Causes of a tsunami

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.

On fig. 1 shows a diagram of folded mountain systems and areas of concentration of earthquake epicenters. This diagram clearly identifies two areas of the globe that are most prone to earthquakes. 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.

The immediate cause of 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 at the bottom of the sea 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 sea depth at the place of the break 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.

On fig. Figure 2a shows the mechanism of tsunami generation 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 bottom, the hearth rushes to the 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 revealed. 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 crests of which is 100–300 km, and the height when the waves approach the shore reaches 30 m or more.

Another cause of tsunamis is volcanic eruptions rising above the sea surface in the form of islands or located on the ocean floor (Fig. 2b). 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 washed away, and fishing boats are abandoned on land at a distance of several kilometers from the ocean coast. 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. AT Atlantic Ocean they reached the Isthmus of Panama, and in the Pacific Ocean - Alaska and San Francisco.

Cases of tsunamis during volcanic eruptions are also known in Japan. So, on September 23 and 24, 1952, there was a strong eruption of an underwater volcano on the Meijin reef, several hundred kilometers from Tokyo. The resulting waves reached the island of Khotidze to the northeast of the volcano. During this disaster, the Japanese hydrographic vessel Kaie-Maru-5, from which observations were carried out, perished.

The third reason for the occurrence of a tsunami is the fall of huge rock fragments 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 broke off from a height of 200 m, which caused the emergence of a single wave 15 m high.

Tsunami off the coast South America

The Pacific coast within Peru and Chile is prone to frequent earthquakes. Changes in the topography of the bottom of the coastal part of the Pacific Ocean lead to the formation of large tsunamis. highest height(27 m) tsunami waves reached the Callao region during the Lima earthquake in 1746.

If usually the lowering of the sea level, which precedes the onset of tsunami waves on the coast, lasts from 5 to 35 minutes, then during the earthquake in Pisco (Peru), the receding sea waters returned only after three hours, and at Santa even after a day.

Often, the advance and retreat of tsunami waves occur here several times in a row. So, in Iquique (Peru) on May 9, 1877, the first wave hit the coast half an hour after the main shock of the earthquake, and then within four hours the waves attacked five more times. During this earthquake, the epicenter of which was located 90 km from the Peruvian coast, tsunami waves reached the coasts of New Zealand and Japan.

On August 13, 1868, on the coast of Peru in Arica, 20 minutes after the start of the earthquake, a wave of several meters high surged, but soon receded. With an interval of a quarter of an hour, it was followed by several more waves, smaller in size. After 12.5 hours, the first wave reached the Hawaiian Islands, and after 19 hours - the coast of New Zealand, where 25,000 people became its victims. average speed tsunami waves between Arica and Valdivia at a depth of 2200 m was 145 m/s, between Arica and Hawaii at a depth of 5200 m - 170-220 m/s, and between Arica and the Chatam Islands at a depth of 2700 m - 160 m/s.

The most frequent and strongest earthquakes characterize the area of ​​the Chilean coast from Cape Concepcion to the island of Chiloe. It is known that since the catastrophe of 1562, the city of Concepción suffered 12 strong earthquakes, and the city of Valdivia suffered 7 earthquakes during the period from 1575 to 1907. During the earthquake on January 24, 1939, 1,000 people died in and around Concepción and 70,000 people were left homeless.

The destruction caused by the 1960 tsunami waves in the city of Puerto Monte

On May 21, 1960, a new earthquake shook the Chilean coast near Cape Concepción, and then shook the entire southern part of the country for 1,500 km for 10 days. During this time, about a thousand people died and about 350,000 people were left homeless. In the cities of Concepcion, Puerto Monte, Temuco and the island of Chiloe, 65,000 buildings were completely destroyed and 80,000 seriously damaged. The strongest shock was on May 22, when the maximum amplitude of soil vibration in Moscow was 1500 microns. This is three times the amplitude of the oscillations caused by the 1948 Ashgabat earthquake, whose epicenter was located six times closer to Moscow.

The catastrophic shaking on May 22 gave rise to tsunami waves that propagated across the Pacific Ocean and beyond at a speed of 650-700 km/h. On the Chilean coast, fishing villages and port facilities were destroyed; hundreds of people were swept away by the waves. On the island of Chiloe, waves destroyed four-fifths of all buildings.

Aftermath of the 1960 tsunami in the Hawaiian Islands

The giant shaft not only devastated the Pacific coast as far as California, but also crossed the Pacific Ocean, hitting Hawaii and the Philippines, the coast of Australia and New Zealand, the Kuril Islands and Kamchatka. In Hawaii, in the city of Hilo, dozens of people died during the tsunami, many residents were missing and injured.

Aftermath of the 1960 tsunami off the coast of Japan

On the Japanese islands, 36,000 houses were flooded, 900 ships and fishing boats were capsized. On the island of Okinawa, 180 people died or went missing, and 150 people died in the village of Momoishi. It has never been noted that tsunami waves, having covered such a huge distance, retained their destructive power.

At about 6 am on May 24, the tsunami waves, having traveled 16,000 km, reached the Kuril Islands and the shores of Kamchatka. A wave of five meters high rushed to the shore. However, measures to evacuate the population were taken in a timely manner and there were no human casualties. On the island of Paramushir, where the ramparts were the highest, the berths of the local fishing collective farm were slightly damaged.

Tsunami off the coast of Japan

Tsunamis usually accompany the most powerful, catastrophic earthquakes that occur on the Japanese islands on average every seven years. Volcanic eruptions can be called another reason for the formation of a tsunami off the coast of Japan. It is known, for example, that as a result of a volcanic explosion on one of the Japanese islands in 1792, rocks with a volume of about 1 cubic meter were thrown into the sea. km. A sea wave about 9 m high, formed as a result of falling into the sea of ​​the eruption products, demolished several coastal villages and brought the death of more than 15,000 inhabitants.

The tsunami during the earthquake of 1854, which destroyed Largest cities countries are Tokyo and Kyoto. First, a wave of nine meters high came to the shore. However, she soon receded, draining the coast for long distance. Over the next 4-5 hours, another five or six large waves hit the shore. And after 12.5 hours, the tsunami waves, moving at a speed of more than 600 km / h, reached the coast of North America in the San Francisco area.

After this formidable catastrophe, stone walls were erected in some parts of the coast of the island of Honshu to protect the coast from destructive waves. However, despite the precautions taken, during the earthquake on June 15, 1896, the island of Honshu was again badly damaged by devastating waves. An hour after the earthquake began, six to seven large waves hit the coast at intervals of 7 to 34 minutes, the maximum height of one of which was 30 m. The waves completely washed away the city of Minco, destroyed 10,000 buildings and brought the death of 27,000 people. And 10 years later, during the earthquake of 1906, about 30,000 people died again on the east coast of the country during the onset of a tsunami.

During the well-known catastrophic earthquake of 1923, which completely destroyed the Japanese capital, tsunami waves devastated the coast, although they did not reach especially large sizes, at least in Tokyo Bay. In the southern regions of the country, the consequences of the tsunami were even more significant: several villages in this part of the coast were completely washed away, and the Japanese naval base Yokosuka, located 12 km south of Yokohama, was destroyed. The city of Kamakura, located on the shores of Sagami Bay, was also badly damaged by sea waves.

On March 3, 1933, 10 years after the 1923 earthquake, a new strong earthquake hit Japan, not much inferior to the previous one. Tremors swept the entire eastern part of the island of Honshu. The greatest disasters of the population during this earthquake were associated with the onset of tsunami waves that swept the entire northeastern coast of Honshu 40 minutes after the earthquake began. The wave destroyed the port city of Komaishi, where 1,200 houses were destroyed. Big number villages on the coast were demolished. According to newspaper reports, about 3,000 people died and went missing during this disaster. In total, more than 4,500 houses were destroyed by the earthquake and washed away by waves, and more than 6,600 houses were partially damaged. More than 50,000 people were left homeless.

Destruction in the city of Komami after the tsunami in March 1933

Tsunami off the Pacific coast of Russia

The shores of Kamchatka and the Kuril Islands are also subject to tsunamis. Initial information about catastrophic waves in these places dates back to 1737. A well-known domestic traveler-geographer wrote: “... the shaking began and continued in waves for about a quarter of an hour so strongly that many Kamchadal yurts collapsed and booths fell. Meanwhile, there was a terrible noise and excitement at sea, and suddenly it surged onto the shore of water three sazhens high, which, without even standing, ran into the sea and moved away from the coast to a considerable distance. Then the earth shook a second time, the waters came against the former, but at low tide it ran so far that it was impossible to see the sea. At the same time, rocky mountains appeared at the bottom of the sea in the strait between the first and second Kuril Islands, which had never been seen before, although earthquakes and floods had occurred before.

A quarter of an hour after all this, shocks of a terrible earthquake, incomparable in its strength, followed, and then a wave of thirty fathoms high rushed onto the shore, which, as before, quickly ran back. Soon the water entered its shores, oscillating at long intervals, sometimes covering the shores, sometimes escaping into the sea.

During this earthquake, massive rocks collapsed, the oncoming wave threw blocks of stone weighing several pounds onto the shore. The earthquake was accompanied by various optical phenomena in the atmosphere. In particular, the abbe Prevost, another traveler who observed this earthquake, wrote that fiery "meteors" could be seen on the sea, scattered over a large area.

noticed all the most important features of a tsunami: an earthquake, a lowering of the ocean level preceding the flood, and, finally, the onset of huge destructive waves.

Grandiose tsunamis on the coasts of Kamchatka and the Kuriles took place in 1792, 1841, 1843, 1918. A whole series of earthquakes during the winter of 1923 caused repeated attacks of catastrophic waves. A description of the tsunami on February 4, 1923 is known, when “three waves rushed to the land of the eastern coast of Kamchatka one after another, tore off the coastal ice (fast ice as thick as a fathom), moved along with it over the coastal spit, flooded low places. Ice on a low place near Semyachik turned out to be thrown out almost 1 verst 400 sazhens from the coast; on the hills, the ice remained at a height of three sazhens above sea level. In the sparsely populated areas of the east coast, this unprecedented phenomenon caused some damage and destruction. natural disaster a vast coastal zone with a length of 450 km was covered.

On April 13, 1923, renewed tremors caused tsunami waves up to 11 m high, which completely destroyed the coastal buildings of fish canning plants, some of which were cut off by hummocky ice.

Strong tsunamis were noted on the coast of Kamchatka and the Kuril Islands in 1927, 1939 and 1940.

On November 5, 1952, an earthquake occurred on the eastern coast of Kamchatka and the Kuril Islands, reaching 10 points and accompanied by an exceptional tsunami in its consequences, which caused severe destruction in Severo-Kurilsk. It started at 3:57 local time. At 04:24, i.e., 26 minutes after the start of the earthquake, the ocean level quickly dropped and in some places the water receded from the coast by 500 m. Then strong tsunami waves hit the coast of Kamchatka from Sarychev Island to the Kronotsky Peninsula. Later, they reached the Kuril Islands, capturing a strip of coastline about 800 km long. The first wave was followed by a second, even stronger one. After her arrival on the island of Paramushir, all buildings located no higher than 10 m above sea level were destroyed.

One of the houses in the city of Severo-Kurilsk, carried by a wave to the port part of the city during the tsunami in November 1952

Tsunami in the Hawaiian Islands

The coasts of the Hawaiian Islands are often subject to tsunamis. In the last half century alone, destructive waves have hit the archipelago 17 times. The tsunami in Hawaii in April 1946 was very powerful.

From the area of ​​the epicenter of the earthquake in the area of ​​Unimak Island (Aleutian Islands), the waves moved at a speed of 749 km/h. The distance between the crests of the waves reached about 150 km. The well-known American oceanologist, who witnessed this natural disaster, F. Shepard noted a gradual increase in the height of the waves that hit the shore with an interval of 20 minutes. The tide gauge readings were successively 4, 5, 2 and 6.8 m above the tide level.

The damage caused by the sudden onset of the waves was very great. Much of the city of Hilo on the island of Hawaii was destroyed. Part of the houses collapsed, others were carried by water over a distance of more than 30 m. The streets and embankments were cluttered with debris, blocked off by barricades of warped cars; here and there rose the ugly wrecks of small ships, abandoned by the waves. Bridges and railways were destroyed. On the coastal plain, among the crumpled, uprooted vegetation, numerous blocks of corals were scattered, and the corpses of people and animals were visible. The disaster claimed 150 human lives and caused a loss of $25 million. This time, the waves reached the shores of North and South America at prices, while the largest wave was noted near the epicenter - in the western part of the Aleutian Islands. The lighthouse Scotu-cap, which stood at an altitude of 13.7 m above sea level, was destroyed, and the radio mast was also demolished.

A boat washed ashore during the tsunami in 1946 in the Hawaiian Islands

Application

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Rice. Fig. 2. Scheme of the occurrence of tsunami waves during the displacement of a section of the seabed (a) and during an underwater eruption (b)

Literature:

1. Tsunami. - Leningrad: 1964

2. Seismic sea waves prices. - Leningrad: 1981

3. Understand the prices. - Leningrad: 1965

4. The tsunami problem. Digest of articles. - M.: 1968

5. , Go tsunami on the East Pacific coast. - M.: 1975

6. , Go tsunami on the west coast of the Pacific Ocean. - M.: 1974

A tide gauge is a device that records fluctuations in sea level.

Huge waves, reaching a height of tens of meters and falling with terrible force on the coast, are called tsunami. The name comes from a Japanese phrase. It is denoted by two hieroglyphs and means in translation: "a big wave flooding the bay." In reality, the wave is not just big, it is gigantic. Its height can reach up to 30-40 meters, and it can cover the land for many kilometers. At the same time, the element sweeps away everything in its path. People and animals are dying, houses are being destroyed, utility networks are being mutilated and destroyed, and the fertile layer of soil is being washed away.

Human casualties can reach tens of thousands of people, since such catastrophes do not know pity, while material losses are incalculable. But no less terrible is the grief of those who lost their loved ones in this terrible natural disaster. The consequences of the tsunami are so terrible that they tremble the entire planet, and another disaster is entered into the historical annals of the world's greatest tragedies.

Causes of a tsunami

There are several reasons for the occurrence of huge waves.. The most basic, which causes up to 85% of all tsunamis - underwater earthquakes, during which there are sharp fluctuations in the seabed. The huge energy released in this case is transferred to the water column. The oceanic masses begin to revolt and scatter in waves from the epicenter of the earthquake.

Killer Wave Behavior

In the vast expanses of the sea, such waves are almost imperceptible. They have a flat shape, with a height not exceeding one meter and a length reaching hundreds of kilometers. The energy in such a wave is dispersed over a huge area, and even a fragile boat will not feel all the strength and power that will pass under it.

These fluctuations in the aquatic environment propagate at great speed. It can be equal to 500, and 700, and even 1000 km / h - it all depends on the thickness sea ​​water. When approaching the shore, the depth decreases, the speed decreases accordingly and the wavelength shortens. Its height begins to grow rapidly. It turns into a huge water shaft, which with a roar falls on the coastal zone. These thousands and thousands of tons of raging elements sweep away everything in their path.

Tsunami near the coast

Having done its terrible job and wasting all its energy, the ocean exhaustedly crawls away from the land, calms down, accumulates strength - this can last for 20, and 40, and 60 minutes. But here the coastal water begins to slowly recede from the shore, exposing an uneven muddy bottom. The surrounding tormented world anxiously freezes in anticipation of something terrible and bad. Silence thickens, the air is filled with anxiety, turning into horror.

In the sea distance, a second, even larger wave of water begins to grow. It expands before our eyes, closes the horizon, breaking the silence with a terrible roar, collapses onto the earth's firmament, finishing the terrible deed begun by the first wave. Deadly energy destroys everything that is still alive, kills everything that is still alive. Plenty of fun with their impunity and permissiveness, the elements are leaving, but the end of this horror is still far away.

An hour or so passes, and the long-suffering earth takes the third terrible blow. The nightmare can go on for five or six hours. Only after this time has passed, having fully satisfied its basest instincts, does the ocean calm down. Having spent all the negativity, the marine environment before our eyes turns into a quiet, gentle, gentle and obedient blue expanse of water. Only the mutilated land reminds of the horror experienced, on which uprooted trees are scattered in disarray, the remains of houses are scattered, roads and flowering gardens are destroyed.

After the tsunami

Tsunami in the Pacific Ocean

This is the picture of this terrible natural phenomenon, which appeared when the oceans arose. In general, a terrible cataclysm occurs in different coastal zones 6-7 times a century. But these are large tsunamis. Small ones are ten times more common. Most of all, the waters of the Pacific Ocean gravitate towards the terrible killer waves, since the bottom of this huge reservoir is cut by numerous gutters and faults, like deep wounds.

It is in these places that the various tectonic plates come into contact. Geological processes are going on here continuously, and hence the increased seismic activity. The western peripheral zone of the Pacific Ocean poses a great danger. The untrustworthy Kuril-Kamchatka Trench and the Japanese Trench are located here. To the north is the Aleutian Trench, whose behavior also leaves much to be desired.

In the east of the Great Ocean, the Peruvian-Chile Trench sets the tone, simply terrorizing the waters of South America. In the southern part of a huge body of water, north of New Zealand, the Kermadec trough stretched out straight as an arrow, bursting with seismically active processes. Well, off the eastern coast of North America, exactly along cloudy California, there are as many as five faults. Completes this far from optimistic picture of the Central American Trench, which can be considered native to Mexico, Guatemala and El Salvador.

The earth's crust in places of faults and trenches is constantly shaking, so earthquakes are frequent guests in these areas. But not every one of them is capable of generating a tsunami. To move huge masses of water, titanic energy is needed. This can only be provided by very strong uplifts and subsidences of the seabed. On the twelve-point Richter scale, this is a magnitude of 7 or more. It can only be higher than 9 points, there are no large magnitudes on Earth, so shocks of such strength are quite rare.

Otherwise, huge killer waves would feverish the coastal zone as often as a change in wind direction or seasonal fluctuations temperatures. True, small tsunamis often appear along various coasts. But the supply of their energy is so negligible that they cannot cause serious harm with all their desire. It is in their power to really spoil the nerves, upset someone because of the loss of a fishing boat or boat, but such situations, as a rule, arise due to absent-mindedness or inattention of the people themselves.

Tsunami in Japan

The height of the terrible waves largely depends on the shape and topography of the coastline. The wave comes in a wide front and in those places where a steep coast or a bay deeply cutting into the land, the roaring shaft reaches its maximum height. If you are in a closed bay, then you can not even guess that just a few kilometers from this place everything collapses and dies.

Landslides and underwater eruptions

Another reason for the occurrence of killer waves is such a geological process as landslides.. In terrestrial conditions, this is a common thing when a large mass of rocks slides down the slope of a valley or river bank. Such a movement can last for decades, or it can start unexpectedly, take place rapidly and end in a short time. Piles of earth slide into a valley or into a river, causing some damage to the environment.

Similar processes take place on the seabed, since there are no less mountains and hills than on land. Sedimentary rocks accumulate on the slopes of underwater mountain ranges. Over time, their mass becomes critical, and they collapse down, creating vibrations in the surrounding aquatic environment. If there is enough energy, then a tsunami will arise, which in size may not be inferior to a similar wave formed by an earthquake.

Due to the fault of landslides, such waves appear on the sea surface much less frequently. From total number tsunami is only 7%. Even rarer (5%) tsunamis are caused by volcanic eruptions. It also releases a huge amount of energy that can disturb the thickness of the ocean waters. In these cases, the wave can be even more powerful than during earthquakes, since additional energy is absorbed when it comes into contact with magma.

Here are perhaps all the main reasons that give rise to terrible waves and tremble the huge masses of people who, by the will of fate, are forced to live in coastal zones. As for the opposition to this element, then the picture is very pessimistic. The determining factor here is timely notification of the population about an impending disaster. Forewarned is forearmed. This famous saying is universal, guided by it, you can save many, many lives.

Ships washed ashore by the tsunami

Preventive measures

Today it is known that killer waves are always the result of an earthquake. To fix powerful underwater tremors in time means with sufficient probability to predict the appearance of huge waves off the coast. True, the notification of areas inhabited by people should be instantaneous. After all, the perturbation of the aquatic environment spreads with great speed and in half an hour can move hundreds of kilometers away from the epicenter of the earthquake.

Given the causes of tsunamis, many states pay great attention to the creation of seismic stations in those places where active geological processes are taking place. The International Service for Warning the Population of an Imminent Catastrophe has been formed. Its centers are located on the island of Oahu in the suburbs of Honolulu and on six other islands of the Hawaiian archipelago. Employees are on duty here around the clock, processing information from dozens of seismic stations scattered across the Pacific Ocean.

In the event of a suspected tsunami, huge areas are immediately notified, plans to mobilize the population from dangerous zones come into force. Fortunately, in most of these cases, huge waves do not occur. Given the peculiarities of the human psyche, the medal also has a reverse side. Frequent unreasonable alarms lead to the fact that people gradually become discouraged, they begin to ignore messages about danger. The element is very insidious and is only waiting for a person to relax and lose caution.

How to behave during a disaster

In any case, no matter how frequent reports of an impending disaster are, it is better not to look at careless people, but to rely only on your common sense and sense of self-preservation. The first sign of tragedy is the disappearance of water near the shore. The ocean is slowly moving away from the coastal zone, preparing to deliver a powerful blow. If this happened - there is no doubt that the killer wave is already close. After that, there is nothing to think about and hope for a chance. Procrastination is like death.

You need to immediately pick up children, documents, money and leave or leave as far from the coast as possible. It is strictly forbidden to move inland along the riverbed - it is necessary to keep from it at the maximum possible distance. The best option is to climb to a distant hill. This will be the safest place in the coastal zone. The most optimal thing is to move away from the coastline for several kilometers: even very high waves are unlikely to reach the mark of five or more thousand meters from the ocean boundary.

But ships or yachts, peacefully dozing in the roadstead, when a tsunami approaches, have only one way out - they need to immediately weigh anchor and go into the open ocean. As paradoxical as it sounds, they must rush at full speed towards the terrible wave. In open sea spaces, it is almost imperceptible, and gains power, strength and height only near the coast.

All of the above are not empty words, but quite real guide to action. Tsunami is a terrible force. Only those who do not value their lives can underestimate it. Numerous historical facts serve as clear evidence of this.

History reference

Terrible waves crashed on the earth's firmament in all ages, but the first detailed description, with an attempt scientific justification, this catastrophe was given by the great Spanish historian and geographer, a member of the Jesuit order, José de Acosta (1539-1600). Just before leaving for Spain in 1586, fate gave him the opportunity to observe a killer wave in Peru. It was a terrible sight when, after a strong earthquake, a 25-meter-high water shaft hit the capital of Lima. He broke into the depths of the land for 10 km, having done trouble hundreds of times more than the most cruel invaders would have done.

Krakatoa volcano eruption

Volcano Krakatoa

Truly monstrous were the consequences caused by the tsunami that arose as a result of the eruption Krakatoa volcano in 1883. At that time, this name was not given to an active volcano on the island of Rakita, but to an island of quite decent size located in the Sunda Strait, between the islands of Sumatra and Java.

The volcanic eruption on this island began in May 1883. It lasted until the end of August and represented strong ejections of magma and gas from the bowels of the earth following one after another. Logically, over time, the intensity and strength of the emissions should have weakened. But in this case, events began to develop according to a different scenario.

The volcano became more and more inflamed, gradually falling into uncontrollable ecstasy. In the end, on a cloudy and gloomy morning on August 27, an explosion of terrible force occurred. A huge column of ash soared into the air to a crazy height of 30 km. After that, having apparently exhausted all its magmatic energy, the volcano subsided exhaustedly. One could breathe easy, but it was the calm before the storm.

The fact is that a void of enormous volume and area formed under the volcano, since all the rock deposited here was thrown into the atmosphere. Everything would be nothing, but this empty space was much lower than the level of the oceans. Innumerable tons of water began to press on the thin walls left without support. The problem was aggravated by the island's firmament, which now simply hung in the air.

The climax came the next day in August. The walls of the empty underground chamber of the volcano could not withstand the terrible loads. Cracks ran across the surface of the island: rocky rocks collapsed down. Sea water rushed into the openings, widening its passage, with a roar.

In fact, it turned out an open wound in the earth's crust. The red-hot magma, located deep below, entered into interaction with a cold liquid medium. The result was a terrible explosion, the shock wave from which spread over 300 km, breaking trees on the islands, demolishing roofs of houses, maiming animals and people. The roar of the explosion was heard at a distance of 4 thousand km.

Location of Krakatoa volcano on the map

Even worse than the shock wave was a huge tsunami, the height of which reached 30 meters. She hit the shores of Indonesia with frenzied fury, the coastline of Southeast Asia experienced her strength. The killer wave reached the western coast of Australia, with a roar hit the shores of the island of Ceylon and the eastern coast of the Hindustan peninsula. Its echoes have recognized the island of Madagascar and the entire east coast of Africa.

Due to the killer wave, 48 thousand people died. The vast coastal areas were mutilated beyond recognition. Tens of thousands of people were left homeless. The tragedy of the island of Krakatoa has written another bloody page in the history of world catastrophes.

Killer waves in the 20th century

The twentieth century tried to keep up with previous centuries in terms of the number of tsunamis. In November 1952, 150 km. an earthquake measuring 8.5 on the Richter scale occurred off the coast of Kamchatka. As a result, a perturbation of the aquatic environment arose. Giant waves, the height of which reached 20 meters, swept the city of Severo-Kurilsk off the face of the earth. Nearby settlements were also destroyed. According to the most conservative estimate, 3,000 people died.

Throughout the second half of the 20th century, Alaska fought off terrible waves. In total, there were about ten tsunamis here, while there were three large ones that caused human casualties and destruction. Became a victim of evil rock and New Guinea. In 1998, a huge wave caused the death of one and a half thousand people.

Killer waves in the 21st century

The beginning of the 21st century was marked by killer waves together with all of humanity. True, they were exactly 4 years late, but they compensated for this with human casualties. This tragedy happened at the end of December 2004. As a result of a strong earthquake (8.5 on the Richter scale), a giant wave arose that hit the shores of Thailand, Sri Lanka and Myanmar. The number of victims exceeded 200 thousand people.

In 2007, in the Solomon Islands, located east of New Guinea, a huge wave, the height of which reached 12 meters, destroyed many residential buildings, causing great damage to people. In this wave, 48 people found their death.

The terrible tragedies associated with the tsunami will apparently continue until the leaping forward scientific and technological progress comes up with effective ways fight them. It is clear that this is a matter of the distant future, but in our time only those who live in the depths of the continents can sleep peacefully, and do not appear on the coasts of the oceans at all or go there no more than once a year.

Taking into account the fact that 85% of the entire population of the planet have chosen the coastal zones of the oceans and seas, this problem is very acute for all mankind. In this situation, one can only hope for the composure, attentiveness and mobility of people, as well as the clear and well-functioning work of warning services.

By the way, when in January 2005 a powerful earthquake occurred dangerously close to the Izu Islands (Japan), the population managed to evacuate in time, not a single person was injured. Well, what can I say - the Japanese are again ahead of the rest.

The article was written by ridar-shakin

Based on materials from foreign and Russian publications

18.07.2018 20:16 1627

A tsunami is a wave that reaches very large sizes. It appears far in the ocean and moves towards the shore at high speed. The word tsunami means "wave in the harbor" in Japanese. The Japanese name came from the fact that Japan is most often affected by this natural phenomenon.

There are several reasons for these terrible and dangerous waves. Most often, tsunamis occur as a result of underwater earthquakes. At the same time, the water level rises sharply due to the displacement of the seabed. Unlike ordinary waves, when a tsunami occurs, the entire water column is involved, and not just the surface of the sea.

In addition to underwater earthquakes, tsunamis can cause landslides and underwater volcano eruptions.

The incident that led to the occurrence of a tsunami due to a landslide occurred in Alaska in 1958. Huge masses of earth and ice fell into the water from a great height. As a result, a giant wave was formed, the height of which reached 500 meters near the shore!

When an underwater volcano erupts, an explosion occurs, which also contributes to the oscillation of the water and the formation of large waves.

If you guys lightly touch a glass or bucket filled with water, you will see how small ripples form on the water surface. The same effect occurs when a tsunami appears, only the strength of the wave is much greater.

A tsunami moves at a speed of 50 to 1000 km/h. Its height can reach 50 meters or more! The closer the wave approaches the shore, the larger it becomes. This is due to the fact that the coast is shallower. The consequences of this natural disaster are dire. Tsunami waves hit coastal areas with terrible force and demolish everything in their path.

To combat the elements in some countries, including Russia, tsunami warning services have been created. They study the situation of seismic activity (the danger of an earthquake) and, in the event of a tsunami, notify the population about this so that people can get away from the sea to a safe distance.

Most often, tsunamis occur in the waters of the Pacific Ocean. Many underwater volcanoes are concentrated at its bottom and earthquakes occur in these places.

Causes of a tsunami
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.
The immediate cause 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 at the bottom of the sea 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 sea depth at the place of the break 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.
Another cause of tsunamis is volcanic eruptions rising above the sea surface in the form of islands or located on the ocean floor (Fig. 2b). 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 shore. 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.
Cases of tsunamis during volcanic eruptions are also known in Japan. So, on September 23 and 24, 1952, there was a strong eruption of an underwater volcano on the Meijin reef, several hundred kilometers from Tokyo. The resulting waves reached the island of Khotidze to the northeast of the volcano. During this disaster, the Japanese hydrographic vessel Kaie-Maru-5, from which observations were carried out, perished.
The third reason for the occurrence of a tsunami is the fall of huge rock fragments 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 broke off from a height of 200 m, which caused the emergence of a single wave 15 m high.
Tsunami off the coast of South America
The Pacific coast within Peru and Chile is prone to frequent earthquakes. Changes in the topography of the bottom of the coastal part of the Pacific Ocean lead to the formation of large tsunamis. The greatest height (27 m) of the tsunami wave reached in the Callao region during the earthquake in Lima in 1746.
If usually the lowering of the sea level, which precedes the onset of tsunami waves on the coast, lasts from 5 to 35 minutes, then during the earthquake in Pisco (Peru), the receding sea waters returned only after three hours, and at Santa even after a day.
Often, the advance and retreat of tsunami waves occur here several times in a row. So, in Iquique (Peru) on May 9, 1877, the first wave hit the coast half an hour after the main shock of the earthquake, and then within four hours the waves attacked five more times. During this earthquake, the epicenter of which was located 90 km from the Peruvian coast, tsunami waves reached the coasts of New Zealand and Japan.
On August 13, 1868, on the coast of Peru in Arica, 20 minutes after the start of the earthquake, a wave of several meters high surged, but soon receded. With an interval of a quarter of an hour, it was followed by several more waves, smaller in size. After 12.5 hours, the first wave reached the Hawaiian Islands, and after 19 hours - the coast of New Zealand, where 25,000 people became its victims. The average speed of tsunami waves between Arica and Valdivia at a depth of 2200 m was 145 m/s, between Arica and Hawaii at a depth of 5200 m - 170-220 m/s, and between Arica and the Chatam Islands at a depth of 2700 m - 160 m/s.
The most frequent and strongest earthquakes characterize the area of ​​the Chilean coast from Cape Concepcion to the island of Chiloe. It is known that since the catastrophe of 1562, the city of Concepción suffered 12 strong earthquakes, and the city of Valdivia suffered 7 earthquakes during the period from 1575 to 1907. During the earthquake on January 24, 1939, 1,000 people died in and around Concepción and 70,000 people were left homeless.

The destruction caused by the 1960 tsunami waves in the city of Puerto Monte
On May 21, 1960, a new earthquake shook the Chilean coast near Cape Concepción, and then shook the entire southern part of the country for 1,500 km for 10 days. During this time, about a thousand people died and about 350,000 people were left homeless. In the cities of Concepcion, Puerto Monte, Temuco and the island of Chiloe, 65,000 buildings were completely destroyed and 80,000 seriously damaged. The strongest shock was on May 22, when the maximum amplitude of soil vibration in Moscow was 1500 microns. This is three times the amplitude of the oscillations caused by the 1948 Ashgabat earthquake, whose epicenter was located six times closer to Moscow.
The catastrophic shaking on May 22 gave rise to tsunami waves that propagated across the Pacific Ocean and beyond at a speed of 650-700 km/h. On the Chilean coast, fishing villages and port facilities were destroyed; hundreds of people were swept away by the waves. On the island of Chiloe, waves destroyed four-fifths of all buildings.

Aftermath of the 1960 tsunami in the Hawaiian Islands
The giant shaft not only devastated the Pacific coast as far as California, but also crossed the Pacific Ocean, hitting Hawaii and the Philippines, the coast of Australia and New Zealand, the Kuril Islands and Kamchatka. In Hawaii, in the city of Hilo, dozens of people died during the tsunami, many residents were missing and injured.
Aftermath of the 1960 tsunami off the coast of Japan
On the Japanese islands, 36,000 houses were flooded, 900 ships and fishing boats were capsized. On the island of Okinawa, 180 people died or went missing, and 150 people died in the village of Momoishi. It has never been noted that tsunami waves, having covered such a huge distance, retained their destructive power.
At about 6 am on May 24, the tsunami waves, having traveled 16,000 km, reached the Kuril Islands and the shores of Kamchatka. A wave of five meters high rushed to the shore. However, measures to evacuate the population were taken in a timely manner and there were no human casualties. On the island of Paramushir, where the ramparts were the highest, the berths of the local fishing collective farm were slightly damaged.
Tsunami off the coast of Japan
Tsunamis usually accompany the most powerful, catastrophic earthquakes that occur on the Japanese islands on average every seven years. Volcanic eruptions can be called another reason for the formation of a tsunami off the coast of Japan. It is known, for example, that as a result of a volcanic explosion on one of the Japanese islands in 1792, rocks with a volume of about 1 cubic meter were thrown into the sea. km. A sea wave about 9 m high, formed as a result of falling into the sea of ​​the eruption products, demolished several coastal villages and brought the death of more than 15,000 inhabitants.
The tsunami during the earthquake of 1854, which destroyed the country's largest cities - Tokyo and Kyoto, was especially powerful. First, a wave of nine meters high came to the shore. However, it soon receded, draining the coast at a great distance. Over the next 4-5 hours, another five or six large waves hit the shore. And after 12.5 hours, the tsunami waves, moving at a speed of more than 600 km / h, reached the coast of North America in the San Francisco area.
After this formidable catastrophe, stone walls were erected in some parts of the coast of the island of Honshu to protect the coast from destructive waves. However, despite the precautions taken, during the earthquake on June 15, 1896, the island of Honshu was again badly damaged by devastating waves. An hour after the earthquake began, six to seven large waves hit the coast at intervals of 7 to 34 minutes, the maximum height of one of which was 30 m. The waves completely washed away the city of Minco, destroyed 10,000 buildings and brought the death of 27,000 people. And 10 years later, during the earthquake of 1906, about 30,000 people died again on the east coast of the country during the onset of a tsunami.
During the famous catastrophic earthquake of 1923, which completely destroyed the Japanese capital, tsunami waves devastated the coast, although they did not reach particularly large sizes, at least in Tokyo Bay. In the southern regions of the country, the consequences of the tsunami were even more significant: several villages in this part of the coast were completely washed away, and the Japanese naval base Yokosuka, located 12 km south of Yokohama, was destroyed. The city of Kamakura, located on the shores of Sagami Bay, was also badly damaged by sea waves.
On March 3, 1933, 10 years after the 1923 earthquake, a new strong earthquake hit Japan, not much inferior to the previous one. Tremors swept the entire eastern part of the island of Honshu. The greatest disasters of the population during this earthquake were associated with the onset of tsunami waves that swept the entire northeastern coast of Honshu 40 minutes after the earthquake began. The wave destroyed the port city of Komaishi, where 1,200 houses were destroyed. A large number of villages along the coast were demolished. According to newspaper reports, about 3,000 people died and went missing during this disaster. In total, more than 4,500 houses were destroyed by the earthquake and washed away by waves, and more than 6,600 houses were partially damaged. More than 50,000 people were left homeless.

Destruction in the city of Komami after the tsunami in March 1933
Tsunami off the Pacific coast of Russia
The shores of Kamchatka and the Kuril Islands are also subject to tsunamis. Initial information about catastrophic waves in these places dates back to 1737. The well-known domestic traveler and geographer S.P. Krasheninnikov wrote: “... the shaking began and continued in waves for about a quarter of an hour so strongly that many Kamchadal yurts collapsed and booths fell. Meanwhile, there was a terrible noise and excitement at sea, and suddenly it surged onto the shore of water three sazhens high, which, without even standing, ran into the sea and moved away from the coast to a considerable distance. Then the earth shook a second time, the waters came against the former, but at low tide it ran so far that it was impossible to see the sea. At the same time, rocky mountains appeared at the bottom of the sea in the strait between the first and second Kuril Islands, which had never been seen before, although earthquakes and floods had occurred before.
A quarter of an hour after all this, shocks of a terrible earthquake, incomparable in its strength, followed, and then a wave of thirty fathoms high rushed onto the shore, which, as before, quickly ran back. Soon the water entered its shores, oscillating at long intervals, sometimes covering the shores, sometimes escaping into the sea.
During this earthquake, massive rocks collapsed, the oncoming wave threw blocks of stone weighing several pounds onto the shore. The earthquake was accompanied by various optical phenomena in the atmosphere. In particular, the abbe Prevost, another traveler who observed this earthquake, wrote that fiery "meteors" could be seen on the sea, scattered over a large area.
S. P. Krasheninnikov noticed all the most important features of a tsunami: an earthquake, a lowering of the ocean level preceding the flood, and, finally, the onset of huge destructive waves.
Grandiose tsunamis on the coasts of Kamchatka and the Kuriles took place in 1792, 1841, 1843, 1918. A whole series of earthquakes during the winter of 1923 caused repeated attacks of catastrophic waves. A description of the tsunami on February 4, 1923 is known, when “three waves rushed to the land of the eastern coast of Kamchatka one after another, tore off the coastal ice (fast ice as thick as a fathom), moved along with it over the coastal spit, flooded low places. Ice on a low place near Semyachik turned out to be thrown out almost 1 verst 400 sazhens from the coast; on the hills, the ice remained at a height of three sazhens above sea level. In the sparsely populated areas of the east coast, this unprecedented phenomenon caused some damage and destruction. The natural disaster covered a vast coastal zone with a length of 450 km.
On April 13, 1923, renewed tremors caused tsunami waves up to 11 m high, which completely destroyed the coastal buildings of fish canning plants, some of which were cut off by hummocky ice.
Strong tsunamis were noted on the coast of Kamchatka and the Kuril Islands in 1927, 1939 and 1940.
On November 5, 1952, an earthquake occurred on the eastern coast of Kamchatka and the Kuril Islands, reaching 10 points and accompanied by an exceptional tsunami in its consequences, which caused severe destruction in Severo-Kurilsk. It started at 3:57 local time. At 4 hours 24 minutes, i.e. 26 minutes after the start of the earthquake, the ocean level quickly dropped and in some places the water receded from the coast by 500 m. Then, strong tsunami waves hit the Kamchatka coastline from Sarychev Island to the Kronotsky Peninsula. Later, they reached the Kuril Islands, capturing a strip of coastline about 800 km long. The first wave was followed by a second, even stronger one. After her arrival on the island of Paramushir, all buildings located no higher than 10 m above sea level were destroyed.

Plan:

Causes of a tsunami

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.

On fig. 1 shows a diagram of folded mountain systems and areas of concentration of earthquake epicenters. This diagram clearly identifies two areas of the globe that are most prone to earthquakes. 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.

The immediate cause 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 at the bottom of the sea 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 sea depth at the place of the break 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.

On fig. Figure 2a shows the mechanism of tsunami generation 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 bottom, the hearth rushes to the 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 revealed. 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 crests of which is 100–300 km, and the height when the waves approach the shore reaches 30 m or more.

Another cause of tsunamis is volcanic eruptions rising above the sea surface in the form of islands or located on the ocean floor (Fig. 2b). 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 shore. 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.

Cases of tsunamis during volcanic eruptions are also known in Japan. So, on September 23 and 24, 1952, there was a strong eruption of an underwater volcano on the Meijin reef, several hundred kilometers from Tokyo. The resulting waves reached the island of Khotidze to the northeast of the volcano. During this disaster, the Japanese hydrographic vessel Kaie-Maru-5, from which observations were carried out, perished.

The third reason for the occurrence of a tsunami is the fall of huge rock fragments 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 broke off from a height of 200 m, which caused the emergence of a single wave 15 m high.

Tsunami off the coast of South America

The Pacific coast within Peru and Chile is prone to frequent earthquakes. Changes in the topography of the bottom of the coastal part of the Pacific Ocean lead to the formation of large tsunamis. The greatest height (27 m) of the tsunami wave reached in the Callao region during the earthquake in Lima in 1746.

If usually the lowering of the sea level, which precedes the onset of tsunami waves on the coast, lasts from 5 to 35 minutes, then during the earthquake in Pisco (Peru), the receding sea waters returned only after three hours, and at Santa even after a day.

Often, the advance and retreat of tsunami waves occur here several times in a row. So, in Iquique (Peru) on May 9, 1877, the first wave hit the coast half an hour after the main shock of the earthquake, and then within four hours the waves attacked five more times. During this earthquake, the epicenter of which was located 90 km from the Peruvian coast, tsunami waves reached the coasts of New Zealand and Japan.

On August 13, 1868, on the coast of Peru in Arica, 20 minutes after the start of the earthquake, a wave of several meters high surged, but soon receded. With an interval of a quarter of an hour, it was followed by several more waves, smaller in size. After 12.5 hours, the first wave reached the Hawaiian Islands, and after 19 hours - the coast of New Zealand, where 25,000 people became its victims. The average speed of tsunami waves between Arica and Valdivia at a depth of 2200 m was 145 m/s, between Arica and Hawaii at a depth of 5200 m - 170-220 m/s, and between Arica and the Chatam Islands at a depth of 2700 m - 160 m/s.