Volcanic eruptions. Signs of a volcanic eruption The main phenomena of a volcanic eruption

The lands located at the foot of volcanoes are some of the most fertile areas of our planet. And all because the eruptions that the volcano produces saturate the soil with a huge amount of nutrients and minerals. Even if the volcano has been dormant for a long time and does not show itself in any way, the wind blowing its stones carries substances necessary for the earth in different directions.

Apparently, this is why people constantly settle not only at the foot of volcanoes, but also on the slopes of mountains, and do not pay the slightest attention to the periodic tremors in the region. And completely in vain. Everyone knows the sad fate of the inhabitants of Pompeii, who died during the famous eruption of Vesuvius almost two thousand years ago. The tragedy could well have been avoided if they had paid at least a little attention to the more frequent earthquakes with a magnitude of five to six.

Where do volcanoes originate? Fire-breathing mountains appear above the places where lithospheric plates collide with each other, in the weakest places of the earth’s crust, through which our planet throws out hot magma, flammable gases and a wide variety of volcanic material, which these mountains subsequently form.

As for the word “volcano,” it itself is of Latin origin - this is what the locals called the god of fire in Ancient Rome. Interestingly, Mount Etna was the first to receive this name (it was there, according to local residents, that Vulcan’s forge was located).

There are different types of volcanoes. Currently, geologists count about one and a half thousand active volcanoes on our planet, not counting underwater ones. As for the latter, about 20% of the total number of all existing volcanoes in the world, including extinct ones, are located in the oceanic and sea depths. It is to them that we owe new land masses that sometimes arise in the middle of the vast ocean: after underwater volcanoes erupt huge amounts of lava, their peaks eventually reach the ocean surface and form islands (for example, Hawaiian or Canary Islands).

The largest number of volcanoes (two thirds) are located in the so-called Pacific Ring of Fire, framing the edges of the huge Pacific plate, which is in constant motion and constantly collides with neighboring plates.

The role of volcanoes in the life of our planet

It is impossible to downplay the role of volcanoes in the life of our planet. First of all, because if it weren’t for them, it is quite possible that the Earth would still be a hot cosmic ball: it was the fire-breathing mountains that at one time brought water vapor out from the bowels of the globe, thereby cooling the lithosphere and atmosphere of the planet.

According to geologists, a single eruption of a fiery mountain on one of the Indonesian islands more than 75 thousand years ago plunged our entire planet into the Ice Age, and sulfuric acid formed in the atmosphere.

Throughout the history of the globe, they have actively participated in the creation and destruction of various land areas. For example, quite recently, in 1963, near the southwestern coast of Iceland, one of the underground volcanoes created the small island of Surtsey, with an area of ​​2.5 square meters. km.

In the distant past (in the 16-17th century BC), another similar volcano almost completely destroyed the island of Santorini (Aegean Sea). In this case, a decisive role was played by a long-dormant volcano, which suddenly, with unexpected force, demolished the top of the mountain and erupted lava for many days (until it almost completely destroyed the island, thereby destroying the Minoan civilization and causing a huge tsunami). All that remained of the island after the end of the eruption was a large crescent-shaped islet with the largest caldera in the world.

How does a volcano work?

Before understanding the crater of a volcano and the causes of a volcanic eruption, you first need to clarify for yourself what our planet is like in cross-section. To put it simply, its structure is a bit like an egg, in the center of which there is an extremely hard core surrounded by the mantle and lithosphere.

From above, our planet is protected by a rather thin, but at the same time, hard shell, in other words, the earth’s crust, the lithosphere. On land, its thickness usually varies from 70 to 80 km, on the ocean floor - around twenty.

Under the lithosphere there is a viscous, like hot tar, layer of hot mantle: its temperature in the depths of the planet reaches thousands of degrees (the closer to the center of the Earth, the hotter it is). To obtain its temperature indicators, volcanologists use special electric “thermocouple” thermometers - devices made of glass melt in it almost immediately. The life of our planet from the inside looks like this:

• The part of the mantle that is closer to the lithosphere and the part that is near the core constantly mixes with each other: the hot one rises up, the cold one goes down.
• Since the mantle itself has an extremely viscous structure, from the outside it may seem that the earth’s crust is floating in it, going a little deeper under the pressure of its own weight.
• Having reached the earth's crust, the gradually cooling lava moves along it for some time, after which, having cooled, it falls down.
• Moving along the lithosphere, magma sets in motion individual sections of the earth's crust (in other words, lithospheric plates), which because of this periodically collide with each other.
• The part of the lithospheric plate that appears below sinks into the hotter mantle and almost immediately begins to melt, forming magma - a viscous mass consisting of molten rocks and containing various gases and water vapor. Despite the fact that the resulting magma is not as thick as the mantle, it still remains a fairly viscous consistency.
• Since magma is much lighter in structure than the surrounding rocks, it rises again and gradually accumulates in magma chambers that are located along all the places where lithospheric plates collide.

The role of magma

But then magma, in its behavior, resembles yeast dough: it increases in volume and occupies absolutely all the free territory that it can reach, rising from the bowels of our planet along all the cracks accessible to it.

Having reached the least densely clogged places, under the influence of the gases contained in it, which try to leave it in any way (this process is called degassing of magma), it breaks through the earth's crust and, having knocked out the “plug” of the volcano, breaks out.

Eruption

The more tightly the mountain is sealed, the stronger the eruption will be. Typically, experts designate the strength of volcanic emissions (VEI) from 0 (weakest) to 8 (strongest) points. For example, the active activity of Mount St. Helens in 1980 was assessed by volcanologists as moderate, although the eruption itself was equated in power to the explosion of five hundred atomic bombs.

Having risen to the top and escaped from a confined space, magma almost immediately loses gases and water vapor, and becomes lava (magma depleted in gases), capable of moving at a speed of about 90 km/h.

The gases that escape are flammable and explode in the crater of a volcano (a volcano crater is a funnel-shaped depression at the top or slope of a volcanic cone), leaving behind a huge crater (caldera) in the mountain. The volcano erupts as follows:

• After the magma knocks out the plug of the volcano, the pressure in the magma chamber (its upper part) instantly decreases. The dissolved gases below continue to bubble and continue to be part of the magma;
• The closer to the vent, the more gas bubbles there are. When there are too many of them, they decisively rush upward, outward, raising molten magma with them.
• At the same time, a foamy mass accumulates near the crater of the volcano, known to us in its frozen form as pumice.
• Once free, the gases completely leave the magma, which because of this transforms into lava and carries ash, steam and rock fragments from the depths of the globe (among which there are often blocks the size of a house). As for the eruption itself, it is also characterized by an alternation of weak and powerful explosions.
• The height of the rise of substances ejected from the bowels of the Earth usually varies from one to five kilometers, but it can also be much higher. For example, in the 50s of the last century, the height of ejected debris from the Bezymyanny volcano (Kamchatka) reached 45 km, and the emissions themselves scattered throughout the area over a distance of several tens of thousands of kilometers.
• In the event of an extremely strong eruption, the volume of volcanic emissions can be several tens of cubic kilometers, and the amount of ash can be so enormous that absolute darkness occurs, which can usually only be observed in a space completely closed from light.

Volcanic eruption products are divided into different types. They can be gaseous (volcanic gases), liquid (lava) and solid (volcanic rocks). Depending on the nature of the products of volcanic eruptions and the composition of the magma, structures of various shapes and heights are formed on the surface.

Ending the process

When gases leave the magma with noise and explosions, the pressure that previously arose in the magma chamber is significantly reduced, and the eruption stops. After this, the erupting crater of the volcano is closed by cooling lava, and sometimes it does it quite firmly, and sometimes not quite. And then small amounts of gases (fumaroles) or fountains of boiling water (geysers) continue to erupt onto the earth’s surface, and the volcano itself is considered active. This means that magma will soon begin to gather below again, and, having reached a certain volume, the eruption will begin again.

Types of volcanoes

Volcanologists have often wondered what kind of volcanoes are there? During the research, several species were identified.

How to survive a disaster

Despite the danger, people continue to live at the foot of a dangerous neighbor; volcanologists have developed a whole range of measures, the purpose of which is to warn the local population about the approaching danger, and if they find themselves in a dangerous situation, to know how to act in order to save their lives.

First of all, it is imperative to follow all warnings from volcanologists about the possible start of a volcanic eruption.

If it is not possible to leave the dangerous territory, at the first warning of danger, you need to stock up on autonomous lighting sources and heaters, as well as water and food for several days. If it was not possible to leave a dangerous area before the eruption begins, it is necessary to tightly and securely close all window and door openings, as well as ventilation and smoke ducts.

Pet owners should be sure to bring them into completely enclosed areas. If volcanic emissions find a person on the street, he must in any way protect his body (primarily his head) from falling stones and ash.

Since a volcanic eruption is usually accompanied by various natural disasters (floods, mudflows), at this time it is necessary to move away from rivers and valleys so as not to end up in a flood zone or to avoid being buried under mud (it is advisable to be at some elevation at this time) .

Having survived the eruption, before going outside, you must cover your mouth and nose with a gauze bandage, as well as wear protective glasses and clothing that will prevent burns. You should not escape from the disaster zone by car immediately after the ash falls - it will be disabled almost immediately. After leaving the room, it is necessary to clear the roof of the house (shelter) from ash and other volcanic emissions, otherwise it may collapse, unable to withstand the enormous load.

Volcano- a place where the hot substance of the earth's interior - magma - breaks out to the surface.

The interior of the Earth is constantly in a heated state. At depths of 10 to 30 km, molten rocks or magma accumulate. During tectonic processes, cracks form in the earth's crust. Magma rushes along them to the surface under the pressure of water vapor and gases; when it reaches the surface, the magma pours out in the form of lava. From the vapors and gases released into the atmosphere, sediments of volcanic rock called tephra settle on the ground.

According to the degree of activity, volcanoes are classified into active, dormant and extinct. Active ones include those that erupted in historical times. Extinct ones, on the contrary, did not erupt. Dormant ones are characterized by the fact that they periodically manifest themselves, but it does not come to an eruption.

There are currently several hundred active volcanoes known on the globe. Most of them are located along the shores of the Pacific Ocean, including in Russia on Kamchatka and the Kuril Islands.

The most dangerous phenomena accompanying volcanic eruptions:

- lava flows,

- loss of tephra,

- volcanic mud flows,

- volcanic floods,

- scorching volcanic cloud,

- volcanic gases,

- release of volcanic ash.

Lava flows - these are molten rocks with a temperature of about 1000 0C. The flow speed most often does not exceed 1 km/h.

Tephra consists of fragments of solidified lava. Its loss leads to the destruction of animals, plants, and in some cases, the death of people.

Mud flows - these are thick layers of ash on the slopes of the volcano that are in an unstable position. When new portions of ash fall on them, they slide down the slope. In some cases, the ash becomes saturated with water, resulting in the formation of volcanic mud flows. Their speed can reach several tens of kilometers per hour. Due to the high speed of movement, it is difficult to carry out rescue operations and evacuate the population.

Volcanic floods . When glaciers melt during volcanic eruptions, huge amounts of water can form very quickly, which leads to floods. For example, the height of the peak, where the main crater of the Klyuchevskaya Sopka volcano in Kamchatka is located, is 4750 m. At such a height, powerful glaciers are formed, which melt during strong eruptions, and then rapid streams of water rush from the mountain.

Scorching volcanic cloud . It is a mixture of hot gases and tephra. Its damaging effect is caused by the appearance of a shock wave (strong wind), spreading at a speed of up to 40 km/h, and a wave of heat with a temperature of up to 1000 0C.

Volcanic gases . Eruptions are always accompanied by the release of gases mixed with water vapor - a mixture of sulfur and sulfur oxides, hydrogen sulfide, hydrochloric and hydrofluoric acids in a gaseous state, as well as carbon dioxide and carbon monoxide in high concentrations, which are deadly to humans. The release of these gases can continue for a very long time even after the volcano has stopped throwing out lava and ash.

The intense emission of volcanic ash impairs visibility, creates a great danger for aviation flights (ash getting into the engine), and large quantities of ash accumulate on the roofs of houses.

Protective measures:

 Choosing a place of residence away from active volcanoes.

- Evacuation of the population.

 Impact on a lava flow: deflection of the flow, dividing it into several small ones, cooling, creating barriers.

 Destruction of the crater wall (by bombardment) and the direction of lava flow in a safe direction.

 Deviation in the safe direction of mud flows.

- Throwing volcanic ash from the roofs of houses.

Question. Landslides, landslides, mudflows, avalanches.

Sel- a rapid, stormy mud or mud-stone flow, consisting of a mixture of water, sand, clay and rock fragments, suddenly appearing in the basins of small mountain rivers. The reason for its occurrence is intense and prolonged downpours, rapid melting of snow or glaciers, breakthrough of reservoirs, less often - earthquakes, volcanic eruptions.

Having a large mass and high speed of movement (up to 40 km/h), mudflows destroy buildings, roads, power lines, and lead to the death of people and animals. The steep leading front of a mudflow wave with a height of 5 to 15 m forms the “head” of a mudflow (the maximum height of the water-mud flow shaft can reach 25 m), the length of mudflow channels ranges from several tens of meters to several tens of kilometers.

Mudflows are especially active in the North Caucasus. Due to the negative role of the anthropogenic factor (destruction of vegetation, quarrying, etc.), mudflows began to develop on the Black Sea coast of the North Caucasus (Novorossiysk region, Dzhubga - Tuapse - Sochi section).

Protective measures:

 Strengthening mountain slopes (planting forests);

 Anti-mudflow dams, dikes, ditches;

 Periodic release of water from mountain reservoirs;

 Construction of protective walls along river beds;

 Reducing the rate of snow melting in the mountains by creating smoke screens.

 Catching mudflows in special pits located in river beds.

 Effective warning and warning system.

Collapse- this is a rapid separation (separation) and fall of a mass of rocks (earth, sand, clay stones) on a steep slope due to loss of slope stability, weakening of cohesion, and integrity of rocks.

A collapse occurs under the influence of weathering processes, movement of ground and surface water, erosion or dissolution of rock, and soil vibrations. Most often, collapses occur during rainy periods, snow melting, and during blasting and construction work.

The damaging factors of a collapse are the fall of heavy masses of rocks that can damage or crush even strong structures or cover them with soil, blocking access to them. Another danger of landslides is the possible damming of rivers and collapse of the banks of lakes, the waters of which, in the event of a breakthrough, can cause floods or mudflows.

Signs of a possible collapse are numerous cracks in steep rocks, overhanging blocks, the appearance of individual rock fragments, blocks separating from the main rock.

Landslide- sliding displacement of rock masses down the slope under the influence of gravity; occurs, as a rule, as a result of erosion of the slope, waterlogging, seismic tremors and other factors.

The following factors can be the causes of landslides.

1. Natural:

earthquakes;

waterlogging of slopes with precipitation;

increase in slope steepness as a result of erosion by water;

weakening of the strength of hard rocks due to weathering, washing out or leaching

presence of softened clays, quicksand, fossil ice in the soil:

2. Anthropogenic:

cutting down forests and bushes on slopes. Moreover, deforestation can occur much higher than the site of a future landslide, but water will not be retained by the plants above, as a result of which the soils become waterlogged far below;

blasting operations, which are essentially a local earthquake and contribute to the development of cracks in rocks;

plowing slopes, excessive watering of gardens and vegetable gardens on slopes;

destruction of slopes by pits, trenches, road cuts,

clogging, clogging, blocking of groundwater outlets;

construction of housing and industrial facilities on slopes, which leads to destruction of the slopes and an increase in the force of gravity directed down the slope.

The damaging factor of landslides is heavy masses of soil that fall asleep or destroy everything in its path. Therefore, the main indicator of a landslide is its volume, measured in cubic meters.

Unlike landslides, landslides develop much more slowly, and there are many signs that allow timely detection of an incipient landslide.

Signs of an incipient landslide:

ruptures and cracks in the ground, on roads;

disruption and destruction of underground and surface communications;

displacement, deviation from the vertical of trees, poles, supports, uneven tension or broken wires;

curvature of the walls of buildings and structures, the appearance of cracks on them;

change in water level in wells, boreholes, and any reservoirs.

Landslide prevention measures include: monitoring the condition of slopes; analysis and forecasting of the possibility of landslides; carrying out complex engineering protective works; training of persons living, working and resting in a hazardous area on life safety rules.

Snow avalanches arise as a result of the accumulation of snow on mountain peaks during heavy snowfalls, strong snowstorms and a sharp drop in air temperature. Avalanches can also occur when deep frost forms, when a loose layer (quicksand snow) appears in the thickness of the snow.

Snow avalanches are observed annually in the mountainous regions of the North Caucasus, Sakhalin, Kamchatka, Magadan region, in the Khibiny Mountains, and in the Urals.

Most avalanches descend along certain chutes - narrow hollows on steep mountain slopes. 200–300, and sometimes up to 500 thousand tons of snow can fall down these hollows at the same time.

In addition to flume avalanches, there are basic and jumping avalanches. Major avalanches slide down the mountain slopes in unspecified places; as a rule, they are small and do not pose any particular danger. Jumping avalanches are trough avalanches that encounter “springboards” on their way and “jump” over them with great force, acquiring an increasing speed of movement, and as a result, the force of destruction increases.

Avalanches often occur suddenly and begin their initial movement silently. When avalanches move in narrow mountain gorges, an air wave of increasing strength moves ahead of them, causing even greater destruction in comparison with the falling mass of snow. Repeated avalanches leave deep traces in the mountain landscape. Avalanches often fall into river beds and block them, forming dams for a long time.

Avalanche danger is caused by sudden changes in weather, heavy snowfalls, heavy snowstorms, and rain. To prevent avalanche danger, there is a special mountain avalanche service.

Catastrophic avalanches in the world occur on average at least once every two years, and in some mountainous areas - at least once every 10–12 years.

When people fall under avalanches, it should be remembered that a person, being covered with avalanche snow, can remain alive for only a few hours, and the chance of survival is higher, the thinner the layer of snow above him. Among people who were in an avalanche for no more than 1 hour, up to 50% can survive; after 3 hours, the probability of remaining alive does not exceed 10%. Therefore, work to rescue people caught in an avalanche must begin even before the rescue team arrives.

If you find someone covered, first of all, free your head, clear your mouth, nose, and ears of snow; then carefully (taking into account the possibility of fractures) they remove him from under the snow, transfer him to a place protected from the wind, wrap him in dry clothes, give him a hot drink, and if there are no signs of life, begin artificial ventilation and other resuscitation measures.

D actions of the population in case of threat of landslides, landslides, mudflows

The population living in landslide-, mudflow- and landslide-hazardous zones should know the sources, possible directions of movement and the main characteristics of these dangerous phenomena. The population of mountainous areas is obliged to strengthen their houses and the territories on which they are built, as well as to participate in the construction of protective hydraulic and other protective engineering structures.

Warning of the population about natural disasters is carried out through sirens, radio, television broadcasting, as well as through local warning systems that directly connect the hydrometeorological service unit with populated areas in hazardous areas.

Before leaving a house or apartment during evacuation, it is necessary to remove property from the yard or balcony into the house; the most valuable property that cannot be taken with you should be protected from moisture and dirt; doors, windows, ventilation and other openings should be tightly closed, and the electricity should be turned off. , gas and water.

Flammable and toxic substances should be removed from the house and, if possible, buried in a hole or hidden in a cellar.

In all other respects, citizens must act in accordance with the procedure established for organized evacuation.

If there was no warning about the danger or it was made immediately before the natural disaster, then residents, without caring about their property, should quickly go to a safe place. Natural places for escape from a mudflow or landslide are mountain slopes and hills that are not prone to landslides, landslides or flooding by mudflows. When climbing to safe slopes, do not use valleys, gorges and recesses, since side channels of the main mudflow may form in them. In the case when people, buildings and structures find themselves on the surface of a moving landslide area, they should, after leaving the premises, move upward if possible, when braking a landslide, beware of stones, fragments of structures, earthen ramparts, and screes rolling down from its rear part. When a fast-moving landslide stops, a strong shock is possible. This poses a great danger to people in the landslide.

Question. Classification of wind by speed. Definition of "storm". Types of storms. Definitions of the terms “hurricane”, “cyclone” and “tornado”. Types of Hurricanes

Wind is the movement of air parallel to the earth's surface, resulting from the uneven distribution of heat and atmospheric pressure and directed from a zone of high to a zone of low pressure.

Many words are used to denote the movement of wind: tornado, storm, hurricane, gale, typhoon, cyclone and many local names. To systematize them, the Beaufort scale is used all over the world, which allows you to very accurately estimate the strength of the wind in points (from 0 to 12) by its effect on ground objects or by waves at sea. This scale is also convenient because it allows you to quite accurately determine the wind speed without instruments based on the characteristics described in it.

From the group of meteorological and agrometeorological phenomena of natural origin, extremely dangerous natural disasters are storms (storms), hurricanes (typhoons), tornadoes (tornadoes), cyclones, which are extremely fast and strong, often catastrophic air movement, causing destruction of buildings, loss of life and animals.

According to wind speed, they are distinguished: weak wind - up to 5 m/s, strong - up to 10 m/s, very strong 15-18 m/s, storm (storm) - 18–29 m/s, hurricane (typhoon) - over 29 m/s, sometimes reaching 120–210 m/s.

Storm- a very strong and prolonged wind, causing great destruction on land and rough seas (storm). Depending on the time of year and the involvement of various particles in the air flow, dusty, dustless, snow and squall storms are distinguished.

Dust (sand) storms accompanied by the transfer of large quantities of soil and sand particles. They occur in deserts, semi-desert and plowed steppes and are capable of transporting millions of tons of dust over hundreds of kilometers and covering areas of several thousand kilometers.

In Russia, the border of distribution of such storms goes through the Saratov and Samara regions, the cities of Ufa and Orenburg, and the foothills of Altai.

Dustless storms are characterized by the absence of dust entrainment in the air flow and a relatively smaller scale of destruction and damage.

Blizzards arise in winter and move huge masses of snow through the air. Their duration ranges from several hours to several days. They have a relatively narrow range of action. They visit Siberia more often.

Squalls characterized by an almost sudden onset, an equally rapid ending, a short duration of action and enormous destructive power.

Hurricane is a vortex with a huge speed of movement of air masses and low atmospheric air pressure in the central part. The speed of air movement can exceed 120 m/s in an area with a diameter of 500–1000 km and an altitude of up to 10–12 km. Hurricanes occur in areas of contact between warm and cold air masses with the most pronounced temperature contrasts and are accompanied by heavy clouds, heavy rains, thunderstorms and hail. Hurricanes have different names: in the Philippines - begwiz; in Australia - wili-wili; in North America - hurricanes.

Hurricanes most often occur in regions with a tropical climate, where they have the greatest destructive power. In some cases, powerful hurricanes can be equated to earthquakes in their destructive power. In Russia, the most likely region for hurricanes to occur is the Pacific coast. At the same time, hurricane winds and heavy rainfall are often observed in the coastal areas of the Arctic seas, the seas of the Far East, the Black Sea, as well as in the Volga region and the North Caucasus republics. During hurricanes, floods often occur as a result of intense rainfall, which occurred in the Primorsky Territory. As a result of hurricanes, structures are destroyed, fires break out, people die, and a huge number of the population needs medical care.

Cyclone- a giant atmospheric vortex in which pressure decreases towards the center, air currents circulate around the center counterclockwise (in the Northern Hemisphere) or clockwise in the Southern Hemisphere.

During a cyclone, cloudy weather prevails. The greatest danger is posed by tropical cyclones with storm and hurricane winds and air movement strengths of 9 and 12, respectively, on the Beaufort scale. Wind speed with strong upward movement sometimes reaches 70 m/s, and individual gusts - 100 m/s; dense continuous clouds develop with heavy rainfall (up to 1000 mm per day or more) and thunderstorms.

In Southeast Asia, tropical cyclones are called typhoons, and in the Caribbean Sea - hurricanes. During thunderstorms, atmospheric vortices often arise, spreading down to the very surface of the earth. Their diameter can be tens of meters over the sea and hundreds over land. Such a whirlwind is called a tornado (a blood clot in Western Europe, a tornado in the USA).

Tornado- This is the most destructive atmospheric phenomenon. It is a huge vortex with a vertically directed axis of rotation, resembling a funnel in shape with a “trunk” extended upward. The air in a tornado rotates at a speed of several tens of meters per second, simultaneously rising in a spiral to a height of up to 800–1500 m. The tornado travels 40–60 km, moving along with the cloud, is accompanied by a thunderstorm, rain, hail, and is capable of causing great destruction.

Tornadoes are formed when the atmosphere is in an unstable state, when the air in its lower layers is very warm, and in the upper layers it is cold, and powerful vertical movement of air masses occurs. Low atmospheric pressure is formed inside the vortex flow, so the tornado draws into itself, like a giant vacuum cleaner, dust, water and all objects encountered along the path of its movement, lifting them high up and carrying them over long distances.

Protective measures after receiving a “storm warning”:

 Notifying the population about the time of hurricane approach.

 Transition to safe operating modes of various industries.

 Reducing stocks of hazardous substances at enterprises, increasing the reliability of their storage.

 Preparation of shelters and basements to protect the population.

- Partial evacuation of the population.

 Increasing the security of buildings, structures and other human habitats (close windows, doors, ventilation openings, cover glass, protect windows and display cases with shutters and shields).

 Secure fragile structures and objects or remove them, empty balconies of things.

 Creation of reserves of food and water, items to support life.

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Example 1
Arecas Volcano is located in the Colombian Andes in northern South America, 150 km northwest of the capital of Colombia, Bogota. The last time it erupted in 1595, it was considered dormant. On November 13, 1985, the volcano suddenly awoke. The explosions that began during its eruption caused the rapid melting of snow and ice in the crater of the volcano. Huge masses of water, mud, stones and ice rushed into the Lagunilla River valley, sweeping away everything in its path.
About 40 km from the volcano, in the river valley, there was the town of Armero with a population of 21 thousand people, and another 25 thousand people lived in the surrounding villages. On November 13, at 23:00, a stream of mud covered the city with a 5-6-meter layer and 20 thousand people almost instantly died in the raging mess of mud. Only those who, hearing the approaching roar, jumped out of the house and ran to the nearest hills, managed to escape.
Example 2
The eruption of the Mont Pelee volcano on the island of Martinique (Lesser Antilles) occurred in May 1902. At 7:50 a.m., colossal explosions shook the volcano and powerful ash clouds shot up to a height of more than 10 km. Simultaneously with these explosions, which followed continuously one after the other, a black cloud burst out of the crater, sparkling with crimson flashes. At a speed of more than 150 km/h, it rushed down the slope of the volcano towards the city of Saint-Pierre, located 10 km from the Mont Pelee volcano. This heavy, hot cloud pushed in front of itself a dense clot of hot air, which turned into a gust of hurricane wind and hit the city a few seconds after the volcanic eruption began. And after another 10 seconds, a cloud covered the city. A few minutes later, 30 thousand residents of the city of Saint-Pierre were dead. The scorching cloud of the Mont Pelee volcano in the blink of an eye wiped out the city of Saint-Pierre from the face of the Earth.

A volcanic eruption is characterized by:
-volcanic gases begin to emerge from the crater
-then lava is ejected from the vent with varying activity
-from the outside, the lava turns into magma and spreads in a hot form over the surrounding area, destroying all life in its path
- huge masses of ash are thrown into the air and settle on nearby territories, villages, cities, visibility deteriorates sharply and it becomes impossible to breathe
-volcanic eruptions can be accompanied by earthquakes
-consequences of the volcano. there may be a powerful tsunami, fires, panic, injury and death, release of radioactivity, chemicals. and other substances, major ground accidents and disasters.
The most famous case of a volcanic eruption, which brought terrible destructive power (destroyed 3 cities, including Pompeii) and claimed a large number of human lives, is considered to be the eruption of Mount Vesuvius in 79 BC.
As a rule, it is possible to predict the eruption of a volcano, but if you find yourself in the immediate vicinity. proximity to the volcano, then:
-protect your respiratory organs and eyes from ash and leave the volcano site as soon as possible
- hide in a shelter
-follow all instructions from the rescue/evacuation service

Volcanoes usually gravitate towards areas of modern tectonic activity. In Russia this is the Kuril-Kamchatka zone.

Volcanic eruptions can be accompanied by flows of lava, ash, the formation of a caldera (collapse of a cavity), the release of volcanic bombs (up to 50 cm), lahars - mud flows that form from volcanic craters.

Volcanic eruptions turn into emergencies in the presence of nearby cities, towns, economic facilities and other cases of danger to people and material assets.

Disasters associated with slope instability are a particular hazard in mountainous areas. Any slope can be a potential cause of disaster. Under the influence of gravity and loss of stability, the slope can collapse, causing serious consequences.

Catastrophic events occurring on slopes do not necessarily have to be rapid. The slow sliding of a rocky shore with buildings into the sea over the course of a year is no less dangerous a disaster than rapid displacements. Progressive failure of slopes can be brittle (occurs quickly) or creep type (occurs slowly). Slopes composed of loose rocks are characterized by slope stability. Critical slope height (Fig. 186):

h c = W(b; j),

where b is the angle of repose; g– wedge weight; φ – angle of internal friction; WITH– adhesion (included in strength); W– landslide mass; h c– slope height.

In general, the design of slopes is carried out in accordance with the mentioned criteria. In addition, the stability analysis must take into account the influence of pore water, which weakens the shear strength of rocks.

Slopes composed of rocks are also calculated using the critical height parameter. The difference here lies in the mechanism of displacement: displacement occurs along cracks crossing the slope. On high (more than 80 m) slopes, the weight of the rocks causes stress concentration at the base of the slope.

The most dangerous phenomena that accompany volcanic eruptions include lava flows, tephra fallout, volcanic mud flows, volcanic floods, scorching volcanic clouds and volcanic gases.

Lava flows consist of lava - molten rocks heated to 900–1000°C. Depending on the composition of the rocks, lava can be liquid or viscous. When a volcano erupts, lava flows from cracks in the volcano's slope or overflows the edge of the volcano's crater and flows down to its base. The more powerful the lava flow, the greater the slope of the volcano cone and the thinner the lava, the faster it moves. The speed range of lava flows is quite wide: from a few centimeters per hour to several tens of kilometers per hour. In some, most dangerous cases, the speed of lava flows can reach 100 km per hour. Most often it does not exceed 1 km per hour.

Lava flows at deadly temperatures pose a danger only when populated areas are in their path. However, even in this case, there is still time to evacuate the population and carry out various protective measures.

Tephra consists of fragments of solidified lava, older subsurface rocks, and fragmented volcanic material that forms the volcanic cone. Tephra is formed during the volcanic explosion that accompanies a volcanic eruption. The largest tephra fragments are called volcanic bombs , somewhat smaller ones - lapillas, even smaller ones - volcanic sand, and the smallest ones - ash.

Volcanic bombs fly several kilometers from the crater. Lapilla and volcanic sand can spread for tens of kilometers, and ash in the high layers of the atmosphere can circle the globe several times. The volume of tephra during some volcanic eruptions significantly exceeds the volume of lava; sometimes tephra emissions amount to tens of cubic kilometers.

The fall of tephra leads to the destruction of animals, plants, and possible death of people. The likelihood of tephra falling on a populated area largely depends on the direction of the wind.

Thick layers of ash on the slopes of the volcano are in an unstable position. When new portions of ash fall on them, they slide down the slope of the volcano. In some cases, the ashes become saturated with water, resulting in the formation of volcanic mud flows . The speed of mud flows can reach several tens of kilometers per hour. Such flows have significant density and can entrain large blocks during their movement, which increases their danger. Due to the high speed of movement of mud flows, rescue operations and evacuation of the population are difficult.

When glaciers melt during volcanic eruptions, a huge amount of water can immediately form, which leads to volcanic floods . It is difficult to calculate exactly how much water the glacier released, although it is important for planning measures to protect against volcanic flooding. This is because glaciers have many internal cavities filled with water, which is added to the water produced when glaciers melt during a volcanic eruption.

Scorching volcanic cloud is a mixture of hot gases and tephra. The damaging effect of a scorching cloud is due to the shock wave formed when it occurs (wind at the edges of the cloud), spreading at a speed of up to 40 km/h, and a wave of heat (up to 1000°C). In addition, the cloud itself can move at high speed (90–200 km/h).

A volcanic eruption is always accompanied by the release of volcanic gases and a mixture with water vapor.

Volcanic gases are a mixture of sulfur dioxide and sulfur oxides, hydrogen sulfide, hydrochloric and hydrofluoric acids in a gaseous state,
as well as carbon dioxide and carbon monoxide in high concentrations, which are deadly to humans. The release of volcanic gases can continue for tens of millions of years even after the volcano has stopped spewing lava and ash.

Sharp climate fluctuations are caused by changes in the thermophysical properties of the atmosphere due to its pollution by volcanic gases and aerosols. During the largest eruptions, volcanic emissions spread in the atmosphere over the entire planet. The admixture of carbon dioxide and silicate particles can create a greenhouse effect leading to warming of the earth's surface; Most aerosols in the atmosphere lead to cooling. The specific effect of an eruption depends on the chemical composition, the amount of material ejected, and the location of its source.

Tsunamis often occur during eruptions of island and underwater volcanoes. In addition, clouds of flaming gases and steam formed during underwater eruptions can cause the death of sea vessels. It is possible that gas is capable of being released not only at the points of the eruption, but also in large areas of the seabed adjacent to it, covered with sediments with a high content of gas hydrates. The latter can disintegrate into water and gas with fairly small changes in pressure, temperature, and chemical composition of the overlying water column.

Volcanoes are geological formations on the surface of the earth's crust where magma comes to the surface, forming lava, volcanic gases, "volcanic bombs" and pyroclastic flows. The name “volcano” for this type of geological formation comes from the name of the ancient Roman god of fire “Vulcan”.

Deep below the surface of our planet Earth, the temperature is so high that rocks begin to melt, turning into a thick, viscous substance - magma. The molten substance is much lighter than the solid rock around it, so the magma, as it rises, accumulates in so-called magma chambers. In the end, part of the magma erupts to the surface of the Earth through faults in the earth's crust - this is how a volcano is born - a beautiful, but extremely dangerous natural phenomenon, often bringing with it destruction and casualties.

The magma that escapes to the surface is called lava; it has a temperature of about 1000 ° C and flows rather slowly down the slopes of the volcano. Due to its low speed, lava rarely causes human casualties, however, lava flows cause significant destruction of any structures, buildings, and structures encountered along the path of these “rivers of fire.” Lava has very poor thermal conductivity, so it cools very slowly.

The greatest danger comes from stones and ash erupting from the crater of the volcano during an eruption. Hot stones, thrown into the air at great speed, fall to the ground, causing numerous casualties. Ashes fall to the ground like “loose snow”, and if people, animals, plants all die from lack of oxygen.

This happened with the notorious city of Pompeii, developing and prospering, and destroyed by the eruption of Mount Vesuvius in a matter of hours. However, pyroclastic flows are rightfully considered the deadliest of all volcanic phenomena. Pyroclastic flows are a boiling mixture of solid and semi-solid rocks and hot gas flowing down the slopes of a volcano. The composition of the streams is much heavier than air; they rush down like a snow avalanche, only hot, filled with toxic gases and moving at a phenomenal, hurricane speed.

Classification of volcanoes

There are several classifications of volcanoes based on certain characteristics. For example According to the degree of activity, scientists divide volcanoes into three types: extinct, dormant and active..

Volcanoes that have erupted during a historical period of time and are likely to erupt again are considered active. Dormant volcanoes are those that have not erupted for a long time, but still have the potential to erupt. Extinct volcanoes are volcanoes that have ever erupted, but the likelihood of them erupting again is zero.

Classification According to the shape of the volcano, it includes four types: cinder cones, dome, shield volcanoes and stratovolcanoes.

• The most common type of volcano on land, a cinder cone is made up of small fragments of solidified lava that escaped into the air, cooled, and fell near the vent. With each eruption, such volcanoes become higher.
• Dome volcanoes form when viscous magma is too heavy to flow down the sides of a volcano. It accumulates at the vent, clogging it and forming a dome. Over time, gases knock out such a dome like a cork.
• Shield volcanoes have the shape of a bowl or shield with gentle slopes formed by basaltic lava flows - traps.
• Stratovolcanoes emit a mixture of hot gas, ash and rocks, as well as lava, which are alternately deposited on the volcano's cone.

Classification of volcanic eruptions

Volcanic eruptions are an emergency situation that is carefully studied by volcanologists to be able to predict the possibility and nature of eruptions in order to minimize the scale of the disaster.

There are several types of eruptions:

• Hawaiian,
• strombolian,
• Peleian,
• Plinian,
• hydroexplosive.

Hawaiian is the calmest type of eruption, characterized by the release of lava with a small amount of gas, which forms a shield-shaped volcano. The Strombolian type of eruption, named after the Stromboli volcano, which has been continuously erupting for several centuries, is characterized by the accumulation of gas in the magma and the formation of so-called gas plugs in it. Moving upward along with the lava, reaching the surface, giant gas bubbles burst with a loud bang due to the difference in pressure. During an eruption, such explosions occur every few minutes.

The Peleian type of eruption is named after the most massive and destructive eruption of the 20th century. – Montagne Pelee volcano. The erupting pyroclastic flows killed 30,000 people in a matter of seconds. The Pelian type is characteristic of an eruption similar to the eruption of Mount Vesuvius. This type received its name from the chronicler who described the eruption of Vesuvius that destroyed several cities. This type is characterized by the ejection of a mixture of stones, gas and ash to a very high altitude - often the column of the mixture reaches the stratosphere. Volcanoes located in shallow waters in the seas and oceans erupt using the hydroexplosive type. In such cases, large amounts of steam are generated when the magma comes into contact with seawater.

Volcanic eruptions can create many dangers not only in the immediate vicinity of the volcano. Volcanic ash can pose a threat to aviation, posing a risk of failure of aircraft turbojet engines.

Large eruptions can also affect the temperature in entire regions: ash and sulfuric acid particles create areas of smog in the atmosphere and, partially reflecting sunlight, lead to cooling of the lower layers of the Earth's atmosphere over a particular region, depending on the power of the volcano, wind strength and direction movement of air masses.