Volcanoes and volcanism

Introduction

Volcanoes called cone-shaped or dome-shaped elevations above channels, explosion pipes and cracks in the earth's crust, through which gaseous products, lava, ash, and rock fragments are erupted from the bowels. Manifestations of volcanism are one of the most characteristic and important geological processes of great importance in the history of the development and formation of the earth's crust. Not a single area on Earth - be it a continent or an ocean trench, a folded region or a platform - has formed without the participation of volcanism. High practical significance these phenomena led to the choice of the topic of the course work. The main purpose of the work is to study volcanoes and volcanism. In accordance with this goal, the following tasks are considered in the work. The first chapter discusses the history of the emergence of volcanoes and their prevalence on the earth's surface, as well as the products of volcanic eruptions, which are solid in the form of volcanic bombs and ash and liquid in the form of lava. The second chapter deals with the manifestation of volcanism and the structure of the volcano. So we learn that volcanoes are of three types: 1) areal 2) fissure 3) central and very complex structure.

General information about volcanoes

In the Tyrrhenian Sea in the group of Aeolian Islands there is a small island of Vulcano. The ancient Romans considered this island the entrance to hell, as well as the possession of the god of fire and blacksmithing, Vulcan. After this island, the fire-breathing mountains later became known as volcanoes. Eruption may continue several days or even months. After a strong eruption, the volcano again comes to rest for several years and even decades. Such volcanoes are called active. There are volcanoes that erupted long ago. Some of them have retained the shape of a beautiful cone. There is no information about their activities. They are called extinct. In ancient volcanic regions, there are deeply destroyed and eroded volcanoes. In our country, such regions are the Crimea, Transbaikalia and other places.

If you climb to the top of an active volcano during its calm state, you can see crater(in Greek - a large bowl) - a deep depression with steep walls, similar to a giant bowl. The bottom of the crater is covered with fragments of large and small stones, and steam jets and gases rise from cracks in the bottom and walls of the crater. Sometimes they calmly come out from under stones and crevices, and sometimes they break out violently with a whistle and hiss. The crater is being filled asphyxiating gases; rising up they form a cloud at the top of the volcano. For months and years, the volcano can quietly smoke until an eruption occurs. This event is often preceded by an earthquake; an underground rumble is heard, the release of vapors and gases intensifies, clouds thicken over the top of the volcano. Then, under the pressure of gases escaping from the bowels of the earth, the bottom of the crater explodes. Thick black clouds of gases and water vapors mixed with ash are ejected for thousands of meters, plunging the surroundings into darkness. Simultaneously with the explosion, pieces of red-hot stones fly from the crater, forming giant sheaves of sparks. From black, thick clouds, ash falls on the ground, sometimes heavy rains fall, forming streams of mud that roll down the slopes and flood the surroundings. The flash of lightning continually cuts through the darkness. The volcano rumbles and trembles, and red-hot lava rises along its mouth. It seethes, pours over the edge of the crater and rushes like a fiery stream along the slopes of the volcano, destroying everything in its path. In some volcanic eruptions, lava does not erupt.

Volcanic eruptions also occur at the bottom of the seas and oceans. Navigators find out about this when they suddenly see a column of steam above the water or floating on the surface. stone foam” - pumice. Sometimes ships come across unexpectedly manifested shoals formed by new volcanoes at the bottom of the sea. Over time, these shoals - igneous masses - are washed away by sea waves and disappear without a trace. Some underwater volcanoes form cones that protrude above the surface of the water in the form of islands. In ancient times, people did not know how to explain the causes of volcanic eruptions. Therefore, this formidable phenomenon of nature plunged a person into horror.

Geography of volcanoes

At present, over 4,000 have been identified worldwide. volcanoes. Volcanoes that erupt and exhibit solfataric activity (release of hot gases and water) for the last 3500 years of the historical period are referred to as active ones. In 1980, there were 947 of them. Potentially active volcanoes include Holocene volcanoes erupting 3500-13500 years ago. There are approximately 1343 of them. Conditionally extinct volcanoes are classified as not showing activity in the Holocene, but retaining their external forms (younger than 100,000 years old). Extinct volcanoes significantly reworked by erosion, dilapidated, not showing activity during the last 100 thousand years. years. Modern volcanoes are known in all large geological structural elements and geological regions of the Earth. However, they are unevenly distributed. The vast majority of volcanoes are located in the equatorial, tropical and temperate regions. In the polar regions, beyond the Arctic and Southern polar circles, there are extremely rare areas of relatively weak volcanic activity, usually limited to the release of gases.

There is a direct relationship between their number and the tectonic activity of the area: the largest number of active volcanoes per unit area falls on island arcs (Kamchatka, the Kuril Islands, Indonesia) and other mountain structures (South and North America). The most active volcanoes of the world, characterized by the highest frequency of eruption, are also concentrated here. The lowest density of volcanoes is characteristic of oceans and continental platforms; here they are associated with rift zones - narrow and extended areas of splits and subsidence of the earth's crust (East African rift system), the Mid-Atlantic Ridge.

It has been established that volcanoes are confined to tectonically active belts where most earthquakes occur. Volcano development areas are characterized by a relatively large fragmentation of the lithosphere, an anomalously high heat flux (3-4 times more than background values), increased magnetic anomalies, and an increase in the thermal conductivity of rocks with depth. To the areas of juvenile sources of thermal waters mud of geysers. Volcanoes located on land are well studied; for them, the dates of past eruptions are precisely determined, and the nature of the erupted products is known. However, most active volcanic activity appears to occur in the seas and oceans that cover more than two-thirds of the planet's surface. The study of these volcanoes and the products of their eruptions is difficult, although with a powerful eruption there may be so many of these products that the volcanic cone formed by them appears from the water, forming a new island. So, for example, in the Atlantic Ocean, south of Iceland, on November 14, 1963, fishermen noticed clouds of smoke rising above the surface of the ocean, as well as stones flying out of the water. After 10 days, at the site of the eruption, an island about 900m long, up to 650m wide and up to 100m high was already formed, called Surtsey. The eruption continued for more than a year and a half and ended only in the spring of 1965, forming a new volcanic island with an area of ​​2.4 km2 and a height of 169 m above sea level. Geological studies of the islands show that many of them are of volcanic origin. With the frequent recurrence of eruptions, their long duration and the abundance of released products, very impressive structures can be created. So, the chain of Hawaiian Islands of volcanic origin is a system of cones with a height of 9.0-9.5 km (relative to the bottom of the Pacific Ocean), that is, exceeding the height of Everest!

There is a known case when a volcano did not grow from under water, as was considered in the previous case, but from underground, right in front of eyewitnesses. It happened in Mexico on February 20, 1943; after many days of weak shocks, a crack appeared on the plowed field and the release of gases and steam began from it, the eruption of ash and volcanic bombs - clots of lava of a bizarre shape, thrown out by gases and cooled in the air. The subsequent outpouring of lava led to the active growth of the volcanic cone, the height of which in 1946 has already reached 500m (Parikutin Volcano).

Products of volcanic eruptions

During a volcanic eruption, products of volcanic activity are released, which can be liquid, gaseous and solid. Gaseous - fumaroles and sophioni, play an important role in volcanic activity. During the crystallization of magma at a depth, the released gases raise the pressure to critical values ​​​​and cause explosions, throwing clots of red-hot liquid lava to the surface. Also, during volcanic eruptions, a powerful release of gas jets occurs, creating huge mushroom clouds in the atmosphere. Such a gas cloud, consisting of droplets of molten (over 7000c) ash and gases, formed from the cracks of the Mont Pele volcano, in 1902, destroyed the city of Saint-Pierre and 28,000 of its inhabitants. The composition of gas emissions largely depends on temperature. The following types of fumaroles are distinguished:

a) Dry - temperature about 5000C, contains almost no water vapor; saturated with chloride compounds. b) Acidic, or hydrochloric-hydrogen-sulphurous - the temperature is approximately equal to 300-4000C. c) Alkaline, or ammonia - the temperature is not more than 1800C. d) Sulphurous, or solfatars - temperature is about 1000C, mainly consists of water vapor and hydrogen sulfide. e) Carbon dioxide, or mophers - the temperature is less than 1000C, mainly carbon dioxide.

Liquid - characterized by temperatures in the range of 600-12000C. Represented by lava. The viscosity of lava is determined by its composition and depends mainly on the content of silica or silicon dioxide. With its high value (more than 65%), the lavas are called acid, they are relatively light, viscous, inactive, contain a large amount of gases, and cool slowly. A lower content of silica (60-52%) is characteristic of medium lavas; they, like acidic ones, are more viscous, but they are usually heated more strongly (up to 1000-12000s) compared to acidic ones (800-9000s). Basic lavas contain less than 52% silica and are therefore more fluid, mobile, and free-flowing. When they solidify, a crust forms on the surface, under which further movement of the liquid occurs. solid foods include volcanic bombs, lapilli, volcanic sand and ash. At the time of the eruption, they fly out of the crater at a speed 500-600m/s.

Volcanic bombs are large pieces of hardened lava with a diameter ranging from a few centimeters to 1 m or more, and in mass they reach several tons (during the eruption of Vesuvius in 79 AD, volcanic bombs "tears of Vesuvius" reached tens of tons). They are formed during an explosive eruption, which occurs when the gases contained in the magma are rapidly released from the magma. Volcanic bombs come in 2 categories: 1st, arising from more viscous and less gas-saturated lava; they retain their correct shape even when they hit the ground due to the hardening crust formed when they cool. 2nd, formed from more liquid lava, during the flight they take on the most bizarre shapes, further complicated by impact. Lapilli are relatively small fragments of slag 1.5-3 cm in size, having a variety of shapes. Volcanic sand - consists of relatively small particles of lava (і 0.5 cm). Even smaller fragments, ranging in size from 1 mm or less, form volcanic ash, which, settling on the slopes of the volcano or at some distance from it, forms volcanic tuff.

Volcanism

According to modern concepts, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the bowels of the Earth to its surface. At a depth of 50 to 350 km, in the thickness of our planet, foci of molten matter - magma - are formed. In the areas of crushing and fractures of the earth's crust, magma rises and pours out to the surface in the form of lava (it differs from magma in that it contains almost no volatile components, which, when the pressure drops, are separated from the magma and go into the atmosphere. With these outpourings of magma on the surface, they form volcanoes. Volcanoes are of three types:

2.1. Areal volcanoes.

Currently, such volcanoes are not found, or one might say they do not exist. Since these volcanoes are confined to the release of a large amount of lava on the surface of a large area; that is, from here we see that they existed at the early stages of the development of the earth, when the earth's crust was rather thin and in some areas it could be completely melted.

2.2. Fissure volcanoes.

They are manifested in the outpouring of lava onto the earth's surface along large cracks or splits. In certain periods of time, mainly at the prehistoric stage, this type of volcanism reached a rather large scale, as a result of which a huge amount of volcanic material, lava, was brought to the surface of the Earth. Powerful fields are known in India on the Deccan plateau, where they covered an area of ​​5.105 km2 with an average thickness of 1 to 3 km. Also known in the northwestern United States, in Siberia. At that time, basaltic rocks of fissure eruptions were depleted in silica (about 50%) and enriched in ferrous iron (8-12%). The lavas are mobile, liquid, and therefore can be traced for tens of kilometers from the place of their outpouring. The power of individual streams was 5-15m. In the United States, as well as in India, many kilometers of strata accumulated, this happened gradually, layer by layer, over many years. Such flat lava formations with a characteristic stepped topography are called plateau basalts or traps. Currently, fissure volcanism is widespread in Iceland (Laki volcano), Kamchatka (Tolbachinsky volcano), and on one of the islands of New Zealand. The largest lava eruption on the island of Iceland along the giant Laki fissure, 30 km long, occurred in 1783, when lava flowed to the surface for two months. During this time, 12 km 3 of basaltic lava erupted, which flooded almost 915 km 2 of the adjacent lowland with a layer 170 m thick. A similar eruption was observed in 1886. on one of the New Zealand islands. For two hours, 12 small craters with a diameter of several hundred meters acted on a segment of 30 km. The eruption was accompanied by explosions and ash emission, which covered an area of ​​10 thousand km2, near the crack, the thickness of the cover reached 75 m. The explosive effect was intensified by the powerful release of vapors from the lake basins adjacent to the fissure. Such explosions, caused by the presence of water, are called phreatic. After the eruption, a graben-like depression 5 km long and 1.5-3 km wide formed at the site of the lakes.

2.3. Central type.

Eruption types

Depending on the quantities, the ratio of erupted volcanic products (gas, liquid or solid) and the viscosity of the lavas, four main types of eruptions have been distinguished: Hawaiian (effusive), Strombolian (mixed), dome (extrusive) and Vulcan.

3.1. Hawaiian type. Hawaiian - volcanic mountains have gentle slopes; their cones are composed of layers of cooled lava. In the crater of active Hawaiian volcanoes, there is a liquid lava of basic composition with a very small content of gases. It boils violently in a crater - a small lake on top of a volcano, representing a magnificent sight, especially at night.

The structure of the Volcano 1 - volcanic bomb; 2 – canonical volcano; 3 – layer of ash and lava; 4 - dike; 5 - the mouth of the volcano; 6 - strength; 7 – magma chamber; 8 - shield volcano.

The dull reddish-brown surface of the lava lake is periodically broken by dazzling lava jets flying upward. During the eruption, the level of the lava lake begins to rise calmly, almost without shocks and explosions, and reaches the edges of the crater, then the lava overflows over the edge and, having a very liquid consistency, spreads over a vast territory, at a speed of about 30 km / h, for tens of kilometers. Periodic eruptions of the volcanoes of the Hawaiian Islands lead to a gradual increase in their volume due to the buildup of slopes of solidified lava. Thus, the volume of the Mauna Loa volcano reaches 21.103 km3; it is larger than the volume of any of the known volcanoes on the globe. According to the Hawaiian type, volcanoes erupt on the islands of Samoa in eastern Africa, on Kamchatka and on the Hawaiian Islands themselves - Mauna Loa and Kilauea.

3.2. Strombolian type. The standard of the Strombolian type is the eruption of the volcano Stromboli (Aeolian Islands) in the Mediterranean Sea. Usually volcanoes of this type are stratovolcanoes and eruptions occurring in them are accompanied by strong explosions and tremors, emissions of vapors and gases, volcanic ash, lapilli. Sometimes there is an outpouring of lava to the surface, but due to the significant viscosity, the length of the flows is small. Eruptions of this type are observed near the Itzalco volcano in Central America; at the Mihara volcano in Japan; near a number of volcanoes in Kamchatka (Klyuchevskoy, Tolbachek and others). A similar eruption, in terms of the sequence of events and released products, but on a larger scale, occurred in 79. This eruption can be attributed to the subtype of the Strombolian eruption and called it Vesuvian. The eruption of Mount Vesuvius, partly Etna and Vulcano (Mediterranean Sea), was preceded by a strong earthquake. Then an expanding column of white steam escaped from the crater. Gradually ejected ashes and rock fragments gave the "cloud" a black color and began to fall to the ground along with a terrible downpour. The outpouring of lava was comparatively small. The lava had an average composition and flowed down the mountainside at a speed of 7 km/h. The main destruction was caused by an earthquake and volcanic ash and bombs falling to the ground, which are rock fragments and hardened lava clots. Ash showers formed liquid mud, with which the cities located on the slopes of Vesuvius were buried - Pompeii (in the south), Herculaneum (in the southwest) and Stabia (in the southeast). 3.3. Volcanoes of Russia and other types.

The dome type is characterized by squeezing and ejection of viscous (andesitic, dacitic or rhyolitic) lava by strong pressure from the volcano channel and the formation of domes (Puy-de-Dome in Auvergne, France; Central Semyachik, in Kamchatka), crypto-domes (Seva-Shinzan on the island of Hokkaido , Japan) and obelisks (Shiveluch in Kamchatka). In the Vulcan type, gases play an important role, producing explosions and ejections of huge clouds, overflowing with a large number of rock fragments, lavas and ash. The lavas are viscous and form small flows (Avachinskaya Sopka and Karymskaya Sopka in Kamchatka). Each of the main types of eruption is divided into several subtypes (Strombolian type, subtype - Vesuvian).

Of these, the Peleian, Krakatau, and Maar are especially distinguished, which, to one degree or another, are intermediate between the domed and Vulcan types. The Peleian subtype was identified by the eruption of the Montagne Pele (Bald Mountain) volcano in the spring of 1902 on the island of Martinique in the Atlantic Ocean. In the spring of 1902 Mount Montagne-Pele, which for many years was considered an extinct volcano and on the slopes of which the city of Saint-Pierre grew, was suddenly shaken by a powerful explosion. The first and subsequent explosions were accompanied by the appearance of cracks on the walls of the volcanic cone, from which black scorching clouds burst out, consisting of droplets of molten lava, incandescent (over 7000s) ash and gases. On May 8, one of these clouds rushed south and within a few minutes literally destroyed the city of Saint-Pierre. About 28,000 inhabitants died; only those who managed to swim away from the shore were saved. The ships that did not have time to moor were burned or were turned over, the water in the harbor began to boil. Only one person survived in the city, protected by the thick walls of the city prison. The volcanic eruption ended only in October. Extremely viscous lava slowly squeezed a 400 m high plug out of the volcanic channel, forming a unique natural obelisk. However, soon the upper part of it broke off along an oblique crack; the height of the remaining acute-angled needle was about 270 m, but even it was destroyed under the influence of weathering processes already in 1903. The eruption of the volcano of the same name, located between the islands of Sumatra and Java, is taken as a standard for the type of Krakatoa. On May 20, 1883, from a German warship sailing through the Sunda Strait (between the islands of Java and Sumatra), they saw a huge pine-shaped cloud rising from the Krakatoa group of islands. A huge height of the cloud was noted - about 10-11 km, and frequent explosions every 10-15 minutes, accompanied by the release of ash to a height of 2-3 km. After the May eruption, the activity of the volcano subsided somewhat, and only in mid-July did a new powerful eruption occur. However, the main catastrophe broke out on August 26. On this day in the afternoon on the ship "Medea" they noticed a column of ash already 27-33 km high, and the smallest volcanic ash was raised to a height of 60-80 km and was in the upper atmosphere for 3 years after the eruption. The sound of the explosion was heard in Australia (5 thousand kilometers from the volcano), and the blast wave went around the planet three times. Even on September 4, that is, 9 days after the explosion, self-recording barometers continued to note slight fluctuations in atmospheric pressure. By evening, rain and ash fell on the surrounding islands. Ashes fell all night; on ships located in the Sunda Strait, the thickness of its layer reached 1.5 m. By 6 o'clock in the morning a terrible storm broke out in the strait - the sea overflowed its banks, the height of the waves reached 30-40m. Waves destroyed nearby cities and roads on the islands of Java and Sumatra; the population of the islands closest to the volcano died completely. The total number of victims, according to official figures, reached 40,000.

A powerful volcanic explosion destroyed two-thirds of the main island of the Krakatau archipelago - Rakata: a part of the island 4x6 km2 with two volcanic cones Danan and Perbuatan was thrown into the air. In their place, a failure formed, the depth of the sea in which reached 360m. The tsunami wave reached the shores of France and Panama in a few hours; off the coast of South America, its propagation speed was still 483 km / h. Maar-type eruptions have occurred in past geological epochs. They were distinguished by strong gas explosions, a significant amount of gaseous and solid products were thrown out. The outpouring of lava did not occur due to the very acidic composition of the magma, which, due to its viscosity, clogged the vent of the volcano and led to explosions. As a result, explosion funnels with a diameter of hundreds of meters to several kilometers arose. These depressions were sometimes surrounded by a low shaft formed from ejected products, among which fragments of lavas are found. Diatmers, similar to maar-type explosion pipes. Their location is known in Siberia, South Africa and elsewhere. These are cylindrical tubes that cross the formations vertically and end in a funnel-shaped extension. Diatmers are filled with breccia - rock with fragments of shales and sandstones. Breccias are diamond-bearing, they are used for commercial diamond mining.

The vast expanses of Russia in Europe and Asia belong to sedentary areas of the earth's crust - platforms - and only on the outskirts (Caucasus, Central Asia, Far East) there are geosynclinal zones, characterized by high seismicity and active volcanism. Of the recently extinct volcanoes in the Main Caucasian Range are the already mentioned Elbrus and Kazbek. in Transcaucasia, Eastern Sayan, Baikal, Transbaikalia, in the Far East and North-East of Russia, young outpourings of effusive rocks are known, and in some places volcanoes have been preserved - signs of recent volcanism here. Active volcanoes in Russia are located only on the easternmost outskirts: on the Kamchatka Peninsula and the Kuril Islands. Studies of Russian volcanoes began in the 18th century. friend and contemporary of M. V. Lomonosov, traveler and geographer S. P. Krasheninnikov, who visited and studied Kamchatka in 1737-1741. His talented book “Description of the Land of Kamchatka”, where two chapters “on fire-breathing mountains” and “0 hot springs” are for the first time devoted to the description of Kamchatka volcanoes and geysers, is the first scientific work on the study of volcanoes and the beginning of Russian volcanology. Later, rare fragmentary information about the volcanoes of Kamchatka came from sailors and travelers and somewhat more detailed information from participants in some expeditions of the last century: A. Postels, A. Erman, K. Ditmar, K. I. Bogdanovich and others. The most profound studies of the volcanoes of Kamchatka began in 1931 by A.N. Zavaritsky, who revealed the connection between the linear arrangement of volcanoes and the internal structure of the peninsula, with deep faults in the earth's crust that are likely in these directions.

In 1935, on the initiative of F. Yu. Levinson-Lessing, a volcanological station of the USSR Academy of Sciences was organized at the foot of Klyuchevskaya Sopka for systematic research observations of the modern activity of Kamchatka volcanoes. Fragmentary information about volcanic activity in the Kuril Islands was published at the end of the last and beginning of the current centuries by travelers B. R. Golovin and F. Kruzenshtern, D. Milne and G. Snow. After the Great Patriotic War, the volcanoes of the Kuril Islands were studied in more detail by G. B. Korsunskaya and B. I. Vlodavets, and at present, their study is continued by scientists from the Kamchatka volcanological station. volcanoes. At present, there are at least 180 volcanoes here, of which 14 are active, 9 are attenuated, and more than 157 are extinct. In addition to volcanoes, Kamchatka abounds in geysers, hot springs and volcanic salsas. The Kamchatka Peninsula is located in a mobile zone of the earth's crust, captured by Alpine folding and volcanism, and belongs to the volcanic Pacific "Ring of Fire". The intense volcanism of Kamchatka u u v is combined with high seismicity, with frequent earthquakes up to magnitude 9. Both of these geological processes have played and are playing a significant role in the formation of both the internal structure and the relief of the peninsula. The nature of the surface of the peninsula is typical for a mountain-volcanic country. Two mountain ranges stretch along the peninsula in a northeasterly direction: the Sredinny Ridge runs in the western part, and the East Kamchatsky Range runs along the eastern coast.

VOLCANISM
a set of processes and phenomena associated with the movement of magma (together with gases and steam) in the upper mantle and the earth's crust, its outpouring in the form of lava or ejection to the surface during volcanic eruptions (see also VOLCANOES). Sometimes large volumes of magma cool and solidify before they reach the Earth's surface; in this case they form igneous intrusions.

MAGMATIC INTRUSIONS
The sizes and shapes of intrusive bodies can be judged when they are at least partially exposed by erosion. Most of the intrusions formed at significant depths (hundreds and thousands of meters) and are under a thick layer of rocks, and only a few reached the surface in the process of formation. Relatively small intrusive bodies were completely exposed as a result of subsequent erosion. Theoretically, intrusive bodies come in any size and any shape, but usually they can be attributed to one of the varieties, characterized by a certain size and shape. Dikes are plate-shaped bodies of intrusive igneous rocks, clearly bounded by parallel walls, which penetrate the host rocks (or lie unconformably with them). Dikes range in diameter from several tens of centimeters to tens and hundreds of meters, however, as a rule, they do not exceed 6 m, and their length can reach several kilometers. Usually in the same area there are numerous dikes, similar in age and composition. One of the mechanisms of dike formation is the filling of cracks in host rocks with magmatic melt. The magma expands the cracks and partially melts and absorbs the surrounding rocks, forming and filling the chamber. Near contact with the wall rock, due to the relatively rapid cooling, dikes usually have a fine-grained structure. The host rock can be altered by the thermal action of the magma. Dikes are often more resistant to erosion than wall rocks and their outcrops form narrow ridges or walls. Sills are sheeted intrusions similar to dykes, but occur in conformity with (usually horizontal) layers of host rock. Sills are similar in thickness and length to dikes, with thicker sills occurring more frequently. The Palisade sill, in the area of ​​the famous Hudson River bank opposite New York, was originally over 100 m thick and ca. 160 km. The thickness of the Wyn sill in the north of England exceeds 27 m. Laccoliths are lenticular intrusive bodies with convex or domed upper surfaces and relatively flat lower surfaces. Like the sills, they lie in conformity with the layers of the enclosing deposits. Laccoliths are formed from magma flowing either through dike-shaped supply channels from below or from sill, such as the well-known laccoliths in the Henry Mountains in Utah, which are several kilometers across. However, larger laccoliths are also found. Bismalites are a special variety of laccoliths - cylindrical intrusions, broken by cracks or faults, with a raised central part. Lopolites are very large lenticular intrusive bodies, concave in the central part (saucer-shaped), occurring more or less according to the structures of the host rocks. One of the largest lopoliths (about 500 km across) was found in the Transvaal (South Africa). Another fairly large lopolith is located in the area of ​​the Sudbury nickel deposit (Ontario, Canada). Batholiths are large irregularly shaped intrusive bodies expanding downwards, going to a considerable depth (as a rule, their soles are not exposed by erosion). The area of ​​batholiths can reach several thousand square kilometers. They are often found in the central parts of the folded mountains, where their strike generally corresponds to that of the mountain system. However, usually batholiths cut through the main structures. The batholiths are composed of coarse-grained granites. The surface of the batholith can be very uneven with outgrowths, protrusions and processes. In addition, large prisms of parent rocks, which are called roof remnants, can be located in the upper part of the batholith. Like many other intrusive bodies, batholiths are surrounded by a zone (halo) of rocks altered (metamorphosed) as a result of the thermal action of magma. The size of the batholiths is so large that it is still not entirely clear how their intrusion occurs. It has been suggested that the formation of the batholith chamber occurs as a result of the collapse of large blocks of bedrock into molten magma, and then their absorption, melting and assimilation by magma (the so-called magmatic collapse hypothesis). A less common hypothesis is that the granitic batholith rocks are remelted and recrystallized wall rocks with a small addition of new igneous material (the granitization hypothesis). Stocks - similar to batholiths, but are smaller. Conventionally, stocks are defined as batholithic intrusive bodies with an area of ​​less than 100 km2. Some of them are domed protrusions on the surface of the batholith. Necks are cylindrical intrusive bodies that fill the vents of volcanoes, usually having a diameter of no more than 1.5 km. Volcanic necks are stronger than the host rocks, due to which, after the destruction of volcanic structures by erosion, they remain in the relief in the form of spiers or steep hills.
Other magmatic intrusions. There are a large number of varieties of small intrusive bodies that are rarer than those discussed above. Among them, phacoliths stand out - conformably occurring, biconvex, lenticular bodies, usually formed in the crests of anticlines or in the depressions (hinges) of synclines; apophyses - branches from larger intrusive bodies that have an irregular shape; conical dikes, or conical layers, arc-shaped dikes, gently plunging towards the center of the arc, presumably formed as a result of the filling of concentric cracks above magma chambers; ring dikes - vertical dikes, having a round or oval shape in plan and formed during the filling of ring faults that occur during the subsidence of the underlying igneous mass.

Collier Encyclopedia. - Open society. 2000 .

Synonyms:

See what "VOLCANISM" is in other dictionaries:

1) a geological doctrine that attributes the formation of the earth's crust and upheavals on the globe to the action of fire. 2) the same as plutonism. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. VOLCANISM The system of geologists, ... ... Dictionary of foreign words of the Russian language

A set of processes and phenomena associated with the movement of magmas. masses and often accompanying gas-water products from the deep parts of the earth's crust to the surface. In a narrow sense, V. the totality of phenomena associated with the volcano. and accompanying her ... ... Geological Encyclopedia

The totality of phenomena caused by the penetration of magma from the depths of the Earth to its surface ... Big Encyclopedic Dictionary

The geological process caused by the activity of magma at the depth of the Earth's surface ... Geological terms

VOLCANISM, volcanic activity. The term is general for all aspects of the process: eruptions of molten and gaseous masses, the formation of mountains and craters, the occurrence of lava flows, geysers and hot springs ... Scientific and technical encyclopedic dictionary

VOLCANISM, volcanism, pl. no, husband. (geol.). The activity of the internal forces of the globe, leading to a change in the geological structure of the earth's crust and accompanied by volcanic eruptions, earthquakes. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 ... Explanatory Dictionary of Ushakov

Exist., number of synonyms: 1 cryovolcanism (1) ASIS Synonym Dictionary. V.N. Trishin. 2013 ... Synonym dictionary

volcanism- a, m. volcanisme m. German A set of phenomena associated with the movement of a molten liquid mass (magma) in the earth's crust and its outpouring onto the surface of the Earth. BAS 2. Here .. for an area approximately equal to the entire area of ​​​​Belgium ... ... Historical Dictionary of Gallicisms of the Russian Language

volcanism- An endogenous process associated with the movement of magmas and associated gas-water products from deep zones to the surface. [Glossary of geological terms and concepts. Tomsk State University] Topics geology, geophysics Generalizing ... ... Technical Translator's Handbook

volcanism- A set of processes and phenomena associated with the outpouring of magma on the surface of the Earth. Syn.: volcanic activity… Geography Dictionary

Volcanic eruption on Io ... Wikipedia

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• Volcanism and sulfide mounds of paleooceanic margins. On the example of pyrite-bearing zones of the Urals and Siberia, Zaikov V.V. The monograph describes the volcanism and ore content of Paleozoic rifts of marginal seas, ensimatic island arcs, and interarc basins. On the example of the Urals of Siberia, it is shown that ...

VOLCANISM, a set of endogenous processes associated with the formation and movement of magma in the bowels of the Earth and its eruption on the land surface, the bottom of the seas and oceans. It is an integral part of magmatism. In the process of volcanism, magma chambers are formed in the depths of the earth, the rocks around which can change under the influence of high temperature and the chemical action of magma. When the magmatic melt reaches the Earth's surface, the most spectacular manifestation of volcanism is observed - a volcanic eruption, which consists in the outpouring or gushing of liquid lava (effusion), squeezing out viscous lava (extrusion), destruction of the volcanic structure by an explosion and ejection of solid products of volcanic activity (explosion). As a result of eruptions of different types and forces, volcanoes of various shapes and sizes are formed, volcanic rocks are formed. Volcanism is associated with phenomena that precede (harbingers), accompany and complete (post-volcanic phenomena) volcanic eruptions. Harbingers observed from several hours to several centuries before the eruption include some volcanic earthquakes, deformations of the earth's surface and volcanic structures, acoustic phenomena, changes in geophysical fields, composition and intensity of fumarolic gases (from active volcanoes), etc.

Phenomena observed during eruptions: volcanic explosions, associated shock waves, sharp jumps in atmospheric pressure, electrified eruptive (eruptive) clouds with Elmo fires, lightning, volcanic ashfalls and acid rains, the occurrence of lahars (mudstone flows), the formation of a tsunami - during falling into the water of huge volumes of landslide and explosive deposits. Volcanic phenomena also include a decrease in the level of solar radiation and temperature, the appearance of purple sunsets caused by clouding of the atmosphere by volcanic dust and aerosols during catastrophic explosive eruptions. After eruptions, post-volcanic phenomena are observed associated with the cooling of the magma chamber - outflows of volcanic gases (fumaroles) and thermal waters (thermal springs, geysers, etc.).

According to the place of manifestation, volcanism is distinguished terrestrial, underwater and subaerial (underwater-surface); according to the composition of the eruption products - sequentially differentiated basalt-andesite-rhyolite, contrast-differentiated basalt-rhyolite (bimodal), alkaline, alkaline-ultrabasic, basic, acidic and other volcanism is most characteristic of the convergent boundaries of lithospheric plates, where in the process of their counter interaction volcanic belts (island-arc and marginal-continental) are formed above the zone of subduction (subduction) of one plate under another or in the area of ​​collision (collision) of their continental parts. Volcanism is also widely manifested at the divergent boundaries of lithospheric plates, confined to mid-ocean ridges, where, as the plates move apart in the course of underwater volcanic activity, a new formation of the oceanic crust occurs. Volcanism is also characteristic of the inner parts of lithospheric plates - structures of hot spots, continental rift systems, trap provinces of continents, and intraoceanic basalt plateaus.

Volcanism began in the early stages of the Earth's development and became one of the main factors in the formation of the lithosphere, hydrosphere and atmosphere. The development of all three shells due to volcanism continues: the volume of rocks in the lithosphere increases annually by more than 5-10 km 3, and an average of 50-100 million tons of volcanic gases per year enter the atmosphere, some of which is spent on the transformation of the hydrosphere. Many deposits of metallic (gold, silver, non-ferrous metals, arsenic, etc.) and non-metallic (sulfur, borates, natural building materials, etc.) minerals, as well as geothermal resources, are genetically associated with volcanism.

Manifestations of volcanism have been identified on all planets of the terrestrial group. On Mercury, Mars, and the Moon, volcanism has probably already ended (or almost ended), and intensively continues only on Venus. At the end of the 20th - beginning of the 21st century, volcanic forms and ongoing volcanic activity were discovered on the satellites of Jupiter and Saturn - Europa, Io, Callisto, Ganymede, Titan. On Europa and Io, a specific type of volcanism is noted - cryovolcanism (eruption of ice and gas).

Lit .: Melekestsev IV Volcanism and relief formation. M., 1980; Rast H. Volcanoes and vulcanism. M., 1982; Vlodavets V. I. Handbook of volcanology. M., 1984; Markhinin E.K. Volcanism. M., 1985.

If we imagine what our planet was like 3-4 billion years ago, then a terrifying picture will arise before us: explosions, an incessant roar, huge fountains of erupting magma, whole seas of molten matter - in a word, a kingdom in the early stages of the formation of the Earth's surface.

The earliest stage of volcanism (often referred to as the 'lunar' stage) cannot be judged from the rocks now available. Primordial volcanic rocks practically did not survive, all of them were processed over billions of years as a result of later processes. However, there are such rocks on the Moon, which stopped tectonic activity much earlier than the Earth, so the “lunar stage” model in the development of volcanism on Earth can be built on the basis of real-life rocks on the Moon.

A set of phenomena associated with the movement of magma in the upper mantle and, as well as on the surface of the Earth. It is characterized by the most concentrated energy per unit area. The most striking examples of volcanic activity are, of course, the volcanoes themselves. Their location is determined, first of all, by the tectonic structure of the earth's crust, therefore, in many respects (although not completely) the areas of volcanism distribution coincide. Scientists distinguish terrestrial and underwater volcanism.

During terrestrial volcanism, the conditions for the transformation of magmatic matter change dramatically. During an eruption, the pressure of the environment drops in it (from 102 to 1 kg / cm2), density (from 2 to 1.3 10 (-3) g / cm3), viscosity, etc. Underwater volcanism proceeds in a denser medium than air. Already at a depth of about 2 km, the pressure of water vapor in the magma becomes less than the pressure of the surrounding water. Vapor formation at great depths is impossible. Volcanoes can also be under the ice. Such volcanoes are observed in and. In the recent past, for example, they existed in the Caucasus, as well as in the Sayans.

Signs of a nearby eruption are some changes in the earth's crust and seismic tremors. This occurs when pressure builds up in the vent of a volcano due to a plug of lava left over from a previous eruption. The material ejected by explosions consists of gases, vapors, liquid lava and solid material. With a small power of explosions, only gases break through to the surface. Sometimes the volume of volcanic material is so significant that hilly plains composed of ash and debris form along the periphery of the volcano.

In 1912, during a strong explosion of the Katmai volcano in the Aleutian Islands, almost 16 km3 of ash and pumice were thrown out. At the foot of the volcano, the thickness of the ash layer reached 15 m, and 160 km from it - 3 m. The explosion was heard 1200 km away. There was so much ash in the air that the volcano and its environs plunged into night darkness; the air smelled of sulfur. During the explosions of Bezymyanny and Sheveluch volcanoes, the same phenomena were observed. During the eruption, not only the materials of old volcanoes are destroyed and ejected, but also the rocks of the crystalline basement. The clastic material is often highly fragmented, and therefore the fragments have an acute-angled shape. Their size reaches 15 m.

Layered volcanoes are commonly referred to by scientists as stratovolcanoes. They are formed in a relatively short time, however, it also differs: Paricutin (Mexico) - in 10 - 12 years; Izalko () - for 200 years. During such a period of time, the volcano erupts a large volume of detrital material to the surface. For example, Klyuchevskaya Sopka (Kamchatka) over the past 50 years has thrown out an average of about 0.03 km3 of debris per year, i.e., almost 45 million tons annually. Volcanic eruptions usually release lava. Sometimes there is so much of it that lava lakes form in the craters. In the caldera (from the Spanish caldera, literally - a large cauldron; here - a cauldron-shaped depression) of the Kilauea volcano in the Hawaiian Islands, such a lava lake appears and disappears. Fountains of magma 20 m high rise above its surface. Part of the lava flows through cracks onto the slopes of the volcano. Eruptions are sometimes accompanied by "scorching clouds" - incandescent clouds. They are saturated with gases and contain a lot of clastic material. The volume of lava flows is measured in hundreds and thousands of cubic meters per second. The flow rate depends on the viscosity of the substance, the slope of the surface and ranges from 10 to 60 km/h. Lava flows form undulating and blocky plains. Wavy plains are formed by the most mobile lavas and by the nature of the relief they resemble huge twisted ropes. At moderate speeds of lava movement, areas with a slab surface are formed, and in the thickness of lavas - voids in the form of tunnels. Blocky plains are composed of more viscous lavas. When the lava flow warps, cracks appear, causing crushing into blocks and blocks with a diameter of up to 5 m. In this case, most of the blocks have an acute-angled shape. Viscous lava is inactive and often accumulates in the form of "squeeze domes" near the vent of the volcano. The extrusion of such lava occurs slowly, over many months and even years. Volcanic activity is accompanied by emissions of hot water. Hydrothermal processes lead to the appearance of geysers.

Channels for the release of vapors having a temperature of 130 - 165 ° C and containing impurities of carbon dioxide, arsenic, hydrogen, sulfur, chlorine and other elements are called fumaroles. Such channels are observed in calderas and craters of extinct volcanoes, in lava flows, on the slopes of volcanoes. Sinter cones, terraces, "tongues" are formed at the place of gas and vapor outlets, composed of rocks formed during the crystallization of minerals. Sometimes large accumulations of sulfur are formed along the periphery of fumaroles (in solfataras).

Underwater volcanism has been less studied than terrestrial volcanism, although there are a lot of underwater volcanoes at the bottom of the oceans. The zone of mid-ocean ridges annually receives 5 - 6 km3 of lava, while on land - only about 1 km3. There are explosions of volcanoes, during which cypress-like columns of matter rise. Clouds (in the water!) of ash and fine earth are separated from the volcano, blocks and volcanic bombs are ejected. However, lava flows here much more slowly than on land. The lavas are composed mainly of basalts and are shaped like globular lavas.

Even less is known about subglacial volcanism than about underwater volcanism. Observations in Iceland and Antarctica have shown that these special volcanic processes arise from the interaction of the solid earth's crust, ice and atmosphere. In Iceland, for example, a number of volcanoes are located at the base of ice caps. The thickness of the ice covering the vents of volcanoes reaches 300 - 500 m. During eruptions, which are accompanied by intense melting of ice, the moraine is released and mixed with pyroclastic material.

Indispensable companions of volcanoes are volcanotectonic uplifts and subsidences of the surface. In Iceland, the length of faults associated with uplifts reaches tens of kilometers, and the amplitude is 30–40 m. When volcanoes become active, not only vertical, but also horizontal movements are observed. Large depressions are known along the periphery of volcanoes, for example, around Klyuchevskaya Sopka, the origin of which is due to the subsidence of the earth's crust after the release of a magmatic source.

INTRODUCTION

The phenomena of volcanic eruptions accompany the entire history of the Earth. It is likely that they influenced the climate and biota of the Earth. Currently, volcanoes are present on all continents, and some of them are active and represent not only a spectacular sight, but also formidable dangerous phenomena.

The volcanoes of the Mediterranean were associated with the deity of fire on Etna and the volcanoes of the islands of Vulcano and Santorini. It was believed that the Cyclopes worked in the underground workshops.

Aristotle considered them to be the result of the action of compressed air in the voids of the Earth. Empedocles believed that the cause of the action of volcanoes is the material melted in the depths of the Earth. In the 18th century, a hypothesis arose that a thermal layer exists inside the Earth, and as a result of folding phenomena, this heated material is sometimes brought to the surface. In the 20th century, factual material is first accumulated, and then ideas arise. They have become most productive since the emergence of the theory of lithospheric plate tectonics. Satellite studies have shown that volcanism is a cosmic phenomenon: traces of volcanism were found on the surface of the Moon and Venus, and active volcanoes were found on the surface of Jupiter's moon Io.

It is also important to consider volcanism from the point of view of the global impact on the geographic envelope in the process of its evolution.

The purpose of the work is to study the processes of volcanism on Earth and its geographical consequences.

In accordance with the goal, the following tasks are solved in the work:

1) Definitions are given: volcanism, volcano, volcano structure, types of volcanic eruptions;

2) The main volcanic belts of the Earth are being studied;

3) Post-volcanic phenomena are being studied;

4) The role of volcanism in the transformation of the relief and climate of the Earth is characterized.

The work used educational materials, scientific publications, Internet resources.

CHAPTER 1. GENERAL CONCEPTS ABOUT VOLCANISM

1.1 The concept of the process of volcanism

A volcano is a place where magma or mud comes to the surface from a vent. In addition, it is possible for magma to erupt along cracks and gases to escape after an eruption outside the volcano. A volcano is also called a form of relief that arose during the accumulation of volcanic material.

Volcanism is a set of processes associated with the appearance of magma on the surface of the Earth. If magma appears on the surface, then this is an effusive eruption, and if it remains at a depth, this is an intrusive process.

If magmatic melts burst to the surface, then volcanic eruptions occurred, which were mostly calm in nature. This type of magmatism is called effusive.

Often, volcanic eruptions are explosive in nature, in which magma does not erupt, but explodes, and cooled melt products, including frozen droplets of volcanic glass, fall onto the earth's surface. Such eruptions are called explosive.

Magma is a melt of silicates located in the deep zones of a sphere or mantle. It is formed at certain pressures and temperatures and, from a chemical point of view, is a melt that contains silica (Si), oxygen (O 2) and volatile substances present in the form of gas (bubbles) or solution and melt.

The viscosity of magmas depends on the composition, pressure, temperature, gas and moisture saturation.

According to the composition, 4 groups of magmas are distinguished - acidic, basic, alkaline and alkaline earth.

According to the depth of formation, 3 types of magmas are distinguished: pyromagma (deep melt rich in gas with T ~ 1200°C, very mobile, speed on slopes up to 60 km/h), hypomagma (at large P, insufficiently saturated and inactive, T = 800-1000 °С, as a rule, acidic), epimagma (degassed and not erupted).

Magma generation is a consequence of fractional melting of mantle rocks under the influence of heat input, decompaction, and an increase in water content in certain zones of the upper mantle (water can reduce melting). This occurs: 1) in rifts, 2) in subduction zones, 3) above hot spots, 4) in transform fault zones.

Magma types determine the nature of the eruption. It is necessary to distinguish between primary and secondary magmas. Primary ones occur at different depths of the earth's crust and upper mantle and, as a rule, have a homogeneous composition. However, moving into the upper levels of the earth's crust, where the thermodynamic conditions are different, primary magmas change their composition, turning into secondary ones and forming different magmatic series. This process is called magmatic differentiation.

If a liquid magmatic melt reaches the earth's surface, it erupts. The nature of the eruption is determined by: the composition of the melt; temperature; pressure; the concentration of volatile components; water saturation. One of the most important causes of magma eruptions is its degassing. It is the gases contained in the melt that serve as the "engine" that causes the eruption.

1.2 Structure of volcanoes

Magma chambers below volcanoes are usually roughly circular in plan, but it is not always possible to determine whether their three-dimensional shape approaches spherical or is elongated and flattened. Some active volcanoes have been intensively studied using seismometers to determine the sources of vibration caused by the movement of magma or gas bubbles, as well as to measure the deceleration of artificially generated seismic waves passing through the magma chamber. In some cases, the existence of several magma chambers at different depths has been established.

In classically shaped volcanoes (a cone-shaped mountain), the magma chamber closest to the surface is usually associated with a vertical cylindrical passage (several meters to tens of meters in diameter), which is called a supply channel. Magma erupted from volcanoes of this shape usually has a basaltic or andesitic composition. The place where the supply channel reaches the surface is called a vent and is usually located at the bottom of a depression on top of a volcano called a crater. Volcanic craters are the result of a combination of several processes. A powerful eruption can expand the vent and turn it into a crater due to the crushing and ejection of surrounding rocks, and the bottom of the crater can sink due to voids left by the eruption and magma leakage. In addition, the height of the rims of the crater may increase as a result of the accumulation of material ejected during explosive eruptions. Volcano vents are not always exposed to the sky, but are often blocked by debris or solidified lava, or hidden under lake waters or accumulated rainwater.

A large, shallow magma chamber containing rhyolitic magma is often connected to the surface by a ring fault rather than a cylindrical conduit. Such a fault allows the overlying rocks to move up or down, depending on the change in the volume of magma within the chamber. A depression formed as a result of a decrease in the volume of magma below (for example, after an eruption), volcanologists call a caldera. The same term is used for any volcanic crater larger than 1 km in diameter, since craters of this size are formed more by subsidence of the earth's surface than by explosive ejection of rocks.

Rice. 1.1. The structure of the volcano 1 - volcanic bomb; 2 - canonical volcano; 3 - layer of ash and lava; 4 - dike; 5 - the mouth of the volcano; 6 - strength; 7 – magma chamber; 8 - shield volcano.

1.3 Types of volcanic eruptions

volcanism climate relief magma

Liquid, solid and gaseous volcanic products, as well as forms of volcanic structures, are formed as a result of eruptions of various types, due to the chemical composition of magma, its gas saturation, temperature and viscosity. There are different classifications of volcanic eruptions, among them there are common types for all.

The Hawaiian type of eruptions is characterized by ejections of very liquid, highly mobile basaltic lava, which form huge flat shield volcanoes (Fig. 1.2.). Pyroclastic material is practically absent, often lava lakes are formed, which, gushing to a height of hundreds of meters, throw out liquid pieces of lava such as cakes, creating shafts and spatter cones. Lava flows of small thickness spread over tens of kilometers.

Sometimes changes occur along faults in a series of small cones (Figure 1.3).

Rice. 1.2. Eruption of liquid basaltic lava. Volcano Kilauea

Strombolian type(from Stromboli volcano in the Aeolian Islands north of Sicily) eruptions are associated with more viscous basic lava, which is ejected by explosions of different strength from the vent, forming relatively short and more powerful flows (Fig. 1.3).

Rice. 1.3. Strombolian type eruption

Explosions form cinder cones and plumes of twisted volcanic bombs. Stromboli Volcano regularly ejects a "charge" of bombs and pieces of red-hot slag into the air.

plinian type(volcanic, Vesuvian) got its name from the Roman scientist Pliny the Elder, who died during the eruption of Vesuvius in 79 AD. (3 large cities were destroyed - Herculaneum, Stabia and Pompeii). A characteristic feature of eruptions of this type are powerful, often sudden explosions, accompanied by emissions of huge amounts of tephra, forming ash and pumice flows. It was under the high-temperature tephra that Pompeii Stabia was buried, and Herculaneum was littered with mud-stone flows - lahars. As a result of powerful explosions, the near-surface magma chamber emptied the summit part of Vesuvius, collapsed and formed a caldera, into which, 100 years later, a new volcanic cone grew - modern Vesuvius. Plinian eruptions are very dangerous and occur suddenly, often without any prior preparation. The grandiose explosion in 1883 of the Krakatoa volcano in the Sunda Strait between the islands of Sumatra and Java belongs to the same type, the sound from which was heard at a distance of up to 5000 km, volcanic ash reached almost 100 km height. The eruption was accompanied by the emergence of huge (25-40 m) waves in the tsunami ocean, in which about 40 thousand people died in coastal areas. A giant caldera formed on the site of the Krakatau group of islands.