Volcanic activity, which is among the most terrible phenomena nature, often brings great disasters to people and national economy. Therefore, it must be borne in mind that although not all active volcanoes cause misfortunes, nevertheless, each of them can be a source of negative events to one degree or another, volcanic eruptions are of varying strength, but only those accompanied by death are catastrophic. and material values.

General ideas about volcanism

“Volcanism is a phenomenon due to which, during the course of geological history, the outer shells of the Earth were formed - the crust, hydrosphere and atmosphere, that is, the habitat of living organisms - the biosphere.” This opinion is expressed by most volcanologists, but this is by no means the only idea about the development of the geographic envelope. Volcanism covers all phenomena associated with the eruption of magma to the surface. When magma is deep in the earth's crust under high pressure, all of its gaseous components remain in a dissolved state. As the magma moves towards the surface, the pressure decreases, gases begin to be released, as a result, the magma pouring onto the surface differs significantly from the original one. To emphasize this difference, magma erupted on the surface is called lava. The process of eruption is called eruptive activity.

Fig.1. Eruption of Mount St. Helens

Volcanic eruptions proceed differently, depending on the composition of the products of the eruption. In some cases, eruptions proceed quietly, gases are released without large explosions, and liquid lava flows freely to the surface. In other cases, eruptions are very violent, accompanied by powerful gas explosions and squeezing or outpouring of relatively viscous lava. The eruptions of some volcanoes consist only in grandiose gas explosions, as a result of which colossal clouds of gas and water vapor saturated with lava are formed, rising to great heights. By modern ideas, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the bowels of the Earth to its surface.

At a depth of 50 to 350 km, in the thickness of our planet, pockets of molten matter - magma - are formed. In areas of crushing and fractures of the earth's crust, magma rises and pours out to the surface in the form of lava (it differs from magma in that it contains almost no volatile components, which, when pressure drops, are separated from magma and go into the atmosphere. In places of eruption, lava covers, flows , volcanoes-mountains, composed of lavas and their pulverized particles - pyroclasts. According to the content of the main component - magma silicon oxide and the volcanic rocks formed by them - volcanic rocks are divided into ultrabasic (silicon oxide less than 40%), basic (40-52%), medium ( 52-65%), acidic (65-75%), basic or basaltic magma is the most common.

Types of volcanoes, composition of lavas. Classification by the nature of the eruption

The classification of volcanoes is based mainly on the nature of their eruptions and on the structure of volcanic apparatuses. And the nature of the eruption, in turn, is determined by the composition of the lava, the degree of its viscosity and mobility, temperature, and the amount of gases contained in it. IN volcanic eruptions three processes are manifested: 1) effusive - the outpouring of lava and its spreading over the earth's surface; 2) explosive (explosive) - an explosion and the release of a large amount of pyroclastic material (solid eruption products); 3) extrusive - squeezing out, or squeezing out, magmatic matter onto the surface in a liquid or solid state. In a number of cases, mutual transitions of these processes and their complex combination with each other are observed. As a result, many volcanoes are characterized by a mixed type of eruption - explosive-effusive, extrusive-explosive, and sometimes one type of eruption is replaced by another in time. Depending on the nature of the eruption, the complexity and diversity of volcanic structures and forms of occurrence of volcanic material is noted. Among volcanic eruptions, the following are distinguished: eruptions of the central type, fissure and areal.


Fig.2. Hawaiian type of eruption

1 - Ash plume, 2 - Lava fountain, 3 - Crater, 4 - Lava lake, 5 - Fumaroles, 6 - Lava flow, 7 - Lava and ash layers, 8 - Rock layer, 9 - Sill, 10 - Magma channel, 11 - Magma chamber, 12 - Dike

Volcanoes of the central type. They have a shape close to round in plan, and are represented by cones, shields, and domes. At the top there is usually a bowl-shaped or funnel-shaped depression called a crater (Greek 'crater'-bowl). From the crater into the depths of the earth's crust there is a magma-supplying channel, or a volcano vent, which has a tubular shape, along which magma from a deep chamber rises to the surface. Among volcanoes of the central type, polygenic ones, formed as a result of repeated eruptions, and monogenic ones, which manifested their activity once, stand out.

polygenic volcanoes. These include most of the known volcanoes in the world. There is no unified and generally accepted classification of polygenic volcanoes. Various types eruptions are most often referred to by the name of known volcanoes, in which one or another process manifests itself most characteristically. Effusive, or lava, volcanoes. The predominant process in these volcanoes is effusion, or the outpouring of lava to the surface and its movement in the form of flows along the slopes of a volcanic mountain. Volcanoes of the Hawaiian Islands, Samoa, Iceland, etc. can be cited as examples of this nature of the eruption.


Fig.3. Plinian type of eruption

1 - Ash plume, 2 - Magma conduit, 3 - Volcanic ash rain, 4 - Lava and ash layers, 5 - Rock layer, 6 - Magma chamber

Hawaiian type. Hawaii is formed by the merged peaks of five volcanoes, of which four were active in historical time (Fig. 2). The activity of two volcanoes is especially well studied: Mauna Loa, towering almost 4200 meters above the level Pacific Ocean, and Kilauea with a height of more than 1200 meters. The lava in these volcanoes is mainly basaltic, easily mobile, and high-temperature (about 12,000). In the crater lake, lava is bubbling all the time, its level either decreases or rises. During eruptions, lava rises, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are released relatively quietly, forming bursts above the crater, lava fountains rising in height from several to hundreds of meters (rarely). Lava foamed by gases splatters and solidifies in the form of thin glass threads ‘Pele’s hair’. Then the crater lake overflows and lava begins to overflow over its edges and flow down the slopes of the volcano in the form of large flows.

Effusive underwater. Eruptions are the most numerous and least studied. They are also associated with rift structures and are distinguished by the predominance of basaltic lavas. At the bottom of the ocean, at a depth of 2 km or more, the water pressure is so great that explosions do not occur, which means that pyroclasts do not occur. Under water pressure, even liquid basaltic lava does not spread far, forming short dome-shaped bodies or narrow and long flows covered from the surface with a glassy crust. A distinctive feature of submarine volcanoes located at great depths is the abundant release of fluids containing high amounts of copper, lead, zinc and other non-ferrous metals.

Mixed explosive-effusive (gas-explosive-lava) volcanoes. Examples of such volcanoes are the volcanoes of Italy: Etna - the highest volcano in Europe (more than 3263 m), located on the island of Sicily; Vesuvius (about 1200 m high), located near Naples; Stromboli and Vulcano from the group of Aeolian Islands in the Strait of Messina. This category includes many volcanoes of Kamchatka, the Kuril and Japanese islands, and the western part of the Cordillera mobile belt. The lavas of these volcanoes are different - from basic (basalt), andesite-basalt, andesitic to acidic (liparitic). Among them, several types are conditionally distinguished.

Fig.4. Subglacial type of eruptions

1 - Cloud of water vapor, 2 - Lake, 3 - Ice, 4 - Layers of lava and ash, 5 - Layer of rock, 6 - Globular lava, 7 - Magma channel, 8 - Magma chamber, 9 - Dike

Strombolian type. It is characteristic of the Stromboli volcano, which rises in the Mediterranean Sea to a height of 900 m. The lava of this volcano is mainly of basalt composition, but lower temperature (1000-1100) than the lava of the volcanoes of the Hawaiian Islands, therefore it is less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from a few minutes to an hour. Gas explosions are ejected at a relatively great height red-hot lava, which then falls on the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly pieces of lava). Characteristically, very little ash is emitted. The cone-shaped volcanic apparatus consists of layers of slag and solidified lava. Such a famous volcano as Izalco belongs to the same type.

Volcanoes are explosive (gas-explosive) and extrusive-explosive. This category includes many volcanoes, in which large gas-explosive processes with the release of a large amount of solid eruption products, almost without lava outpouring (or in limited sizes) are predominant. This nature of the eruption is associated with the composition of the lavas, their viscosity, relatively low mobility and high saturation with gases. In a number of volcanoes, gas-explosive and extrusive processes are simultaneously observed, expressed in the squeezing out of viscous lava and the formation of domes and obelisks towering above the crater.

Peleian type. Especially clearly manifested in the volcano Mont Pele on about. Martinique is part of the Lesser Antilles. The lava of this volcano is predominantly medium, andesitic, highly viscous and saturated with gases. As it solidifies, it forms a solid plug in the crater of the volcano, which prevents the free exit of gas, which, accumulating under it, creates very high pressures. Lava is squeezed out in the form of obelisks, domes. Eruptions occur as violent explosions. There are huge clouds of gases, supersaturated with lava. These incandescent (with a temperature of over 700-800) gas-ash avalanches do not rise high, but roll down the slopes of the volcano at high speed and destroy all life on their way.


Fig.5. Volcanic activity at Anak Krakatoa, 2008

Krakatau type. It is distinguished by the name of the volcano Krakatau, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The oldest of them, Rakata, is composed of basalts, and the other two, younger ones, are andesites. These three merged volcanoes are located in an ancient vast underwater caldera, formed in prehistoric times. Until 1883, for 20 years, Krakatoa did not show active activity. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate strength in May, after some interruptions they resumed again in June, July, August with a gradual increase in intensity. On August 26, there were two large explosions. On the morning of August 27, there was a giant explosion that was heard in Australia and on the islands in the western Indian Ocean at a distance of 4000-5000 km. An incandescent gas-ash cloud rose to a height of about 80 km. Huge waves up to 30 m high, which arose from the explosion and shaking of the Earth, called tsunamis, caused great destruction on the adjacent islands of Indonesia, they were washed away from the shores of Java and Sumatra about 36 thousand people. In some places, destruction and human casualties were associated with a blast wave of enormous power.

Katmai type. It is distinguished by the name of one of the large volcanoes in Alaska, near the base of which in 1912 a large gas-explosive eruption and directed ejection of avalanches, or flows, of a hot gas-pyroclastic mixture occurred. The pyroclastic material had an acid, rhyolitic or andesite-rhyolite composition. This hot gas-ash mixture filled a deep valley located northwest of the foot of Mount Katmai for 23 km. In place of the former valley, a flat plain about 4 km wide was formed. From the flow that filled it, mass releases of high-temperature fumaroles were observed for many years, which served as the basis for calling it the “Valley of Ten Thousand Smokes”.

Subglacial view of eruptions(Fig. 4) is possible when the volcano is under ice or a whole glacier. Such eruptions are dangerous because they provoke the most powerful floods, as well as their spherical lava. So far, only five such eruptions are known, that is, they are a very rare occurrence.

Monogenic volcanoes

Maar type. This type combines only once erupted volcanoes, now extinct explosive volcanoes. In relief, they are represented by flat saucer-shaped basins framed by low ramparts. The swells contain both volcanic cinders and fragments of nonvolcanic rocks that make up this territory. In a vertical section, the crater has the form of a funnel, which in the lower part is connected to a tubular vent, or explosion tube. These include volcanoes of the central type, formed during a single eruption. These are gas-explosive eruptions, sometimes accompanied by effusive or extrusive processes. As a result, small slag or slag-lava cones (from tens to a few hundred meters high) with a saucer-shaped or bowl-shaped crater depression are formed on the surface.

Such numerous monogenic volcanoes are observed in in large numbers on the slopes or at the foot of large polygenic volcanoes. Monogenic forms also include gas-explosive funnels with an inlet pipe-like channel (vent). They are formed by a single gas explosion of great force. Diamond pipes belong to a special category. Explosion pipes in South Africa are widely known as diatremes (Greek “dia” - through, “trema” - hole, hole). Their diameter ranges from 25 to 800 meters, they are filled with a kind of brecciated volcanic rock called kimberlite (according to the city of Kimberley in South Africa). This rock contains ultramafic rocks, garnet-bearing peridotites (pyrope is a companion of diamond), characteristic of the Earth's upper mantle. This indicates the formation of magma under the surface and its rapid rise to the surface, accompanied by gas explosions.

fissure eruptions

They are confined to large faults and cracks in earth's crust, playing the role of magma channels. The eruption, especially in the early phases, can occur along the entire fissure or separate sections of its sections. Subsequently, groups of contiguous volcanic centers appear along the fault line or crack. The erupted main lava, after solidification, forms basalt covers of various sizes with an almost horizontal surface. In historical times, such powerful fissure eruptions of basaltic lava were observed in Iceland. Fissure eruptions are widespread on the slopes of large volcanoes. O lower, apparently, are widely developed within the faults of the East Pacific Rise and in other mobile zones of the World Ocean. Particularly significant fissure eruptions were in the past geological periods when powerful lava sheets formed.

Areal type of eruption. This type includes massive eruptions from numerous closely spaced volcanoes of the central type. They are often confined to small cracks, or the nodes of their intersection. In the process of eruption, some centers die off, while others arise. The areal type of eruption sometimes captures vast areas where the products of the eruption merge, forming continuous covers.



Ecology

Volcanoes on our planet are geological formations on the earth's crust.

From here, magma comes to the surface of the earth , which forms lava, as well as volcanic gases, rocks, and mixtures of gas, volcanic ash, and rocks. Such mixtures are called pyroclastic flows.

It is worth noting that the very word "volcano" came to us from ancient rome where Vulcan was the god of fire.

A lot of interesting things are known about volcanoes, and below you can find a few facts about them.

25. The strongest volcanic eruption (Indonesia)

Of all documented volcanic eruptions, the largest was recorded at the Tambora stratovolcano on the island of Sumbawa, Indonesia, in 1815.

In terms of volcanic explosiveness, the force of the eruption reached 7 points (out of 8).

This eruption lowered average temperature on Earth by 2.5 °C during next year, which was called "a year without a summer."

It should be noted that the volume of emissions into the atmosphere amounted to approximately 150-180 cubic meters. km.

24. Long lasting effects of a volcanic eruption

Gas and other particles released into the atmosphere during the 1991 eruption of Mount Pinatubo on the island of Luzon, Philippines, lowered global temperatures by about 0.5 degrees Celsius over the next year.

23. Lots of volcanic ash

During the 1991 eruption of Mount Pinatubo, 5 cubic kilometers of volcanic material were thrown into the air, which created an ash column 35 km high.

22. Volcano Big Bang

The largest explosion of the 20th century occurred in 1912 during the eruption of Novarupta, one of the Alaska chain of volcanoes - part of the Pacific Ring of Fire. The strength of the eruption reached 6 points.

21. Sustained eruption of Kilauea

One of the most active volcanoes on Earth, Hawaiian Kilauea has been erupting continuously since January 1983.

20 Deadly Volcanic Eruption

The colossal magma chamber, which was located inside the Taupo volcano, continued to fill very for a long time and finally the volcano exploded.

After the eruption in April 1815, the strength of which reached 7 points, from 150 to 180 cubic meters were thrown into the air. km of volcanic material.

Volcanic ash filled the remote islands, which led to a huge number dead. Their number was approximately 71,000. About 12,000 people died directly from the eruption, while the rest died as a result of starvation and disease, which were the result of eruptive fallout.

19. Big mountains

18. Active volcanoes today

Hawaiian volcano Mauna Loa is the largest active volcano in the world, rising to 4,1769 meters above sea level. Its relative height ( from the ocean floor) - 10,168 meters. Its volume is about 75,000 cubic kilometers.

17. The surface of the earth covered with volcanoes

More than 80 percent of the Earth's surface above and below sea level is of volcanic origin.

16 Ashes Everywhere (Volcano St. Helens)

During the eruption of the stratovolcano St. Helens in 1980, about 540 million tons of ash covered an area exceeding 57,000 square meters. km.

15. Disaster from the volcano - landslides

St. Helens eruptions led to the largest landslides on Earth. As a result of this eruption, the height of the volcano was reduced by 400 meters.

14. Underwater volcano eruptions

The deepest recorded volcanic eruption occurred in 2008 at a depth of 1,200 meters.

The reason was the West Mata volcano, located in the Lau Basin near the Fiji Islands.

13. Lava lakes of a volcano in Antarctica

The southernmost active volcano is Erebus, located in Antarctica. It is worth noting that the lava lake of this volcano is the rarest occurrence on our planet.

Only 3 volcanoes on Earth can boast of "non-healing" lava lakes - Erebus, Kilauea in the Hawaiian Islands and Nyiragongo in Africa. And yet, the fiery lake in the midst of eternal snow is a truly impressive phenomenon.

12. High temperature (what comes out when a volcano erupts)

The temperature inside a pyroclastic flow - a mixture of high-temperature volcanic gases, ash and rocks that forms during a volcanic eruption - can exceed 500 degrees Celsius. This is enough to burn and carbonize the wood.

11. First in history (Nabro Volcano)

On June 12, 2011, the active volcano Nabro, which is located in the southern part of the Red Sea, near the borders of Eritrea and Ethiopia, woke up for the first time. According to NASA, this was its first recorded eruption.

10 Volcanoes Of The Earth

There are about 1,500 volcanoes on Earth, not counting the long volcanic belt on the ocean floor.

9. Tears and hair of Pele (parts of the volcano)

Kilauea is the place where, according to myths, Pele, the Hawaiian goddess of volcanoes, lives.

Pele's tears

Several lava formations have been named after her, including "Pele's tears" (small drops of lava cooled in the air) and "Pele's hair" (splashes of lava cooled by the wind).

Pele's hair

8. Supervolcano

A modern person could not witness the eruption of a supervolcano (8 points), which is capable of changing the climate on Earth.

The last eruption occurred approximately 74,000 years ago in Indonesia. In total, there are about 20 supervolcanoes known to scientists on our planet. It is worth noting that on average, the eruption of such a volcano occurs 1 time in 100,000 years.

Volcanoes have always attracted both scientists and laymen. They are called tunnels or passages to the center of the Earth, because when they erupt, lava comes to the surface, filling the deep bowels of our planet. It was the study of volcanoes that allowed scientists to put forward many hypotheses about complex physical and chemical processes occurring at a depth of thousands of kilometers.

Volcanic eruption

Volcanic eruptions can start in different ways. Sometimes a dozing giant warns in advance of his imminent awakening. In this case, small-scale earthquakes occur in its vicinity, and smoke with an admixture of ash comes out of the vent before the outflow of lava, which rises high into the atmosphere and prevents the sun's rays from penetrating to earth's surface. It even happens that the phenomena preceding the actual eruption of the volcano begin several weeks and even months before the release of lava from the volcano. But this is not always the case. Sometimes a volcano erupts almost instantly, with no prior warning signs.

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Earthquakes and volcanoes

The rate of volcanic eruptions

Scientists have found that the speed of this process directly depends on the substance that forms the basis of lava. These substances have different temperature melting and different influences on the flow of lava, in which andesite and dacite predominate in slowly erupting volcanoes, and rhyolite in rapidly erupting volcanoes. Apart from chemical composition lava at the rate of volcanic eruptions big influence Renders the amount of gases dissolved in lava. The more of them, the higher the flow rate. Sometimes, with a very large amount of gases, an explosion can occur, leading to a rapid release of an avalanche from a volcanic vent.

Lava Exit Experiment

Some data about volcanoes have been confirmed in the laboratory: rhyolite was heated to 800 degrees Celsius, which is approximately the temperature of the volcanic interior at the beginning of the eruption. It has been proven that under these conditions this substance becomes very fluid due to its low viscosity. Therefore, in real conditions, it allows him to exit the vent of the volcano at high speed. Unfortunately, the impetus for this experiment was a natural disaster that took place in Chile in the town of Chaiten, which is located 10 kilometers from the volcano of the same name.

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Why do volcanoes erupt?

The tragedy occurred on May 1, 2008. Less than a day before the eruption, intense tremors, and soon smoke and ash began to rise into the atmosphere. Everything happened so quickly that it was almost impossible to carry out rescue measures. The eruption was long and intense, which could be observed even from Earth orbit. It was a global event followed by scientists from many countries. The pumice samples were analyzed by two scientists, Donald Dingwell and Jonathan Castro.

Lava is a hot molten mass rocks ejected to the Earth's surface during volcanic eruptions. Depending on the species, lava can be liquid or viscous, different colors and temperatures.

In fact, the volcano erupts magma from the upper mantle at a depth of approximately 700 km, but during the eruption it cools down, and its gases escape, which changes its properties. When lava solidifies, various effusive rocks are formed.

In Latin, "labes" means collapse or fall. Hence the word "lava" in Italian and its use in Russian speech.

Types of lava

Different volcanoes erupt lava with different characteristics.

  • Carbonate lava is the coldest and most liquid, flowing like water. It is black or dark brown when erupted, but becomes lighter when exposed to air until it turns almost white.
  • Silicon lava is very viscous and for this reason it sometimes freezes in the vent of the volcano and blows it up. Therefore, when the eruption is restored, there is a strong explosion. Hot silicon lava of dark or black-red color. It flows at a speed of several meters a day and after solidification turns black.
  • Basalt lava has the most high temperature and very mobile. It can flow at a speed of 2 m / s, due to which a small layer can spread over tens of kilometers. It has a yellow or yellow-red color.

You learned what lava is, but also read the article

Kilauea in Hawaii (translated from Hawaiian - "spewing") is one of the most active volcanoes on Earth. It has been continuously erupting since 1983.

This lava flow, named "61g", started its journey at a speed of 2 to 15 meters per hour from the Kilauea volcano in May, at the end of July it reached the water. Let's trace the entire path of lava from the Kilauea volcano in Hawaii, and at the same time see if it is possible to stop such a flow.

In my 2016, the overpressure in the Kilauea cone reached a critical point and magma erupted.

Taking a lava sample for chemical analysis.

Sometimes the speed of the lava flow can reach several meters per second. But this is not our case. The lava temperature ranges from 500 to 1200°C.

Heated up to 1,000 degrees Celsius, lava moves in an unpredictable direction, destroying everything around. Attempts to stop or redirect it are largely dependent on the terrain, available resources and luck. Can it be stopped?

Lava tube, June 30, 2016. Lava tubes are channels that are obtained by uneven cooling of lava flowing from the slopes of the volcano.

But we digress. So lava stop idea 1: bomb it.

In 1935, as the lava approached the Hawaiian city of Hilo, the director of the Hawaiian Volcano Observatory, Thomas Jaggar, proposed bombing the lava tubes. The fact is that they help the hot volcanic mass to flow faster and further due to the walls covered with frozen lava. But the craters left over from the bombing soon filled up again with lava. The city survived only due to the fact that the volcano stopped erupting.

Idea 2: fill with water.

In 1973, on the Icelandic island of Heimaey, for several months, lava flows that threatened the city of Vestmannaeyjar were poured from water cannons sea ​​water. Getting on the hot magma, it evaporated, helping it to solidify. A fifth of the city was destroyed before more powerful water cannons were brought there. Soon the lava was stopped and the bay was saved. In total, 6.8 billion liters of water were used for this operation. But not always the lava can be stopped by water: in this particular situation, the lava flowed slowly, and the amount of water for cooling was almost unlimited.

Idea 3: build a barrier.

Etna erupted again in 1983 east coast Sicily, and it threatened to destroy three cities. Barriers of stones and ashes were urgently erected. The lava eventually broke through one of the first barriers, 18 meters high and 10 meters wide, but the second barrier still managed to stop it.

Idea 4: artificial channels.

Ten years later, Etna erupted again, this time threatening the city of Zafferana. The Italian authorities, taking into account previous experience, deployed part of the lava with explosions, directing it into artificial channels. The rest of the stream was diverted with concrete blocks.

In general, the country needs to have sufficient financial capacity to stop the lava. There is an opinion that you can only delay the inevitable if the volcano does not stop itself.