Landscapes of erupting lava. What is volcanic lava and what does it consist of? How many degrees are there in lava?

When volcanoes erupt, hot molten rocks - magma - pour out. In air, the pressure drops sharply, and the magma boils - gases leave it.

The melt begins to cool. In fact, only these two properties – temperature and “carbonation” – distinguish lava from magma. Over the course of a year, 4 km³ of lava spills across our planet, mainly at the bottom of the oceans. Not so much, on land there were regions filled with a lava layer 2 km thick.

The initial temperature of the lava is 700–1200°C and higher. Dozens of minerals and rocks are melted in it. They include almost all known chemical elements, but most of all silicon, oxygen, magnesium, iron, aluminum.

Depending on the temperature and composition, lava can be different colors, viscosity and fluidity. Hot, it's shiny bright yellow and orange; cooling down, it turns red and then black. It happens that blue lights of burning sulfur run above the lava flow. And one of the volcanoes in Tanzania erupts black lava, which, when frozen, becomes like chalk - whitish, soft and brittle.

The flow of viscous lava is slow and flows barely (a few centimeters or meters per hour). Along the way, hardening blocks are formed in it. They slow down traffic even more. This kind of lava solidifies in mounds. But the absence of silicon dioxide (quartz) in lava makes it very liquid. It quickly covers vast fields, forms lava lakes, rivers with a flat surface, and even “lava falls” on cliffs. There are few pores in such lava, since gas bubbles easily leave it.

What happens when lava cools?

As the lava cools, the molten minerals begin to form crystals. The result is a mass of compressed grains of quartz, mica and others. They can be large (granite) or small (basalt). If cooling proceeds very quickly, a homogeneous mass is obtained, similar to black or dark greenish glass (obsidian).

Gas bubbles often leave many small cavities in viscous lava; This is how pumice is formed. Different layers of cooling lava flow down the slopes with at different speeds. Therefore, long, wide voids are formed inside the flow. The length of such tunnels sometimes reaches 15 km.

Slowly cooling lava forms a hard crust on the surface. It immediately slows down the cooling of the mass lying below, and the lava continues to move. In general, cooling depends on the massiveness of the lava, initial heating and composition. There are known cases when, even after several years (!), lava still continued to creep and ignited branches stuck into it. Two massive lava flows in Iceland remained warm centuries after the eruption.

Lava from underwater volcanoes usually hardens in the form of massive “pillows”. Due to rapid cooling, a strong crust forms on their surface very quickly, and sometimes gases rupture them from the inside. The fragments scatter over a distance of several meters.

Why is lava dangerous for people?

Main danger lava - its high temperature. It literally burns living beings and buildings along the way. Living things die without even coming into contact with it, from the heat with which it radiates. True, high viscosity inhibits the flow rate, allowing people to escape and preserve valuables.

But liquid lava... It moves quickly and can cut off the path to salvation. In 1977, during a night eruption of the Nyiragongo volcano in Central Africa. The explosion split the crater wall, and lava gushed out in a wide stream. Very fluid, it rushed at a speed of 17 meters per second (!) and destroyed several sleeping villages with hundreds of inhabitants.

The damaging effect of lava is aggravated by the fact that it often carries clouds of toxic gases released from it, a thick layer of ash and stones. It was this kind of flow that destroyed the ancient Roman cities of Pompeii and Herculaneum. A meeting of hot lava with a body of water can result in a disaster - the instantaneous evaporation of a mass of water causes an explosion.

Deep cracks and gaps form in the flows, so you need to walk on cold lava carefully. Especially if it is glassy - sharp edges and debris hurt painfully. Fragments of cooling underwater “pillows” described above can also injure overly curious divers.

Lava varies from volcano to volcano. It differs in composition, color, temperature, impurities, etc.

Carbonate lava

Half consists of sodium and potassium carbonates. This is the coldest and most liquid lava on earth; it flows along the ground like water. The temperature of carbonate lava is only 510-600 °C. Color hot lava- black or dark brown, but becomes lighter as it cools, and after a few months it becomes almost white. Solidified carbonate lavas are soft and brittle and easily dissolve in water. Carbonate lava flows only from the Oldoinyo Lengai volcano in Tanzania.

Silicon lava

Silicon lava is most typical of the volcanoes of the Pacific Ring of Fire. Such lava is usually very viscous and sometimes freezes in the crater of a volcano even before the end of the eruption, thereby stopping it. A plugged volcano may swell a little, and then the eruption resumes, usually with a powerful explosion. The color of hot lava is dark or black-red. Solidified silicon lavas can form black volcanic glass. Such glass is obtained when the melt cools quickly without having time to crystallize.

Basalt lava

The main type of lava erupted from the mantle is characteristic of oceanic shield volcanoes. Half consists of silicon dioxide, half - from aluminum oxide, iron, magnesium and other metals. Basaltic lava flows are characterized by a small thickness (a few meters) and a large extent (tens of kilometers). The color of hot lava is yellow or yellow-red.

Magma- 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 upon cooling forms magmatic rocks. Erupted magma is lava.

Types of magma

Basalt(mafic) magma appears to be more widespread. It contains about 50% silica, aluminum, calcium, iron and magnesium are present in significant quantities, and sodium, potassium, titanium and phosphorus are present in smaller quantities. Based on their chemical composition, basaltic magmas are divided into tholeiitic (supersaturated with silica) and alkali-basaltic (olivine-basaltic) magma (undersaturated with silica, but enriched with alkalis).

Granite(rhyolite, acidic) magma contains 60-65% silica, it has a lower density, is more viscous, less mobile, and is more saturated with gases than basaltic magma.

Depending on the nature of the movement of magma and the place where it solidifies, 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.Igneous rocks

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 “intrusio” - implementation;

effusive(outpoured) from the Latin word “effusio” - outpouring.

Intrusive(deep) rocks are formed by the slow gradual cooling of magma embedded in the lower layers earth's crust, in conditions high blood pressure and high temperatures. The release of minerals from the magma substance as it cools occurs strictly in a certain sequence; each mineral has its own temperature of formation. First, refractory dark-colored minerals are formed (pyroxenes, hornblende, biotite, ...), then ore minerals, then feldspars, and the last one is released in the form of quartz crystals. The main representatives of intrusive igneous rocks are granites, diorites, syenites, gabbros, and peridotites. Effusive(extrusive) rocks are formed when magma cools as lava on or near the surface of the Earth's crust. In terms of their 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 some depth from it. The main representatives of effusive igneous rocks are obsidians, tuffs, pumice, basalts, andesites, trachytes, liparites, dacites, rhyolites. Basic distinctive features effusive (outpoured) igneous rocks, which are determined by their origin and conditions of formation:

Most soil samples are characterized by a non-crystalline, fine-grained structure with individual crystals visible to the eye;

Some soil samples are characterized by the presence of voids, pores, and spots;

in some soil samples there is some pattern in the spatial orientation of the components (color, oval voids, etc.).

Differences between effusive rocks and intrusive rocks

rocks from each other are determined by the conditions of their formation and the material composition of the magma, which is manifested in their different colors (light - dark) and composition of components. At the core chemical classification is the percentage of silica (SiO2) in the rock. According to this indicator, ultra-acidic, acidic, medium, basic and ultrabasic rocks are distinguished.

The question of what lava is has been of interest to many scientists for a long time. The composition of this substance, as well as its shape, speed of movement, temperature and other aspects have become the subject of a number of studies and scientific works. This can be explained by the fact that it is its frozen flows that represent almost the only source of information regarding the state of the Earth’s interior.

General concept

First, you need to figure out what lava is in the modern sense? Scientists call it the material in a molten state located in the upper part of the mantle. While in the bowels of the earth, the composition of the substance is homogeneous, but as soon as it approaches the surface, the process of boiling begins with the release of gas bubbles. They are the ones who move the hot material towards the cracks in the bark. However, not all of the liquid erupts to the surface. Speaking about the meaning of the word “lava”, it should be noted that this concept applies only to the spilled part of the matter.

Basalt lava

The most common type on our planet is basaltic lava. Most of all geological processes, which occurred on Earth many thousands of years ago, were accompanied by numerous eruptions of this particular type of hot substance. After it solidified, a black rock of the same name was formed. Half of the composition of basaltic lavas is magnesium, iron and some other metals. Due to them, the melt temperature reaches about 1200 degrees. At the same time, the lava flow moves at a speed of about 2 meters per second, which is comparable to a running person. As studies show, in the future they move much faster in the so-called “hot pursuit”. Basaltic lava from the volcano is thin. It flows quite far (up to several tens of kilometers from the crater). It should be noted that this variety is typical for both land and ocean.

Acidic lava

In the case when the substance contains 63% or more silica, it is called acidic lava. The heated material is very viscous and practically incapable of flow. The speed of the flow often does not even reach several meters per day. The temperature of the substance is in the range from 800 to 900 degrees. Melts of this kind are associated with the formation of unusual rocks (ignimbrites, for example). If acidic lava becomes highly saturated with gas, it boils and becomes mobile. After being ejected from the crater, it quickly flows back into the resulting depression (caldera). The consequence of this is the appearance of pumice - an ultra-light material whose density is less than that of water.

Carbonate lava

Speaking about what lava is, many scientists still cannot determine the principle of formation of its carbonate variety. This substance also contains sodium. It erupts from only one volcano on the planet - Oldoinyo Lengai, which is located in Northern Tanzania. Carbonate lava is the most liquid and cold of all existing types. Its temperature is approximately 510 degrees, and it moves along the slopes at the same speed as water. Initially, the substance has a dark brown or black color, but after just a few hours of being on the outside it becomes lighter, and after a few months it turns completely white.

Conclusions

To summarize, we should focus on the fact that one of the most pressing geological problems is associated with lava. It lies in the fact that this substance heats up the bowels of the earth. Foci of hot material rise to the earth's surface, after which they melt it and form volcanoes. Even the world's leading scientists cannot give a clear answer to the question of what lava is. At the same time, we can say for sure that it is only a tiny part global process, driving force which is hidden very deep underground.

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 flows out of a volcanic vent during an eruption. Unlike magma, it does not contain gases, since they escape during explosions.

2. Lava began to be called “lava” only after the eruption of Vesuvius in 1737. Geologist Francesco Serao, who was researching the volcano in those years, initially called it “labes”, which means “collapse” in Latin, and later the word acquired its modern meaning.

3. Different volcanoes have different lava compositions. Most often it is composed of basalts and is characterized by a slow flow, like batter.

Basaltic lava at Kilauea Volcano

4. The most liquid lava, resembling water, contains potassium carbonates and is found only on.

5. In the depths of the Yellowstone supervolcano there is rhyolite magma, which has an explosive nature.

6. The most dangerous lava is corium, or lava-like fuel found in nuclear reactors. It is a fusion of the contents of the reactor with concrete, metal parts and other debris that is generated as a result of a nuclear crisis.

7. Despite the fact that corium has a technical origin, its flows are under Chernobyl nuclear power plant outwardly resemble cooled 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 gas, which, when released from the vents, turns into a liquid state and glows blue.

9. You can determine its temperature by the color of lava. Yellow and bright orange are considered the hottest and have a temperature of 1000 °C and above. Dark red is relatively cool, with temperatures ranging from 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, which give it a dark tint. The lava flows at the summit are quite cool - with a temperature of no more than 540 °C. When cooled, they become silvery in color, creating bizarre landscapes around the volcano.

11. On the Pacific Ring of Fire, volcanoes erupt mainly silicon lava, which has a viscous consistency and solidifies in the mouth of the mountain, stopping its eruption. Subsequently, under pressure, the frozen plug is knocked out of the crater, 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.

It is known that lavas and loose emissions during volcanic eruptions have a temperature of about 500-700 ° C, but often during volcanic eruptions also high temperatures, exceeding 1000° C. Flames are often visible above erupting volcanoes. Such temperatures and flaming combustion of 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 a temperature above 450, maximum 500 ° C.

The presence of substances such as CO2, SO2, H2S, CH4, H2, C12, etc. among the gaseous products of volcanic eruptions gives reason to believe that exothermic processes can take place during volcanic eruptions, which, releasing heat, produce additional heating of the lava and other eruption products. Such processes may include the interaction of oxygen-containing compounds with hydrogen and methane. In this case, for example, ferric iron will transform into divalent iron according to the equations:

The fact that such reactions lead to the reduction of iron is also evidenced by the fact that freshly fallen glass ashes have white, but soon they usually darken and turn brown due to the oxidation of divalent iron by atmospheric oxygen into ferric iron.

The intensive combustion processes of gaseous products of volcanic emissions are evidenced by their clearly observed slow heating to a light heat after leaving the crater, as can be seen in filming made by G. Taziev.

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In the depths of planet Earth, processes of volcanism (volcanic activity) are constantly taking place, based on the movement of magma to the surface along the faults of tectonically moving plates of the earth's crust. The formidable, uncontrollable element of volcanoes creates a colossal threat to life on earth, but it extends the beauty and scale of its external manifestation.

Photo 2 - Pacific Ring of Fire on the map

The greatest 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 ring of volcanism are New Zealand, coast of Antarctica, over 200 kilometers along the California Peninsula, about 1500 kilometers north of Vancouver Island.

There are 540 volcanoes in the world. The Pacific Ring of Fire region, home to about 500 million people, is home to 526 volcanoes.

The first classification of eruption types was proposed in 1907.

Italian scientist G. Mercalli. Later, in 1914, it was supplemented by A.

Lacroix and G. Wolf. It is based on the names of the first volcanoes from characteristic properties eruptions.

Photo 3 – Mauna-Loa volcano

Hawaiian type compiled based on the eruption of the Mauna Loa volcano in the Hawaiian archipelago.

Lava pours out from the central vent and side craters. There are no sudden outbursts or rock explosions. The fiery stream spreads over long distances, freezes, and forms a flat “shield” around the perimeter. The dimensions of the “shield” of the 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 and basalt slag from the depths of the volcano.

Photo 5 - the Vulcano volcano is named by name ancient Roman god fire of Vulcan

Vulcano type. The volcano located on the Aeolian Islands is named after the ancient Roman god of fire, Vulcan.

It is characterized by the eruption of lava with high melt viscosity. The volcano's crater is periodically clogged with magma products. Under colossal pressure, an explosion occurs with the release of lava, ash, and rock fragments to great heights.

Photo 6 – eruption of Mount Vesuvius

Photo 7 – Vesuvius volcano in the present tense

Ethno-Vesuvian (Plinian) type corresponds to the characteristics of the eruption of Mount Vesuvius near Naples.

Periodic blockages of the volcano's crater, powerful explosions, ejections of volcanic bombs from several centimeters to one meter over long distances are clearly visible. mud flows, colossal emissions of ash and lava. Temperature lava flows from 8000 °C to 10000 °C.

Photo 8 – Mount Etna

An example is Mount Etna.

Photo 9 – eruption of the Mont Pele volcano in 1902

Peleian type is based on the natural features of the Mont Pelée volcano on the island of Martinique in the Lesser Antilles group of islands in the Atlantic Ocean.

The eruption is accompanied by powerful jets of gases, creating a huge mushroom cloud in the atmosphere.

Photo 10 is an example of pyroclastic flows (a mixture of rocks, ash and gases) during a volcanic eruption

The temperature inside the molten ash cloud can exceed 7000°C.

Viscous lava in the main mass accumulates around the crater, forming a volcanic dome.

Photos 11, 12 - an example of a gas type volcanic eruption

Gas or phreatic type eruptions in which no lava is 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 subglacial volcano Grimsvotn

Sub-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 threat of dangerous floods and tsunami waves. To date, only five eruptions of this type have been observed.

Plumes of steam, ash and smoke reached a height of 100 meters.

Scientists have found that in the thickness of ocean waters there is much more volcanoes(about 32 thousand) than on land (about 1.5 thousand).

Almost all of the oceanic elevations are active or already extinct volcanoes. Leadership belongs to the Pacific Ocean.

Other articles about volcanoes:

Solid fragments are usually heavily crushed, ground and represented by ash. Eruptions are most often associated with magma of acidic or intermediate composition. The magma chambers that feed these volcanoes are located at great depths, and the magma from them does not always reach the Earth's surface. There are several types of volcanoes in this category:

- Peleian,

- Krakatauan,

- Maarskiy,

- Bandaisan.

P e leisk type

Received its name from the Mont Pele volcano on the island.

Martinique in the Lesser Antilles island arc. The eruption of April 23, 1902 became a classic one. 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, an explosion occurred, accompanied by a terrible roar, the top of the mountain was blown to pieces, and then a dense fiery cloud of gas and sprayed lava moved down the slope at a speed of 180 km/h.

In this fiery cloud the temperature reached 450-6000. It destroyed the city of Saint-Pierre, and 30 thousand of its inhabitants died. A few weeks after the release of gases, a lava dome with steep slopes appeared at the bottom of the crater.

It consisted of hot, thick, acidic lava. In mid-October 1902, a huge lava obelisk began to rise on the eastern side of the dome, resembling a giant finger in shape. 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.

Peleian-type eruptions with the extrusion of viscous lava are called extrusive. Similar eruptions took place in Kamchatka, Alaska, etc.

K r a k a t a u s k i t i p

Characterized by unusually strong explosions with the release of huge amounts of gases and ash. Lava almost never appears on the surface.

The type is named after the Krakatoa volcano, which forms an island in the Sunda Strait between the islands of Sumatra and Java.

Volcanic eruptions of this type are associated with acidic viscous magma, judging by the pumice and ash of dacite composition (65% silica).

M a r s k i t i p

It includes volcanoes with a single eruption, now extinct. In this case, flat saucer-shaped crater depressions appear, along the edges of which low shafts are formed, composed of slag and rock fragments ejected from the crater.

A volcanic channel, or explosion tube, called in ancient volcanoes, approaches the bottom of the crater diatreme. On Ch. 400-500 m explosion tubes are filled with basaltic lava or derivatives of ultramafic magma. Above them are ground blue clay and crushed fragments of volcanic rocks (kimberlite).

Diamonds, pyropes, etc. are found in kimberlites. 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. The explosion tubes have a diameter from several meters to several kilometers.

B a n d a i s a n s k i i t i 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, Bandaisan-type volcanoes do not have 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 channels and cracks in the earth’s crust, through which eruption products are brought to the surface from deep magma chambers.

Volcanoes usually have the shape of a cone with a summit crater (from several to hundreds of meters deep and up to 1.5 km in diameter). During eruptions, a volcanic structure sometimes collapses with the formation of a caldera - a large depression with a diameter of up to 16 km and a depth of up to 1000 m. As the magma rises, the external pressure weakens, associated gases and liquid products escape to the surface, and a volcanic eruption occurs. If ancient rocks, and not magma, are brought to the surface, and water vapor formed during heating predominates among the gases groundwater, then such an eruption is called phreatic.

Active volcanoes include those that erupted in historical times or showed other signs of activity (emission of gases and steam, etc.). Some scientists consider active volcanoes that are reliably known to have erupted within the last 10 thousand.” years.

For example, the Arenal volcano in Costa Rica should be considered active, since during archaeological excavations the site primitive man Volcanic ash was discovered in this area, although for the first time in human memory its eruption occurred in 1968 and before that there were no signs of activity. Volcanoes are known not only on Earth. Images taken from spacecraft reveal huge ancient craters on Mars and many active volcanoes on Io, a moon of Jupiter.

Lava is magma that flows onto the earth's surface during eruptions and then hardens.

Lava eruptions can come from the main summit crater, a side crater on the side of the volcano, or from fissures associated with a volcanic chamber. It flows down the slope as a lava flow. In some cases, lava outpourings occur in rift zones of enormous extent. For example, in Iceland in 1783, within the chain of Laki craters, stretching along a tectonic fault for a distance of about 20 km, an outpouring of -12.5 km3 of lava occurred, distributed over an area of -570 km2. Composition of lava: hard rocks formed when lava cools , contain mainly silicon dioxide, oxides of aluminum, iron, magnesium, calcium, sodium, potassium, titanium and water.

Typically, lavas contain more than one percent of each of these components, and many other elements are present in smaller quantities.

There are many types of volcanic rocks, varying in chemical composition.

Most often there are four types, the membership of which is determined by the content of silicon dioxide in the rock: basalt - 48-53%, andesite - 54-62%, dacite - 63-70%, rhyolite - 70-76%. Rocks that contain less silicon dioxide contain large amounts of magnesium and iron.

When lava cools, a significant part of the melt forms volcanic glass, in the mass of which individual microscopic crystals are found. The exception is the so-called.

phenocrystals are large crystals formed in magma in the depths of the Earth and brought to the surface by a flow of liquid lava. Most often, phenocrysts are represented by feldspars, olivine, pyroxene and quartz. Rocks containing phenocrysts are usually called porphyrites. The color of volcanic glass depends on the amount of iron present in it: the more iron, the darker it is.

Thus, even without chemical analysis, one can guess that the light-colored rock is rhyolite or dacite, the dark-colored rock is basalt, gray- andesite. The type of rock is determined by the minerals visible in the rock. For example, olivine, a mineral containing iron and magnesium, is characteristic of basalts, quartz is characteristic of rhyolites.

As the magma rises to the surface, the released gases form tiny bubbles with a diameter often up to 1.5 mm, less often up to 2.5 cm. They are stored in the solidified rock.

This is how bubbly lavas are formed. Depending on chemical composition Lavas vary in viscosity, or fluidity. With a high content of silicon dioxide (silica), lava is characterized by high viscosity.

The viscosity of magma and lava largely determines the nature of the eruption and the type of volcanic products. Liquid basaltic lavas with low silica content form extensive lava flows more than 100 km long (for example, one lava flow in Iceland is known to stretch for 145 km). The thickness of lava flows usually ranges from 3 to 15 m.

More fluid lavas form thinner flows. Flows 3-5 m thick are common in Hawaii. When solidification begins at the surface of a basalt flow, its interior may remain in liquid state, continuing to flow and leaving behind an elongated cavity, or lava tunnel. For example, on about. Lanzarote (Canary Islands) a large lava tunnel can be traced for 5 km.

The surface of a lava flow can be smooth and wavy (in Hawaii, such lava is called pahoehoe) or uneven (aalawa).

Hot lava, which is highly fluid, can move at speeds of more than 35 km/h, but more often its speed does not exceed several meters per hour. In a slow-moving flow, pieces of the solidified upper crust can fall off and be covered by lava, “resulting in the formation of a zone enriched with debris in the bottom part.

When lava hardens, columnar units (multifaceted vertical columns with a diameter of several centimeters to 3 m) or fracturing perpendicular to the cooling surface are sometimes formed. When lava flows into a crater or caldera, a lava lake forms and cools over time. For example, such a lake formed in one of the craters of the Kilauea volcano on the island. Hawaii during the 1967–1968 eruptions.

when lava entered this crater at a speed of 1.1 x 106 m3/h (part of the lava subsequently returned to the crater 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 tuff rings. Very viscous lava (most often of dacite composition) during eruptions through the main crater or side fissures does not form flows, but a dome with a diameter of up to 1.5 km and a height of up to 600 m. For example, such a dome was formed in the crater of Mount St. Helens (USA) after exceptionally strong eruption in May 1980

The pressure under the dome may build up, and weeks, months or years later it may be destroyed by the next eruption.

In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks protrude above its surface - blocks or spiers of solidified lava, often tens and hundreds of meters high.

After the catastrophic eruption in 1902 of the Montagne Pelee volcano on the island. In Martinique, a lava spire formed in the crater, which grew by 9 m in a day and as a result reached a height of 250 m, and collapsed a year later. On the Usu volcano on the island. Hokkaido (Japan) in 1942, during the first three months after the eruption, the Showa-Shinzan lava dome grew by 200 m. The viscous lava that composed it made its way through the thickness of the previously formed sediments. Maar is a volcanic crater formed during an explosive eruption (most often during high humidity rocks) without lava outpouring.

A ring shaft of debris ejected by the explosion is not formed, unlike tuff rings - also explosion craters, which are usually surrounded by rings of debris products.

Types of volcanoes and their structure

All volcanoes, based on the shape of the vent and the morphology of the structure, are divided into volcanoes central And linear type (Fig. 5.5), which, in turn, according to the complexity of their structure are divided into monogenic And polygenic.

Monogenic buildings of the central type Most of them are associated with polygenic volcanoes and are second-order volcanoes.

They are presented slag cones or extrusion domes and they are composed, as a rule, of rocks of similar composition.

Polygenic volcanoes of the central type By geological structure and form are divided into stratovolcanoes, shield, domed And combined, representing a combination of the listed volcanic structures.

In turn, these structures can be complicated by a summit or peripheral, in relation to the volcano, caldera.

Stratovolcanoes- this is when, in polygenic volcanoes of the central type, a clearly defined, gently sloping (or steep) layered cone with a slope of 20-30º, composed of interlayered lavas, tuffs, lava breccias, slags, slag lavas, as well as sedimentary rocks of marine or continental origin, develops around the vent ( rice.

Basic lavas are less viscous compared to acidic lavas, and, spreading over longer distances, form less steep structures (no steeper than 10º).

Shield volcanoes They are relatively simple, low volcanic structures (Fig.

5.1a), composed mainly of basalts with transverse dimensions up to several tens of km and slopes no steeper than 3-5º (for example, Tskhun volcanoes in Armenia, Uzon in Kamchatka, etc.).

Dome volcanoes or volcanic domes and structure are very diverse in shape (from faintly noticeable convex structures to peaks hundreds of meters high) and in structure (according to the fluidity pattern) - from the regular forms of a bulbous, fan-shaped, funnel-shaped structure to complex vortices (Fig.

5.6). Domes can be repeatedly breached by subsequent portions of lava or, in the process of uneven squeezing, enclose brecciation zones, as well as have complex combinations of these heterogeneities. Extrusive and protrusive domes, breaking through volcanogenic strata, capture monoliths of these rocks, partially melting them, thereby complicating their structure.

The geological position of the domes is determined by the nature of volcanism, the type of magma chambers, and their location in various types volcanic structures and relation to magma chambers.

Basaltic volcanism contributes to the formation of rootless domes on shield volcanoes, and on stratovolcanoes - single and group domes located both in the central part of the volcano and along the periphery.

When differentiated (contrasting) volcanics erupt, domes of very diverse structure, shape and genesis appear. Acid and intermediate volcanism contributes to the appearance of extrusive and protrusive domes.

During the formation of large calderas and ring volcano-tectonic structures, domes are very often located along ring faults and outlining near-surface magma chambers.

Sometimes extrusions are located within the entire field of near-surface intrusion.

Volcanic domes can be divided into three groups: 1 - domes without any visible connection with the intrusion; 2 - formed above the intrusion; 3—rootless volcanic domes.

● Volcanic domes without visible connection with intrusion – effusive(periclinal and bulbous of symmetrical or asymmetrical structure), extrusive(mushroom-shaped and fan-shaped or funnel-shaped) and protrusive(peak-shaped and broom-shaped) (Fig.

5.6). An example of a peaked dome is the “Igloo” of pyroxene andesites of the Mont Pelee volcano on the island. Martinique. After the catastrophic eruption of 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 had 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 for three years (1946-1948. ) grew 600 m above the crater with a diameter of about 1 km at the bottom and about 0.5 km at the top.

The growth rate of blocks varied from 1 to 15 m per day.

● Volcanic domes, formed over an intrusion, uh then – positive structures in which a transition from effusive to intrusive rocks is observed down the section.

The height of elevated structures can reach 800 m. They are widely developed in the volcanic belts of Kamchatka, the Urals, the Caucasus, Central Asia etc.

● Rootless volcanic domes can be of two types: 1 – squeezed out portions of lava on lava flows; 2 – deformed (curved) lava flows, forming hemispheres, and arising during outpouring in front of a barrier as dome-shaped piles of lava or as lava remains flowing out from the middle part of the flow, sometimes taking a subvertical position.

The domes of the first type are small - up to 50-70 m, and the second is even smaller - up to 10 m. Both of them are found in Kamchatka.

Monogenic linear volcanoes are represented by fissure squeezes - single-act fissure volcanoes of acidic or intermediate composition. TO polygenic linear volcanoes These include fissure volcanoes that form lava ridges and lava plateaus, and which may be complicated by summit grabens, outer grabens, or a combination of grabens.

Modern fissure-type eruptions, for example in Iceland, are associated with linear devices that are 3-4 km long and up to several hundred meters wide. In Armenia, a volcanic plateau is known, formed in the Pliocene-Quaternary due to lava outpourings from >10 volcanoes located along two faults.

For example, Mount Etna is surrounded by 200 side craters.

The duration of volcanic activity can be variable 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 vary greatly, but there are three main characteristics by which they can be classified: 1) scale (volume of rock erupted); 2) the composition of the erupted material; 3) dynamics of the eruption.

By scale, all volcanic eruptions are divided into five classes (km3):

Class I - the volume of erupted material is more than 100;

Class II - from 10 to 100;

III class - from 1 to 10;

IV class - from 0.1 to 1;

V class - less than 0.1.

The composition of the erupted material, which we will discuss in detail below, especially the gas component, determines the dynamics of the eruption.

The process of mantle degassing is one of important reasons its eruption depends on the amount of gases, their composition and temperature. According to the method and rate of separation of volatiles, three main forms of eruption are distinguished: effusive - with a quiet release of gas and outpouring of lava; explosive - with the violent release of gases, causing the boiling of magma and powerful explosive eruptions; extrusive - viscous magma of low temperature is squeezed out of the crater.

There is also mixed types- effusive-explosive; extrusive-explosive, etc. During mixed eruptions important characteristic, according to E.K. Markhinin, is the explosiveness coefficient - the percentage content of the amount of pyroclastic material from total mass eruption products.

Therefore, the essence of each eruption can be expressed by a formula. For example, 4B exp. 100, which means: class IV eruption, basaltic, explosive, explosiveness coefficient 100. Each form of eruption is characterized by one or more volcanoes that most clearly express its features.

Effusive eruptions are extremely widespread and are associated with the outpouring of magma, mainly of basaltic composition. Typical eruptions of such dynamics are confined to spreading zones of mid-ocean ridges and subduction zones of active continental margins.

In mid-ocean ridges, under conditions of stretching of the earth's crust, fissure volcanism becomes most widespread. This type includes the volcanoes of Iceland - Laki, Eldgja, located in the axial part of the Mid-Atlantic Ridge.

During the eruption in 1783, lava began to flow from the Laki fissure, 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 180 m deep and covered an area with a total area of 565 km2. The average thickness of the lava cover exceeded 30 m, and the volume of the lava was 12 km3.

The same fissure eruptions are characteristic of Hawaiian Islands- Hawaiian type, where eruptions occur with emissions of very liquid, highly mobile basaltic lava.

As the power of lava flows increases, as a result of repeated eruptions, grandiose shield volcanoes are formed, the largest of which is the above-mentioned Mauna Loa.

In the subduction zones of the active continental Pacific margin, powerful fissure eruptions of the Plosky 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 hot pyroclastic material formed a fire “candle” up to 2.5 km high, and the gas and ash column reached a height of 5-6 km.

Then the eruption continued through a system of newly opening fissures with the formation of new cinder cones, the height of which reached 108, 278 and 299 m (Fig.

11.5). Total area The distribution of the lava field on one of the breakthroughs with a cinder-block surface, with an average thickness of 28 m, amounted to 35.9 km2 (Fig. 11.6). The eruption products are represented by basalts. Due to its high fluidity and characteristic morphology of flows, the lava is close to Hawaiian-type eruptions. Total quantity released gases (mainly H2O) - 180 million tons, which is comparable to the average annual release into the atmosphere during eruptions of all land-based volcanoes in the world.

The fissure eruptions of Plosky Tolbachik are the only major historical eruption of this kind on the territory of Russia.

Explosive eruptions. Volcanoes with gas-explosive eruption dynamics are widespread in subduction zones - the immersion of lithospheric plates.

Eruptions accompanied by powerful explosions depend to a certain extent on the composition of viscous, sedentary acidic magma containing a large amount of gases. A typical example of such an eruption is the Krakatoa type. The Krakatau volcano is located in the Sunda Strait between the islands of Java and Sumatra and its eruption is associated with a deep fault in the Eurasian plate, which arose as a result of pressure from below the Indo-Australian plate (Fig.

11.7).

Academician N. Shilo describes the mechanism of the Krakatau eruption as follows: in the process of rising mantle material saturated with gases along a deep fault from the magma chamber, it is segregated - separated into two immiscible melts.

Lighter granitoid magma, saturated with volatile gases, rises upward and a moment comes when, as the pressure increases, the chamber cover cannot withstand the accumulation of magma and a powerful explosion occurs with the release of acidic products saturated with gases.

This is what 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 over a distance of up to 5,000 km, and the volcanic ash, rising to a height of one hundred kilometers, spread over tens of thousands of kilometers.

In April 1982

The most powerful eruption of the Galunggung volcano in the last 25 years occurred, as a result of which 40 villages were wiped off the map. Volcanic ash covered an area of 180,000 hectares.

Galunggung is one of the most active Indonesian volcanoes, whose height reaches 2168 m.

This also includes the Bandaisan type, named after the Bandaisan volcano located on the island. Honshu, whose eruptions are distinguished by colossal explosions. Explosive eruptions also include ephemeral volcanoes, maars and diatremes.

The formation of maars as a result of single-act explosions is typical for the Tyatya volcano in the Kuril Islands. During the eruption in the summer of 1973, with the formation of maars, old lava flows composing the slopes of the volcano were blown up, and deposits with a thickness of 20-30 m were formed at the edge of the maars.

The total volume of silicate products released from the maars was twice the volume of the maars themselves.

Extrusive eruptions. A typical example of this eruption is the Mont Pele volcano, after which the Peleian type is named.

The Mont Pele volcano is located on the island. Martinique in the Lesser Antilles archipelago. The powerful explosive eruptions of this volcano are associated with extremely viscous silicic magma.

A gigantic explosion on April 28, 1902 destroyed the top of the hitherto dormant volcano, and a red-hot cloud (“scorching cloud”) that erupted from the crater 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 began to be squeezed out of the crater - “Pele’s Needle”.

in Kamchatka. First, there was a powerful explosion that destroyed 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 the snow, formed powerful mud flows. At the site of the summit, a crater with a depth of 700 m and an area of about 4 km2 formed.

Then the eruption of pyroclastic flows began, filling the river valleys at the foot of the volcano, after which an intracrater extrusion 320 m high with a diameter at the base of 600-650 m began to form. The products of the eruption are represented by andesites and andesite-basalts. Such extrusive domes are characteristic of volcanic eruptions in Kamchatka (Fig.

11.8).

Mixed eruptions. Volcanoes characterized by emissions of gaseous, liquid and solid products belong to this category.

This type of eruption is characteristic of the volcanoes Stromboli, Vesuvius, and Etna.

Strombolian type- the Stromboli volcano on the Aeolian Islands is characterized by eruptions of basic lava, alternating with emissions of volcanic bombs and hot slag.

The lavas are mobile, hot, their temperature reaches 1100-1200°C. The total height of the volcanic cone with its underwater part is 3500 m (altitude above sea level - 1000). The volcano is characterized by regular eruptions.

Vesuvian (Plinian) type named after the Roman scientist Pliny the Elder, who died in 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 perished under a layer of volcanic ash and lava, was described by Pliny the Younger and depicted in the painting “The Last Day of Pompeii” by K. Bryullov. A characteristic feature of eruptions of this type are powerful sudden explosions, accompanied by emissions of huge amounts of gases, ash, and pumice.

At the end of the eruption, rain poured in and the resulting mud-stone flows completed the burial of the cities. As a result of the explosion, the top of the volcano collapsed, and in its place a deep caldera formed, in which a new volcanic cone grew 100 years later.

Such volcanic building called a somma, an example of which is the Tyatya volcano (Fig. 11.9).

A very strong eruption of Vesuvius occurred in 1631, as a result of which a hot lava flow almost completely destroyed the city of Torre del Greco. Vesuvius has also erupted in recent years, threatening the residents of Naples.

The largest volcano in Kamchatka, Klyuchevskoy, is characterized by a mixed explosive-effusive nature of the eruption (Fig.

11.10). This is a typical stratovolcano with a regular cone, with a height of 4750 m - the highest active volcano in Europe and Asia. The volcano is young, its age is 7000 years, and it is very active. Between 1932 and 1987

The volcano has erupted 21 times, sometimes lasting 18 months. The volcano has both summit and side eruptions. A feature of the summit eruptions of 1978-1980, 1984-1987. there was an outpouring of lava flows on the slopes of the volcano, which were accompanied by continuous avalanches of hot debris, ejection of ash and bombs.

As a result of the contact of lava and ice, powerful mud flows and lahars (mud-stone flows) were formed, which, cutting deep canyons in the glaciers, spread more than 30 km from the foot of the volcano.

The eruption products are represented by ash, volcanic bombs and basaltic lavas. The length of the lava flows reached 12 km, and the thickness reached 30 m.

Volcanic eruptions continue to this day.

Ethnic 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 one and they are often combined together.