What causes tsunamis in most cases. Tsunami: definition, origin, history and ecological consequences
Tsunami(Jap. 津波 IPA: where 津 is “port, bay”, 波 is “wave”). Translated from Japanese, it means "big wave in the harbor" or simply "wave in the harbor." Tsunamis are long waves generated by a powerful impact on the entire water column in the ocean or other body of water.
They have spatial scales from several hundred meters to several hundred kilometers. Tsunami Wave Speed (c) is described by the formula Lagrange:
c=√gh,
where h- depth of the ocean;
g- acceleration of gravity.
Causes of a tsunami.
Tsunamis are not always generated by any one phenomenon, their combination can be the cause. For example, an earthquake and a landslide, a volcanic eruption accompanied by an earthquake and a landslide, and so on.
Most tsunamis are caused by underwater earthquakes(today it is believed that this is the reason that accounts for about 85 % of all tsunamis), during which there is a sharp displacement (raising or lowering) of a section of the seabed. Not every underwater earthquake is accompanied by a tsunami. A tsunami that generates a wave is usually an earthquake with a shallow source. The only problem is the lack of the ability to 100% recognize such earthquakes, because warning services are guided only by magnitude indicators.
Second reason are landslides(near 7% all tsunamis). Having arisen, a landslide immediately generates a wave. An earthquake can cause a landslide. Most often, underwater landslides occur in river deltas.
The third reason are volcanic eruptions(near 5% all tsunamis). Large underwater eruptions have the same effect as earthquakes. A classic example is the tsunami that formed after the Krakatoa eruption in 1883. Huge tsunamis from the Krakatau volcano were observed in harbors around the world and destroyed a total of 5,000 ships and, as a result, about 36,000 people died.
In the age of the use of atomic energy, man has in his hands a means for independently causing concussions, previously available only to nature. Therefore, it should be understood that fourth reason is an human activity . It should be recalled here that in 1946 the United States produced an underwater nuclear explosion with a TNT equivalent of 20 thousand tons. The wave that arose at a distance of 300 m from the explosion rose to a height of 28.6 m, and 6.5 km from the epicenter it still reached 1.8 m. And, although international treaties currently prohibit underwater testing atomic weapons, but, as practice shows, such agreements are of a formal nature and serve only for the personal reassurance of the citizens of the adjacent territories in their imaginary safety and comfort.
A small, but not so safe percentage of this falls on meteorological reasons(such as the fall of a major celestial body) and other potential causes, labeled in scientific circles as "unknown" (but very dangerous). Meteorological reasons are a rather little-studied phenomenon today. They are recorded mainly in the Pacific, Atlantic and Indian oceans.
Features of tsunami propagation
Far from the coast, the height of a tsunami is no more than 2-2.5 m, and their length can reach several hundred kilometers. These tsunamis are very gentle and almost imperceptible to ships passing over them.
The speed of tsunamis depends entirely on their depth and can reach speeds of up to 800 km/h. The most interesting thing is that tsunamis are invisible in the open ocean, although they move at a speed of 700-800 km / h, but when approaching the coast, the speed noticeably decreases with a significant increase in the height of the impending wave.
If the tsunami moves towards the coast, then its height, reaching shallow water, begins to increase to 20-30 m, and in some cases it can reach 30-60 m. Near the coast, the tsunami becomes steeper and higher, reaching its peak point along the entire path of its journey.
This leads to huge destruction and numerous human casualties. Examples of such a phenomenon were the coasts of Thailand, Indonesia, India and Sri Lanka during the tsunami on December 26, 2004. in the Indian Ocean, as well as the northeastern part of Japan on March 11, 2011 (the magnitude of the earthquake that generated the tsunami was 9.0 points).
From the point of view of the development of science today, it can be said that the height of a tsunami on the coast and the features of movement inland depend on the size of the initial perturbation of the sea level, the slopes of the bottom, and the configuration of the coastline of the terrain.
Tsunamis are most dangerous in narrowing bays and straits, as well as in the mouth sections of rivers flowing into the sea. Tsunamis travel the farthest along river valleys. Examples of such areas are: the Second Kuril Strait, Tuharka Bay on Paramushir Island, Crabovaya Bay on Shikotan Island, the mouth of the Kamchatka River, and others.
The threat of a tsunami during the day at any point can sharply increase or decrease depending on the fluctuations in the tidal level.
The very first harbingers are animals and birds, which, anticipating danger, leave their habitats in the period from several hours to several days, or even weeks before the impending disaster. As if our Mother Earth herself is taking care to warn the living of danger through various energy waves caught by animals and birds.
For example, residents of earthquake-prone Japan have been determining the danger of tremors by the behavior of aquarium fish for hundreds of years. So, on the eve of the tsunami, Japanese catfish literally try to jump out of the aquarium and constantly rush from wall to wall. Multiple observations, including those conducted by scientists from the Experimental Oceanological Laboratory of the Russian Hydrometeorological University, have also confirmed that oceanic fish also leave coastal waters a few hours before the tsunami. Studies have shown that stingrays, cyprinids, catfish and long-clawed crayfish are especially sensitive to changes in electromagnetic fields before natural disasters.
It is no coincidence that biochemist H. Tributsch notes that, shortly before the onset of earthquakes and the subsequent occurrence of a tsunami, a powerful stream of charged particles or ions rushes from the soil surface into the atmosphere, which saturate the air with electricity to the limit, causing people to have increased excitability, nausea, and headaches. Exactly these electrostatic fields force animals to leave dangerous areas. And a group of German researchers from Tübingen, headed by Professor W. Ernst, also found a change in the color of the leaves of flowers, shrubs and trees a few weeks before the earthquakes. Such changes can be recorded using space satellites, which will allow people to be warned of danger in advance.
Signs of a tsunami may also include:
- Sudden rapid withdrawal of water from the shore for a considerable distance and drying of the bottom.
- The occurrence of an earthquake. In tsunami-prone regions, there is a rule that if an earthquake is felt, it is better to move further from the coast and at the same time climb a hill in order to prepare in advance for the arrival of the wave.
- During a storm, only surface layer water. During a tsunami - the entire water column, from the bottom to the surface.
- A tsunami, as a rule, generates not one, but several waves. The first wave, not necessarily the largest, “wets the surface”, reducing the resistance for subsequent waves.
- The speed of tsunami waves, even near the coast, exceeds the speed of wind waves. Kinetic energy tsunami waves also have thousands of times more.
The consequences of the tsunami.
The consequences of the tsunami are huge human casualties. Already alone human life is an invaluable gift and gift.
According to the first of the seven AllatRa foundations, the highest value in this world is human life. And it is very important to cherish the life of any person as one's own, because although it is fleeting, it gives everyone a chance to increase their main value - their inner spiritual wealth, the only thing that opens the way for the Personality to true spiritual immortality.
The most terrible consequence of a tsunami is the loss of at least one priceless human life.
But, in addition to the death of people, tsunamis also cause flooding of significant coastal areas, salinization and soil erosion, destruction of buildings and structures, damage to ships moored off the coast. The tsunami deals a huge blow to the economy of the country in which such a disaster occurred. The economic losses from the tsunami are colossal and amount to truly astronomical sums of money allocated to eliminate the consequences and restore the destroyed infrastructure of the region.
An example of this is the event in Japan. According to experts, a year after the earthquake and the resulting tsunami, the damage to Japan is estimated at 210.00 billion US dollars. This tsunami not only became the most expensive natural disaster in history. But it also destroyed 128,582 and partially destroyed 243,914 buildings. Some 320,000 people lost their homes and 15,848 lost their lives. Another 3305 people are considered missing.
What to do in the event of a tsunami?
Care must be taken to ensure that the documents necessary minimum things and products were always at hand.
Arrange with family members for a rendezvous point after a disaster, consider evacuation routes from a dangerous coastal area, or designate places to escape if evacuation is not possible. It can be local hills or high capital buildings. It is necessary to move to them by the shortest route, avoiding low places. A distance of 2-3 km is considered safe. from the shore.
It is important to understand that when observing tsunami warnings, tremors, or local tsunami warnings, the time to rescue can be measured in minutes. Therefore, it is necessary to act instantly, remaining collected and as calm as possible.
The occurrence of distant tsunamis is recorded by warning systems, and the forecast is reported on radio and television. Such messages are preceded by the sounds of sirens.
It is impossible to predict the number, height of waves, as well as the interval between them. Therefore, after each wave, it is dangerous to approach the shore for 2-3 hours. It is advisable to use the gap between the waves to find the safest place.
Any earthquake felt on the seashore should be considered a tsunami hazard.
You can not approach the coast to look at the tsunami. It is believed that if you see a wave and are in a low place, it is too late to save yourself.
Compliance with these simple rules of conduct, knowledge of tsunami precursors could reduce the number of victims of the tsunami in the Indian Ocean in 2004. Indeed, according to eyewitnesses (this can also be seen on the recorded videos), many people used such a tsunami harbinger as the ebb before the arrival of the wave to walk along the seabed and collect marine animals, shells, as well as various things left after the rapid “leaving” of water during low tide.
With the right behavior, the number of saved people could reach tens of thousands.
It is necessary to pay attention to the development of the sciences in the field of observation of animals, birds, fish and the entire surrounding world, so that, along with these harbingers of the coming changes, be fully armed and informed as much as possible about the impending future.
It is important to understand that in order to reduce the damage from the consequences of the tsunami, it is necessary to treat construction with great responsibility, which should be carried out outside the tsunami impact zone. If this is not possible, build buildings so that they take blows with their short side, and / or place them on strong columns. In this case, the wave will pass freely under the building without damaging it.
If there is a threat of a tsunami, ships moored near the coast must be taken out to sea.
You should also pay attention to your understanding that there are no territories of states on planet Earth.
These are the people themselves, according to their desire and choice, share one indivisible planet, one whole and the only one, splitting it up in all possible ways - for which there is only enough imagination and greed. All this division is just an appearance for the mind and an outlet for the ego, especially the alleged owners of artificially created territories in a distant and not so distant history. We are all Earthlings. We are all inhabitants of the Earth. And it doesn’t matter, in fact, what complexion each of us has, where we live and what we believe.
It is important to support each other, lend a helping hand to your neighbor, take care of the people around you in every possible way. And then no disaster will become an obstacle in the life of every person, but will only be a temporary task, overcoming which by joint forces will be easy and least painful for people “affected” by disasters.
On the pages of our site, we have already talked about one of the most dangerous natural phenomena- about earthquakes: .
These fluctuations earth's crust often give rise to tsunamis, which mercilessly destroy buildings, roads, piers, leading to the death of people and animals.
Let us consider in more detail what a tsunami is, what are the causes of their occurrence and the consequences they cause.
What is a tsunami
Tsunamis are high, long waves generated by a powerful impact on the entire thickness of ocean or sea water. The term "tsunami" itself is of Japanese origin. Its literal translation sounds like this - “a big wave in the harbor” and this is not in vain, since they appear in all their might on the coast.
Tsunamis are generated by a sharp vertical displacement of the lithospheric plates that make up the earth's crust. These gigantic vibrations vibrate the entire water column, creating a series of alternating ridges and troughs on its surface. And in the open ocean, these waves are harmless enough. Their height does not exceed one meter, since the bulk of the oscillating water extends under its surface. The distance between the crests (wavelength) reaches hundreds of kilometers. The speed of their propagation, depending on the depth, ranges from several hundred kilometers to 1000 km/h.
Approaching the shore, the speed and wavelength begin to decrease. Due to braking in shallow water, each subsequent wave overtakes the previous one, transferring its energy to it and increasing the amplitude.
Sometimes their height reaches 40-50 meters. Such a huge mass of water, having fallen on the shore, completely devastates the coastal zone in a matter of seconds. The length of the area of destruction inland in some cases can reach 10 km!
Causes of the tsunami
The connection between tsunamis and earthquakes is obvious. But do fluctuations in the earth's crust always generate tsunamis? no, tsunami are generated only by underwater earthquakes with a shallow source and magnitude over 7. They account for about 85% of all tsunami waves.
Other reasons include:
- Landslides. Often there is a whole chain natural disasters- the shift of the lithospheric plates leads to an earthquake, it generates a landslide that generates a tsunami. It is this picture that can be traced in Indonesia, where landslide tsunamis occur quite often.
- Volcanic eruptions cause up to 5% of all tsunamis. At the same time, giant masses of earth and stone, shot up into the sky, then plunge into the water. A huge mass of water is shifting. Ocean waters rush into the formed funnel. This dislocation generates a tsunami wave. An example of a catastrophe of absolutely terrifying proportions is the tsunami from the Karatau volcano in 1883 (also in Indonesia). Then 30-meter waves led to the death of about 300 cities and villages on neighboring islands, as well as 500 ships.
- Despite the fact that our planet has an atmosphere that protects it from meteorites, the largest "guests" from the universe overcome its thickness. When approaching the Earth, their speed can reach tens of kilometers per second. If such meteorite has a large enough mass and falls into the ocean, it will inevitably cause a tsunami.
- Technological progress has brought not only comfort to our lives, but has also become a source of additional danger. Conducted underground testing nuclear weapons, this is another reason for the appearance of tsunami waves. Realizing this, the powers possessing such weapons concluded a treaty prohibiting their testing in the atmosphere, space and in water.
Who and how studies this phenomenon
The destructive effect of the tsunami and its consequences are so enormous that humanity has become the problem is to find an effective defense against this disaster.
The monstrous masses of water rolling onto the shore cannot be stopped by any artificial protective structures. The most effective protection in such a situation can only be the timely evacuation of people from the danger zone. For this a sufficiently long-term forecast of the coming disaster is needed. This is done by seismologists in collaboration with scientists of other specialties (physicists, mathematicians, etc.). Research methods include:
- data of seismographs registering tremors;
- information supplied by sensors taken out into the open ocean;
- tsunami remote measurement open space with the help of special satellites;
- development of models for the occurrence and propagation of tsunamis under various conditions.
For many, the danger of a tsunami is a kind of exotic danger. However, changes in nature last years are such that surprises can be expected. Even in a small lake, under certain circumstances, a large wave can occur. Of course, the appearance of large waves is much more likely - a tsunami in the sea and ocean. A very small proportion of the population of Russia lives near the sea, the absolute majority are not threatened by a tsunami. But if you went on vacation to the open sea or ocean...
Where do tsunamis occur most often?
Most earthquakes occur on the Pacific coasts. Accordingly, tsunamis most often occur in the Pacific Ocean. In our country, the Far Eastern shores are exposed to tsunami attacks: Kamchatka, the Kuril and Commander Islands, and partly Sakhalin. Tsunamis also occur in the Indian Ocean. The greatest risk of disaster exists in coastal areas with increased seismic activity. In 2011, a very strong tsunami hit Japan, killing a large number of people, a vast territory was washed out and it was the tsunami that provoked an accident on nuclear power plant"Fukushima-1"
Quite often there is a threat of a tsunami in the Philippines, Indonesia, and other Pacific island states.
Going on vacation to such places, it will not be superfluous to have theoretical knowledge of how to behave and what to do during, before and after the tsunami.
Causes of a tsunami
The cause of a tsunami is an underwater earthquake. Powerful shocks create a directed movement of huge masses of water, which roll onto the shore with waves over 10 meters high. Thousands of tons of water with great speed fall on the coast. No residential building can withstand such a load. Houses that are in the way of the waves are washed away completely. There is no chance to survive in the epicenter. The further the wave goes to the ground, the less its strength, but the danger is no less, as the wave turns into a mixture of building materials, stones, fragments of fittings, cars, trees that crush and destroy all life in its path. But the danger doesn't end there either. When the wave passes, these thousands of tons of water huge amount floating debris will begin to return to the ocean. Pulling everything you can. People who find themselves in such a stream can be carried out into the open ocean.
Tsunami alert, how to know about a tsunami
The first reason to think about the threat of a tsunami is the announcement of increased seismic activity in coastal areas. In case seismologists managed to predict tremors in advance, residents of settlements on the coast should ensure their own safety in case of a tsunami. Such warnings are relevant even if the strength of the earthquake in the city itself is small, because a tsunami occurs when the epicenter of the earthquake is under water.
How can residents and tourists find out about an impending tsunami?
Watch reports and warnings about seismic activity in the region in advance!
To date, in all settlements where there is a possibility of a tsunami, there are special services to warn the population about the danger. But there is a catch. Earthquakes happen very often, but few reach the tsunami. Therefore, it is not always possible to determine in time. how strong the earthquake will be and whether it will lead to the appearance of a tsunami. And one more thing, if the epicenter of the tsunami is hundreds of kilometers from the coast, then after the notification, the residents will have time to react and evacuate from the dangerous area. But if the epicenter is near the coast, then even if there is an alert, there may not be enough time for evacuation. This is exactly what happened in Japan on the island of Okushiri, during the earthquake off Hokkaido in 1993. Then 230 people died from the tsunami.
At times of increased tsunami threat, one should carefully monitor the messages of the authorities on radio, television via the Internet and SMS informing. In most cases, the danger becomes known in a few hours, which gives residents the opportunity to react. Animals are sensitive to the approach of a giant wave. Long before the onset of a tsunami, they show concern Many wild animals and birds tend to leave the danger area in advance.
The approach of a tsunami in the next 15-20 minutes can be judged by such signs as the rapid retreat of water along the coastline, the sharp attenuation of the surf noise. In some cases, the drift of unusual objects is also observed: fragments of ice or coastal debris raised from the bottom by the current of water. The immediate approach of the wave is accompanied by thunderous sounds, a rumble.
What to do during a tsunami
How to protect yourself and play it safe in case of a tsunami?
In places where there is a high probability of a tsunami, it will not be superfluous to think over your actions in advance. These points should be discussed with the family, agree on a meeting place in case the coast is under threat, and mobile communications turn out to be
inaccessible. In addition, it is important to plan a retreat route in a calm environment, taking into account the terrain, avoiding bottlenecks, bays, rivers, places of potential congestion of vehicles and crowds of people. All the most valuable things that will be needed during the evacuation should be at hand and be ready at any time. First of all, documents, a minimum of clothing and a two-day supply of food that does not deteriorate should always be in a specially designated place. You also need a supply of water, a first aid kit, possibly some kind of signaling means (flare gun, hunter's signal), a knife, a rope (paracord), a flashlight, matches in sealed packaging. All this can be folded into a small backpack in case of a quick evacuation.
It is important for residents of coastal areas to take an active part in public events on which protection from the tsunami of the area depends - the construction of dams, shelterbelts, breakwaters.
How to survive a tsunami
In the event that an alarm is announced about the approach of a tsunami, you should urgently leave the coastal area, moving perpendicular to the coastal
lines. Relative safety is provided by an elevation of 30-40 meters above sea level or a distance of 2-3 kilometers from the coast. Such a retreat provides a significant reduction in risk, even if the area is threatened by large tsunamis. But in order to be 100% safe, it is better to move even further or higher.
Retreating from the danger zone, you need to avoid the bed of rivers, streams, ravines. These places are the first to be flooded.
Tsunamis in lakes or reservoirs are less dangerous, but even then caution should be exercised. A safe elevation is considered to be 5 meters above the water level. For this purpose, tall buildings are quite suitable.
With a large tsunami on the sea or ocean, many buildings simply cannot withstand the pressure of the wave of water and collapse. However, if the situation leaves no choice, then high capital buildings are the only chance to survive. They should climb to the highest floors, close windows and doors. How
suggest the rules of behavior during earthquakes, the safest areas in the building are areas near the columns, load-bearing walls, in the corners.
A tsunami is usually a series of several waves and in most cases the first wave is not the strongest. This must be remembered and not to lose vigilance.
If a wave has overtaken a person, it is very important to hold on to a tree, pole, building, and avoid collision with large debris. As soon as the opportunity arises, you need to find a shelter in case of repeated waves.
Photo: a ship washed ashore during a tsunami
How to behave after a tsunami
The main danger of a tsunami is repeated waves, each of which can be stronger than the previous one. It is worth returning back only after the official cancellation of the alarm or not earlier than 2 hours after the cessation of heavy seas at sea. The break between large waves can reach 40-60 minutes.
After returning home after a tsunami, as well as after other natural disasters, you should carefully examine the building for stability, gas leaks, and damage to electrical wiring. Flooding after a tsunami may represent a separate danger.
Mankind has been able to adapt and survive in difficult conditions. Now it is known how to cure many diseases, technologies have been developed for maximum comfort, however, nature is not tamed. There are still forces capable of causing great harm. One such force is the tsunami.
How to predict a tsunami
In order to understand whether it is possible to predict a tsunami, one must understand the origin of this phenomenon. A tsunami is a series of huge waves, the strength of which is so great that they can go beyond the coast and destroy coastal buildings. These waves are formed due to the fact that some phenomenon affects the level in the ocean or sea. It can be a large underwater earthquake, an eruption of an underwater volcano, a fall into the ocean of a large cosmic body. The strength of a tsunami is directly dependent on the scale of these phenomena.
Fortunately, these phenomena can be fixed. For example, during an earthquake, seismic waves are formed, the speed of which is higher than the speed of water. In addition, now there are services that track all earthquakes and eruptions, assess their scale and calculate the level of threat. Such measures give coastal residents several hours to evacuate. If we talk about ordinary person located on the shore, he can also predict the appearance of a tsunami. If the water moves away from the shore faster than at low tide, you can expect a tsunami.
How to escape from a tsunami - an algorithm of action
- When an evacuation signal is received, it is necessary to act immediately. No need to go look at the exposed bottom of the sea, or hide. When the wave is in sight, it will be difficult to escape from it.
- In the room you need to turn off the light and gas and leave it. A safe place can be considered a place located at a distance from the coast at a distance of a couple of kilometers and located at an altitude of at least thirty meters above sea level. It is worth remembering that rivers are a threat - they can also overflow their banks.
- If there is a means of transportation, you need to move in the direction from the coast. If possible, you need to pick up those who do not have transport.
- If there is no way to leave, you need to close all doors and windows and move as high as possible. If possible, choose the most reliable building.
- Inside the building, the safest places are the load-bearing parts of the building: walls, columns, intersections of load-bearing walls. It is dangerous to be near objects that can break or fall. If possible, they should be removed.
- Outside the room you need to try to be as high as possible. In extreme cases, you can climb a tree and cling to it.
- When being in the water, you need to get rid of everything that hampers movement, if possible, it is best to cling to some object. Water is dangerous not only in itself, it can carry debris from destroyed structures.
- A tsunami consists of several waves, you need to be prepared for this.
A tsunami is a wave of destructive force. The safest place is at the maximum distance from the coast.
If there is no way to retire, any high place will do. You need to climb to a height of thirty to forty meters. Roofs of houses, natural hills will do.
If it is not possible to leave the building, you need to turn off the electricity and gas, close all doors and windows and climb as high as possible. If possible, choose the most durable building. In houses, the safest places are near load-bearing walls, columns, in the corners that are formed by load-bearing walls. In addition, it is necessary, if possible, to remove from the room everything that can fall or break. Especially glass items.
How to survive a tsunami
It is worth remembering that tsunamis are the consequences of an earthquake. That it can accompany the wave.
There may be several tsunami waves. You need to prepare for the fact that the next wave may be stronger than the previous one. To return, not to meet with a new wave, you need to wait official information: radio or television will announce when the danger has passed. Only after a signal from official sources, for example, local authorities, can you go back. It is worth remembering the destruction that the wave could cause and think of alternative paths.
When the elements subside and the water recedes, it will be necessary to eliminate the consequences of its revelry. It can be destroyed buildings, destroyed infrastructure, victims. Power lines and fuel tanks may also be destroyed. There may be a lack of water supply and food supply. You need to be prepared for diseases and psychological support for those who find it difficult to mentally survive such a shock. You need to think in advance how to protect yourself and loved ones.
In order to correct the consequences of the disaster as soon as possible and prevent new victims from the absence of drinking water, food and proper conditions for the victims, you need to start recovery. The local authorities certainly foresaw the emergence of a critical situation and drew up a plan of action, however, a group of activists can help deal with the consequences more quickly.
First of all, you need to take care of creating a supply of water. Filtered or bottled - any fresh water is needed. At a minimum, so that people do not suffer from dehydration, as a maximum, to ensure proper care for the victims.
In the houses left without damage, it is necessary to accommodate those who have lost their homes. In this way, an increase in casualties can be avoided. We need to think about the organization of power generators, which can help establish communications in hospitals, for cooking and maintaining cleanliness.
Every effort must be made to restore medical services as soon as possible and eliminate leaks of dangerous and toxic substances.
The word "tsunami" is a Japanese term and means "wave in the bay". V modern usage, tsunami - an ocean wave that causes the displacement of water and it is fundamentally different from a normal wave. As a rule, an ordinary wave is formed by winds or the natural gravitational influence of the Sun and Moon. Underground earthquakes, volcanic eruptions, landslides, or even underwater explosions can displace masses of water, creating big wave or a series of waves - a phenomenon known as a tsunami.
Tsunamis are often referred to as tidal waves, but this is not an accurate description as tides have little effect on giant waves. Scientists often use the term "seismic sea waves' as a more accurate name for what we usually call a tsunami or tidal wave. In most cases, a tsunami is not a single wave, but a series of large waves.
How does a tsunami start?
The strength and behavior of a tsunami is difficult to predict. Any earthquake or underwater event can be a precursor to a tsunami, although most underwater earthquakes or other seismic events do not create giant waves, which is why they are so difficult to predict. A fairly large earthquake may not cause a tsunami at all, but a small one may provoke very large, destructive waves. Scientists believe that this is not so much the strength of the earthquake as its origin. An earthquake, in which the tectonic plates move abruptly vertically, is more likely to cause a tsunami than a horizontal movement.
Far out in the ocean, tsunami waves are not very high, but they move very fast. National Administration The Oceanic and Atmospheric Administration (NOAA) reports that some tsunami waves can travel at speeds in excess of 100 km/h. Away from the sea, where the water depth is great, the wave can be almost imperceptible, but as the tsunami approaches land and the ocean depth decreases, the tsunami wave speed slows and the height increases dramatically - along with the damaging potential.
How does a tsunami approach the coast?
A strong earthquake in the coastal zone is a signal that a tsunami may occur and therefore an immediate evacuation is necessary. In areas where the threat of a tsunami persists, the authorities should have a system of sirens or other means of transmitting information, as well as established plans for the evacuation of low-lying areas. Once the tsunami hits the shore, the waves can last from 5 to 15 minutes, and they do not follow any particular pattern. NOAA warns that the first wave is usually not the biggest.
One of the signals that a tsunami is approaching is that the water moves away from the coast very quickly (but in such a situation you will have very little time to evacuate). Unlike the depiction of tsunamis in films, the most dangerous tsunamis are not those that hit the coast like high waves, but those that have long waves containing a huge volume of water. V scientific terms the most destructive are waves that come ashore with a significant wavelength and not necessarily a large amplitude. On average, a tsunami lasts about 12 minutes - six minutes of "take-off", during which water can flow inland for considerable distances, and then it recedes for about six minutes. However, sometimes tsunamis can last for several hours.
Tsunami in history
- The first historically recorded tsunami occurred in 426 BC, and was described by the ancient Greek historian Thucydides in the book "History of the Peloponnesian War", in which he wrote that earthquakes in the ocean are the cause of such waves.
- An earthquake caused a tsunami in 365 AD that devastated Alexandria in North Africa.
- The Messina earthquake and tsunami in 1908 killed more than 123,000 people in Sicily and Calabria.
- There was a strong earthquake off the coast of Indonesia. The energy released by the earthquake triggered tsunamis that hit the coasts of Indonesia, Sri Lanka, India and Thailand. Over 200,000 people died.
- In March 2011, a magnitude 9 earthquake rocked Japan, sending a huge array of waves onto its coast. More than 18,000 people became victims; buildings, roads, seaports and railways; There was a serious accident at a nuclear power plant.
Ecological consequences of the tsunami
The human suffering and death caused by tsunamis understandably causes environmental problems, but a tsunami that destroys everything in its path also causes pollution and change. When the water moves away from the flooded land, it takes with it a large amount of debris: trees, building materials, vehicles, containers, ships, and pollutants such as oil or chemicals.
