Report “Earthquake. Catastrophic volcanic eruptions

Some people still think that earthquakes are a rare and unusual phenomenon. This is far from true. Severe, catastrophic earthquakes really do not happen very often - 1-2 times a year; weaker ones - much more often. In total, hundreds of thousands of earthquakes occur on the globe every year! It turns out that our Earth, which appears in folk tales, proverbs and sayings as a symbol of inviolability and stability, is in fact not so immutable. People have been wondering for a long time: what are the causes these menacing natural phenomena - earthquakes?

Possible causes of the earthquake

Attempts to explain the causes of earthquakes were made already in ancient times and were reflected in various peoples in numerous legends and traditions. For a long time the origin of earthquakes was explained by supernatural causes. Thus, among the tribes that inhabited Siberia, there was an idea that earthquakes were caused by giant underground monsters. The legends widespread among the Turkmen told about a monstrous dragon. When he walks on the ground, it shakes and trees burst with a crash. Ancient Russian sources spoke about whales on which the Earth supposedly rests. When whales turn from side to side, echoes of this noise are heard on the earth's surface - an earthquake occurs. Churchmen used earthquakes, along with other menacing natural phenomena, as proof of the power of God, explaining them as “God’s punishment” sent to people for their sins.

Scientific approach

Causes earthquakes are easy to name, if you turn to science to find out the opinion of scientists. An earthquake is vibrations of the earth's crust caused by various reasons. Depending on them There are three types of earthquakes:

• Landslides.

In many places there are rocks that are soluble in water, such as limestone and salt. Groundwater gradually dissolves them, and over time, cracks, voids, and caves form underground. They often reach significant sizes. Eventually, the roof of the cave may not be able to withstand the pressure of the layers located above and collapse. In this case, an underground shock or even a series of tremors occurs - an earthquake. The source of a landslide earthquake can be other phenomena, for example, a landslide in the mountains. Earthquakes of this type have little strength and are felt only in the immediate vicinity of the collapse site.

• Volcanic.

Volcanic eruptions, which are quite formidable natural phenomena in themselves, are very often accompanied by earthquakes. They are often destructive, but their distribution is usually limited to a small area adjacent to the volcano.

• Tectonic.

Most often, earthquakes are not associated with landslides or volcanic eruptions. These are so-called tectonic earthquakes - the most powerful earthquakes, sometimes covering areas of millions of square kilometers. They are caused by movements of vast areas of the earth's crust. And these movements are caused by the fact that the matter in the bowels of the globe is in continuous movement. Where it rises, the earth's crust bends upward; Where matter sinks, the earth's crust also sinks. These movements, completely invisible to the eye, ultimately lead to the rupture of rock layers.

Thus, the causes of earthquakes are: rock falls (and consequent tremors), volcanic eruptions, but main reason Most earthquakes are movements of large areas of the earth's crust.

What is the cause of destruction during an earthquake?

Imagine that you are bending a flexible rod with your hands. At first it bends. The further you go, the stronger the resistance of the rod; Finally, it breaks with a crash. Much the same thing happens with rocks. If one section of the earth's crust rises and the neighboring one falls, then elastic forces gradually accumulate, which ultimately lead to rupture of the layers. However, these breaks and cracks are not always visible on the earth's surface. It happens that they pass at a depth of tens of kilometers from the surface of the earth.

Sometimes rocks move along the formed cracks to a considerable height, which is clearly visible on the surface. In 1906, a catastrophic earthquake destroyed the city of San Francisco. First, a fault in the earth's crust formed. During the earthquake along the fault line, gigantic layers of earth dropped in places up to 7 m. In Assam (India), during a very strong earthquake, a section of the earth's crust dropped by more than 10 m and a so-called fault was formed over tens of miles. Apparently, such movements more often occur where cracks, faults, and shifts previously occurred and where the earth’s crust is already weakened.

Earthquakes are usually observed in areas of young folded mountains, where the movement of matter in the earth's interior is especially active. Areas of oceanic depressions are also prone to earthquakes, what is the cause of destruction during an earthquake.

In the Pacific Ocean, deep-sea depressions stretch along island arcs and continental coasts. There are high young mountains adjacent to these areas of the ocean. Apparently, the further development of these mountains and depressions causes frequent earthquakes on the shores of Pacific Ocean. Often a crack formed as a result of a tectonic earthquake opens up an exit to earth's surface magma. This is how a volcano arises.

Along with areas prone to earthquakes, there are vast areas where they almost never occur. Such aseismic areas are said to include, for example, the East European Plain, where Moscow and St. Petersburg are located, and West Siberian Lowland. They are so-called platforms, stable sections of the earth's crust.

Possible consequences of earthquakes

Earthquakes bring enormous disasters to people, destroying entire areas. Possible consequences of earthquakes are so severe that the affected states have to develop plans for economic recovery, as usually happens after wars:

• walls of houses collapse, cities are destroyed;
• Residents are dying under the rubble of houses;
• An earthquake causes significant changes in the topography of the seabed. The vibrations of the seabed, in turn, set in motion huge masses of water, forming a tsunami;
• Communication is interrupted, electricity supply is cut off, water supply system fails;
• roads, buildings, bridges are destroyed;
• Huge cracks form on the earth's surface;
• tremors can cause landslides and collapses in the mountains;
• earthquakes cause topographical changes in topography: new mountains, rivers, lakes appear, and some that previously existed disappear. New islands are appearing in the sea, while others that were recently on the maps are disappearing under the water.

Protection against the consequences of earthquakes

So, immediate reasons and possible consequences earthquakes known to science. Is it not possible to predict earthquakes and thereby prevent the colossal disasters that befall people from time to time? This question has occupied scientists for a long time. As a result of long-term observations, seismically dangerous areas, that is, prone to strong earthquakes, have been identified: Crimea, Caucasus, Pamir, Tien Shan, Baikal region, Kuril-Kamchatka arc and some others.

It is known exactly how strong earthquakes can occur in a particular seismic area. This makes it possible to draw up special seismic zoning maps, which indicate areas prone to earthquakes and indicate their possible strength. Thus, to make an earthquake forecast, only one factor is missing - the time of the earthquake's onset. In order to learn to predict this, it is necessary to better know the structure of the earth's interior.

But if it is not yet possible to prevent or accurately predict an earthquake, then it is already possible to combat its destructive effects. It has been established that the use of certain materials in construction, such as reinforced concrete, and the use of special building structures can significantly reduce and sometimes even prevent their destruction. Anti-seismic construction is now being carried out in earthquake-prone areas. They don't build there multi-storey buildings. Houses are built on reinforced foundations with lightweight roofs. Brick walls tied with reinforced concrete belts. All these measures significantly increase the reliability of buildings, and they do not fall apart during earthquakes.

This, of course, is not all measures to protect against the consequences of earthquakes: in the future, scientists will be able to accurately predict the onset of earthquakes and thousands of people will be saved from death. This is how science equips people with ever more powerful means to combat natural disasters, relieves them of fear of menacing natural phenomena.

In the form in which we know it now: with oceans, seas, islands, continents, volcanoes played a huge role. What are volcanoes?

Volcano- this is a gap in earth's crust, through which hot, hot water emerges from the bowels of the earth onto its surface. high temperature a substance called lava. Along with the lava the world various gases and vapors. Since the temperature of the lava is very high, upon contact with air it forms ash and smoke. This whole process is accompanied by large, noisy eruptions, even rumbling explosions.

Externally, volcanoes are similar to an ordinary mountain, the difference is that at its top there is a hole from which smoke can come. This hole is called crater. The slopes of these mountains are nothing more than frozen lava and ash. Currently, volcanic eruptions are not so frequent and do not cause significant damage to either nature or people.

Of course, there are also formidable active volcanoes that are very powerful and have destructive power. The eruption of such volcanoes is accompanied by gushing emissions of hot lava, which, flowing from the slopes of the volcano, can flood large areas, burning all living things in its path. Modern science and scientists (seismologists) continuously monitor the life of volcanoes in order to accurately determine the time of their possible activity and warn people about possible danger.

The life of a volcano is accompanied earthquakes. Another reason for the formation of earthquakes can be mountain collapses and, the most powerful, from movements of the earth's layers at great depths. The place where an earthquake occurs is called the focus. Most great strength There will be an earthquake near this center (epicenter), and less as it moves away from it.

The earth shakes constantly. More than 10,000 such phenomena are observed in a year alone, but most of them are weak and not felt at all. The strength of an earthquake is measured using points from 1 to 12..
With powerful and strong earthquakes shifts occur in the earth's crust, cracks form in the surface of the earth, rockfalls begin in the mountains and failures in the plains. If so a natural phenomenon occurs near populated areas, this is accompanied by catastrophic destruction and numerous casualties.

Sometimes the earth's crust begins to move: an earthquake occurs - a formidable natural phenomenon that everyone has probably heard about. Up to a million weak and several thousand strong earthquakes are recorded annually.

Strong earthquakes can cause serious destruction. In a few seconds, the surrounding area can become unrecognizable from destroyed buildings and structures. Earthquakes often kill many people.

Earthquakes typically occur near plate boundaries. As you already know, these plates are in constant motion. The plates move both horizontally and vertically. When the edges of touching plates get stuck, the plates shift and tremors occur. Areas where earthquakes are particularly frequent are called seismically active (from the Greek word “seismos” - earthquake).

The place where rupture and displacement of rocks occurs is called the source of an earthquake. It is usually located at a depth of several kilometers.

Above the source on the earth's surface is the place of greatest manifestation of the earthquake. It is called the epicenter (from the Greek word “epi” - above).

Earthquakes are dangerous due to their suddenness. For a long time, people have sought to learn how to predict these natural phenomena.

A whole network of stations has been organized around the world that constantly monitor the state of the earth's crust. They register everything, even weak earthquakes, capturing those waves that diverge from the site of underground impacts. Unfortunately, it is not yet possible to reliably and accurately predict earthquakes.

Volcanic eruptions are a formidable and dangerous natural phenomenon for people. Volcanoes are figuratively called fire-breathing mountains. The very name of these mountains comes from the name of the ancient Roman god of fire, Vulcan.

A volcano is a mountain, in the upper part of which there is a depression - a crater, to which a crater approaches. Under the volcano there is a special chamber - a source of magma.

Magma is the molten substance of the mantle (from the Greek word “magma” - dough, mash).

Volcanoes form in areas of the Earth where deep cracks in the Earth's crust create pathways for magma to escape to the surface. 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 that flows to the surface is called lava. This usually occurs near plate boundaries. The areas of greatest distribution of volcanoes coincide with seismically active areas.

If the lava is thick and viscous, then it cools quickly enough, forming a high mountain with steep slopes, shaped like a cone. This is a conical volcano. More liquid lava spreads faster and cools more slowly, so it has time to flow over considerable distances. The slopes of such a volcano are gentle. This is a shield volcano.

Sometimes very viscous lava can solidify in the channel, forming a plug. However, after some time, pressure from below pushes it out, and violent eruption 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, and clouds of ash. Dust and ash are carried hundreds and thousands of kilometers. During the enormous eruption of the Krakatoa volcano in Indonesia (1883), particles of volcanic dust and ash formed after the explosion of the volcano flew around the Earth twice.

In the kingdom of restless earth and fire-breathing mountains

Volcanoes that have erupted at least once in human memory are called active. They can erupt continuously or periodically. If no information has been preserved about volcanic eruptions, they are called extinct.

Typically, volcanic eruptions are accompanied by underground noise and sometimes earthquakes. Lava flows cause fires, destroy roads, and flood fields.

Now there are several hundred active volcanoes on land. 20-30 eruptions occur annually.

Our country has many active volcanoes in Kamchatka and the Kuril Islands. The largest of them - Klyuchevskaya Sopka - is located in Kamchatka. Its height is 4688 m. There are many volcanoes at the bottom of the oceans. Underwater eruptions occur there.

1. Name the main areas where volcanoes occur.
2. Which continent has no volcanoes?
3. Where in Russia are located active volcanoes?
4. Why do earthquakes occur?
5. What is the source and epicenter of an earthquake?
6. What is the structure of a volcano?
7. What causes a volcanic eruption?
8. How does a volcano erupt?

An earthquake occurs when two sections of plates suddenly shift. The place in the depths where rupture and displacement of rocks occurs is called the focus of an earthquake. Above it on the earth's surface is the epicenter. Volcanoes are located primarily along plate boundaries. In these places, magma flows to the surface in the form of lava during a volcanic eruption.

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With a further increase in temperature in the bowels of the Earth, rocks, despite high pressure, melt to form 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 go where the pressure is lower. It fills cracks in the earth's crust, breaks and lifts the layers of its constituent rocks. Part of the magma, before reaching the earth's surface, solidifies in the thickness of the earth's crust, forming magma veins and laccoliths. Sometimes magma breaks out to the surface and erupts in the form of lava, gases, volcanic ash, rock fragments and frozen lava clots.

Volcanoes. Each volcano has a channel through which lava erupts (Fig. 24). This vent, which always ends in a funnel-shaped expansion - 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 Uzon 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 a cone-shaped mountain. An example is the Kilauza volcano in the Hawaiian Islands. The crater of this volcano is a round lake with a diameter of about 1 km, filled with bubbling liquid lava. The level of lava, like water in the bowl of a spring, then falls, then rises, splashing out over the edge of the crater.

Rice. 24. Volcanic cone in section

More widespread are volcanoes with viscous lava, which, when cooled, forms a volcanic cone. The cone always has a layered structure, which indicates that eruptions occurred many times, and the volcano grew gradually, from eruption to eruption.

The height of volcanic cones ranges 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 1,500 volcano mountains, active and extinct. Among them are such giants as Elbrus in the Caucasus, Klyuchevskaya Sopka in Kamchatka, Fuji in Japan, Kilimanjaro in Africa and many others.

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

Rice. 25. Zones of volcanism and earthquakes

In the Earth's geological past, 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 onto the earth's surface. Continuous or patchy lava covers were created, leveling the terrain. The thickness of the lava reached 1.5-2 km. This is how they were formed lava plains. Examples of such plains are certain 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 eruptions, mountain collapses. But the most powerful 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 of the mantle and lithosphere. The origin of an earthquake is called hypocenter or hearth. On the surface of the Earth, above the hypocenter, is epicenter earthquakes (Fig. 26). Here the strength of the earthquake is greatest, and as it moves away from the epicenter it weakens.

Rice. 26. Hypocenter and epicenter of earthquake

The earth's crust shakes continuously. Over 10,000 earthquakes are observed during the year, but most of of them is so weak that it is not felt by humans and is 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 failures in the plains form. If they occur in densely populated areas, then great destruction and numerous casualties occur. Major earthquakes in history are Messina (1908), Tokyo (1923), Tashkent (1966), Chilean (1976) and Spitak (1988). In each of these earthquakes, tens, hundreds and thousands of people died, and cities were destroyed almost to the ground.