Volcanic activity, which is among the most terrible phenomena nature, often brings great disasters to people and national economy. Therefore, it must be borne in mind that although not all active volcanoes cause misfortunes, nevertheless, each of them can be a source of negative events to one degree or another, volcanic eruptions are of varying strength, but only those accompanied by death are catastrophic. and material values.

General ideas about volcanism

“Volcanism is a phenomenon due to which, during the course of geological history, the outer shells of the Earth were formed - the crust, hydrosphere and atmosphere, that is, the habitat of living organisms - the biosphere.” This opinion is expressed by most volcanologists, but this is by no means the only idea about the development of the geographic envelope. Volcanism covers all phenomena associated with the eruption of magma to the surface. When magma is deep in the earth's crust under high pressure, all of its gaseous components remain in a dissolved state. As the magma moves towards the surface, the pressure decreases, gases begin to be released, as a result, the magma pouring onto the surface differs significantly from the original one. To emphasize this difference, magma erupted on the surface is called lava. The process of eruption is called eruptive activity.

Fig.1. Eruption of Mount St. Helens

Volcanic eruptions proceed differently, depending on the composition of the products of the eruption. In some cases, eruptions proceed quietly, gases are released without large explosions, and liquid lava flows freely to the surface. In other cases, eruptions are very violent, accompanied by powerful gas explosions and squeezing or outpouring of relatively viscous lava. The eruptions of some volcanoes consist only in grandiose gas explosions, as a result of which colossal clouds of gas and water vapor saturated with lava are formed, rising to great heights. By modern ideas, 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, pockets of molten matter - magma - are formed. In 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 pressure drops, are separated from magma and go into the atmosphere. In places of eruption, lava covers, flows , volcanoes-mountains, composed of lavas and their pulverized particles - pyroclasts. According to the content of the main component - magma silicon oxide and the volcanic rocks formed by them - volcanic rocks are divided into ultrabasic (silicon oxide less than 40%), basic (40-52%), medium ( 52-65%), acidic (65-75%), basic or basaltic magma is the most common.

Types of volcanoes, composition of lavas. Classification by the nature of the eruption

The classification of volcanoes is based mainly on the nature of their eruptions and on the structure of volcanic apparatuses. And the nature of the eruption, in turn, is determined by the composition of the lava, the degree of its viscosity and mobility, temperature, and the amount of gases contained in it. Three processes are manifested in volcanic eruptions: 1) effusive - the outpouring of lava and its spreading over the earth's surface; 2) explosive (explosive) - an explosion and the release of a large amount of pyroclastic material (solid eruption products); 3) extrusive - squeezing out, or squeezing out, magmatic matter onto the surface in a liquid or solid state. In a number of cases, mutual transitions of these processes and their complex combination with each other are observed. As a result, many volcanoes are characterized by a mixed type of eruption - explosive-effusive, extrusive-explosive, and sometimes one type of eruption is replaced by another in time. Depending on the nature of the eruption, the complexity and diversity of volcanic structures and forms of occurrence of volcanic material is noted. Among volcanic eruptions, the following are distinguished: eruptions of the central type, fissure and areal.


Fig.2. Hawaiian type of eruption

1 - Ash plume, 2 - Lava fountain, 3 - Crater, 4 - Lava lake, 5 - Fumaroles, 6 - Lava flow, 7 - Lava and ash layers, 8 - Rock layer, 9 - Sill, 10 - Magma channel, 11 - Magma chamber, 12 - Dike

Volcanoes of the central type. They have a shape close to round in plan, and are represented by cones, shields, and domes. At the top there is usually a bowl-shaped or funnel-shaped depression called a crater (Greek 'crater'-bowl). From the crater into the depths of the earth's crust there is a magma-supplying channel, or a volcano vent, which has a tubular shape, along which magma from a deep chamber rises to the surface. Among volcanoes of the central type, polygenic ones, formed as a result of repeated eruptions, and monogenic ones, which manifested their activity once, stand out.

polygenic volcanoes. These include most of the known volcanoes in the world. There is no unified and generally accepted classification of polygenic volcanoes. Various types eruptions are most often referred to by the name of known volcanoes, in which one or another process manifests itself most characteristically. Effusive, or lava, volcanoes. The predominant process in these volcanoes is effusion, or the outpouring of lava to the surface and its movement in the form of flows along the slopes of a volcanic mountain. Volcanoes of the Hawaiian Islands, Samoa, Iceland, etc. can be cited as examples of this nature of the eruption.


Fig.3. Plinian type of eruption

1 - Ash plume, 2 - Magma conduit, 3 - Volcanic ash rain, 4 - Lava and ash layers, 5 - Rock layer, 6 - Magma chamber

Hawaiian type. Hawaii is formed by the merged peaks of five volcanoes, of which four were active in historical time (Fig. 2). The activity of two volcanoes is especially well studied: Mauna Loa, towering almost 4200 meters above the level Pacific Ocean, and Kilauea with a height of more than 1200 meters. The lava in these volcanoes is mainly basaltic, easily mobile, and high-temperature (about 12,000). In the crater lake, lava is bubbling all the time, its level either decreases or rises. During eruptions, lava rises, its mobility increases, it floods the entire crater, forming a huge boiling lake. Gases are released relatively quietly, forming bursts above the crater, lava fountains rising in height from several to hundreds of meters (rarely). Lava foamed by gases splatters and solidifies in the form of thin glass threads ‘Pele’s hair’. Then the crater lake overflows and lava begins to overflow over its edges and flow down the slopes of the volcano in the form of large flows.

Effusive underwater. Eruptions are the most numerous and least studied. They are also associated with rift structures and are distinguished by the predominance of basaltic lavas. At the bottom of the ocean, at a depth of 2 km or more, the water pressure is so great that explosions do not occur, which means that pyroclasts do not occur. Under water pressure, even liquid basaltic lava does not spread far, forming short dome-shaped bodies or narrow and long flows covered from the surface with a glassy crust. A distinctive feature of submarine volcanoes located at great depths is the abundant release of fluids containing high amounts of copper, lead, zinc and other non-ferrous metals.

Mixed explosive-effusive (gas-explosive-lava) volcanoes. Examples of such volcanoes are the volcanoes of Italy: Etna - the highest volcano in Europe (more than 3263 m), located on the island of Sicily; Vesuvius (about 1200 m high), located near Naples; Stromboli and Vulcano from the group of Aeolian Islands in the Strait of Messina. This category includes many volcanoes of Kamchatka, the Kuril and Japanese islands, and the western part of the Cordillera mobile belt. The lavas of these volcanoes are different - from basic (basalt), andesite-basalt, andesitic to acidic (liparitic). Among them, several types are conditionally distinguished.

Fig.4. Subglacial type of eruptions

1 - Cloud of water vapor, 2 - Lake, 3 - Ice, 4 - Layers of lava and ash, 5 - Layer of rock, 6 - Globular lava, 7 - Magma channel, 8 - Magma chamber, 9 - Dike

Strombolian type. It is characteristic of the Stromboli volcano, which rises in the Mediterranean Sea to a height of 900 m. The lava of this volcano is mainly of basalt composition, but lower temperature (1000-1100) than the lava of the volcanoes of the Hawaiian Islands, therefore it is less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from a few minutes to an hour. Gas explosions are ejected at a relatively great height red-hot lava, which then falls on the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly pieces of lava). Characteristically, very little ash is emitted. The cone-shaped volcanic apparatus consists of layers of slag and solidified lava. Such a famous volcano as Izalco belongs to the same type.

Volcanoes are explosive (gas-explosive) and extrusive-explosive. This category includes many volcanoes, in which large gas-explosive processes with the release of a large amount of solid eruption products, almost without lava outpouring (or in limited sizes) are predominant. This nature of the eruption is associated with the composition of the lavas, their viscosity, relatively low mobility and high saturation with gases. In a number of volcanoes, gas-explosive and extrusive processes are simultaneously observed, expressed in the squeezing out of viscous lava and the formation of domes and obelisks towering above the crater.

Peleian type. Especially clearly manifested in the volcano Mont Pele on about. Martinique is part of the Lesser Antilles. The lava of this volcano is predominantly medium, andesitic, highly viscous and saturated with gases. As it solidifies, it forms a solid plug in the crater of the volcano, which prevents the free exit of gas, which, accumulating under it, creates very high pressures. Lava is squeezed out in the form of obelisks, domes. Eruptions occur as violent explosions. There are huge clouds of gases, supersaturated with lava. These incandescent (with a temperature of over 700-800) gas-ash avalanches do not rise high, but roll down the slopes of the volcano at high speed and destroy all life on their way.


Fig.5. Volcanic activity at Anak Krakatoa, 2008

Krakatau type. It is distinguished by the name of the volcano Krakatau, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The oldest of them, Rakata, is composed of basalts, and the other two, younger ones, are andesites. These three merged volcanoes are located in an ancient vast underwater caldera, formed in prehistoric times. Until 1883, for 20 years, Krakatoa did not show active activity. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate strength in May, after some interruptions they resumed again in June, July, August with a gradual increase in intensity. On August 26, there were two large explosions. On the morning of August 27, there was a giant explosion that was heard in Australia and on the islands in the western Indian Ocean at a distance of 4000-5000 km. An incandescent gas-ash cloud rose to a height of about 80 km. Huge waves up to 30 m high, which arose from the explosion and shaking of the Earth, called tsunamis, caused great destruction on the adjacent islands of Indonesia, they were washed away from the shores of Java and Sumatra about 36 thousand people. In some places, destruction and human casualties were associated with a blast wave of enormous power.

Katmai type. It is distinguished by the name of one of the large volcanoes in Alaska, near the base of which in 1912 a large gas-explosive eruption and directed ejection of avalanches, or flows, of a hot gas-pyroclastic mixture occurred. The pyroclastic material had an acid, rhyolitic or andesite-rhyolite composition. This hot gas-ash mixture filled a deep valley located northwest of the foot of Mount Katmai for 23 km. In place of the former valley, a flat plain about 4 km wide was formed. From the flow that filled it, mass releases of high-temperature fumaroles were observed for many years, which served as the basis for calling it the “Valley of Ten Thousand Smokes”.

Subglacial view of eruptions(Fig. 4) is possible when the volcano is under ice or a whole glacier. Such eruptions are dangerous because they provoke the most powerful floods, as well as their spherical lava. So far, only five such eruptions are known, that is, they are a very rare occurrence.

Monogenic volcanoes

Maar type. This type combines only once erupted volcanoes, now extinct explosive volcanoes. In relief, they are represented by flat saucer-shaped basins framed by low ramparts. The swells contain both volcanic cinders and fragments of nonvolcanic rocks that make up this territory. In a vertical section, the crater has the form of a funnel, which in the lower part is connected to a tubular vent, or explosion tube. These include volcanoes of the central type, formed during a single eruption. These are gas-explosive eruptions, sometimes accompanied by effusive or extrusive processes. As a result, small slag or slag-lava cones (from tens to a few hundred meters high) with a saucer-shaped or bowl-shaped crater depression are formed on the surface.

Such numerous monogenic volcanoes are observed in in large numbers on the slopes or at the foot of large polygenic volcanoes. Monogenic forms also include gas-explosive funnels with an inlet pipe-like channel (vent). They are formed by a single gas explosion of great force. Diamond pipes belong to a special category. Explosion pipes in South Africa are widely known as diatremes (Greek “dia” - through, “trema” - hole, hole). Their diameter ranges from 25 to 800 meters, they are filled with a kind of brecciated volcanic rock called kimberlite (according to the city of Kimberley in South Africa). This rock contains ultramafic rocks, garnet-bearing peridotites (pyrope is a companion of diamond), characteristic of the Earth's upper mantle. This indicates the formation of magma under the surface and its rapid rise to the surface, accompanied by gas explosions.

fissure eruptions

They are confined to large faults and cracks in earth's crust, playing the role of magma channels. The eruption, especially in the early phases, can occur along the entire fissure or separate sections of its sections. Subsequently, groups of contiguous volcanic centers appear along the fault line or crack. The erupted main lava, after solidification, forms basalt covers of various sizes with an almost horizontal surface. In historical times, such powerful fissure eruptions of basaltic lava were observed in Iceland. Fissure eruptions are widespread on the slopes of large volcanoes. O lower, apparently, are widely developed within the faults of the East Pacific Rise and in other mobile zones of the World Ocean. Particularly significant fissure eruptions were in the past geological periods when powerful lava sheets formed.

Areal type of eruption. This type includes massive eruptions from numerous closely spaced volcanoes of the central type. They are often confined to small cracks, or the nodes of their intersection. In the process of eruption, some centers die off, while others arise. The areal type of eruption sometimes captures vast areas where the products of the eruption merge, forming continuous covers.



» Lava Movement

The speed of lava movement is different, depending on its density and on the slope of the area where it makes its way. Relatively small lava flows pouring down steep slopes move forward extremely rapidly; the stream thrown out by Vesuvius on August 12, 1805, rushed along the steep slopes of the cone with amazing speed and in the first four minutes made 5 ½ km, and in 1631 another stream of the same volcano reached the sea within one hour, i.e. traveled 8 miles during this time. Especially liquid lavas are released by open basaltic volcanoes of the island of Hawaii; they are so mobile that they form real lava falls on the cliffs and can move with the slightest slope of the soil, even in G. It has been repeatedly observed how these lavas traveled 10-20 and even 30 km per hour. But such rapidity of movement is, in any case, one of the exceptions; even the lava observed by Scrope in 1822 and which, within 15 minutes, managed to descend from the edge of the crater of Vesuvius to the foot of the cone, is far from ordinary. On Etna, the movement of lava is already considered fast if it occurs at a speed of 1 km in 2-3 hours. Usually, lava moves even more slowly and in some cases only moves 1 m per hour.

The lava flowing out of the volcano in a molten state has a white-hot luster and retains it inside the crater for a long time: this can be clearly seen where, due to cracks, the deep parts of the stream are exposed. Outside the crater, the lava cools rapidly, and the flow is soon covered with a hard crust, consisting of a dark slag mass; within a short time it becomes so strong that a person can safely walk on it; sometimes on such a crust, covering a still moving stream, one can climb to the point where the lava flows out. Solid slag crust forms something like a pipe, inside which a liquid mass moves. The front end of the lava flow is also covered with black hard crust; with further movement, the lava presses this crust to the ground and flows further along it, being covered in front by a new slag shell. This phenomenon does not occur only with very fast lava movement; in other cases, by dropping and moving the slag, a layer of solidified lava is formed, along which the flow moves. The latter presents a rare sight: the front of his Pullet Scrope compares to a huge heap of coals, which, under the influence of some pressure from behind, are piled on top of each other. Its movement is accompanied by a noise like that of pouring metal; this noise is due to the friction of individual lumps of lava, their fragmentation and contraction.

The hard crust of a lava flow usually does not present a flat surface; it is covered with many cracks through which liquid lava sometimes flows; blocks formed as a result of the fragmentation of the original cover collide with each other, like ice floes during ice drift. It is difficult to imagine a wilder and more gloomy picture than that presented to us by the outer surface of a blocky lava flow. Even more peculiar is the form of the so-called wavy lava, which is observed less often, but is well known to every visitor to Vesuvius. The road from Rezina to the observatory was laid for a considerable distance along such a lava; the latter was thrown out by Vesuvius in 1855. The cover of such streams does not break into pieces, but is a continuous mass, the uneven surface of which, with its peculiar appearance, resembles intestinal plexuses.

Volcanoes have always attracted both scientists and laymen. They are called tunnels or passages to the center of the Earth, because when they erupt, lava comes to the surface, filling the deep bowels of our planet. It was the study of volcanoes that allowed scientists to put forward many hypotheses about complex physical and chemical processes occurring at a depth of thousands of kilometers.

Volcanic eruption

Volcanic eruptions can start in different ways. Sometimes a dozing giant warns in advance of his imminent awakening. In this case, small-scale earthquakes occur in its vicinity, and smoke with an admixture of ash comes out of the vent before the outflow of lava, which rises high into the atmosphere and prevents the sun's rays from penetrating to earth's surface. It even happens that the phenomena preceding the actual eruption of the volcano begin several weeks and even months before the release of lava from the volcano. But this is not always the case. Sometimes a volcano erupts almost instantly, with no prior warning signs.

Related materials:

Earthquakes and volcanoes

The rate of volcanic eruptions

Scientists have found that the speed of this process directly depends on the substance that forms the basis of lava. These substances have different temperature melting and different influences on the flow of lava, in which andesite and dacite predominate in slowly erupting volcanoes, and rhyolite in rapidly erupting volcanoes. Apart from chemical composition lava at the rate of volcanic eruptions big influence Renders the amount of gases dissolved in lava. The more of them, the higher the flow rate. Sometimes, with a very large amount of gases, an explosion can occur, leading to a rapid release of an avalanche from a volcanic vent.

Lava Exit Experiment

Some data about volcanoes have been confirmed in the laboratory: rhyolite was heated to 800 degrees Celsius, which is approximately the temperature of the volcanic interior at the beginning of the eruption. It has been proven that under these conditions this substance becomes very fluid due to its low viscosity. Therefore, in real conditions, it allows him to exit the vent of the volcano at high speed. Unfortunately, the impetus for this experiment was a natural disaster that took place in Chile in the town of Chaiten, which is located 10 kilometers from the volcano of the same name.

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Why do volcanoes erupt?

The tragedy occurred on May 1, 2008. Less than a day before the eruption, intense tremors, and soon smoke and ash began to rise into the atmosphere. Everything happened so quickly that it was almost impossible to carry out rescue measures. The eruption was long and intense, which could be observed even from Earth orbit. It was a global event followed by scientists from many countries. The pumice samples were analyzed by two scientists, Donald Dingwell and Jonathan Castro.

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 erupts from a volcanic vent during an eruption. Unlike magma, it does not contain gases, as 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 studying the volcano in those years, originally called it “labes”, which means “collapse” in Latin, and later the word acquired its modern sound.

3. Lava has a different composition for different volcanoes. Most often it is composed of basalts and differs slow flow like liquid dough.

Basalt lava at Kilauea volcano

4. The most liquid lava, resembling water, contains potassium carbonates in its composition 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 found in nuclear reactors. It is an alloy of the contents of the reactor with concrete, metal parts and other debris that is formed as a result of a nuclear crisis.

7. Despite the fact that the corium is of technical origin, its flows are under Chernobyl nuclear power plant externally resemble chilled basalt flows.

8. The most unusual in the world is the so-called "blue lava" on the Ijen volcano in Indonesia. In fact, the brightly glowing streams are not lava, but sulfur dioxide, which, when exiting the vents, turns into a liquid state and shines with blue light.

9. The color of the lava can determine its temperature. Yellow and bright orange are considered the hottest and have a temperature of 1000 ° C and above. Dark red is relatively cool, with a temperature of 650 to 800 ° C.

10. The only black lava is found in the Tanzanian volcano Ol Doinyo Lengai. As mentioned above, it consists of carbonates, giving it dark shade. The lava flows of the summit are rather cool - the temperature is no more than 540 °C. When cooled, they become silvery, creating bizarre landscapes around the volcano.

11. On the Pacific Ring of Fire, volcanoes erupt mainly silicic 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 early days of its existence, our planet was covered with lava oceans, layered in structure.

13. When lava flows down slopes, it cools unevenly, so sometimes lava tubes form inside the flows. The length of these tubes can reach several kilometers, and the width inside is 14-15 meters.

Inside a lava tube in Hawaii

» » Cooling lava

The time required for lava to cool cannot be precisely determined: depending on the power of the flow, the structure of the lava and the degree of initial heat, it varies greatly. In some cases, lava solidifies extremely quickly; so, for example, one of the streams of Vesuvius in 1832 froze in two months. In other cases, the lavas are in motion for up to two years; often, after several years, the temperature of the lava remains extremely high: a piece of wood stuck into it instantly lights up. Such was, for example, the lava of Vesuvius in 1876, four years after the eruption; in 1878 it had already cooled down.

Some streams form fumaroles for many years. On Horullo, in Mexico, in the springs passing through the lava that poured out 46 years ago, Humboldt observed a temperature of 54 °. Streams of significant power freeze even longer. Skaptar-iokul in Iceland in 1783 identified two lava flows, the volume of which exceeded that of Motzblan; there is nothing surprising in the fact that such a powerful mass solidified gradually over the course of five years.

We have seen that lava flows quickly solidify from the surface and are dressed in a solid crust in which the liquid mass moves, as if in a pipe. If after this the amount of released lava decreases, then such a pipe will not be completely filled with it: the upper cover will gradually descend, stronger in the middle and less at the edges; instead of the usual convex surface, which is any thick fluid mass, you get a concave surface in the form of a trough. However, the hard bark that dresses the stream does not always descend: if it is powerful and strong enough, it will withstand its own weight; in such cases, voids form inside the frozen stream; no doubt, it was in this way that the famous grottoes of Iceland arose. The most famous among them is Surtskhellir ("Black Cave") at Kalmanstung, located among a huge lava field; its length is 1600 m, width 16-18 m and height 11-12 m. It consists of a main hall with a number of side chambers. The walls of the grotto are covered with glassy shiny formations, magnificent lava stalactites descend from the ceiling; long stripes are visible on the sides - traces of a moving fiery-liquid mass. Many lava flows of the island of Hawaii are cut through by long grottoes, like tunnels: in some places these grottoes are very narrow, sometimes they expand up to 20 m and form vast high halls decorated with stalactites; they sometimes stretch for many kilometers and meander, following all directions of the lava flow. Similar tunnels have also been described on the volcanic islands of Bourbon (Reunion) and Amsterdam.