The many faces of volcanoes, where and how they arise. The largest volcano in the world

In this lesson we will learn what volcanoes are, how they are formed, we will get acquainted with the types of volcanoes and their internal structure.

Topic: Earth

Volcanism- a set of phenomena caused by the penetration of magma from the depths of the Earth to its surface.

The word "volcano" comes from the name of one of the ancient Roman gods - the god of fire and blacksmithing - Vulcan. The ancient Romans believed that this god had a forge underground. As Vulcan begins to work in his forge, smoke and flames erupt from the crater. In honor of this god, the Romans named the island and the mountain on the island in the Tyrrhenian Sea - Vulcano. And later all fire-breathing mountains began to be called volcanoes.

The globe is structured in such a way that under the solid crust there is a layer of molten rocks (magma), and under great pressure. When cracks appear in the Earth's crust (and on earth's surface in this place, hills are formed), then the magma under pressure rushes into them and comes to the surface of the earth, breaking up into hot lava (500-1200 ° C), caustic volcanic gases and ash. The spreading lava hardens, and the volcanic mountain increases in size.

The resulting volcano becomes vulnerable spot earth's crust, even after the end of the eruption, inside it (in the crater), gases constantly come out of the earth’s bowels to the surface (the volcano “smokes”), and with any slightest shifts or shocks in the earth’s crust, such a “dormant” volcano can wake up at any time. Sometimes a volcano awakens without obvious reasons. Such volcanoes are called active.

Rice. 2. The structure of the volcano ()

Volcano crater- a cup-shaped or funnel-shaped depression on the top or slope of a volcanic cone. The diameter of the crater can be from tens of meters to several kilometers and the depth from several meters to hundreds of meters. At the bottom of the crater there are one or more vents through which lava and other volcanic products rise from the magma chamber through an outlet channel to the surface. Sometimes the crater floor is covered by a lava lake or a small newly formed volcanic cone.

Volcano mouth- a vertical or almost vertical channel connecting the center of a volcano with the surface of the earth, where the vent ends in a crater. The shape of the vents of lava volcanoes is close to cylindrical.

Magma hotspot- a place under the earth's crust where magma collects.

Lava- erupted magma.

Types of volcanoes (according to the degree of their activity).

Active - which erupt, and information about this in the memory of mankind. There are 800 of them.

Extinct - no information about the eruption has been preserved.

Those who have fallen asleep are those who have gone out and suddenly begin to act.

According to their shape, volcanoes are divided into conical and panel.

The slopes of the conical volcano are steep, the lava is thick, viscous, and cools quite quickly. The mountain has the shape of a cone.

Rice. 3. Conical volcano ()

The slopes of a shield volcano are gentle, very hot and liquid lava spreads quickly over considerable distances and cools slowly.

Rice. 4. Shield volcano ()

Geyser - a source that periodically releases a fountain hot water and a couple. Geysers are one of the manifestations of the later stages of volcanism and are common in areas of modern volcanic activity.

A mud volcano is a geological formation that is a hole or depression on the surface of the earth, or a cone-shaped elevation with a crater, from which mud masses and gases, often accompanied by water and oil, constantly or periodically erupt onto the surface of the Earth.

Rice. 6. Mud volcano ()

- a lump or piece of lava thrown out during a volcanic eruption in a liquid or plastic state from a vent and obtained a specific shape when squeezed out, during flight and solidification in air.

Rice. 7. Volcanic bomb ()

An underwater volcano is a type of volcano. These volcanoes are located on the ocean floor.

Most modern volcanoes are located within three main volcanic belts: Pacific, Mediterranean-Indonesian and Atlantic. As evidenced by the results of studying the geological past of our planet, underwater volcanoes are significantly larger than volcanoes on land in terms of their scale and volume of ejection products coming from the bowels of the Earth. Scientists believe that this is the main source of tsunamis on Earth.

Rice. 8. Underwater volcano ()

Klyuchevskaya Sopka(Klyuchevskoy volcano) is an active stratovolcano in the east of Kamchatka. With a height of 4850 m, it is the highest active volcano on the Eurasian continent. The age of the volcano is approximately 7000 years.

Rice. 9. Volcano Klyuchevskaya Sopka ()

1. Melchakov L.F., Skatnik M.N. Natural history: textbook. for 3.5 grades avg. school - 8th ed. - M.: Education, 1992. - 240 pp.: ill.

2. Bakhchieva O.A., Klyuchnikova N.M., Pyatunina S.K. and others. Natural history 5. - M.: Educational literature.

3. Eskov K.Yu. and others. Natural history 5 / Ed. Vakhrusheva A.A. - M.: Balass.

3. The most famous volcanoes on Earth ().

1. Tell us about the structure of the volcano.

2. How are volcanoes formed?

3. How is lava different from magma?

4. * Prepare small message about one of the volcanoes of our country.

The volcano in the picture below is called a compound volcano because it is made up of alternating layers of lava and ash. Over long periods of time they formed a cone with steep slopes.

1. The place under the earth's crust where magma collects is called a magma chamber or volcanic chamber

2. Vent - the main channel in the middle of the volcano;

3. Dyke - a magma-filled channel running from the vent to the surface;

4. Layers of ash and lava;

5. The hole at the very top of the volcano is called a crater;

6. Dust, ash and gases;

7. Pieces of lava called volcanic bombs.

The majestic cone on the surface of the Earth is only the tip of the volcano. No matter how large a volcano may seem, its above-ground part is very small compared to the underground part where the magma comes from. The volcanic cone is composed of products of its eruption. At the top there is a crater - a bowl-shaped depression, sometimes filled with water.

The volcano feeds through an opening called the main channel, or vent. Gases emerge through the vent, as well as rock fragments and melts that rise from the depths, which gradually form a relief on the surface of the volcano. Connected to the vent the whole system volcanic fissures, side channels and magma chambers located from one to tens of kilometers from the Earth’s surface. The primary magma chamber is located at a depth of 60-100 km, and the secondary magma chamber, which directly feeds the volcano, is at a depth of 20-30 km. As magma moves toward the surface, significant changes occur.

There are small volcanoes, the cone of which rises from the surface of the Earth several hundred meters. There are huge ones, reaching 3000-5000 m in height. The largest volcano on the planet, Mauna Loa, is located on the island of Hawaii. It rises 4170 m above sea level, and its base rests at a depth of 5000 m. As a result, its height is more than 9 km.

Causes of eruptions. The causes of volcanic eruptions may include numerous chemical, physical, and geological factors. Therefore, eruptions are not always easy to predict.

If you shake a bottle of a carbonated drink before opening it, the gas dissolved in the drink tends to escape when the bottle is uncorked, forming foam. So in the crater of a volcano, foaming magma is thrown out by gases released from it. Under pressure, it rises through cracks in the earth's crust and rushes into the mouth of the volcano to erupt from the crater. Having lost a significant amount of gas, magma pours out of the crater and flows like lava along the slopes of the volcano.

Why do volcanic eruptions occur? The heat accumulated in the depths of the Earth heats up the material of the earth's core. Its temperature is so high that this substance should have melted, but under the pressure of the upper layers of the earth's crust it is kept in a solid state. In those places where the pressure of the upper layers weakens due to the movement of the earth's crust and the formation of cracks, the hot masses turn into a liquid state. A mass of molten rock (magma), saturated with gases, under strong pressure, melting the surrounding rocks, makes its way to the top. It happens that the vent is already clogged with solidified lava like a plug, which creates conditions for pressure to increase until it is high enough to push this plug out. The penetration of surface water, as well as the physical and chemical processes occurring within the magma itself, also create the conditions under which a volcanic eruption can occur.

A volcano is a geological formation on the surface of a planet where molten internal rocks come to the surface of the earth, forming lava, volcanic gases and stones, in the form of volcanic bombs and pyroclastic flows. Translated from Latin vulkanus - fire

News

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Artificial intelligence will warn about an upcoming eruption

11.02.19 // China, USA, Ecuador
Galapagos volcanoes are fed by a mantle plume

24.01.19 // Russia, France
No volcanic activity was found under Lake Vostok

Our planet consists of several layers, like a hard-boiled egg. The surface layer, about 50 km thick, is called the earth's crust (like the shell of an egg). In some places, especially at the bottom of the oceans, this layer is thinner. Below, under the crust layer to a depth of 900 km, is the upper mantle. Beneath it, up to 2900 km, the lower mantle extends (both mantles are like the white of an imaginary egg). And even lower, to approximately 6300 km, the core (yolk) is located. The upper mantle is the place on the planet where the hot stuff of volcanoes is formed.

As you move from the surface deeper into the planet, the temperature increases by one degree every 33 meters. It is clear that at a depth of tens of kilometers the temperature reaches such values that rocks will melt. But increasing pressure restrains this process, and a certain balance is established. The Earth's crust consists of several solid lithospheric plates located on a layer of the mantle. They swim on its surface, moving at a speed of 2 - 3 centimeters per year. When moving at the boundaries of lithospheric plates, faults are formed, which are called rifts.

Internal structure of the volcano

Shifts in the earth's crust - faults, subsidence, uplift - lead to an imbalance between temperature and pressure in the bowels of the planet, a drop in pressure and the formation of magma - a molten mixture of minerals saturated with gases. A focus is formed. True, as it turned out, near-surface foci can also be observed. The melt, making its way with steam and gases, rushes to the surface of the earth - an explosion and volcanic eruption occurs. The flow releases excess pressure and pours out lava. At the site of the explosion, a funnel remains - a caldera, which is a bowl-shaped depression from where lava flows.

If the gaseous component of the magma is large, the lava breaks into small drop-shaped structures and the eruption takes on the appearance of a fiery fountain. If there is not too much gas and steam, the lava flows freely. When the active activity of the volcano ends, gas and steam still continue to escape from cracks on the slopes of the volcano, forming so-called fumaroles.

Thus, the emergence and eruption of volcanoes is tied to places of increased internal activity of the planet. There are three special celebrations on Earth active area: Pacific coast, Mediterranean-Indonesian belt and Atlantic belt, located at the junction of continental and oceanic plates.

Features of volcanoes

In general, the mechanism of volcano formation is quite typical, but some features are introduced by additional factors, such as the location of the volcano’s formation, the characteristics of the magma source, the characteristics of the magma itself, and so on. They talk about different types volcanoes depending on their specific properties. So, they are divided into active, dormant and extinct. An active volcano is considered to have erupted in historical time or in the Holocene. Dormant volcanoes are considered to be inactive volcanoes that may erupt. Extinct - on which it is unlikely.

There are fissure and central volcanoes. Fissures may not rise high above the ground, having the appearance of cracks from which magma flows. In some parts of the world, entire basalt rivers are known, covering hundreds of square kilometers of area. So on the territory of Siberia, the thickness of these flows reaches several kilometers - the so-called Siberian traps. They are formed by the breakthrough of magma into the upper layers of the earth's crust with outpouring through cracks. This event took place about 240 million years ago, when the surface of the planet was still quite actively forming. Central volcanoes usually have the shape of a cone from which gas and magma emerge during an eruption. Such volcanoes have a channel through which magma rises - a vent - and one or more craters, from where it then pours out.

Volcanoes that rise above the ground (mountain volcanoes) are divided into several categories. Cone-shaped (stratovolcanoes) have a classic shape - a truncated cone with a crater at the top: Etna (Italy), Krakatoa (Indonesia), Popocatepetl (Mexico), Pinatubo (Philippines). They are usually formed in coastal zone and on islands in the subduction zone, where the continental layer is pushed onto the oceanic one. These volcanoes are distinguished by rare but powerful eruptions. They have a layered structure ("strato" - layer), which is replenished with each eruption. Lava and pyroclastic ("broken by fire") fragments gradually form a gentle slope of the volcano, since the lava is quite viscous.

Shield volcanoes are the largest, but this is not noticeable by appearance. Most often they resemble a gladiator's shield lying on the ground. An example is Belknam Crater in the Cascade Mountains of central Oregon. Their low slopes are deceptive. Beneath them are magma lakes larger than terrestrial mountains. Their lava is less viscous and moves further from the eruption site, which gives these volcanoes their flat shape. Their eruptions are frequent and are accompanied by a long outpouring of lava, due to which such volcanoes reach enormous sizes.

Dome volcanoes so called because the viscous granitic magma cannot flow down the slope and solidifies at the top, forming a dome and plugging the vent. Over time, it will be torn off by accumulated gases.

Slag cones are formed by the accumulation of large fragments of porous slag around the crater, and small ones form a slope. Such volcanoes are insignificant in height and, as a rule, erupt once.

An interesting hypothesis is that of “hot spots”, which explains the appearance of volcanic ridges consisting of chains of volcanoes. These points are fixed and represent certain zones within which mantle jets reach the earth's surface. Active volcanoes arise above them and, in the case of an underwater location, islands may appear. When lithospheric plates move, volcanoes move along with them and move away from the mantle flow, falling asleep. A "hot spot" ( plume) burns through the lithospheric plate directly above it, forming a new volcano. Over time, a chain of volcanoes is formed - a volcanic ridge.

Yellowstone, an ancient supervolcano in America, about which there is now so much talk, is also suspected of having a “hot spot”. Supervolcanoes are the most insidious of the entire explosive family. When they erupt, they explode themselves, destroying rather than creating tall structures. Their magma chambers are colossal, but there is no such recognizable crater. They are not like volcanoes. So in Yellowstone there are several places of ancient lava outcrops. It is believed that they are explained by the presence of a plume, which, due to the movement of the lithospheric plate, each time makes a new hole to discharge the accumulated magma. Let us recall that this supervolcano erupted five times - 6 million years ago, 4 million years ago, 2.1 million years ago, 1.27 million years ago and 640 thousand years ago. And now scientists believe that the chances of a new super-eruption are quite high. The giant wakes up and some symptoms are very alarming to researchers.

Underwater volcanoes

There are also zones of volcanic activity in the oceans, where underwater volcanoes operate and chains of seamounts and islands form. These are volcanoes of island arcs and active continental margins, the eruptions of which are often catastrophic. Most of the volcanoes that rise above sea level belong to them. Oceanic rift zones often develop cracks and fissures through which magma flows. The thickness of the earth's crust at the bottom of the ocean is less and it is more easily destroyed.

Almost all islands and seamounts in the inland ocean are either active volcanoes or were active in the past. In the southern part Pacific Ocean there is a whole belt of island and underwater volcanoes such as “hot spots” (for example Hawaiian Islands and Imperial Submarine Ridge). It is located perpendicular to the rift zone of the East Pacific Rise and is located in the area where the rate of divergence is maximum. Volcanism marginal seas poorly studied. Shallow volcanoes are located on the crust continental type and are few in number.

There are more than 1,500 active volcanoes known on Earth. Of these, 95% are located at the points of convergence (divergence) of two plates. Another 5% are formed by “hot spots”. And 80% of total number are underwater and located along ocean ridges and faults.

In general, you and I owe something in this life to these hot guys - volcanoes. It was they who created the atmosphere and water shell of the planet, and, in many ways, the surface too. And not only. Anthropologists noticed that all secondary civilizations chose to live in places with increased tectonic activity, with the presence of volcanoes in the vicinity. Apparently, here the nights were warmer, the cooling volcanic fields could be used as an oven; on them you can find boiled animals, whose meat was quickly tasted by the ancestors. Astrophysicists believe that a reasonable middle ground was important, since too active volcanic activity can make the planet uninhabitable, drowning it in flows of lava and gas, and weak tectonic activity leads to extinction carbon dioxide and sterilization of the planet. So, volcanoes, let's live together!

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There is, perhaps, not a single person on earth who would not be fascinated by an incredible action - a volcanic eruption.

It's dangerous, it's scary and it's incredibly beautiful! It is beyond human control to stop or prevent a volcanic eruption, but it is possible to find out the causes of volcanoes and their activity.

· causes

Volcanism itself is a process in which huge amounts of hot magma come to the surface of the earth from beneath its depths through an open volcanic crater. Plasma-shaped hot rivers of boiling lava destroy all life in their path. Emissions of sulfur dioxide and carbon dioxide pollute the atmosphere and cause acid rain.

During the eruption from the crater terrible force Huge stones and other volcanic debris are flying.

causes of volcanoes

The main reason is internal structure planets. In section Earth consists of three layers: core, mantle, and crust. The magma that flows out during an eruption is upper layer the mantle, the so-called asthenosphere.

· Why do magma emissions occur?

The earth's crust consists of several lithospheric plates. They move slowly, sliding through liquid hot magma. Periodically, the plates run over each other or diverge. Lithospheric plates, with their mass, exert pressure on the plasma-like liquid. That is why, when cracks form, boiling magma comes out.

reasons for the eruption

Processes in the depths of our planet are in continuous dynamics.

As a result, lava is formed. An excess of lava underground leads to its regular emissions in one or another part of the globe.

What kind of magma is there?

Explaining in simple language magma comes in two types:

- regular

- sour.

An ordinary one easily conducts gases, and therefore, when it approaches the mouth of a river of fiery lava, it pours out of the crater without explosions or rockfalls.

Acid magma flows contain high pressure due to the gases accumulated inside.

Lava comes out with an explosion, clouds of smoke, ash and is accompanied by a hail of stones. Such eruptions are especially dangerous. Due to the columns of ash, which sometimes reach more than 13 thousand meters in the air, air travel is prohibited, and it becomes impossible to breathe within a radius of tens of kilometers.

Eruption is a phenomenon in which water spills out from the depths of the Earth onto the earth's surface. magma flows and various rock fragments. Magma that reaches the surface is called lava. During a volcanic eruption, thick clouds of ash also erupt from the vent. And lightning can flash in these black clouds, for which the phenomenon is called a dirty thunderstorm, although you can often hear another name - volcanic lightning.

Description

Volcanoes are such small (and sometimes large) mountains that have a vent - a vertical channel leading through the earth's crust deep into the lithosphere (the hard shell of the planet). Although, it is worth noting that volcanoes are not always mountains, sometimes they are only a small hill, and sometimes they even appear out of the blue, although very rarely. But what they all have in common is that they can spew magma.

To summarize, volcanoes are cracks in the surface of the planet leading to the Earth’s mantle, where magma is located.

And there are a lot of such faults on our planet. They are available on each continent. And since main reason Since the formation of volcanoes consists in the movement of lithospheric plates, in some regions of the planet entire chains of these objects are formed.

Fortunately for us, most of the volcanoes on the planet, in given time They do not pose a threat, since they have either been extinct for a long time or are dormant.

In addition, a considerable part of them are under water, usually at the bottom of the oceans. Well, active volcanoes on land also don’t worry everyone very much, since eruptions occur with some regularity, which makes them predictable. Well, tracking this phenomenon using seismological instruments is also not particularly difficult.

Causes of volcanic eruptions

There is a lot going on in the depths of our planet. various processes. Much there is in constant motion.

Of course, the lithosphere has been practically unstudied, but the available information allows us to assert that the processes occurring in the bowels of the Earth are extremely interesting.

It is because of them that large amounts of magma accumulate in some places underground. And since she has nowhere to go from there, she begins to gradually rise. Volcanoes are channels that allow excess magma to splash out, reducing pressure in some areas of the lithosphere.

It is worth noting that the eruption is not always as colorful as many people think.

The fact is that magma itself comes in two types. Ordinary magma allows gases to pass through well, so when it rises through the vent, no explosions, destruction, or the like occur. It simply flows calmly to the surface. But acidic magma practically does not allow gases to pass through, so when it rises, high pressure is formed, which is why the eruption occurs in the form big bang, as a result of which magma flies out to the earth's surface.

Types of eruptions

Exist different kinds volcanic eruptions.

This depends on many factors, but, in general, these types are not tied to anything specific. That is, one volcano can have different types eruptions. Or he may possess only one, over a long period of time.

Types of volcanic eruptions are usually named after famous volcanoes where this type observed.

Plinian type.
Dangerous due to its unpredictability. During eruptions of this type, unpredictable powerful explosions occur, during which, in addition to lava, a huge amount of ash is released.
Peleian type.
Huge flows of viscous lava, flowing from the vent, linger at its edges (due to viscosity), as a result of which they grow and form lava domes.
After which the lava streams rush down.
The crack of thunder.
Liquid magma rises through cracks to the crater, after which it bursts out with big amount explosions.
Gas or phreatic type.
During this type of eruption, lava does not flow out of the vent. From there, only clouds of gases burst out and fragments of solid rocks are thrown out.
Hydroexplosive eruptions.
They occur in shallow waters of seas and oceans.
Accompanied by the appearance of huge clouds of steam formed due to boiling water.
Icelandic type. It is characterized by the presence of very liquid lava, which flows not only through the crater, but also through the slightest cracks.
Eruption of ash flows.
They were observed only in ancient times. They are streams of minerals, volcanic glass, magma and ash surrounded by a gas shell, rushing at great speed.
Strombolian type.
Viscous streams of lava and hot slag are ejected from the vent in explosions of varying power.
Sub-ice type.
As the name suggests, the main action takes place under the ice.
They are dangerous due to possible floods due to melting.

Consequences of volcanic eruptions

Volcanic eruptions are considered very dangerous natural phenomena. Sometimes the consequences can be simply terrifying. But even if there is no destruction or casualties, this phenomenon still causes a lot of harm to both nature and people. Where lava passes, scorched earth remains for many years. The ash clouds emitted pollute the air.

Sulfur rain may begin to fall from the clouds.

Causes of volcanic eruptions

Also, as a result of this phenomenon, water bodies are polluted, and if the phenomenon occurs in places where drinking water and so it is not enough, then it can become a disaster.

Particularly powerful volcanic eruptions capable of causing disaster not only on a single piece of land, but over vast territories. And they can cause trouble for the whole world. There is a possibility that ash clouds rising into the atmosphere will completely cover the sky, blocking the Sun's access to the earth's surface. Due to the lack of heat, winter will come, and precipitation consisting of sulfuric acid will fall on the ground, all because of the same ash.

Fortunately, such powerful eruptions are very rare, and measures to counteract them exist.

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A central-type volcano is a cone-shaped geological formation that is topped by a crater - a depression shaped like a funnel or bowl.

Magma is a molten fiery mass that has a predominantly silicate composition. It is born in the earth's crust, where its hearth is located, and having risen to the top, it pours out onto the surface of the earth in the form of lava. An eruption is usually accompanied by the release of small splashes of magma, which form ash and gases, which, interestingly, are 98% magma.

They are joined by various impurities in the form of flakes of volcanic ash and dust. What is the structure of a volcano))

There are many rumors on the Internet about the secret schemes of the Vulcan casino, but they are supposedly available only to a select few. All this is complete nonsense, because even you can now try a scheme to deceive the virtual club Vulcan for money! The algorithms work absolutely legally, it’s just that people experienced in this matter found a gap in the operation of certain gambling games.

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, rocks (volcanic bombs) and pyroclastic flows.

The word "volcano" comes from ancient roman mythology and comes from the name ancient Roman god fire of Vulcan.

The science that studies volcanoes is volcanology and geomorphology.

Volcanoes are classified by shape (shield, stratovolcanoes, cinder cones, domes), activity (active, dormant, extinct), location (terrestrial, underwater, subglacial), etc.

Volcanic activity

Volcanoes are divided depending on the degree of volcanic activity into active, dormant, extinct and dormant. An active volcano is considered to be a volcano that erupted during a historical period of time or in the Holocene. The concept of active is quite inaccurate, since a volcano with active fumaroles is classified by some scientists as active, and by others as extinct. Dormant volcanoes are considered to be inactive volcanoes where eruptions are possible, and extinct volcanoes are considered to be those where they are unlikely.

However, there is no consensus among volcanologists on how to define an active volcano. The period of volcanic activity can last from several months to several million years. Many volcanoes exhibited volcanic activity tens of thousands of years ago, but are not considered active today.

Astrophysicists, from a historical perspective, believe that volcanic activity, caused, in turn, by the tidal influence of other celestial bodies, may contribute to the emergence of life. In particular, it was volcanoes that contributed to the formation of the earth's atmosphere and hydrosphere, releasing significant amounts of carbon dioxide and water vapor. Scientists also note that too active volcanism, such as on Jupiter's moon Io, can make the planet's surface uninhabitable. At the same time, weak tectonic activity leads to the disappearance of carbon dioxide and sterilization of the planet. “These two cases represent potential boundaries for planetary habitability and exist alongside the traditional parameters of habitable zones for systems of low-mass main sequence stars,” the scientists write.

Types of volcanic structures

IN general view volcanoes are divided into linear and central, but this division is conditional, since most volcanoes are confined to linear tectonic disturbances (faults) in the earth's crust.

Linear volcanoes or fissure-type volcanoes have extensive supply channels associated with a deep split in the crust. As a rule, basaltic liquid magma flows out of such cracks, which, spreading to the sides, forms large lava covers. Along the cracks, gentle spatter shafts, wide flat cones, and lava fields appear. If the magma has a more acidic composition (higher silicon dioxide content in the melt), linear extrusive ridges and massifs are formed. When explosive eruptions occur, explosive ditches can appear tens of kilometers long.

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

There are monogenic and polygenic volcanoes. The former arose as a result of a single eruption, the latter as a result of multiple eruptions. Viscous, acidic in composition, low-temperature magma, squeezed out of the vent, forms extrusive domes (Montagne-Pelé needle, 1902).

In addition to calderas, there are also large negative forms of relief associated with subsidence under the influence of the weight of erupted volcanic material and a pressure deficit at depth that arose during the unloading of the magma chamber. Such structures are called volcanotectonic depressions. Volcanotectonic depressions are very widespread and often accompany the formation of thick strata of ignimbrites - volcanic rocks of acidic composition, having different genesis. They are lava or formed by sintered or welded tuffs. They are characterized by lens-shaped segregations of volcanic glass, pumice, lava, called fiamme, and a tuff or tofo-like structure of the main mass. As a rule, large volumes of ignimbrites are associated with shallow magma chambers formed due to the melting and replacement of host rocks. Negative relief forms associated with central-type volcanoes are represented by calderas - large rounded failures several kilometers in diameter.

Classification of volcanoes by shape

The shape of a volcano depends on the composition of the lava it erupts; Five types of volcanoes are usually considered:

Shield volcanoes, or "shield volcanoes". Formed as a result of repeated ejections of liquid lava. This form is characteristic of volcanoes that erupt low-viscosity basaltic lava: it flows for a long time both from the central vent and from the side craters of the volcano. Lava spreads evenly over many kilometers; Gradually, a wide “shield” with gentle edges is formed from these layers. An example is the Mauna Loa volcano in Hawaii, where lava flows directly into the ocean; its height from its base on the ocean floor is approximately ten kilometers (while the underwater base of the volcano is 120 km long and 50 km wide).
Cinder cones. When such volcanoes erupt, large fragments of porous slag are piled up around the crater in layers in the shape of a cone, and small fragments form sloping slopes at the foot; With each eruption the volcano gets higher. This is the most common type of volcano on land. They are no more than a few hundred meters in height. An example is the Plosky Tolbachik volcano in Kamchatka, which exploded in December 2012.
Stratovolcanoes, or "layered volcanoes". Periodically erupt lava (viscous and thick, quickly solidifying) and pyroclastic matter - a mixture of hot gas, ash and hot stones; as a result, deposits on their cone (sharp, with concave slopes) alternate. Lava from such volcanoes also flows out of cracks, solidifying on the slopes in the form of ribbed corridors that serve as the support of the volcano. Examples - Etna, Vesuvius, Fuji.
Dome volcanoes. They are formed when viscous granite magma, rising from the depths of the volcano, cannot flow down the slopes and hardens at the top, forming a dome. It clogs its mouth, like a cork, which over time is expelled by the gases accumulated under the dome. Such a dome is now forming over the crater of Mount St. Helens in the northwestern United States, formed during the 1980 eruption.
Complex (mixed, composite) volcanoes.

Eruption

Volcanic eruptions are classified as geological emergency situations, which can lead to natural disasters. The eruption process can last from several hours to many years. Among the various classifications there are common types eruptions:

Hawaiian type - emissions of liquid basaltic lava, often forming lava lakes, which should resemble scorching clouds or red-hot avalanches.
Hydroexplosive type - eruptions that occur in shallow conditions of oceans and seas are characterized by the formation large quantities steam generated by the contact of hot magma and sea water.

Post-volcanic phenomena

After eruptions, when the activity of the volcano either stops forever, or it “dormants” for thousands of years, processes associated with the cooling of the magma chamber and called post-volcanic processes persist on the volcano itself and its surroundings. These include fumaroles, thermal baths, and geysers.

During eruptions, a volcanic structure sometimes collapses with the formation of a caldera - a large depression with a diameter of up to 16 km and a depth of up to 1000 m. As the magma rises, the external pressure weakens, associated gases and liquid products escape to the surface, and a volcanic eruption occurs. If ancient rocks, and not magma, are brought to the surface, and water vapor formed during heating predominates among the gases groundwater, then such an eruption is called phreatic.

Lava that rises to the earth's surface does not always reach this surface. It only raises layers of sedimentary rocks and hardens in the form of a compact body (laccolith), forming a unique system of low mountains. In Germany, such systems include the Rhön and Eifel regions. In the latter, another post-volcanic phenomenon is observed in the form of lakes filling the craters of former volcanoes that failed to form a characteristic volcanic cone (the so-called maars).

Heat sources

One of the unresolved problems of volcanic activity is determining the heat source necessary for local melting of the basalt layer or mantle. Such melting must be highly localized, since the passage of seismic waves shows that the crust and upper mantle are usually in solid state. Moreover, the thermal energy must be sufficient to melt huge volumes of solid material. For example, in the USA in the Columbia River basin (Washington and Oregon states) the volume of basalts is more than 820 thousand km³; the same large strata of basalts are found in Argentina (Patagonia), India (Deccan Plateau) and South Africa (Great Karoo Rise). Currently there are three hypotheses. Some geologists believe that the melting is caused by local high concentrations of radioactive elements, but such concentrations in nature seem unlikely; others suggest that tectonic disturbances in the form of shifts and faults are accompanied by the release of thermal energy. There is another point of view, according to which the upper mantle under conditions high pressures is in a solid state, and when the pressure drops due to cracking, it melts and liquid lava flows through the cracks.

Areas of volcanic activity

The main areas of volcanic activity are South America, Central America, Java, Melanesia, Japanese islands, Kurile Islands, Kamchatka, northwestern USA, Alaska, Hawaiian Islands, Aleutian Islands, Iceland, Atlantic Ocean.

Mud volcanoes

Mud volcanoes are small volcanoes through which it is not magma that comes to the surface, but liquid mud and gases from the earth's crust. Mud volcanoes are much smaller in size than ordinary ones. Mud typically comes to the surface cold, but the gases emitted by mud volcanoes often contain methane and can ignite during the eruption, creating what looks like a miniature volcano eruption.

In our country, mud volcanoes are most common on the Taman Peninsula; they are also found in Siberia, near the Caspian Sea and in Kamchatka. On the territory of other CIS countries, the most mud volcanoes are in Azerbaijan; they are found in Georgia and Crimea.

Volcanoes on other planets

Volcanoes in culture

Painting by Karl Bryullov “The Last Day of Pompeii”;
Movies "Volcano", "Dante's Peak" and a scene from the film "2012".
The volcano near the Eyjafjallajökull glacier in Iceland became a hero during its eruption huge number humorous programs, TV news stories, reports and folk art discussing events in the world.

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