Volcanic eruption from space (14 photos). When did the most famous volcanic eruptions occur?

Chaiten is an active volcano in Chile
The height above sea level is 1122 m. The volcano's caldera is about 3 km in diameter, and there are several crater lakes at its bottom. The volcano was inactive for 9400-9500 years, until a major eruption began on May 2, 2008, with ejecta reaching 30 km in height. On May 6, the lava reached the village, and almost the entire population within a radius of 50 km was evacuated. (NASA Photo):

Volcano Sarycheva, Russia
Sarychev Volcano is an active stratovolcano on the island of Matua in the Great Kuril Ridge; one of the most active volcanoes of the Kuril Islands. The early stages of the 2009 eruption were recorded on June 12 from the International Space Station. (NASA Photo):

Klyuchevskaya Sopka, Russia
Klyuchevskaya Sopka (Klyuchevskoy volcano) is an active stratovolcano in the east of Kamchatka. With a height of 4,850 m, it is the highest active volcano on the Eurasian continent. The volcano is approximately 7,000 years old. (NASA Photo):

Volcano Klyuchevskaya Sopka. Also see the article “Volcanoes of Kamchatka”. (NASA Photo):

Pavlova Volcano, Alaska
Pavlova Volcano is an active stratovolcano near the southern tip of the Alaska Peninsula. The diameter of the volcano is approximately 7 km. It is one of the most active volcanoes in Alaska, with more than 40 historical eruptions. The last major volcanic eruption occurred in 2013. (NASA Photo | ISS Crew Earth Observations):

Puyehue, Chile
Puyehue is an active volcano in southern Chile. The height above sea level of the peak is 2,236 m. On June 4, 2011, several small tremors occurred in the area of the volcano, and in the evening an eruption began. A huge column of smoke and ash rose above the Puyehue volcano. A cloud of volcanic ash moves with the wind towards Argentina. According to the country's National Geology and Mining Service, the volcano emitted an ash column up to 10 km high. (NASA Photo | GSFC | Jeff Schmaltz | MODIS Land Rapid Response Team):

Eruption of Eyjafjallajokull volcano, Iceland
The eruption of a volcano near the Eyjafjallajökull glacier in Iceland began on the night of March 20/21, 2010. The main consequence of the eruption was the release of a cloud of volcanic ash, which disrupted air traffic in Northern Europe. (NASA Photo | GSFC | Jeff Schmaltz | MODIS Land Rapid Response Team):

Volcano Nyiragongo, Congo
Since 1882, 34 eruptions have been recorded; At the same time, it also happened that volcanic activity continued continuously for many years. The main crater of the volcano is 250 meters deep and 2 km wide; a lava lake sometimes forms in it. One of Nyiragongo's most powerful eruptions occurred in 1977; then several hundred people died from the fiery streams. (NASA Photo):

Shin-Moedake Volcano, Japan
Following a powerful earthquake, the Shin-Moedake volcano awoke in Japan. It is located in the southwest of the country - on the island of Kyushu. The volcano threw piles of stones into the sky, and a giant ash cloud formed over the mountain. (NASA Photo | Jeff Schmaltz | MODIS Rapid Response Team):

Volcano Merapi, Indonesia
Merapi is the largest active volcano in Indonesia, located on the island of Java near the city of Yogyakarta. Height 2914 meters. Major eruptions occur on average every 7 years. One of the most destructive eruptions was recorded in 1673, when several cities and many villages at the foot of the volcano were destroyed. . (NASA Photo):

In this lesson we will learn what volcanoes are, how they are formed, we will get acquainted with the types of volcanoes and their internal structure.

Topic: Earth

Volcanism- a set of phenomena caused by the penetration of magma from the depths of the Earth to its surface.

The word "volcano" comes from the name of one of the ancient Roman gods - the god of fire and blacksmithing - Vulcan. The ancient Romans believed that this god had a forge underground. As Vulcan begins to work in his forge, smoke and flames erupt from the crater. In honor of this god, the Romans named the island and the mountain on the island in the Tyrrhenian Sea - Vulcano. And later all fire-breathing mountains began to be called volcanoes.

The globe is structured in such a way that under the solid crust there is a layer of molten rocks (magma), and under great pressure. When cracks appear in the Earth's crust (and hills form on the earth's surface in this place), the magma under pressure in them rushes and comes to the surface of the earth, breaking up into hot lava (500-1200 ° C), caustic volcanic gases and ash. The spreading lava hardens, and the volcanic mountain increases in size.

The resulting volcano becomes a vulnerable place in the earth’s crust; even after the end of the eruption, inside it (in the crater) gases constantly escape from the bowels of the earth to the surface (the volcano “smokes”), and with any slightest shifts or shocks in the earth’s crust, such a “dormant” volcano can wake up any time. Sometimes a volcano awakens without obvious reasons. Such volcanoes are called active.

Rice. 2. The structure of the volcano ()

Volcano crater- a cup-shaped or funnel-shaped depression on the top or slope of a volcanic cone. The diameter of the crater can be from tens of meters to several kilometers and the depth from several meters to hundreds of meters. At the bottom of the crater there are one or more vents through which lava and other volcanic products rise from the magma chamber through the outlet channel to the surface. Sometimes the crater floor is covered by a lava lake or a small newly formed volcanic cone.

Volcano mouth- a vertical or almost vertical channel connecting the center of a volcano with the surface of the earth, where the vent ends in a crater. The shape of the vents of lava volcanoes is close to cylindrical.

Magma hotspot- a place under the earth's crust where magma collects.

Lava- erupted magma.

Types of volcanoes (according to the degree of their activity).

Active - which erupt, and information about this in the memory of mankind. There are 800 of them.

Extinct - no information about the eruption has been preserved.

Those who have fallen asleep are those who have gone out and suddenly begin to act.

According to their shape, volcanoes are divided into conical and panel.

The slopes of the conical volcano are steep, the lava is thick, viscous, and cools quite quickly. The mountain has the shape of a cone.

Rice. 3. Conical volcano ()

The slopes of a shield volcano are gentle, very hot and liquid lava spreads quickly over considerable distances and cools slowly.

Rice. 4. Shield volcano ()

A geyser is a source that periodically releases a fountain of hot water and steam. Geysers are one of the manifestations of the later stages of volcanism and are common in areas of modern volcanic activity.

A mud volcano is a geological formation that is a hole or depression on the surface of the earth, or a cone-shaped elevation with a crater, from which mud masses and gases, often accompanied by water and oil, constantly or periodically erupt onto the surface of the Earth.

Rice. 6. Mud volcano ()

- a lump or piece of lava thrown out during a volcanic eruption in a liquid or plastic state from a vent and obtained a specific shape when squeezed out, during flight and solidification in air.

Rice. 7. Volcanic bomb ()

An underwater volcano is a type of volcano. These volcanoes are located on the ocean floor.

Most modern volcanoes are located within three main volcanic belts: Pacific, Mediterranean-Indonesian and Atlantic. As evidenced by the results of studying the geological past of our planet, underwater volcanoes are significantly larger than volcanoes on land in terms of their scale and volume of ejection products coming from the bowels of the Earth. Scientists believe that this is the main source of tsunamis on Earth.

Rice. 8. Underwater volcano ()

Klyuchevskaya Sopka (Klyuchevskoy volcano) is an active stratovolcano in the east of Kamchatka. With a height of 4850 m, it is the highest active volcano on the Eurasian continent. The age of the volcano is approximately 7000 years.

Rice. 9. Volcano Klyuchevskaya Sopka ()

1. Melchakov L.F., Skatnik M.N. Natural history: textbook. for 3.5 grades avg. school - 8th ed. - M.: Education, 1992. - 240 pp.: ill.

2. Bakhchieva O.A., Klyuchnikova N.M., Pyatunina S.K. and others. Natural history 5. - M.: Educational literature.

3. Eskov K.Yu. and others. Natural history 5 / Ed. Vakhrusheva A.A. - M.: Balass.

3. The most famous volcanoes on Earth ().

1. Tell us about the structure of the volcano.

2. How are volcanoes formed?

3. How is lava different from magma?

4. * Prepare a short report about one of the volcanoes of our country.

I always listened with bated breath about what a volcano is when I sat in life safety lessons. It seemed to me that I would never be able to see him live. When I came to the Philippines, I decided not to miss this once-in-a-lifetime opportunity. Now you will find out everything.

What is a volcano

The volcano is geological formation, which is located on the surface of the earth's crust. He sometimes erupts pyroclastic flows, including ash and rocks, as well as volcanic gas and lava.

Now I'll tell you about volcano classifications, which is accepted in our time. They are:

active;
sleeping;
extinct.

An active volcano erupts periodically, which allows us to find out the mechanisms that lead to this. Scientists who observe this process receive important information related to this formidable phenomenon.

A volcano that is dormant is called not valid at the moment, but he can wake up at any time.

Extinct were once active, but they will not cause trouble in the future. They say that such volcanoes will never erupt.

Why does a volcano erupt?

Planet Earth consists of a single piece of stone, which has its own structure. On top is the lithosphere, which is also called the “hard shell”. Its thickness is equal to only one percent of the radius of the globe. Below it is the mantle, where the temperature is so high that it is always in a liquid state, and in its center there is a solid core. To be honest, I can’t even imagine how hot it is there.

Because lithospheric plates are always in motion, then this leads to emergence of a magma chamber. If they break out to the surface of the earth's crust, the volcano will begin to erupt.

Magma gradually rises and accumulates in places called hotbeds. They become those spaces where there are faults in the earth's crust. First, magma occupies the free space located in the source, and then begins to rise through cracks in the earth’s crust. Thin sections of the earth's crust are eroded during this process. Exactly This is how volcanoes erupt.

Where can you see the volcano?

I was very lucky to see this miracle with my own eyes when I was on vacation in the Philippines. I had excursion to the volcano, which is called Pinatubo. You need to take a plane from Manila to get there. In its crater there is a beautiful lake, where I and other tourists had a wonderful swim. You can rent a boat to see the lava remains, which were preserved from the previous eruption.

VOLCANOES
separate elevations above channels and cracks in the earth's crust, through which eruption products are brought to the surface from deep magma chambers. Volcanoes usually have the shape of a cone with a summit crater (from several to hundreds of meters deep and up to 1.5 km in diameter). During eruptions, a volcanic structure sometimes collapses with the formation of a caldera - a large depression with a diameter of up to 16 km and a depth of up to 1000 m. As the magma rises, the external pressure weakens, associated gases and liquid products escape to the surface and a volcanic eruption occurs. If ancient rocks, and not magma, are brought to the surface, and the gases are dominated by water vapor formed when groundwater is heated, then such an eruption is called phreatic.

MAIN TYPES OF VOLCANOES The extrusive (lava) dome (left) has a rounded shape and steep slopes cut by deep grooves. A plug of frozen lava may form in the crater of a volcano, which prevents the release of gases, which subsequently leads to an explosion and destruction of the dome. The steeply inclined pyroclastic cone (right) is composed of alternating layers of ash and slag.

Active volcanoes include those that erupted in historical times or showed other signs of activity (emission of gases and steam, etc.). Some scientists consider active volcanoes that are reliably known to have erupted within the last 10 thousand years. For example, the Arenal volcano in Costa Rica should be considered active, since volcanic ash was discovered during archaeological excavations of a prehistoric site in this area, although for the first time in human memory its eruption occurred in 1968, and before that no signs of activity appeared. see also VOLCANISM.

Volcanoes are known not only on Earth. Images taken from spacecraft reveal huge ancient craters on Mars and many active volcanoes on Io, a moon of Jupiter.
VOLCANIC PRODUCTS
Lava is magma that flows onto the earth's surface during eruptions and then hardens. Lava may erupt from the main summit crater, a side crater on the side of the volcano, or from fissures associated with a volcanic chamber. It flows down the slope as a lava flow. In some cases, lava outpourings occur in rift zones of enormous extent. For example, in Iceland in 1783, within the chain of Laki craters, stretching along a tectonic fault for a distance of approx. 20 km, there was an outpouring of VOLCANA 12.5 km3 of lava, distributed over an area of VOLCANA 570 km2.

Composition of lava. The hard rocks formed when lava cools contain mainly silicon dioxide, oxides of aluminum, iron, magnesium, calcium, sodium, potassium, titanium and water. Typically, lavas contain more than one percent of each of these components, and many other elements are present in smaller quantities.
There are many types of volcanic rocks, varying in chemical composition. Most often there are four types, the membership of which is determined by the content of silicon dioxide in the rock: basalt - 48-53%, andesite - 54-62%, dacite - 63-70%, rhyolite - 70-76% (see table). Rocks that contain less silicon dioxide contain large amounts of magnesium and iron. When lava cools, a significant part of the melt forms volcanic glass, in the mass of which individual microscopic crystals are found. The exception is the so-called phenocrystals are large crystals formed in magma in the depths of the Earth and brought to the surface by a flow of liquid lava. Most often, phenocrysts are represented by feldspars, olivine, pyroxene and quartz. Rocks containing phenocrysts are usually called porphyrites. The color of volcanic glass depends on the amount of iron present in it: the more iron, the darker it is. Thus, even without chemical analysis, one can guess that a light-colored rock is rhyolite or dacite, a dark-colored rock is basalt, and a gray rock is andesite. The type of rock is determined by the minerals visible in the rock. For example, olivine, a mineral containing iron and magnesium, is characteristic of basalts, and quartz is characteristic of rhyolites. As the magma rises to the surface, the released gases form tiny bubbles with a diameter often up to 1.5 mm, less often up to 2.5 cm. They are stored in the solidified rock. This is how bubbly lavas are formed. Depending on the chemical composition of lavas, they vary in viscosity, or fluidity. With a high content of silicon dioxide (silica), lava is characterized by high viscosity. The viscosity of magma and lava largely determines the nature of the eruption and the type of volcanic products. Liquid basaltic lavas with low silica content form extensive lava flows more than 100 km long (for example, one lava flow in Iceland is known to stretch for 145 km). The thickness of lava flows is usually from 3 to 15 m. More liquid lavas form thinner flows. Flows 3-5 m thick are common in Hawaii. When the surface of a basalt flow begins to solidify, its interior may remain liquid, continuing to flow and leaving behind an elongated cavity, or lava tunnel. For example, on the island of Lanzarote (Canary Islands) a large lava tunnel can be traced for 5 km. The surface of a lava flow can be smooth and wavy (in Hawaii, such lava is called pahoehoe) or uneven (aa-lava). Hot lava, which is highly fluid, can move at speeds of more than 35 km/h, but more often its speed does not exceed several meters per hour. In a slow-moving flow, pieces of the solidified upper crust may fall off and be covered by lava; As a result, a zone enriched with debris is formed in the near-bottom part. When lava hardens, columnar units (multifaceted vertical columns with a diameter of several centimeters to 3 m) or fracturing perpendicular to the cooling surface are sometimes formed. When lava flows into a crater or caldera, a lava lake forms and cools over time. For example, such a lake was formed in one of the craters of the Kilauea volcano on the island of Hawaii during the eruptions of 1967-1968, when lava entered this crater at a speed of 1.1 * 10 6 m3/h (part of the lava subsequently returned to the crater of the volcano). In neighboring craters, within 6 months the thickness of the crust of solidified lava on lava lakes reached 6.4 m. Domes, maars and tuff rings. Very viscous lava (most often of dacite composition) during eruptions through the main crater or side cracks does not form flows, but a dome with a diameter of up to 1.5 km and a height of up to 600 m. For example, such a dome was formed in the crater of Mount St. Helens (USA) after an exceptionally strong eruption in May 1980. The pressure under the dome can build up, and weeks, months or years later it can be destroyed by the next eruption. In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks protrude above its surface - blocks or spiers of solidified lava, often tens and hundreds of meters high. After the catastrophic eruption of the Montagne Pelee volcano on the island of Martinique in 1902, a lava spire formed in the crater, which grew by 9 m per day and as a result reached a height of 250 m, and collapsed a year later. On the Usu volcano on Hokkaido (Japan) in 1942, during the first three months after the eruption, the Showa-Shinzan lava dome grew by 200 m. The viscous lava that composed it made its way through the thickness of the sediments formed earlier. Maar is a volcanic crater formed during an explosive eruption (most often with high humidity of the rocks) without the outpouring of lava. A ring shaft of debris ejected by the explosion is not formed, unlike tuff rings - also explosion craters, which are usually surrounded by rings of debris products. The debris released into the air during an eruption is called tephra, or pyroclastic debris. The deposits they form are also called. Pyroclastic rock fragments come in different sizes. The largest of them are volcanic blocks. If the products are so liquid at the time of release that they solidify and take shape while still in the air, then the so-called. volcanic bombs. Material smaller than 0.4 cm in size is classified as ashes, and fragments ranging in size from a pea to a walnut are classified as lapilli. Hardened deposits composed of lapilli are called lapilli tuff. There are several types of tephra, differing in color and porosity. Light-colored, porous, non-sinking tephra is called pumice. Dark vesicular tephra, consisting of lapilli-sized units, is called volcanic scoria. Pieces of liquid lava that remain in the air for a short time and do not have time to completely harden form splashes, often forming small spatter cones near the outlets of lava flows. If this spatter sinteres, the resulting pyroclastic deposits are called agglutinates. A mixture of very fine pyroclastic material and heated gas suspended in the air, ejected from a crater or fissures during an eruption and moving above the ground surface at a speed of 100 km/h VOLCANOES, forms ash flows. They spread over many kilometers, sometimes crossing waters and hills. These formations are also known as scorching clouds; they are so hot that they glow at night. Ash flows may also contain large debris, incl. and pieces of rock torn out from the walls of a volcano. Most often, scorching clouds are formed when a column of ash and gases ejected vertically from a vent collapses. Under the influence of gravity, counteracting the pressure of the erupting gases, the edges of the column begin to settle and descend down the slope of the volcano in the form of a hot avalanche. In some cases, scorching clouds appear along the periphery of a volcanic dome or at the base of a volcanic obelisk. It is also possible for them to be released from the ring cracks around the caldera. Ash flow deposits form the ignimbrite volcanic rock. These flows transport both small and large fragments of pumice. If ignimbrites are deposited thick enough, the internal horizons can be so hot that the pumice fragments melt to form sintered ignimbrite, or sintered tuff. As the rock cools, columnar formations may form in its interior, which are less clear-cut and larger than similar structures in lava flows. Small hills consisting of ash and blocks of various sizes are formed as a result of a directed volcanic explosion (as, for example, during the eruptions of Mount St. Helens in 1980 and Bezymyanny in Kamchatka in 1965).
Directed volcanic explosions are a fairly rare phenomenon. The deposits they create are easily confused with the clastic deposits with which they are often adjacent. For example, during the eruption of Mount St. Helens, an avalanche of rubble occurred immediately before the directed explosion.
Underwater volcanic eruptions. If there is a body of water above the volcanic source, during the eruption the pyroclastic material is saturated with water and spreads around the source. Deposits of this type, first described in the Philippines, were formed as a result of the 1968 eruption of Taal Volcano, located at the bottom of the lake; they are often represented by thin wavy layers of pumice.
We sat down. Volcanic eruptions may be associated with mudflows or mud-stone flows. They are sometimes called lahars (originally described in Indonesia). The formation of lahars is not part of the volcanic process, but one of its consequences. On the slopes of active volcanoes, loose material (ash, lapilli, volcanic debris) accumulates in abundance, ejected from volcanoes or falling from scorching clouds. This material is easily involved in the movement of water after rains, when ice and snow melt on the slopes of volcanoes or when the sides of crater lakes break through. Mud streams rush down the riverbeds at great speed. During the eruption of the Ruiz volcano in Colombia in November 1985, mudflows moving at speeds above 40 km/h carried more than 40 million m3 of debris onto the foothill plain. At the same time, the city of Armero was destroyed and approx. 20 thousand people. Most often, such mudflows occur during an eruption or immediately after it. This is explained by the fact that during eruptions, accompanied by the release of thermal energy, snow and ice melt, crater lakes break through and drain, and slope stability is disrupted. The gases released from the magma before and after the eruption look like white streams of water vapor. When tephra is mixed with them during an eruption, the emissions become gray or black. Low gas emissions in volcanic areas can continue for years. Such releases of hot gases and vapors through openings at the bottom of the crater or the slopes of the volcano, as well as on the surface of lava or ash flows, are called fumaroles. Special types of fumaroles include solfataras, containing sulfur compounds, and mofets, in which carbon dioxide predominates. The temperature of fumarole gases is close to the temperature of magma and can reach 800 ° C, but it can also drop to the boiling point of water (VOLCANOES 100 ° C), the vapors of which serve as the main component of fumaroles. Fumarole gases originate both in shallow near-surface horizons and at great depths in hot rocks. In 1912, as a result of the eruption of the Novarupta volcano in Alaska, the famous Valley of Ten Thousand Smokes was formed, where on the surface of volcanic emissions an area of approx. 120 km2, many high-temperature fumaroles arose. Currently, only a few fumaroles with fairly low temperatures are active in the Valley. Sometimes white streams of steam rise from the surface of a lava flow that has not yet cooled; most often it is rainwater heated by contact with a hot lava flow.
Chemical composition of volcanic gases. The gas released from volcanoes consists of 50-85% water vapor. Over 10% is carbon dioxide, approx. 5% is sulfur dioxide, 2-5% is hydrogen chloride and 0.02-0.05% is hydrogen fluoride. Hydrogen sulfide and sulfur gas are usually found in small quantities. Sometimes hydrogen, methane and carbon monoxide are present, as well as small amounts of various metals. Ammonia was found in gas emissions from the surface of a lava flow covered with vegetation. Tsunamis are huge sea waves, associated mainly with underwater earthquakes, but sometimes generated by volcanic eruptions on the ocean floor, which can cause the formation of several waves, occurring at intervals of several minutes to several hours. The eruption of the Krakatoa volcano on August 26, 1883 and the subsequent collapse of its caldera was accompanied by a tsunami over 30 m high, causing numerous casualties on the coasts of Java and Sumatra.
TYPES OF ERUPTIONS
Products arriving at the surface during volcanic eruptions vary significantly in composition and volume. The eruptions themselves vary in intensity and duration. The most commonly used classification of eruption types is based on these characteristics. But it happens that the nature of eruptions changes from one event to another, and sometimes during the same eruption. The Plinian type is named after the Roman scientist Pliny the Elder, who died in the eruption of Vesuvius in 79 AD. Eruptions of this type are characterized by the greatest intensity (a large amount of ash is thrown into the atmosphere to a height of 20-50 km) and occur continuously for several hours and even days. Pumice of dacite or rhyolite composition is formed from viscous lava. Products of volcanic emissions cover a large area, and their volume ranges from 0.1 to 50 km3 or more. An eruption may result in the collapse of a volcanic structure and the formation of a caldera. Sometimes an eruption produces scorching clouds, but lava flows are not always formed. Fine ash is carried over long distances by strong winds at speeds of up to 100 km/h. Ash emitted in 1932 by the Cerro Azul volcano in Chile was discovered 3,000 km away. The Plinian type also includes the strong eruption of Mount St. Helens (Washington, USA) on May 18, 1980, when the height of the eruptive column reached 6000 m. During 10 hours of continuous eruption, approx. 0.1 km3 of tephra and more than 2.35 tons of sulfur dioxide. During the eruption of Krakatoa (Indonesia) in 1883, the volume of tephra was 18 km3, and the ash cloud rose to a height of 80 km. The main phase of this eruption lasted approximately 18 hours. An analysis of the 25 most violent historical eruptions shows that the quiet periods preceding Plinian eruptions averaged 865 years.
Peleian type. Eruptions of this type are characterized by very viscous lava, which hardens before leaving the vent with the formation of one or several extrusive domes, the squeezing of the obelisk above it, and the emission of scorching clouds. The 1902 eruption of the Montagne-Pelée volcano on the island of Martinique belonged to this type.
Vulcan type. Eruptions of this type (the name comes from the island of Vulcano in the Mediterranean Sea) are short-lived - from a few minutes to a few hours, but recur every few days or weeks for several months. The height of the eruptive column reaches 20 km. The magma is fluid, basaltic or andesitic in composition. The formation of lava flows is typical, and ash emissions and extrusive domes do not always occur. Volcanic structures are built from lava and pyroclastic material (stratovolcanoes). The volume of such volcanic structures is quite large - from 10 to 100 km3. The age of stratovolcanoes ranges from 10,000 to 100,000 years. The frequency of eruptions of individual volcanoes has not been established. This type includes the Fuego volcano in Guatemala, which erupts every few years; basaltic ash emissions sometimes reach the stratosphere, and their volume during one of the eruptions was 0.1 km3.
Strombolian type. This type is named after the volcanic island. Stromboli in the Mediterranean Sea. The Strombolian eruption is characterized by continuous eruptive activity over several months or even years and a not very high height of the eruptive column (rarely above 10 km). There are known cases when lava was splashed within a 300 m radius of VOLCANA, but almost all of it returned to the crater. Lava flows are typical. Ash covers have a smaller area than during Vulcan-type eruptions. The composition of eruption products is usually basaltic, less often - andesitic. The Stromboli volcano has been active for more than 400 years, the Yasur volcano on Tanna Island (Vanuatu) in the Pacific Ocean has been active for more than 200 years. The structure of the vents and the nature of the eruptions of these volcanoes are very similar. Some Strombolian-type eruptions produce cinder cones composed of basaltic or, less commonly, andesitic scoria. The diameter of the cinder cone at the base ranges from 0.25 to 2.5 km, the average height is 170 m. Cinder cones are usually formed during a single eruption, and volcanoes are called monogenic. For example, during the eruption of the Paricutin volcano (Mexico) during the period from the beginning of its activity on February 20, 1943 to the end on March 9, 1952, a cone of volcanic slag 300 m high was formed, the surrounding area was covered with ash, and the lava spread over an area of 18 km2 and destroyed several populated areas .
Hawaiian type eruptions are characterized by outpourings of liquid basaltic lava. Fountains of lava ejected from cracks or faults can reach a height of 1000 and sometimes 2000 m. Few pyroclastic products are ejected; most of them are splashes falling near the source of the eruption. Lavas flow from fissures, holes (vents) located along a fissure, or craters, sometimes containing lava lakes. When there is only one vent, the lava spreads radially, forming a shield volcano with very gentle slopes - up to 10° (stratovolcanoes have cinder cones and slope steepness of about 30°). Shield volcanoes are composed of layers of relatively thin lava flows and do not contain ash (for example, the famous volcanoes on the island of Hawaii - Mauna Loa and Kilauea). The first descriptions of volcanoes of this type relate to volcanoes in Iceland (for example, the Krabla volcano in northern Iceland, located in the rift zone). The eruption of the Fournaise volcano on Reunion Island in the Indian Ocean is very close to the Hawaiian type.
Other types of eruptions. Other types of eruptions are known, but they are much less common. An example is the underwater eruption of the Surtsey volcano in Iceland in 1965, which resulted in the formation of an island.
SPREAD OF VOLCANOES
The distribution of volcanoes across the surface of the globe is best explained by the theory of plate tectonics, according to which the Earth's surface consists of a mosaic of moving lithospheric plates. When they move in the opposite direction, a collision occurs, and one of the plates sinks (moves) under the other in the so-called. subduction zone, where earthquake epicenters are located. If the plates move apart, a rift zone forms between them. Manifestations of volcanism are associated with these two situations. Subduction zone volcanoes are located along the boundaries of subducting plates. The oceanic plates that form the floor of the Pacific Ocean are known to subduct beneath continents and island arcs. Subduction areas are marked in the topography of the ocean floor by deep-sea trenches parallel to the coast. It is believed that in zones of plate subduction at depths of 100-150 km, magma is formed, and when it rises to the surface, volcanic eruptions occur. Since the plunging angle of the plate is often close to 45°, volcanoes are located between the land and the deep-sea trench at a distance of approximately 100-150 km from the axis of the latter and in plan form a volcanic arc that follows the contours of the trench and coastline. There is sometimes talk of a "ring of fire" of volcanoes around the Pacific Ocean. However, this ring is intermittent (as, for example, in the region of central and southern California), because subduction does not occur everywhere.

THE GREATEST MOUNTAIN OF JAPAN FUJIYAMA (3776 m above sea level) is the cone of a “dormant” volcano since 1708, covered with snow for most of the year.

Rift zone volcanoes exist in the axial part of the Mid-Atlantic Ridge and along the East African Rift System. There are volcanoes associated with “hot spots” located inside plates in places where mantle plumes (hot magma rich in gases) rise to the surface, for example, the volcanoes of the Hawaiian Islands. It is believed that the chain of these islands, elongated in a westerly direction, was formed during the westward drift of the Pacific Plate while moving over a “hot spot.” Now this “hot spot” is located under the active volcanoes of the island of Hawaii. Towards the west of this island, the age of the volcanoes gradually increases. Plate tectonics determines not only the location of volcanoes, but also the type of volcanic activity. The Hawaiian type of eruptions predominates in areas of “hot spots” (Fournaise volcano on Reunion Island) and in rift zones. Plinian, Peleian and Vulcanian types are characteristic of subduction zones. There are also known exceptions, for example, the Strombolian type is observed in various geodynamic conditions. Volcanic activity: recurrence and spatial patterns. Approximately 60 volcanoes erupt annually, and about a third of them erupted in the previous year. There is information about 627 volcanoes that have erupted over the past 10 thousand years, and about 530 in historical time, and 80% of them are confined to subduction zones. The greatest volcanic activity is observed in the Kamchatka and Central American regions, with quieter zones in the Cascade Range, the South Sandwich Islands and southern Chile.
Volcanoes and climate. It is believed that after volcanic eruptions, the average temperature of the Earth’s atmosphere drops by several degrees due to the release of tiny particles (less than 0.001 mm) in the form of aerosols and volcanic dust (while sulfate aerosols and fine dust enter the stratosphere during eruptions) and remains so for 1 -2 years. In all likelihood, such a decrease in temperature was observed after the eruption of Mount Agung on Bali (Indonesia) in 1962.
VOLCANIC HAZARD
Volcanic eruptions threaten human lives and cause material damage. After 1600, as a result of eruptions and associated mudflows and tsunamis, 168 thousand people died, and 95 thousand people became victims of disease and hunger that arose after the eruptions. As a result of the eruption of the Montagne Pelee volcano in 1902, 30 thousand people died. As a result of mudflows from the Ruiz volcano in Colombia in 1985, 20 thousand people died. The eruption of the Krakatoa volcano in 1883 led to the formation of a tsunami that killed 36 thousand people. The nature of the danger depends on the action of various factors. Lava flows destroy buildings, block roads and agricultural lands, which are excluded from economic use for many centuries until new soil is formed as a result of weathering processes. The rate of weathering depends on the amount of precipitation, temperature, runoff conditions and the nature of the surface. For example, on the wetter slopes of Mount Etna in Italy, agriculture on lava flows resumed only 300 years after the eruption. As a result of volcanic eruptions, thick layers of ash accumulate on the roofs of buildings, which threatens their collapse. The entry of tiny ash particles into the lungs leads to the death of livestock. Ash suspended in the air poses a danger to road and air transport. Airports are often closed during ashfalls. Ash flows, which are a hot mixture of suspended dispersed material and volcanic gases, move at high speed. As a result, people, animals, plants die from burns and suffocation and houses are destroyed. The ancient Roman cities of Pompeii and Herculaneum were affected by such flows and were covered with ash during the eruption of Mount Vesuvius. Volcanic gases released by volcanoes of any type rise into the atmosphere and usually cause no harm, but some of them may return to the earth's surface in the form of acid rain. Sometimes the terrain allows volcanic gases (sulfur dioxide, hydrogen chloride or carbon dioxide) to spread near the surface of the earth, destroying vegetation or polluting the air in concentrations exceeding permissible limits. Volcanic gases can also cause indirect harm. Thus, the fluorine compounds contained in them are captured by ash particles, and when the latter fall onto the earth's surface, they contaminate pastures and water bodies, causing severe diseases in livestock. In the same way, open sources of water supply to the population can be contaminated. Mud-stone flows and tsunamis also cause enormous destruction.
Eruption forecast. To forecast eruptions, volcanic hazard maps are compiled showing the nature and distribution areas of products of past eruptions, and eruption precursors are monitored. Such precursors include the frequency of weak volcanic earthquakes; If usually their number does not exceed 10 in one day, then immediately before the eruption it increases to several hundred. Instrumental observations of the most minor surface deformations are carried out. The accuracy of measurements of vertical movements, recorded, for example, by laser devices, is VOLCANO 0.25 mm, horizontal - 6 mm, which makes it possible to detect a surface slope of only 1 mm per half kilometer. Data on changes in height, distance, and slope are used to identify the center of heave preceding an eruption or surface subsidence after an eruption. Before an eruption, the temperatures of the fumaroles increase, and sometimes the composition of volcanic gases and the intensity of their release change. The precursor phenomena that preceded most of the fairly fully documented eruptions are similar to each other. However, it is very difficult to predict with certainty exactly when an eruption will occur.
Volcanological observatories. To prevent a possible eruption, systematic instrumental observations are carried out in special observatories. The oldest volcanological observatory was founded in 1841-1845 on Vesuvius in Italy, then in 1912 the observatory on the Kilauea volcano on the island of Hawaii began operating and at about the same time several observatories in Japan. Monitoring of volcanoes is also carried out in the USA (including at Mount St. Helens), Indonesia at the observatory at the Merapi volcano on the island of Java, in Iceland, Russia by the Institute of Volcanology of the Russian Academy of Sciences (Kamchatka), Rabaul (Papua New Guinea), on the islands of Guadeloupe and Martinique in the West Indies, and monitoring programs have been launched in Costa Rica and Colombia.
Notification methods. Civil authorities, to whom volcanologists provide the necessary information, must warn about impending volcanic danger and take measures to reduce the consequences. The public warning system can be sound (sirens) or light (for example, on the highway at the foot of the Sakurajima volcano in Japan, flashing warning lights warn motorists about ash fall). Warning devices are also installed that are triggered by elevated concentrations of dangerous volcanic gases, such as hydrogen sulfide. Roadblocks are placed on roads in hazardous areas where an eruption is taking place. Reducing the dangers associated with volcanic eruptions. To mitigate volcanic danger, both complex engineering structures and very simple methods are used. For example, during the eruption of the Miyakejima volcano in Japan in 1985, cooling of the lava flow front with sea water was successfully used. By creating artificial gaps in the hardened lava that limited the flows on the slopes of volcanoes, it was possible to change their direction. To protect against mud-stone flows - lahars - fencing embankments and dams are used to direct the flows into a certain channel. To avoid the occurrence of lahar, the crater lake is sometimes drained using a tunnel (Kelud volcano on Java in Indonesia). In some areas, special systems are being installed to monitor thunderclouds, which could bring downpours and activate lahars. In places where eruption products fall out, various shelters and safe shelters are built.
LITERATURE
Luchitsky I.V. Fundamentals of paleovolcanology. M., 1971 Melekestsev I.V. Volcanism and relief formation. M., 1980 Vlodavets V.I. Handbook of volcanology. M., 1984 Active volcanoes of Kamchatka, vol. 1-2. M., 1991

Collier's Encyclopedia. - Open Society. 2000 .

On August 24, 79, people looked at their patron in horror and could not understand why they had angered the gods so much. How did it happen that their protector suddenly began to spew out flames that spread across the ground and destroyed everything in its path? The residents of Pompeii already knew: unexpectedly for everyone, the volcano woke up. What it is, what volcanoes are like and why they suddenly wake up, we will look at today in this article.

What is a volcano?

A volcano is a kind of formation on the surface of the earth's crust, which from time to time is capable of erupting pyroclastic flows (a mixture of ash, gas and stones), volcanic gases, and lava. It is in zones of volcanic activity that opportunities for using geothermal energy open up.

Types of volcanoes

Scientists have adopted a classification of volcanoes into active, dormant and extinct.

Active volcanoes are those that erupt during a historical period of time. It is thanks to them that one can understand what a volcano is and the mechanisms that make it act, because direct observation of the process provides much more information than the most thorough excavations.
Dormant volcanoes are called dormant volcanoes that are currently inactive, however, there is a high probability of their awakening.
Extinct volcanoes include those that were active in the past, but today the probability of their eruption is zero.

What shapes do volcanoes come in?

If you ask a schoolchild what shape a volcano has, he will undoubtedly say that it looks like a mountain. And he will be right. The volcano actually has the shape of a cone, which was formed during its eruption.

The volcanic cone has a vent - this is a kind of outlet channel through which lava rises during an eruption. Quite often there is more than one such channel. It may have several branches that serve to bring volcanic gases to the surface. The vent always ends in a crater. It is into this that all materials are thrown out during an eruption. A curious fact is that the vent is open only during the period of volcanic activity. The rest of the time it is closed, until the next manifestation of activity.

The time during which the volcanic cone formed varies individually. It mainly depends on how much material the volcano releases during its eruption. Some require 10 thousand years to do this, others can form it in one eruption.

Sometimes the opposite processes also happen. During an eruption, the volcanic cone collapses, and in its place a large depression is formed - a caldera. The depth of such a depression is at least one kilometer, and the diameter can reach 16 km.

Why do volcanoes erupt?

We figured out what a volcano is, but why does it erupt?

As you know, our planet does not consist of a single piece of rock. It has its own structure. On top is a thin, hard “shell” that scientists call the lithosphere. Its thickness is only 1% of the radius of the globe. In practice, this means from 80 to 20 kilometers, depending on whether it is land or the bottom of the oceans.

Beneath the lithosphere is a layer of mantle. Its temperature is so high that the mantle is constantly in a liquid, or rather viscous, state. At the center is the solid core of the earth.

As a result of the fact that lithospheric plates are in constant motion, magma chambers can arise. When they break out to the surface of the earth's crust, a volcanic eruption begins.

What is magma?

Here, it is probably necessary to explain what magma is and what chambers it can form.

Being in constant motion (albeit invisible to the naked human eye), lithospheric plates can collide or creep onto each other. Most often, slabs whose dimensions are larger “win” those whose thickness is smaller. Therefore, the latter are forced to plunge into the boiling mantle, the temperature of which can reach several thousand degrees. Naturally, at this temperature the plate begins to melt. This molten rock with gases and water vapor is called magma. Its structure is more fluid than the mantle, and also lighter.

How does a volcano erupt?

Thanks to these structural features of magma, it begins to slowly rise and accumulate in places called foci. Most often, such centers become places where the earth's crust breaks.

Gradually, magma occupies all the free space of the source and, for lack of any other way out, begins to rise through cracks in the earth’s crust. If magma finds a weak spot, it does not miss the opportunity to break out to the surface. In this case, thin sections of the earth's crust are broken through. This is how a volcano erupts.

Places of volcanic activity

So what places on the planet, given volcanic activity, can be considered the most dangerous? Where are the most dangerous volcanoes in the world located? Let's find out...

Merapi (Indonesia). This is the largest volcano in Indonesia, and also the most active. It does not allow local residents to forget about itself, even for one day, constantly releasing smoke from its crater. At the same time, small eruptions occur every two years. But you don’t have to wait long for big ones either: they happen once every 7-8 years.
If you want to know where volcanoes are, you should probably take a trip to Japan. This is truly a “paradise” of volcanic activity. Take, for example, Sakurajima. Since 1955, this volcano has constantly disturbed local residents. Its activity shows no sign of decreasing, and the last major eruption occurred not so long ago - in 2009. A hundred years ago, the volcano had its own island, but thanks to the lava that it erupted from itself, it was able to connect with the Osumi Peninsula.
Aso. And again Japan. This country is constantly suffering from volcanic activity, and the Aso volcano is proof of this. In 2011, an ash cloud appeared above it, the area of which was more than 100 kilometers. Since that time, scientists have constantly recorded tremors, which can indicate only one thing: the Aso volcano is ready for a new eruption.
Etna. This is the largest volcano in Italy, which is interesting because it has not only a main crater, but also many small ones located along its slope. In addition, Etna is distinguished by enviable activity - small eruptions occur every two to three months. It must be said that the Sicilians have long been accustomed to such a neighborhood, and are not afraid to populate the slopes.
Vesuvius. The legendary volcano is almost half the size of its Italian brother, but this does not prevent it from setting many of its own records. For example, Vesuvius is exactly the volcano that destroyed Pompeii. However, this is not the only city that has suffered from his activities. According to scientists, Vesuvius more than 80 times destroyed cities that were not lucky enough to be close to its slopes. The last major eruption occurred in 1944.

Which volcano on the planet can be called the highest?

Among the named volcanoes there are quite a lot of record holders. But which one can bear the title “The highest volcano on the planet”?

It is necessary to take into account: when we say “the highest,” we do not mean the height of the volcano above the surrounding area. We are talking about the absolute altitude above sea level.

Thus, scientists call the Chilean Ojos del Salado the highest active volcano in the world. For a long time he was classified as sleeping. This status of the Chilean allowed the Argentinean Llullaillaco to bear the title “The highest volcano in the world.” However, in 1993, Ojos del Salado produced an ash release. After that, it was carefully examined by scientists who managed to find fumaroles (steam and gas outlets) in its crater. Thus, the Chilean changed his status, and, without knowing it, brought relief to many schoolchildren and teachers, for whom pronouncing the name Llullaillaco is not always easy.

To be fair, Ojos del Salado does not have a high volcanic cone. It rises above the surface only 2000 meters. While the relative height of the Llullaillaco volcano is almost 2.5 kilometers. However, it is not for us to argue with scientists.

The whole truth about the Yellowstone volcano

You cannot boast that you know what a volcano is if you have never heard of Yellowstone, which is located in the USA. What do we know about him?

First of all, Yellowstone is not a tall volcano, but for some reason it is called a supervolcano. What's the matter here? And why was Yellowstone discovered only in the 60s of the last century, and even then with the help of satellites?

The fact is that the Yellowstone cone collapsed after its eruption, resulting in the formation of a caldera. Considering its gigantic size (150 km), it is no wonder that people could not see it from Earth. But the collapse of the crater does not mean that the volcano can be reclassified as dormant.

There is still a huge chamber of magma under the Yellowstone crater. According to scientists' calculations, its temperature exceeds 800 °C. Thanks to this, many thermal springs were formed in Yellowstone, and, in addition, jets of steam, hydrogen sulfide and carbon dioxide constantly come to the surface of the earth.

Not much is known about the eruptions of this volcano. Scientists believe that there were only three of them: 2.1 million, 1.27 million and 640 thousand years ago. Considering the frequency of eruptions, we can conclude that we may witness the following. It must be said that if this really happens, the Earth will face the next Ice Age.

What troubles do volcanoes bring?

Even if we do not take into account the fact that Yellowstone can suddenly wake up, the eruptions that other volcanoes in the world can prepare for us also cannot be called harmless. They cause enormous destruction, especially if the eruption happened suddenly and there was no time to warn or evacuate the population.

The danger is not only lava, which can destroy everything in its path and cause fires. Don’t forget about toxic gases that spread over vast areas. In addition, the eruption is accompanied by emissions of ash, which can cover vast areas.

What to do if the volcano “comes to life”?

So, if you find yourself at the wrong time and in the wrong place when a volcano suddenly wakes up, what should you do in such a situation?

First of all, you need to know that the speed of the lava is not that high, only 40 km/h, so it is quite possible to escape, or rather, drive away from it. This must be done in the shortest way, that is, perpendicular to its movement. If this is not possible for some reason, you need to look for shelter on a hill. It is also necessary to take into account the likelihood of a fire, therefore, if possible, it is necessary to clear the shelter of ash and hot debris.

In open areas, a body of water can save you, although much depends on its depth and the force with which the volcano erupts. Photos taken after the eruption show that people often find themselves defenseless before such a powerful force.

If you are one of the lucky ones and your house survived the eruption, be prepared to spend at least a week there.

And most importantly, do not trust those who say that “this volcano has been sleeping for thousands of years.” As practice shows, any volcano can wake up (photos of destruction confirm this), but there is not always someone to tell about it.