cone-shaped volcanoes. Reasons for the activity of volcanoes. Types, structure of calderas and shop domes

On August 24, 79, people looked in horror at their patron and could not understand: why did they anger the gods so much. How did it happen that their protector suddenly began to spew fire that spread across the ground and destroyed everything in its path? The inhabitants of Pompeii already knew: unexpectedly for everyone, a volcano woke up. What is it, what are volcanoes and why do they suddenly wake up, we will consider 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 spewing pyroclastic flows (a mixture of ash, gas and stones), volcanic gases, and also lava. It is in zones of volcanic activity that opportunities for the use of geothermal energy open up.

Types of volcanoes

Scientists have adopted a classification of volcanoes into active, dormant and extinct.

Volcanoes that erupt during a historical period of time are called active volcanoes. It is thanks to them that one can understand what a volcano is and the mechanisms that make it work, because direct observation of the process provides much more information than the most thorough excavations.
Sleeping volcanoes are called, which are currently not active, 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 equal to zero.

What shape are volcanoes?

If you ask a schoolboy what shape a volcano has, he will undoubtedly say that it looks like a mountain. And he will be right. The volcano really has the shape of a cone, which 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 crater always ends in a crater. It is into it that all materials are thrown during the eruption. An interesting fact is that the mouth is open only during the active period of the volcano. The rest of the time it is closed, until the next manifestation of activity.

The time during which a volcanic cone formed is individual. Basically, it depends on how much material the volcano throws out during its eruption. Some take 10,000 years to do so, while others can form it in a single eruption.

Sometimes the opposite happens as well. During an eruption, the volcanic cone collapses, and a large depression, the caldera, forms in its place. The depth of such a depression is at least one kilometer, and the diameter can reach 16 km.

Why do volcanoes erupt?

What is a volcano, we figured it out, but why does it erupt?

As you know, our planet does not consist of whole piece stone. It has its own structure. Above - a thin solid "shell", which scientists call the lithosphere. Its thickness is only 1% of the radius of the globe. In practice, this means between 80 and 20 kilometers, depending on whether it is land or the bottom of the oceans.

Beneath the lithosphere is the mantle layer. Its temperature is so high that the mantle is constantly in a liquid, or rather viscous, state. In the center is the solid core of the earth.

As a result of the fact that the 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, perhaps, it is necessary to explain what magma is and what chambers it can form.

Being in constant motion (albeit invisible to the naked eye of a person), lithospheric plates can collide or crawl into each other. Most often, the plates, the dimensions of which are larger, "win" those whose thickness is less. Therefore, the latter are forced to sink 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. In its structure, it is more liquid than the mantle, and also lighter.

How does a volcano erupt?

Due to the named features of the magma structure, it begins to slowly rise and accumulate in places called foci. Most often, such foci are places of a break in the earth's crust.

Gradually, magma occupies all the free space of the hearth and, in the absence of another way out, begins to rise along cracks in the earth's crust. If magma finds a weak point, it does not miss the opportunity to break out to the surface. At the same time, thin sections of the earth's crust break 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 peace? Let's figure it out...

Merapi (Indonesia). It is the largest volcano in Indonesia and also the most active. He does not let the locals forget about him even for one day, constantly releasing smoke from his crater. At the same time, small eruptions occur every two years. But large ones do not have to wait long: they happen every 7-8 years.
If you want to know where the 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 been constantly disturbing local residents. Its activity does not even think of decreasing, and the last major eruption occurred not so long ago - in 2009. A hundred years ago, the volcano had own island, however, thanks to the lava that he spewed from himself, he managed to connect with the Osumi Peninsula.
Aso. And Japan again. This country is constantly suffering from volcanic activity, and the Aso volcano is proof of this. In 2011, an ash cloud appeared over it, the area of \u200b\u200bwhich was more than 100 kilometers. Since that time, scientists have been constantly recording tremors, which can only indicate one thing: the Aso volcano is ready for a new eruption.
Etna. This is the most big volcano Italy, which is interesting in that it has not only the 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 him from setting many of his own records. Vesuvius, for example, is the volcano that destroyed Pompeii. However, this is not the only city that has suffered from his activity. According to scientists, Vesuvius destroyed cities that were not lucky enough to be close to its slopes more than 80 times. The last major eruption happened in 1944.

Which volcano on the planet can be called the highest?

There are quite a few record holders among these volcanoes. But what can bear the title "The highest volcano on the planet"?

Keep in mind: when we say "highest", we do not mean the height of the volcano above the surrounding area. This is the absolute height above sea level.

So, scientists call the Chilean Ojos del Salado the highest active volcano in the world. For a long time he was referred to as sleeping. This status of the Chilean allowed the Argentinean Lullaillaco to bear the title of "The Highest Volcano in the World". However, in 1993, Ojos del Salado produced an ash ejection. After that, he was carefully examined by scientists who managed to find fumaroles (outlets of steam and gas) in his mouth. Thus, the Chilean changed his status, and, without knowing it, brought relief to many schoolchildren and teachers, for whom it is not always easy to pronounce the name Llullaillaco.

For the sake of justice, it must be said that Ojos del Salado does not have a high volcanic cone. It rises above the surface only 2000 meters. While relative height Volcano Lullaillaco is almost 2.5 kilometers away. However, it is not for us to argue with scientists.

The Truth About 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 high volcano, but for some reason it is called a supervolcano. What is the matter here? And why was it possible to discover Yellowstone only in the 60s of the last century, and even then with the help of satellites?

The fact is that the cone of Yellowstone collapsed after its eruption, resulting in the formation of a caldera. Given 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 magma chamber under the Yellowstone crater. According to the calculations of scientists, its temperature exceeds 800 ° C. Thanks to this, many thermal springs, and, in addition, jets of steam, hydrogen sulfide and carbon dioxide constantly come out 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. Given the frequency of eruptions, we can conclude that we may witness the following. I must say that if this really happens, the Earth will face the next Ice Age.

What troubles do volcanoes bring?

Even if you 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 cannot be called harmless either. They lead to huge 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. Do not forget about the poisonous gases that spread over vast areas. In addition, the eruption is accompanied by ash emissions, which can cover vast areas.

What to do if the volcano "comes to life"?

So, if you were at the wrong time and in the wrong place when the volcano suddenly woke up, what to do in such a situation?

First of all, you need to know that the speed of the lava is not that great, only 40 km / h, so it is quite possible to run away, or rather, leave it. This must be done in the shortest way, that is, perpendicular to its movement. If this is not possible for some reason, you need to seek shelter on a hill. It is necessary to take into account the likelihood of a fire, therefore, if possible, it is necessary to clean the shelter from ash and incandescent 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. The photos that were taken after the eruption show that a person is often defenseless in front of such a powerful force.

If you were among 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 the destruction confirm this), but there is not always someone to tell about it.

Classification of volcanoes and eruptions

The word "volcano" comes from the name of the island of Vulcane (named after the ancient Roman god of fire) in the Mediterranean Sea, formed from solidified magma. The science that studies volcanoes is called volcanology.

Volcanoes are geological formations above cracks in the earth's crust, spewing lava, volcanic gases, water vapor, ash, loose rocks, stones (so-called volcanic bombs) and pyroclastic flows to the surface. Lava makes up a relatively small part of the total emissions. Most of Volcanoes is a mountain, inside of which there is a break in the surface. As you know, the outer core of the Earth consists of a liquid mass of extremely high temperatures - molten basalts and metals.

Among volcanologists, there is a special classification of volcanoes: according to their shape, degree of activity, location, etc. Depending on the degree of volcanic activity, volcanoes are divided into active, dormant, and extinct. A volcano that erupted in a historical period of time or in the Holocene epoch of the Anthropogenic period of the Cenozoic era is considered to be active. The concept of active is rather inaccurate, since volcanoes that have fumaroles (hissing cracks spewing gas) are classified by some scientists as active, and some as extinct. Dormant volcanoes are considered inactive, on which eruptions are possible, and extinct - on which they are unlikely.

The period of volcano activity can last from several months to several million years. Many volcanoes showed volcanic activity several tens of thousands of years ago, but are not currently considered active. The total number of active volcanoes on Earth is 1343, many of which are underwater, and their activity leads to the formation of islands from solidified lava. So, in 1963, as a result of the eruption of an underwater volcano, the island of Surtsey appeared off the south of Iceland. In February 1971 in pacific ocean near the island of New Hebrides, the underwater volcano Karua erupted. During the explosion, a cloud of smoke and ash rose to a height of 1 km. Several times a minute, large fragments of rocks flew out of the water. Approximately a day after the start of the eruption, an island of ash appeared above the surface of the ocean, reaching a height of 1 m above the tidal level, almost 200 m long and about 70 m wide. formed island was littered with rubble. Underwater volcano Karua has erupted for the third time in the last 150 years and formed an island for the third time. But the ashes are quickly washed away by water, and therefore the island exists for no more than six months.

The usual location of volcanoes is a fault or connection of lithospheric plates, since there is a constant movement of hot rocks, which are periodically ejected to the surface. The main areas of volcanic activity are as follows: South and Central America, Java, Melanesia, Japanese and Kuril Islands, Kamchatka, Northwestern USA, Alaska, Hawaiian and Aleutian Islands, Iceland, Atlantic Ocean. Most active volcanoes is located in Indonesia, where 77 out of 200 fire-breathing mountains have erupted in historically observable times. The volcano itself, or rather, the mountain, in the form of which almost everyone imagines it, is formed due to layers of magma and lava, which, cooling in the air, freeze.

Volcanic activity is a clear manifestation of the ongoing tectonic changes of our planet. The theory of "continental drift" suggests that the earth's crust consists of separate blocks - lithospheric plates, which slowly move in different directions. Between the earth's crust and mantle there is a fairly thin (up to 10 km) layer called the asthenosphere. In it, the rocks are in a partially molten state, so the asthenosphere serves as a "lubricant" along which the lithospheric plates move. When the plates move, they collide (subduction) and grow (spreading). As a result of plate movement in subduction and spreading zones, earthquakes occur and volcanic activity increases.

Volcanoes form over holes and fissures in the earth's crust and often occur at the point where two tectonic plates both on land and at sea. During an eruption, magma is pushed towards the earth's surface as a result of the pushing of a tectonic plate into the so-called magma chamber. The increase in pressure pushes magma to the surface.

By origin, volcanoes are divided into linear and central. Linear volcanoes, or fissure-type volcanoes, have extended supply channels associated with a deep split in the crust. As a rule, basaltic liquid magma pours out of such cracks, which, spreading to the sides, forms large lava covers. Gently sloping spatter ridges, wide flat cones, and lava fields appear along the fissures. If the magma has a more acidic composition, linear extrusive rolls and massifs are formed. When explosive eruptions occur, explosive ditches tens of kilometers long can occur.

volcano shapes central type depend on the composition and viscosity of the magma. Hot and easily mobile basaltic magmas create vast and flat shield volcanoes (for example, Mauna Loa, Hawaiian Islands). The most famous type of volcanoes is conical. At the same time, liquid burning magma flows out of the vent and, solidifying, forms a conical shape with a crater at the top. At the next eruption, a new layer of ash and lava lies on top of the old one, and the volcano grows in height, resembling a smoking mountain. If a volcano periodically erupts lava or pyroclastic material, a cone-shaped layered structure, or stratovolcano, arises. 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 slag, tuffs and similar formations, or they can be mixed - stratovolcanoes.

There are monogenic and polygenic volcanoes. The first arose as a result of a single eruption, the second - after multiple eruptions. Viscous, acidic in composition, low-temperature magma, squeezing out from the vent, forms extrusive domes (Mont Pele needle, 1902).

Negative landforms associated with volcanoes of the central type are represented by calderas - large rounded pits, several kilometers in diameter. In addition to calderas, there are also large negative landforms associated with sagging 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. Volcano-tectonic depressions are very widespread and often accompany the formation of thick strata of ignimbrites - acidic volcanic rocks of different genesis. They are lava or formed by baked or welded tuffs. They are characterized by lenticular segregations of volcanic glass, pumice, lava, called fiamme, and a tuff or tuff-like structure of the groundmass. As a rule, large volumes of ignimbrites are associated with shallow magma chambers formed due to melting and replacement of host rocks.

Volcanic eruptions are geological emergencies that can lead to natural disasters. More recently, the “awakening of the fiery dragon” in the bowels of the planet seemed to people a manifestation of the power of supernatural forces and the wrath of the gods. The eruption process can last from several hours to many years. Among the various classifications, common types are distinguished:

Hawaiian type - ejections of liquid basaltic lava, lava lakes are often formed. Lava flows of small thickness spread over tens of kilometers;

Strombolian type - an eruption of a more viscous basic lava, which is ejected by explosions of different strength from the vent, forming relatively short and more powerful lava flows;

Plinian type - powerful, often sudden explosions, accompanied by emissions of a huge amount of tephra, forming pumice and ash flows. Plinian eruptions are dangerous because they occur suddenly, often without foreshadowing events;

Peleian type - characterized by the formation of grandiose hot avalanches or scorching clouds, as well as the growth of extrusive domes of extremely viscous lava;

Gas (phreatic) type - emissions into the air of fragments of solid, ancient rocks, due either to magmatic gases, or associated with overheated groundwater;

Subglacial type - eruptions occurring under ice or glacier can cause dangerous floods, lahars and globular lava;

Hydroexplosive type - eruptions occurring in shallow 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;

Ash flow eruptions, widespread in the recent geological past, but not observed by man. To some extent, these eruptions should resemble scorching clouds or hot avalanches.

“A mountain spewing hellfire, bringing death and devastation. Volcano-killer, volcano-destroyer…” - this is how awakened volcanoes are usually called. However, volcanologists believe that "fire dragons" create more than they destroy. The volcano, at least at the time of its inception, is not a mountain, but rather a hole. A hole in the earth's crust through which red-hot magma erupts. Solidifying, it, together with other products of the eruption - ash, rock fragments - forms cone-shaped mountains. Thus, volcanoes build themselves, and also play the role of a supplier of materials from which the earth's crust was created and continues to be created. According to estimates, the total number of active volcanoes on Earth erupts annually from 3 to 6 billion tons of matter - about a thousand pyramids of Cheops. During eruptions, the soil is enriched with various chemical elements: potassium, sodium, magnesium, iron, aluminum. It is also enriched and strengthened by the ash and sand that have fallen on it. Of course, hundreds and thousands of years are needed for all these substances to be assimilated by the soil under the influence of rains, winds, and microorganisms, but the result is remarkable.

One of the unsolved problems of manifestation of volcanic activity is the determination of the heat source necessary for the 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 United States in the Columbia River basin (Washington and Oregon), the volume of basalts is more than 820 thousand cubic meters. km; the same large strata basalts are found in Argentina (Patagonia), India (Decan Plateau) and South Africa (Great Karoo Rise). There are currently three hypotheses. Some geologists believe that the melting is due to 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 is in a solid state under conditions of high pressures, and when the pressure drops due to cracking, it melts, and liquid lava flows out of the cracks.

After eruptions, when the activity of the volcano either ceases forever, or it “dozes” 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 environs. These include fumaroles, thermal baths and geysers. In fumaroles - places where hot volcanic gases come out - of the Katiai volcano in Alaska (USA) in 1912, a record high temperature of 6450 ° C was recorded.

Scientists around the world are closely monitoring volcanoes, noting even the smallest manifestations of the activity of the “fire dragon”. This is necessary in order to prepare for the eruption in a timely manner, eliminating all sorts of surprises that lead to loss of life or other emergencies. However, during the period of “calmness” of the volcano, it can be quite freely explored. Climbers and researchers often descend inside the crater to study this phenomenon in more detail.

The greatest benefit from the activity of volcanoes located on the territory of one country, specialists from Iceland were able to extract. The heat of the fire-breathing mountains is used here to heat greenhouses and even living quarters. Volcanic ash has also found worthy use - it is a valuable fertilizer for increasing the yield of vegetables and southern fruits.

From the book Professional Crime author Gurov Alexander Ivanovich

Classification of criminals After the publication of the works of C. Lombroso, which were essentially the beginning of the study of the personality of the criminal, in a number of countries studies of the psychological properties of the offender began, in which scientists tried to find the core reason

From the book Ideas for a million, if you're lucky - for two author Bocharsky Konstantin

Classification of robbers Among the criminals who specialize in the open theft of property (robbery, robbery), there are three main categories: Money at the facilities of the financial system; 2) stealing property of citizens in their homes; 3)

From the book Fundamentals of Meta-Satanism. Part I. The Forty Rules of the Meta-Satanist author Morgen Fritz Moiseevich

Stage 1. Classification of problems The task of the stage is to understand: what kind of problems are there in general? First, you can start from the complexity of the problem. For example, a simple solution - pulled the rope on the balcony; a little more complicated - connected a washing machine; difficult - made a warm floor on

From the book Gennady Shichko and his method the author Drozdov Ivan

Classification of people: from the homeless to the president Manipulating the site took me less time than I expected, and I was left with an unspent supply of energy. This

From the book Fundamentals of Scientific Anti-Semitism author Balandin Sergey

From the book Destroyers of the Brain (On Russian Pseudoscience). author Arin Oleg

Classification of the goyim Above, we considered Jewry as a people, as a nation, as a religious denomination, etc., but goyism cannot be considered in any of these categories, because the goyim have neither a special "goy culture", nor any kind of common "goy religion", and therefore,

From the book The Bible of the medical representative. Territory management author Volchenkov Alexander Evgenievich

Classification of scientists in Russia And now let's look at the Russian reality from the point of view of the words that define "scientists". To a large extent, what has been said below also applies to Western science. Let's start with the lowest rank - Candidate of Sciences. This is the first degree

From the book NOT our Russia [How to return Russia?] author Mukhin Yury Ignatievich

Classification of the tasks of a medical representative In the work of a medical representative, there are a variety of tasks. On the one hand, there are tasks of the salon, there are tasks of the company, and there are personal tasks of the medical representative. All these tasks require time and effort to solve them, and sometimes it is very difficult

From the book 1000 wonders from around the world author Gurnakova Elena Nikolaevna

Classification Marx's error in classification needs to be corrected. Mankind should first of all be divided into three classes: according to the goal that these individuals pursue in life. And only then, if necessary, classify according to other criteria, for example, according to

From the author's book

Facts of Volcanic Eruptions Volcanologists believe that every two years the Earth gives birth to an average of three new volcanoes. And every third of them - not on land, but under water. The highest volcano is the snow-covered peak of the dormant volcano Aconcagua, located high in the Andes on

The most typical representation of a volcano is a mountain in the form of a cone with shimmering lava and poisonous gases erupting from a crater at the top. But this is only one of many types of volcano, and the characteristics of other volcanoes can be much more complex.

The structure and behavior of a volcano depends on many factors. Many volcano peaks are formed by lava cones rather than craters. Thus, volcanic materials (lava, or magma that has escaped from the depths, and ash) and gases (mainly steam and magma gases) can escape anywhere on the surface. .

Types of volcanoes

1. Vent crack

This is a view of a volcano with a flat fault at the top in the form of a line, through which lava erupts.

2. Shield Volcano

This type of volcano is named because of its wide shield-like profile, formed by the eruption of inviscid lava, which can spread over long distances from the fissure, but this does not generally lead to catastrophic consequences. Non-viscous lava does not contain much silicon oxide, so shield volcanoes are found mainly in the ocean and not on continents.

3. Cryptovolcanoes

Cryptovolcanoes form when viscous lava works its way up and causes a lava cone to form. The volcanic eruption on Saint Helena in 1980 was an example of a cryptovolcano. The lava was under tremendous pressure and formed a lava dome at the top of the mountain, which was unstable and therefore moved down the northern slope.

4. Cinder cone

Volcanic or cinder cones are formed as a result of the eruption of small pieces of cinder and pyroclasts (both formations look like small cylinders, which gave the name to the volcano), forming around the hydrothermal corridor. The eruption takes place for quite a short time and forms a cone-shaped hill 30-40 meters high. Most cinder cones erupt only once. They may form as end hydrothermal corridors on big volcanoes or form on their own. Paricutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico, about 60 cinder cones were formed in the Caja del Río volcanic field.

5. Stratovolcanoes

Stratovolcanoes, or as they are also called composite volcanoes, are characterized as high conical structures consisting of layers of lava and other products of a volcanic eruption, the so-called layers - strata - which gave the name this species volcanoes. Stratovolcanoes are formed from slag, ash and lava. As a result of volcanic activity, slag and ash settle on the top of the mountain in layers (ash over slag), and lava flows down the ash layer, where it cools and hardens, then the process repeats. Typical examples of stratovolcanoes are Mount Fiji in Japan, Mawon Volcano in the Philippines, and Mount Vesuvius and Stromboli in Italy.

6. Lava dome

Lava domes are formed during the eruption of inviscid lava. Sometimes they form in the crater of a volcano that erupted some time ago, as on Mount Saint Helena, but they can also form independently of previous eruptions, as in the case of Lassen Peak. Like stratovolcanoes, they are accompanied by violent explosive eruptions, but their lava generally does not extend far from the hydrothermal corridor.

7. Supervolcanoes

A supervolcano is usually characterized by a caldera spread over a vast area, which can potentially pose a huge danger, sometimes even on a continental scale. Eruptions of such volcanoes can be the cause of severe global cooling, lasting several years in a row, as a result of huge masses of sulfur and ash entering the atmosphere. A supervolcano is the most dangerous type of volcano. Examples include the Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico, Lake Taupo in New Zealand, Lake Toba in Sumatra and Ngorongoro Crater in Tanzania, Krakatoa near Java and Sumatra. A difficult task for volcanologists is to determine the boundaries of the huge calderas of supervolcanoes, the territory of which has increased over the centuries. Huge regions volcanic origin are also characterized as supervolcanoes if they are covered by huge layers of erupted basaltic lava, but they are considered incapable of volcanic activity.

8 Underwater Volcanoes

It is well known that underwater volcanoes are located on the ocean floor. Some of them are active great depths, can be determined visually from the eruption of steam and rocks above sea level. However, many are at great depths, where huge masses of water prevent steam and gases from erupting to the surface. However, it is possible to determine the activity of such volcanoes using underwater vehicles and the discoloration of the water on the surface, which occurs due to the chemical processes of combining water with erupting gases.

Pumice can also be the product of an eruption. However, even a large eruption does not disturb the surface of the ocean in any way due to the rapid cooling of the eruption products in water, in relation to gases in the atmosphere, water also reduces the rate of spread of volcanic materials. Submarine volcanoes often form columns above a hydrothermal corridor. Such columns can become so high that they can appear above the surface of the oceans and form new islands. Lava under water forms in the form of balls, which is typical characteristic underwater volcanoes. Hydrothermal corridors are often adjacent to such volcanoes and even support a separate ecosystem built on walls of molten minerals.

9. mud volcanoes

Mud volcanoes are small volcanoes through which not magma comes to the surface, but liquid mud and gases from the earth's crust. Mud volcanoes are much smaller than ordinary volcanoes. The mud usually comes to the surface cold, but the gases erupted by mud volcanoes often contain methane and can ignite during the eruption, creating a picture similar to a miniature eruption of an ordinary volcano. The largest mud volcanic structure is 10 kilometers in diameter and about 700 meters high.

10. Subglacial volcanoes

Subglacial volcanoes form under ice caps. Erupted lava flows over large lava boulders and basaltic tuff that were formed from previous volcanic eruptions. During such eruptions, the ice caps melt and the lava at the top goes down, leveling the surface and forming a flat top. Such a volcano is also called flat-topped or thuy. Typical examples are the mountains of Iceland, as well as British Columbia. The flat tops of volcanoes were first explored there, in the area of the Tuya River and the Tuya Range in northern British Columbia. Tuya Butte - the natural landscape was first explored by volcanologists and gave its name to this group of volcanoes. Also recently formed national park Tuya Mountains in the northern area of Lake Tuya and south of the Jennings River near Yukon Territory to protect the rare landscape of Arena volcanoes. Currently, such volcanoes are not found, or one might say they do not exist.

11. Fissure Volcanoes

They are manifested in the outpouring of lava onto the earth's surface along large cracks or splits. In certain periods of time, mainly at the prehistoric stage, this type of volcanism reached a rather large scale, as a result of which a huge amount of volcanic material, lava, was brought to the surface of the Earth. Powerful fields are known in India on the Deccan Plateau, where they covered an area of 5.105 km2 with an average thickness of 1 to 3 km. Also known in the northwestern United States, in Siberia. At that time, basaltic rocks of fissure eruptions were depleted in silica (about 50%) and enriched in ferrous iron (8-12%). The lavas are mobile, liquid, and therefore can be traced for tens of kilometers from the place of their outpouring. The power of individual streams was 5-15m. In the United States, as well as in India, many kilometers of strata accumulated, this happened gradually, layer by layer, over many years. Such flat lava formations with a characteristic stepped topography are called plateau basalts or traps. Currently, fissure volcanism is widespread in Iceland (Laki volcano), Kamchatka (Tolbachinsky volcano), and on one of the islands of New Zealand. The largest lava eruption on the island of Iceland along the giant Laki fissure, 30 km long, occurred in 1783, when lava entered the day surface for two months.

A volcanic eruption is a phenomenon that clearly illustrates the power of nature and human helplessness. Volcanoes can be both 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, as well as get acquainted with many other fun facts on this topic.

What is a volcano?

Volcano - a geological formation that occurs at the site of a fault in the earth's crust and erupts a number of products: lava, ash, combustible gases, rock fragments. When our planet was just beginning to exist, it was almost completely covered with volcanoes. Now on Earth there are several areas in which the main number of volcanoes is concentrated. All of them are located along tectonically active areas and large faults.

Magma and plates

What is the very combustible liquid that erupts from a volcano? 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 in 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 solid thickness, but if you compare it with the dimensions of the Earth, the crust resembles the skin on an apple.

Under the outer crust is the thickest mega-layer - the mantle. It has a high temperature, but practically does not melt and does not 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 on the surface of the mantle, "lubricated" by the asthenosphere - a soft layer. What happens at the junction of the plates is the main cause of the ejection of magma. In the place where the plates meet, there are several options for their interaction.

Separation of plates from each other

In the place where the two plates parted to the sides, a ridge is formed. This can happen both on land and underwater. The resulting gap is filled with deposits of the asthenosphere. Since the pressure here is low, a solid surface is formed at the same level. Cooling, the risen magma solidifies and creates a crust.

One plate goes under another

If, upon impact of the plates, one of them went under the other and plunged into the mantle, a huge depression forms at this place. As a rule, this can be found at the bottom of the ocean. When the hard edge of the slab is pushed into the mantle, it heats up and melts.

The bark is wrinkled

This happens if, when impacting tectonic plates, none of them finds a place for itself under the other. As a result of this interaction of plates, mountains are formed. Volcanic activity such a process does not. With time, mountain range, which was formed at the junction of plates crawling to each other, can grow, imperceptibly to humans.

Formation of volcanoes

Most volcanoes form in places where one tectonic plate has sunk under another. When a hard edge melts into magma, it expands in volume. Therefore, the molten rock with great force tends to the top. If the pressure reaches a sufficient level, or the hot mixture finds a crack in the bark, it is ejected to the outside. At the same time, the outflowing magma (or rather, already lava) forms a cone-shaped structure of volcanoes. Which volcano has a structure 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 due to its overheating. The substance of the mantle gradually melts 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. By itself, the hot spot is motionless, which cannot be said about tectonic plates. Therefore, over the millennia, in such places a "line of dead volcanoes" is formed. Likewise, they were created Hawaiian volcanoes, whose age, 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 hearth is a place where an excess of magma is formed. Up the red-hot magma rises along the vent. Thus, the vent is a channel that unites the hearth and the surface of the earth. It is formed by magma solidifying along the way and narrows as it approaches the surface of the Earth. 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 complicated than the external one, but there is nothing special about it.

The force of the eruption

In some volcanoes, magma oozes so slowly that you can safely walk on them. But there are also such 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 pressure of the gases. 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, which are called vesicles. They try to free themselves outside, and blow up the rock. After the eruption, some of the bubbles solidify in 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, it will be difficult for the gas bubbles to escape and will push more rock up, resulting in a violent eruption. When the viscosity of the magma is low, gas is quickly released from it, so the lava is not ejected with such force. Usually the viscosity of magma depends on the content of silicon in it. The gas content of the 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 included in its composition. 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. Shop streams can harm local nature and infrastructure, but due to the low speed of movement, they are not dangerous to people. Otherwise, the volcano intensively ejects magma into the air. The eruption column usually consists of combustible gas, solid volcanic material and ash. At the same time, lava moves rapidly, destroying everything in its path. A cloud forms over the volcano, the diameter of which can reach hundreds of kilometers. These are the consequences that volcanoes can cause.

Types, structure of calderas and shop domes

Hearing about a volcanic eruption, a person immediately imagines a conical mountain, from the top of which orange lava flows. 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 the Earth can be called a volcano, where certain rocks are ejected from the inner part of the planet to the outside.

The structure of the volcano, the description of which was given above, is the most common, but not the only one. There are also calderas and shop domes.

The caldera differs from the 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 a massive lava eruption occurred, as a result of which the magma chamber was completely freed. The shell formed over this void collapses over time, and a huge crater appears, inside which the birth of a new volcano is quite likely. One of the more famous collapse calderas is the 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.

Explosive calderas form in a slightly different way. A large magma chamber rises to the surface, it cannot seep due to the dense earth's crust. The magma contracts, and when, due to the pressure drop in the “reservoir”, the gases expand, a huge explosion occurs, which entails the formation of a large cavity in the Earth.

As for shop domes, they are formed if there is not enough pressure to break the rocks of the earth. The result is a bulge at the top of the volcano, which can grow over time. This is how interesting the structure of the volcano can be. Pictures of some calderas look more like an oasis than a place where an eruption once occurred - a process that is detrimental to all living things.

How many volcanoes are on Earth?

We already know the structure of volcanoes, now let's talk about how the situation with volcanoes is today. There are over 500 active volcanoes on our planet. Somewhere the same number are considered sleeping. A large number of volcanoes are declared dead. This distinction is considered highly subjective. The criterion for determining the activity of a volcano is the date of the last eruption. It is assumed that if last eruption happened in a historical period (the time when people record 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. Usually, these eruptions are not large enough to endanger human life. However, sometimes there are major eruptions. Over the past two centuries, there have been 19 of them. A little more than 1,000 people died in them.

The benefits of volcanoes

It is hard to believe in this, but such a terrible phenomenon as a volcano can be useful. Volcanic products, due to their unique properties, are used in many areas of human activity.

The oldest use of volcanic rock is construction. The famous French cathedral of Clermont-Ferrand is built entirely of dark lava. Basalt, which is part of the igneous material, is often used in paving roads. Small particles of lava are used in the production of concrete and for filtering water. Pumice serves as an excellent sound insulator. Its particles are also part of stationery gum 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, generates electricity at special geothermal stations. Diamonds, gold, opal, amethyst and topaz are often found in volcanoes.

Passing through the 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 bathe in separate sources, 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 are ejections of magma, which, in turn, is a molten mantle. Thus, considering volcanoes, it would be useful to recall the structure of the Earth. Volcanoes consist of a hearth, a vent, and a crater. They can be both destructive and beneficial to various industries.

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

Theme: Earth

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

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

Earth it is so arranged that under the solid earth's crust there is a layer of molten rocks (magma), moreover, under high pressure. When cracks appear in the Earth's crust (and hills form on the earth's surface in this place), the magma under pressure in them rushes and exits to the earth's surface, breaking up into red-hot lava (500-1200 ° C), caustic volcanic gases and ash. The spreading lava hardens, and the volcanic mountain increases in size.

The formed volcano becomes a vulnerable place in the earth's crust, even after the end of the eruption inside it (in the crater), gases constantly come out of the earth's interior to the surface (the volcano "smokes"), and with any slightest shifts or shocks of the earth's crust, such a "sleeping" volcano can wake up at any time. Sometimes the awakening of the volcano occurs without obvious reasons. Such volcanoes are called active.

Rice. 2. The structure of the volcano ()

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

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

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

Lava- erupted magma.

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

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

Extinct - no information has been preserved about the eruption.

Asleep - those that are extinguished, and suddenly begin to act.

Volcanoes are classified according to their shape. conical and shield.

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

Rice. 3. Conical Volcano ()

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

Rice. 4. Shield volcano ()

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

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

Rice. 6. Mud volcano ()

- a lump or piece of lava thrown out during a volcanic eruption in a liquid or plastic state from a crater and received a specific shape during squeezing, during flight and solidification in air.

Rice. 7. Volcanic bomb ()

An underwater volcano is a type of volcano. These volcanoes are located at the bottom of the ocean.

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

Rice. 8. Underwater volcano ()

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

Rice. 9. Volcano Klyuchevskaya Sopka ()

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

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

3. Eskov K.Yu. et al. Natural History 5 / Ed. Vakhrusheva A.A. - M.: Balass.

3. Most famous volcanoes Earth().

1. Tell us about the structure of the volcano.

2. How are volcanoes formed?

3. How is lava different from magma?

4. * Prepare a short message about one of the volcanoes in our country.