Major earthquakes and volcanoes. Some causes of earthquakes. An earthquake is a subterranean vibration or tremor that results from the displacement of the earth's crust or the upper part of the mantle. Elastic earthquake oscillations can be transmitted to very

What is an earthquake?

• Earthquake These are subterranean vibrations or tremors that result from the displacement of the earth's crust or the upper part of the mantle. Elastic earthquake oscillations can be transmitted over very long distances, sometimes reaching hundreds of kilometers.

• Earthquakes can hardly be felt by a person, they can destroy cities, can cause other natural disasters such as tsunamis. The intensity of the earthquake is estimated in seismic scores. Energetically, earthquakes are classified according to the Richter scale. Scientists involved in the study of earthquakes are called seismologists.

• Strong earthquakes are catastrophic, yielding only typhoons by number of victims and significantly (in dozens of times) ahead of volcanic eruptions. The material damage of one destructive earthquake can amount to hundreds of millions of dollars. The number of weak earthquakes is much greater than the number of strong ones.

• Pakistan, China, 2008  - there was a powerful earthquake of magnitude 7.9, which claimed the lives of up to 87 thousand people, 370 thousand were injured, five million people were left homeless.

The strongest earthquakes of the 21st century

• Indonesia, 2009 -there was a devastating earthquake of magnitude 5.8, with 300 victims, 1,500 injured.

The strongest earthquakes of the 21st century

• Haiti, 2010 wastwo powerful earthquakes of 7 and 5.9. More than 120 thousand people died.

The strongest earthquakes of the 21st century

• An earthquake of magnitude 9.0 occurred in Japan on March 11, it caused a tsunami with a height of more than ten meters.

• The great earthquake of East Japan, as it is called the largest natural disaster in the history of the country, has become the fourth strongest earthquake in the world.

Where and why earthquakes occur

Earthquakes most often occur along geological faults - narrow zones where large masses of rocks of the earth's crust move relative to each other. The lines of the main faults of the Earth are located along the edges of huge tectonic plates that make up the earth's crust, the largest earthquakes on Earth occur mainly in belts that coincide with the boundaries of tectonic plates.

You must have an emergency team. This can be a small but important set of some of the simplest elements, such as water and non-perishable foods. You need to add batteries and radios. You can also have torches or flashlights only in case of a power outage and have a first aid kit in case someone is hurt.

All these materials should be stored in an easily accessible place, for example, on your car, just in case, if it needs to be evacuated or ordered. If possible, try adding masks or glasses to see through the ash clouds. A natural disaster, such as an erupting volcano, can occur at any time, which means that you or your family can not be at home when this happens. That's why you need to think carefully about all possible events and have a good plan for the family to meet again.

• The most important belt of seismic activity is the Pacific belt, which affects many densely populated coastal regions around the Pacific Ocean, such as New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska and the west coast of the Americas.

• Earthquakes also often occur in volcanic areas and are caused there by both tectonic faults and the movement of magma in volcanoes. Such earthquakes can be an early warning of volcanic eruptions.

• And now let's talk about volcanoes.

What is a volcano?

A volcano is a naturally formed hole in the earth's crust through which a molten rock, called lava, as well as gases, vapors and ashes break out, often in the form of large and noisy eruptions or explosions. Usually the volcano is a cone-shaped mountain (whose walls consist of frozen lava and ash) with a hole in the center, or a crater-through which eruptions occur.

These are simple plans, but if you live in an area near an active volcano, they can save your life and the life of your family. You may not realize or understand that the active volcano is about to break out, you need to know what can happen, and how the volcano works, even if it is a natural disaster that can not be domesticated or predicted.

When a rash occurs, lava can spread and cause massive devastation. Even if the lava does not move quickly to a local city or city, there are still many dangers that can be harmful. Ashen clouds can be very dangerous for humans, since they can be toxic gases and debris and flying stones. It may seem that the volcano is not so dangerous, if it does not work for many years, but it is still dangerous.

Many eruptions do not cause significant damage to the environment. But there are eruptions that are very powerful and devastating. During such eruptions, lava can pour out and drain down from the volcano, flooding the adjacent territories; down can suffocate strangling clouds of steam, ash, hot gases and rocks that descend at high speed to the ground, covering it for many kilometers around.

According to official sources, it is considered the most devastating earthquake in the country in the last three decades, at least, and more than 1000 wounded. Although work continues to save and search for victims, the material and human damage caused by the earthquake has also been recorded by an unmanned aerial vehicle, as it was assembled a few hours ago.

The earthquake in Ecuador with a magnitude of 7, 8 was the most devastating earthquake in the last thirty years. The location of the hypocentre in front of Pedernales, only twenty kilometers, explains the terrible material consequences and deaths of people after the earthquake in Ecuador.

Types of volcanoes.

• Theoretically, there are three types of volcanoes. But one of the types - area volcanoes today does not exist, as they met only in the early stages of the development of the earth. (Fig. 1)

• Fissured volcanoes. The outflow of lava occurs over large cracks and splits. (Fig. 2)

• The central type. It is considered the most common type. This type is characterized by the fact that it is accompanied by the formation of so-called cone-shaped volcanic mountains. (Fig. 4)

The strongest volcanic eruptions.

• Here is a brief overview of some of the most grandiose eruptions of our planet

Eruption to Santorini.

• Around 1650 BC, on the island of Santorini, one of the most violent eruptions of volcanoes in human history occurred. Literally exploding, the Santorini volcano changed beyond recognition beyond recognition all the Mediterranean Sea, and the sound wave from the explosion several times rounded the entire planet.

Eruption of Vesuvius.

In the year 79 BC. Vesuvius released a huge cloud of ash into the atmosphere that covered the sky, and then suddenly collapsed down by pyroclastic streams, reaching speeds of more than 100 km / h. A few hours after that, the volcano began a massive eruption, accompanied by the ejections of a huge amount of red-hot gas, lava and volcanic bombs, completely destroying two prosperous cities and all the inhabitants who were in them, and buried their remains under a multi-meter layer of stones and ash. The eruption of Vesuvius lasted only a few hours ...

Learning to live with earthquakes

"We must learn to co-exist with earthquakes," explains Hipertextual Dr. Maria Jose Jurado Rodriguez, a researcher at the Earth Sciences Institute of Jaume Almera. The expert states that after the terrible earthquake in Ecuador, we should "know them better by exploring and ready to avoid their consequences for construction."

These are buildings that are destroyed due to earthquakes that cause victims. It is necessary to improve and strengthen these buildings. "The truth is that earthquakes do not lead to casualties in general, there are as many landslides in mountains with unstable slopes as it happened in Tibet," the scientist says. "These are the destroyed structures that cause the victims," ​​he clarifies. This is what happened in the earthquake that affected Ecuador, where the tremor of the earth ended with buildings, bridges or crossings to roads in two.

The eruption of Krakatoa.

The Krakatoa volcano island is located in Indonesia, in the Strait of Zand, near the island of Java. Before the eruption in 1883, on the island in close proximity to each other were three volcanoes: Danan, Perbuvatan and Rakata. After the succession of April earthquakes that shuddered the islands of Sumatra and Java, in May 1883, suddenly all three craters on the island began to erupt. After the beginning of lava emissions, cracks formed on the slopes of the island, which allowed sea water to enter the very mouth of volcanoes. This led to an incredible explosion. The eruption of Krakatoa caused consequences for the whole planet. The volcanic gases and ash that escaped into the atmosphere rose into the atmosphere and were there for about 3 years. As a result, the intake of ultraviolet radiation has significantly decreased and the temperatures for several years have significantly decreased.

As a consequence of subduction, "tension arises in the terrain that causes it to break down or, what is the same, that failures occur," explains Jurado Rodriguez. This means that the blocks move in the bowels and, as a consequence, the stresses that cause earthquakes are released. In other words, the movements of the subduction of the Nazca plate, descending below the continental plate, occur not only in Ecuador. After giving examples of these boundaries between plates and subduction processes, the geologist recalls places along the Pacific coast of South America.

The eruption of Mont-Pele.

• The eruption of the volcano Mont Pelay, on the island of Martinique, was one of the most disastrous in the twentieth century. It happened in 1902, claimed the lives of 30,000 people.

With a further increase in temperature in the interior of the Earth, the rocks, despite the high pressure, are melted, forming magma. At the same time, a lot of gases are released. This further increases both the volume of the melt and its pressure on the surrounding rocks. As a result, a very dense, magma saturated with gases tends to where the pressure is less. It fills the cracks in the earth's crust, tears and lifts the layers of its constituent rocks. Part of the magma, not reaching the earth's surface, freezes in the thickness of the earth's crust, forming magmatic veins and laccoliths. Sometimes magma breaks to the surface, and it erupts in the form of lava, gases, volcanic ash, debris of rocks and frozen lava clots.

Volcanoes.  Each volcano has a channel through which a lava eruptions (Fig. 24). it muzzle,  which always ends with a funnel-like extension - crater.  The diameter of the craters varies from several hundred meters to many kilometers. For example, the diameter of the crater of Vesuvius is 568 m. Very large craters are called calderas. For example, the caldera of the Uzon volcano on Kamchatka, which is filled by Lake Kronotsky, reaches 30 km across.

The shape and height of volcanoes depend on the viscosity of the lava. Liquid lava flows quickly and easily and does not form a cone-shaped mountain. An example is the Kilauz 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 the spring, then falls, then rises, spilling over the edge of the crater.

Fig. 24.  Volcanic cone in section

More widely spread volcanoes with viscous lava, which, when cooling, forms a volcanic cone. The cone always has a stratified structure, which indicates that outpourings occurred many times, and the volcano grew gradually, from eruption to eruption.

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

Mountain volcanoes, active and extinct, number about 1500. Among them, 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 "fire ring", and in the Mediterranean-Indonesian belt. Only in Kamchatka is known 28 active volcanoes, and there are more than 600 of them. Active volcanoes are regularly distributed - they are all confined to the mobile zones of the earth's crust (Figure 25).

Fig. 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, fissures flowed. From giant cracks (fractures) in the earth's crust, stretching for tens and hundreds of kilometers, the lava erupted on the earth's surface. Continuous or mottled lava coverings were created, leveling the terrain. The thickness of the lava reached 1.5-2 km. So formed lava plains.  Examples of such plains are the individual parts of the Central Siberian plateau, the central part of the plateau Dekan in India, the Armenian plateau, the Columbia plateau.

Earthquakes.  The causes of earthquakes are different: the eruption of volcanoes, 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 are usually formed at great depth, on the boundary of the mantle and the lithosphere. The place of origin of the earthquake is called hypocentre  or hearth.  On the surface of the Earth, above the hypocenter, is located epicenter  earthquake (Figure 26). Here, the strength of the earthquake is greatest, and when it moves away from the epicenter, it weakens.

Fig. 26.  Hypocenter and earthquake epicenter

The earth's crust shakes continuously. Over a year, there are over 10,000 earthquakes, but most of them are so weak that it is not felt by humans and is fixed only by instruments.

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