Volcanic eruptions are dangerous natural disasters for humans. What do volcanoes erupt?

Each person interprets the nature of the volcano in his own way. One believes that eruptions are sent by fate, the second believes in the sinful essence of humanity, which causes disasters, and the third is quite rightly confident in scientific basis volcanism. Regardless of views on this issue, few people are familiar with the mechanism of volcanoes and the reasons that prompt them to be active. Why do they erupt?

Each volcano has a channel through which molten underground rocks rise from the depths of the Earth to the surface. Under the mountain there is a magma chamber - a reservoir containing large volumes of molten magma. When pressure begins to build in this reservoir, an eruption occurs. The reasons for the increase in pressure can be both internal processes and reactions occurring below or above the magma chamber.

Processes below the magma chamber

Many volcanoes are located in subduction zones—places where one tectonic plate sinks beneath another. As the lower plate sinks into the mantle, it warms up and releases volatile substances that enter the upper layers of the solid mantle and melt it. As a result, new portions of magma are formed, which enter the magma reservoir of the volcano. When the chamber is completely filled and can no longer accommodate the incoming molten rocks, excess magma exits to the Earth's surface through volcanic conduits.

Processes occurring below the magma chamber are usually cyclical, so volcanic eruptions are fairly easy to predict. For example, the Papandayan volcano in West Java is located in the subduction zone of the Eurasian and Indo-Australian plates and has a 20-year cycle. Considering that it last erupted in 2002, it can be assumed that its next volcanic activity will begin in 2022.

Processes inside a magma chamber

Activities inside a magma chamber can also lead to an eruption. Due to the decrease in temperature, the magma inside the reservoir gradually crystallizes and sinks to the bottom. As it sinks, it displaces lighter molten rocks into the upper part of the chamber, which exert pressure on the chamber lid. If the lid cannot withstand the pressure, it breaks off, resulting in an eruption. Such processes are also cyclical and can be predicted.

In addition to the sinking of crystallized magma, other phenomena occur within the chamber. In particular, magma can mix with surrounding rocks and, as it assimilates, put pressure on the reservoir lid. If the volcano has a channel, it pours out through it; if not, it finds places with the lowest pressure, resulting in the collapse of the chamber walls.

Imagine what will happen if you throw a brick into a bucket of water. The first thing that will happen is water splashing out of the bucket. A similar situation occurs inside the chamber when, after a collapse, its walls fall into the molten rock. Magma splashes out and causes an eruption. Such a process is unpredictable and can happen at any time.

Empty magma chamber from the inside

Processes above the magma chamber

Sometimes eruptions occur due to a loss of pressure above magma chamber. This can be caused by various reasons, such as a decrease in the density of the rocks above the reservoir. Due to changes in their mineral composition, the rocks surrounding the magma chamber gradually soften and, as a result, cannot retain the pressure of the magma.

What causes these mineralogical changes? Sometimes volcanoes develop cracks on the surface through which melt and rainwater seeps into the reservoir and interacts with the magma. In this case, it is very important where the molten rocks come to the surface. If lava is formed not in the crater, but on the slopes, then the dome may collapse under the force of gravity. In this case, very large eruptions occur.

Global warming may lead to eruptions due to melting glaciers. If large volumes of ice melt, the pressure above the magma chamber decreases, the magma becomes unbalanced and breaks through volcanic conduits. A similar eruption occurred in 2010 at the Eyjafjallajökull volcano. Given that Iceland loses about 11 billion tons of ice every year, more volcanic explosions should be expected.

A strong typhoon passing over the summit could also make matters worse. In 1991, the powerful eruption of Pinatubo in the Philippines occurred after Typhoon Yuna struck the volcano and its surrounding area. Before this, Pinatubo only grumbled, but thanks to the cyclone it exploded. This happened because the high speed of the typhoon led to a change in pressure around the mountain and, as a result, the column of air above the volcano was drawn into the cyclone.

Given the important role of magma in triggering volcanic eruptions, studying it more closely could help predict these spectacular natural events.

The products of volcanic eruptions are liquid, solid and gaseous.
LIQUID VOLCANIC PRODUCTS. This is, first of all, the magma itself, pouring out in the form of lava (by the way, mud flows used to be called lava). The shape, size, features of the internal and external structure of lava flows very much depend on the nature of the magma.

The most widespread are basaltic lava flows. Initially heated to 1000-1200° C, basalt lavas remain fluid even at 700° C. Basalt “rivers” flow at speeds of up to 40-50 km/h. When they come out onto level ground, they spread over a wide area. In 1783, when basalts erupted from the fissure volcano Laki in Iceland, their volume was truly gigantic - 12 km 3.

Lava begins to cool quickly in the air and becomes covered with a thin crust. With further movement of the flow, it wrinkles and finally hardens, resembling lying thick ropes. Therefore, such lava is called “rope lava”, or in Hawaiian - “pahoehoe”. Hot lava sometimes completely flows out from under the solidified crust, and then a kind of tunnel appears under it with icicles of solidified lava hanging from the “ceiling”.

If the lava flow flows slowly, the crust on it hardens faster and becomes thicker. Under its own weight, it often breaks repeatedly and hardens again. The surface of the flow eventually forms a chaotic accumulation of angular debris of various sizes, bearing the Hawaiian name "aa". Lava flows of type “aa” are very widespread and are characteristic not only of basalts, but also of andesites.

When it comes into contact with water, lava cools very quickly, turning into a glassy rock (resembling glass), because the melt, having hardened, does not have time to crystallize, i.e. Numerous mineral crystals did not form in it. When basaltic lavas erupt at great depths in the ocean, they are usually squeezed out of cracks, forming giant “rollers” resembling sausages or pillows, which are called “pillow” lavas (from the English pillow - “pillow”). .

If the lava is viscous and its temperature is relatively low, which is typical for magma containing a lot of silica (more than 65%), then the lava flows are shorter - several kilometers, and their surface is covered with a thicker blocky crust of the “aa” type. The blocks, moving with the flow, fall from its steep front edge and are blocked by the flow itself, creeping onto them. Therefore, in cross section, such frozen lava is a monolithic rock, bordered above and below by an accumulation of blocks - breccia. In the middle, inner part of a solidified lava flow, hexagonal or pentagonal pillars often form. They arise as a result of cooling and subsequent cracking of the lava flow, and are always located perpendicular to the surface on which the lava flow erupted. Such “colonnades” look extremely impressive. They can be seen in the Greater Caucasus in lava flows going down the slopes of Kazbek, in cliffs near the village of Gudauri, in the valley of the Aragvi River, on the Georgian Military Road south of the Cross Pass, on the southern slope of Elbrus.

Viscous lava flows, when solidified, create unique relief forms. The sides of the stream rise above its surface. Pressure shafts appear on it, consisting of blocks of lava and facing the convex side along the flow of the flow, which seem to “crawl” onto each other. The front part of the stream rises above its main mass and drops steeply down. This whole amazing picture resembles spilled thick sour cream.

A different relief occurs in cases where liquid lava gushes from volcanic vents. This happened repeatedly on the island of Hawaii in the middle of the Pacific Ocean. Liquid magma, splashing out in the form of “drops”, “cakes” and “flakes”, forms small volcanic cones. That's what they're called - splash cones,

SOLID VOLCANIC PRODUCTS are thrown to the ground from the crater of a volcano during powerful explosive eruptions.
The most common volcanic bombs are fragments more than 7 cm long. When ejected from the vent, they were still in a molten state, but, having flown many hundreds of meters, they cooled in the air and fell onto the slopes of the volcano, already strongly hardened. The shapes of these bombs are quite varied. They look like pieces of flat or twisted tape, like large “drops”, which, rotating in the air, acquire a spindle-shaped shape. There are round bombs with a surface resembling the crust of freshly baked bread (they are called “bread crust” bombs), as well as porous pieces of lava such as slag. Pieces of magma that have not yet cooled down fall onto the slopes of the volcano and are flattened, and therefore are called “cow pat” bombs. Sometimes large blocks, more than 1 m long, are also thrown out.

Volcanic fragments smaller than 7 cm are called lapilli (from Lat. lapillus - “ball”, “small stone”). Very interesting are drops of basalt melt frozen in the air in the form of bizarre small (no more than 1-2 cm) black glassy crescents, pears and other figures. In honor of the Hawaiian goddess of volcanoes, they are called “Pele’s tears,” and thin threads of glassy lava are called “Pele’s hair.”

Volcanic particles smaller than 2 mm are called ash. But this ash, of course, is not a combustion product. It looks like a collection of dust. Under a microscope at high magnification, it is clearly visible that the ash particles are fragments of volcanic glass in the form of flyers and triangles. They are thin partitions of magma between expanding gas bubbles, instantly frozen during an explosive eruption. Being thrown upward, they will then fall to the ground in the form of glassy ash. Sometimes ash occurs when older volcanic rocks are violently crushed; in other cases it may consist only of crystal fragments. The most common type is glassy ash. Let us recall the eruption of the Mont Pelee volcano: the scorching cloud that covered the city of Saint-Pierre consisted of an accumulation of hot ash and gases. When Vesuvius erupted, ash, lapilli and volcanic bombs buried Pompeii and Stabia.

Powerful eruptions throw fine ash into the upper atmosphere, where it can remain for a very long time. This was the case, for example, with the gigantic explosion of the Krakatau volcano in the Sunda archipelago (Indonesia) in 1883. Ash particles thrown into the stratosphere to a height of 40 km circled the globe 3 times. It is to him that noctilucent clouds at sunset, observed many years after this eruption in various countries of the world, owe their appearance.

The history of eruptions is known for powerful ashfalls. In June 1912, after the catastrophic explosion of the Katmai volcano in Alaska, fine glassy ash fell for two days. It covered Kodiak Island and other islands with a 25 cm thick layer. Residents were forced to evacuate. B 3 thousand km from the volcano, in southern California, due to volcanic dust, solar radiation decreased by 20%. It was estimated that a total of 25 km 3 of ash was emitted. The eruption of the El Chichon volcano in Central America was so strong that roofs collapsed under the weight of the ash. The last explosions of the Pinatubo volcano in the Philippines in 1992 were accompanied by a catastrophic ash fall that forced the Americans to evacuate their military bases. The powerful eruption of the Klyuchevskaya Sopka volcano on Kamchatka in September 1994 raised masses of ash to a height of 10-20 km, which made it difficult for aircraft to fly.

Explosive eruptions accompanied by ashfalls can affect the Earth's climate. Thus, the already mentioned eruption of the fissure volcano Laki in Iceland in 1783 threw so much ash into the upper layers of the atmosphere that over the next year the air temperature dropped by 1-2 ° C, and the Northern Hemisphere became sharply colder.

Layers of ash embedded in ancient sediments provide evidence of eruptions that occurred hundreds of thousands or millions of years ago and help geologist reconstruct the history of volcanic activity. Back in 1911, near Voronezh, in sediments about 1 million years old, layers of ash almost 1 m thick were discovered. The nearest volcanoes active at that time were either in the Caucasus or in Italy - at a distance of at least 1-2 thousand km What a force the explosions must have been and what a huge amount of ash was thrown into the air! But apparently the most powerful volcanic explosion that people remember occurred in 1815 on the island of Sumbawa in Indonesia. Then, during the explosion of the Tambora volcano, the volume of erupted ash reached 80 km 3.

GASEOUS VOLCANIC PRODUCTS. In addition to liquid and solid products of volcanic eruptions, various gases are always released, the share of which in the total volume of volcanic products is very large. It is hot gases that lift ash particles to a height of tens of kilometers.

Gases are an indispensable companion of volcanic processes and are released not only during violent eruptions, but also during periods of weakening volcanic activity. Through cracks in craters or on the slopes of volcanoes, calmly or violently, cold or heated to 1000 ° C, gases burst out.

What is the composition of volcanic gases? Numerous samples taken by scientists at different volcanoes show that water vapor predominates in any volcanic gases, accounting for 95-98%. Part of this water is juvenile (from Latin juvenilis - “young”), i.e. water released from magma, where it was previously part of various chemical compounds, and with a decrease in pressure and a drop in temperature it turned into the familiar water vapor. However, the other part of the water vapor is vadose (from vadosus - “shallow”), i.e. atmospheric, water that penetrated inside the volcanic structure through cracks and heated the magma there.

The second place after water vapor in the composition of volcanic gases is carbon dioxide (CO 2); followed by gases containing sulfur (S, SO 2, SO 3), hydrogen chloride (HC1) and other less common gases such as hydrogen fluoride (HF), ammonia (NH 3), carbon monoxide (CO), etc.

Places where volcanic gases come to the surface are called fumaores (from the Latin fumus - “smoke”). The temperature of the gases in them ranges from 40-50 to 1000° C. Sometimes fumaroles last a very long time, for thousands of years. Not far from Vesuvius, on the northern coast of the Gulf of Naples of the Tyrrhenian Sea, in the crater of the Solfatara volcano, the gas temperature reaches 120-400 ° C. They contain a high content of sulfur compounds. The great Italian poet of the early Renaissance, Dante Alighieri, considered one of these fumaroles, from which sulfur dioxide gas whistled out, leaving yellow deposits of sulfur on the stones, as the gates of a dark hell - the entrance to the underworld.

Often fumaroles emit “cold” gas with a temperature of about. 100°C and below. Such releases of cold gases are called mofets (from the Latin mofeta - “evaporation”). Their composition is most characteristic of carbon dioxide. Accumulating in depressions, it poses a mortal danger to all living things, because you can die in it from suffocation immediately. Thus, in Iceland in 1948, during the eruption of the Hekla volcano, carbon dioxide accumulated in a hollow at the foot of the volcano. The sheep there died, while the shepherds didn’t even feel anything - after all, their heads were above the level of carbon dioxide.

In Cameroon (Central Africa) you will find the Nyos volcano, in the crater of which there is a lake. On August 21, 1986, residents of nearby villages heard a sound resembling a loud bang. After some time, a gas cloud that escaped from the water of the crater lake and covered an area of ​​about 25 km 2 caused the sudden death of more than 1,700 people and huge amount livestock The deadly gas turned out to be carbon dioxide released into the atmosphere from a not yet extinct volcano.

The release of gases is observed on seemingly long-extinct volcanoes. So, in the Greater Caucasus mountains, on the slope eastern peak Elbrus, at an altitude of more than 5 km, there is a small fumarole field, free of snow and ice even in winter. The smell of sulfur is constantly noticeable here.

One of the most amazing and mysterious geological formations on Earth are volcanoes. However, many of us have only a superficial understanding of them. What is the nature of volcanism? Where and how does a volcano form?

Before considering how a volcano is formed, it is worth delving into the etymology and meaning of the term. Ancient Roman myths mention a blacksmith god named Vulcan, whose home was underground. If he was angry, the earth began to shake, and smoke and flames erupted from the depths. This is where the name of such mountains comes from.

The word "volcano" comes from the Latin "vulcanus", which literally means fire. Volcanoes are geological formations that appear directly above fissures earth's crust. It is through these cracks that lava, ash, a mixture of gases with water vapor and rocks erupt onto the surface of the earth. By studying this mysterious phenomenon The sciences are geomorphology and volcanology.

Classification and structure

All volcanoes, according to the nature of their activity, are active, dormant and extinct. And by location - terrestrial, underwater and subglacial.

To understand how a volcano forms, you must first take a closer look at its structure. Each volcano consists of the following elements:

1. Vent (the main channel in the center of the geological formation).
2. Dyke (channel with erupted lava).
3. Crater (large hole at the top in the form of a bowl).
4. Volcanic bomb (solidified pieces of erupted magma).
5. Volcanic chamber (an area below the earth's surface where magma is concentrated).
6. Cone (the so-called “mountain” formed by erupted lava and ash).

Despite the fact that the volcano looks like a huge mountain, its underground part is much larger than what is on the surface. Craters are often filled with water.

Why do volcanoes form?

The process of volcano formation begins with the formation of a magma chamber underground. Gradually, liquid hot magma heats up in it, which puts pressure on the earth's crust from below. It is for this reason that the earth begins to crack. Magma erupts upward through cracks and faults, and in the process of its movement it melts rocks and significantly widens the cracks. This is how a volcanic vent is formed. How is a volcano formed? During the eruption, various rocks come to the surface, which subsequently settle on the slope, resulting in the formation of a cone.

Where are the volcanoes?

Where do volcanoes form? These geological formations are distributed extremely unevenly on Earth. If we talk about the pattern of their distribution, then a large number of them are located near the equator. There are much fewer of them in the southern hemisphere than in the northern hemisphere. In the European part of Russia, Scandinavia, Australia and Brazil they are completely absent.

But if we talk about Kamchatka, Iceland, the Mediterranean, west coast Northern and South America, Indian and Pacific Ocean, Central Asia and central Africa, there are plenty of them here. They are mainly located near islands, archipelagos, and coastal areas of continents. The dependence of their activity and processes associated with the movement of the earth's crust is generally recognized.

How does a volcano erupt?

How and why processes lie in the bowels of the Earth. During the accumulation of magma, a large amount of thermal energy is generated. The temperature of the magma is quite high, but it is not capable of melting because the crust presses on it from above. If the layers of the earth's crust put less pressure on the magma, the hot magma becomes liquid. It gradually becomes saturated with gases, melts rocks on its way and in this way makes its way to the surface of the earth.

If a volcanic vent is already filled with frozen and solidified lava, then an eruption will not occur until the amount of magma pressure is sufficient to push out this plug. always accompanied by an earthquake. Ash can be thrown up to a height of several tens of kilometers.

Volcanoes are mountain-shaped formations from which hot magma erupts. How is a volcano formed? When there are cracks in the earth's crust, hot magma erupts toward its surface under pressure. The slopes of a volcano are formed as a result of the sedimentation of rocks, lava, and ash near the vent.

Volcanoes are geological formations that arise above cracks in the earth's crust. This is due to the fact that lava, gases and rock fragments can escape to the surface through them. This process is called “volcanic eruption”.

Why does this process occur?

Volcanic eruptions are caused by the layers of magma that lie underneath them. Under normal conditions, it is under great pressure, and comes out through cracks in the bark. For comparison, we can give the following example: if you shake a bottle of any carbonated drink and then open it, the contents will flow out very violently.

How do volcanoes erupt?

Warning signs of activity include volcanic earthquakes and loud noises. An eruption usually begins with the release of gases with cold lava particles, which are gradually replaced by hot debris. Sometimes this stage may be accompanied by an outpouring of lava. The height of the emission ranges from one to five kilometers (the highest column of matter occurred during the eruption of the Bezymyanny volcano in Kamchatka - forty-five kilometers). After this, the emissions are transported over distances of up to several tens of thousands of kilometers, and then settle on the Earth’s surface. Sometimes the concentration of ash can be so high that even sunlight cannot penetrate through it. During an eruption, there is an alternation of strong and weak lava emissions. After some time, a culminating paroxysm occurs - an explosion of maximum force, after which activity begins to decline. The consequences of a volcanic eruption are tens of cubic kilometers of spilled lava, as well as tons of ash that falls both onto the surface and into the atmosphere.

What groups are volcanoes divided into?

• According to activity - extinct, asleep, active.
• The shape of the cracks in the bark is central and fissure.
• In appearance, the volcano is cone-shaped, dome-shaped, flat shield-shaped.

What are volcanic eruptions like?

This process can also be characterized from several sides. For example, in terms of time, eruptions can be long-lasting (up to several centuries!) and short-term (several hours). Eruption products can be solid (rocks), liquid (lava) and gaseous.

Types of eruptions

Volcanoes are located in those places on the planet where there are faults in the earth's crust, at the edges lithospheric plates, especially where part of one slab lies on another. Many volcanoes are located on the ocean floor. Often sea water entering the crater provokes the next explosion. When cooled lava rises above the water level, entire islands of igneous rocks are formed. An example would be Hawaiian Islands.

Volcanoes are divided into active, dormant and extinct. The former constantly release gases, lava and ash from the vent. A natural disaster can happen at any time. Dormant volcanoes do not actively release eruption products, but in principle it can occur. Often the vents of such volcanoes are filled with cooled lava. This lava plug is difficult to break through even with the strongest flow of magma and gases. But if this happens, then an eruption of enormous proportions begins. For example, the Krakatoa volcano on Mount St. Helens in 1883 caused a powerful natural disaster. Echoes of this incident were observed throughout the globe.

Inactive volcanoes do not erupt for tens or hundreds of years. But it cannot be guaranteed that they will not begin their destructive activities again. This happened with the Bezymyanny volcano in 1955-1956. It did not function for more than nine hundred years and was considered extinct, woke up in 1955, and it all ended with an explosion in 1956.

But if there are few dissolved gases in the magma and there are no obstacles in its path, the eruption proceeds relatively calmly, and lava lakes are formed. With thick lava, the volcano looks cone-shaped and often has several craters - holes through which magma escapes. If water gets inside the crater, it is thrown back in the form of a geyser - a stream of hot water and volcanic particles. In addition to lava and gases, a huge cloud of ash often flies out of the volcano’s mouth, covering the sun for many kilometers around.

Volcanic eruptions are preceded by the appearance of magma chambers. They appear at the place of movement of lithosphere plates - the rocky shell of the Earth. Under the influence of high pressure, magma breaks out in places where there are faults or the shell is thinned. The result is a volcanic eruption.

In order to find out when a volcanic eruption occurs, you should consider the structure of the Earth. The outer shell of the planet is called the lithosphere (from the Greek “stone shell”). Its thickness on land reaches 80 km, and on the ocean floor - only 20-30 km. This is about 1% of the radius of the earth's crust. The layer next to the crust is the mantle. It has two parts - upper and lower. The temperature in these layers reaches several thousand degrees. At the center of the Earth is a solid core.

The lower layer of the mantle, located closer to the core, heats up more than the upper layer. The temperature difference causes the layers to mix: the hot substance rises up, and the cold substance sinks. Simultaneously with this process, the surface layers cool and the internal layers heat up. For this reason, the mantle is in constant motion. Its consistency resembles hot resin, because in the center of the planet there is very high pressure. The lithosphere “floats” on the surface of this viscous medium, plunging its lower part into it.

Since the stone shell is immersed in the mantle, it involuntarily moves with it. Its individual parts, lithospheric plates, can creep on top of each other. The plate at the bottom sinks deeper and deeper into the mantle and melts under the influence of high temperatures. Gradually it turns into magma (from the Greek “dough”) - a thick mass of molten rocks, with water vapor and gases.

Magma chambers are formed along the line of collision of lithospheric plates. Magma collects in them and rises to the surface. In outbreaks, it behaves like dough rising with yeast: it increases in volume, rises from the bowels of the Earth through cracks and fills all available space. Where the crust is thinned or there are faults, a volcanic eruption occurs.

It occurs when degassing (release of gases to the outside) of the magma has occurred. In the hearth, the mixture is under high pressure, which pushes it out of the depths as soon as the opportunity arises. Rising upward, magma is deprived of gases and turns into flowing lava.

Video on the topic

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• Eruptions
• Why does a volcano erupt?

A volcano is a geological formation above cracks and channels in the earth's crust, which has the shape of a cone with a crater at the top. During a volcanic eruption on earth's surface lava, rock fragments, ash and gases erupt.

Volcanic emissions can be divided into lava, in which there is virtually no loose pyroclastic products, and explosive, accompanied by a sudden release of rock and ash. The main types of emissions from a volcanic eruption are lava, debris, ash and gases.

Lava

The most famous product of volcanic activity is lava, which consists of compounds of silicon, aluminum and other metals. It is curious that all the elements of the periodic table can be found in lava, but the bulk of it is silicon oxide.

By its nature, lava is hot magma that flowed from the crater of a volcano onto the surface of the earth. When reaching the surface, the composition of the magma changes slightly under the influence of atmospheric factors. The gases that escape with the magma and mix with it give the lava its bubbly structure.

Lava flows out in streams ranging from 4 to 16 m wide. The average temperature of the lava is 1000 ° C, it destroys everything that comes in its way.

Debris and Ashes

When a volcano erupts, debris is thrown upward, also called pyroclastic debris, or tephra. The largest pyroclastic fragments are volcanic bombs, which are formed by the release of liquid products that solidify in the air. Fragments ranging in size from a pea to a walnut are classified as lapilli, and material smaller than 0.4 cm in size are classified as ashes.

Fine particles of volcanic dust and heated gas spread at a speed of 100 km/h. They are so hot that they glow dark time days. Ash flows spread over a huge radius, sometimes overcoming hills and bodies of water.

Gases

A volcanic eruption is accompanied by the release of gases, which include hydrogen, sulfur dioxide and carbon dioxide. Minor amounts contain carbon monoxide, hydrogen sulfide, carbonyl sulfide, hydrochloric acid, hydrogen, methane, hydrofluoric acid, boron, bromic acid, mercury vapor, as well as small amounts of metals, semimetals and some noble metals.

The gases released from the crater of a volcano look like white water vapor. When tephra is mixed with gases, the clouds of gases turn black or gray.

In the area of ​​the volcanic eruption, a strong smell of hydrogen sulfide spreads. For example, the smell of the Soufrir Hill volcano on the island of Montserrat spreads over a radius of 100 km.

Small gas emissions in volcanic areas can continue for years. However, volcanic gases are poisonous. Sulfur dioxide mixes with rainfall to form sulfuric acid. Fluorine, which is contained in gases, poisons water.

Sources:

• How does a volcano erupt?
• Products of volcanic eruptions
• Volcanoes
• Volcanic eruptions

Natural disasters can be different. These include a volcanic eruption. Every day there is an eruption of 8-10 famous volcanoes. Most of them go unnoticed, since there are many underwater volcanoes among the active and erupting ones.

What is a volcano

A volcano is a geological formation on the surface of the earth's crust. In these places, magma comes to the surface and forms lava, volcanic gases and stones, which are also called volcanic bombs. Such formations received their name from the ancient Roman god of fire Vulcan.

Volcanoes have their own classification according to several criteria. Based on their shape, they are usually divided into shield volcanoes, stratovolcanoes, cinder cones and domes. They are also divided into terrestrial, underwater and subglacial according to their location.

For the average person, the classification of volcanoes according to their degree of activity is much more understandable and interesting. There are active, dormant and extinct volcanoes.

An active volcano is a formation that erupted during a historical period of time. Dormant volcanoes are considered to be inactive volcanoes where eruptions are still possible, while extinct ones include those where they are unlikely.

However, volcanologists still do not agree on which volcano is considered active and therefore potentially dangerous. The period of activity at a volcano can be very long in time and can last from several months to several million years.

Why does a volcano erupt?

A volcanic eruption is essentially the release of hot lava flows to the surface of the earth, accompanied by the release of gases and clouds of ash. This happens due to gases accumulated in the magma. These include water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide and hydrogen chloride.

Magma is under constant and very high pressure. This is why gases remain dissolved in liquid. Molten magma, displaced by gases, passes through cracks and enters the hard layers of the mantle. There it melts weak spots in the lithosphere and spills out.

Magma that reaches the surface is called lava. Its temperature can exceed 1000oC. When some volcanoes erupt, they emit clouds of ash that rise high into the air. The explosive power of these volcanoes is so great that huge blocks of lava the size of a house are thrown out.

The eruption process can last from several hours to many years. Volcanic eruptions are classified as geological emergencies.

Today there are several areas of volcanic activity. These are South and Central America, Java, Melanesia, Japanese, Aleutian, Hawaiian and Kurile Islands, Kamchatka, northwestern USA, Alaska, Iceland and almost the entire Atlantic Ocean.