Where is lava located? Types of volcanic eruptions. Submarine volcano eruptions

26.05.2022

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, and aluminum.

Depending on the temperature and composition, lava has 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 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 crawl 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?

The main danger of lava is 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.

) or a very viscous (extrusion) mass from a rock melt, predominantly of silicate composition (SiO 2 from about 40 to 95%), pouring onto the surface of the Earth during volcanic eruptions.

Term

Word lava borrowed from Italian (lava, Latin labor) and French (lave) in the 18th century. It means “falling, crawling, sliding, descending (down)”, or “that which descends” as a result of a volcanic eruption.

Lava formation

Lava is formed when a volcano releases magma onto the Earth's surface. Due to cooling and interaction with gases that make up the atmosphere, magma changes its properties, forming lava. Many volcanic island arcs are associated with deep fault systems. The centers of earthquakes are located approximately at a depth of up to 700 km from the earth's surface, that is, the volcanic material comes from the upper mantle. On island arcs it often has an andesitic composition, and since andesites are similar in composition to the continental crust, many geologists believe that the continental crust in these areas builds up due to the influx of mantle material.

Volcanoes that operate along oceanic ridges (such as the Hawaiian ridge) erupt predominantly basaltic material, such as aa lava. These volcanoes are probably associated with shallow earthquakes, the depth of which does not exceed 70 km. Because basaltic lavas are found both on continents and along ocean ridges, geologists hypothesize that there is a layer just below the Earth's crust from which basaltic lavas come.

However, it is unclear why in some areas both andesites and basalts are formed from mantle material, while in others only basalts are formed. If, as is now believed, the mantle is indeed ultramafic (enriched in iron and magnesium), then lavas derived from the mantle should have a basaltic rather than andesitic composition, since andesites are absent in ultramafic rocks. This contradiction is resolved by the theory of plate tectonics, according to which the oceanic crust moves under island arcs and melts at a certain depth. These molten rocks erupt in the form of andesite lavas.

Types of lava

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

By composition

Basalt lava

The main type of lava erupted from the mantle is characteristic of oceanic shield volcanoes. It is half silicon dioxide and half oxides of aluminum, iron, magnesium and other metals. This lava is very mobile and can flow at a speed of 2 m/s. It has a high temperature (1200-1300 °C). Basaltic lava flows are characterized by a small thickness (meters) and a large extent (tens of kilometers). The color of hot lava is yellow or yellow-red.

Carbonate lava

Half is composed of sodium and potassium carbonates. This is the coldest and most liquid lava, it spreads like water. The temperature of carbonate lava is only 510-600 °C. The color of hot lava is black or dark brown, but as it cools it becomes lighter, 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

Most characteristic of the volcanoes of the Pacific Ring of Fire. It 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 somewhat, and then the eruption resumes, usually with a powerful explosion. The average flow rate of such lava is several meters per day, and the temperature is 800-900 °C. It contains 53-62% silicon dioxide (silica). If its content reaches 65%, then the lava becomes very viscous and slow. 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

Volcanic activity, one of the most dangerous natural phenomena, often brings enormous disasters to people and the national economy. Therefore, it is necessary to keep in mind that although not all active volcanoes cause misfortunes, nevertheless, each of them can be, to one degree or another, a source of negative events, volcanic eruptions come in varying strengths, but only those that are accompanied by loss of life are classified as catastrophic and material assets.

General ideas about volcanism

“Volcanism is a phenomenon due to which, during geological history, the outer shells of the Earth were formed - the crust, hydrosphere and atmosphere, i.e. the habitat of living organisms - the biosphere.” This opinion is expressed by the majority of volcanologists, but this is far from the only idea about the development of the geographical 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 its gas components remain in a dissolved state. As magma moves toward the surface, the pressure decreases, gases begin to be released, and as a result, the magma pouring onto the surface is significantly different from the original one. To emphasize this difference, magma that flows to the surface is called lava. The process of eruption is called eruptive activity.

Fig.1. Eruption of Mount St. Helens

Volcanic eruptions occur differently, depending on the composition of the eruption products. In some cases, eruptions proceed calmly, 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 the squeezing or outpouring of relatively viscous lava. The eruptions of some volcanoes consist only of grandiose gas explosions, as a result of which colossal clouds of gas and water vapor saturated with lava are formed, rising to enormous heights. According to modern concepts, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the interior of the Earth to its surface.

At a depth of 50 to 350 km, pockets of molten matter - magma - form in the thickness of our planet. Along areas of crushing and fractures of the earth's crust, magma rises and pours out onto 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 the magma and go into the atmosphere. In places of eruption, lava covers and flows appear , volcanoes-mountains composed of lavas and their dispersed particles - pyroclasts. Based on the content of the main component - silicon oxide, magmas and the volcanic rocks formed by them - volcanics are divided into ultrabasic (silicon oxide less than 40%), basic (40-52%), intermediate ( 52-65%), acidic (65-75%). The most common is basic, or basaltic, magma.

Types of volcanoes, composition of lavas. Classification according to the nature of the eruption

The classification of volcanoes is based mainly on the nature of their eruptions and the structure of the volcanic apparatus. 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 it contains. Three processes occur in volcanic eruptions: 1) effusive - the outpouring of lava and its spreading over the earth's surface; 2) explosive (explosive) - explosion and release of a large amount of pyroclastic material (solid eruption products); 3) extrusive - squeezing, or extrusion, of igneous substance 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 over time. Depending on the nature of the eruption, the complexity and diversity of volcanic structures and forms of occurrence of volcanic material are noted. Among the volcanic eruptions, the following are distinguished: central type, fissure and areal eruptions.

Fig.2. Hawaiian type of eruption

1 - Ash plume, 2 - Lava fountain, 3 - Crater, 4 - Lava lake, 5 - Fumaroles, 6 - Lava flow, 7 - Layers of lava and ash, 8 - Rock layer, 9 - Sill, 10 - Magma conduit, 11 - Magma chamber, 12 - Dyke

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 cup-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 supply channel, or a volcano crater, which has a pipe-like shape, through which magma from the deep chamber rises to the surface. Among the volcanoes of the central type, there are polygenic ones, formed as a result of multiple eruptions, and monogenic ones, which manifested their activity once.

Polygenic volcanoes. These include most of the world's famous volcanoes. There is no unified and generally accepted classification of polygenic volcanoes. Different types of eruptions are most often identified by the names of famous volcanoes in which a particular process manifests itself most characteristically. Effusive, or lava, volcanoes. The predominant process in these volcanoes is effusion, or the outpouring of lava onto the surface and its movement in the form of streams along the slopes of a volcanic mountain. Examples of this type of eruption include the volcanoes of Hawaii, Samoa, Iceland, etc.

Fig.3. Plinian type of eruption

1 - Ash plume, 2 - Magma conduit, 3 - Volcanic ash rain, 4 - Layers of lava and ash, 5 - Rock layer, 6 - Magma chamber

Hawaiian type. Hawaii is formed by the merged peaks of five volcanoes, four of which were active in historical times (Fig. 2). The activity of two volcanoes has been especially well studied: Mauna Loa, rising almost 4200 meters above the level of the Pacific Ocean, and Kilauea, more than 1200 meters high. The lava in these volcanoes is mainly basaltic, easily mobile, high-temperature (about 12,000). In the crater lake, the lava bubbles all the time, its level either decreases or increases. During eruptions, lava rises, its mobility increases, it fills the entire crater, forming a huge boiling lake. Gases are released relatively calmly, forming splashes above the crater, lava fountains, rising in height from several to hundreds of meters (rarely). Lava foamed with gases splashes and hardens 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 streams.

Effusive underwater. The eruptions are the most numerous and least studied. They are also confined to rift structures and are distinguished by the dominance of basaltic lavas. On the ocean floor at a depth of 2 km or more, the water pressure is so high that explosions do not occur, which means that pyroclasts do not form. Under water pressure, even liquid basaltic lava does not spread far; it forms short dome-shaped bodies or narrow and long flows, covered on the surface with a glassy crust. A distinctive feature of underwater volcanoes located at great depths is the abundant release of hydrothermal 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 Aeolian Islands group in the Strait of Messina. Many volcanoes of Kamchatka, the Kuril and Japanese Islands and the western part of the Cordilleran mobile belt belong to the same category. The lavas of these volcanoes are different - from basic (basaltic), andesite-basaltic, andesitic to acidic (liparitic). Among them, several types are conventionally 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 - Ball lava, 7 - Magma conduit, 8 - Magma chamber, 9 - Dyke

Strombolian type. 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 basaltic composition, but lower temperature (1000-1100) than the lava of the volcanoes of the Hawaiian islands, therefore less mobile and saturated with gases. Eruptions occur rhythmically at certain short intervals - from several minutes to an hour. Gas explosions eject hot lava to a relatively small height, which then falls onto the slopes of the volcano in the form of spirally curled bombs and slag (porous, bubbly pieces of lava). It is characteristic that very little ash is thrown out. The cone-shaped volcanic apparatus consists of layers of slag and hardened lava. The famous volcano 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 predominate, with the release of large quantities of solid eruption products, with almost no outpouring of lavas (or in limited quantities). 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 rising above the crater.

Peleian type. It was especially pronounced in the Mont Pele volcano on the island. Martinique, part of the Lesser Antilles group. The lava of this volcano is predominantly medium, andesitic, highly viscous and saturated with gases. When it solidifies, it forms a solid plug in the crater of the volcano, preventing the free escape of gas, which, accumulating under it, creates very high pressures. Lava is squeezed out in the form of obelisks and domes. Eruptions occur as violent explosions. Huge clouds of gases appear, oversaturated with lava. These hot (with temperatures above 700-800) gas-ash avalanches do not rise high, but roll down the slopes of the volcano at high speed and destroy all living things on their way.

Fig.5. Volcanic activity at Anak Krakatoa, 2008

Krakatoa type. Identified by the name of the Krakatoa volcano, located in the Sunda Strait between Java and Sumatra. This island consisted of three fused volcanic cones. The most ancient 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 submarine caldera formed in prehistoric times. Until 1883, Krakatoa was not active for 20 years. In 1883, one of the largest catastrophic eruptions occurred. It began with explosions of moderate force in May, and after some breaks they resumed again in June, July, and August with a gradual increase in intensity. On August 26, two large explosions occurred. On the morning of August 27, a gigantic explosion occurred, which was heard in Australia and on the islands in the western Indian Ocean at a distance of 4000-5000 km. A hot 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 washed away about 36 thousand people from the shores of Java and Sumatra. In some places, destruction and casualties were associated with a blast wave of enormous force.

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

Subglacial view of eruptions(Fig. 4) is possible in the case when the volcano is located under ice or an entire glacier. Such eruptions are dangerous because they provoke powerful floods, as well as because of their spherical lava. To date, only five such eruptions are known, which means they are a very rare occurrence.

Monogenic volcanoes

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

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

Fissure eruptions

They are confined to large faults and cracks in the earth's crust, which play the role of magma channels. An eruption, especially in the early phases, can occur along the entire Mother-in-law or individual sections of its sections. Subsequently, groups of close 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, similar powerful fissure eruptions of basaltic lava were observed in Iceland. Fissure eruptions are widespread on the slopes of large volcanoes. O below, 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 occurred in past geological periods, when thick lava covers were formed.

Areal type of eruption. This type includes massive eruptions from numerous nearby central-type volcanoes. They are often confined to small cracks or their intersection points. During the eruption process, some centers die off, while others arise. The areal type of eruption sometimes covers vast areas where the eruption products merge to form continuous covers.

In today's article we will look at the types of lava based on temperature and viscosity.

As you probably know, lava is molten rock that erupts from an active volcano onto the surface of the earth.

The outer shell of the globe is the earth's crust; beneath it lies a hot, liquid layer called the mantle. Hot magma makes its way to the top through cracks in the earth's crust.

The entry points of hot magma into the earth's surface are called "hot spots", which means hot spots

(pictured left). This usually occurs within the boundaries between tectonic plates and gives rise to entire volcanic chains.

What is the temperature of the lava?

Lava has a temperature of 700 to 1200C. Depending on the temperature and composition, lava is divided into three types of fluidity.

Liquid lava has the highest temperature, more than 950C, and its main component is basalt. With such a high temperature and fluidity, lava can flow for several tens of kilometers before it stops and hardens. Volcanoes that erupt this type of lava are often very gentle, since it does not linger at the vent, but spreads around.

Lava with a temperature of 750-950C is andesitic. It can be recognized by its frozen round blocks with a broken crust.

Lava with the lowest temperature of 650-750C is acidic and very rich in silica. A characteristic feature of this lava is its slow speed and high viscosity. Very often, during an eruption, this type of lava forms a crust over the crater (pictured on the right). Volcanoes with this temperature and type of lava often have steep slopes.

Below we will show you some photos of hot lava.

Lava is molten rock ejected from the depths of a volcano during an eruption and turns into hardened rock after cooling. During an eruption directly from the volcano's nozzle, the temperature of the lava reaches 1200 degrees Celsius. Molten lava flowing down a slope can be 100,000 times faster than water before it cools and hardens. In this collection you will find bright and beautiful photographs of erupting lava from various parts of our planet.

Lava flows occur during a non-explosive expansive eruption. When the hot rock cools, it hardens to form igneous rock. It is composition rather than eruption temperature that determines the behavior of lava flows. Below you will find many amazing photos for which brave photographers braved extreme temperatures. Many of the images were taken in seismically active locations such as Iceland, Italy and Mount Etna and of course Hawaii. Here, for example, is the volcano with the longest name: Eyjafjallajökull in Iceland: