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What is a volcano? Volcano

A volcanic eruption is a sight to behold. This makes the volcano an interesting object of study. What is a volcano? A volcano is a geological formation on the surface of the earth through which hot magma emerges. Magma that reaches the surface forms lava, rocks, and volcanic gases. The volcano itself usually looks like a mountain, inside of which there is a fault in the earth's crust. Nowadays, volcanoes still continue to form, but much less frequently than before.

What is a volcano made of?

The volcano consists of two main parts - the vent and the crater. The vent of a volcano is the neck through which magma comes to the surface. The depression at the top of the mountain to which the vent leads is called a crater.

What is a volcanic eruption?

Volcanoes appear in unstable, seismically active places planets, where underground plates move and faults form in the earth’s crust. A liquid, hot, molten mixture of rocks (magma) from the depths of our planet accumulates inside and is gradually squeezed out. Magma comes out under great pressure and sooner or later breaks through the crater of the volcano. When a volcano erupts, a huge amount of ash and smoke comes out into the air, lumps of lava and stones fly, and the eruption is often accompanied by an earthquake.

Types of volcanoes

Not all volcanoes erupt equally intensely. Depending on their activity, they can be active, dormant or sleeping. Active volcanoes are those whose eruption is possible in the foreseeable future, extinct are those whose eruption is unlikely, and dormant ones are no longer capable of erupting. Also in science, there are many types of volcanic eruptions based on the spread of lava, smoke and ash.

In the Tyrrhenian Sea in the Aeolian group of islands there is a small island of Vulcano. Most of it is occupied by a mountain. Even in time immemorial, people saw clouds of black smoke, fire and fire sometimes bursting from its top. greater height hot stones were thrown out.

The ancient Romans considered this island the entrance to hell, as well as the domain of the god of fire and blacksmithing, Vulcan. After the name of this god, the fire-breathing mountains were later called volcanoes.

A volcanic eruption can last for several days, sometimes months and even years. After a strong eruption, the volcano calms down again for several years and even decades. Such volcanoes are called active.

There are volcanoes that erupted in times long past. Some of them have retained the shape of a regular cone. No information has been preserved about the activity of such volcanoes. They are called extinct, like, for example, the Elbrus Mountains in the Caucasus. and Kazbek, whose peaks are covered with sparkling, dazzling white glaciers. In ancient volcanic areas, severely destroyed and eroded volcanoes are found. In our country, the remains of ancient volcanoes can be seen in Crimea, Transbaikalia and other places. Volcanoes are usually cone-shaped with slopes that are gentle at their bases and steeper at their summits.

If you climb to the top of an active volcano when it is calm, you can see crater 1 - a deep depression with steep walls, similar to a giant bowl. The bottom of the crater is covered with fragments of large and small stones, and jets of gas and steam rise from cracks in the bottom and walls. They calmly emerge from under stones and from cracks or burst out violently, with hissing and whistling. The crater is filled with suffocating gases: rising upward, they form a cloud at the top of the volcano. The volcano can quietly smoke for months and years until an eruption occurs.

Volcanologists have already developed methods that make it possible to predict the time of a volcanic eruption. This event is often preceded by earthquakes; an underground rumble is heard, the release of vapors and gases increases; their temperature rises; clouds thicken over the top of the volcano, and its slopes begin to “swell.”

Then, under the pressure of gases escaping from the bowels of the Earth, the bottom of the crater explodes. Thick black clouds of gases and water vapor mixed with ash are thrown up thousands of meters, plunging the surrounding area into darkness. With an explosion and roar, pieces of red-hot stones fly from the crater, forming giant sheaves of sparks. Ashes fall from black, thick clouds onto the ground, sometimes torrential rains fall, and streams of mud are formed that roll down the slopes and flood the surrounding area. The flash of lightning continuously cuts through the darkness. The volcano rumbles and trembles, molten fiery liquid lava rises through its crater. It seethes, overflows over the edge of the crater and rushes in a fiery stream along the slopes of the volcano, burning and destroying everything in its path.

Eruption of Mount Etna. Photo: gnuckx

1 From the Greek word "krater" - a large bowl.

Section of the volcano: 1 - magma chamber; 2 - lava flows; 3 - cone; 4 - crater; 5 - channel through which gases and magma rise to the crater; 6 - layers of lava flows, ash, lapilli and loose materials from earlier eruptions; 7 - remains of an old volcano crater.

During some volcanic eruptions, when the lava is highly viscous, it does not pour out as a liquid stream, but is piled up around the vent in the form of a volcanic dome. Often, during explosions or simple collapses, hot rock avalanches fall down the slopes along the edges of such a dome, which can cause great destruction at the foot of the volcano. During the eruption of some volcanoes, such hot avalanches erupt directly from the crater.

During weaker eruptions, only periodic explosions of gases occur in the crater of the volcano. In some cases, during explosions

pieces of hot, luminous lava are thrown out, in others (at a lower temperature) the already completely frozen lava is crushed and large blocks of dark, non-luminous volcanic ash rise up.

Volcanic eruptions also occur at the bottom of seas and oceans. Sailors learn about this when they suddenly see a column of steam above the water or “stone foam” floating on the surface - pumice. Sometimes ships encounter unexpected shoals formed by new volcanoes at the bottom of the sea. Over time, these shallows erode" sea waves and disappear without a trace. Some underwater volcanoes form cones that protrude above the surface of the water in the form of islands.

In ancient times, people did not know how to explain the causes of volcanic eruptions. This formidable natural phenomenon plunged people into horror. However, already the ancient Greeks and Romans, and later the Arabs, came to the idea that in the depths of the Earth there was a sea of underground fire. They believed that the waves of this sea caused volcanic eruptions on the earth's surface.

At the end of the last century, a special science, volcanology, separated from geology. Now close to some active volcanoes they organize volcanological stations - observatories, where volcanologists constantly monitor volcanoes. We have such volcanological stations in Kamchatka at the foot of the Klyuchevsky volcano in the village of Klyuchi and on the slope of the Avacha volcano - not far from the city of Petropavlovsk-Kamchatsky. When one of the volcanoes begins to act, volcanologists immediately go to it and observe the eruption.

Volcanologists also study extinct and destroyed ancient volcanoes. The accumulation of such observations and knowledge is very important for geology. Ancient destroyed volcanoes, active tens of millions of years ago and almost leveled with the surface of the Earth, help scientists recognize how molten masses located in the bowels of the Earth penetrate into the solid crust and what is obtained from their contact with rocks. Usually, at the points of contact, as a result of chemical processes, mineral ores are formed - deposits of iron, copper, zinc and other metals.

Jets of steam and volcanic gases in volcanic craters, called fumaroles, carry with them some substances in a dissolved state. Sulfur, ammonia, and boric acid, which are used in industry, are deposited in the cracks of the crater and around it, around the fumaroles.

Volcanic ash and lava contain many compounds of the element potassium and over time turn into fertile soils. They plant gardens or engage in field cultivation. Therefore, although it is unsafe to live in the vicinity of volcanoes, villages or cities almost always grow there.

Why do volcanic eruptions occur and where does such enormous energy come from within the globe?

The discovery of the phenomenon of radioactivity in some chemical elements, especially uranium and thorium, suggests that heat accumulates inside the Earth from the decay of radioactive elements. The study of atomic energy further supports this view. The accumulation of heat in the Earth at great depths heats up the Earth's substance. The temperature rises so high that this substance should melt, 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, saturated with gases, formed deep in the bowels of the earth is called magma. Foci of magma are located under the earth's crust, in the upper part of the mantle, at a depth of 50 to 100 km. Under strong pressure from the released gases, magma, melting the surrounding rocks, makes its way and forms a vent, or channel, of the volcano. The released gases explosively clear a path along the vent, break apart solid rocks and throw pieces of them to great heights. This phenomenon always precedes the outpouring of lava.

Just as the gas dissolved in a fizzy drink, when the bottle is uncorked, tends to escape, forming foam, so in the crater of a volcano, foaming magma is rapidly ejected by the gases released from it. Having lost a significant amount of gas, magma pours out of the crater and flows like lava along the slopes of the volcano. If magma in the earth's crust does not find its way to the surface, then it hardens in the form of veins in cracks in the earth's crust. Sometimes magma penetrates along a crack, raises a layer of earth like a dome and freezes in a shape similar to a loaf of bread.

Lava varies in composition and, depending on this, can be liquid or thick and viscous. If lava is liquid, it spreads relatively quickly, forming lava falls along its path. Gases escaping from the crater emit hot fountains of lava, the splashes of which freeze into stone drops - lava tears. Thick lava flows slowly, breaks into blocks that pile up on top of each other, and the gases escaping from it tear off pieces of viscous lava from the blocks, throwing them high. If clots of such lava rotate during takeoff, they take on a spindle-shaped or spherical shape.

Solidified lava. Photo: Mike Weston

Such frozen pieces of lava of various sizes are called volcanic bombs. When lava, filled with gases, hardens, stone foam - pumice - is formed. Due to its lightness, pumice floats on water and floats to the surface of the sea during underwater eruptions. The pea-sized or hazelnut-sized fragments of lava ejected during an eruption are called lapilli. Even finer, loose igneous material is volcanic ash. It falls on the slopes of the volcano and is carried by the wind over a long distance. On the surface of the earth, the ash gradually turns into tuff. There are huge tuff deposits in Armenia.

There are currently several hundred active volcanoes known on the globe. Most of them are located along the banks Pacific Ocean, including our volcanoes in Kamchatka and the Kuril Islands. Among the active volcanoes in Kamchatka, Klyuchevskaya Sopka stands out. Typically, its eruptions repeat every 6-7 years and sometimes last for several months. Lava flows often descend a dozen kilometers down the slope. The height of the peak, where the main crater of Klyuchevskaya Sopka is located, is 4750 m. At such a height, powerful glaciers are formed, which melt during strong eruptions, and then rapid streams of water rush from the mountain.

Near Klyuchevskaya Sopka there is a group of extinct volcanoes. One of them - Bezymyanny volcano - suddenly awakened. On March 30, 1956, a gigantic explosion occurred. It was one of the largest volcanic eruptions in the last century. A cloud of ash rose almost 40 km in height. A significant part of the volcano's cone was blown up. At a distance of 25--30 km Trees were broken and burned by the force of the explosion. A huge hot lava flow with a capacity of 20-30 m and length 18 km. On an area of about 500 km 2 hot ash fell, under the cover of which the snow instantly melted, forming mud flows up to 90 km. Ash thrown into the high layers of the atmosphere was noticed two days later in the North Pole area, and 4 days later over England.

Near Petropavlovsk-Kamchatsky there is an active Avacha volcano. Near it are located extinct volcanoes- Koryak and Kozelskaya hills. Avacha eruptions occur much less frequently than Klyuchevskaya Sopka. Shiveluch volcano is located north of Klyuchevskaya Sopka.

The Kamchatka volcanic arc continues south to Kuril Islands, where volcanoes rise straight from the sea. On the northernmost island is the Alaid volcano. Its beautiful snow cone rises above the water by almost 2.5 km. In 1946, there was a strong eruption on one of the central islands - Matua, where the majestic volcano - Sarychev Peak - is located. Hot lavas descended along its slopes, above which huge clouds of swirling ash rose. From the sea it seemed that the entire island was on fire. In 1952, an eruption occurred at Krenitsyn Peak (Onekotan Island), which rises from a vast ancient crater filled with lake water. In 1957, there was a strong eruption on the island of Simushir in the Zavaritsky caldera. As a result of the eruption, part of the lake in the caldera was covered with volcanic slag, and a small lava flow erupted. There are 39 active volcanoes on the Kuril Islands, and 26 on Kamchatka.

On geographical map it is clear that the Kuril Islands, located in an arc, adjoin Japan. A similar arc is formed by Japanese islands with numerous volcanoes, among which the famous Mount Fuji stands out. To the south of Japan, a similar arc of the Philippine and Moluccan volcanic islands continues. Thus, along the entire Pacific coast of Asia there is a strip of volcanoes, passing further through New Zealand and Antarctica to the American mainland.

IN South America numerous volcanoes - Calbuco, Osorno, Villarrica, Cotopaxi. Sangai - crowned mountain ranges Andes. There are many volcanoes in Central America.

On the Pacific Coast North America The volcanoes are almost extinct. Only the Lassen Peak volcano is weakly active here. The Aleutian Islands stretch in an arc from Alaska to Kamchatka, where there are many active volcanoes. Thus, the Pacific Ocean is surrounded by volcanoes on almost all sides.

In the central part of the Pacific Ocean, on the Hawaiian Islands, there is a special type of volcano called Kilauea. At the bottom of its wide, flat crater, about 5 km in diameter, among frozen blocks of black lava during eruptions, a fiery lake of molten lava appears 700-800 wide m. The gases released from the liquid lava cause it to constantly move. At night it is a very beautiful sight. The surface of the lake, cooling, becomes covered with a stone crust, which is broken through by the released gases, forming a moving network of winding fiery cracks. Fountains of fiery liquid lava rise from them from time to time. The level of the lava lake either decreases or rises. Sometimes lava overflows the crater lake, overflows the edges and spreads throughout the caldera. The lava of Hawaiian volcanoes is very liquid.

There are few such volcanoes with lava lakes in the crater on Earth: on the Hawaiian Islands - Mauna Loa and Kilauea and on the mainland of Africa (almost on the equator) - Nyamlaghira. Between Asia and Australia, on the Greater Sunda Islands, there are numerous active volcanoes.

Among Antilles in the Atlantic Ocean there is the island of Martinique with the terrible volcano Mont Pele. In 1902, during its eruption, a huge cloud of hot gases and fine ash burst out of the crater. With great speed she rolled down the mountainside, leaving devastation and death in her path. Within a few minutes, the thriving city of Saint-Pierre at the foot of Mont Pelée was destroyed. The entire population of the city died - about 30 thousand inhabitants!

In the north of the Atlantic Ocean there is the island of Iceland with many active volcanoes that have poured out huge amounts of liquid lava at different times. Among the volcanoes of Iceland, the active Hekla volcano is widely known. In the Mediterranean Sea, the volcanoes Etna, Vesuvius, Stromboli, and Vulcano have not calmed down since ancient times.

The strong eruption of Vesuvius in 79 occurred unexpectedly: until that time, Vesuvius was considered an extinct volcano. After the eruption, all flowering vegetation disappeared under clouds and streams of mud. Pieces of thrown stones and ash covered the slopes and surroundings of Vesuvius, while three cities - Pompeii, Herculaneum and Stabia - were destroyed, flooded by mud flows and covered with ash. Only seventeen centuries later, when people had already forgotten about the disappeared cities, marble statues of Greek gods were accidentally found while digging a well. Soon excavations began, and archaeologists discovered the buried city of Pompeii, and then two others. Since then, Vesuvius has erupted many times and has been studied in detail by scientists. A strong eruption of Vesuvius occurred in 1944, and its surroundings were damaged. The lava moved at high speeds, reaching 5 km per day.

East of Mediterranean Sea Scattered in a wide strip are the extinct volcanoes of Asia Minor and the Caucasus Range: Ararat, Kazbek and Elbrus. The depths of volcanoes contain enormous amounts of thermal energy. Some of this heat is carried to the Earth's surface. Scientists are solving the problem of using this thermal energy.

Underwater volcanoes

The ocean floor is often shaken by earthquakes. Underwater volcanoes spew out ash and lava, islands suddenly rise from the bottom and sometimes also suddenly disappear. Most ocean islands located far from continents are of volcanic origin.

Many of them are topped by extinct or active volcanoes, but many more are hidden by ocean water. It is assumed that single mountains rising on a relatively flat ocean floor also former volcanoes. They are distinguished by one curious feature that has not yet been solved: they have completely flat tops. Some scientists think that in distant geological times these underwater peaks rose above sea level. Over millions of years, the tireless surf cut off their tops like a knife. However, it remains unknown what reasons caused these mountains to sink into the depths of the ocean - after all, there is now a 1000-meter layer of water above their peaks.

Among various natural phenomena, volcanic activity has attracted special human attention.

Volcanoes are geological formations that arise in the earth's crust above channels or cracks through which fiery liquid lavas, fragments of hot rocks, ash, hot gases, and vapors erupt from the bowels of the earth. In general terms, a volcano is usually understood as a cone-shaped mountain with a slightly truncated peak.

The structure of the volcano. At the top of such a mountain there is a cup-shaped depression (crater). The latter connects to the leading canal (vent). The most important thing in a volcano is not the mountain, which may or may not form above the volcanic outlet, but the outlet itself, or the vent, from where volcanic products emerge from the depths: steam, gases, ash and lava. Gases escaping from the volcano eject loose material that falls around the exit, and lava immediately pours out; These loose materials with lava, piling up at the exit, gradually form a mountain. This is the most common, but not the only form of volcanoes.

The emergence of volcanoes, their life and activity are associated with the concentration of the Earth's internal thermal energy and its subsequent loss.

It is known that both the earth's crust and the underlying upper mantle are in a solid state. If we mentally follow into the depths of the Earth, we will be convinced that every 33 meters the temperature rises by 1 0 C. This is the so-called geometric gradient. At a depth of several tens of kilometers, the temperature reaches a level at which rocks usually melt. However, with depth, the pressure that prevents melting also increases. Over time, various movements in the earth's crust and upper mantle (faults, vertical movements of blocks, etc.) upset the balance and then at great depths the solid substance turns into an alloy, creating a source. With the help of gas and steam, the melt from this source rushes to the surface - a volcanic eruption occurs.

This melt is called magma. The name was proposed back in the last century by the German scientist G. Rosenbusch. In Greek, magma means dough. The name does not accurately reflect the state of the substance, since magma does not always look like dough. Magma contains a lot of gases and vapors, its viscosity has an unusually wide range - sometimes it is a liquid mass, sometimes it is solid - plastic.

The magma that comes to the surface during volcanic eruptions is far from uniform in composition. The main indicator for determining the composition is the content of silica (SiO 2) in it. If it is no more than 45–55%, the magma is considered basic. The most typical rocks of basic magma are basalts. If the silica content is 55–65%, the magma already has an average composition. From such magma rocks called andesites are formed. Magma belonging to the silicic series contains 65–75% silica. Its most typical rocks are dacites and liparites. The composition of magma determines the nature of volcanic products, the shape of volcanic structures, and the type of volcanic eruptions.

Gases, vapors of water and some acids, with which the magma is saturated at a certain stage, are the lifting lever that moves the melt first closer to the surface, and then to the surface. When the path to the surface has not yet been paved, the melt, supersaturated with gases and vapors, is pushed by force and overcomes the obstacle - an explosion occurs. During an explosive eruption, solid products are thrown out - pieces of lava or slag, pumice, volcanic bombs of the most varied shapes and sizes (from 10–15 cm to 1 m or more in diameter).

During explosive eruptions, the deeper parts of the melt are depleted in gases and vapors. Now it is less saturated with them and therefore flows relatively calmly to the surface in the form of lava flows, which move on the surface at high speed - sometimes up to 30 km/h.

Thus, both solid and liquid products are formed from the same melt. The role of gases and vapors in this case is very important: if the melt is supersaturated with them, it arrives at the surface in crushed form, if there are relatively few of them, the melt pours out calmly.

Gases and vapors are the longest-lived volcanic phenomena. When the active activity of the volcano has passed, they still hover for a long time from cracks on the slopes of volcanoes, lava flows or craters. This is the so-called fumarole stage of volcanic activity (fumare - Italian for “smoke”).

Historically, the idea of volcanoes is associated with their cone-shaped shape. And this is understandable, since most of the well-known volcanoes in the Mediterranean or Indonesia are of this shape. Therefore, mainly the Mediterranean (Italy) was the source of our knowledge about volcanoes. And since hot volcanic products were emitted from cone-shaped volcanoes (Vesuvius, Stromboli, Etna, etc.), or fiery streams poured out, this idea of cone-shaped volcanoes was fixed in people’s memory.

Cone-shaped volcanic mountains are very widespread. Magnificent volcanic cones are found in Kamchatka.

The origin of volcanic structures of this type is now known. In the vast majority of cases, they are formed by alternating loose, or explosive, products and lava flows coming from the crater of the volcano. The result is a layered mountain called a stratovolcano. Its slopes are usually steep. Of course, the shape of the cone also depends on the composition of the magma. If liquid, mobile lavas predominated during the eruption, the slopes of the cone may be flat.

Tyatya volcanoes (Figure 1) in the Kuril island ridge, as well as Klyuchevskaya Sopka, Vilyuchik, Kronotsky and some others in Kamchatka have an ideal summit cone. Such structures are called central-type volcanoes.

It happens that during subsequent eruptions the volcanic cone partially or completely explodes and is destroyed, leaving only its outer edge. During subsequent eruptions, a new cone is formed in the same place. This will already be a double volcano, or a cone within a cone. These types of volcanoes are called Somma-Vesuvius.

Figure 1 – Tyatya volcano

Volcanic products (mostly lavas) coming to the surface from the central channel are of low viscosity, therefore they are highly mobile and cover huge areas. When lava hardens, it forms flat, sheet-like bodies. But the eruption is repeated many times and, ultimately, a powerful shield, or shield volcano, is obtained. It is characterized by very gentle slopes, not exceeding 10 - 12, and at the foot even less - only a few degrees.

As an illustrative example, the volcanoes of the Hawaiian Islands are given, in particular the Mauna Loa volcano (Figure 2). This is the largest volcano on our planet. The height of its surface part alone is 4170 m, and the total height of the volcano exceeds 9000 m. Shield volcanoes are also widespread in Iceland, although they are not so large there.

Another type of volcanic structure stands out - a plateau. They are formed, like some volcanoes, as a result of fissure eruptions and often occupy huge areas. The most famous are basalt plateaus. They are widespread in Siberia. In India, the famous Deccan Plateau with an area of about 650 thousand km is known, and in the USA - the Columbia Plateau, which occupies an area of over 500 thousand km. There are basalt plateaus in Iceland and many other places. But plateaus are not always built by basalts. Some of them are composed of extremely acidic rocks - rhyolites (an extremely acidic type of calc-sodium rocks). Rhyolite plateaus are known in New Zealand, Indonesia, the USA and other places.

Lava flow plays an important, sometimes dominant role in the formation of volcanoes. Lava flows from the main or side crater and follows down the slope. Depending on the terrain and melt temperature, they continue to move beyond the foothills of the volcanoes. As observations by Kamchatka volcanologists show, basaltic andesite lavas flowing from the side craters of Klyuchevsky volcano have

Figure 2 – Mauna Loa Volcano

temperature 1100–1200. The surface of the stream quickly cools, and its lower parts remain hot for 2–3 years.

Streams are different. There are flows of Hawaiian block lava, the surface of which consists of semi-sintered fragments and small blocks; the latter have an uneven fracture and wrinkled boundaries. The type of Santorini block lava is somewhat different. Its surface is formed from a free pile of large blocks with a flat and smooth surface. In some cases, basalt flows have a smooth surface, like a river surface, and move at enormous speeds - 15 - 20 km/h.

In the cross section of the lava flow, three layers are distinguished: the upper layer is blocky; when the flow moves, these blocks fall in the direction of movement, forming its base; the middle of the flow is monolithic.

Volcanic eruptions often produce mud flows that have nothing to do with lava flows. They arise as a result of the fact that hot, finely crushed volcanic material falls onto a large area covered with snow. Rapid melting of snow occurs, and powerful mud flows are formed (they are also called lahars).

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 rocks, in the form of volcanic bombs and pyroclastic flows. Translated from Latin vulkanus - fire

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 about 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. However, 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 particularly active regions on Earth: the Pacific coast, the Mediterranean-Indonesian belt and the Atlantic belt, located at the junction of the 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 of volcanoes depending on their specific properties. So, they are divided into active, dormant and extinct. A volcano that erupted in historical times or the Holocene is considered active. 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 usually form in coastal zones and on islands in subduction zones, where continental strata are pushed over oceanic ones. 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. Above them arise active volcanoes 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 buildings. 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 South Pacific Ocean there is a whole belt of island and submarine volcanoes of the “hot spot” type (for example Hawaiian Islands and the 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 in marginal seas has been poorly studied. Shallow-water volcanoes are located on continental-type crust 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 the total 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 the disappearance of carbon dioxide and sterilization of the planet. So, volcanoes, let's live together!

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The word “volcano” itself began to be used in everyday life in Ancient Rome, since this was the name of the ancient god of fire - Vulcan. The ancient Romans believed that every volcano from which smoke or lava erupts was a chimney from the forge of a god.

You can understand the structure of a volcano, since its principle is quite simple. In fact, a volcano is essentially a hole in the Earth’s crust, and through this hole a mixture of molten rock (lava), ash, steam and gases is ejected to the surface under high pressure. When a volcano erupts, a large amount of volcanic ash rises into the air, which then covers everything in the area.

In most cases, a volcano is a single mountain or hill that is made up of materials that are ejected during an eruption. Almost always, the top of a volcano is its crater; in fact, it is a hearth from which, during an eruption, all the substances described above are ejected. The crater necessarily has a connection with the vent, although sometimes this connection is blocked by frozen rock.

In 1943, on the territory of Mexico in one of its regions local residents were eyewitnesses unique phenomenon, which not everyone can see. At one point, in the center of the field where the corn was growing, smoke appeared from the ground, and then lava began to appear. In just 90 days, in place of a flat field, a cone-shaped mountain was formed, the height of which was about 300 meters. The action of this new volcano left two nearby towns desolate, and an even larger area of land around was simply killed by a large layer of volcanic ash, and some was scorched by burning lava.

How are volcanoes formed in general, according to what principle and algorithm? We need to start with the fact that in the depths of our planet there are quite high temperatures and the closer we get to the center of the Earth, the hotter it becomes. If you find yourself at a depth of about 40 kilometers, you can see that everything around is in a molten state, these are various rocks that we are used to seeing in solid form.

The fact is that as soon as minerals go from solid to liquid, their volume increases sharply, so they need to look for a way out from time to time. It is for this reason that new mountain ranges form from time to time in different parts of the globe.

Due to this rise of the earth's crust and the formation of hard rocks from igneous masses, the pressure at great depths of the earth's crust decreases. True, real lakes are formed under the so-called “young” mountains, which consist of hot magma.

This same magma is essentially molten minerals and they rise upward, filling the cracks that appeared during the formation of mountain ranges. Day by day, the pressure in the underground burning lakes increases, and at a certain point it becomes critical. It is at such moments that the stone vault cannot withstand high pressure, cracks and lava bursts through them. This is the algorithm for the appearance of new volcanoes on our planet.

On Earth, the largest number of volcanoes are concentrated in places of tectonic regions and large faults; they are also present on island arcs and on the ocean floor.

In 98 percent of cases, volcanoes have the correct conical shape:

if lava of viscous consistency is squeezed out, then the volcano becomes dome-shaped;
if liquid lava pours out of the crater, then a shield-shaped volcano is formed.

Today there are the following types of volcanoes: