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 on the planet, 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, while 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.
A truly amazing sight - a volcanic eruption. But what is a volcano? How does a volcano erupt? Why do some of them spew out huge streams of lava at different intervals, while others sleep peacefully for centuries?
What is a volcano?
Externally, the volcano resembles a mountain. There is a geological fault inside it. In science, a volcano is a formation of geological rock located on the surface of the earth. Magma, which is very hot, erupts through it. It is magma that subsequently forms volcanic gases and rocks, as well as lava. Most of the volcanoes on earth were formed several centuries ago. Today, new volcanoes rarely appear on the planet. But this happens much less frequently than before.
How are volcanoes formed?
If we briefly explain the essence of the formation of a volcano, it will look like this. Under the earth's crust there is a special layer under strong pressure, consisting of molten rocks, it is called magma. If cracks suddenly begin to appear in the earth’s crust, then hills form on the surface of the earth. Through them, magma comes out under strong pressure. At the surface of the earth, it begins to break down into hot lava, which then solidifies, causing the volcanic mountain to become larger and larger. The emerging volcano becomes such a vulnerable spot on the surface that it spews volcanic gases onto the surface with great frequency.
What is a volcano made of?
In order to understand how magma erupts, you need to know what a volcano is made of. Its main components are: a volcanic chamber, a vent and craters. What is a volcanic source? This is the place where magma is formed. But not everyone knows what a volcano’s crater and crater are? A vent is a special channel that connects the hearth with the surface of the earth. A crater is a small bowl-shaped depression on the surface of a volcano. Its size can reach several kilometers.
What is a volcanic eruption?
Magma is constantly under intense pressure. Therefore, there is a cloud of gases above it at any time. Gradually they push hot magma to the surface of the earth through the crater of the volcano. This is what causes an eruption. However, just a short description of the eruption process is not enough. To see this spectacle, you can use the video, which you need to watch after you have learned what the volcano is made of. In the same way, in the video you can find out which volcanoes do not exist nowadays and what the volcanoes that are active today look like.
Why are volcanoes dangerous?
Active volcanoes pose a danger for a number of reasons. The dormant volcano itself is very dangerous. It can “wake up” at any time and begin to erupt streams of lava, spreading over many kilometers. Therefore, you should not settle near such volcanoes. If an erupting volcano is located on an island, a dangerous phenomenon such as a tsunami may occur.
Despite their danger, volcanoes can serve humanity well.
How are volcanoes useful?
- During the eruption, a large amount of metals appears that can be used in industry.
- The volcano produces the strongest rocks that can be used for construction.
- Pumice, which appears as a result of the eruption, is used for industrial purposes, as well as in the production of stationery erasers and toothpaste.
On August 24, 79, people looked at their patron in horror and could not understand why they had angered the gods so much. How did it happen that their protector suddenly began to spew out flames that spread across the ground and destroyed everything in its path? The residents of Pompeii already knew: unexpectedly for everyone, the volcano woke up. What it is, what volcanoes are like and why they suddenly wake up, we will look at today in this article.
What is a volcano?
A volcano is a kind of formation on the surface of the earth's crust, which from time to time is capable of erupting pyroclastic flows (a mixture of ash, gas and stones), volcanic gases, and lava. It is in zones of volcanic activity that opportunities for using geothermal energy open up.
Types of volcanoes
Scientists have adopted a classification of volcanoes into active, dormant and extinct.
- Active volcanoes are those that erupt during a historical period of time. It is thanks to them that one can understand what a volcano is and the mechanisms that make it act, because direct observation of the process provides much more information than the most thorough excavations.
- Dormant volcanoes are called dormant volcanoes that are currently inactive, however, there is a high probability of their awakening.
- Extinct volcanoes include those that were active in the past, but today the probability of their eruption is zero.
What shapes do volcanoes come in?
If you ask a schoolchild what shape a volcano has, he will undoubtedly say that it looks like a mountain. And he will be right. The volcano actually has the shape of a cone, which was formed during its eruption.
The volcanic cone has a vent - this is a kind of outlet channel through which lava rises during an eruption. Quite often there is more than one such channel. It may have several branches that serve to bring volcanic gases to the surface. The vent always ends in a crater. It is into this that all materials are thrown out during an eruption. A curious fact is that the vent is open only during the period of volcanic activity. The rest of the time it is closed, until the next manifestation of activity.
The time during which the volcanic cone formed varies individually. It mainly depends on how much material the volcano releases during its eruption. Some require 10 thousand years for this, others can form it in one eruption.
Sometimes the opposite processes also happen. During an eruption, the volcanic cone collapses, and in its place a large depression is formed - a caldera. The depth of such a depression is at least one kilometer, and the diameter can reach 16 km.
Why do volcanoes erupt?
We figured out what a volcano is, but why does it erupt?
As you know, our planet does not consist of a single piece of rock. It has its own structure. On top is a thin, hard “shell” that scientists call the lithosphere. Its thickness is only 1% of the radius of the globe. In practice, this means from 80 to 20 kilometers, depending on whether it is land or the bottom of the oceans.
Beneath the lithosphere is a layer of mantle. Its temperature is so high that the mantle is constantly in a liquid, or rather viscous, state. At the center is the solid core of the earth.
As a result of the fact that lithospheric plates are in constant motion, magma chambers can arise. When they break out to the surface of the earth's crust, a volcanic eruption begins.
What is magma?
Here, it is probably necessary to explain what magma is and what chambers it can form.
Being in constant motion (albeit invisible to the naked human eye), lithospheric plates can collide or creep onto each other. Most often, slabs whose dimensions are larger “win” those whose thickness is smaller. Therefore, the latter are forced to plunge into the boiling mantle, the temperature of which can reach several thousand degrees. Naturally, at this temperature the plate begins to melt. This molten rock with gases and water vapor is called magma. Its structure is more fluid than the mantle, and also lighter.
How does a volcano erupt?
Thanks to these structural features of magma, it begins to slowly rise and accumulate in places called foci. Most often, such centers become places where the earth's crust breaks.
Gradually, magma occupies all the free space of the source and, for lack of any other way out, begins to rise through cracks in the earth’s crust. If magma finds a weak spot, it does not miss the opportunity to break out to the surface. In this case, thin sections of the earth's crust are broken through. This is how a volcano erupts.
Places of volcanic activity
So what places on the planet, given volcanic activity, can be considered the most dangerous? Where are the most dangerous volcanoes in the world located? Let's find out...
- Merapi (Indonesia). This is the largest volcano in Indonesia, and also the most active. It does not allow local residents to forget about itself, even for one day, constantly releasing smoke from its crater. At the same time, small eruptions occur every two years. But you don’t have to wait long for big ones either: they happen once every 7-8 years.
- If you want to know where volcanoes are, you should probably take a trip to Japan. This is truly a “paradise” of volcanic activity. Take, for example, Sakurajima. Since 1955, this volcano has constantly disturbed local residents. Its activity shows no sign of decreasing, and the last major eruption occurred not so long ago - in 2009. A hundred years ago, the volcano had its own island, but thanks to the lava that it erupted from itself, it was able to connect with the Osumi Peninsula.
- Aso. And again Japan. This country constantly suffers from volcanic activity, and the Aso volcano is proof of this. In 2011, an ash cloud appeared above it, the area of which was more than 100 kilometers. Since that time, scientists have constantly recorded tremors, which can indicate only one thing: the Aso volcano is ready for a new eruption.
- Etna. This is the largest volcano in Italy, which is interesting because it has not only a main crater, but also many small ones located along its slope. In addition, Etna is distinguished by enviable activity - small eruptions occur every two to three months. It must be said that the Sicilians have long been accustomed to such a neighborhood, and are not afraid to populate the slopes.
- Vesuvius. The legendary volcano is almost half the size of its Italian brother, but this does not prevent it from setting many of its own records. For example, Vesuvius is exactly the volcano that destroyed Pompeii. However, this is not the only city that has suffered from his activities. According to scientists, Vesuvius more than 80 times destroyed cities that were not lucky enough to be close to its slopes. The last major eruption occurred in 1944.
Which volcano on the planet can be called the highest?
Among the named volcanoes there are quite a lot of record holders. But which one can bear the title “The highest volcano on the planet”?
It is necessary to take into account: when we say “the highest,” we do not mean the height of the volcano above the surrounding area. We are talking about the absolute altitude above sea level.
Thus, scientists call the Chilean Ojos del Salado the highest active volcano in the world. For a long time he was classified as sleeping. This status of the Chilean allowed the Argentinean Llullaillaco to bear the title “The highest volcano in the world.” However, in 1993, Ojos del Salado produced an ash release. After that, it was carefully examined by scientists who managed to find fumaroles (steam and gas outlets) in its crater. Thus, the Chilean changed his status, and, without knowing it, brought relief to many schoolchildren and teachers, for whom pronouncing the name Llullaillaco is not always easy.
To be fair, Ojos del Salado does not have a high volcanic cone. It rises above the surface only 2000 meters. While the relative height of the Llullaillaco volcano is almost 2.5 kilometers. However, it is not for us to argue with scientists.
The whole truth about the Yellowstone volcano
You cannot boast that you know what a volcano is if you have never heard of Yellowstone, which is located in the USA. What do we know about him?
First of all, Yellowstone is not a tall volcano, but for some reason it is called a supervolcano. What's the matter here? And why was Yellowstone discovered only in the 60s of the last century, and even then with the help of satellites?
The fact is that the Yellowstone cone collapsed after its eruption, resulting in the formation of a caldera. Considering its gigantic size (150 km), it is no wonder that people could not see it from Earth. But the collapse of the crater does not mean that the volcano can be reclassified as dormant.
There is still a huge chamber of magma under the Yellowstone crater. According to scientists' calculations, its temperature exceeds 800 °C. Thanks to this, many thermal springs were formed in Yellowstone, and, in addition, jets of steam, hydrogen sulfide and carbon dioxide constantly come to the surface of the earth.
Not much is known about the eruptions of this volcano. Scientists believe that there were only three of them: 2.1 million, 1.27 million and 640 thousand years ago. Considering the frequency of eruptions, we can conclude that we may witness the following. It must be said that if this really happens, the Earth will face the next Ice Age.
What troubles do volcanoes bring?
Even if we do not take into account the fact that Yellowstone can suddenly wake up, the eruptions that other volcanoes in the world can prepare for us also cannot be called harmless. They cause enormous destruction, especially if the eruption happened suddenly and there was no time to warn or evacuate the population.
The danger is not only lava, which can destroy everything in its path and cause fires. Don’t forget about toxic gases that spread over vast areas. In addition, the eruption is accompanied by emissions of ash, which can cover vast areas.
What to do if the volcano “comes to life”?
So, if you find yourself at the wrong time and in the wrong place when a volcano suddenly wakes up, what should you do in such a situation?
First of all, you need to know that the speed of the lava is not that high, only 40 km/h, so it is quite possible to escape, or rather, drive away from it. This must be done in the shortest possible way, that is, perpendicular to its movement. If this is not possible for some reason, you need to look for shelter on a hill. It is also necessary to take into account the likelihood of a fire, therefore, if possible, it is necessary to clear the shelter of ash and hot debris.
In open areas, a body of water can save you, although much depends on its depth and the force with which the volcano erupts. Photos taken after the eruption show that people often find themselves defenseless before such a powerful force.
If you are one of the lucky ones and your house survived the eruption, be prepared to spend at least a week there.
And most importantly, do not trust those who say that “this volcano has been sleeping for thousands of years.” As practice shows, any volcano can wake up (photos of destruction confirm this), but there is not always someone to tell about it.
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 of the ancient Roman god of fire, 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, can 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, volcanoes are divided into linear and central, but this division is arbitrary, since most volcanoes are confined to linear tectonic faults (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 geological emergencies that can lead to natural disasters. The eruption process can last from several hours to many years. Among the various classifications, general types of eruptions are distinguished:
- 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 of a large amount of steam that occurs when hot magma and sea water come into contact.
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 the gases are dominated by water vapor formed when groundwater is heated, 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 a 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 of high pressure is in a solid state, and when, due to fracturing, the pressure drops, 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, the Japanese Islands, the Kuril Islands, Kamchatka, the northwestern part of the USA, Alaska, the Hawaiian Islands, the Aleutian Islands, Iceland, and the 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 during its eruption became the subject of a huge number of humorous programs, television news stories, reports and folk art discussing events in the world.
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A volcanic eruption is a phenomenon that clearly illustrates the power of nature and human helplessness. Volcanoes can be at the same time majestic, deadly, mysterious and at the same time very picturesque and even useful. Today we will analyze in detail the formation and structure of the volcano, and also get acquainted with many other interesting facts on this topic.
What is a volcano?
A volcano is a geological formation that arises at the site of a fracture in the earth’s crust and erupts a number of products: lava, ash, flammable gases, rock fragments. When our planet was just beginning to exist, it was almost completely covered with volcanoes. Now there are several areas on Earth in which the majority of volcanoes are concentrated. All of them are located along tectonically active areas and major faults.
Magma and plates
What does the flammable liquid that erupts from a volcano consist of? It is a mixture of molten rock, with clots of more refractory rocks and gas bubbles. To understand where lava comes from, you need to remember the structure of the earth's crust. Volcanoes should be considered as the last link of a large system.
So, the Earth consists of many different layers, which are grouped into three so-called mega-layers: core, mantle, crust. Humans live on the outer surface of the crust, its thickness can vary from 5 km under the oceans to 70 km under land. It seems that this is a very respectable thickness, but if you compare it with the dimensions of the Earth, the bark resembles the skin on an apple.
Beneath the outer crust is the thickest mega-layer - the mantle. It has a high temperature, but practically does not melt or spread, because the pressure inside the planet is very high. Sometimes the mantle does melt, forming magma that pushes its way through the Earth's crust. In 1960, scientists created a revolutionary theory that tectonic plates cover the Earth. According to this theory, the lithosphere, a rigid material consisting of the crust and the upper layer of the mantle, is divided into seven large and several smaller plates. They slowly drift along the surface of the mantle, “lubricated” by the asthenosphere - a soft layer. What happens at the junction of the plates is the main reason for the release of magma. Where the plates meet, there are several options for how they interact.
Separating the plates from each other
At the point where the two plates move apart, a ridge forms. This can happen both on land and under water. The resulting gap is filled with asthenosphere deposits. Since the pressure here is low, a solid surface is formed at the same level. As the rising magma cools, it solidifies and creates a crust.
One slab goes under another
If, upon impact of the plates, one of them went under the other and plunged into the mantle, a huge depression is formed in this place. As a rule, this can be found at the bottom of the ocean. When the hard edge of the plate is pushed into the mantle, it heats up and melts.
The bark is crushed
This happens when, when tectonic plates strike, none of them finds a place under the other. As a result of this interaction of plates, mountains are formed. This process does not involve volcanic activity. Over time, a mountain range that was formed at the junction of plates creeping towards each other can grow, unnoticed by humans.
Formation of volcanoes
Most volcanoes form in places where one tectonic plate has subducted under another. When the solid edge melts in the magma, it increases in volume. Therefore, the molten rock tends upward with enormous force. If the pressure reaches a sufficient level, or the hot mixture finds a crack in the bark, it is released outward. In this case, the flowing magma (or rather, lava) forms a cone-shaped structure of volcanoes. What kind of structure a volcano has and how intensely it erupts depends on the composition of the magma and other factors.
Sometimes magma comes out right in the middle of the plate. Excessive activity of magma is caused by its overheating. The mantle material gradually melts through the well, and creates a hot spot under a certain area of the earth's surface. From time to time, magma breaks through the crust and an eruption occurs. The hot spot itself is motionless, which cannot be said about tectonic plates. Therefore, over millennia, a “row of dead volcanoes” forms in such places. In a similar way, Hawaiian volcanoes were created, the age of which, according to researchers, reaches 70 million years. Now let's look at the structure of the volcano. The photo will help us with this.
What is a volcano made of?
As you can see in the photo above, the structure of the volcano is very simple. The main components of a volcano are: hearth, vent, and crater. A chamber is a place where excess magma is formed. Hot magma rises up the vent. Thus, the vent is a channel connecting the hearth and the surface of the earth. It is formed by magma solidifying along the way and narrows as it approaches the Earth's surface. And finally, a crater is a bowl-shaped depression on the surface of a volcano. The diameter of the crater can reach several kilometers. Thus, the internal structure of the volcano is somewhat more complex than the external one, but there is nothing special about it.
Eruption force
In some volcanoes, magma oozes so slowly that you can safely walk on them. But there are also volcanoes, the eruption of which in a matter of minutes destroys everything in its path, within a radius of several kilometers. The severity of the eruption is determined by the composition of the magma and the internal gas pressure. A very impressive amount of gas dissolves in magma. When the pressure of the rocks begins to exceed the vapor pressure of the gas, it expands and forms bubbles called vesicles. They try to free themselves and blow up the rock. After the eruption, some of the bubbles solidify in the magma, resulting in the formation of porous rock from which pumice is made.
The nature of the eruption also depends on the viscosity of the magma. As you know, viscosity is the ability to resist flow. It is the opposite of fluidity. If the magma is highly viscous, the gas bubbles will have a hard time escaping and will push more rock upward, resulting in a violent eruption. When the magma's viscosity is low, gas is released quickly, so lava is not ejected as forcefully. Typically, the viscosity of magma depends on its silicon content. The gas content in magma also plays an important role. The larger it is, the stronger the eruption will be. The amount of gas in magma depends on the rocks that make up it. The structure of volcanoes does not affect the destructive power of the eruption.
The majority of eruptions occur in stages. Each stage has its own degree of destruction. If the viscosity of the magma and the content of gases in it are low, then the lava will slowly flow along the ground with a minimum number of explosions. Lava flows can harm local nature and infrastructure, but due to their low speed, they are not dangerous to people. Otherwise, the volcano intensively releases magma into the air. An eruption column typically consists of flammable gas, solid volcanic material and ash. At the same time, the lava moves rapidly, destroying everything in its path. And a cloud forms above the volcano, the diameter of which can reach hundreds of kilometers. These are the consequences that volcanoes can cause.
Types, structure of calderas and bench domes
Hearing about a volcanic eruption, a person immediately imagines a conical mountain with orange lava flowing from the top. This is a classic diagram of the structure of a volcano. But in fact, such a concept as a volcano describes a much wider range of geological phenomena. Therefore, in principle, any place on Earth where certain rocks are ejected from the interior of the planet to the outside can be called a volcano.
The structure of the volcano, described above, is the most common, but not the only one. There are also calderas and bench domes.
A caldera differs from a crater in its enormous size (the diameter can reach several tens of kilometers). Volcanic calderas arise for two reasons: explosive volcanic eruptions, the collapse of rocks into a cavity freed from magma.
Collapse calderas occur in places where there has been a massive eruption of lava, resulting in the complete release of the magma chamber. The shell formed above this void collapses over time, and a huge crater appears, within which the birth of a new volcano is quite likely. One of the most famous collapse calderas is Crater Caldera in Oregon. It was formed 7700 years ago. Its width is about 8 km. Over time, the caldera filled with melt and rain water, forming a picturesque lake.
Explosion calderas are formed in a slightly different way. A large magma chamber rises to the surface; it cannot seep out due to the dense earth's crust. The magma is compressed, and when the gases expand due to a drop in pressure in the “reservoir,” a huge explosion occurs, which entails the formation of a large cavity in the Earth.
As for shop domes, they form when the pressure is not enough to break the ground rocks. This creates a bulge at the top of the volcano, which can grow larger over time. This is how interesting the structure of a volcano can be. Pictures of some calderas look more like an oasis than a place where an eruption once occurred - a destructive process for all living things.
How many volcanoes are there on Earth?
We already know the structure of volcanoes, now let’s talk about the situation with volcanoes today. There are more than 500 active volcanoes on our planet. Somewhere the same number are considered sleeping. A large number of volcanoes are considered dead. This division is considered very subjective. The criterion for determining the activity of a volcano is the date of the last eruption. It is generally accepted that if the last eruption occurred during the historical period (the time when people keep records of events), then the volcano is active. If this happened outside the historical period, but earlier than 10,000 years ago, then the volcano is considered dormant. And finally, those volcanoes that have not erupted for the last 10,000 years are called extinct.
Of the 500 active volcanoes, 10 erupt daily. Typically these eruptions are not large enough to endanger human life. However, large eruptions occasionally occur. Over the past two centuries there have been 19 of them. A little more than 1000 people died in them.
Benefits of volcanoes
It’s hard to believe, but such a terrible phenomenon as a volcano can be useful. Volcanic products, due to their unique properties, find application in many areas of human activity.
The most ancient use of volcanic rock is construction. The famous French Cathedral of Clermont-Ferrand is built entirely from dark lava. Basalt, which is part of the igneous material, is often used in paving roads. Small lava particles are used in concrete production and for water filtration. Pumice serves as an excellent sound insulator. Its particles are also included in the composition of stationery erasers and some types of toothpaste.
Volcanoes erupt many metals valuable for industry: copper, iron, zinc. Sulfur collected from volcanic products is used to make matches, dyes and fertilizers. Hot water, obtained naturally or artificially from geysers, produces electricity at special geothermal stations. Diamonds, gold, opal, amethyst and topaz are often found in volcanoes.
Passing through volcanic rock, the water is saturated with sulfur, carbon dioxide and silica, which help with asthma and respiratory diseases. At thermal stations, patients not only drink healing water, but also swim in separate springs, take mud baths and undergo additional treatment.
Conclusion
Today we discussed such a fascinating issue as the formation and structure of volcanoes. Summarizing the above, we can say that volcanoes arise due to the movement of tectonic plates, and represent emissions of magma, which, in turn, is the molten mantle. Thus, when considering volcanoes, it would be useful to remember the structure of the Earth. Volcanoes consist of a chamber, a vent and a crater. They can be both destructive and beneficial for various areas of industry.
