually, a wide “shield” with gentle edges is formed from these layers.
2. Slag cones
During the eruption of such volcanoes, large fragments of porous slags are piled up around the crater with layers in the form of a cone, and small fragments form sloping slopes at the foot; with each eruption the volcano gets higher
3. Stratovolcanoes
Periodically erupt lava (viscous and thick, quickly setting) pyroclastic substance - a mixture of hot gas, ash and hot stones; as a result, deposits on their cone (acute, with concave slopes) alternate. Lava of such volcanoes also flows out of cracks, solidifying on the slopes in the form of ribbed corridors that serve as a support for the volcano.
4. Dome volcanoes
Formed when viscous granite magma, rising from the depths of a volcano, cannot flow down the slopes and freezes at the top, forming a dome. It clogs its mouth like a cork, which over time will knock out the gases that have accumulated under the dome.
5. Complex volcano
a volcanic structure that has more than one shaping element (vent, lava shield, etc.). Such a volcano is formed as a result of several eruptions of different types that occurred, usually at different times.

Sources used:
1. kaldera.info
2. ecosystema.ru
3. vulkaninfo.ru
4. allforchildren.ru
5. world-volkanos.ru
6. ru.wikipedia.org

-Thyroid Volcanoes   formed as a result of repeated emissions of liquid lava. This form is typical for volcanoes spewing low viscosity basalt lava: it flows both from the central crater and from the slopes of the volcano. Lava spreads evenly for miles. Like, for example, on the volcano Mauna Loa in the Hawaiian Islands where it flows directly into the ocean.

-Slag cones   Only loose substances such as stones and ashes are ejected from their vents: the largest fragments accumulate in layers around the crater. Because of this, the volcano with each eruption is getting higher. Light particles fly off for a longer distance, which makes the slopes gently sloping.

-Stratovolcanoes, or "layered volcanoes," periodically erupt lava and pyroclastic matter - a mixture of hot gas, ash, and hot stones. Therefore, the deposits on their cone alternate. On the slopes of stratovolcanoes ribbed corridors of frozen lava form, which serve as a support for the volcano.

-Dome volcanoes   form when granite, viscous magma rises above the edges of a volcanic crater and only a small amount seeps out, flowing down the slopes. Magma clogs the mouth of a volcano, like a cork, which the gases accumulated under the dome literally knock out of the mouth.

\u003e Volcanic eruptions

Volcanic eruptions are geological emergencies that can lead to natural disasters. The eruption process can last from several hours to many years. Among the various classifications are common types:

Hawaiian type   - emissions of liquid basaltic lava, often formed by lava lakes. should resemble scorching clouds or hot avalanches.

Hydroexplosive type- eruptions occurring in the shallow conditions of the oceans and seas, are characterized by the formation of a large amount of steam that occurs when hot magma and seawater come into contact.

\u003e Signs of an impending eruption

Increased seismic activity (from barely noticeable fluctuations of lava to a real earthquake).

- "Grumbling", coming from the crater of the volcano and from under the ground.

The smell of sulfur emanating from the rivers and streams flowing near the volcano.

Acid rains.

Pumice dust in the air.

Gases and ash escaping from the crater from time to time.

\u003e The actions of people during a volcanic eruption

Knowing about the eruption, you can change the path of lava flows with the help of special gutters and trays. They allow you to put the stream around the dwellings, to keep it in the right direction. In 1983, on the slopes of the famous Etna, it was possible to create a directional channel for lava by explosions, which saved the nearest villages from the threat.

Sometimes the cooling of the lava flow with water helps - this method was used by the inhabitants of Iceland in the fight against the volcano that “woke up” on January 23, 1973. About 200 men left after the evacuation sent firefighters to the lava creeping to the port. Cooling down from the water, the lava stone. It was possible to save most of the city of Weistmannayayar, the port, and no one was hurt. True, the struggle with the volcano dragged on for almost six months. But this is the exception rather than the rule: a huge amount of water was required, and the island was small.

How to prepare for a volcanic eruption

Watch for a warning of a possible volcanic eruption. You will save your life if you leave the dangerous territory in time. When you receive a warning about falling ash, close all windows, doors and smoke dampers.

Put the cars in the garages. Place animals in enclosed spaces. Stock up on sources of lighting and heat with autonomous power, water, food for 3 - 5 days.

How to act during a volcanic eruption

At the first "symptoms" of a beginning eruption, you need to carefully listen to the reports of the Ministry of Emergency Situations and follow all their instructions. It is advisable to urgently leave the disaster area.

What if an eruption caught you in the street?

1. Run to the road, try to protect your head.

2. If you are driving, be prepared for the wheels to get stuck in the ash layer. Do not try to save the car, leave it and go on foot.

3. If a ball of hot dust and gases appears in the distance, save yourself by hiding in an underground shelter that is being built in earthquake-prone areas, or dive into the water until the hot ball rushes further.

What measures should be taken if evacuation is not needed?

1. Do not panic, stay home, closing doors and windows.

2. Going out on the street, remember that you can not wear synthetic clothes, as they can catch fire, while your clothes should be as comfortable as possible. Mouth and nose must be protected with a damp cloth.

3. Do not hide in the basement, so as not to be buried under a layer of dirt.

4. Stock up on water.

5. Make sure that falling stones do not cause a fire. As soon as possible, clean the roof of the ashes, extinguish the fire.

6. Follow the Ministry of Emergency Situations on the radio.

How to act after a volcanic eruption

Cover the mouth and nose with a gauze bandage to prevent ash inhalation. Wear safety glasses and clothing to prevent burns. Do not try to drive a car after falling out of ash - it will lead to its failure. Clean the roof of the house from ashes to prevent its overload and destruction.