All about volcanoes. Types of volcanic structures. The largest volcanoes on earth

We will try to answer this question, remembering that the god of fire among the ancient Romans was called Vulcan (in Greek mythology, Hephaestus). He forged armor in his forge, which, according to legends, was inside a mountain on one of the Aeolian Islands near Sicily (in southern Italy). This island is called Vulcano, and clouds of smoke continuously erupt from the depression at the top of the mountain. According to the ideas of the Romans, it worked forge for the god of fire. Therefore, the most common definition of a volcano is this: it is a hill, a mountain or a hill with a depression at the top - a crater from which magma comes to the surface.

The most common volcanoes of the central type. Magma rises through the tubular channel - the mouth ending at the top with a cup-shaped recess - a crater (from the term “crater” - “bowl”). The volcano erupts, ejected debris, ash, lava poured out remain on its slopes. The height of the mountain increases, and with it the crater moves higher and higher. Often, secondary vents branch off from the main vent to the side, and then side craters arise on the side of the cone.

The most characteristic example of volcanoes of the central type are stratovolcanoes (from the Latin. Stratum - “layer”). Their cones with slightly concave-shaped slopes, such as at Mount Fuji in Japan or at Klyuchevskaya Sopka in Kamchatka, are composed of alternating layers of lava and loose material — ashes, volcanic bombs, tuffs, etc. If volcanoes are formed only by loose products thrown out during explosions, they are called bulk. Lava volcanoes consist of lava flows repeatedly overlapping each other. Such volcanoes have the shape of an irregular cone and are smaller in height than other volcanoes. However, there are also giant lava volcanoes - for example, in the Hawaiian Islands - reaching a height of more than 9 km from the level of the ocean floor, with craters up to 2 km in diameter. The fact is that only the upper part of the volcanoes rises above the ocean, and most of the volcanoes are hidden under the water. In the craters of such volcanoes, basalt magma splashes and from time to time it pours out from there in the form of very liquid lava flows. If lava covers form a huge shell or shield around a volcano, then such volcanoes are called shield - for example, Mauna Kea, Mauna Loa, Kilauea in Hawaii.

Another type of volcano is linear or fractured. Their occurrence is associated with the rise, as a rule, of liquid basalt magma along a crack in the earth's crust. From it lava flows in both directions. Liquid lava spread over a huge area, forming lava sheets. A striking example of a fissure-type eruption is the breakthrough of basalt magma through the Lucky fissure in Iceland in 1783. The erupted lava covered an area of ​​about 600 km 2. While frozen, the lava blocked the crack, but a number of new cracks began to form, from which basalts erupted again.

Sometimes magma that rises along the mouth of a volcano is not able to break through higher and already frozen volcanic rocks. But the growing pressure of gases finally "knocks out the cork" from the vent, and a powerful explosion occurs. The summit of the volcano collapses, and a recess with steep walls - a caldera (from the Spanish. Caldera - "boiler") is formed. In the future, an extrusive dome can grow from a very viscous magma in the caldera. It happened in 1956 on the volcano Bezymyanny in Kamchatka; so it was on Vesuvius after the eruption in 79 AD

In the Aegean Sea, about 100 km north of Crete, is a small island of Santorini (St. Irina Island), which is part of the Cycladic island arc. Santorina was destined not only to become a magnificent geological monument, but also to reveal many secrets of the most ancient history of the Mediterranean.

The modern island of Santorini is a paradise for tourists who attack its beaches in the hot summer months, sailing on numerous ships and yachts and landing on small planes (the airfield of the island is very small). The island of Santorini (another name is Fera, or Thira), together with several other small islands, form a ring, inside of which is a lagoon with a diameter of up to 10 km. Santorini, the largest of the islands, has a length of 11 km, others are smaller. The unique feature of this group of islands is that their outer slopes facing the open sea are relatively flat, while the inner ones facing the lagoon are vertical cliffs more than 100 m high. And in the center of the blue lagoon surrounded by islands above the water two small islands, Paleo-Kameni and Neo-Kameni, are formed, formed by heaps of blocks of black and dark red lava, which gives them a dark color of some original stone chaos.



  If it were possible to “pump out” all the water from the lagoon, then our eyes would open a giant bowl - a caldera - up to 500 m / s in depth with a volcanic cone in the center. All this is very similar (only in much larger sizes) to a double volcano - a cone inside a destroyed cone, when a new, smaller volcano grows in the vast caldera, as was the case with Vesuvius. In the walls of the caldera are visible hollow layers of lavas, loose tuffs and ashes of gray and black colors. From above, they are covered with a powerful, up to 40 m thick, layer of white pumice, which stands out clearly against the dark background of other rocks. This pumice stone is evidence of a grand catastrophe that occurred in the Aegean Sea around 1520 BC. and ruined the famous Minoan civilization.
  Let us recall the great discoveries of the German merchant and archeologist Heinrich Schliemann, who believed in ancient Greek myths and unearthed Troy and the “gold-rich” Mycenae, the city of the legendary Agamemnon. The honor of discovering another center of civilization of that time (mid-2nd millennium BC) belongs to the English archaeologist Arthur Evans, who in 1900 discovered the ruins of a large city with the famous Knossos palace on the north coast of Crete. Culture, discovered by Evans, was named Minoan in honor of the legendary Minos - the lord of Crete.

In the early 30s. XX century. Greek archaeologist Spiridon Marinatos, excavating the port of Amniss in Crete, which belonged to Minos and served as the sea gate of the Cretan capital of Knossos, found pumice fragments in one of the houses. They had to get here from afar, because on Crete there were no young (in the geological sense) volcanoes. And then Marinatos, examining the volcanoes of Santorini and other islands, thought: Could not the powerful explosion of the volcano, located 100 km north of Crete, cause the destruction of the port of Amniss and Knossos? With great enthusiasm, Marinatos began to investigate this problem, and he smiled at happiness - he discovered an ancient civilization with an unusually high level of development, buried under a multimeter layer of ash and pumice, namely the pumice stone that so effectively crowns the black walls of the Santorini caldera.

On the Santorini cape of Akrotiri Marinatos, he excavated a city with two- and three-storey houses, in which amazing frescoes are preserved, now exhibited in a special room of the Athens Archaeological Museum. The disaster occurred, as mentioned above, around 1520.g. BC, and after it, the inhabitants no longer returned to the city. The destruction of the centers of the Minoan culture in Crete also dates back to this time. Perhaps a grandiose explosion or several explosions on Santo Rin, which destroyed the summit of a large volcano, could be accompanied by earthquakes and strong waves in the sea (tsunami), as well as powerful peplo and pumicefall. The eruption essentially led to the decline of Minoan culture. On the ruins of Minoan cities subsequently, completely different tribes built their homes.

It is possible that the legends about the so-called Deukalionovy flood are also associated with this disaster. It is possible that Atlantis, this mysterious and vanished continent, mentioned by Plato, must be sought in the Aegean Sea and the legend related

About her death with the catastrophic eruption of Santorina in the middle of the XVI century. BC. This is how geological events and ancient history intertwined so closely.
Large calderas, formed in historical and prehistoric times, are known in many parts of the world. In the Cascade Mountains of the western United States, in the state of Oregon, is the most picturesque Lake Crater, which has filled a 10-kilometer caldera with a cinder cone-island in the center. After a catastrophic explosion in 1883, the caldera of the Krakatau volcano in the Sunda archipelago was formed. There are also calderas in Kamchatka, within which new lava cones have grown.

There are much smaller, flat-bottomed depressions formed as a result of single, mainly gas explosions; they are not associated with large volcanoes. Usually their diameter is hundreds of meters (rarely more); the depressions are rounded, occupied by lakes and called maaras - from the name of the Maar area in Germany. Such maars are found in the west of Germany, in the Eifel region; in the Swabian Jura in the foothills of the Alps (south of Germany), as well as in France (the hills of the Auvergne region).

Volcanoes are not only on land; there are also in the oceans and seas. Especially effective is the sudden appearance of volcanoes from the “sea depths”. So at the end of September 1957, a new volcano, Kapelyansh, appeared in a small island Faial in the Azores archipelago, which “grew” in two weeks to a height of 200 m; its diameter at the base was more than 1 km. Subsequently, this volcano was blurred by the waves.

Volcanic explosions under water at shallow depths or shallow beneath the surface of the earth, where groundwater is located, are amplified many times due to the fact that water, in contact with hot magma, instantly evaporates and is ejected in the form of powerful steam jets. Eruptions of this type are called phreatic (from the Greek. "Frear" - "well").

An eruption of this type occurred on November 14, 1963 in the Atlantic Ocean south of Iceland. It began with emissions of black tuff, ash and volcanic bombs that formed the island of Surtsey. The power of the eruption indicated that the explosions were intensified due to the contact of magma with water. But when the cone with the crater grew so much that the ocean waters penetrated it, the nature of the eruption changed, became more moderate. In the following months and years, up to 1967, more and more new underwater volcanoes appeared in this area, as if strung on a line of an invisible underwater crack. They turned into islands, which then collapsed under the influence of ocean waves and disappeared.

In Central Japan is located volcano Bandai. July 15, 1888, after a thousand years of silence, thanks to the heating of the groundwater by the heat of magma, powerful phreatic explosions occurred, and a cloud of ash and tuffs reached a height of 6 km. Subsequently, ash covered an area of ​​about 100 km 2. In the 90s. XIX century. a large caldera formed on it, at the edges of which new volcanoes later grew.

Volcanic deposits tell us about the nature of the eruptions of distant eras. In many parts of the world, huge covers of the so-called rhyolites were discovered, i.e. volcanic rocks with a silica content of 65 to 75%. Rhyolite deposits hundreds of meters thick occupy hundreds and thousands of square kilometers. Often they occur in large depressions that form above the partially empty magma chamber and resemble calderas. During eruption, these volcanic rocks behave like liquid lava, flooding And smoothing out uneven terrain. They consist of debris; under a microscope, they are usually clearly visible ash flyers, acute-angled fragments of crystals and pumice stones, closely welded together, as if welded to each other. According to all the laws of geology, such a volcanic rock must be very viscous and unable to spread to the sides of the centers of eruptions; however, in reality everything was different.

The history of the study of such volcanic rocks, called ignimbrites (from the Latin. Ignis - "fire", imber - "rain"), is very long and confusing. But only in the 60s. The XX century was the idea that they are formed from ash streams, i.e. from the mass of volcanic ash, which does not rise when it explodes up above the vent of a volcano, but as if flowing over a crater and like a liquid rushing down even along a gentle slope. In essence, it should be a heavy scorching cloud of hot ash, saturated with gas, the release of which supports the particles of ash as it were; air cushion. Such ash streams can travel tens of kilometers from the place of their eruption. After the end of the movement, the smallest debris under the influence of still high temperature and its own weight begin to sinter with each other, forming a dense volcanic rock.

The eruptions of these ash flows were not observed during the existence of human civilization, so volcanologists can only guess how they occurred.

Developments

There are about 1500 volcanoes on Earth that can be activated at any time. They form when molten rock, called magma, rises to the surface of the earth and breaks through its thin layers. Flows of magma can remain underground for hundreds of years and then abruptly escape to the surface. Below you can find some interesting facts about volcanoes.

1. Volcanic pumice stone   - This is the only volcanic stone that floats on the surface of the water. It is usually gray in color, with hollow holes that are formed when hot gases leave the stone when it cools.

2. Most huge volcanoes   called supervolcanoes. Their eruptions can lead to horrific effects: fire rain thousands of miles from the volcano itself, global climate change due to ash in the atmosphere. Usually such volcanoes erupt several times in 100,000 years. One of them is located in Yellowstone National Park, and scientists say that it may be ready for the next eruption.

3. Largest eruption   happened on the Indonesian island of Sumbawa: it was Tambor volcano. During the eruption killed 100,000 people. It is believed that Indonesia has the largest number of historically active volcanoes - 76.

4. Most of the volcanoes   appear at the edges of tectonic plates that form the surface of the earth. But some volcanoes, like Yellowstone, are located in other hot spots, where magma erupts from the depths.

5. In Iceland, the land of fire and ice, there is the largest number of volcanoes   in the mid oceanic Atlantic ridge. The recent explosion of Eyyafyatlayokutlya pales in comparison with the eruption of Scaptar, which destroyed the food reserves of the island, and caused the famine that caused the death of a fifth of the population.

6. The eruption of the volcano Pinatubo in the Philippines in 1991 led to more severe consequences.   He threw 22 million tons of sulfur dioxide, which encircled the entire planet, and led to a decrease in temperature by 0.5 degrees.

7. Volcanoes can grow:   when lava and ash are collected, they add meters to the surface of the volcano.

8. Volcanoes can be extinct:   they get this name if scientists are sure that there will be no more eruptions. Those volcanoes whose activity has subsided only for a while are called sleeping.

9. Sometimes during volcanic eruptions. the walls holding back magma are destroyed,   and a giant crater is formed, called the caldera.

10. The largest volcano on earth - Hawaiian Mauna Loa. Being one of the five volcanoes of the island, it rises 4000 meters above sea level.

11. Volcanic eruptions make sunsets more colorful:   orange and coral shades appear. This is due to the fact that small particles of ash scatter the sun's rays.