Tsunami (Japanese for "big harbor wave") are marine gravitational waves that result from the upward or downward displacement of extended sections of the seabed during underwater and coastal earthquakes. The propagation speed is from 50 to 1000 km / h. The height in the area of ​​occurrence is from 0.1 to 5 m, near the coast - from 10 to 50 m and above.

Tsunamis produce devastating destruction on land. For centuries, this unbridled natural phenomenon has kept people in fear, and therefore there are many inconsistencies about these killer waves.

A tsunami is a huge wave. Firstly, this is not one wave, but a whole series of waves coming ashore one after another. Their number ranges from 3 to 25.
Secondly, not every wave is a tsunami. Storm, ship and other waves are the movement of only the upper layer of water, while the tsunami is the movement of its entire thickness.

A tsunami is generated by an underwater earthquake. A seaquake causes a tsunami in most cases, but not always. Typhoons, tropical cyclones, underwater landslides, or volcanic eruptions can also be causes. The largest waves are formed when a cosmic body - a comet or a meteorite - enters the ocean. The consequences of such a catastrophe can only be imagined and are unlikely to survive. At one time, even dinosaurs died from this.

Any seaquake threatens to cause a tsunami. For a tsunami to occur, the displacement of the bottom surface must be lightning fast and large enough to set the water column in motion. In addition, the earthquake source should not be too deep (up to 20 km.). Therefore, not every change in the relief of the ocean floor generates a giant wave.

Tsunamis occur only in warm seas. This myth arose because tsunamis occur most of all in the Pacific Ocean, where seaquakes and eruptions of underwater volcanoes occur, and Japan and the Pacific islands most often suffer from their effects. If we talk about landslide tsunamis that occur due to the collapse of rocks of sea cliffs, then they can happen everywhere! In 1964, as a result of an earthquake and the subsequent collapse of the ice, a tsunami occurred in Alaska. It hit the height of its waves: 60 meters!

Before the start of the tsunami, the water recedes from the shore. Canadian mathematician Walter Craig came to the conclusion that only in half of the cases the water really moves away from the coast, foreshadowing a tsunami. It depends, first of all, on the wavelength, and not on the power of the tsunami, as previously thought.

A tsunami is always a high wave! Revealing the secret of the occurrence of this natural phenomenon, it must be said that in fact the height of the tsunami depends on its energy. And the farther from the epicenter, the higher the wave level. Whereas in the open sea a tsunami does not exceed a meter, but moves at a frantic speed, on the shallows the wave speed decreases and gains height. By the way, there may be no waves at all, and the tsunami will pass like a series of rapid ebb and flow. So a tsunami is not just a wall of water falling on the shore, but the movement of the entire water layer, multiplying its destructive power when it meets land.

The tsunami comes unnoticed, which is why it is so difficult to escape from it. Indeed, the hallmark of a tsunami is its sudden appearance. But still, it makes itself felt, and if you are attentive, you can notice the approach of a catastrophe. If an earthquake causes a giant wave, everyone on the shore feels the tremors, even if they are not strong. With a strong movement of water, small marine organisms glow. If a tsunami occurs in cold seas, ice breaks and undercurrents arise. In addition, water can move away from the shore, draining the bottom or, on the contrary, slowly flow.

The first wave of a tsunami is always the largest. This is not true. Since tsunami waves move one after another, and the distance between them can reach several tens and even hundreds of kilometers, they reach the coast after a certain time (from a couple of minutes to an hour). After the first wave, the shore gets wet, thereby reducing the resistance for subsequent waves. They are always more destructive.

Animals always feel the approach of a tsunami. Indeed, during the huge tsunami on the coast of Sri Lanka in 2004, not a single animal corpse was found. Eyewitnesses claim that even the fish tried to hide from the impending elements, hiding in the corals. But the truth is that not all animals are catastrophe predictors. For some, the threat will become clear, while the other will not react to it in any way. Therefore, it would be wrong to rely on the intuition of our smaller brothers in everything.

From the tsunami saves only a quick escape deep into the coast. Indeed, this is true, but it is important not only to run away from the coastline, but also to fulfill the simplest requirements: firstly, do not move along the riverbed, where the tsunami wave will quickly overtake you. Secondly, going into the mountains, move up the slope, rising to a height of at least 30 meters from the coastline. Thirdly, if you are on a ship, boat or any other vessel, it is pointless to seek salvation on the shore, and it is better to go farther into the sea. And finally, it should be remembered that the tsunami is back. Only after a certain time you can return to the shore.

How and why do tsunamis occur?

Many people have heard the word "tsunami" more than once, but not everyone knows what it really is. From Japanese, it literally translates as "harbor" ("tsu") and "wave" ("nami").

This manifestation of nature makes us once again think about her majesty and freeze in front of her incommensurable power.

Tsunami danger

The danger that a tsunami carries with it has several factors at once. For starters, this is a remarkable force of destruction that moves with water. Compared to this power, a person is just a small straw. Secondly, it is very difficult, almost impossible, to predict the time of occurrence of a tsunami and a specific location. Thirdly, it is impossible to see the water column moving towards the shore either from the air or from a ship. The fact is that the wave that will bring the tsunami ashore is visually no different from any other. Its peculiarity lurks below, in the water itself. It takes with it not only the upper surface of the liquid, but "scoops" it from the very bottom.

In the end, from the place of "birth" of a tsunami wave to its deadly arrival, distances of several thousand kilometers can lie. That is, the wave passes all this distance in the water column, and, as you know, under such circumstances it is not very loyal to all objects that stand in its way. Due to the lack of resistance on the way, it saves and accumulates a colossal supply of energy, which then falls on land and people.

Related materials:

Waves, ebbs and flows

But what generates these deadly waves? Some are mistaken, claiming that the tsunami originates in seismically hazardous areas. This reason is far from the only one. For example, volcanic eruptions at the bottom of the ocean, landslides (they can have starting points below sea level) also lead to the release of a huge amount of energy that has to be thrown somewhere. First, the lower layers of water are displaced, causing very strong vibrations that force the entire water column to budge and move towards the shore, carrying enormous reserves of energy.

Tsunami- an incredibly dangerous phenomenon of nature. Terrifying consequences make you feel unimportant. But, as they say, you need to know your enemy by sight, so let's find out more about this evil joke of nature:

The most at risk from tsunamis are: California, Hawaii, Oregon and Washington. Hawaii is the most at risk and has about 1 tsunami per year and a dangerous tsunami about every 7 years.

On March 28, 1964, an extremely strong earthquake hit Alaska. This caused tsunami waves that were very destructive in southeast Alaska, Vancouver and Canada. Waves ranged in size from 6 to 21 feet. The tsunami killed more than 120 people and caused more than $106 million in damage. It was the most costly tsunami for the western United States and Canada.
The scientists concluded that the impact of a moderately large asteroid (about 5-6 km in diameter) in the middle of the Atlantic Ocean would generate a tsunami that would travel all the way to the upper two-thirds of the United States. Coastal cities will be destroyed by such a tsunami.
Nuclear explosions can create tsunamis, but there are no test results yet. In addition, such testing is currently prohibited by international treaties.

In an underwater earthquake or other major disturbance that causes sudden increases or decreases in the mass of water above the affected area. This sudden movement of water creates a series of powerful waves.
Underwater earthquakes, which cause significant changes to the ocean floor and the movement of large volumes of water, are the most common cause of tsunamis.
Tsunamis can also be triggered by other underwater events such as volcanic eruptions and landslides.
Tsunamis can also be associated with events above the ocean floor. These events may include meteorite impacts into the ocean, large landslides near coastlines, material from an erupting volcano, or the formation of a landslide. The consequences of a tsunami caused by such factors are usually localized.
More than 75 percent of tsunamis are caused by underwater earthquakes.

Where do tsunamis occur?

Most tsunamis occur in the Indian and Pacific Oceans. The borders of the Pacific Ocean experience frequent earthquakes. This border is known as the "Ring of Fire". There are two major subduction zones in the Indian Ocean that can also generate tsunamis.
Earthquake subduction zones are the most common source of destructive tsunamis. These earthquakes are formed when two tectonic plates meet and one slides under the other. The sinking plate is pulled towards the top plate, resulting in a bend. The top plate is restored to its original position, displacing sea water.

In December 2004, an earthquake off the coast of Indonesia led to the fact that 10 minutes after the event, the sea surface was displaced in the direction from the epicenter, like a tsunami. In this figure, the red arrows indicate the direction in which the top plate deforms due to drag and releases the bottom plate.

• In the deep waters of the ocean, waves are created with long wavelengths, but usually no more than one meter high. Tsunami waves can be hundreds of kilometers long, and they travel at very high speeds and over long distances without losing much of their energy.
• You can see a mini tsunami if you throw a large object into the water.
• Tsunamis in the open ocean can move at a speed of 950 kilometers per hour (this is the speed of a passenger aircraft). A tsunami loses speed as it approaches the ground, but it doesn't lose much of its energy.

• In the open ocean, it can be difficult to spot tsunami waves. However, as the tsunami wave approaches and moves to a shallower depth, the leading edge of the wave slows down, while the waves at the rear still travel at their original speed. This causes the water to crumple into a heap and results in an increase in wave height. This process is known as "shallowing". When a wave hits the ground, it can behave like a series of surfs or just a big powerful wave.
• The huge energy of the wave can cause a large amount of water to rush inland, far beyond the coastal zone.
• Some of the largest tsunami waves were generated by the eruption of the Krakatau volcano in 1883. That tsunami reached a height of 37 m. In 1737, the tsunami had a wave height of 64 m and above (its impact fell on Cape Lopatka, in northeastern Russia).
• Tsunami waves are different from normal waves!Normal waves generated by wind and water moving near the surface. In a tsunami, all the water moves from the surface to the bottom of the ocean, and this movement is formed due to the displacement of water (as a rule, this is caused by earthquakes). In the open ocean, tsunamis create little traffic and a great threat to shipping.
• When a tsunami reaches the coast, its wavelength can be more than 100 km. A tsunami can last for hours or even days, depending on the location. This is quite different from the waves we are used to seeing on the beach. Typical ocean waves typically last less than a minute and are only 100 meters long.
• The energy from the tsunami is enough to de-sand the entire beach, uproot trees, and crush buildings.
• People and boats are powerless against the force of the tsunami. The amount of water involved in a tsunami is capable of flooding large areas of ordinary dry land.

The most famous tsunamis in recent times:

• Solomon Islands April 2, 2007

On April 2, 2007, an earthquake struck with a magnitude of 8.1 on the Richter scale. The earthquake struck in shallow water early in the morning and was quickly followed by a tsunami. The waves were up to 10 m high. More than 50 have been registered and thousands have been left homeless. Tsunami warnings were issued in Australia and Alaska 15 minutes after the quake.

• Samoa September 29, 2009

At 6:49 am, an 8.0 magnitude earthquake triggered this tsunami, which caused extensive damage to property and the natural environment, and resulted in over 100 deaths.

• Chile February 27, 2010

It was caused by an 8.8 magnitude earthquake. The epicenter of the earthquake was located 115 km from Concepción. The epicenter of the earthquake was 230 km. This earthquake was the result of plate movement in the eastern Pacific and the South American plate. The first waves hit about 34 minutes after the earthquake. Buildings were severely damaged and over 200 lives were lost.

• Papua New Guinea 17 July 1998

An earthquake measuring 7.0 on the Richter scale just off the northern coast triggered a devastating tsunami. Waves up to 10 meters passed through the villages in the Aitape region very quickly. More than 2,000 people were killed, and the tsunami caused severe damage to buildings and farmland.

• December 26, 2004 Indian Ocean Tsunami

This tsunami has become one of the most devastating natural disasters in recent years.. The earthquake that caused it occurred just west of the Indonesian island of Sumatra and measured 9.0 on the same Richter scale, making it largest earthquake worldwide in the last 40 years . The death toll in March 2005 was over 273,000, with many missing.

And now the turn of incredible video materials:

Tsunami Thailand - 2004

Japan 2011 tsunami video

Tsunami in Khao Lak

Introduction

Natural disasters in our country are always considered unexpected. And what can we say about such an exotic natural hazard as a tsunami, and this danger only concerns the coastal Far Eastern regions, and it manifests itself extremely rarely. In other words, we perceived the tsunami as something distant and unrealistic.

But at the end of December 2004, in Thailand, Sri Lanka, and the Maldives, this natural disaster of incredible strength and fury occurred - a tsunami, which, due to its scale and consequences, can be called "megatsunamis" - super-destructive tsunamis. This term was introduced by the British geologist Simon Day and the American Stephen Worth, a specialist in the field of computer modeling. Of the Russian scientists, tsunami studies are carried out by such scientists as B.V. Levin, E.N. Pelinovsky

Megatsunamis often refer to tsunamis with wave heights of 40 meters or more. Almost overnight, tens of thousands of people died on the coast of the Indian Ocean - in Indonesia, Thailand, India, Sri Lanka, Malaysia, the Maldives and Somalia. The total number of deaths left more than 300 thousand people.

Another catastrophic event that occurred on March 11, 2011 in Japan was the earthquake and the subsequent tsunami, with a wave height exceeding 10 meters, which brought more than 12 thousand victims and caused the accident at the Fukushima I nuclear power plant.

It was these historical tsunamis, which caused huge loss of life and property damage, that aroused a new interest in tsunamis, when a lot of responses to the topic of this natural phenomenon immediately appeared, and the world community was concerned about the problems of creating modern tsunami warning systems and warning systems and informing about such natural hazards in all over the globe.

The relevance of the course work lies in the fact that tsunamis are still a serious danger. Despite the fact that scientists are still unable to determine with mathematical accuracy the place and time of the occurrence of a hydrospheric hazard. In view of this, the problem remains almost at the same level as many centuries ago.

The purpose of the course work is not only to reveal the basic concepts of a tsunami, but also to study the causes and geographical consequences in detail.

The implementation of the goal is carried out by disclosing the following main tasks:

define the concept of tsunami;

study the causes of tsunamis;

mechanism of tsunami occurrence;

geographical distribution of the tsunami;

tsunami impact on the coast;

show the importance of tsunami warning systems;

The study of hydrospheric hazard is one of the primary tasks in many countries. Preventing such a phenomenon is impossible in most cases, but their timely prevention, the development of the most effective methods for eliminating the consequences is an important task for scientists around the world.

Research methods include - analysis and generalization of the occurrence and consequences of such a natural disaster as a tsunami in Russia and abroad based on the study of information materials.

1. Causes of a tsunami

tsunami coast natural wave

Now, tsunami is an accepted international scientific term, derived from a Japanese word that means "a large wave that floods the bay." The exact definition of a tsunami sounds like this - these are long waves of a catastrophic nature, arising mainly as a result of tectonic movements on the ocean floor. The distribution of tsunamis is associated, as a rule, with areas of strong earthquakes. It is subject to a clear geographical pattern, determined by the connection of seismic regions with areas of recent and modern mountain building processes. It is known that most earthquakes are confined to those belts of the Earth within which the formation of mountain systems continues, especially young ones dating back to the modern geological epoch. Earthquakes are most pure in the areas of close proximity of large mountain systems with depressions of the seas and oceans. Two zones of the globe that are most prone to earthquakes are clearly identified. One of them occupies a latitudinal position and includes the Apennines, the Alps, the Carpathians, the Caucasus, the Kopet-Dag, the Tien Shan, the Pamirs and the Himalayas. Within this zone, tsunamis are observed on the coasts of the Mediterranean, Adriatic, Aegean, Black and Caspian Seas and the northern part of the Indian Ocean. Another zone is located in the meridional direction and runs along the shores of the Pacific Ocean. The latter is, as it were, bordered by underwater mountain ranges, the peaks of which rise in the form of islands (the Aleutian, Kuril, Japanese islands and others). Tsunami waves are formed here as a result of gaps between rising mountain ranges and sinking deep-sea troughs parallel to the ridges, separating island chains from a sedentary region of the Pacific Ocean floor.

1.1 Tsunami caused by volcanoes

Tsunamis are caused by volcanic eruptions that rise above the sea surface in the form of islands or located on the ocean floor. The most striking example in this regard is the formation of a tsunami during the eruption of Krakatoa volcano in the Sunda Strait in August 1883. The eruption was accompanied by the release of volcanic ash to a height of 30 km. The menacing voice of the volcano was heard simultaneously in Australia and on the nearest islands of Southeast Asia. On August 27 at 10 am, a gigantic explosion destroyed the volcanic island. At that moment, tsunami waves arose that spread throughout the oceans and devastated many islands of the Malay Archipelago. In the narrowest part of the Sunda Strait, the wave height reached 30-35 m. In some places, the waters penetrated deep into Indonesia and caused terrible destruction. Four villages were destroyed on Sebezi Island. The cities of Angers, Merak and Bentham were destroyed, forests and railways were washed away, and fishing boats were abandoned on land several kilometers from the ocean. The shores of Sumatra and Java became unrecognizable - everything was covered with mud, ash, corpses of people and animals. This catastrophe brought the death of 36,000 inhabitants of the archipelago. Tsunami waves spread throughout the Indian Ocean from the coast of India in the north to the Cape of Good Hope in the south. In the Atlantic Ocean they reached the Isthmus of Panama, and in the Pacific Ocean they reached Alaska and San Francisco.

1.2 Tsunami triggered by landslide/landslide

A landslide may be the cause of a tsunami. Tsunamis of this type occur quite rarely. It is known that, unlike tsunamis of purely seismic origin, "landslide" tsunamis are usually local in nature. However, in terms of their destructive power, they are in no way inferior to "seismic" waves. Such tsunamis are especially dangerous in narrow straits, fiords and in closed bays and bays.

July 1958, as a result of an earthquake in Alaska, a landslide occurred in Lituya Bay. A mass of ice and terrestrial rocks collapsed from a height of 900 m. A wave formed, reaching a height of 600 m on the opposite shore of the bay. Such cases are very rare and, of course, are not considered as a standard.

The next reason for the occurrence of a tsunami is the fall of huge fragments of rocks into the sea, caused by the destruction of rocks by groundwater. The height of such waves depends on the mass of the material that fell into the sea and on the height of its fall. So, in 1930, on the island of Madeira, a block fell off from a height of 200 m, which caused the emergence of a single wave 15 m high.

1.3 Tsunami caused by earthquakes

Another reason for the occurrence of tsunami waves is most often the changes in the relief of the ocean floor that occur during earthquakes, leading to the formation of large faults, sinkholes, etc.

The scale of such changes can be judged from the following example. During an earthquake in the Adriatic Sea off the coast of Greece on October 26, 1873, ruptures of a telegraph cable laid on the seabed at a depth of four hundred meters were noted. After the earthquake, one of the ends of the broken cable was found at a depth of more than 600 m. Consequently, the earthquake caused a sharp subsidence of the seabed to a depth of about 200 m. were at a depth different from the previous one by several hundred meters. Finally, a year after the new shocks, the depth of the sea at the place of the rupture increased by 400 m. Still greater disturbances of the bottom topography occur during earthquakes in the Pacific Ocean. So, during an underwater earthquake in the Sagami Bay (Japan), with a sudden rise in a section of the ocean floor, about 22.5 cubic meters were displaced. km of water, which hit the shore in the form of tsunami waves.

2. Tsunami generation

It is currently believed that tsunamis are formed when rocks move vertically along a fault during a strong earthquake, as shown in the diagram.

During underwater earthquakes, the mechanism for generating tsunami waves is as follows:

ü When an earthquake occurs, there is a significant movement of the oceanic crust;

ü There may be a sharp rise or fall of the ocean floor;

ü If this occurs, the sea surface above the ocean floor deformation zone is also subject to similar deformation, but if the deformation of the ocean floor is constant, the deformation of the surface is not constant.

The main cause of destructive tsunamis should be considered as sharp vertical displacements of individual sections of the basin bottom due to seismotectonic movements. The resulting residual displacements of the ocean floor displace the liquid in such a way that the shape of the displacements of the free surface of the ocean repeats the shape of the displacements of the bottom. At present, modern seismic measurements make it possible to calculate, with satisfactory accuracy, the shape of the seabed displacements resulting from the strong underwater earthquake Okada, 1985. However, it is known that not all strong earthquakes cause bottom faults with vertical displacements of the crust and, accordingly, tsunami waves. One of the most important problems of seismology is the development of methods for determining the parameters of a seismic source and assessing its "tsunamigenicity" for the task of operational forecasting.

Although earthquakes that occur along horizontal faults sometimes produce tsunamis, they are usually local in nature and do not travel long distances. Some scientists have noticed that large earthquakes along horizontal faults near the coasts of Alaska and British Columbia produced tsunamis that extended no more than 100 kilometers. As mentioned earlier, tsunamis usually occur after strong earthquakes with a small depth of focus under the oceans. However, there have been several cases of tsunami formation due to earthquakes that occurred on land. Therefore, it can be concluded that tsunamis can be formed either due to changes in the seabed (faulting), or due to the action of seismic surface waves passing through a shallow continental shelf. Long-period surface waves (the so-called Rayleigh waves) have a vertical component and transmit a significant part of the energy of earthquakes. The return of the sea level to normal causes the formation of a series of waves propagating in all directions from the original deformation zone.

Most tsunami waves are caused by underwater earthquakes. During an earthquake, a vertical crack forms under water, and part of the bottom sinks. The bottom suddenly ceases to support the column of water lying above it. The surface of the water begins to oscillate vertically, trying to return to its original level - the mean sea level - and generates a series of waves.

In the deep ocean, the mass of such an unsupported column of water is enormous. When the dumping of the bottom stops, this column finds a new, lower “pedestal” for itself and, by such a movement, creates waves with a height equivalent to the distance that this column has moved. The movement during earthquakes usually has a height of about 50 cm, but the area is huge - tens of square kilometers. Therefore, the excited tsunami waves have a small height and a very long length, these waves carry an enormous amount of energy.

Mechanism of tsunami formation as a result of an earthquake. At the moment of a sharp subsidence of a section of the ocean floor and the appearance of a depression on the sea floor, water rushes to its center, overflows the depression and forms a huge bulge on the surface. With a sharp rise in a section of the ocean floor, significant masses of water are displaced. At the same time, tsunami waves arise on the surface of the ocean, quickly diverging in all directions. Usually they form a series of 3-9 waves, the distance between the crests of which is 100-300 km, and the height when the waves approach the shore reaches 30 m or more.

3. Tsunami spread

The pattern of tsunami propagation is also very complex, because the speed of a tsunami wave is determined by the depth of the ocean and therefore is variable along the entire path. Some parts of the wave front are ahead of others, the front loses its ring shape, bends, and sometimes even breaks. The waves begin to cross each other. There is a reflection from the coast. The reflected waves are superimposed on the direct ones - they interfere. A complex pattern of tsunami movement emerges.

The propagation speed of such waves averages (at a depth of 4 km) approximately 720 km/h. When a tsunami approaches the shore and enters shallow water, the wave speed sharply decreases, the bottom part of the flow slows down due to friction against the bottom, the steepness of the wave quickly increases, and the flow rushes to the shore at a speed of about 70 km/h, falling on the coastline tens of kilometers long. kilometers. Wave speed in the open ocean can be calculated using the formula , where g is the gravitational acceleration and H is the depth of the ocean (the so-called shallow water approximation, when the wavelength is much greater than the depth).

Several general concepts about wave refraction and diffraction should be considered. These phenomena are important for understanding the mechanism of tsunami propagation.

Wave refraction

Traveling waves with a wavelength much greater than the depth of the water where they travel. These are called shallow water waves or long waves. Since the waves are long, different parts of the wave may be at different depths (especially near coasts) at a given time. Due to the fact that the speed of a long wave depends on depth, different parts of the wave propagate at different speeds, causing the waves to bend. This is called refraction.

Wave diffraction

Diffraction is a well known phenomenon, especially in optics and acoustics. This phenomenon can be roughly considered as the curvature of waves around objects. It is this movement that allows the waves to pass through obstacles in the harbour, as the energy is transferred transverse to the crest of the wave, as shown in the diagram below. This curvature (which is rather difficult to explain) is on a much smaller scale than the refraction discussed above, which is a simple response to changes in speed.

Rice. 5 (Wave refraction)

Rice. 6 (Wave Diffraction)

3.1 Tsunamis of remote origin

When tsunamis travel long distances across the oceans, the sphericity of the Earth must be taken into account to determine the effect of the tsunami on distant coasts. Waves that diverge in different directions near the source of formation may converge again at a point at the opposite end of the ocean. An example of this was the 1960 tsunami with a source on the coast of Chile at 39.5 south latitude (S) and 74.5 west longitude (W). The coast of Japan is located between 30 and 45 degrees north latitude (N) and 135 and 140 degrees east longitude (E), which is a difference of 145 and 150 degrees longitude from the source zone. As a result of the convergence (convergence) of the unrefracted rays of the waves on the coast of Japan, severe destruction occurred and many people died.

It should be remembered that in addition to the indicated effect, the rays of the tsunami waves also deviate from their natural path along the maximum circles due to the refraction of the rays under the influence of the difference in the depth of places, tending to deeper places. The influence of such refraction on tsunami waves of remote origin leads to the fact that tsunami waves do not always converge in one place at the opposite end of the ocean.

There is another mechanism of wave refraction on water, even at great depths and in the absence of topographical irregularities. It has been proven that currents directed at an angle to waves can change their direction of propagation and affect the wavelength.

When a tsunami approaches the coast, the waves are modified by the various characteristics of the coastal and coastal topography. Submarine ridges and reefs, continental shelf, headlands and bays, steepness of the coastline can change the period of the wave and wave height, cause wave resonance, reflection of wave energy and / or transform waves into a tidal bar (boron) that falls on the shore.

Ocean ridges provide very little protection to the coast. Although a small amount of tsunami energy may be reflected off the underwater ridge, most of the energy is carried across the ridge to the coastline. The 1960 tsunami along the coast of Chile is a prime example of this. The waves of this tsunami were high along the entire coast of Japan, including the islands of Shikoku and Kyushu, which are located behind the ridge of Southern Honshu.

3.2 Local tsunamis

When a local tsunami occurs, it impacts the coastline immediately after the event that caused the tsunami (earthquake, underwater volcanic eruption or collapse). Sometimes there were cases when a tsunami arrived on the nearest coast 2 minutes after the moment of its formation.

For this reason, the tsunami warning system is useless in this case, and recommendations from the competent authorities on how to behave and what to do in the event of such tsunamis should not be expected. The low efficiency of tsunami warning systems is also explained by the fact that communication systems and other infrastructures can fail during an earthquake. Therefore, it is very important to develop the right plan of action in case of a tsunami.

4. Impact on the coast

The impact of a tsunami on the coast mainly depends on the topography of the seabed and land at a given location, as well as the direction of wave arrival.

.1 Wave height

The height of a sea wave is the vertical distance between the crest and the bottom of a wave. Directly above the source of a tsunami, the wave height is from 0.1 to 5 m. This wave is usually not visible either from a ship or from an aircraft. The people on the ship do not even suspect that a tsunami wave passed under them. But unlike wind waves (surface waves on the water caused by the wind), which capture only the surface water layer, tsunami waves involve the entire water column from the bottom to the surface in motion. Getting into shallow water, it reduces the speed of movement, and its energy is used to increase the height. The wave grows higher and higher, as if “stumbling” in shallow water. At the same time, its foundation is delayed, and something like a water wall is created with a height of 10 to 50 m or more.

Parameters Wind Tsunami waves Propagation speed up to 100 km/h up to 1000 km/h Wave length up to 0.5 km up to 1000 km Period up to 20 seconds up to 2.5 hours

The height of tsunami waves in the ocean decreases with distance from the place of their origin in proportion to the distance, taken to the power of 5/6. It is impossible to predict which of the tsunami waves will be the most destructive. The theory shows that tsunami waves alternate in their relative growth as they move away from their point of origin. So, in the immediate vicinity of the epicenter, the second wave turns out to be higher than the first one, but as the distance from the epicenter increases, the maximum wave has a higher serial number.

The final wave height depends on the topography of the ocean floor, the contour and topography of the coast. On flat, wide coasts, the height of a tsunami is usually no more than 5-6 m. Waves of high height form on separate, relatively small sections of the coast with narrow bays and valleys. In Japan, as one of the most tsunami-affected countries, waves with a height of 7-8 m occur about 1 time in 15 years, and with a height of 30 m or more have been observed 4 times over the past 1500 years. The largest was the wave that hit the coast of the Kamchatka Peninsula near Cape Lopatka in 1737. It reached a height of almost 70 m. In 1968, in the Hawaiian Islands (USA), the wave rolled over the tops of coastal palms.

This explains the different heights of tsunami waves in different places on the same coast.

.2 Tsunami run ashore

The vertical increase in the height of the water level is called the tsunami run-up height. When tsunami waves approach the shore, the water level may increase to 30 meters or more in some exceptional cases. Increasing the level to 10 meters happens quite often. The wave run-up height is able to overcome the mark of 30 m, and the splash range often exceeds 2-3 km.

The height of the tsunami will vary at different points along the coast. Changes in the height of the tsunami and the topographic characteristics of the coastline cause a change in the characteristics of the run-up of the tsunami at different points on the coastline.

Tsunamis become destructive precisely near the coastline. Tsunamis are deep waves, they capture a much more powerful layer of water than wind waves that develop only on the surface of the sea and shallow from it.

An example of such a large difference in the features of the tsunami run-up is given by some scientists: on the island of Kauai, Hawaii, a gradual increase in water level was observed on the western slope of the bay, while just one mile to the east, waves violently crashed onto the coast, destroying groves of trees and destroying many houses .

It should be noted that the characteristics of individual waves also change when they arrive on the same coast. Scientists give examples from the history of the Hawaiian Islands, when the first waves were so smooth that a person could easily walk up to his chest in the water towards the coming waves. Later, the waves became so strong that they destroyed many houses and threw debris to the forest at a distance of 150 meters from the shore.

There are three scenarios of wave behavior during the run-up:

) running ashore (flooding of the coast) without breaking the wave;

) destruction of the wave near its crest with the preservation of the symmetrical shape as a whole;

) complete destruction of the wave, its overturning and the formation of bore.

4.3 Tsunami consequences

Tsunami triggers include shockwave, blur, flooding.

Tsunami intensity is a characteristic of the energy impact of a tsunami on the coast, estimated on a conditional six-point scale:

1 point - very weak tsunami. The wave is noted (registered) only by seamen.

2 points - weak tsunami. Can flood the flat coast. Only specialists notice it.

3 points - average tsunami. Everyone celebrates. The flat coast is flooded, light ships can be washed ashore. Port facilities are subject to weak destruction.

4 points - strong tsunami. The coast is flooded. Coastal buildings damaged. Large sailing and small motor boats are washed ashore and then washed back into the sea. The shores are littered with sand and silt. fragments of stones, trees, debris. Human casualties are possible.

5 points - very strong tsunami. The coastal areas are flooded. Breakwaters and breakwaters are badly damaged. Large ships washed ashore. The damage is also great in the interior parts of the coast. Buildings and structures have destruction of varying degrees of complexity, depending on the distance from the coast. Everything around is strewn with rubble. Storm surges are high at river mouths. Loud water noise. There are human casualties.

6 points - catastrophic tsunami. Complete devastation of the coast and coastal areas. The land is flooded for a considerable distance inland from the seashore.

The intensity of a tsunami depends on the length, height, and phase velocity of the incoming wave. The energy of a tsunami is usually between 1 and 10% of the energy of the earthquake that caused it.

The colossal kinetic energy of the wave allows the tsunami to destroy almost everything that comes in its path. A catastrophic tsunami, almost without slowing down, is able to pass through a medium-sized settlement, turn it into ruins and destroy all life. After the passage of the tsunami, the coast changes its appearance, the ships are brought ashore at a distance of hundreds, and sometimes thousands of meters from the sea edge. In the port of Corral (Chile) in 1960, a tsunami wave threw a ship with a displacement of 11,000 tons from the harbor through the city into the open sea. Along with material losses, the tsunami leads to the death of people. In the period 1947-1983. the number of victims was 13.6 thousand people. The most powerful known tsunami, later named Sanriku, came from an underwater earthquake 240 km from the coast of Japan on June 15, 1896. Then a huge wave 30 m high hit the island. Honshu. 27122 people died. 19,617 houses were washed into the sea. The first "seaquake" in Russia was registered in Kamchatka in 1737. In 1979, a tsunami with a wave height of 5 m hit the Pacific coast of Colombia. 125 people died.

In 1994, a 15 m high tsunami in the Philippines destroyed 500 houses and 18 bridges to the ground. More than 60 people died.

The biggest tsunamis

11.1952 Severo-Kurilsk (USSR).

It was caused by a powerful earthquake (magnitude estimates vary from 8.3 to 9 according to various sources), which occurred in the Pacific Ocean 130 kilometers from the coast of Kamchatka. Three waves up to 15-18 meters high (according to various sources) destroyed the city of Severo-Kurilsk and caused damage to a number of other settlements. According to official figures, more than two thousand people died.

03.1957 Alaska, (USA).

Caused by an earthquake with a magnitude of 9.1 that occurred on the Andreyanovsky Islands (Alaska), which caused two waves, with an average wave height of 15 and 8 meters, respectively. In addition, as a result of the earthquake, the Vsevidov volcano, located on the island of Umnak, woke up and had not erupted for about 200 years. More than 300 people died in the disaster.

07.1958 Lituya Bay, (southwest Alaska, USA).

An earthquake that occurred north of the bay (on the Fairweather fault) initiated a strong landslide on the slope of the mountain located above Lituya Bay (about 300 million cubic meters of earth, stones and ice). All this mass filled the northern part of the bay and caused a huge wave of a record height of 524 meters (or 1724 feet), moving at a speed of 160 km / h.

03.1964 Alaska, (USA).

The largest earthquake in Alaska (magnitude 9.2), which occurred in the Prince William Sound, caused a tsunami of several waves, with the highest height - 67 meters. As a result of the disaster (mainly due to the tsunami), according to various estimates, from 120 to 150 people died.

07.1998 Papua New Guinea

A magnitude 7.1 earthquake off the northwestern coast of New Guinea triggered a powerful underwater landslide that triggered a tsunami that killed more than 2,000 people. century

Tsunami propagation in the Indian Ocean

September 2004 coast of Japan

Two strong earthquakes (magnitudes up to 6.8 and 7.3, respectively) occurred 110 km off the coast of the Kii Peninsula and 130 km off the coast of Kochi Prefecture, causing a tsunami with a wave height of up to one meter. Several dozen people were injured.

December 2004 Southeast Asia.

At 00:58 a powerful earthquake occurred - the second most powerful of all recorded (magnitude 9.3), which caused the most powerful of all known tsunamis. Asian countries (Indonesia - 180 thousand people, Sri Lanka - 31-39 thousand people, Thailand - more than 5 thousand people, etc.) and African Somalia suffered from the tsunami. The total number of deaths exceeded 235 thousand people.

January 2005 Izu and Miyake Islands (East Japan)

An earthquake with a magnitude of 6.8 caused a tsunami with a wave height of 30-50 cm. However, thanks to a timely warning, the population from dangerous areas was evacuated.

April 2007 Solomon Islands (archipelago)

Caused by a magnitude 8 earthquake in the South Pacific. Waves several meters high reached New Guinea. The tsunami killed 52 people.

March 2011 Japan

The strongest earthquake of magnitude 9.0 with an epicenter located 373 km northeast of Tokyo caused a tsunami with a wave height exceeding 10 meters. According to the data received, the epicenter of the earthquake was at a depth of 32 km. The source of the earthquake was located to the east of the northern part of the island of Honshu and extended for a distance of about 500 km, which can be seen from the aftershock map. The exact number of victims as of March 18, 2011 is not known.

5. Tsunami protection

It is impossible to completely protect any coastline from the destructive power of a tsunami. In many countries, they tried to build breakwaters and breakwaters, dams and other structures in order to weaken the force of the tsunami and reduce the height of the waves.

In Japan, engineers built wide embankments to protect ports and breakwaters in front of harbor entrances to narrow these entrances and divert or reduce the energy of powerful waves.

No type of defensive structures could provide one hundred percent protection for low-lying coasts. In fact, barriers can sometimes only exacerbate destruction if tsunami waves breach them, violently hurling chunks of concrete at houses and other structures like projectiles.

In some cases, trees can provide protection from tsunami waves. Tree groves alone or in addition to coastal defenses can dampen tsunami energy and reduce the height of tsunami waves.

Electronic computers became assistants to scientists in the fight against the tsunami. Many universities around the world have compiled programs for mathematical modeling of catastrophic tsunamis based on the laws of hydrodynamics. With the help of such models, many variants of the appearance and behavior of a catastrophic wave, its speed, level, friction, depending on the terrain and other parameters are calculated.

Tsunami Warning System

The main purpose of the Pacific Tsunami Warning System is to identify and pinpoint areas of strong earthquakes in the Pacific, determine whether they have caused tsunamis in the past, and provide timely and effective information and warning to the people of the Pacific in order to reduce tsunami hazards. especially in terms of human life and well-being. To achieve this goal, the Tsunami Warning System continuously monitors seismic conditions and ocean levels in the Pacific region.

The Tsunami Warning System is an international program that requires the participation of many services that deal with seismicity, tidal events, communications and information dissemination from various countries in the Pacific region. Administratively, the participating countries are united within the framework of the International Oceanographic Commission as members of the International Coordinating Group for the Pacific Tsunami Warning System (ICG/ITSU). At the request of the International Oceanographic Commission, the International Tsunami Information Center was established, which performs numerous tasks in support of ICG/ITSU participants and to reduce the risk associated with tsunamis in the Pacific region. The Pacific Tsunami Warning Center (PTWC) is the operations center for the Pacific Tsunami Warning System.

The Pacific Tsunami Warning Center (PTWC = PTWC) collects and evaluates data provided by member countries and issues relevant fact sheets to all members about major earthquakes and the likely or confirmed likelihood of tsunamis.

The operation of the System begins from the moment any seismic station of one of the participating countries detects an earthquake of such magnitude that the alarm device installed at this station is triggered. Station staff immediately interpret the received seismograms and send the information to the TTPC. After receiving data from one of the seismic stations of the participating country or after the signaling device is triggered in the TCPC itself, the center sends requests for data from other stations of the System.

When enough data is received at the TCPC to determine the coordinates of the epicenter of the earthquake and its magnitude, a decision is made regarding further actions. If an earthquake is strong enough to cause a tsunami, the TCWC sends requests to the participating countries' tide stations closer to the epicenter to monitor readings for tsunami detection. Tsunami Warning/Watching Bulletins are issued to dissemination organizations for all earthquakes of magnitude greater than 7.5 (greater than 7.0 for the Aleutian Islands region) to alert the public to the possibility of a tsunami and the need for safety measures. The data received from tide monitoring stations are evaluated; if they show that a tsunami has formed that is dangerous to part or all of the population of the Pacific region. The Tsunami Warning/Watch Bulletin is being expanded or updated as a Pacific-Wide Warning. Relevant organizations then carry out the evacuation of people from dangerous areas according to pre-designed schemes. If tide stations indicate the formation of a non-dangerous tsunami (or no tsunami), the TPWC will cancel the content of the Tsunami Warning/Watch Bulletin previously sent out.

Several areas of the Pacific Basin have national and regional tsunami warning systems that provide timely and effective tsunami warning to the public. For the population of coastal areas where tsunami generation is possible, the speed of notification and transmission of tsunami data is especially important. Given the time it takes to collect and evaluate seismic and tidal data, the TSWC cannot provide timely tsunami warnings to people in areas where tsunamis form in local waters. In order to take at least some security measures in the first hour after the formation of a tsunami in a given region, some countries have established national and regional tsunami warning systems. Regional warning systems are able to issue an alarm in the shortest possible time and warn the population living near the earthquake epicenter of a possible tsunami based on earthquake data alone, without waiting for information about a possible tsunami formation.

These regional systems typically have information from a number of seismic and tide stations to function effectively. This data is transmitted instantly via telemetry to the central headquarters. Local earthquakes are usually 15 minutes away or even less, so a seismic warning is immediately sent to the population of the area. Due to the fact that warnings are issued only on the basis of seismological data, it can be assumed that sometimes these warnings are not confirmed by the formation of a tsunami. But since these warnings, given very quickly, are only valid for a limited area, this is acceptable, since a higher level of protection for people is achieved.

The most sophisticated state warning systems have been created in France, Japan, Russia and the United States. In the case of the United States of America, the PTWC and the Alaska Tsunami Warning Center (ATWC) are the State Tsunami Warning Centers for the United States and provide all tsunami warning services that may be of public interest to the United States. Besides. The RTWS Center (RTWC) serves as the Regional Tsunami Warning Center for Hawaii in relation to tsunamis generated in the Hawaiian Islands area.

Conclusion

Based on this study, a number of conclusions can be drawn:

) The most dangerous marine geological phenomena of natural origin are tsunamis.

) Tsunamis are a type of sea waves that occur during underwater and coastal earthquakes, landslides, large areas of land into the ocean, underwater shear and landslide.

) The closest relationship exists between earthquakes and tsunamis.

) Tsunamis are formed in two ways: 1) during a sharp vertical movement of rocks along a fault during a strong earthquake; 2) during earthquakes that occur along horizontal faults, usually have a local character and do not spread over long distances.

) Tsunami waves are formed in a source (or focus), which usually has an extended shape - its length is from 100 to 400 km. From the source, tsunami waves propagate in the reservoir as a long gravitational wave of small amplitude.

) The phenomena of refraction and diffraction of waves are the mechanism of formation of tsunami waves.

) As a result of the geological displacement of tectonic plates on the ocean floor, tsunamis occur, which are of two types: tsunamis of remote origin and local tsunamis.

) The impact of a tsunami on the coast mainly depends on the topography of the seabed, the contour and topography of the land at a given location, as well as the direction of wave arrival.

) The shallower the ocean floor, the greater the height of the wave from the bottom surface.

) The greatest, destructive force of the shock wave is formed on separate, relatively small sections of the coast with narrow bays and valleys.

) Changes in the height of tsunami waves and the topographic characteristics of the coastline cause a change in the characteristics of the run-up of the tsunami at different points on the coastline.

) Tsunamis are characterized by the following indicators: sea wave height; sea ​​wave length; phase velocity of the wave.

) The intensity of a tsunami depends on the length, height, and phase velocity of the incoming wave.

) It is impossible to completely protect any coast from the destructive power of a tsunami. Tsunamis can only be prevented.

) A detailed study of all the features of the occurrence and conditions for the formation of a tsunami allowed a person to most successfully protect his life, health and property in the event of a hydrospheric hazard.

) When taking into account the experience of preventing hydrospheric hazards, eliminating the consequences of their onset, mankind has the opportunity to increase the level and accuracy of forecasting and warning of an approaching danger.

List of sources used

1.Yu.L. Vorobyov, V.A. Akimov, Yu.I. Sokolov M, 2006

2.DOTSENKO S.F., Solovyov C.JI. On the role of residual displacements of the ocean floor in the generation of tsunamis by underwater earthquakes // Oceanology V.35, No. 1, pp. 25-31, 1995.

DOTSENKO S.F., Sergeevsky B.Yu. Dispersion effects in the generation and propagation of a directed tsunami wave II Tsunami Research No. 5, Moscow: MGFK RAS. 1993, pp. 21-32.

Levin B.V., Nosov M.A. Physics of tsunamis and related phenomena in the ocean. M.: Janus-K, 2005.

Local tsunamis: prevention and risk reduction, collection of articles./ Edited by Levin B.V., Nosov M.A. - M.: Janus-K, 2002.

Pelinovsky E.N. Hydrodynamics of tsunami waves / IAP RAS. Nizhny Novgorod, 1996. 276 p.

Journal // Science and Life No. 1, 2011.

Journal // Science No. 2, M.: 1987, S. 27-34.

9.www.o-b-g.narod.ru

Www.puzikov.com

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I remember it now: I’m about 9 years old. I come home from school, sit down for lunch, turn on the TV - and all the channels terrible tsunami in thailand. Everything is destroyed, the announcer constantly repeats about the many victims.

Then I was very sorry for the Thais, right up to tears. I thought about how good it is to live in Russia- here such horrors doesn't happen. But it turned out that this Not certainly in that way.

What is a tsunami and how does it form?

A tsunami is a huge wave (or, more often, a series of waves) that occurs if something affects the entire water column.

How does this happen?

• For example, an earthquake occurred underwater.
• The bottom moves unevenly, some parts are above or below others. With him moving water masses.
• The water is moving trying to come to the original state.
• Formedbig wave, which at great speed can demolish everything in its path.

Tsunami in the Russian Federation

Most often when talking about tsunami, we think that in Russia- something like that won't happen. However, in our country, they may well occur - in the Far East region.

Basically, it's about about Kamchatka, Sakhalin or the Kuril Islands.

Tsunamis and mythical cities

May be, Have there been tsunamis before? Can it happen that mythical lost islands- this is victims this terrible phenomenon.

Some scientists suggest that wave of great power really capable of destroying an entire island. If so, the story of Atlantis may not be a beautiful fairy tale, a reality.

There is also a much less well-known the legend of the lost island of Teonimanu. This island, according to legend, fell a victim of a jealous husband, imposed on him curse.

Seven waves in a row washed Theoniman from the face of the earth. Again, it may be remembered that tsunamis hit the ground in groups of waves that follow each other. Doesn't it remind you of anything?

True, the researchers believe that everything was a bit the other way around. it first on the island there was an earthquake, which ruined it. And it has already become the cause of the tsunami, from there and "seven waves" from the legend.

Whether to believe in these stories - let everyone judge for himself, but science has not yet found 100% confirmation of these hypotheses.

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Hearing the word tsunami, I immediately remember the school “What? Where? When? ”, the sixth grade, or even earlier. So, there was a question about which waves are most dangerous for ships, deep or surface. We, thinking that the answer to surface waves is too simple, decided to bet on deep ones. As it turned out, it is the deep waves that lead to the tsunami.

What is a tsunami

In different sources, you will stumble upon a bunch of definitions, but in general cunami is a big and long wave, extending beyond the sea, that is, on land. Essentially, this is large volume of water, which was pushed, and when it approaches the shore, where the depth of the sea becomes less, then a wave rises, which comes to land.

Tsunami principle Causes of tsunami formation

It is much more interesting to know not what a tsunami is, but how does it appear. It must be understood that tsunamis are essentially caused by the displacement of water and the causes of displacement are different:

• earthquakes(although more precisely, seismic activity, that is, shifts of lithospheric plates);
• landslides(falling rock or ice displaces water, and thereby creates a wave);
• volcanic eruptions(explosions that accompany volcanic eruptions create deep waves);
• human(with the invention of nuclear weapons and their testing in the ocean, we also joined this list).

The most famous tsunamis

The "materiel" is over, and now to the realities of this phenomenon. Do you want to evaluate the destructiveness? Then let's remember the most famous and destructive tsunamis 21st century. Two examples will be enough to understand the dimensions:

• The 2004 tsunami that occurred in Southeast Azii.

The cause of the tsunami is an earthquake in the Indian Ocean, the total number dead over 235 thousand people.

• The 2011 tsunami caused by the Tokuhu earthquake.

Japan was mostly affected, more than 25 thousand dead. Caused an accident at Fokushima nuclear power plant.

That tsunami of 2004 And now good news. The location of most of the country in center of the mainland and in seismically inactive zones leads to the fact that we are not afraid of tsunamis.

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All my life I watched on TV the terrible consequences caused by disasters. I have never seen such a terrifying, but at the same time fascinating spectacle anywhere else. I began to study what is a tsunami? Tsunami is a truly impressive phenomenon, unpredictable, but at the same time captivating with its strength and scale. This word was invented in Japan and it means " big wave flooding the bay.

What does a tsunami bring with it?

What are effects:

• earthquakes;
• eruption of volcanoes;
• landslides.

We all understand what terrible consequences these catastrophes can cause: destruction, collapses, deaths... In order to prevent disasters, it is necessary to understand what is a tsunami. At the time of the origin of the tsunami, a large plot the ocean floor is sinkingway down, water rushes into the depression. And having filled the depression, the water continues to stay by inertia, and on the surface formedhuge bulge. The same bulge is formed if the bottom rises sharply or an eruption begins.

How does a tsunami happen

Everyone can imagine circles on the water from a thrown stone. The same circles of enormous size come from bulges . This is the tsunami. The speed of these waves is amazing, it reaches up to 1000 kilometers, a length before 300 kilometers. But in the ocean, such waves are not felt. Approaching the shore, the waves meet the resistance of the bottom near the shore, begin to grow before50 meters. When the main wave approaches the shore, we can see a big, powerful ebb or the shore is flooded by a smaller wave. And then twenty minutes later from the sea comes wall of water and collapseson beach, destroying everything, carrying people, fragments of buildings, animals into the sea. Ahead of the tsunami is an air wave, which is also very dangerous. In addition to earthquakes and eruptions, tsunamis can trigger landslides. This is rare and is usually small.

Examples and consequences

But, as we know, there are exceptions. Yes, far away 1899 on the Alaska a mass of earth and snow with a volume of 30 million cubic meters slid down. He formed a huge wave that washed away everything in its path. Fortunately, a catastrophic tsunami is very rare. Most often they appear in quietocean, especially in Japan.

The scariest thing was tsunamiin1883 during the famous explosion Krakatoa volcano. Waves of enormous height reached the shores of Alaska and the Isthmus of Panama.

But, thanks to the latest technology, the number of people who died from the tsunami decreased, as they began to practice alerts of people about approaching so dangerous tsunami.

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I have a girlfriend, Lara, and she has a four-year-old son, Tyomka. So when this little, unstoppable energizer comes to visit me - after him the apartment, as after tsunami paradise island - everything is upside down. Today, perhaps only a baby does not know what a tsunami is and how they arise. Disaster movies often use pictures a huge wave that sweeps entire cities in its path.

History of the tsunami

This word came from the Land of the Rising Sun not just like that. It was the Japanese islands in the not very distant past that were most often hit by the "big wave" - ​​this is how the word tsunami is translated from Japanese. Long, gravitational waves, that arose from the shift of a large section of the seabed fell on the coast, sweeping away everything in its path. Russia first heard about this phenomenon only in the 18th century from botanist and traveler Stepan Krasheninnikov, who witnessed this wave in Kamchatka. However, the Russian scientific community was not interested in this news, and no one ever began to study this phenomenon. Only in the twentieth century, when the Kuril Islands became part of the USSR and a huge wave in 1952, a city with a population of five thousand, Severo-Kurilsk, was completely washed away, only after that in Russia they began to seriously study this wave.

Tsunami classification

It all depends on the cause of this wave. It also depends on it whether the water recedes from the shore before the wave or not. There are two main reasons:

1. Rapid upward movement of the bottom.
2. Rapid downward movement of the bottom.

It is in the second case that at first the water leaves the coast for several kilometers into the ocean, in order to then fall on it in a wave.

Today, the term "tsunami" refers not only to giant waves, but also absolutely insignificant bursts arising from the displacement of the bottom. According to the degree of destructive power, it turns out that there are tsunamis that no one will notice. There are 6 types of tsunami:

• 1 point- very weak, it is recorded only by seagraphers;
• 2 points- weak, it is also noticed only by specialists;
• 3 points- the average, oh, this is already something - it floods the flat coast, it can even throw small boats ashore;
• 4 points- strong, "save yourself, who can!" - will destroy coastal structures, casualties are possible;
• 5 points- very strong - colossal damage has been done to the coast, there are dead;
• 6 points- disaster! Hundreds of kilometers inland, everything is completely destroyed, many dead.

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To my happiness, I only had to see the tsunami in movies and on the news on TV, it was at such moments that I was glad that I live so far from the sea. And I am not afraid of this terrible and destroying everything in its path element. By the way, I have never been very brave, and the little one even thought that I would never fly to the sea in my life. Now, of course, I have matured and love the sea very much, so I overcome my fears and follow the forecasts.

The natural phenomenon of the tsunami, what is it

Tsunami is one of the most destructive natural disasters. representing huge wave size,destructive practically all on his way.

I have always wondered where such huge waves come from, as it turned out, they are consequences of other natural disasters, such as:

The terrible consequences of the elements

Tsunami is a natural disaster with dire consequences:

Tsunami and storm, why the first is more dangerous

And tsunami and storm water disasters associated with huge waves, but the consequences of the former are much stronger, here's why it happens:

• Storm- this is surface movement of water, upon occurrence tsunami in movement comes all the water from the bottom to the surface.
• Storm, usually, coming slowly so people can evacuate. Tsunami always comes suddenly there is practically no time to save.
• The speed of tsunami waves and their energy are many times higher than during a storm.

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At the mention of the tsunami, I immediately recall the "Perfect Storm" with J. Clooney and M. Wahlberg. And specifically, that fragment with giant wave, which slowly swallowed the ship.

I can't even imagine a situation where 4 0 meter wave rushing towards me at great speed. And it doesn’t matter at all what distance separates us, and how fast I can run, because the tsunami will be faster ...

The essence of the tsunami

Tsunami- it's like ordinary waves, only bigger, much more ... And they form differently.

Compared to regular waves:

• seismic activity of the seabed determine much more energy than simple sea waves (these are formed due to the wind that pushes their upper layer)
• by an order of magnitude greater distance between wave crests: for medium sea waves - from 90 to 180 m, and for tsunamis this distance can reach hundreds of kilometers.
• wave height too more because of the amount of water that presses on her from behind. It can reach 50 meters, and for an ordinary sea wave in a strong storm it is 7-8 m.

Tsunami formation factors

If the wind is the catalyst for ordinary sea waves, then in a tsunami it is mainly - seafloor movement. Movement of individual sections during an earthquake displaces some of the water and lets her go on a "long voyage".

The main reasons for this ares:

• Underwater earthquakes and landslides.

• Explosion and eruption.

A volcano explosion can produce underwater earthquake, what displaces a layer of water, and tons of soot and soot, rolling straight into the sea, will help him in this.

• The fall of some cosmic body right into the water column.

According to the calculations of scientists, an asteroid with a radius of 5 km., Falling into the waters of the Atlantic Ocean, would give rise to a tsunami that swept away most of Europe and the eastern part.

All of the above factors have a common goal - displace some water and set the pace. And this same water "with horror and screams" rushing from the epicenter of the underwater cataclysm, turning into slowly into the same tsunami wave, which reaches its apogee in shallow water.

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I don't like watching the news, but reports of natural disasters still reach my ears. Wherever a tsunami happens, all channels talk about it. This is really a terrible natural force with which a person, despite all the technical achievements, cannot cope. When I watch videos and photos of the tsunami, I get scared. But at the same time it captures with its grandeur and power.

Tsunami is a Japanese word

The word "tsunami" going on from Japanese. And this is not surprising, because it was the country of the “rising sun” that most often fought this “sea monster”. What becomes the cause of the tsunami? Predominantly, this coastal and submarine earthquakes. BUT tsunami- it's simple wave, which formed due to earth tremors. AT open ocean her height no more than a meter. But what closer to the coast- topics the wave gets bigger. Height this powerful wave can reach tens and tens of meters, a length - hundreds of kilometers. And now all this mass of water falls on the populated coast with speed of 800-900 kilometers per hour.

For tsunami predictions today two devices are used:

• seismograph- signals about tremors;
• tide gauge- detects water level fluctuations.

This makes it possible to predict the occurrence of a tsunami (although not always accurately) and to evacuate people.

Pacific Ocean not quiet at all. Exactly here more often just happen tsunami. They easily destroy both thatched huts and concrete skyscrapers. But tsunamis are also a very interesting phenomenon. :

1. First, who tied up occurrence tsunami with underground processes, was Greek Thucydides.
2. long lost the capital once mighty kingdom - Mamallapuram city, opened the tsunami in the Indian Ocean.
3. Some scientists believe that 3.5 million years ago meteorite fall Led to tsunami, which and destroyed all life on earth.
4. Palm trees withstand tsunami impacts.
5. Tsunami can poison fresh water and soil.

Tsunami is a phenomenon that fascinates. And as scientists say in the near future, this cataclysm will occur more often. The reason is global warming and melting glaciers.