All three active volcanoes in operation, and geologists knew about the eruption approaching. Preheating the top Klyuchevskaya hills  (another name for Klyuchevsky volcano) was noticeable even from a satellite, and Villarrica is considered to be the most active volcano in Chile.

Near all three peaks there are no large settlements, they are constantly monitored, therefore, even in the case of a large-scale eruption, catastrophic consequences can not be expected. But some other volcanoes do pose a serious threat.

What are the dangerous volcanoes and why?

The severity of the consequences of the eruption is determined by several factors. First, the location is important: located in Antarctica, Erebus threatens only the Antarctic station McMurdo (up to a thousand people in the summer season), but from Vesuvius to the millionth of Naples is only 15 kilometers. The Italian volcano is to blame not only for the destruction of the ancient Roman years of Pompeii and Stabia: in the last century (by geological standards only very recently), it burned two villages at its foot.

Karl Bryullov, "The Last Day of Pompeii", 1833

Secondly, the type of volcano and the nature of the eruption are important. Hawaiian eruptions (named so because it is the Hawaiian Islands that occur most often) lead to the emergence of a large volume of lava on the surface, but explosions with the spread of stone debris and ash clouds do not usually occur. The lava can flow for tens of kilometers, flood the settlements, but you can get away from it on foot. Sometimes tourists even calmly approach the lava flows.

The eruptions of the Plinian (first described by the ancient Roman writer Pliny the Elder) are much more dangerous, since the vertex of the volcano literally explodes, throwing out a glowing stream of ash and gases. Warmed to colossal temperatures and flowing at a tremendous speed, the flow leaves no chance of surviving to those who are on its way. It is precisely such flows, called pyroclastic ones, that caused the death of the inhabitants of Pompeii, and also accompanied one of the most destructive eruptions - the eruption of the volcano Krakatoa in 1883.

  A modern snapshot of Pompeii. The mountain in the background is Vesuvius. Photo: Morn the Gorn / Wikimedia

Thrown into the upper layers of the troposphere and the stratosphere, ashes are dangerous for aircraft (there are known cases of engine failure due to ash), and in large quantities can even lead to a temporary cooling on the entire planet. The eruption of the Icelandic volcano Eyjafjadlayekudl nearly paralyzed air traffic not only in Iceland, but also in Great Britain, and also in Northern Europe for almost a week.

The third factor that determines the danger of eruption is the volume of ejected matter, lava and ash. With him everything is simple: the more, the worse. There is an international scale VEI, and it, like the magnitude of earthquakes, is logarithmic, that is, each next stage assumes a tenfold greater volume.

  The beginning of the eruption of Eyjafjadlayekudl in 2010. Photo by Boaworm / Wikimedia

Given all these data, we can distinguish five volcanoes, which really should be feared by the inhabitants of the planet Earth. Let us emphasize some convention of this list. He, for example, does not coincide with list  of 17 volcanoes Decade Volcanoes, which is compiled by volcanologists as a list of potentially dangerous and requiring additional study of fire-breathing mountains. To consider whether a sleeping super volcano is more dangerous than an active volcano is a difficult question. We'll start with the super-volcanoes.

Yellowstone, super volcano, USA

The 50-kilometer caldera (hollow, essentially a giant crater), located in the Rocky Mountains in the United States, is the crater of the now inactive volcano. 2.1 million years ago, the volcano threw out 2,500 cubic kilometers of ash and lava. This is enough to fill the territory of the middle-sized state with a layer of tens of meters. About how the super-eruption affected the animal and plant world of the Earth is still unknown, but nowadays it would lead to the destruction of settlements within a radius of many hundreds of kilometers, cover ashes most of the US and Canada, and would cause global crop failure on the whole planet due to a cooling a few degrees.

Since then, there have been two more catastrophic eruptions. The probability of repetition of the geologists estimate about one and a half ten thousandth percent for the year.

  It looks like a typical mountain landscape, but in fact the mountains behind are the edge of the volcanic crater, from which the picture was taken. Photo: Ed Austin / Herb Jones

Toba, super volcano, Indonesia

It is his "work" associated with a sharp decline in the number of people about 70 thousand years ago. In scale, the eruption is close to that described above: about 2800 cubic kilometers of magma, significant destruction in a radius of over a thousand kilometers, a year or even several years of global cooling.

The modern status of Toba - dormant volcano, but it is located in a seismically dangerous area, and the northern slope of the caldera is devoid of vegetation in one place - scientists do not exclude the possibility that this is the result of a small, and comparatively recent, eruption.

  Completely caldera with the Toba lake located inside is visible only from the satellite. Snapshot: NASA Landsat

Santorini, volcano, Crete

This volcano in the Mediterranean destroyed the civilization of ancient Crete (Aegean) in 1645-1640 BC. In the documented history of mankind, this is the only case of an eruption that has scored seven points on the VEI scale (eight are already supervolcanoes), and Santorini - active volcano. The last eruption occurred in 1950, and in 2011 and 2012, the sensors installed by scientists recorded a suspicious deformation of the surface - perhaps magma accumulates again beneath the volcano. This may indicate a rapid eruption, but it is impossible to accurately assess the risks and scales.

  Caldera Santorini. The scale can be estimated from the right of the airport's runway. Snapshot: NASA

Krakatoa, Indonesia

After an explosive eruption in 1883, a flooded crater formed on the site of Mount Krakatau. The height of the tsunami in the Indian Ocean and the Javan Sea reached thirty meters, and the wave destroyed thousands of settlements: the total number of victims exceeded one hundred thousand people. The power of the explosion is estimated by different scientists with a wide spread, but even by cautious estimates it exceeded the indicator of "Tsar-bomb" - the most powerful thermonuclear charge in human history (it was created in the USSR and blown up on Novaya Zemlya in 1961, the power of the explosion in TNT equivalent more than 50 megatons, which is 2700 times more than the "Baby", which destroyed Hiroshima).

Now, in place of Krakatau, a new volcano, Anak (Child) Krakatau literally grows. The cone appeared above the surface of the water at the beginning of the last century, continuous eruptions practically do not stop, and every week the mountain becomes higher by approximately 13 centimeters.

  A piece of a coral reef that was torn off and thrown away by the tsunami after the eruption of Krakatoa. A picture of the year 1885 from the archives of the Tropenmuseum of the Royal Tropical Institute (KIT)

Lucky, Iceland

This volcano is known for the eruption of 1783-1784. It was not accompanied by a devastating explosion, but it lasted almost ten months. During this time, about 15 cubic kilometers of lava came to the surface. The poisonous gases released from it and the associated ash emissions killed half of all the cattle in Iceland, and the particles that rose into the stratosphere led to a cooling in all of Europe. True, there have been no new eruptions since.

  Lucky these days. Photo: Chmee2 / Valtameri / Wikimedia

Volcanoes can be exciting, exciting, but at the same time dangerous. Any of them is capable of causing harmful or fatal phenomena both during the eruption and during the rest period. Understanding what the volcano can do is the first step to mitigating its danger. But even if scientists have studied this or that peak for decades, this does not mean that they know absolutely everything about it. Volcanoes are natural systems in which there is always an element of unpredictability. What are the threats of the giants?

Lava Flows

Lava is a molten rock that flows out of cracks or volcanic vents. Depending on the composition and temperature, it can be very liquid or very sticky (viscous). Liquid has a higher temperature and flows faster; it can form entire rivers or spread around the neighborhood by separate streams. Viscous streams are cooler, move for short distances, and sometimes create lava domes or cork in craters.

Lava flows of Kilauea volcano in Hawaii

Most lava flows do not pose a threat to humans, since they move slowly - it's easy to escape from them. However, having a temperature of about +1000 ... + 2000 ° C, they burn everything on their way, destroying buildings, vegetation, road infrastructure. Sometimes the streams move with rapid speed. For example, lava can flow off the slopes at a speed of about 100 km / h.

Pyroclastic flows

Pyroclastic flows are an explosive volcanic phenomenon. They are a mixture of dust, rock debris, ash and hot gases. Such flows can move at speeds up to 1000 km / h, easily overcome obstacles, spread over the water surface, and sometimes their upper, lighter part separates from the main mass and moves by itself.

All are considered fatal, since their temperature reaches +400 ° C. Given the speed combined with power and high heat, it can be said with certainty that it is almost impossible to avoid their destructive power. These volcanic phenomena destroy everything that they find in the course of motion, burning or splitting into small parts.

One of the most striking examples of destruction caused by pyroclastic flows is the city. When the Soufriere volcano began to erupt in 1996, a mixture of gas and volcanic materials collapsed into a populated area and completely destroyed it. Now this city stands in ruins, and on its territory you can see the remains of buildings that were destroyed or buried under a layer of ash.

Ash Falls

Ash falls, also known as volcanic deposits, occur when tephra (particles of volcanic material ranging in diameter from a few millimeters to tens of centimeters) are emitted from the crater during the eruption. It falls to the ground at a distance from the volcanic hole (from a few meters to several kilometers), and in strong explosions it enters the stratosphere and spreads hundreds or even thousands of kilometers.

If a person is far from the volcano, he will not be threatened with large fragments of tephra. However, some ash falls contain toxic chemicals that are absorbed by plants or enter drinking sources and can be hazardous to the health of both humans and animals. A serious threat is in the large particles of tephra, especially after the rain. Most of the damage caused by ash falls occurs when wet ash and slag settles on the roofs of buildings - unable to withstand a lot of weight, the houses are destroyed.

Getting into the atmosphere can lead to global consequences. If the ash cloud is too large, it can block sunlight and cause a volcanic winter. After the ash-plume became the cause of the temperature decrease on the whole planet, which led to extreme weather conditions, crop failures and famine.

Lahari

Lahar volcano Gilanggung in Indonesia

Lahari is a specific type of mudflows, consisting of water and volcanic debris. They are formed when the slopes of the volcano collapse, when a pile of stones and debris rushes down, mixing along the way with melted glaciers, water from volcanic lakes or rainfall. Their consistency resembles wet concrete, they flow down the flanks of the volcano at a speed of up to 80 km / h and cover distances up to several tens of kilometers. Often, mixing with the red-hot lava, all the way lahars keep the temperature to + 60 ... + 70 ° C.

Such flows are not so fast and hot as pyroclastic, but can be extremely destructive. In 1985, during the eruption of a volcano in Colombia, a huge lakhar completely destroyed the town of Armero and killed 23,000 people. Fortunately, most mudflows are detected beforehand by acoustic (sound) monitors, which allows for timely evacuation.

Volcanic gases

Volcanic gases are no less effective component of any eruption, capable of becoming one of the most deadly. Most of the gases released from volcanic activity contain water vapor and are relatively harmless, but the erupting peaks also produce carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen sulfide (H2S), fluorine gas (F2), fluoride hydrogen (HF) and other substances. Under certain conditions, they all represent a mortal danger.

Carbon dioxide is not toxic, but it displaces oxygen-containing air, has no smell and color. Due to its higher density, it accumulates in depressions in the vicinity of the mountain and leads to strangulation of humans and animals. It can also dissolve in water and collect in the bottom sediments of lakes; in some situations, water in these bodies of water suddenly splashes huge bubbles of carbon dioxide that kill vegetation, livestock and people living nearby. Such a case occurred in the Cameroonian lake of Nyos in 1986 - from the released carbonic acid from its bottom, more than 1700 people and 3500 head of cattle in the nearby villages were suffocated.

Sulfur dioxide and hydrogen sulphide have the smell of a rotten egg. When combined with water vapor, SO2 forms an aggressive sulfuric acid (H2SO4), which is toxic even in small amounts. With large volumes, it is converted into volcanic fog and spreads around, irritating soft tissues (eyes, nose, throat, lungs, etc.). If sulfur-based aerosols enter the upper atmosphere, they can block sunlight and destroy ozone, which leads to long-term adverse effects on the climate.

One of the most unpleasant volcanic substances is gaseous fluorine. It has a yellowish-brown color and is extremely toxic. Like carbon dioxide, fluoride accumulates in the lowlands, but it presents a much greater danger. A person who has fallen into the place of gas accumulation, there are severe burns, the development of calcium in the bone system is disrupted. Even after dispersal, the gas is absorbed into the plants and continues to poison people and animals for a long time. After the eruption of the Icelandic volcano Lucky in 1783, famine and fluoride poisoning led to the death of more than half the livestock in the country and almost a quarter of the population.

No wonder they say "live like a volcano." Everyone who, by the will of fate, was born and lives near these peaks, is in constant danger. And the main task of scientists and volcanologists is not only to study the possibilities of volcanoes, but also to try with all their might to prevent the threat they bring to human life and the natural environment.

Volcanoes are faults on the surface of the earth's crust, through which later magma emerges, turning into lava and accompanied by volcanic bombs. They are found absolutely on all continents, however there are places of their special accumulation on the Earth. The latter is due to a variety of geologically active processes. All volcanoes, depending on their location and activity, are divided into several main categories: terrestrial, subglacial and underwater, extinct, asleep and active. The science involved in their study is called volcanology. This is an official discipline recognized throughout the world. The eruption of volcanoes, as a rule, occurs with a certain regularity. At the same time, the atmosphere is emitted a large number of volcanic gases and ash. Several hundred years ago, people believed that these processes are caused by the wrath of the gods. At present, mankind knows that the eruption is of a natural nature, and the causes of volcanic eruptions lie in the deep layers of the earth where liquid molten magma accumulates. In some places, it gradually begins to rise along the vents of volcanoes to the surface. Conventional magma quite easily passes various gas evaporation, and therefore lava leaves relatively quietly. It all looks like it's pouring out. Acid magma, which is more dense in its structure, keeps gas evaporation much longer, resulting in high pressure, and volcanic eruptions take place in the form of a big explosion. This phenomenon can also be caused by the movement of tectonic plates and earthquakes. The eruption of terrestrial-type volcanoes causes the formation of deadly pyroclastic flows, different in their power. They consist of hot gas and ash and are carried along the slopes at great speed. In addition, the release of toxic substances into the atmosphere and hot lava flows to the surface. The consequences of the eruption of submarine-type volcanoes are directly related to the formation of lethal waves and tsunamis. The faults related to the subglacial as a result of its large eruption, depending on the geological and geographical location, can lead to the formation of landslides, powerful mudflows and the collapse of the glaciers themselves. The eruption of volcanoes, as a rule, is associated with the loss of ground cover, air pollution, pollution of water bodies, lakes, rivers, and hence, drinking water. Separately it is worth noting failures in the work of a variety of infrastructures, the destruction of residential buildings and non-residential facilities, hunger and the spread of various kinds of infections. Consequences of the eruption powerful volcanoes  have a direct impact on climate change and can trigger the onset of the so-called volcanic winter. Ashes and gases formed during the explosion reach the atmospheric layer and, like a blanket, completely cover the Earth. The rays of the sun will cease to penetrate, and sulfuric acid will precipitate to the surface as precipitation. The effect that will result from such processes will be similar to the consequences of a nuclear winter. Eruptions of this kind are quite rare, and today scientists are doing everything possible to reduce the likelihood of their occurrence

A volcano is an opening or crack in the surface of the earth's crust, through which molten, solid or gaseous substances are released. The main products of the eruption are molten or solid minerals from the silicate group and gases. The nature of the erupted products varies greatly depending on the physical conditions and the chemical composition of the molten substance in the interior of the earth's crust (magma). Volcanoes exist not only on Earth; for example, it was recently found that on Triton, the largest of Neptune's two satellites, volcanoes spout nitrogen fountains.

Most seismically active zone  on the Earth - Fiery ring, belt active volcanoes, around the Pacific Ocean. Volcanoes are located at the junctions of tectonic plates, along the edges of the continents. Many large cities of the world are located in areas where the danger of earthquakes and volcanic eruptions is great.

VOLCANO SMITH

Not surprisingly, volcanoes, as well as other catastrophic unpredictable phenomena, have been attributed to supernatural power since ancient times. The very word "volcano" comes from the name of the island of Vulcano, a small islet to the north of Sicily. There, often there were eruptions, so the Romans believed that there is a smithy of Vulcan - the god of fire and the weapons master.

DISTRIBUTION OF VOLCANOES ON THE PLANET

Currently, there are more than 1500 active volcanoes on Earth. Usually they are located near the ocean coasts - most of the volcanoes on the planet are concentrated along the edges of the continents around the Pacific (Ring of Fire). There are exceptions to this rule - for example, volcanoes in the Hawaiian Islands. The location of volcanoes depends on global tectonics - the movement of lithospheric plates, solid fragments with a thickness of 10 to 80 km, which make up the upper layer of the earth's surface.

BOUNDLES OF PLATE

Some of these plates diverge in different directions, others converge, others slide along each other. Volcanoes are usually located on the boundaries of slabs, especially where they converge or diverge. On the divergent (divergent) boundaries, the tectonic plates are stretched, becoming thinner, as a result of which the hot semi-molten substance of the mantle rises up the cracks and melts finally, forming magma. Magma can break through slabs and spill onto the surface at once in several places, with such volcanoes as Kilimanjaro, Mount Kenya and Ol-Doinho-Lengai, located along the East African fault zone.

VOLCANOES OF MIDDLE-OCEANIC RIDGES

Where the plates diverge particularly quickly, the earth's crust becomes so thin that it breaks over a large distance, and along the crack along its entire length a continuous chain of active volcanoes appears. In this process, mid-ocean ridges are formed, for example, the Mid-Atlantic Ridge, from Jan Mayen Island east of Greenland to Bouvet Island in the South Atlantic. Along the whole ridge, small eruptions occur every now and then. They usually occur in fissures up to 15 km long or in isolated volcanoes located in the rift zone in the middle of the ridge.

ERADICATIONS IN ICELAND

On the island of Iceland, located in the middle of the Atlantic Ocean, where the mid-oceanic ridge comes to the surface, almost all igneous magma, or lava, has a liquid character. But the volume of the expiring lava is extremely large, because in this place under the ridge there is an ascending heat flow from the mantle (the so-called hot zone). In 1783-1784, during the eruption from the crack of Lucky, the longest in the history of the outflow of lava occurred - the lava flow retired 70 km from the place of origin. Accompanying emissions of sulfur-containing gases led to climate change, and in the following years, winters in the north-west of Europe were unusually severe. In Iceland, agricultural crops and cattle were killed, and a terrible famine began. About 25% of the population of Iceland died of hunger and disease.

HOT ZONES

The centers of volcanic activity are often located near the "hot zones" in the middle of tectonic plates. One such zone is the Hawaiian Islands, located in the middle of the Pacific plate. Almost all the eruptions associated with hot zones have moderate strength, but they last extremely long. For example, the volcanic eruption of Puuyo on the Hawaiian island of Kilauea lasted 16 years. The lava was very liquid and therefore covered huge areas.

VOLCANOES IN SUB-DEPOSIT ZONES

Much more powerful and devastating are volcanic eruptions that occur along convergent boundaries, where tectonic plates converge. The most volcanically active convergent boundaries are located where oceanic plates move under continental (subduction zones). This is what happens in the Pacific Ring of Fire. In these areas, magma, due to its chemical composition, is thicker than magma on divergent boundaries. Therefore, viscous lava often freezes under the ground, forming in the channels and cracks solid plugs. Lava, locked under such a cork, continues to secrete bubbles of gas, the pressure in it increases and eventually becomes so high that the lava plug spills out like a cork from a bottle of champagne. Sometimes this cork is destroyed by the earthquake, and the eruption of the volcano begins.

MOUNTAINS OF SAINT HELENS

On March 21, 1980, after 123 years of inaction, earthquakes began around Mount St. Helens in Washington State. On the northern slope there was a dome of magma, locked in the vole of the volcano. He grew at a speed of 1.5 m per day. Then on May 18, 1980, an earthquake measuring 5.1 points led to the fact that this dome broke and slid down the slope. The pressure that held the magma beneath him disappeared. There followed a grandiose collapse with a rockfall, accompanied by strong emissions of pumice and ash. Down the slope of the volcano rushed at least 17 pyroclastic outbursts - clouds of ash, rocks and gas with a temperature of more than 1500 ° C. The flow rate exceeded 100 km per hour. A powerful explosion carried the top of a mountain more than 400 m high.

THAN DANGEROUS VOLCANOES

The dangers that volcanoes carry in themselves are very diverse. Volcanic eruptions destroy houses, burn crops, destroy cattle and kill people. However, fertile soils, fertilized with volcanic ash, again and again attract people, and they persistently inhabit the slopes of volcanoes. For example, the extremely densely populated slopes of Soufriere volcano on the Caribbean island of Montserrat were completely devastated by the eruption of the volcano in 1997.

PYROKLASTIC EMISSIONS

The most formidable factor of eruptions are pyroclastic discharges, consisting of hot asphyxiating ashes, poisonous gases and huge flying stones. Flaring at speeds of up to 300 km per hour, they can envelop the area of ​​many square kilometers. The most famous pyroclastic outburst in history occurred during the eruption of Vesuvius in southern Italy in the year 79. Under the avalanche of red-hot ash and poisonous gases, many residents of Pompeii and Herculaneum died.

VOLCANIC POLLUTION

There is another problem with large volcanic eruptions. They throw into the atmosphere such a quantity of matter that this has an impact on the climate. About 74,000 years ago, the eruption of the volcano Toba in Sumatra threw into the air so much volcanic material that the chemical composition of the atmosphere has changed and a cold snap has occurred on Earth.

CLOUDS OF ASH, MUD FLOWS AND FLOODS

No less dangerous can be the side effects of volcanic eruptions. In 1985, a cloud of red-hot ash from a small Nevado del Ruiz volcano in Colombia melted snow and ice around the summit. Streams of thawed water, mixed with ash, rushed down the slopes of the mountain, destroyed a small town and destroyed more than 20,000 people. The eruption of the Grimsvötn volcano in Iceland in 1996 led to a colossal flood (they are called "yokkulhaup"), at which time water was falling at a rate of 50,000 cubic meters per second.

WHAT ARE THE VOLCANOES

Volcanic activity is not always harmful. In Iceland, geothermal heat released by underground magma is used to generate electricity and to heat greenhouses where food is grown, which otherwise would have to be imported. Soils formed during weathering of lava are very rich in mineral substances and can be extremely fertile when cultivated.

FORECAST OF EJECTIONS

To avoid catastrophes, it is very important to learn how to predict the time of volcanic eruptions and the alleged eruption force. Although it is often easy to recognize the early warning signs of an impending eruption, scientists can not yet foresee exactly when the eruption will begin and in which direction the lava will flow and ashes will fly. The eruption of volcanoes depends on many geological factors, many of which are not yet fully understood or can not be observed. Continuous tracking of seismic activity and volcanic gases help to decipher the first warning signs, however, it seems that an accurate prediction of volcanic eruptions will only be possible in the distant future.

In the year 79 AD. at the eruption of the volcano Vesuvius was thrown out a huge cloud of hot ash and gas, which was buried under the ancient Roman city of Pompeii. The burnt bodies left cavities in the ashes. Subsequently, these cavities were flooded with cement.

What are volcanoes: volcanic danger? Meaning and interpretation of the word vulkany vulkanicheskaja opasnost, definition of the term

To the article VOLCANOES

Volcanic eruptions threaten people's lives and cause material damage. After 1600, as a result of eruptions and associated mudflows and tsunamis, 168 thousand people died, 95 thousand people became victims of diseases and famine that arose after eruptions. Due to the eruption of the Montagne-Pele volcano in 1902, 30,000 people died. As a result of the descent of mudflows from the volcano Ruiz in Colombia in 1985, 20 thousand people died. The eruption of the volcano Krakatoa in 1883 led to the formation of a tsunami that killed 36,000 people.

The nature of the danger depends on the effect of various factors. Lava flows destroy buildings, block roads and agricultural lands, which for many centuries are excluded from economic use, until a new soil forms as a result of weathering processes. The rate of weathering depends on the amount of precipitation, the temperature regime, the conditions of the runoff and the nature of the surface. For example, on the more humid slopes of the Etna volcano in Italy, agriculture on lava flows resumed only 300 years after the eruption.

Due to volcanic eruptions on the roofs of buildings, powerful layers of ash accumulate, which threatens their collapse. The ingress of light particles of ash into the lungs leads to the loss of livestock. A suspension of ash in the air poses a danger to road and air transport. Often during the ash falls, airports are closed.

Ash streams, which is an incandescent mixture of suspended particulate matter and volcanic gases, move at high speed. As a result, people, animals, plants and houses are destroyed from burns and suffocation. The ancient Roman cities of Pompeii and Herculaneum fell into the zone of action of such streams and were covered with ashes during the eruption of the volcano Vesuvius.

Volcanic gases released by volcanoes of any type rise into the atmosphere and usually do no harm, but in part they can return to the earth's surface in the form of acid rain. Sometimes the relief of the terrain contributes to the fact that volcanic gases (sulfur dioxide, hydrogen chloride or carbon dioxide) spread near the surface of the earth, destroying vegetation or polluting the air in concentrations exceeding the permissible limits. Volcanic gases can cause and indirect harm. Thus, the fluorine compounds contained in them are captured by ash particles, and when the latter fall on the earth's surface, pastures and ponds are infected, causing severe diseases of livestock. In the same way, open sources of water supply for the population can be contaminated.

Huge destruction also causes mudstone flows and tsunami.

Forecast of eruptions. Volcanic hazard maps are drawn up for forecasting eruptions, showing the nature and distribution areas of products of past eruptions and monitoring of the precursors of eruptions. Such precursors include the frequency of weak volcanic earthquakes; if usually their number does not exceed 10 per day, then immediately before the eruption increases to several hundred. Instrumental observations of the slightest deformations of the surface are carried out. The accuracy of measurements of vertical movements, fixed, for example, by laser instruments, is 0.25 mm, horizontal. 6 mm, which allows you to detect the slope of the surface of only 1 mm per half a kilometer. Data on changes in height, distance, and inclinations are used to identify the center of swelling preceding the eruption, or the deflection of the surface after it. Before the eruption, the temperatures of fumaroles rise, sometimes the composition of volcanic gases and the intensity of their release change.

The precursor phenomena, which preceded the majority of quite well documented eruptions, are similar to each other. However, it is very difficult to predict with certainty when the eruption will occur.

Volcanological observatories. To prevent possible eruptions, systematic instrumental observations are conducted in special observatories. The oldest volcanological observatory was founded in 1841-1845 on Mount Vesuvius in Italy, then an observatory on Kilauea volcano on Hawaii Island began operating in 1912 and around the same time several observatories in Japan. Volcanoes are also monitored in the USA (including the St. Helens volcano), Indonesia at the observatory at the Merapi volcano on Yava Island, in Iceland, Russia by the Institute of Volcanology of the Russian Academy of Sciences (Kamchatka), Rabaule (Papua New Guinea), on the islands of Guadeloupe and Martinique in the West Indies, monitoring programs have been launched in Costa Rica and Colombia.

Notification methods. Warn about the imminent volcanic danger and take measures to mitigate the consequences should the civil authorities, which volcanologists provide the necessary information.

The public warning system can be sound (siren) or light (for example, on the highway at the foot of Sakurajima volcano in Japan, flashing signal lights warn motorists of ash deposition). Also, warning devices are installed that operate at elevated concentrations of dangerous volcanic gases, for example hydrogen sulphide. On roads in dangerous areas, where there is an eruption, place road barriers.

Reducing the danger associated with volcanic eruptions. To mitigate volcanic hazards, both complex engineering structures and very simple methods are used. For example, during the eruption of the Miyakejima volcano in Japan in 1985 the cooling of the lava flow front with sea water was successfully applied. Arranging artificial gaps in the frozen lava, which limits flows on the slopes of volcanoes, it was possible to change their direction. For protection against mud-stone flows. Lahars. use fencing embankments and dams, guiding streams in a certain channel. To avoid the occurrence of lakhara, the crater lake is sometimes lowered by means of a tunnel (the volcano Kelud on Jawa Island in Indonesia). In some areas, special tracking systems for thunderstorms are installed, which could bring down showers and activate lahars. In the places where the products fall out, eruptions are constructed by various canopies and safe shelters.

volcanoes: volcanic danger

To the article VOLCANOES Volcanic eruptions threaten people's lives and cause material damage. After 1600, as a result of eruptions and associated mudflows and tsunamis, 168 thousand people died, 95 thousand people became victims of diseases and famine that arose after eruptions. Due to the eruption of the Montagne-Pele volcano in 1902, 30,000 people died. As a result of the descent of mudflows from the volcano Ruiz in Colombia in 1985, 20 thousand people died. The eruption of the volcano Krakatoa in 1883 led to the formation of a tsunami that killed 36,000 people. The nature of the danger depends on the effect of various factors. Lava flows destroy buildings, block roads and agricultural lands, which for many centuries are excluded from economic use, until a new soil forms as a result of weathering processes. The rate of weathering depends on the amount of precipitation, the temperature regime, the conditions of the runoff and the nature of the surface. For example, on the more humid slopes of the Etna volcano in Italy, agriculture on lava flows resumed only 300 years after the eruption. Due to volcanic eruptions on the roofs of buildings, powerful layers of ash accumulate, which threatens their collapse. The ingress of light particles of ash into the lungs leads to the loss of livestock. A suspension of ash in the air poses a danger to road and air transport. Often during the ash falls, airports are closed. Ash flows, which are a hot mixture of suspended particulate matter and volcanic gases, move at high speed. As a result, people, animals, plants and houses are destroyed from burns and suffocation. The ancient Roman cities of Pompeii and Herculaneum fell into the zone of action of such streams and were covered with ashes during the eruption of the volcano Vesuvius. Volcanic gases released by volcanoes of any type rise into the atmosphere and usually do no harm, but in part they can return to the earth's surface in the form of acid rain. Sometimes the relief of the terrain contributes to the fact that volcanic gases (sulfur dioxide, hydrogen chloride or carbon dioxide) spread near the surface of the earth, destroying vegetation or polluting the air in concentrations exceeding the permissible limits. Volcanic gases can cause and indirect harm. Thus, the fluorine compounds contained in them are captured by ash particles, and when the latter fall on the earth's surface, pastures and ponds are infected, causing severe diseases of livestock. In the same way, open sources of water supply for the population can be contaminated. Huge destruction also causes mudstone flows and tsunami. Forecast of eruptions. Volcanic hazard maps are drawn up for forecasting eruptions, showing the nature and distribution areas of products of past eruptions and monitoring of the precursors of eruptions. Such precursors include the frequency of weak volcanic earthquakes; if usually their number does not exceed 10 per day, then immediately before the eruption increases to several hundred. Instrumental observations of the slightest deformations of the surface are carried out. The accuracy of measurements of vertical movements, fixed, for example, by laser instruments, is 0.25 mm, horizontal. 6 mm, which allows you to detect the slope of the surface of only 1 mm per half a kilometer. Data on changes in height, distance, and inclinations are used to identify the center of swelling preceding the eruption, or the deflection of the surface after it. Before the eruption, the temperatures of fumaroles rise, sometimes the composition of volcanic gases and the intensity of their release change. The precursor phenomena, which preceded the majority of quite well documented eruptions, are similar to each other. However, it is very difficult to predict with certainty when the eruption will occur. Volcanological observatories. To prevent possible eruptions, systematic instrumental observations are conducted in special observatories. The oldest volcanological observatory was founded in 1841-1845 on Mount Vesuvius in Italy, then an observatory on Kilauea volcano on Hawaii Island began operating in 1912 and around the same time several observatories in Japan. Volcanoes are also monitored in the USA (including the St. Helens volcano), Indonesia at the observatory at the Merapi volcano on Yava Island, in Iceland, Russia by the Institute of Volcanology of the Russian Academy of Sciences (Kamchatka), Rabaule (Papua New Guinea), on the islands of Guadeloupe and Martinique in the West Indies, monitoring programs have been launched in Costa Rica and Colombia. Notification methods. Warn about the imminent volcanic danger and take measures to mitigate the consequences should the civil authorities, which volcanologists provide the necessary information. The public warning system can be sound (siren) or light (for example, on the highway at the foot of Sakurajima volcano in Japan, flashing signal lights warn motorists of ash deposition). Also, warning devices are installed that operate at elevated concentrations of dangerous volcanic gases, for example hydrogen sulphide. On roads in dangerous areas, where there is an eruption, place road barriers. Reducing the danger associated with volcanic eruptions. To mitigate volcanic hazards, both complex engineering structures and very simple methods are used. For example, during the eruption of the Miyakejima volcano in Japan in 1985 the cooling of the lava flow front with sea water was successfully applied. Arranging artificial gaps in the frozen lava, which limits flows on the slopes of volcanoes, it was possible to change their direction. For protection against mud-stone flows. Lahars. use fencing embankments and dams, guiding streams in a certain channel. To avoid the occurrence of lakhara, the crater lake is sometimes lowered by means of a tunnel (the volcano Kelud on Jawa Island in Indonesia). In some areas, special tracking systems for thunderstorms are installed, which could bring down showers and activate lahars. In the places where the products fall out, eruptions are constructed by various canopies and safe shelters.