Why do volcanoes happen? Processes above the magma chamber. Debris and Ashes

Our Earth is not all solid stone through and through; rather, it resembles an egg: on top there is a thin hard shell, under it there is a viscous layer of hot mantle, and in the center there is a solid core. The earth's "shell" is called lithosphere, which means “stone shell” in Greek. The thickness of the lithosphere is on average about 1% of the radius of the globe: on land it is 70-80 kilometers, and in the depths of the oceans it can be only 20 kilometers. The lithosphere is all cut up by faults and resembles a mosaic.

The temperature of the mantle is thousands of degrees: closer to the core the temperature is higher, closer to the shell it is lower. Due to the difference in temperature, the substance of the mantle is mixed: hot masses rise upward, and cold masses descend (just like boiling water in a pan or kettle, but this only happens thousands of times slower). Although the mantle is heated to enormous temperatures, due to the colossal pressure in the center of the Earth, it is not liquid, but viscous - like very thick tar. The “shell” lithosphere seems to float in the viscous mantle, plunging slightly into it under the weight of its weight.

Reaching the base of the lithosphere, the cooling mass of the mantle moves horizontally for some time along the solid rock “shell”, but then, having cooled, it descends again towards the center of the Earth. While the mantle moves along the lithosphere, pieces of the “shell” (lithospheric plates) inevitably move along with it, while individual parts of the stone mosaic collide and creep onto each other.

The part of the plate that was below (on which another plate crawled) gradually sinks into the mantle and begins to melt. This is how it is formed magma - a thick mass of molten rocks containing gases and water vapor. Magma is lighter than the surrounding rocks, so it slowly rises to the surface and accumulates in so-called magma chambers, which are most often located along the line of plate collision. The magma is more fluid than the mantle, but still quite thick; Translated from Greek, “magma” means “thick paste” or “dough.”

The behavior of hot magma in a magma chamber really resembles yeast dough: the magma increases in volume, occupies all available space and rises from the depths of the Earth along cracks, trying to break free. Just as dough lifts the lid of a pan and flows over the edge, so magma breaks through the earth's crust in the weakest places and breaks out to the surface. This is a volcanic eruption.

A volcanic eruption occurs due to degassing magma Everyone knows the degassing process: if you carefully open a bottle of a carbonated drink (lemonade, Coca-Cola, kvass or champagne), a pop is heard, and smoke appears from the bottle, and sometimes foam - this is gas coming out of the drink (that is, it is degassing) . If a bottle of champagne is shaken or heated before opening, a powerful stream will burst out of it, and it is impossible to stop this process. And if the bottle is not tightly closed, then this jet can itself knock the cork out of the bottle.

The magma in a magma chamber is under pressure, just like a carbonated drink in a closed bottle. In the place where the earth’s crust was “loosely closed,” magma can escape from the bowels of the Earth, knocking out the “plug” of the volcano, and the stronger the “plug” was, the stronger the volcanic eruption will be. Rising upward, magma loses gases and water vapor and turns into lava- magma depleted in gases. Unlike fizzy drinks, the gases released during a volcanic eruption are flammable, so they ignite and explode in the crater of the volcano. The force of a volcano explosion can be so powerful that a huge “funnel” remains in the place of the mountain after the eruption ( caldera), and if the eruption continues, then a new volcano begins to grow right in this depression.

However, it happens that magma manages to find an easy way out to the surface of the Earth, then lava flows out of volcanoes without explosions at all - like boiling porridge, gurgling, overflowing over the edge of a pan (for example, volcanoes erupt in the Hawaiian Islands). Magma does not always have enough strength to reach the surface, and then it slowly solidifies at depth. In this case, a volcano does not form at all.

How does a volcano work anyway? When a “valve” in the Earth opens (the plug of a volcano is knocked out), the pressure in the upper part of the magma chamber decreases sharply; Below, where the pressure is still high, dissolved gases are still part of the magma. In the crater of the volcano, gas bubbles are already beginning to be released from the magma: the higher you go, the more of them there are; these light “balloons” rise upward and carry the viscous magma with them. A continuous foamy mass has already formed near the surface (frozen volcanic stone foam is even lighter than water - this is known to everyone pumice). Degassing of magma is completed at the surface, where, once released, it turns into lava, ash, hot gases, water vapor and rock fragments.

After a rapid degassing process, the pressure in the magma chamber decreases and the volcanic eruption stops. The volcano’s mouth is closed with solidified lava, but sometimes not very firmly: enough heat remains in the magma chamber, so volcanic gases can escape to the surface through cracks ( fumaroles) or jets of boiling water ( geysers). In this case, the volcano is still considered active. At any moment, a large amount of magma can accumulate in the magma chamber, and then the eruption process will begin again.

There are known cases when volcanoes erupted and remained silent for 300, 500, and 800 years. Volcanoes that have erupted at least once in human memory (and can erupt again) are called sleeping.

Extinct (or ancient) volcanoes are those that were active in the distant geological past. For example, the capital of Scotland, the city of Edinburgh, stands on an ancient volcano that erupted more than 300 million years ago (there were no dinosaurs then).

Let's summarize.

As a result of the movement of lithospheric plates, magma chambers can arise. If liquid magma erupts to the surface of the Earth, a volcanic eruption begins. Often a volcanic eruption is accompanied by powerful explosions, this is due to the degassing of magma and the explosion of flammable gases. The volcano falls asleep if the supply of new portions of magma from the magma chamber stops, but can wake up (come to life) if plate movement continues and the magma chamber fills again. Volcanoes go out completely if the movement of plates in the area stops.

Answered: Vladimir Pechenkin, Yuri Kuznetsov, Albert

Volcanoes are geological formations on the surface of the earth's crust where magma comes to the surface, forming lava, volcanic gases, "volcanic bombs" and pyroclastic flows. The name “volcano” for this type of geological formation comes from the name of the ancient Roman god of fire “Vulcan”.

Deep below the surface of our planet Earth, the temperature is so high that rocks begin to melt, turning into a thick, viscous substance - magma. The molten substance is much lighter than the solid rock around it, so the magma, as it rises, accumulates in so-called magma chambers. In the end, part of the magma erupts to the surface of the Earth through faults in the earth's crust - this is how a volcano is born - a beautiful, but extremely dangerous natural phenomenon, often bringing with it destruction and casualties.

The magma that escapes to the surface is called lava; it has a temperature of about 1000 ° C and flows rather slowly down the slopes of the volcano. Due to its low speed, lava rarely causes human casualties, however, lava flows cause significant destruction of any structures, buildings, and structures encountered along the path of these “rivers of fire.” Lava has very poor thermal conductivity, so it cools very slowly.

The greatest danger comes from stones and ash erupting from the crater of the volcano during an eruption. Hot stones, thrown into the air at great speed, fall to the ground, causing numerous casualties. Ashes fall to the ground like “loose snow”, and if people, animals, plants all die from lack of oxygen.

This happened with the notorious city of Pompeii, developing and prospering, and destroyed by the eruption of Mount Vesuvius in a matter of hours. However, pyroclastic flows are rightfully considered the deadliest of all volcanic phenomena. Pyroclastic flows are a boiling mixture of solid and semi-solid rocks and hot gas flowing down the slopes of a volcano. The composition of the streams is much heavier than air; they rush down like a snow avalanche, only hot, filled with toxic gases and moving at a phenomenal, hurricane speed.

Classification of volcanoes

There are several classifications of volcanoes based on certain characteristics. For example According to the degree of activity, scientists divide volcanoes into three types: extinct, dormant and active..

Volcanoes that have erupted during a historical period of time and are likely to erupt again are considered active. Dormant volcanoes are those that have not erupted for a long time, but still have the potential to erupt. Extinct volcanoes are volcanoes that have ever erupted, but the likelihood of them erupting again is zero.

Classification According to the shape of the volcano, it includes four types: cinder cones, dome, shield volcanoes and stratovolcanoes.

• The most common type of volcano on land, a cinder cone is made up of small fragments of solidified lava that escaped into the air, cooled, and fell near the vent. With each eruption, such volcanoes become higher.
• Dome volcanoes form when viscous magma is too heavy to flow down the sides of a volcano. It accumulates at the vent, clogging it and forming a dome. Over time, gases knock out such a dome like a cork.
• Shield volcanoes have the shape of a bowl or shield with gentle slopes formed by basaltic lava flows - traps.
• Stratovolcanoes emit a mixture of hot gas, ash and rocks, as well as lava, which are alternately deposited on the volcano's cone.

Classification of volcanic eruptions

Volcanic eruptions are an emergency situation that is carefully studied by volcanologists to be able to predict the possibility and nature of eruptions in order to minimize the scale of the disaster.

There are several types of eruptions:

• Hawaiian,
• strombolian,
• Peleian,
• Plinian,
• hydroexplosive.

Hawaiian is the calmest type of eruption, characterized by the release of lava with a small amount of gas, which forms a shield-shaped volcano. The Strombolian type of eruption, named after the Stromboli volcano, which has been continuously erupting for several centuries, is characterized by the accumulation of gas in the magma and the formation of so-called gas plugs in it. Moving upward along with the lava, reaching the surface, giant gas bubbles burst with a loud bang due to the difference in pressure. During an eruption, such explosions occur every few minutes.

The Peleian type of eruption is named after the most massive and destructive eruption of the 20th century. – Montagne Pelee volcano. The erupting pyroclastic flows killed 30,000 people in a matter of seconds. The Pelian type is characteristic of an eruption similar to the eruption of Mount Vesuvius. This type received its name from the chronicler who described the eruption of Vesuvius that destroyed several cities. This type is characterized by the ejection of a mixture of stones, gas and ash to a very high altitude - often the column of the mixture reaches the stratosphere. Volcanoes located in shallow waters in the seas and oceans erupt using the hydroexplosive type. In such cases, a large amount of steam is generated when the magma comes into contact with seawater.

Volcanic eruptions can create many dangers not only in the immediate vicinity of the volcano. Volcanic ash can pose a threat to aviation, posing a risk of failure of aircraft turbojet engines.

Large eruptions can also affect the temperature in entire regions: ash and sulfuric acid particles create areas of smog in the atmosphere and, partially reflecting sunlight, lead to cooling of the lower layers of the Earth's atmosphere over a particular region, depending on the power of the volcano, wind strength and direction movement of air masses.