Volcanic lava is called the blood of the Earth. It is an integral companion of eruptions and each volcano has its own composition, color and temperature.
1. Lava is magma that pours out of a volcanic vent during an eruption. Unlike magma, it does not contain gases, since they evaporate during explosions.
2. Lava began to be called “lava” only after the eruption of Vesuvius in 1737. The geologist Francesco Serao, who was engaged in the study of the volcano in those years, originally called it “Labes,” which in Latin means “collapse,” and later the word acquired its modern sound.
3. For different volcanoes, lava has a different composition. Most often, it is composed of basalts and is characterized by a slow flow, like batter.
Basaltic Lava on Kilauea Volcano
4. The most liquid lava, resembling water, contains potassium carbonates and is found only on.
5. In the bowels of the Yellowstone supervolcano is rhyolitic magma, which has an explosive character.
6. The most dangerous lava is corium, or lava-like fuel contained in nuclear reactors. It is an alloy of the contents of the reactor with concrete, metal parts and other debris, which is formed as a result of a nuclear crisis.
7. Despite the fact that the corium is of technical origin, its flows under the Chernobyl nuclear power plant look like chilled basalt flows.
8. The most unusual in the world is the so-called “blue lava” on the Ijen volcano in Indonesia. In fact, brightly luminous streams are not lava, but sulfur dioxide, which, when leaving the ventilation holes, becomes liquid and shines with blue light.
9. The color of the lava can determine its temperature. Yellow and bright orange is considered the hottest and has a temperature of 1000 ° C and above. Dark red is relatively cool, with temperatures from 650 to 800 ° C.
10. The only black lava is located in the Tanzanian volcano Ol-Doinho-Lengai. As mentioned above, it consists of carbonates, giving it a dark shade. The lava flows of the peak are quite cool - with a temperature of no more than 540 ° C. When cooled, they become silver, creating bizarre landscapes around the volcano.
11. On the Pacific Ring of Fire, volcanoes erupt mainly silicon lava, which has a viscous consistency and freezes in the mouth of the mountain, stopping its eruption. Subsequently, under pressure, the frozen cork is knocked out of the vent, resulting in a powerful explosion.
12. According to research, in the first days of its existence, our planet was covered with lava oceans, layered in structure.
13. When the lava flows down the slopes, it cools unevenly, so sometimes lava tubes form inside the streams. The length of these tubes can reach several kilometers, and the width inside - 14-15 meters.
Types of Volcanoes
- Hawaiian type of volcanoes. In these volcanoes, there is no significant emission of vapors and gases, their lava is liquid.
- Strombolic type of volcanoes. The lava of these volcanoes is also liquid, however they emit a lot of vapors and gases, but they do not emit ash; when cooling, the lava becomes wavy.
- Volcanoes like Vesuvius characterized by a more viscous lava, vapors, gases, volcanic ash and other solid eruption products are abundantly released. When cooling, the lava becomes clumpy.
- Peleus type of volcanoes. Very viscous lava causes strong explosions with the release of hot gases, ash and other products in the form of scorching clouds, destroying everything in its path, etc.
Hawaiian type of volcanoes
Hawaiian type volcanoes calmly and abundantly pour out only liquid lava during the eruption. These are the volcanoes of the Hawaiian Islands. Hawaiian volcanoes, the foot of which lie on the bottom of the ocean, at a depth of approximately 4600 meters, undoubtedly occurred as a result of powerful underwater eruptions. The strength of these eruptions can be judged by the fact that the absolute height of the extinct volcano Mauna Kea (that is, the "white mountain") reaches from the bottom of the ocean 8828 meters (the relative height of the volcano is 4228 meters). The most famous are Mauna Loa, otherwise “high mountain” (4168 meters), and Kilauea (1231 meters). Kilauea has a huge crater -5.6 kilometers long and 2 kilometers wide. At the bottom of it, at a depth of 300 meters, lies a seething lava lake. During eruptions, powerful lava fountains up to 280 meters high are formed on it, with a diameter of about 30 meters. Kilauea Volcano. Droplets of liquid lava thrown to such a height are pulled in the air into thin strings, called by the indigenous population “Pele hair” - the goddess of fire of the ancient inhabitants of the Hawaiian Islands. The lava flows during the Kilauea eruption sometimes reached enormous magnitude — up to 60 kilometers long, 25 kilometers wide and 10 meters thick.Strombolic type of volcanoes
Strombolic type of volcanoes emitting mainly only gaseous products. For example, the volcano Stromboli (900 meters high), on one of the Aeolian Islands (north of the Strait of Messina, between the island of Sicily and the Apennine Peninsula).
Volcano Stromboli on the island of the same name. At night, the reflection of his fire vent in a column of vapors and gases, clearly visible at a distance of up to 150 kilometers, serves as a natural beacon for sailors. Another natural lighthouse is widely known among sailors all over the world, in Central America off the coast of Salvador - the volcano Tsalko. Gently every 8 minutes, he throws a column of smoke and ash rising up to 300 meters. Against a dark tropical sky, it is effectively illuminated by a crimson gleam of lava. Volcanoes like Vesuvius
The most complete picture of the eruption is given by volcanoes of the type. A volcanic eruption is usually preceded by a strong underground rumble accompanying the shocks and tremors of earthquakes. From the cracks on the slopes of the volcano suffocating gases begin to be released. The release of gaseous products - water vapor and various gases (carbon dioxide, sulphurous, hydrochloric, hydrogen sulfide and many others) is enhanced. They are released not only through the crater, but also from fumaroles (fumaroles - a derivative of the Italian word “fumo” - smoke). Clubs of steam along with volcanic ash rise several kilometers into the atmosphere. Masses of light gray or black volcanic ash, representing the smallest pieces of frozen lava, spread thousands of kilometers. The ashes of Vesuvius, for example, reaches Constantinople and North America. Black puffs of ash cover the sun, turning a bright Day into a dark night. Strong electric stress from the friction of ash particles and vapors manifests itself in electrical discharges and thunderbolts. Vapors raised to a considerable height gather in clouds, from which instead of rain spills streams of dirt. Volcanic sand, stones of various sizes, as well as volcanic bombs — rounded pieces of lava frozen in the air — are thrown from the volcano’s vent. Finally, lava emerges from the mouth of the volcano, which rushes along the mountainside with a fiery stream.Volcano of the same type - Klyuchevskaya Sopka
This is how the picture of the eruption of this type of volcano - Klyuchevskaya Sopka, on October 6, 1737, (in more detail:), the first Russian explorer of Kamchatka acad. S.P. Krasheninnikov (1713-1755). In the Kamchatka expedition, he participated as a student of the Russian Academy of Sciences in 1737-1741.The whole mountain seemed like a hot stone. The flame, which was visible through the crevices inside, sometimes rushed down, like rivers of fire, with a terrible noise. In the grief there was heard thunder, crackle and, as if with powerful bellows, a swelling from which all the nearby places were trembling.An unforgettable picture of the eruption of the same volcano on the night of the new, 1945 gives a modern observer:
A sharp orange-yellow cone of flame, one and a half kilometers high, seemed to pierce into the clouds of gases rising by a huge mass from the crater of the volcano by about 7000 meters. Hot volcanic bombs fell from the top of the fire cone in a continuous stream. There were so many of them that they gave the impression of a fabulous fiery snowstorm.The figure shows samples of various volcanic bombs, these are lava clumps that have taken a certain shape. They acquire a rounded or spindle-shaped shape, rotating during flight.
- Spherical volcanic bomb - sample from Vesuvius;
- Trass - porous trachyte tuff - sample from Eichel, Germany;
- Spindle-shaped volcanic bomb - sample from Vesuvius;
- Lapilli - small volcanic bombs;
- The crusted volcanic bomb is a sample from southern France.
Peleus type of volcanoes
Peleus type of volcanoes presents an even more terrible picture. As a result of a terrible explosion, a significant part of the cone is suddenly sprayed in the air, blocking the impenetrable mist of sunlight. That was the eruption. The Japanese volcano Bundai-San also belongs to this type. For more than a thousand years, it was considered extinct, and suddenly in 1888 a significant part of its cone 670 meters high takes off into the air.
Volcano Bandai-san. The awakening of the volcano from long rest was terrible: a blast wave tore up trees and caused terrible destruction. Sprayed rocks in dense veil remained in the atmosphere for 8 hours, covering the sun, and a bright day gave way to a dark night ... Liquid lava was not released.Such eruptions of Peleus type volcanoes are explained the presence of very viscous lava, preventing the release of vapor and gases accumulated under it.
The rudimentary forms of volcanoes
There are, in addition to the listed types, rudimentary forms of volcanoeswhen the eruption was limited to a breakthrough to the surface of the earth only vapors and gases. These rudimentary volcanoes, called "Maars", are found in Western Germany near the city of Eiffel. Their craters are usually filled with water and, in this regard, the Maars look like lakes surrounded by a low rampart of rock fragments ejected by a volcanic explosion. Rock fragments also fill the bottom of the maar, and deeper the ancient lava begins. The richest deposits of diamonds in South Africa, located in ancient volcanic channels, are by their nature, apparently, formations similar to the Maars.Lava type
The content of silica is distinguished acidic and basic lavas. In the first, its amount reaches 76%, and in the second it does not exceed 52%. Sour Lava differ in light color and low specific gravity. They are rich in vapors and gases, mating and inactive. When cooling, they form the so-called block lava.
Main lavaon the contrary, they are dark in color, fusible, poor in gases, have great mobility and significant specific gravity. When cooled, they are called "wavy lavas." 
Lava of Mount Vesuvius
The chemical composition of the lava is different not only in volcanoes of various types, but also in the same volcano, depending on the periods of eruptions. For example, Vesuvius in modern times, light (sour) trachyte lavas pours out, the more ancient part of the volcano, the so-called Somma, is composed of heavy basaltic lavas.Lava Movement Speed
Average lava speed - five kilometers per hour, but in some cases, liquid lava moved at a speed of 30 kilometers per hour. The spilled lava soon cools, a dense slag-like crust forms on it. Due to the poor thermal conductivity of the lava, it is quite possible to walk along it, like on the ice of a frozen river, even during the movement of the lava flow. However, inside the lava it remains at a high temperature for a long time: metal rods lowered into the cracks of the cooling lava flow quickly melt. Under the outer crust, the slow movement of lava continues for a long time - it was noted in a stream 65 years ago, traces of heat were established in one case even 87 years after the eruption.Lava flow temperature
Lava Vesuvius, seven years after the eruption of 1858, still temperature at 72 °. The initial lava temperature was determined for Vesuvius at 800-1000 °, and the lava of the Kilauea crater (Hawaiian Islands) - 1200 °. It is interesting in this regard to learn how two researchers at the Kamchatka Volcanological Station measured the temperature of the lava flow.In order to make the necessary research, they jumped onto the moving crust of the lava flow with a danger to life. They had asbestos boots on their feet that did not conduct heat well. Although it was a cold November and a strong wind was blowing, however, in asbestos boots the legs were still so heated that they had to alternately stand on one or the other foot, so that the sole would cool slightly. The temperature of the lava crust reached 300 °. Brave researchers continued to work. Finally, they managed to break through the crust and measure the temperature of the lava: at a depth of 40 centimeters from the surface, it was 870 °. Having measured the temperature of the lava and taking a gas sample, they safely jumped onto the frozen side of the lava flow.Due to the poor thermal conductivity of the lava crust, the air temperature above the lava flow changes so weakly that the trees continue to grow and bloom even on small islands bordered by the sleeves of the fresh lava flow. The outpouring of lava occurs not only through volcanoes, but also through deep cracks in the earth's crust. Iceland meets lava flows, frozen between layers of snow or ice. Lava, filling the cracks and voids of the earth's crust, can maintain its temperature for many hundreds of years, which explains the presence of hot springs in volcanic areas.
Lava is different for different volcanoes. It differs in composition, color, temperature, impurities, etc.
Carbon lava
Half composed of sodium and potassium carbonates. This is the coldest and most liquid lava on earth, it flows through the earth like water. The temperature of carbonate lava is only 510-600 ° C. The color of the hot lava is black or dark brown, however, as it cools, it becomes lighter, and after a few months it becomes almost white. Frozen carbonate lavas are soft and brittle, easily dissolved in water. Carbonate lava flows only from the volcano Aldoinho-Lengai in Tanzania.
Silicon lava
Silicon lava is most characteristic of the volcanoes of the Pacific Ring of Fire. Such lava is usually very viscous and sometimes freezes in the vent of the volcano even before the end of the eruption, thereby terminating it. A corked volcano can swell slightly, and then the eruption resumes, usually with a massive explosion. The color of the hot lava is dark or black-red. Frozen silicon lavas can form black volcanic glass. A similar glass is obtained when the melt cools quickly, not having time to crystallize.
Basaltic lava
The main type of lava erupted from the mantle is characteristic of oceanic shield volcanoes. Half consists of silicon dioxide, half of aluminum oxide, iron, magnesium and other metals. Basalt lava flows are characterized by a small thickness (first meters) and a large extent (tens of kilometers). The color of the hot lava is yellow or yellow red.
Magma - It is a natural, most often silicate, hot, liquid melt that occurs in the earth's crust or in the upper mantle, at great depths, and when cooled forms magmatic rocks. The spilled magma is lava.
Varieties of magma
Basalt (primary) magma appears to be more common. It contains about 50% silica, a significant amount of aluminum, calcium, iron and magnesium are present, and to a lesser extent sodium, potassium, titanium and phosphorus. By their chemical composition, basaltic magmas are subdivided into tholeiitic (oversaturated with silica) and alkaline-basaltic (olivine-basaltic) magmas (undersaturated with silica, but enriched with alkalis).
Granite (rhyolitic, acidic) magma contains 60-65% silica, it has a lower density, more viscous, less mobile, more saturated than gas basaltic magma.
Depending on the nature of the movement of magma and the place of its solidification, two types of magmatism are distinguished: intrusive and effusive. In the first case, magma cools and crystallizes at depth, in the bowels of the Earth, in the second - on the earth's surface or in near-surface conditions (up to 5 km).
11.Magmatic rocks
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Igneous rocks are rocks formed directly from magma (a molten mass of predominantly silicate composition) as a result of its cooling and solidification. According to the conditions of formation, two subgroups of igneous rocks are distinguished: intrusive(deep), from the Latin word “intrusion” - introduction; effusive (pouring out) from the Latin word “effusio” is an outpouring. Intrusive(deep) rocks are formed by the slow gradual cooling of magma embedded in the lower layers of the earth's crust, under conditions of high pressure and high temperatures. The selection of minerals from the substance of magma during its cooling occurs strictly in a certain sequence, each mineral has its own formation temperature. First, refractory dark-colored minerals are formed (pyroxenes, hornblende, biotite, ...), then ore minerals, then feldspars and the last to be quartz crystals. The main representatives of intrusive igneous rocks are granites, diorites, syenites, gabbros, peridotites. Effusive (overflowing) rocks are formed when cooling magma in the form of lava on the surface of the earth's crust or near it. In terms of material composition, effusive rocks are similar to deep rocks, they are formed from the same magma, but under different thermodynamic conditions (pressure, temperature, etc.). On the surface of the earth's crust, magma in the form of lava cools much faster than at a certain depth from it. The main representatives of effusive igneous rocks are obsidian, tuff, pumice, basalt, andesite, trachyte, liparite, dacite, rhyolite. The main distinguishing features of effusive (poured) igneous rocks, which are determined by their origin and formation conditions: most soil samples are characterized by a non-crystalline, fine-, fine-grained structure with individual crystals visible to the eye; for some soil samples characterized by the presence of voids, pores, spots; in some soil samples, there is some pattern of spatial orientation of the components (color, oval voids, etc.). Differences between effusive rocks from each other, as well as intrusive rocks from each other, are determined by the conditions of their formation and the material composition of magma, which is manifested in their different colors (light - dark) and the composition of the components. The chemical classification is based on the percentage of silica (SiO2) in the rock. According to this indicator, ultra-acidic, acidic, medium, basic and ultrabasic rocks are distinguished. |
It is known that lavas and loose emissions during volcanic eruptions have a temperature of about 500-700 ° C, but often during volcanic eruptions there are also high temperatures exceeding 1000 ° C. Often, flames are visible above the erupting volcanoes. Such temperatures and flame combustion of the erupting gases are possible in the presence of high-temperature sources, however, superheated and supercritical steam in the drainage shell, as a rule, should not have temperatures above 450, maximum 500 ° C.
The presence of substances such as СО2, SO2, H2S, CH4, H2, С12, etc. among the gaseous products of volcanic eruptions, gives reason to believe that exothermic processes can occur in the processes of volcanic eruptions, which, when released by heat, produce additional heating of the lava and other eruption products. Such processes may include processes of interaction of oxygen-containing compounds with hydrogen and methane. In this case, for example, ferric iron will go into divalent according to the equations:
The fact that such reactions lead to the reduction of iron is also evidenced by the fact that freshly poured glass ashes are white, but soon they usually darken and turn brown due to the oxidation of ferrous iron by trivalent iron.
The intense combustion processes of gaseous products of volcanic emissions is evidenced by their clearly observed slow heating to light heat after leaving the crater, as is seen in the filming made by G. Taziev.
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In the bowels of planet Earth, volcanism (volcanic activity) is constantly going on, based on the movement of magma to the surface along the faults of tectonically moving plates of the earth's crust. The terrible uncontrollable element of volcanoes creates a tremendous threat to life on earth, but lends itself with beauty, scale of external manifestation.
Photo 2 - Pacific ring of fire on the map
The highest concentration of active volcanoes can be traced on the islands and shores of the Pacific and Atlantic oceans, forming the Pacific ring of fire.
The zones of rupture of the volcanic ring are New Zealand, the coast of Antarctica, over 200 kilometers along the California Peninsula, about 1,500 kilometers north of Vancouver Island.
In total, there are 540 volcanoes in the world. In the Pacific Ring of Fire region with a population of about 500 million people, there are 526 volcanoes.
The first classification of eruption types was proposed in 1907.
italian scientist J. Mercalli. Later, in 1914, A. was supplemented.
Lacroix and G. Wolf. It is based on the names of the first volcanoes with characteristic eruption properties.
Photo 3 - Mauna Volcano - Loa
Hawaiian type compiled on the basis of the eruption of the volcano Mauna Loa of the Hawaiian archipelago.
Lava flows from the central vent and side craters. There are no sharp emissions and explosions of the rock. The fiery stream spreads over long distances, freezes, forms a flat “shield” around the perimeter. The dimensions of the shield of Mauna Loa Volcano are already 120 km long and 50 km wide.
Photo 4 - Stromboli volcano on the Aeolian Islands (Italy)
Strombolian type classified based on observations of the Stromboli volcano in the Aeolian Islands.
Outpourings of strong flows of more viscous lava are accompanied by explosions with the ejection of large solid pieces of rock, basalt slag, from the bowels of the volcano.
Photo 5 - Volcano volcano named after the ancient Roman god of fire Vulcan
Type Vulcano. The volcano located on the Aeolian Islands is named for the ancient Roman god of fire Vulcan.
It is characterized by an eruption of lava with a high melt viscosity. Occasionally, the volcanic vent is blocked by magma products. Under tremendous pressure, an explosion occurs with the release of lava, ash, rock fragments, to a great height.
Photo 6 - eruption of the volcano Vesuvius
Photo 7 - Volcano Vesuvius in the present tense
Ethno-Vesuvian (Plinian) type corresponds to the characteristics of the eruption of the volcano Vesuvius near Naples.
Periodic blockages of the volcano’s vent, powerful explosions, long-range emissions of volcanic bombs from several centimeters to one meter, mud flows, and huge exhausts of ash and lava are clearly expressed. The temperature of lava flows is from 8000 ° С to 10000 ° С.
Photo 8 - Mount Etna
An example is Mount Etna.
Photo 9 - the eruption of the volcano Mont Pele in 1902
Peleus type based on the nature features of the Mont Pele volcano of Martinique, a group of Lesser Antilles in the Atlantic Ocean.
The eruption is accompanied by powerful jets of gases that create a huge mushroom cloud in the atmosphere.
Photo 10 - an example of pyroclastic flows (a mixture of stones, ash and gases) during a volcanic eruption
The temperature inside a cloud of molten ash may exceed 7,000 ° C.
Viscous lava in the bulk accumulates around the crater, forming a volcanic dome.
Photo 11, 12 - an example of a gas type of volcanic eruption
Gas or phreatic type eruptions in which lava is not observed.
Under the pressure of magmatic gases, fragments of solid ancient rocks fly into the air. The phreatic type of volcanoes is associated with the release of superheated groundwater under pressure.
Photo 13 - Icelandic ice volcano Grimsvotn
Ice type eruptions refers to volcanoes located under glaciers.
Such eruptions form spherical lava, lahars (a mixture of hot magma products with cold waters).
There is a danger of dangerous floods, tsunami waves. To date, only five eruptions of this type have been observed.
Clubs of steam, ash and smoke reached a height of 100 meters.
Scientists have found that in the depths of ocean waters there are much more volcanoes (about 32 thousand) than on land (about 1.5 thousand).
Almost all elevations of the ocean topography are active or already extinct volcanoes. Leadership belongs to the Pacific.
Other articles about volcanoes:
Hard debris is usually very fragmented, frayed and represented by ashes. Eruptions are most often associated with magma of acidic or medium composition. The magma chambers that feed these volcanoes are located at great depths, and magma from them does not always reach the Earth's surface. There are several types of volcanoes in this category:
- peleysky,
- Krakatau,
- Maar
- bandaysan.
PELEISK TYP
Got a name from the volcano Mont Pele on about.
Martinique in the Lesser Antilles island arc. The eruption on April 23, 1902 became a classic. Frequent earthquakes and emissions of ash, water vapor and toxic gases lasted two weeks. All this time the mountain was surrounded by a white cloud of steam, and on May 8 there was an explosion accompanied by a terrible roar, the top of the mountain was smashed to pieces, and then a dense fire cloud of gas and sprayed lava moved down the hill at a speed of 180 km / h.
In this cloud of fire, the temperature reached 450-6000. She destroyed the city of Saint-Pierre, and 30 thousand of its inhabitants were killed. A few weeks after the release of gases, a lava dome with steep slopes appeared at the bottom of the crater.
It consisted of red-hot thick lava of acidic composition. In mid-October 1902, a huge lava obelisk resembling a giant finger began to rise on the eastern side of the dome. Its height increased daily by 10 m, finally it reached a height of 900 m above the level of the crater and began to collapse.
A year later, in August 1903, the obelisk fell apart.
Peleus type eruptions with extrusion of viscous lava are called extrusive. Similar eruptions occurred in Kamchatka, Alaska, etc.
K r ak a t a u c k y y t and p
It is characterized by unusually strong explosions with emissions of a huge amount of gases and ash. Lava almost never appears on the surface.
The name of the type is given for the volcano Krakatau, which makes up the island in the Sunda Strait between the islands of Sumatra and Java.
Eruptions of volcanoes of this type are associated with acidic viscous magma, judging by the pumice and ash of the dacitic composition (65% silica).
M a and r s to and y t and p
One-act eruptions, now extinct, belong to it. In this case, flat saucer-shaped crater depressions arise, along the edges of which low shafts are formed, composed of slag and rock fragments ejected from the crater.
A volcanic canal or explosion tube, referred to as ancient volcanoes, approaches the bottom of the crater diatreme. On ch. 400-500 m explosion tubes are filled with basaltic lava or ultrabasic magma derivatives. Above them are frayed blue clay and crumpled fragments of volcanic rocks (kimberlite).
In kimberlites, diamonds, pyropes, etc. are found. The nature of the rock indicates very high pressures and temperatures during the explosion and the rise of magma from great depths, from the mantle. Explosion tubes have a diameter of several meters to several kilometers.
B a n d a y s a n s c i y t and p
The nature of the eruptions resembles the previous type of this category, but the explosions in this case are not associated with magmatic gases, but with water vapor, which, penetrating to great depths, turns into steam and gives an explosion.
Unlike real gas-explosive eruptions, the Bandaysan type volcanoes lack fresh volcanic eruption products.
Volcanoes of this type are known in Indonesia, Japan, etc.
Definition and characteristics of a volcano, lava, magma, scorching cloud.
Volcanoes are individual elevations above the channels and cracks of the earth's crust, through which eruption products are brought to the surface from deep magmatic foci.
Volcanoes usually have the shape of a cone with a vertex crater (a depth of several to hundreds of meters and a diameter of up to 1.5 km). During eruptions, a volcanic structure sometimes collapses with the formation of a caldera - a large hollow with a diameter of up to 16 km and a depth of up to 1000 m.When magma rises, external pressure weakens, the gases and liquid products associated with it burst to the surface, and the volcano erupts. If ancient rocks, and not magma, are carried to the surface, and water vapor prevails among the gases formed during the heating of groundwater, then this eruption is called phreatic.
Active include volcanoes that erupted in historical time or showed other signs of activity (emission of gases and steam, etc.). Some scientists consider those volcanoes to be active, which are reliably known that they erupted over the past 10 thousand. " years old.
For example, the Arenal volcano in Costa Rica should be classified as active, since archaeological excavations of a primitive man’s site in this area revealed volcanic ash, although for the first time it was erupted in memory of people in 1968 and before that there were no signs of activity. Volcanoes are known not only on Earth. In the pictures taken from spacecraft, huge ancient craters on Mars and many active volcanoes on Io, the satellite of Jupiter, were discovered.
Lava is magma flowing to the earth's surface during eruptions and then hardening.
The outpouring of lava can occur from the main vertex crater, a lateral crater on the slope of the volcano, or from cracks associated with the volcanic focus. It flows down the slope in the form of a lava flow. In some cases, an outflow of lava occurs in rift zones of great length. For example, in Iceland in 1783, within a chain of Laki craters stretching along a tectonic fault for a distance of about 20 km, an outflow of -12.5 km3 of lava spread over an area of \u200b\u200b-570 km2. Lava composition: solid rocks formed during cooling of the lava mainly contain silicon dioxide, oxides of aluminum, iron, magnesium, calcium, sodium, potassium, titanium and water.
Typically, in lava, the content of each of these components exceeds one percent, and many other elements are present in smaller quantities.
There are many types of volcanic rocks, differing in chemical composition.
Four types are most often found, belonging to which is determined by the content of silicon dioxide in the rock: basalt — 48–53%, andesite — 54–62%, dacite — 63–70%, rhyolite — 70–76%. Species in which the amount of silicon dioxide is less in large quantities contain magnesium and iron.
During cooling of the lava, a significant part of the melt forms volcanic glass, in the mass of which there are individual microscopic crystals. The exception is the so-called.
phenocrysts - large crystals formed in magma even in the bowels of the Earth and brought to the surface by a stream of liquid lava. Most often phenocrysts are represented by feldspars, olivine, pyroxene and quartz. Rocks containing phenocrysts are commonly called porphyrites. The color of the volcanic glass depends on the amount of iron present in it: the more iron, the darker it is.
Thus, even without chemical analyzes, one can guess that the light-colored rock is rhyolite or dacite, dark-colored rock is basalt, gray is andesite. The minerals distinguishable in the rock determine its type. So, for example, olivine - a mineral containing iron and magnesium, is characteristic of basalts, quartz - for rhyolites.
As the magma rises to the surface, the released gases form tiny bubbles with a diameter of up to 1.5 mm more often, less often up to 2.5 cm. They are stored in the frozen rock.
So bubbly lavas are formed. Depending on the chemical composition of the lava, 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 to a large extent determines the nature of the eruption and the type of volcanic products. Liquid basaltic lavas with a low silica content form extended lava flows with a length of more than 100 km (for example, it is known that one of the lava flows in Iceland stretches for 145 km). The thickness of lava flows is usually from 3 to 15 m.
More liquid lavas form thinner flows. Flows in 3-5 m thick are common in Hawaii. When solidification begins on the surface of the basaltic stream, its interior can remain in a liquid state, continuing to flow and leaving behind an elongated cavity, or lava tunnel. For example, on about. Lanzarot (Canary Islands) large lava tunnel can be traced for 5 km.
The surface of the lava flow is smooth and wavy (in Hawaii such lava is called pahoehoe) or uneven (aalava).
Hot lava, with high fluidity, can move at a speed of more than 35 km / h, but more often its speed does not exceed several meters per hour. In a slowly moving stream, pieces of the frozen upper crust can fall off and overlap with lava, “as a result, a zone enriched in debris forms in the bottom part.
When the lava solidifies, sometimes columnar formations (multifaceted vertical columns with a diameter of a few centimeters to 3 m) or fracture perpendicular to the cooling surface are formed. When lava flows into a crater or caldera, a lava lake forms, which cools over time. For example, such a lake was formed in one of the craters of the Kilauea volcano on about. Hawaii during the eruptions of 1967-1968
when the lava entered this crater at a speed of 1.1 x 106 m3 / h (partially, the lava subsequently returned to the mouth of the volcano). In neighboring craters, over 6 months, the thickness of the crust of solidified lava on lava lakes reached 6.4 m.
Domes, maars and tufa rings. A very viscous lava (most often a dacite composition) during eruptions through the main crater or lateral 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 formed in the crater of St. Helens (USA) after extremely strong eruption in May 1980
The pressure under the dome can increase, and after a few weeks, months or years, it can be destroyed during the next eruption.
In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks - blocks or spiers of frozen lava, often tens or hundreds of meters high, protrude above its surface.
After the catastrophic eruption in 1902 of the volcano Montagne-Pele on about. Martinique formed a lava spire in the crater, which grew by 9 m per day and as a result reached a height of 250 m, and after a year collapsed. On the Usu volcano on about. Hokkaido (Japan) in 1942, during the first three months after the eruption, the lava dome of the Seva-Shinzan increased by 200 m. The viscous lava that composed it broke through the thickness of the previously formed sediments. Maar is a volcanic crater formed during an explosive eruption (most often with high humidity of rocks) without an outpouring of lava.
An annular shaft of detrital rocks ejected by the explosion does not form, in contrast to tuff rings - also explosive craters, which are usually surrounded by rings of detrital products.
Varieties of volcanoes and their structure
All volcanoes by vent shape and morphology of the building are divided into volcanoes central and linear type (Fig. 5.5), which, in turn, are divided by the complexity of the structure into monogenic and polygenic.
Monogenic central type buildings for the most part are associated with polygenic volcanoes and are volcanoes of the second order.
They are represented slag cones or extrusive domes and they are usually composed of rocks of close composition.
Polygenic volcanoes of the central type by geological structure and form are divided into stratovolcanoes, shield, domed and combinedrepresenting a combination of the listed volcanic structures.
In turn, these buildings can be complicated by the summit or peripheral, relative to the volcano, caldera.
Stratovolcanoes - this is when in polygenic volcanoes of the central type, a clearly defined, flat (or steep) layered cone with a steepness of 20-30º, formed by interbedded lavas, tuffs, lava breccias, slags, slag rocks, and sedimentary rocks of marine or continental origin develops around the vent fig.
The main lavas are less viscous compared to acidic lavas, and, spreading over more considerable distances, form less steep structures (no steeper than 10º).
Shield volcanoes are relatively simple low volcanic structures (Fig.
5.1a), composed mainly of basalts with transverse dimensions up to several tens of kilometers and slopes no steeper than 3-5º (for example, Tskhun volcanoes in Armenia, Uzon in Kamchatka, etc.).
Dome Volcanoesor volcanic domes and structure are very diverse in shape (from faintly convex structures to peaks hundreds of meters high) and in structure (according to fluidity pattern) - from regular forms of bulbous, fan-shaped, funnel-shaped structures to complex vortices (Fig.
5.6). Domes can repeatedly erupt with subsequent portions of lava or, in the process of uneven squeezing, enclose brecciation zones, as well as possess complex combinations of these inhomogeneities. Extrusive and protrusive domes, breaking through volcanic strata, capture the monoliths of these rocks, partially melt them, thereby complicating their structure.
The geological position of the domes is determined by the nature of volcanism, the type of magma chambers, confinement to various types of volcanic structures, and the relation to magma chambers.
Basaltic volcanism contributes to the formation of rootless domes on shield volcanoes, and to single and group domes on stratovolcanoes located both in the central part of the volcano and on the periphery.
With the eruption of differentiated (contrast) volcanics, domes of a very diverse structure, shape and genesis arise. Sour and medium volcanism contributes to the emergence of extrusive and protrusive domes.
With the formation of large calderas and ring volcanic-tectonic structures, domes are very often located along ring faults and outlining near-surface magma chambers.
Sometimes extrusion is located within the entire field of near-surface intrusion.
Volcanic domes can be divided into three groups: 1 - domes with no apparent connection with intrusion; 2 - formed over the intrusion; 3 - rootless volcanic domes.
● Volcanic domes without visible connection with intrusion – effusive (periclinal and bulbous symmetric or asymmetric structures), extrusive (mushroom-shaped and fan-shaped or funnel-shaped) and protrusive (pike and broom) (Fig.
5.6). An example of a peak-like dome is the Igloo of pyroxene andesites of Mon Pele volcano on about. Martinique. After a catastrophic eruption on May 8, 1902, the needle, which appeared in October 1902, reached by May 1903.
height of about 345 m. Its diameter at the base was about 135 m. It could have a height of about 850 m if it had not been destroyed during the eruption in 1905. The broom-shaped dome of Seulich in Kamchatka in three years (1946-1948). ) grew 600 m above the crater with a diameter below about 1 km and above about 0.5 km.
The growth rate of the blocks varied from 1 to 15 m per day.
● Volcanic domes, formed over intrusion, ethen - positive structures in which a transition from effusive rocks to intrusive rocks is observed down the section.
The height of the raised structures can reach 800 m. They are widely developed in the volcanic zones of Kamchatka, the Urals, the Caucasus, Central Asia, etc.
● rootless volcanic domes can be of two types: 1 - squeezed portions of lava on lava flows; 2 - deformed (curved) lava flows forming hemispheres, and arising during outpouring before the obstacle as dome-shaped piles of lava or as lava remnants flowing from the middle of the stream, sometimes assuming a subvertical position.
Domes of the first type are small - up to 50-70 m, and the second even smaller - up to 10 m. Both of them are found in Kamchatka.
Monogenic linear volcanoes represented by fissured squeezes - one-act fissured volcanoes of acidic or medium composition. TO linear polygenic volcanoes include fissure volcanoes that form lava ridges and lava plateaus, and which may be complicated by summit, external grabens or a combination of grabens.
Modern fracture-type outpourings, for example, in Iceland, are associated with linear apparatuses that are 3-4 km long and up to several hundred meters wide. In Armenia, a volcanogenic plateau is known that formed in the Pliocene-Quaternary due to the outpouring of lavas from\u003e 10 volcanoes located along two faults.
For example, Mount Etna is surrounded by 200 side craters.
The duration of volcanic activity can be varied and intermittent. For example, the Elbrus volcano has been active for 3 million years.
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Classification and types of volcanic eruptions
Volcanic eruptions are very diverse, but there are three main characteristics by which they can be classified: 1) scale (volume of erupted rocks); 2) the composition of the erupted material; 3) the dynamics of the eruption.
In scale, all volcanic eruptions are divided into five classes (km3):
Grade I - the volume of erupted material is more than 100;
II class - from 10 to 100;
Grade III - from 1 to 10;
IV class - from 0.1 to 1;
V class - less than 0.1.
The composition of the erupted material, which will be discussed in detail below, especially the gas component, determines the dynamics of the eruption.
The process of mantle degassing is one of the important reasons for its eruption, depending on the amount of gases, their composition and temperature. According to the method and speed of separation of volatiles, three main forms of eruption are distinguished: effusive - with quiet gas evolution and outpouring of lava; explosive - with the rapid release of gases that cause boiling of magma and powerful explosive eruptions; extrusive - viscous magma of low temperature is squeezed out of the crater.
There are also mixed types - effusive-explosive; extrusive-explosive, etc. With mixed eruptions an important characteristic, according to E.K. Markhinin, is the coefficient of explosivity - the percentage of the amount of pyroclastic material from the total mass of eruption products.
Therefore, the essence of each eruption can be expressed by the formula. For example, 4B exp. 100, which means: Class IV eruption, basaltic, explosive, explosivity coefficient 100. Each form of eruption has one or more volcanoes that most clearly express its features.
Effusive eruptions extremely widespread and associated with the outpouring of magma mainly basaltic composition. The characteristic eruptions of such dynamics are confined to the spreading zones of mid-ocean ridges and subduction zones of active continental margins.
In the mid-ocean ridges under conditions of stretching of the earth's crust, fissure volcanism acquires the greatest scope. This type includes the volcanoes of Iceland - Laki, Eldgya, located in the axial part of the Mid-Atlantic Range.
During an eruption in 1783, a lava began to pour out of the Laki crack, the length of which reached 32 km, after a strong explosion with the release of slag and ash, the flows of which completely filled the gorge with a depth of 180 m and covered the territory with a total area of \u200b\u200b565 km2. The average thickness of the lava cover exceeded 30 m, and the volume of lava was 12 km3.
The same fissure outflows are characteristic of the Hawaiian Islands - the Hawaiian type, where eruptions occur with the release of very liquid highly mobile basaltic lava.
As the lava flow power increases as a result of multiple eruptions, grandiose shield volcanoes form, the largest of which is the above-mentioned Mauna Loa.
In subduction zones of the active continental Pacific margin, powerful fissure eruptions of the Flat Tolbachik volcano were observed in Kamchatka in 1975-1976. The eruption began with the formation of a crack 250-300 m long and the release of a huge amount of ash, slag and bombs. The red-hot pyroclastics formed a fiery “candle” with a height of up to 2.5 km, and the gas and ash column reached a height of 5-6 km.
Then, the eruption continued through a system of newly opening cracks with the formation of new slag cones, whose heights reached 108, 278, and 299 m (Fig.
11.5). The total distribution area of \u200b\u200bthe lava field at one of the breakthroughs with a slag-block surface, with an average thickness of 28 m, was 35.9 km2 (Fig. 11.6). Eruption products are represented by basalts. In terms of high fluidity and characteristic morphology of lava flows, it is close to Hawaiian type eruptions. The total amount of released gases (mainly H2O) is 180 million tons, which is comparable to the average annual release into the atmosphere during eruptions of all terrestrial volcanoes in the world.
The fissure outflows of Plosky Tolbachik are the only major historical eruption of this kind in Russia. 
Explosive eruptions. Volcanoes with gas-explosive dynamics of eruption are widespread in subduction zones - immersion lithospheric plates.
Eruptions accompanied by powerful explosions to a certain extent depend on the composition of viscous inactive acidic magma containing a large amount of gases. A typical example of such an eruption is the Krakatau type. The Krakatau volcano is located in the Sunda Strait between Java and Sumatra and its eruption is associated with a deep fracture of the Eurasian Plate that arose as a result of pressure from the bottom of the Indo-Australian Plate (Fig.
11.7).
Academician N. Shilo describes the mechanism of the Krakatau eruption in this way: during the ascent of a mantle substance saturated with gases as it rises along a deep fault from a magma chamber, it segregates — stratification into two immiscible melts.
Lighter granitoid magma, saturated with volatile gases, rises up and there comes a moment when, as the pressure rises, the chamber lid does not withstand the accumulation of magma and a powerful explosion occurs with the release of acidic products saturated with gases.
This happened during the grandiose eruption of Krakatoa in 1883, which began with the release of ash, pumice, and volcanic bombs, followed by a colossal explosion that destroyed the island of the same name. The sound of the explosion spread to a distance of 5,000 km, and volcanic ash, rising to a hundred-meter height, spread to tens of thousands of kilometers.
April 1982
the most powerful eruption of the Galunggung volcano occurred in the last 25 years, as a result of which 40 villages were wiped off the face of the earth. Volcanic ash covered an area of \u200b\u200b180,000 hectares.
Galunggung is one of the most active Indonesian volcanoes, the height of which reaches 2168 m.
This also includes the Bandaysan type, named after the volcano Bandaysan, located on about. Honshu, whose eruptions are distinguished by colossal explosions. Explosive eruptions also include volcanoes - one-day ones - Maars and diatremes.
The formation of Maars as a result of one-act explosions is typical of the Tyatya volcano on the Kuril Islands. During the eruption in the summer of 1973, with the formation of the Maars, old lava flows were blown up, composing the slopes of the volcano, and sediments with a thickness of 20-30 m formed at the edge of the Maars.
The total volume of silicate products ejected from the Maars was two times the volume of the Maars themselves.
Extrusive eruptions. A typical example of this eruption is the Mon Pele volcano, by which the Peleus type is named.
The volcano Mont Pele is located on about. Martinique in the Lesser Antilles archipelago. The powerful explosive eruptions of this volcano are associated with extremely viscous acidic magma.
On April 28, 1902, the gigantic blast destroyed the top of the still dormant volcano, and a red-hot cloud ("scorching cloud") escaping from the vent destroyed the city of Saint-Pierre with 40,000 inhabitants in a few seconds. After the eruption, a mass of viscous lava about 500 m high - “Igla Pele” began to be squeezed out.
in Kamchatka. Initially, a powerful explosion occurred, destroying the top of the volcano and its eastern slope. The ash cloud rose to a height of 40 km, and hot avalanches descended along the slopes of the volcano, which, melting snow, formed powerful mud streams. At the peak site, a crater with a depth of 700 m and an area of \u200b\u200babout 4 km2 was formed.
Then an eruption of pyroclastic flows began, which filled the river valleys at the foot of the volcano, after which an intracrater extrusion of 320 m high with a base diameter of 600-650 m began to form. The eruption products are represented by andesites and andesite-basalts. Such extrusive domes are characteristic of Kamchatka's volcanic eruptions (Fig.
11.8).
Eruptions are mixed. This category includes volcanoes characterized by emissions of gaseous, liquid and solid products.
This nature of the eruption is inherent in the volcanoes of Stromboli, Vesuvius, Etna.
Strombolian type - Stromboli volcano on the Aeolian Islands is characterized by eruptions of the main lava, alternating with the emission of volcanic bombs and incandescent slags.
Lavas are mobile, hot, their temperature reaches 1100-1200 ° C. The total height of the volcanic cone with the underwater part is 3500 m (height above sea level - 1000). The volcano is characterized by regular eruptions.
Vesuvian (Plinian) type named after the Roman scientist Pliny the Elder, who died during the eruption of Mount Vesuvius in 79
n e. Vesuvius is located on the shores of the Gulf of Naples, near the city of Naples. The catastrophic eruption of Vesuvius, as a result of which four cities died under a layer of volcanic ash and lava, is described by Pliny the Younger and captured in the picture of K. Bryullov “The Last Day of Pompeii”. A characteristic feature of eruptions of this type are powerful sudden explosions, accompanied by emissions of a huge amount of gases, ash, pumice.
At the end of the eruption, rain poured and the resulting mudstone flows completed the burial of cities. As a result of the explosion, the top of the volcano collapsed, and a deep caldera formed in its place, in which a new volcanic cone grew 100 years later.
Such a volcanic structure is called somma, an example of it is the Tyatya volcano (Fig. 11.9). 
A very strong eruption of Vesuvius occurred in 1631, as a result of which a red-hot lava flow almost completely destroyed the city of Torre del Greco. Vesuvius erupted in recent years, threatening the inhabitants of Naples.
The mixed explosive-effusive nature of the eruption is distinguished by the largest volcano in Kamchatka - Klyuchevskaya (Fig.
11.10). This is a typical stratovolcano with a cone of regular shape, 4750 m high - the highest of the active volcanoes in Europe and Asia. The volcano is young, its age is 7000 years, it is very active. Between 1932 and 1987
the volcano erupted 21 times, and sometimes the duration of the eruption is 18 months. At the volcano, both vertex and side eruptions are noted. A feature of the vertex eruptions 1978-1980, 1984-1987. there was an outpouring of lava flows on the slopes of the volcano, which were accompanied by continuous avalanches of red-hot debris, throwing ashes and bombs.
As a result of the contact of lava and ice, powerful mud flows and lahars (mud-stone flows) were formed, which, sawing through deep canyons in glaciers, spread more than 30 km from the foot of the volcano.
The eruption products are represented by ash, volcanic bombs and lavas of basaltic composition. The length of the lava flows reached 12 km, and the thickness reached 30 m.
Volcanic eruptions continue at the present time. 
Ethninsky type named after the volcano Etna, the cone of which rises above sea level by more than 3000 m. By the nature of the eruption, this type is close to the Vesuvian and often combine them together.
Volcanoes of this type are common in the Kuril Islands, Kamchatka, in South America, Japan and the Mediterranean.