How the ocean leaves before the tsunami. The ocean is gone! A rare occurrence - Hurricane Irma drained the coast of the Bahamas. Signs of a tsunami

Tsunami - disaster that anyone can face. Even if you do not live in a tsunami-prone area, you may find yourself in one on vacation or on a business trip. Therefore, any person should know how to behave when such a phenomenon occurs.

You need to understand that a tsunami is not just a big wave, but a much more powerful force, which is described by a separate physical formula and has a force of almost equal to strength explosion. In the sea, the tsunami is practically invisible - the wave acquires its height and power when it comes to shallow water.

What not to do during a tsunami

To begin with, we will tell you what not to do during a tsunami so that you do not make serious mistakes.

Firstly, one cannot stand bewitched and stare at a huge wave rooted to the spot. You may find this recommendation strange: who would think to stand and watch? But, as practice shows, many do just that. Either out of horror, or out of interest.

Secondly, if the tsunami is already very close, just running will not help, because the wave moves at a speed of 800 km per hour (airplane speed), but the closer to the coast, the slower it becomes: the speed decreases to 80 km per hour.

Thirdly, if the tsunami is still far away, but it is already known about it, most likely you have no more than 15-20 minutes to escape. Therefore, instead of collecting our things, we use the time to escape. We take only the essentials. Save not things, but life!

Fourth, you should not run near riverbeds: it is the riverbeds that will flood in the first place during a tsunami.

Tsunami Signs

When a tsunami hit the shores of Thailand in 2004, vacationers marveled that the bottom was exposed for many kilometers and various shells that people began to collect became visible. But on one beach, the holidaymakers were saved by the knowledge of a schoolgirl, who the day before in a geography lesson was studying the topic of a tsunami and recognized in time that the seabed was exposed as sure sign the onset of the wave, and also informed everyone around about it, so that they managed to evacuate.

Signs of a tsunami include:

• earthquake
• unusual behavior of water: it either recedes many meters, or, on the contrary, begins to "lubricate" the surface of the earth, going beyond the boundaries of the water area
• animals have escaped the shore or are behaving anxiously
• the appearance of a white wave edge on the horizon
• a sharp rise in the horizon of the sea
• all people flee from the sea
• warning siren howls

What to do during a tsunami

If you do not see the tsunami yet, but the warning siren is already howling, or you only saw a tsunami on the horizon, then you have from 10 to 20 minutes to leave the place.

Immediately start running away from the sea. Do not stop until you have moved 3-4 kilometers inland or at an altitude of 30 meters. Usually this is enough to be saved.

If you are trapped and cannot leave the shore, climb up. This is not the best solution, so we only use it if all other solutions are not available. You can climb to the roof of the building, or you can choose a strong tall tree for shelter.

When you take a position where you will wait for the wave to come or start running, try to get rid of heavy parts of clothing (jackets, etc.) on the move, which, if the wave overtakes you, will drown you.

If you get into the water, climb onto the floating object and use it as a raft. Try climbing a tree, building, or other safe place whenever possible.

Once in a tsunami, you have a chance to die not from drowning, but from the impact of some floating object. Therefore, try to protect yourself from such items.

When the wave reaches its limit on land, it will begin to recede back with tremendous power. It is extremely dangerous to be in the water at this time, as you will simply be carried away into the ocean. Therefore, whenever possible, try to get out of the water, even if just by grabbing onto a tree, in order to overcome the force that carries you into the ocean.

What to do after the tsunami

When the tsunami has receded, you cannot return to your house or hotel, go to the shore. The first wave can be followed by the second and third, and they can be stronger. Therefore, you need to stay away from the coast, or even better, try to go deeper into the island or mainland so that the second and third stronger waves do not overtake you. Only when the authorities give a signal that the waves are over, you can return to the house.

When you enter the house, if something is left of it, you need to beware of objects that can fall on your head. You can also get an electric shock. Therefore, you can enter the room only after making sure that everything is in order.

If you are just going on vacation

Of course, it is not very pleasant to think about the bad before going on vacation. But still, forewarned is forearmed. So first find out if this coastal region has been hit by tsunamis before. Although even if they did not collapse, this is not a guarantee. It is worth considering that most tsunamis occur in a place called the "volcanic belt". It is an area in the Pacific Ocean known for its volcanic activity... However, tsunamis occur in all oceans, so if you are on the ocean coast, it is potentially dangerous. You should not give up such a vacation, you just need to study the signs of a tsunami and strictly follow all the rules.

Boxing Day 2004

How nice it is in Thailand in winter! The rainy season ends in November and the heat only starts in May. But do you know everything about Thailand?

I want to talk about what travel agencies are silent about. After all, we have been to Thailand for many years in a row. And I'm also a seismologist.

For the Christmas holidays, under the palm trees on golden sand at an air temperature of +30 C and a water temperature of +29 C, chilled northern residents flock to Thailand: Canadians, British, Germans, Scandinavians, Russians. IN last years Russians are the most. Pattaya and Patong acquired the glory of "Russian cities". Not only recreation, but also the purchase of real estate by Russians in Thailand is in full swing. Only the prudent Germans are in no hurry for some reason. "Well, stupid" - the famous humorist would say. Or maybe they are not stupid, but remember Boxing Day?

According to Christmas traditions, on the night of December 25-26, Santa Claus puts gifts in beautiful boxes under the New Year tree. The morning of December 26 begins with untying the ribbons on these boxes. But Earth has prepared another "gift" for Boxing Day 2004. The world shuddered.

On December 26, 2004, at 00:58:53 UTC (07:58:53 local time), an underwater earthquake occurred in the Indian Ocean, the hypocenter of which was recorded near the northern tip of Sumatra at a depth of about 30 km. The hypocenter of an earthquake (from the Greek "hypo" - "under", "below") is the point of the beginning of the rupture inside crust when a significant amount of energy is suddenly released.

The US Geological Survey estimated that the energy released during the earthquake of December 26, 2004 was equal to the energy of 23,000 atomic bombs dropped on Hiroshima.

The Sumatran earthquake on December 26, 2004 affected 11 countries, of which Indonesia, Sri Lanka, Thailand, India, and the Maldives were the most affected.

This was the second or third most powerful earthquake in the entire history of observation. The moment magnitude was determined by different sources equal from Mw = 9.1 to Mw = 9.3. Magnitude is a dimensionless quantity that is a measure of the energy released during an earthquake and is determined by the logarithm of the amplitudes of seismic waves. The scale of moment magnitudes is theoretically infinite, but the focus of an earthquake with Mw = 10 would cover the entire globe. On December 24, 2004, an earthquake with a moment magnitude Mw = 9.3 shook the entire Indian Ocean and went down in history as " The great Indian Earthquake ".

The moment magnitude Mw is related to the seismic moment Mo, which determines the amount of energy released by an earthquake. Mo is equal to the product of the shear modulus of rocks in the hypocenter region, the total area of ​​the fault region containing the fracture of geological rocks, and the average rock displacement in this region. These parameters are determined from seismograms and are therefore objective.

As for subjective assessments, what will you feel when you see a corpse that was thrown ashore by the waves? And three corpses? And next to it on the sand is a blackened old woman, crying to the gods: "Why? Why did you leave me to live on earth, and took my daughter-in-law and grandchildren into the depths of the sea !?" Now increase human grief not three, but three hundred thousand times.

300,000 people is the approximate number of victims of the Sumatran earthquake on December 26, 2004.

The true number of victims will never be established, since most of them were carried away by the sea.

The source of the earthquake in its development reached the ocean floor and formed a vertical scarp over 100 km long with a bottom displacement of more than 20 meters. This triggered a tsunami, which is considered the deadliest natural disaster in modern history... "The Deadliest Tsunami in History" or "Boxing Day 2004" - this is how 3 minutes entered the history of mankind, claiming 300,000 innocent lives.

Tsunami

"Tsunami" in Japanese means "big wave in the harbor."

Most volcanoes and earthquake foci are located in subduction zones, i.e. in places where the oceanic crust sinks into the mantle. Deep-water trenches are also located in these zones. The most famous subduction zones are in the Pacific Ocean. Magellan, who gave this name to the ocean, was just lucky, because for three months his expedition did not encounter a single storm. But most of the sources of underwater earthquakes that generate a giant tidal wave of tsunami are located in the Pacific, truly Great, ocean. Subduction zones are also Sumatra and Java, where underwater earthquakes generate giant waves - tsunamis. Having formed at the epicenter of the earthquake, the tsunami spreads at a speed of 800 - 1000 km per hour, raising a wave up to 5 meters. Having reached shallow water, the wave height reaches from 10 and even up to 50 meters. For every meter of coastal land, more than one hundred thousand tons of water is thrown out with enormous destructive force.

Earthquakes are unpredictable phenomena and cannot be predicted. But a tsunami can be predicted before it reaches the coast. This requires a corresponding network of registration devices and a corresponding notification service.

Before the beginning of the tsunami, the water in the ocean recedes very far from the coast, the seabed is exposed for several kilometers. In time, the low tide lasts within 30 minutes, and the farther the sea has moved, the higher the waves of the upcoming tsunami will be.

By the way, in the first wave of the tsunami, many were saved by a little Scandinavian girl who simply knew what was written in textbooks and popular encyclopedias. When the water suddenly began to go into the sea, the girl ran along the exposed beach and shouted: "Save yourself! This happens before a tsunami!" But people fled not to the shore, but after the departing sea. Greed drove them to collect shells and quivering fish on the unexpectedly exposed seabed... The main casualties were because of this. And then the first tsunami wave appeared on the horizon, it approached at the speed of an airplane, belching terrifying thunderous sounds.

On December 26, 2004, more than 6,000 people died in Thailand, with the largest number of victims in the Phi Phi backpackers' paradise. According to the BBC, "More than 6,000 people died in Thailand alone - and the backpacker haven of Phi Phi was one of the worst-affected areas. "

Three tsunami waves hit the island of Phi Phi Don.

Phi Phi Don. Tsunami. (Source http://www.yachtaragorn.com/Thailand.htm)

On the island of Phi Phi Don, the first Killer Wave washed away the most comfortable and populated bay of Londalum. The second destroyed all the wooden buildings. The Third Wave Killer washed away the stone buildings as if they were children's sand castles. The wave height reached 15 meters. Everything lasted only 3 minutes (from 10 hours 29 minutes to 10 hours 32 minutes). At this time, all the tourists were on the beach or in the sea. During these 3 minutes, 700 people died on the small island of Phi Phi Don alone.

The 2004 Indian Ocean earthquake was caused by pressure in the subduction zone where the Indian Plate slides under the Burma Plate at a speed of 6 cm / yr. Along the border, where the Indo-Australian and Eurasian plates meet, the Javan Trench or the Javan (Sunda) Trench is formed - the deepest oceanic trench in the Indian Ocean, 5370 m long, the greatest depth of the Java Trench is 7450 m, which is the deepest point in the Indian Ocean. The Javan Trench is seismically active; it is part of the Pacific volcanic Ring of Fire.

As you can see, on the territory of Russia, with the exception of the Kuril Islands and Kamchatka, we are not threatened with earthquakes or volcanic eruptions. In this sense, we are lucky. But behind each of the bright circles of the Ring of Fire is a natural disaster, tears, grief and human lives that are so small in comparison with the life of the Earth, but so unique.

So where are Hell and Heaven? On the map, the earthly Paradise is where the most beautiful mountains rise and the most beautiful seas turn blue. And under them in the thickness of the earth's rocks is Hell. On Boxing Day, December 26, 2004, the distance between Heaven and Hell was only 30 km vertically.

And at this time on earth ...

This picture was not an accusation against the forces of nature, but against the diving business, who flooded the Internet and the island of Phuket with the advertisement "Everything for diving!" and did not warn naive tourists about the seismic hazard of this region.

I do not want to spoil anyone's upcoming vacation in Thailand, I only ask some Russian women not to walk topless on Patong Beach. It's not just that Thailand is a very religious country. Buddhism is practiced here, and the nightly crowds of "girls" of the former male, telling everyone: "I love you" - this is their job, there is no other. But here the number of victims is remembered.

I can't forget the scary documentary photos exhibited in downtown Seoul the day after the tsunami. Black corpses in black mud. Then the central square of Seoul City Hall Plaza was surrounded by ambulances equipped to receive blood. Koreans stood in silent lines to donate blood for those who suffered in Indonesia, Sri Lanka, Thailand, India, and the Maldives. Koreans do not know how to rest, they only know how to work and help. Both the Chinese and other peoples helped the victims. For example, Jackie Chang financed the construction of a new village on the destroyed island of Sumatra. "No - I said - let the travel agencies promise anything, but we will not go to Thailand to rest on corpses."

After the main blow on December 26, the focus of the Sumatran earthquake continued its life. A series of lower-magnitude aftershocks followed, with smaller tsunamis. Aftershock is a repeated seismic shock of lower intensity compared to the main seismic shock. As you know, strong earthquakes are always accompanied by numerous aftershocks, the magnitude and number of which decrease with time, but the duration of the manifestation of aftershocks can last for months.

The next strong earthquake, i.e. an aftershock with an instantaneous magnitude of 7.9 occurred two weeks after the main impact on December 26. The resulting tsunami wave overturned the ship with tourists. Many believed then that this was the revenge of the gods or ancient spirits. They also said that the foreshock of these events was the film "The Beach", the shooting of which destroyed the island of Phi Phi Lei. Or perhaps the warning to the dealers was the "Golden Raspberry", which DiCaprio got for being false in the role of a backpacker and for blaspheming against the Buddha statue in this film.

The real backpackers, of those who survived, after the tsunami did not leave their destroyed Paradise on the Phi Phi Islands and remained there to find the corpses of their comrades and help clear the island from the debris. We met with them only a year later. And the locals still ask us:

Have you been to Phi Phi before or after the tsunami?

After.

After the first, after the second?

After the second ....

So what do you do? Where to go to rest? - you ask.

Honestly, winter is best in Thailand.

You just need to know that the source of a possible earthquake is located not far from the island of Sumatra, so on the Andaman islands, it is better to choose the eastern shores, and while on the western ones, remember where to run in the event of a tsunami. This is indicated by the inscriptions on special boards installed in risk areas.

Other hazards such as sea ​​urchins at the bottom and poisonous insects on the ground, as well as the simplest methods of treatment, I will tell you later.

And now I wish everyone to spend their vacation in an interesting and healthy way.

© Copyright Boyko-Nazarova Tatiana Alexandrovna ([email protected] )

♦ Heading:,.

Tsunamis (Japanese for "big wave in the harbor") are sea gravity waves resulting from upward or downward movement of extended sections of the seabed during underwater and coastal earthquakes. Propagation speed from 50 to 1000 km / h. The height in the area of ​​origin is from 0.1 to 5 m, near the coast - from 10 to 50 m and higher.

Tsunamis wreak havoc on land. For centuries, this unbridled natural phenomenon has kept people in fear, and therefore there is a lot of understatement about these killer waves.

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

Tsunami occurs from an underwater earthquake. A seaquake is the culprit in most tsunamis, but not always. Typhoons, tropical cyclones, underwater landslides, or volcanic eruptions can also be the cause. The largest waves are formed when a cosmic body - a comet or a meteorite - hits the ocean. The consequences of such a catastrophe can only be imagined and are unlikely to be survived. At one time, even dinosaurs died from this.

Any seaquake threatens 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 source of the earthquake should not be too deep (up to 20 km.). Therefore, not every change in the relief of an oceanic day generates a giant wave.

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

Before the tsunami begins, the water recedes from the coast. Canadian mathematician Walter Craig came to the conclusion that only half of the time the water really moves away from the coast, foreshadowing a tsunami. This depends primarily on the wavelength, and not on the power of the tsunami, as previously thought.

Tsunami is always a tall wave! Revealing the secret of the emergence of this natural phenomenon, I must say that in fact the height of a tsunami depends on its energy. And the farther from the epicenter, the higher the level of the wave. Whereas in the open sea the tsunami does not exceed a meter, but moves at a breakneck speed, on the shallows the wave slows down and gains altitude. By the way, there may be no waves at all, and the tsunami will pass like a series of rapid ebb and flow. So the tsunami is not just a wall of water crashing onto the shore, but the movement of the entire water layer, increasing its destructive force when it meets land.

Tsunami comes imperceptibly, which is why it is so difficult to escape from it. Really, distinctive feature tsunami is its sudden appearance. But all the same, it makes itself felt, and if you are careful, you can notice the approach of a catastrophe. If an earthquake is the cause of a giant wave, everyone on the shore will feel 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, underwater currents arise. In addition, water can leave the coast, draining the bottom, or, conversely, slowly tide.

The first tsunami wave is always the largest. This is not true. Since tsunami waves move one after another, and the distance between them can reach several tens or even hundreds of kilometers, they reach the coast after a certain time (from a couple of minutes to a whole 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 off the coast of Sri Lanka in 2004, not a single animal was found. Eyewitnesses claim that even the fish tried to hide from the oncoming elements, hiding in corals. But the truth is, not all animals are catastrophe predictors. For some, the threat will become obvious, while the other will not react to it in any way. Therefore, it would be wrong to rely on the intuition of our younger brothers in everything.

The only thing that saves you from the tsunami is a quick flight inland. Indeed, this is so, 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 river beds, 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 rescue on the shore, and it is better to go farther out to sea. Finally, remember that the tsunami is returning. Only after a certain time has elapsed, you can return to the shore.

There are so many elements on Earth: tornadoes, tsunamis, earthquakes, volcanic eruptions, avalanches, floods, fires and so on. Many of them are destructive. We'll talk more about tsunami. Many people know firsthand what it is. “Big wave in the harbor” is how the word “tsunami” is translated. It is about marine gravitational waves that occur as a result of earthquakes (underwater, coastal) or displacement of individual sections of the seabed.

Indeed, many people know about the destructive power of tsunamis. People are very much afraid of this unbridled phenomenon. And this fear is passed down from generation to generation. Sometimes tsunamis are even called "killer waves" because they have already claimed millions of lives.

Tsunami has the following characteristics:< ul >

• wave height reaches 50 meters and above;
• the speed of its propagation is 50-1000 km / h;
• the number of waves arriving on the shore ranges from 5 to 25;
• the distance between waves can reach 10-100 kilometers or more.
• Do not confuse tsunamis and ship storm waves. In the first case, the entire thickness of the wave moves, in the second, only the surface layer.

Tsunami: what is it - causes and signs

Scientists have been studying the nature of such a phenomenon as tsunami for decades. Among the reasons that cause it are presented:

• underwater landslides;
• falling into the ocean or sea of ​​meteorites, comets or other celestial bodies;
• volcanic eruptions (underwater);
• underwater earthquakes;
• tropical cyclones, typhoons;
• excessively strong wind;
• testing of military weapons.

As a result of any of the above reasons, occurring on the seabed, a force is released that forms the lightning movement of water. Most often, tsunamis are caused by underwater earthquakes.

Scientists can guess what the consequences will be after such a disaster. But it is extremely difficult for people to experience this, and more often it is impossible. No wonder why all the dinosaurs died at one time.

Is it possible to know in advance that a tsunami is impending? Of course, scientists have identified a number of signs that indicate that a tsunami is about to happen. The first sign of a tsunami is an earthquake. Therefore, having felt the first intense tremors, one can understand that the wave will be strong. The second sign is a sharp ebb. The more water goes deep into the ocean or sea, the higher the waves will be.

Tsunami: myths and truth

People live and do not know that not all those tsunami tales that circulate among people are true.
Myths:

1. Tsunamis can occur exclusively in warm seas. This is not true. They happen all over the place. It's just that tsunamis most often occur in the Pacific Ocean.
2. The power of the tsunami depends on how far the water has moved away from the coast before the elements. In fact, it is the wavelength that depends on the flow of water, not its power. And the coast is not always shallow before the tsunami. Sometimes, on the contrary, the water comes before the tsunami.
3. A tsunami is always accompanied by a big wave. No, a tsunami is not just a wall of water that crashes onto the shore. In some cases, such a wall may not exist.
4. The arrival of a tsunami is always invisible. Yes, the element does not clearly warn of its coming. But attentive scientists always notice the approach of a tsunami.
5. The largest is the first tsunami wave. Again, this is not the case. Waves reach the coast after a certain period of time (from several minutes to an hour). And it is the waves following the first one that often turn out to be more destructive, since they “fall” on the wet shore when the resistance has already been reduced.

The truth is that animals always sense when a tsunami breaks out. They try to leave the dangerous area ahead of time. Therefore, after the tsunami, you may not find the corpses of animals at all. At the same time, fish try to hide in corals. Perhaps it makes sense to listen to the "call" of pets to everyone who lives in seismically dangerous zones ?!

How to save yourself from a tsunami?

The only thing that can save lives in such a catastrophic situation is a flight inland. People who have become hostages of the elements must leave as soon as possible, run away from the coastline. In this case, you should make your route far from the river beds, because there tsunami waves can overtake very quickly. Ideally, you should climb a mountain to a height of over thirty meters. Those who are caught by the elements at sea should sail on a ship farther into the sea, since sailing to the shore is simply pointless - certain death awaits there.
By following the recommendations, keeping calm and alert, and having good preparation, you can always save yourself from such a destructive element. But best advice: If you are very afraid of dying in a tsunami, leave seismically hazardous areas. As you know, tsunamis are frequent guests of the coast, the Pacific Ocean (about 80% of all volcanoes of the Earth that are in an active state are concentrated here), Sakhalin Islands, the Maldives, the coasts of Australia, Japan, India, Peru, Thailand, Madagascar.

Signs of a tsunami

· Sudden rapid withdrawal of water from the coast for a considerable distance and drying of the bottom. The further the sea recedes, the higher the tsunami waves can be. People on the shore and not aware of the danger may stay out of curiosity or to collect fish and shells. Such a rule should be followed when, for example, in Japan, on the Indian Ocean coast of Indonesia, Kamchatka. In the case of teletsunami, the wave usually comes up without the water retreating.

· Earthquake. The epicenter of an earthquake is usually in the ocean. On the coast, an earthquake is usually much weaker, and often there is none at all. In tsunami hazardous regions, there is a rule that if an earthquake is felt, it is better to go further from the coast and at the same time climb a hill, thus preparing in advance for the arrival of a wave.

· Unusual drift of ice and other floating objects, formation of cracks in the solder.

· Huge reverse faults at the edges of stationary ice and reefs, formation of swells, currents.

Reasons for the large number of tsunami victims

It may be incomprehensible why a tsunami several meters high turned out to be catastrophic, while waves of the same (and even much higher) height, which arose during a storm, do not lead to casualties and destruction? There are several factors that can lead to disastrous consequences:

· The wave height near the coast in the case of a tsunami, generally speaking, is not a determining factor. Depending on the configuration of the bottom near the coast, the tsunami phenomenon can pass without a wave at all, in the usual sense, but as a series of rapid ebb and flow, which can also lead to casualties and destruction.

· During a storm, only the near-surface layer of water comes into motion, during a tsunami - the entire thickness. And during the tsunami, much larger masses of water are splashed onto the shore.

· The speed of tsunami waves, even off the coast, exceeds the speed of wind waves. Kinetic energy tsunami waves have more.

· Tsunamis, as a rule, generate not one, but several waves. The first wave, not necessarily the largest, wets the surface, reducing resistance for subsequent waves.

· With a storm, the excitement builds up gradually, people usually have time to move to a safe distance before the arrival of large waves. Tsunami comes suddenly.

· The force of a tsunami may increase in the harbor - where the wind waves are weakened, and therefore, residential buildings can be located close to the coast.

· Lack of basic knowledge of the population about the possible danger. So, during the tsunami of 2004, when the sea receded from the coast, many local residents remained on the shore - out of curiosity or out of a desire to collect fish that did not have time to leave. In addition, after the first wave, many returned to their homes - to assess the damage or try to find loved ones, not knowing about the subsequent waves.

· The tsunami warning system is not available everywhere and does not always work.

· Destruction of coastal infrastructure exacerbates the disaster, adding disastrous man-made and social factors. Flooding of lowlands and river valleys leads to soil salinization.

Tsunami warning systems

Tsunami warning systems are based mainly on the processing of seismic information. If an earthquake has a magnitude of more than 7.0 (in the press this is called a Richter scale) and the center is located under water, then a tsunami warning is given. Depending on the region and coastal population, the conditions for generating an alarm can be different.

The second possibility of tsunami warning is “in fact” warning - a more reliable method, since there are practically no false alarms, but often such a warning can be generated too late. The factual warning is useful for teletsunami - global tsunamis that affect the entire ocean and arrive at other boundaries of the ocean several hours later. So the Indonesian tsunami in December 2004 is teletsunami for Africa. The Aleutian tsunamis are a classic case - after a strong splash in the Aleuts, one can expect a significant splash in the Hawaiian Islands. Bottom hydrostatic pressure sensors are used to detect tsunami waves in the open ocean. A warning system based on such sensors with satellite communication from a near-surface buoy, developed in the United States, is called DART (en: Deep-ocean Assessment and Reporting of Tsunamis). Having found a real wave in one way or another, it is possible to accurately determine the time of its arrival in various settlements.

An essential point of the warning system is the dissemination of relevant information to the population.

The largest tsunamis

Tsunami from the Aleutian Islands

After this tsunami, a special institution was created to study and deal with the consequences of such disasters. For decades, the Hawaiian Islands have played the role of a "lost paradise", where travelers from all over the world flocked to enjoy the extraordinary beauty of these places. But on April 1, 1946, this "paradise" turned into a living hell. The worst tsunami wave ever to reach the archipelago wreaked havoc on the island of Hawaii. But not all of the consequences were negative. Thanks to this tsunami, a service appeared, which has since been studying giant waves and warning of their possible appearance.

In English-speaking and other countries around the world, April 1 is celebrated as the day of jokes. On the same day, an underwater earthquake that occurred south of the Aleutian Islands, which are located west of Alaska, caused a tsunami that destroyed part of the Hawaiian Islands. Some believe that a warning of a danger, if it came on such a day, could well be taken for a joke. But, to the greatest regret, there was no such warning.

An underwater earthquake 150 km south of Unimak Island generated a huge wave. Its epicenter was recorded at a depth of about 25 km, which is still controversial today. In 1946, its strength was estimated at 7.2 points on the Richter scale, but later, after research, this value was changed to 8.6 points, and in this case it becomes clear why so much destruction was brought about by the tsunami.

Another mystery surrounding the underwater earthquake is the question of what exactly happened in the bowels of the earth? Was it a rift on the fault line? Or a shift? Let's hope that over time, technical progress will clarify this issue. In the meantime, the opinions of scientists about the cause of the earthquake differ. The resulting earthquake wave only slightly affected Alaska, but the Aleutian Islands were hit hard to protect this remote US territory.

A giant wave, born of movement in the bowels of the earth, headed through Pacific Ocean to the Hawaiian archipelago. By virtue of its geographic location these islands are very vulnerable to ocean tsunamis. FROM early XIX century in Hawaii, 50 tsunamis were recorded, 7 of which caused extensive damage. The most powerful were the tsunami waves in 1960 and 1946: in the first case, the wave was caused by a sudden earthquake that devastated part of Chile, the second will now be discussed.