Recent powerful earthquakes show that our planet is in the process of a profound transformation. Relationship between earthquakes and volcanic eruptions

Volcanic activity is considered very dangerous. This is due to the fact that many active volcanoes are part of complex mountain ranges located in areas with increased seismic activity. Volcanism itself is an external effusive form of magmatism, i.e. movement of magma from the lower layers of the earth's crust to its surface.

Magma is a liquid hot composition that forms at a depth of 50 to 350 kilometers. The appearance of cracks on the surface of the earth's crust reduces the pressure inside globe. This leads to the fact that magma flows into the cracks mentioned above and tries to get out through them. In the process of its movement, gases are released. They enter the atmosphere, so the soil does not come into contact with pure magma, but with red-hot lava. As a rule, it enters the earth through the vents of volcanoes.

There are a huge number of volcanoes on the territory of our planet. Most of them are located near the Pacific volcanic ring.

There is a classification of volcanoes. Depending on the level of their activity, they are:

1. Operating;

2. Sleeping;

3. Dormant;

4. Extinct.

Active volcanoes are considered the most dangerous, i.e. these are those that erupted in recent times. Extinct volcanoes have the lowest level of danger. The probability of their eruption is extremely low. As for the duration of volcanic activity, it can be equal to several months or several thousand or even millions of years.

Depending on the shape, volcanoes are:

1. Thyroid;

2. Slag;

3. Dome;

4. Complicated;

5. Stratovolcanoes.

What will be the eruption depends on chemical composition lava and its viscosity. According to the type of eruption, there is a division of volcanoes into:

1. Hawaiian (effusive);

2. Dome (extrusive);

3. Strombolian (mixed);

4. Vulcan (explosive).

Those areas of land that have ever experienced the impact of red-hot lava are subject to many post-volcanic processes: geysers, fumaroles, thermal baths.

At present, mankind has not yet found a way by which it would be possible to reduce the level of potential danger posed by volcanoes to a minimum. Despite this, the eruptions of the latter sometimes allow people to get tangible benefits. For example, the Japanese and Icelanders use thermal volcanic energy in the field of medicine. In particular, we are talking about healing underground waters, bathing in which improves health. Also high level volcanic activity often results in the formation of gemstones. In addition to this, modern scientists have found that before the volcanic eruption, in the region where it is located, it rains or other precipitation falls. Thus, by artificially resuming the work of an extinct volcano, it is potentially possible to humidify the climate in this area.

Earthquakes and the mechanism of their formation

Earthquakes are fraught with great danger. They lead to human casualties and cause significant damage to nature. Earth tremors have the strongest impact on the earth's crust. Because of this, about 100 thousand earthquakes happen every year.

Statistics show that seismic tremors occur at a frequency of 1 time in 5 minutes. They are mostly weak, so people do not notice them, which cannot be said about seismographs. In addition, it was found that every year there are about a dozen earthquakes, the strongest of which are equated with disasters.

Official figures indicate that earthquakes claim the lives of approximately 10,000 people every year. Sometimes real tragedies happen. For example, 140 thousand people became victims of the earthquake that occurred in Japan in 1923, and about 700 thousand people died in China from the same disaster in 1976.

As for the nature of earthquakes, scientists are convinced that it is explained by the theory of elastic recoil. This means that strong tremors appear as a result of the release of a large amount of energy, which leads to deformation inside the globe. The surface of the planet is exposed to high pressure from the inside. Over time, the stress level increases, which leads to the appearance of faults.

Long before an earthquake, tectonic movements occur in the lower layers of the earth's crust. Over time, their speed increases, as evidenced by the increase in seismic activity. The maximum speed indicator is achieved due to the operational "discharge" of the reserves of "elastic" energy. It lasts for 10-15 seconds, but sometimes this time can be equal to a minute.

As the earthquake grows, rocks that are deep enough are destroyed. For this reason, their strength is noticeably reduced, and dislocation develops. In the area that will be the weakest, a fault will occur.

The forces leading to the rupture of the earth's crust are based on two models. The first of these is based on the forces at the center of action. Their power increases as they approach the line of discontinuity. The second model is based on the fact that 2 pairs of forces remain active in the focus zone, which are perpendicular to each other.

Thus, an earthquake is a shaking of the planet's surface, which occurred as a result of the strongest seismic vibrations that appear when the integrity of a certain area of ​​the earth's crust is violated and the so-called "elastic" energy is released. All earthquakes are divided into natural, i.e. having a natural origin, and artificial, i.e. arising from the fault of man.

Volcanic earthquakes

Earthquakes of varying power occur in volcanic areas. This is due to the fact that the gases and lava released from the magma are trying to break out. They cause shocks, which lead to volcanic tremere, i.e. a series of weak earthquakes or volcanic tremors.

Tremere indicates that soon the volcano will begin to erupt. Volcanic trembling can stretch for long time. During its course, explosions occur inside the earth's crust. They destroy rocks, which leads to the appearance of seismic and acoustic waves.

Local earthquakes occur even under those volcanoes that have long been extinct, but can become active. In the described situation, tremors have a calm character. As they intensify, the volcano is able to “wake up”. Thus, thanks to seismic activity, it is possible to predict the upcoming eruption of an extinct volcano.

Japanese and American scientists have developed effective method, with the help of which it is not difficult to predict a future earthquake. It is based on the registration of tremors and the study of data obtained from satellites, therefore, it allows you to constantly monitor the activity of lava inside the vent of the volcano.

Volcanic regions are located in the same place as the zones of tectonic earthquakes. In this regard, it is impossible to determine the type of these phenomena.

Any volcanic earthquake has two features, namely:

• Its center is located near the volcano;
• The magnitude remains small.

In 1883, the Krakatoa volcano erupted and a strong earthquake occurred simultaneously on Indonesian territory. Most of the volcano was blown up, and powerful tremors led to serious destruction on several large islands at once. Then all the inhabitants of the island of Borneo died, and the tsunami wave caused significant damage to the islands of the Sunda Strait.

Examples volcanic earthquakes enough. For example, as a result of the eruption of the Ipomeo volcano, the Italian town of Casamichol was destroyed. Earthquakes also occur regularly in Russia. In particular, such volcanoes as Shiveluch, Klyuchevaya Sopka and others remain active in Kamchatka.

Volcanic earthquakes have a certain similarity with tectonic ones. They differ from each other only in scale and range. The latter in the described type of earthquake remains small.

Volcanic earthquakes often occur in Europe. For example, the largest active volcano is Etna, in Sicily. It erupted more than 2 hundred times, and weak tremors were constantly observed before the lava eruption.

Seismic activity in volcanic areas is constantly monitored. The study of micro-earthquakes makes it possible to determine the direction of magma movement and to know its approximate chemical composition.

The growth of volcanic activity is inherent not only in powerful earthquakes, but also in other processes. For example, before the eruption of Vesuvius, the earth's crust experienced strong tremors.

With a further increase in temperature in the bowels of the Earth, rocks, despite high pressure, melt, forming magma. This releases a lot of gases. This further increases both the volume of the melt and its pressure on the surrounding rocks. As a result, very dense, gas-rich magma tends to where the pressure is less. It fills cracks in the earth's crust, breaks and lifts the layers of its constituent rocks. Part of the magma, not reaching the earth's surface, solidifies in the thickness of the earth's crust, forming magmatic veins and laccoliths. Sometimes magma breaks out to the surface, and it erupts in the form of lava, gases, volcanic ash, rock fragments and hardened lava clots.

Volcanoes. Each volcano has a channel through which lava erupts (Fig. 24). it vent, which always ends with a funnel-shaped extension - crater. The diameter of the craters ranges from several hundred meters to many kilometers. For example, the diameter of the Vesuvius crater is 568 m. Very large craters are called calderas. For example, the caldera of the Uzona volcano in Kamchatka, which is filled by Lake Kronotskoye, reaches 30 km in diameter.

The shape and height of volcanoes depend on the viscosity of the lava. Liquid lava spreads quickly and easily and does not form cone-shaped mountains. An example is the Kilauza volcano in the Hawaiian Islands. The crater of this volcano is a rounded lake with a diameter of about 1 km, filled with bubbling liquid lava. The level of lava, like water in a spring bowl, then falls, then rises, splashing over the edge of the crater.

Rice. 24. Sectional volcanic cone

Volcanoes with viscous lava are more widespread, which, when cooled, form a volcanic cone. The cone always has a layered structure, which indicates that the outpourings occurred repeatedly, and the volcano grew gradually, from eruption to eruption.

The height of volcanic cones varies from several tens of meters to several kilometers. For example, the Aconcagua volcano in the Andes has a height of 6960 m.

There are about 1500 active and extinct mountain volcanoes. Among them are such giants as Elbrus in the Caucasus, Klyuchevskaya Sopka in Kamchatka, Fujiyama in Japan, Kilimanjaro in Africa and many others.

Most of the active volcanoes are located around the Pacific Ocean, forming the Pacific "Ring of Fire", and in the Mediterranean-Indonesian belt. There are 28 active volcanoes known in Kamchatka alone, and there are more than 600 of them in total. Active volcanoes are naturally widespread - all of them are confined to mobile zones of the earth's crust (Fig. 25).

Rice. 25. Zones of volcanism and earthquakes

In the geological past of the Earth, volcanism was more active than it is now. In addition to the usual (central) eruptions, fissure eruptions occurred. From giant cracks (faults) in the earth's crust, stretching for tens and hundreds of kilometers, lava erupted on earth's surface. Solid or patchy lava covers were created, leveling the terrain. The thickness of the lava reached 1.5-2 km. This is how lava plains. Examples of such plains are individual sections of the Central Siberian Plateau, the central part of the Deccan Plateau in India, the Armenian Highlands, and the Columbia Plateau.

Earthquakes. The causes of earthquakes are different: volcanic eruption, landslides in the mountains. But the strongest of them arise as a result of movements of the earth's crust. Such earthquakes are called tectonic. They usually originate at great depths, at the boundary between the mantle and the lithosphere. The origin of an earthquake is called hypocenter or hearth. On the Earth's surface, above the hypocenter, is epicenter earthquakes (Fig. 26). Here, the strength of the earthquake is greatest, and with distance from the epicenter, it weakens.

Rice. 26. Hypocenter and epicenter of an earthquake

The earth's crust is constantly shaking. Over 10,000 earthquakes are observed during the year, but most of them are so weak that they are not felt by humans and are recorded only by instruments.

The strength of earthquakes is measured in points - from 1 to 12. Powerful 12-point earthquakes are rare and are catastrophic. During such earthquakes, deformations occur in the earth's crust, cracks, shifts, faults, landslides in the mountains and dips in the plains are formed. If they occur in densely populated areas, then there is great destruction and numerous human casualties. The largest earthquakes in history are the Messinian (1908), Tokyo (1923), Tashkent (1966), Chilean (1976) and Spitak (1988). In each of these earthquakes, dozens, hundreds and thousands of people died, and cities were destroyed almost to the ground.

10 most catastrophic volcanic eruptions

Volcano Unzen (Unzen), 1792

The largest eruption of the Unzen volcano occurred in 1792. From the volcanic eruption, earthquake and, as a result, the occurrence of a tsunami, 15,000 people died.

200 years after this eruption, the volcano was calm.

In 1991, the volcano became active again, in the same year there was an eruption with the release of lava, while 43 people died, including a group of scientists and journalists. The Japanese authorities were forced to evacuate thousands of residents. The volcano was active, ejecting lava and ash until about 1995. Since 1995, the activity has decreased and at the moment it is in a static state.

El Chichon Volcano, Mexico, 1982

The eruption of the El Chichon volcano in 1982, led to the death of 2,000 residents of nearby areas in the state of Chiapas, Mexico. After the eruption, a lake filled with chamois formed in the crater of the volcano.

A feature of the eruption of this volcano was that a large number of aerosols, about 20 million tons in this aerosol was the content of sulfuric acid.

The cloud hit the stratosphere and enlarged it average temperature at 4 C, the destruction of the ozone layer was also observed.

Mount Pinatubo, Philippines, 1991

The 1991 eruption of Mount Pinatubo in the Philippines was the second largest eruption of the 20th century. The volcanic rating index was 6.

This is more than the eruption of St. Helens in 1980, but less than Tambora in 1815. Pinatubo, on June 15, 1991, ejected about two and a half cubic kilometers of matter, including lava, ash and toxic gases. In total, about 10 square kilometers of matter was ejected during the eruption. About 800 people died as a result of the eruption.

Volcano St. Helens, USA, 1980

On May 18, 1980, Mount St. Helens erupted in the United States. The volcanic eruption killed 57 people (according to other sources, 62 people).

The release of gases into the atmosphere reached a height of 24 kilometers, before the eruption there was an earthquake of magnitude 5.1 points, which caused a huge landslide.

The eruption lasted 9 hours. The released energy can be compared to the energy of an explosion of 500 atomic bombs dropped on Hiroshima.

Volcano Nevada del Ruiz, Colombia, 1985

The eruption of the Nevada del Ruiz volcano in 1985 killed 20,000 people in the nearby village of Armero. It is the second most fatal volcano in the 20th century.

The volcanic eruption melted the glacier on it, and the mudflow mass completely destroyed Armero.

But the tragedy happened first in the village of Chinchina - the authorities did not have time to completely evacuate the inhabitants and 2,000 people died. The total death toll is estimated at 23,000 to 25,000.

Kilauea Volcano, USA, 1983 (present)

The Kilauea volcano may not be the most destructive, but its peculiarity is that it erupts continuously for over 20 years, making it one of the most active volcanoes in the world. According to the diameter of the crater (4.5 km), the volcano is considered the largest in the world.

Vesuvius exploded in 79, he buried the entire city of Pompeii under a veil of ash and pumice, which fell from the sky during the day. Ash layer reached 3 meters. According to modern estimates, 25,000 people became victims of the volcano. Excavations were carried out on the site of the city of Pompeii, such a number of victims was caused by the fact that people began to leave their homes not immediately, but tried to pack and save their property.

After 79 years, the volcano erupted dozens of times, last time in 1944.

The Pele volcano exploded on the Caribbean island of Martinique in 1902, killing 29,000 people and destroying the entire city of Saint-Pierre. For several days, the volcano spewed gases and a small part of the ash, the inhabitants saw it, and on May 8, Pele exploded.

Witnesses on ships just off the coast described the sudden appearance of a massive mushroom-shaped cloud filled with fiery hot ash and volcanic gases that covered the island in seconds.

Only two people survived the explosion of the volcano.

Volcano Krakatoa, Indonesia, 1883

The explosion of Krakatoa in 1883 can be compared to the power of 13,000 atomic bombs.

Over 36,000 people died. The height of the ejected ash reached 30 km. After the eruption, the island seemed to have formed, that is, the island itself fell into the void under the volcano, all this was covered with masses of ocean waters. Since the surface temperature was high and the sinking of the land was fast, this led to the emergence (formation) of a tsunami wave that moved towards the island of Sumatra, which led to the death of more than 2,000 people on it.

At the moment, a new active volcano has formed on the site of the old volcano, which is growing in height by 6-7 meters per year.

Volcano Tambora, Indonesia, 1815

The Tambora volcano eruption was the largest volcanic eruption ever recorded on the planet.

10,000 people died instantly under lava flows and from poisoning by toxic gases.

The total number of deaths from the volcano and the tsunami is about 92,000 people, not counting those who died from the famine that followed.

The scale of the eruption is evidenced by the fact that the amount of substance released into the earth's atmosphere was so large that there was no summer in the northern hemisphere in 1816.

The thing is that particles of matter reflected the Sun's rays and interfered with the warming of the Earth.

The consequence of the eruption was famine around the world.

The power of the eruption was 7 points on the scale of volcanic eruptions.

Earthquakes. Volcanoes

Earthquakes and faults

The strength of the earthquake

Types of seismic waves

Volcanic Products

Magma inside the Earth

Lava at plate boundaries

Volcanic activity

volcanic cone

An earthquake is a shaking or shaking of the earth. What causes an earthquake? Earthquakes can cause powerful explosions, the movement of magma inside the volcano. However, most earthquakes occur as a result of the movement of rocks in the fault zone.

Earthquakes and faults

Imagine what happens if you bend a plastic ruler. If you bend it too hard, the ruler will crack. After that, both halves will straighten again. Rocks in the earth's crust also bend under pressure, break and straighten again. A fault is a gap in the rocks along which the movement of rocks has occurred.

When a rupture occurs, energy is released in the form of seismic waves. This energy makes the earth shake; we feel the earthquake.

With the installation of highly sensitive seismographs in many parts of the world, it is now relatively easy to record seismic disturbances, even if they are not felt by humans. Once seismic waves have been detected and recorded by various seismological stations, it is possible to determine where they originated. There are several organizations that are involved in determining the parameters of earthquakes and seismic activity around the world. Based on this information, the seismic characteristics of zones with high and low seismic activity can be determined.

The diagram shown here shows the distribution of seismic shocks on a global scale.

Global distribution of earthquakes

Based on this scheme, it can be concluded that earthquakes are distributed very unevenly over the earth's surface. Clear boundaries of seismic zones are distinguished. In the mid-oceans, seismic events are concentrated along very narrow bands that coincide with the location of mid-ocean ridges. Away from these zones, most of the ocean floor is aseismic.

The most important of the mid-ocean ridges are the Mid-Atlantic Ridge, the Central Indian Ridge, which bifurcates in the south, and the East Pacific Rise. The East Pacific Rise begins in the Gulf of California and splits into two parts near Easter Island (Chile); one part goes to the southwest, and one to the Taitao Peninsula and mainland Chile. As a rule, seismic activity in these zones is weak.

Similarly, seismic activity is concentrated in structures called island arcs. The most significant island arcs are located in chains along the periphery of the Pacific Ocean. The main island arcs: the islands of the Aleutian arc, the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands. Solomon Islands, New Hebrides, Fiji Islands, Philippines - Sunda-Adaman Islands. In the Atlantic Ocean we see the Lesser Antilles and the South Sandwich Islands. Similar seismic chains are found along the coasts of Central and South America. The most deep-focus and strongest earthquakes in magnitude are recorded in these zones. The wider seismic belt along southern Europe, the Himalayas and Southeast Asia is a more complex zone where earthquakes do not occur as often.

Zones of low seismicity (even zero seismicity) are represented by continental shields, such as the Canadian Shield in the eastern part North America, Brazilian shield in South America, as well as eastern Australia, Central Europe, South Africa and the oceanic bed away from the mid-ocean ridges.

The point inside the Earth where the rupture or relative movement of rocks occurs is called the focus (or hypocenter) of an earthquake. The sources of most earthquakes are located in the thickness of the Earth, where the plates rub against each other; the place on the earth's surface directly above the hypocenter is called the epicenter of an earthquake. If the focus is on the surface of the Earth, then the hypocenter and epicenter coincide.

Section along South America

If the source is located at a depth of 0 to 60 kilometers, the earthquake is considered shallow. If the source is located at a depth of 60 to 300 kilometers, the earthquake has an average source depth. If the source is at a depth of 300 to 700 kilometers, then this is a deep-focus earthquake.

The strength of the earthquake

Two scales are used to measure the strength of an earthquake, one to measure the intensity and the other to measure the magnitude.

The intensity of an earthquake is the degree of shaking of the ground on the Earth's surface, felt at various points in the area affected by an earthquake. The magnitude of the intensity is determined on the basis of an assessment of the actual destruction, the impact on objects, buildings and soil, and the consequences for people. The intensity value is determined in accordance with the developed intensity scale, which can be different in different countries. The intensity is often associated with the magnitude of the ground motion velocity during the passage of a seismic wave.

Most countries in the Americas use the Modified Mercalli Earthquake Intensity Scale, which has 12 intensity levels (points). The following figures show different degrees of intensity (points).

The magnitude of an earthquake is a quantity proportional to the energy released at the source of an earthquake. It is determined using an instrument called a seismograph. Instrument readings (amplitude and period of seismic waves) indicate the amount of elastic deformation energy released during an earthquake. The larger the wave amplitude, the stronger the earthquake. The magnitude scale was developed by American seismologist Charles Richter in 1935. It uses Arabic numerals. The Richter scale is logarithmic and open, i.e. there are no upper or lower limits for the Richter magnitudes. Each increase in magnitude by one whole number corresponds to a 30-fold increase in the amount of energy released.

Seismic waves and their measurement

Sliding of rocks along the fault is initially prevented by friction. As a consequence, the energy that causes movement accumulates in the form of elastic stresses in the rocks. When the stress reaches a critical point exceeding the force of friction, a sharp rupture of the rocks occurs with their mutual displacement; the accumulated energy, being released, causes wave vibrations of the earth's surface - earthquakes. Earthquakes can also occur when rocks are crushed into folds, when the magnitude of the elastic stress exceeds the ultimate strength of the rocks, and they split, forming a fault.

Seismic waves generated by earthquakes propagate in all directions from the source like sound waves. The point at which rock movement begins is called focus , hearth or hypocenter, and a point on the earth's surface above the focus - epicenter earthquakes. Shock waves propagate in all directions from the source, as they move away from it, their intensity decreases.

Seismic wave velocities can reach 8 km/s.

Types of seismic waves

Seismic waves are divided into compression waves and shear waves .

Compression waves, or longitudinal seismic waves, cause the rock particles through which they pass to vibrate along the direction of wave propagation, causing alternating compression and rarefaction in the rocks. Speed ​​of propagation of compression waves by 1.7 times more speed shear waves, so seismic stations are the first to record them. Compression waves are also called primary(P-waves). The speed of the P-wave is equal to the speed of sound in the corresponding rock. At frequencies of P-waves greater than 15 Hz, these waves can be perceived by ear as an underground rumble and rumble.

Shear waves, or transverse seismic waves, cause rock particles to oscillate perpendicular to the direction of wave propagation. Shear waves are also called secondary(S-waves).

There is a third type of elastic waves - long or superficial waves (L-waves). They are the ones that cause the most damage.

Measurement of the strength and impact of earthquakes

The magnitude scale and the intensity scale are used to evaluate and compare earthquakes.

Magnitude scale

The magnitude scale distinguishes earthquakes by magnitude, which is a relative energy characteristic of an earthquake. There are several magnitudes and, accordingly, magnitude scales: local magnitude (ML); magnitude determined from surface waves (Ms); magnitude determined from body waves (mb); moment magnitude (Mw).

The most popular scale for assessing earthquake energy is the local Richter magnitude scale. On this scale, an increase in magnitude by one corresponds to a 32-fold increase in the released seismic energy. An earthquake with a magnitude of 2 is barely perceptible, while a magnitude of 7 corresponds to the lower limit of destructive earthquakes covering large areas. The intensity of earthquakes (cannot be estimated by magnitude) is estimated by the damage they cause in populated areas.

Intensity scales

Intensity is a qualitative characteristic of an earthquake and indicates the nature and scale of the impact of earthquakes on the earth's surface, on people, animals, as well as on natural and artificial structures in the earthquake area. Several intensity scales are used in the world: in the USA - the Modified Mercalli scale (MM), in Europe - the European macroseismic scale (EMS), in Japan - the Shindo scale.

Medvedev-Sponheuer-Karnik scale (MSK-64)

The 12-point Medvedev-Sponheuer-Karnik scale was developed in 1964 and became widespread in Europe and the USSR. Since 1996, the more modern European Macroseismic Scale (EMS) has been used in the countries of the European Union. MSK-64 is the basis of SNiP II-7-81 "Construction in seismic areas" and continues to be used in Russia and the CIS countries. Kazakhstan currently uses SNiP RK 2.03-30-2006 "Construction in seismic regions".

Volcanoes - geological formations on the surface of the earth's crust or the crust of another planet, where magma comes to the surface, forming lava, volcanic gases, rocks (volcanic bombs) and pyroclastic flows.

The word "Vulcan" comes from the name of the ancient Roman god of fire, Vulcan.

The science that studies volcanoes is volcanology, geomorphology.

Volcanoes are classified according to their shape (shield, stratovolcanoes, cinder cones, domes), activity (active, dormant, extinct), location (terrestrial, underwater, subglacial), etc.

Volcanic Products

MAGMA AND LAVA.

As in the case of an earthquake, a volcanic eruption means that some events are taking place in the bowels of the Earth. Study the following questions while you read this section:

What forms when magma is trapped underground?

Where does lava come to the surface of the earth?

What are the consequences of lava emplacement at plate boundaries?

How can volcanoes be classified according to their activity?

How do the shapes of volcanic cones differ?

Magma inside the Earth

Rocks that form as a result of cooling and solidification of magma underground are called intrusive rocks. You can't see intrusive rock unless some kind of geological process brings hidden intrusive rock to the surface. For example, water can wash away the top rock and expose the underlying one. The diagram below shows five intrusive structures at once, so you can see the shapes and relative sizes of each.

The batholith shown in the diagram is so large that it is often not known where its base is located.

Distribution of intrusive and effusive rocks

In fact, the core of many mountain formations are batholiths. The stock is similar to the batholith, but much smaller in size. When magma makes its way between rocks, it forms stratal structures (sills). Mushroom-shaped laccolith forms when magma pushes against overlying rock layers. When magma breaks through existing strata at an angle, dikes form.

Lava on the Earth's surface

When magma erupts on the surface of the earth, it is called lava. Lava reaches the surface through the vents of volcanoes or through cracks in the ground. These gaps are called cracks. Effusive rocks are hardened lava on the earth's surface.

Lava from large cracks can flood large areas spreading sometimes for many kilometers.

Lava at plate boundaries

Most extrusive or effusive rocks form where you can't see them - on the ocean floor. These rocks are new crust, born in the zone of mid-ocean ridges. Huge amounts of lava erupt through fissures or volcanic vents in the rupture boundary zone. Sometimes volcanoes at the bottom of the oceans increase and rise above the surface of the water in the form of islands.

Many volcanoes arise in the thrust boundary zone. The diagram below shows one oceanic plate sliding under another oceanic plate. The descending crust melts in the asthenosphere. The resulting magma rises. This magma forms volcanoes on islands called island arcs. Examples of island arcs are the Japanese and Kuril Islands.

Thrust boundary

Volcanoes can also form on land where an oceanic plate subsides under a continental plate. This type of boundary caused the formation of the Cascade Mountains in the states of Washington and Oregon in the United States of America, and the Andes mountain range in South America.

Volcanic activity

Volcanoes are distinguished by appearance and the nature of the activity. Some volcanoes explode, spewing ash and stones, as well as water vapor and various gases. This type of eruption corresponded to the eruption of Mount St. Helens in the United States of America in 1980. Other volcanoes can safely pour out lava.

Why do some volcanoes explode? Imagine that you are shaking a bottle of warm soda water. The bottle can burst, releasing water and carbon dioxide, which is dissolved in water. Gases and water vapor that are under pressure inside a volcano can also explode. The most powerful volcanic explosion ever recorded in human history was the eruption of Krakatau, a volcanic island in the strait between Java and Sumatra. In 1883, the explosion was so powerful that it was heard at a distance of 3200 kilometers from the explosion site. Most of the island has disappeared from the face of the Earth. Volcanic dust enveloped the entire Earth and was in the air for another two years after the explosion. The resulting giant sea ​​wave claimed the lives of more than 36,000 people on nearby islands.

Very often, before the eruption, volcanoes, as it were, give a warning. This warning may be in the form of gases and vapors escaping from the volcano. Local earthquakes may indicate that magma is rising inside the volcano. The ground around the volcano, or on the volcano itself, swells, and the rocks tilt at a large angle.

If a volcanic eruption occurred in the recent past, such a volcano is considered active or active. A dormant volcano is one that erupted in the past but has not been active for many years. An extinct volcano is one whose eruption is not expected. Most volcanoes in the Hawaiian Islands are considered extinct.

volcanic cone

A mountain formed by a series of volcanic eruptions is called a volcanic cone. It consists of lava, volcanic ash and rocks. Typically, the cone has an internal central channel and a vent. Volcanic matter rises up through the vent. Usually at the very top of the cone there is a crater, a cup-like depression. The shape of a volcano depends on the nature of the eruption and the type of volcanic material erupting from the cone.

Types of volcanic domes

The cinder cone or ash cone pictured above is formed when an eruption ejects mostly rocks and ash but little lava. In Mexico, the Paricutin volcano with its characteristic cinder cone is very famous. In 1943, this volcano appeared in a cornfield. After 6 days, he reached a height of 150 meters! Then it grew to 400 meters in height and went out. Eruptions of a non-explosive type with easily flowing lava form shield cones, shown in the diagram above. The volcanic islands of Hawaii, with their gently dipping slopes, are typical shield volcanoes. Alternating eruptions of dust, ash, and rock, followed by a quiet outpouring of lava, create mixed-type cones, as shown above.

Volcanic domes are formed when lava erupts rapidly, but is so viscous that it hardly spreads. Therefore, the terms extrusive cone or swelling cone are sometimes used for this type of volcano. As can be seen in the diagram, such volcanoes have gentle slopes and domed peaks. Mont Pelee is a domed volcano on the Caribbean island of Martinique. Its strong eruption occurred without any warning in 1902. A fiery cloud of gas and ash rolled down the slope, as a result, almost all the inhabitants of the town below were killed. The consequences of eruptions can be very significant. Huge amounts of volcanic dust in the air cause beautiful sunrises and sunsets. If the density is high enough, volcanic dust can change the weather. Increased cloudiness due to dust can cause rain and even cooling. The fertile soils of the Hawaiian Islands were formed from volcanic ash and rocks. Scientists think that the gases in the air and the water of the oceans were formed as a result of volcanic eruptions in past epochs.

Dangerous and safe regions of Russia

20% of the territory of Russia belongs to seismically active regions (including 5% of the territory is subject to extremely dangerous 8-10 magnitude earthquakes).

Over the past quarter century, about 30 significant earthquakes have occurred in Russia, that is, with a force of more than seven points on the Richter scale. 20 million people live in the zones of possible destructive earthquakes in Russia.

Residents of the Far East region of Russia suffer the most from earthquakes and tsunamis. The Pacific coast of Russia is located in one of the "hottest" zones of the "Ring of Fire". Here, in the transition area from the Asian continent to the Pacific Ocean and the junction of the Kuril-Kamchatka and Aleutian island volcanic arcs, more than a third of the earthquakes in Russia occur, there are 30 active volcanoes, including such giants as Klyuchevskaya Sopka and Shiveluch. Here is the highest density of distribution of active volcanoes on Earth: for every 20 km of the coast - one volcano. Earthquakes here occur no less frequently than in Japan or Chile. Seismologists usually count at least 300 perceptible earthquakes per year. On the seismic zoning map of Russia, the regions of Kamchatka, Sakhalin and the Kuril Islands belong to the so-called eight- and nine-point zone. This means that in these areas the intensity of shaking can reach 8 or even 9 points. Destruction may also be relevant. The most destructive earthquake measuring 9 on the Richter scale occurred on Sakhalin Island on May 27, 1995. About 3 thousand people died, the city of Neftegorsk, located 30 kilometers from the epicenter of the earthquake, was almost completely destroyed.

The seismically active regions of Russia also include Eastern Siberia, where in the Baikal region, Irkutsk region and the Buryat Republic allocate 7-9-point zones.

Yakutia, through which the border of the Euro-Asian and North American plates passes, is not only considered a seismically active region, but also holds a record: earthquakes often occur here with epicenters north of 70 ° N. sh. As seismologists know, the main part of earthquakes on Earth occurs in the equatorial region and in middle latitudes, and in high latitudes such events are recorded extremely rarely. For example, on the Kola Peninsula, a wide variety of traces of earthquakes of great power were found - mostly quite old ones. The forms of the seismogenic relief discovered on the Kola Peninsula are similar to those observed in the zones of earthquakes with an intensity of 9-10 points.

Among other seismically active regions of Russia are the Caucasus, the spurs of the Carpathians, the coasts of the Black and Caspian Seas. These areas are characterized by earthquakes with a magnitude of 4-5. However, during the historical period, catastrophic earthquakes with a magnitude of more than 8.0 were also noted here. Tsunami traces were also found on the Black Sea coast.

However, earthquakes can also occur in areas that cannot be called seismically active. On September 21, 2004, two series of 4-5 earthquakes were recorded in Kaliningrad. The epicenter of the earthquake was located 40 kilometers southeast of Kaliningrad near the Russian-Polish border. According to the maps of the general seismic zoning of the territory of Russia, the Kaliningrad region belongs to a seismically safe region. Here, the probability of exceeding the intensity of such shaking is about 1% for 50 years.

Even residents of Moscow, St. Petersburg and other cities located on the Russian platform have reason to worry. On the territory of Moscow and the Moscow region, the last of these seismic events with a magnitude of 3-4 points took place on March 4, 1977, on the night of August 30-31, 1986 and May 5, 1990. The strongest known seismic tremors in Moscow, with an intensity of over 4 points, were observed on October 4, 1802 and November 10, 1940. These were "echoes" of larger earthquakes in the Eastern Carpathians.

Question 1. Does the earth's crust move?

The earth's crust and the uppermost solid layer of the mantle located under it consists of separate parts - plates. The plates move very slowly over the softened, plastic layer of the mantle. As a result, the continents move on the surface of the Earth.

Question 2. What do you know about earthquakes and volcanoes? Are these phenomena dangerous for humans?

Earthquakes - tremors and vibrations of the Earth's surface, caused mainly by tectonic processes, or artificial processes (explosions, filling of reservoirs, collapse of underground cavities of mine workings). Small shocks can also be caused by the rise of lava during volcanic eruptions.

Volcanoes - geological formations on the surface of the crust of the Earth or another planet, where magma comes to the surface, forming lava, volcanic gases, stones.

Earthquakes and volcanoes are dangerous for humans, as they destroy buildings, roads, other infrastructure, people die because of them.

Question 3. Why do earthquakes occur?

Earthquakes usually occur near plate boundaries. Plates move both horizontally and vertically. When the edges of the adjacent plates "get stuck", the plates move, tremors occur. Areas where earthquakes are especially frequent are called seismically active.

Question 4. What is called the focus and epicenter of an earthquake?

The place where the rupture and displacement of rocks occurs is called the focus of an earthquake. It is usually found at a depth of several kilometers. Above the source on the earth's surface is the place of the greatest manifestation of the earthquake. It is called the epicenter.

Question 5. What is the structure of a volcano?

The volcano is a mountain, in the upper part of which there is a recess - a crater, to which the vent approaches. Under the volcano is a special chamber - a magma chamber. Magma is the molten substance of the mantle.

Question 6. What causes a volcanic eruption?

Volcanoes form in areas of the Earth where deep cracks in the earth's crust create pathways for magma to rise to the surface. This usually happens near plate boundaries. The areas of the greatest distribution of volcanoes coincide with seismically active areas.

Question 7. How does a volcano erupt?

Trying to free itself from the colossal pressure that exists at depth, magma rushes up the vent and pours out onto the earth's surface. Magma erupting to the surface is called lava. If the lava is thick, viscous, then it cools down quickly enough, forming high mountain with steep slopes, having the shape of a cone. More liquid lava spreads faster, cools more slowly, so it has time to flow down considerable distances. The slopes of such a volcano are gentle. Sometimes very viscous lava can solidify in a channel, forming a plug. However, after some time, pressure from below pushes it out, a strong eruption occurs with the release of stone blocks into the air - volcanic bombs. During an eruption, not only lava comes to the surface, but also various gases, water vapor, volcanic dust, clouds of ash.

Question 8. What are the main areas of distribution of volcanoes.

The main areas of distribution of volcanoes are the Pacific coast, the islands of the Pacific Ocean, the Mediterranean coast, the islands of Oceania.

Question 9. Which continent has no volcanoes?

There are no volcanoes in Australia.

Question 10. Where are active volcanoes located in Russia?

In our country, there are many active volcanoes in Kamchatka and the Kuril Islands.

Question 11. Why are earthquakes especially dangerous in mountains and cities?

Because in the mountains, earthquakes can cause landslides, collapses and avalanches. In cities - the destruction of buildings, which can lead to numerous victims.

Question 12. Examine the data in Table 2. When and where did the largest earthquakes and volcanic eruptions occur in terms of the number of victims?

Earthquakes - in China in 1556 and 1976. Volcanoes - in Indonesia in 1815 and in Japan in 1793.