Volcanoes: structure of volcanoes, types and periodicity of eruptions

Today we will consider such an interesting topic as volcanoes. The structure of volcanoes and their classification are described in detail in this article.

Volcanoes received their name after the name of Vulcan, the god of fire. They are geological formations that arise over cracks and channels in the earth's crust. The large volcanoes that erupt before your very eyes are incomparable. On the earth's surface, lava, rock fragments and hot gases from igneous sources are emitted through cracks and canals. Volcanoes are usually composed of products of eruptions of individual mountains. They can reach heights in large sizes. For example, the largest volcanoes in Africa are Kilimanjaro (5895 meters), Cameroon (4,100 meters) and Teide (3,718 meters).

Extinct, asleep and active volcanoes

The current ones are those that are currently erupting periodically or permanently. For example, the active volcanoes of Africa are Nyiragongo, Meru, Carisimbi, Fako, Teide. Those who have fallen asleep are such volcanoes, whose eruptions are not known, but they retained their form and local earthquakes occur under them. The extinct volcanoes are called extinct and strongly destroyed, not active. Photo of the active volcano Arenal, located in Costa Rica, is presented below.

The division of volcanoes into fracture and central

Volcanoes are divided according to the shape of the feed channels into fissures and central ones. Considering the structure of the volcano (the scheme is presented below), it should be noted that in the upper mantle there can be magmatic foci at a depth of about 50-70 kilometers (for example, the Kamchatka volcano Klyuchevskaya Sopka). They can also be in the earth's crust, at a depth of about 5-6 meters (the Italian volcano Vesuvius) or deeper.

Long and short-term eruptions

Volcanic eruptions can be long (from several years to several centuries) and short-term, which are measured by the clock. One can attribute to their precursors acoustic phenomena, volcanic earthquakes, changes in the composition and magnetic properties of fumarolic gases, as well as some other phenomena that are noted before volcanoes erupt. The photo of the erupting volcano is presented below.

How does the eruption begin?

Usually it starts with the fact that there is an increase in emissions of gases. They are thrown out first along with the cold, dark fragments of lavas, and then with the red-hot. In some cases, these emissions are accompanied by the outpouring of lava. From 1 to 5 km, depending on the strength of the explosions, the altitude of the rise of lavas saturated with fragments and the heat of water vapor and gases are fluctuating. And the largest volcanoes can throw out the products of the eruption and to an even greater height. For example, in 1956 in Kamchatka during the eruption of the Bezymyanny volcano it was 45 kilometers. At a distance of several thousand to tens of thousands of kilometers, the ejected material is transferred. Its volume reaches sometimes several cubic kilometers. The concentration in the atmosphere of volcanic ash with some eruptions is so great that there is a darkness comparable to darkness in an enclosed space. It was observed, in particular, in the village of Klyuchi, located 40 km from the Bezymyanny Volcano in 1956.

The mock-up of the volcano, presented below, will help you understand its structure.

What is an eruption?

An eruption is an alternation of strong and weak explosions, as well as the outflow of lavas. The maximum strength of explosions is called culminating paroxysm. Reduction of the force of explosions and then the gradual cessation of eruptions is observed after them. Tens of km³ of poured lava are emitted by the largest volcanoes. The photo below shows the structure of the volcano. This scheme gives a clear idea of how it erupts.

Types of eruptions

The volcanic eruptions are not always the same. Four types are distinguished depending on the viscosity of lavas and the number of products (solid, gaseous and liquid): explosive (Vulcan), extrusive (dome), mixed (Strombolian) and effusive (Hawaiian).

Hawaiian type, most often creating thyroid volcanoes, is characterized by a fairly calm outpouring of basaltic (liquid) lava, which forms lava flows and fire-liquid lakes in the craters. Contained in a small number of gases form fountains, which throw out drops and lumps of liquid lava, stretching into thin glass filaments during the flight.

In the Strombolian type, which is usually created by stratospheric volcanoes, together with the rather abundant outpourings of the lavas of the andesite basalt composition, small explosions predominate, during which slag pieces are dropped, as well as various spindle-shaped and twisted bombs.

In the dome type, gaseous substances play an important role. They produce explosions, as well as ejections of large black clouds, crowded with a lot of wreck debris. Small streams form viscous lavas of andesite composition.

Products of eruptions

Products of eruption of various volcanoes are solid, gaseous and liquid. Volcanic gases that are emitted during the eruption (they are called eruptive), and during the peaceful activity of the volcano (furamol) from the cracks located on the slopes of the volcano, as well as from its crater, pyroclastic rocks and lava flows, form hot springs, passing Through the underground waters.

Lava - hot very viscous or liquid, mostly silicate, the mass that, when volcanic eruptions, pours out to the surface of the Earth (see the photo below the volcano in the section). When it solidifies, effusive rocks form.

Volcanics (volcanic rocks) - rocks that are formed as a result of volcanic eruptions. Distinguish, depending on the nature of the eruption, effusive, or poured (diabase, liparites, trachytes, andesites, basalts, etc.), pyroclastic, or volcanic-detrital (volcanic breccias, tuffs) volcanic rocks.

Volcanic apparatuses

Tectonic fracture (tectonic rupture) is the disturbance of the integrity of rocks (thrusts, faults, shifts, faults, etc.) due to movements of the earth's crust.

The photo below shows the model of the volcano.

Depending on the composition of the magma and the nature of the eruptions, structures of various heights and shapes appear on the surface. Each time the structure of the volcano is unique. The figure above is just an example. Volcanic apparatus consists of a fractured or tubular channel, a vent (the upper part of the channel), volcanic clastic products and accumulations of lavas surrounding the channel from different sides, and a crater (funnel-shaped or cup-shaped depression on a slope or apex of a volcano, whose diameter ranges from several meters to several kilometers ). The most common forms are cone-shaped, with predominance of emissions of various detrital material, and domed (when viscous lava is squeezed).

Not only through the crests of the main crater, eruptions occur, but also through secondary (also called parasitic) craters, which have volcanoes. The structure of volcanoes is characterized by the fact that the side craters are on the slopes, and also at some distance from the tops of the main. Often, with single eruptions of gases, which penetrate the channel to the earth's surface, funnel-shaped depressions are formed. They are fringed by a ring shaft, consisting of blocks of different rocks. Often such funnels are filled with water. They are called maars. Sometimes strong eruptions are accompanied by the fact that parts of volcanic structures collapse. Often this applies to the area, next to which are the volcanoes. The structure of volcanoes sometimes leads to its collapse. The depressions that form in this case, in diameter, reach from several to several tens of kilometers. They are called calderas.

Underwater volcanoes

We disassembled the structure of the volcanoes. It should be noted that one of their varieties is the underwater, located at the bottom of the reservoir. Today, the geographic coordinates of this type of volcanoes are concentrated mainly within the three volcanic belts: Atlantic, Mediterranean-Indonesian and Pacific. According to the results of studying the past of our planet from the point of view of geology, in terms of scale, and also in terms of the volume of emission products coming from the bowels of the Earth, they significantly exceed those on land. If annually on land from 20-30 eruptions on average reaches up to 1.5 km³ of molten magma per year, then underwater volcanoes erupt 12-15 times more material during the same time. The activity of underwater volcanoes is supported by life in the waters of the ocean near its surface. And from it, in turn, the amount of greenhouse gases absorbed by the ocean depends.

Eruptions of underwater volcanoes

If the reservoir is located above the volcanic focus, the pyroclastic material during the eruption is saturated with water and then spread around the hearth. For the first time such deposits were described in the Philippines. They formed in the course of the 1968 eruption of the Taal volcano, which is located at the bottom of the lake. Deposits of this type are often represented by thin, wavy layers of pumice. The islands can form as a result of volcanic eruptions. This, for example, is located in the Indian Ocean volcanic island of Reunion.

Causes of volcanic activity

The geographic location of volcanoes indicates the close connection between the mobile parts of the earth's crust and the volcanic belt. The faults formed in such zones are channels through which magma moves to the earth's surface. This occurs, apparently, under the influence of various tectonic processes. When the pressure of the gases dissolved in the magma becomes at a depth greater than the pressure of the overlying ones, they begin to move toward the surface of the earth, dragging the magma behind them. Perhaps during the crystallization of magma, a gas pressure is created, when the vapor and residual gases enrich its liquid part. Magma seems to boil. A high pressure is created in the source as a result of the release of a large volume of gaseous substances. It can also be one of the reasons for the eruption.

The formation and structure of the volcano are very interesting. In this article, we only briefly examined them. The inner structure of the volcano is still of interest to many researchers. They are still studying it to this day.

For the first time in school years we get acquainted with what a volcano is. Geography gives us an opportunity to get closer to understanding how our planet works. The earth is fraught with many mysteries, which will be solved by the next generations. Of course, in school we are told only the main points when studying the structure of the volcano. Grade 5 - not the age when you should go into this topic. However, sometimes it can and should be done. We hope you learned something new for yourself from this article.