The structure of volcanoes. Types and types of volcanoes. What is a volcano crater?

Ancient Romans, watching as black smoke and fire escaped from the top of the mountain to the sky, believed that before them there was an entrance into hell or into the possession of Vulcan, the god of forge craft and fire. In honor of it, the fire-breathing mountains are still called volcanoes.

In this article, we'll figure out what the structure of the volcano is, and look into its crater.

Active and extinct volcanoes

On Earth, a lot of volcanoes, both asleep and active. Eruption of each of them can last for days, months, and even years (for example, the Kilauea volcano, which is located in the Hawaiian archipelago, woke up in 1983 and still does not stop its work). After that, craters of volcanoes can be frozen for several decades, then again to remind themselves of a new outburst.

Although, of course, there are also such geological formations, whose work was completed in the distant past. Many of them still retained the shape of the cone, but there is no information about how their eruption occurred. Such volcanoes are considered extinct. As an example, you can bring Mount Elbrus and Kazbek, for a long time covered with shining glaciers. And in the Crimea and Transbaikalia there are strongly eroded and destroyed volcanoes, completely lost their original form.

What are the volcanoes

Depending on the structure, activity and location, in geomorphology (the so-called science that studies the described geological formations) separate types of volcanoes are distinguished.

In general, they are divided into two main groups: linear and central. Although, of course, such a separation is very approximate, since most of them are classified as linear tectonic faults of the earth's crust.

In addition, the thyroid and dome structure of volcanoes are distinguished, as well as the so-called slag cones and stratovolcanoes. By activity they are defined as acting, sleeping or extinct, and by location - as ground, underwater and subglacial.

What distinguishes linear volcanoes from central

Linear (fissured) volcanoes, as a rule, do not rise high above the surface of the earth - they have the appearance of cracks. The structure of volcanoes of this type includes long supply channels, associated with deep clefts of the earth's crust, from which liquid magma is emitted, which has a basaltic composition. It spreads in all directions and, solidifying, forms lava covers, wiping forests, filling hollows, destroying rivers and villages.

In addition, during the explosion of a linear volcano on the earth's surface, explosive ditches with a length of several tens of kilometers can arise. In addition, the structure of volcanoes along the cracks is decorated with gently sloping ramparts, lava fields, sprinkles and flat wide cones, radically changing the landscape. By the way, the main component of the relief of Iceland is the lava plateau, which arose in this way.

If the composition of the magma is more acidic (high content of silicon dioxide), then around the mouth of the volcano, extrusive (ie squeezed) shafts having a loose composition grow.

The structure of volcanoes of central type

A central-type volcano is a cone-shaped geological formation that crowns the crater-a depression shaped like a funnel or bowl-on top. By the way, it gradually moves upwards, as the volcanic building itself grows, and its size can be completely different and measured in meters and kilometers.

Craters of volcanoes Are formed during the eruption and can occur even on the slope of the volcanic mountain, in which case they are called parasitic or collateral.

Deep into the volcanic mountain is the muzzle, along which rises to the top, into the crater, magma. Magma is a molten fire mass, which has a predominantly silicate composition. It is born in the earth's crust, where its hearth is, and ascending to the top, lava flows to the surface of the earth.

Eruption, as a rule, is accompanied by the ejection of small sprays of magma, which form ash and gases, which, interestingly, are 98% water. They are joined by various impurities in the form of flakes of volcanic ash and dust.

What determines the shape of volcanoes

The shape of the volcano largely depends on the composition and viscosity of the magma. Easy-moving basaltic magma forms shield (or thyroid) volcanoes. They, as a rule, have a flat shape and a large circle. An example of such types of volcanoes can serve as a geological formation, located in the Hawaiian Islands and called Mauna Loa.

Slag cones are the most common type of volcanoes. They are formed during the eruption of large fragments of porous slags, which, piling up, build a cone around the crater, and their small parts form sloping slopes. Such a volcano with each eruption becomes higher. An example is the volcano Plosky Tolbachik that exploded in December 2012 in Kamchatka.

Features of the structure of domes and stratovolcanoes

And the famous Etna, Fujiyama and Vesuvius are an example of stratovolcanoes. They are also called layered, since they are formed by periodically erupting lava (viscous and rapidly solidifying) and pyroclastic material, which is a mixture of hot gas, hot stones and ash.

As a result of these emissions, these types of volcanoes have sharp cones with concave slopes in which these sediments alternate. And the lava flows out of them not only through the main crater, but also from cracks, while solidifying on the slopes and forming ribbed corridors that serve as a support for this geological formation.

Dome volcanoes are formed with the help of a viscous granite magma, which does not flow down the slopes, but solidifies at the top, forming a dome, which, like a cork, closes the muzzle and is knocked out by the gases accumulated under it with time. An example of such a phenomenon can serve as a dome, which is formed over the volcano St. Helens, which is in the northwest of the US (it was formed in 1980).

What is the caldera

The central volcanoes described above, as a rule, have the form of a cone. But sometimes during the eruption, the walls of such a volcanic structure collapse, and at the same time calderas are formed - huge depressions that can reach a depth of thousands of meters and a diameter of up to 16 km.

From what you have said, you remember that the structure of the volcanoes includes a huge muzzle, along which molten magma rises during the eruption. When all magma is on top, a huge emptiness appears inside the volcano. That's it, and it can collapse the top and walls of the volcanic mountain, forming on the earth's surface fringed by the remains of the wreck extensive cavernous hollows with a relatively flat bottom.

The largest one today is the Toba caldera, located on the island of Sumatra (Indonesia) and completely covered with water. The lake formed in this way has very impressive dimensions: 100/30 km and a depth of 500 m.

What are fumaroles

The craters of volcanoes, their slopes, the foot, and also the crust of cooled lava flows are often covered with cracks or holes, out of which hot gases dissolved in the magma break out. They are called fumaroles.

As a rule, over thick holes, a thick white vapor is curling, because magma, as already mentioned, contains a lot of water. But in addition to it, fumaroles serve as a source of release for carbon dioxide, all kinds of sulfur oxides, hydrogen sulfide, hydrogen halide and other chemical compounds that can be very dangerous for humans.

By the way, volcanologists believe that the fumaroles entering the structure of the volcano make it safer, because gases find a way out and do not accumulate in the depths of the mountain to form a bubble that eventually pushes the lava to the surface.

To this volcano can be attributed the famous Avachinskaya hill, which is located not far from Petropavlovsk-Kamchatsky. The smoke swirling above it, is visible in clear weather for tens of kilometers.

Volcanic bombs are also included in the structure of the volcanoes of the Earth

If a sleeping volcano explodes a long time, then during an eruption from its mouth, so-called volcanic bombs fly out. They consist of fused rocks or debris of frozen lava in the air and can weigh several tons. Their shape depends on the composition of the lava.

For example, if the lava is liquid and does not have enough time to cool in the air, a volcanic bomb that falls to the ground turns into a flat cake. A basalt low-viscous lava rotates in the air, taking as a result a twisted form or becoming similar to a spindle or pear. Viscous - andesite - pieces of lava become after falling similar to the bread crust (they are round or polyhedral and covered with a network of cracks).

The size of the diameter of the volcanic bomb can reach seven meters, and these formations meet on the slopes of almost all volcanoes.

Types of volcanic eruptions

As pointed out in the book "Fundamentals of Geology", considering the structure of volcanoes and types of eruptions, Koronovsky NV, all kinds of volcanic structures are formed as a result of various eruptions. Among them, 6 types are particularly distinguished.

1. The Hawaiian type of eruption is the ejection of a very liquid and mobile lava, which forms huge shield volcanoes having a flat shape.
2. The Stambolian type is the ejection of a more viscous lava, which is pushed out by explosions of different strengths, resulting in the formation of short, powerful currents.
3. The Plinian type is characterized by sudden powerful explosions, which are accompanied by the ejection of a huge amount of tephra (loose material) and the appearance of its flows.
4. Peley type of eruption is accompanied by the formation of hot avalanches and scorching clouds, as well as the growth of extrusive domes from viscous lava.
5. The gas type is an eruption of only fragments of older rocks that are associated with gases dissolved in magma, or with overheating of the groundwaters entering the structure of the volcano.
6. Eruption of heat flow. It is similar to the ejection of a high-temperature aerosol consisting of pieces of pumice stone, minerals and volcanic glass chips surrounded by a red hot shell of gas. This eruption was widespread in the distant past, but in modern times it has long been not observed by people.

When the most famous volcanic eruptions took place

Years of volcanic eruptions can perhaps be attributed to serious landmarks in the history of mankind, because at that time the weather changed, a huge number of people died, and even whole civilizations were erased from Earth (for example, as a result of the eruption of a giant volcano, the Minoan civilization perished in 15 or 16 Century BC).

In the year 79 AD. E. Near Naples, erupted Vesuvius, buried under the seven-meter layer of the ashes of the city of Pompeii, Herculaneum, Stabia and Oplonti, leading to the death of thousands of residents.

In 1669 several eruptions of Mount Etna, and also in 1766 - the volcano Mayon (Philippines) led to terrible destruction and death under the lava flows of many thousands of people.

In 1783, the volcano of Laki, which exploded in Iceland, caused a drop in temperature, which in 1784 led to a crop failure and famine in Europe.

And the volcano of Tambor on the island of Sumbava, who woke up in 1815, left the whole Earth for the next year without summer, having lowered the temperature in the world by 2.5 ° С.

In 1991, the volcano from the Philippine island of Luzon with its explosion also temporarily lowered it, however, by 0.5 ° C.