The ancient Romans, watching how black smoke and fire burst out of the top of the mountain into the sky, believed that before them was the entrance to hell or to the domain of Vulcan, the god of blacksmithing and fire. In honor of him, fire-breathing mountains are still called volcanoes.
In this article we will figure out what the structure of the volcano is and look into its crater.
Active and extinct volcanoes
There are many volcanoes on Earth, both dormant and active. The eruption of each of them can last days, months, or even years (for example, the Kilauea volcano located on the Hawaiian archipelago woke up back in 1983 and still does not stop its work). After that, the craters of volcanoes are able to freeze for several decades, in order to then again remind themselves of themselves with a new ejection.
Although, of course, there are such geological formations, the work of which was completed in the distant past. At the same time, many of them have still retained the shape of a cone, but there is no information about exactly how their eruption took place. Suchvolcanoes are considered extinct. An example is Mount Elbrus and Kazbek, covered with shining glaciers since ancient times. And in the Crimea and Transbaikalia there are heavily eroded and destroyed volcanoes that have completely lost their original shape.
What are 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 division is very approximate, since most of them are attributed to linear tectonic faults in the earth's crust.
In addition, there are also shield-shaped and domed structures of volcanoes, as well as the so-called cinder cones and stratovolcanoes. By activity, they are defined as active, dormant or extinct, and by location - as terrestrial, underwater and subglacial.
What is the difference between linear volcanoes and central volcanoes
Linear (fissure) volcanoes, as a rule, do not rise high above the earth's surface - they look like cracks. The structure of volcanoes of this type includes long supply channels associated with deep cracks in the earth's crust, from which liquid magma, which has a bas alt composition, flows out. It spreads in all directions and, as it freezes, forms lava sheets that erase forests, fill depressions, and destroy rivers and villages.
In addition, during the explosion of a linear volcano, explosive ditches may appear on the earth's surface, havinglength of several tens of kilometers. In addition, the structure of volcanoes along the fissures is decorated with gently sloping ridges, lava fields, splashes and flat wide cones that radically change the landscape. By the way, the main component of the relief of Iceland is the lava plateaus that arose in this way.
If the composition of the magma is more acidic (increased content of silicon dioxide), then extrusive (i.e. squeezed out) shafts with a loose composition grow around the mouth of the volcano.
Structure of central type volcanoes
Volcano of the central type is a cone-shaped geological formation, which crowns the top of the crater - a depression shaped like a funnel or bowl. It, by the way, gradually moves up as the volcanic structure itself grows, and its size can be completely different and measured both in meters and in kilometers.
Volcanic craters are formed during an eruption and can occur even on the slope of a volcanic mountain, in which case they are called parasitic or secondary.
Deep into the volcanic mountain is a vent, which rises up into the crater, magma. Magma is a molten fiery mass that has a predominantly silicate composition. It is born in the earth's crust, where its hearth is located, and having risen upward, it pours out in the form of lava to the surface of the earth.
An eruption is typically accompanied by the ejection of small spurts of magma that form ash and gases, which, interestingly, are 98% water. They are joined by various impurities in the form of flakes of volcanicash and dust.
What determines the shape of volcanoes
The shape of a volcano largely depends on the composition and viscosity of the magma. Easily mobile bas altic magma forms shield (or shield-like) volcanoes. They are usually flat and have a large circumference. An example of these types of volcanoes is the geological formation located in the Hawaiian Islands and called Mauna Loa.
Cinder cones are the most common type of volcanoes. They are formed during the eruption of large fragments of porous slag, which, piling up, build a cone around the crater, and their small parts form sloping slopes. Such a volcano becomes higher with each eruption. An example is the Plosky Tolbachik volcano that exploded in December 2012 in Kamchatka.
Features of the structure of domed and stratovolcanoes
And the famous Etna, Mount Fuji and Vesuvius are examples of stratovolcanoes. They are also called layered, as they are formed by periodically erupting lava (viscous and quickly solidifying) and pyroclastic substance, which is a mixture of hot gas, hot stones and ash.
As a result of such emissions, these types of volcanoes have sharp cones with concave slopes, in which these deposits alternate. And the lava flows from 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 by viscous granitic magma,which does not flow down the slopes, but freezes at the top, forming a dome, which, like a cork, clogs the vent and is kicked out by gases accumulated under it over time. An example of such a phenomenon is the dome that forms over the volcano St. Helens, in the northwestern United States (it formed in 1980).
What is a caldera
The central volcanoes described above are usually cone-shaped. But sometimes, during an 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 a thousand meters and a diameter of up to 16 km.
From what was said earlier, you remember that the structure of volcanoes includes a huge vent, along which molten magma rises during an eruption. When all the magma is on top, a huge void appears inside the volcano. It is precisely in it that the top and walls of a volcanic mountain can fall, forming on the earth's surface vast cauldron-shaped depressions with a relatively flat bottom, bordered by the remnants of the crash.
Today's largest caldera is the Toba caldera, located on the island of Sumatra (Indonesia) and completely covered with water. The lake formed in this way has a very impressive size: 100/30 km and a depth of 500 m.
What are fumaroles
Volcano craters, their slopes, foothills, as well as the crust of cooled lava flows are often covered with cracks or holes, from which dissolved inmagma hot gases. They are called fumaroles.
As a rule, thick white steam swirls over large holes, because magma, as already mentioned, contains a lot of water. But besides it, fumaroles also serve as a source of emissions 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 that make up the structure of the volcano make it safer, as the gases find a way out and do not accumulate in the depths of the mountain to form a bubble that will eventually push the lava to the surface.
The famous Avachinsky Sopka, which is located near Petropavlovsk-Kamchatsky, can be attributed to such a volcano. The smoke swirling above it is visible in clear weather for tens of kilometers.
Volcanic bombs are also part of the structure of Earth's volcanoes
If a dormant volcano explodes for a long time, then the so-called volcanic bombs fly out of its mouth during the eruption. They are composed of fused rocks or lava fragments frozen 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 time to cool enough in the air, a volcanic bomb that has fallen to the ground turns into a cake. And low-viscosity bas alt lavas rotate in the air, taking on a twisted shape or becoming like a spindle or a pear. Viscous - andesitic - pieces of lava become after falling like a bread crust (theyrounded or multifaceted and covered with a network of cracks).
The diameter of a volcanic bomb can reach seven meters, and these formations are found on the slopes of almost all volcanoes.
Types of volcanic eruptions
As pointed out in the book "Fundamentals of Geology", which considers the structure of volcanoes and types of eruptions, Koronovsky N. V., all types of volcanic structures are formed as a result of various eruptions. Among them, 6 types stand out in particular.
- Hawaiian type of eruption - ejection of very liquid and mobile lava, which forms huge shield volcanoes that have a flat shape.
- Strambolian type - ejection of more viscous lava, which is pushed out by explosions of different strengths, resulting in short powerful streams.
- The Plinian type is characterized by sudden powerful explosions, which are accompanied by the release of a huge amount of tephra (loose material) and the occurrence of its flows.
- The Peleian type of eruption is accompanied by the formation of hot avalanches and scorching clouds, as well as the growth of extrusive domes of viscous lava.
- Gas type is an eruption of only fragments of more ancient rocks, which is associated with gases dissolved in magma, or with overheating of groundwater entering the structure of the volcano.
- Heat flow eruption. It is similar to the release of a high-temperature aerosol, consisting of pieces of pumice, minerals and fragments of volcanic glass, surrounded by a hot shell of gas. Such an eruption was widespread in the distant past, but in modern times it has long ceased to exist.observed by people.
When the most famous volcanic eruptions took place
The years of volcanic eruptions can, perhaps, be attributed to serious milestones in the history of mankind, because at that time the weather changed, a huge number of people died, and even entire civilizations were erased from the Earth (for example, as a result of the eruption of a giant volcano, the Minoan civilization in the 15th or 16th century BC).
In A. D. 79 e. near Naples, Vesuvius erupted, burying the cities of Pompeii, Herculaneum, Stabia and Oplontius under a seven-meter layer of ash, leading to the death of thousands of inhabitants.
In 1669, several eruptions of Mount Etna, as well as in 1766 - Mayon Volcano (Philippines) led to terrible destruction and death under lava flows of many thousands of people.
In 1783, the Lucky volcano exploded in Iceland, causing a drop in temperatures that led to crop failure and famine in Europe in 1784.
And the Tambora volcano on the island of Sumbawa, which woke up in 1815, left the whole Earth without summer the next year, lowering the temperature in the world by 2.5 °С.
In 1991, a volcano from the Philippine island of Luzon, with its explosion, also temporarily lowered it, however, already by 0.5 °С.
