Introduction

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

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

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

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

It was these historical tsunamis, which caused huge loss of life and property, that awakened new interest to the tsunami, when a lot of responses to the topic of this natural phenomenon immediately appeared, and the world community was preoccupied with the problems of creating modern tsunami warning systems and warning systems and informing about similar natural hazards around the globe.

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

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

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

define the concept of tsunami;

study the causes of tsunamis;

mechanism of tsunami occurrence;

geographical distribution of the tsunami;

tsunami impact on the coast;

show the importance of tsunami warning systems;

The study of hydrospheric hazard is one of the priority tasks in many countries. Prevention of such a phenomenon is impossible in most cases, but their timely prevention, development of the most effective methods to deal with the consequences is important task for scientists around the world.

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

1. Causes of a tsunami

tsunami coast natural wave

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

1.1 Tsunami caused by volcanoes

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

1.2 Tsunami triggered by landslide/landslide

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

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

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

1.3 Tsunami caused by earthquakes

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

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

2. Tsunami generation

It is currently believed that tsunamis are formed during a sharp vertical movement rocks along the fault during a strong earthquake, as shown in the diagram.

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

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

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

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

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

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

Large quantity Tsunami waves are caused by underwater earthquakes. During an earthquake, a vertical crack forms under water, and part of the bottom sinks. The bottom suddenly ceases to support the column of water lying above it. The surface of the water comes in oscillating motion vertically, trying to return to baseline- mean sea level - and generates a series of waves.

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

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

3. Tsunami spread

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

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

There are several general concepts about refraction and diffraction of waves. These phenomena have importance to understand the mechanism of tsunami propagation.

Wave refraction

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

Wave diffraction

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

Rice. 5 (Wave refraction)

Rice. 6 (Wave Diffraction)

3.1 Tsunamis of remote origin

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

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

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

When a tsunami approaches the coast, the waves are modified by the various characteristics of the coastal and coastal topography. Submarine ridges and reefs, continental shelf, outlines of capes and bays, steepness coastline can change wave period and wave height, cause waves to resonate, reflect wave energy, and/or transform waves into a tidal bar (boron) that crashes onto the shore.

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

3.2 Local tsunamis

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

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

4. Impact on the coast

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

.1 Wave height

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

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

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

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

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

.2 Tsunami run ashore

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

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

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

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

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

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

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

) destruction of the wave near its crest with the preservation symmetrical shape generally;

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

4.3 Tsunami consequences

To damaging factors tsunami relate shock wave, blur, flooding.

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

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

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

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

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

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

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

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

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

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

Most large tsunamis

11.1952 Severo-Kurilsk (USSR).

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

03.1957 Alaska, (USA).

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

07.1958 Lituya Bay, (southwest Alaska, USA).

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

03.1964 Alaska, (USA).

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

07.1998 Papua New Guinea

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

Tsunami propagation in the Indian Ocean

September 2004 coast of Japan

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

December 2004 Southeast Asia.

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

January 2005 Izu and Miyake Islands (East Japan)

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

April 2007 Solomon Islands (archipelago)

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

March 2011 Japan

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

5. Tsunami protection

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

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

No type of defense structures could provide 100% protection for low-lying coasts. In fact, barriers can sometimes only exacerbate destruction if tsunami waves breach them, violently hurling chunks of concrete at houses and other structures like projectiles.

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

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

Tsunami Warning System

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

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

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

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

When the TCPC receives enough data to determine the coordinates of the epicenter of the earthquake and its magnitude, a decision is made regarding further action. If an earthquake is strong enough to cause a tsunami, the TCWC sends requests to the participating countries' tide stations closer to the epicenter to monitor readings for tsunami detection. Tsunami Warning/Watching Bulletins are issued to dissemination organizations for all earthquakes of magnitude greater than 7.5 (greater than 7.0 for the Aleutian Islands region) to alert the public to the possibility of a tsunami and the need for safety measures. The data received from tide monitoring stations are evaluated; if they show that a tsunami has formed, dangerous to part or all of the population of the Pacific region. The Tsunami Warning/Watch Bulletin is being expanded or updated as a Pacific-Wide Warning. Relevant organizations then carry out the evacuation of people from dangerous areas according to predetermined plans. If tide stations indicate the formation of a non-dangerous tsunami (or the absence of a tsunami), the TPWC will cancel the content of the Tsunami Warning/Watch Bulletin previously sent out.

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

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

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

Conclusion

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

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

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

) The closest relationship exists between earthquakes and tsunamis.

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

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

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

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

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

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

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

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

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

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

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

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

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

List of sources used

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

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

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

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

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

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

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

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

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

Www.puzikov.com

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As a result of an earthquake, shifts begin to occur, since one part of the bottom begins to rise, and the rest falls. All this leads to the movement of water reaching the surface, but when all this mass tries to return to its original state, huge waves form.

If a tremors occur in the open ocean, the height of the waves born there very rarely exceeds 1 meter, it is believed that deep oceanic earthquakes are not terrible for navigation, since the waves have a large width between the crests.

When is the movement earth's crust happens closer to the coast, then the wave speed drops, and its height, on the contrary, rises and can sometimes grow to 30 or 40 meters. It is these massive layers of water that crash onto the shore, and it is they who are called tsunamis.

Reasons for the birth of a wave

As mentioned above, an underwater earthquake is one of the most common causes of the formation of huge waves. It accounts for up to 85% of all tsunamis, but scientists say that not all tremors in the ocean provoke the birth of high waves. So, about 7% of huge waves are formed due to landslides. For example, we can cite a case that took place in Alaska: there was a landslide that fell into the water from a height of 1100 meters and thereby provoked the appearance of a tsunami with a wave of more than 500 meters. Of course, such cases are very rare, because landslides occur more often under water in river deltas, and they do not pose a danger.

Another reason for the formation of a tsunami is a volcanic eruption, which accounts for up to 4.99% of the tsunami. Such an eruption under water is similar to an ordinary earthquake. However, the mechanism and consequences of crustal movement are fundamentally different. If it happens strong eruption volcano, not only tsunamis are formed from it, during the eruption the rock cavity cleaned with lava is filled with water, after the eruption an underwater depression or the so-called underwater lake. As a result of the eruption, a very long wave is born. An example of a relatively recent birth of this type of wave is the volcanic eruption of Krakatoa.

The cause of the formation of a tsunami can be meteorites, or rather their fall into the ocean, but such cases are very rare. In each of the above cases, the formation of a tsunami occurs in almost the same way: water moves vertically, and then returns to its original position.

A is the depth of the ocean (the so-called shallow water approximation, when the wavelength is much greater than the depth). With an average depth of 4 km, the propagation velocity is 200 m/s or 720 km/h. In the open ocean, wave height rarely exceeds one meter, and the wave length (distance between crests) reaches hundreds of kilometers, and therefore the wave is not dangerous for navigation. When waves enter shallow water, near the coastline, their speed and length decrease, and their height increases. Near the coast, the height of a tsunami can reach several tens of meters. The highest waves, up to 30-40 meters, are formed near steep banks, in wedge-shaped bays and in all places where focusing can occur. Coastal areas with closed bays are less dangerous. A tsunami usually manifests itself as a series of waves, since the waves are long, more than an hour can pass between wave arrivals. That is why you should not return to the shore after the departure of the next wave, but you should wait a few hours.

The wave height in coastal shallow water (H shallow), which does not have protective structures, can be calculated using the following empirical formula:

H small = 1.3 H deep (B deep / B shallow) 1/4, m

where: H deep - initial wave height in a deep place;

B deep - depth of water in a deep place; B small - water depth in the coastal shallows;

Reasons for the formation of a tsunami

The most common reasons

Other possible causes

• Human activity. In our age of atomic energy, man has in his hands a means to cause concussions, previously available only to nature. In 1946, the United States carried out an underwater atomic explosion in a 60 m deep sea lagoon with a TNT equivalent of 20,000 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. landslides and explosions are always local. If several explosions are made at the same time hydrogen bombs on the ocean floor, along any line, then there will be no theoretical obstacles to the occurrence of a tsunami, such experiments have been carried out, but did not lead to any significant results compared to more available species weapons. At present, any underwater testing of atomic weapons is prohibited by a series of international treaties.

• Falling major celestial body can cause a huge tsunami, because, having a huge falling speed (tens of kilometers per second), these bodies have colossal kinetic energy, and their mass can be billions of tons or more. This energy is transferred to the water, resulting in a wave.

• Wind can cause large waves (up to about 20 m), but such waves are not tsunamis, as they are short-term and cannot cause flooding on the coast. However, the formation of a meteorological tsunami is possible when abrupt change pressure or rapidly moving atmospheric pressure anomalies. This phenomenon is observed in the Balearic Islands and is called rissaga (en: Rissaga).

Signs of a tsunami

• Sudden rapid withdrawal of water from the shore for a considerable distance and drying of the bottom. The further the sea recedes, the higher the tsunami waves can be. People who are on the shore and unaware of the danger may stay out of curiosity or to collect fish and shells. AT this case it is necessary to leave the coast as soon as possible and move away from it to the maximum distance - this rule should be followed, for example, while in Japan, on the Indian Ocean coast of Indonesia, Kamchatka. In the case of a teletsunami, the wave usually approaches without the water receding.
• Earthquake. The epicenter of an earthquake is usually in the ocean. On the coast, the earthquake is usually much weaker, and often there is none at all. 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, thus preparing in advance for the arrival of a wave.
• Unusual drift of ice and other floating objects, formation of cracks in fast ice.
• Huge reverse faults at the edges of immovable ice and reefs, the formation of crowds, currents.

Tsunami danger

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

• The height of the wave 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 take place without a wave at all, in the usual sense, but as a series of rapid tides, which can also lead to casualties and destruction.

• During a storm, only the surface layer of water comes into motion. During a tsunami - the entire water column, from the bottom to the surface. At the same time, a volume of water splashes onto the shore during a tsunami, thousands of times greater than storm waves. It is also worth considering the fact that the length of the crest of storm waves does not exceed 100-200 meters, while in a tsunami the length of the crest extends along the entire coast, and this is more than one thousand kilometers.

• 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.

• 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.

• During a storm, the excitement builds up gradually, people usually have time to move to a safe distance before the arrival of large waves. The tsunami comes suddenly.

• Tsunami damage can increase in harbors, where wind waves are attenuated and, consequently, residential buildings can stand close to the shore.

• Lack of basic knowledge among the population about the possible danger. So, during the 2004 tsunami, when the sea receded from the shore, 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 subsequent waves.

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

• The destruction of coastal infrastructure exacerbates the disaster, adding catastrophic man-made and social factors. Flooding of lowlands, river valleys leads to soil salinization.

Tsunami Warning Systems

Tsunami warning systems are built mainly on the processing of seismic information. If the earthquake has a magnitude of more than 7.0 (in the press this is called points on the Richter scale, although this is an error, since the magnitude is not measured in points. The point is measured in points, which characterizes the intensity of shaking the ground during an earthquake) and the center is located under water, then a tsunami warning is issued. Depending on the region and the population of the coast, the conditions for generating an alarm signal may be different.

The second possibility of a tsunami warning is a "post-warning" - a more reliable method, since there are practically no false alarms, but often such a warning can be generated too late. The warning is actually useful for teletsunamis - global tsunamis that affect the entire ocean and come to other ocean boundaries after a few hours. Thus, the Indonesian tsunami in December 2004 is a teletsunami for Africa. A classic case is the Aleutian tsunami - after a strong surge in the Aleuts, a significant surge can be expected in the Hawaiian Islands. Bottom sensors are used to detect tsunami waves in the open ocean hydrostatic pressure. A warning system based on such sensors with satellite communication from a near-surface buoy, developed in the USA, is called DART (en:Deep-ocean Assessment and Reporting of Tsunamis). Having detected a 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 timely dissemination of information among the population. It is very important that the population is aware of the threat that a tsunami brings with it. Japan has a lot of education programs on natural disasters, and in Indonesia the population is mostly unfamiliar with tsunamis, which was the main reason a large number casualties in 2004. Also important is the legislative framework for coastal development.

The biggest tsunamis

20th century

• November 5, 1952 Severo-Kurilsk (USSR).

see also

Sources

• Pelinovsky EN Hydrodynamics of tsunami waves / IAP RAS. Nizhny Novgorod, 1996. 277 p.
• Local tsunamis: prevention and risk reduction, collection of articles. / Edited by Levin B.V., Nosov M.A. - M .: Janus-K, 2002
• Levin BV, Nosov MA Physics of tsunami and related phenomena in the ocean. M.: Janus-K, 2005
• Earthquakes and Tsunamis - Study Guide - (Contents)
• Kulikov E. A. "Physical foundations of tsunami modeling" (training course)

Tsunami in art

• "Attention, tsunami!" - Feature Film(Odessa Film Studio, 1969)
• "Tsunami" - song by V. S. Vysotsky, 1969
• "Tsunami" - the name of the album of the group "Night snipers" ().
• "Tsunami" - a novel by Gleb Shulpyakov
• "Tsunami" - Korean film, 2009
• "2012 (film)", 2009
• The film "Collision with the abyss", 1998
• Tsunami 3D - thriller 2012
• Catastrophic natural phenomena. The electronic version of the textbook of the rescuer team of authors (Shoigu S. K., Kudinov S. M., Nezhivoy A. F., Nozhevoi S. A., under general edition Vorobyov Yu. L.), published by the Russian Emergencies Ministry in 1997.

Notes

Links

	Tsunami in Wiktionary
	Tsunami at Wikimedia Commons
	Tsunami at Wikinews

• Tsunami Thailand (Koh Phi Phi) 2004 on YouTube (showing several phases of the arrival of the tsunami starting from calm water)

At the end of December 2004, one of the strongest earthquakes in the last half century occurred near the island of Sumatra, located in the Indian Ocean. Its consequences turned out to be catastrophic: due to the displacement of the lithospheric plates, a huge fault was formed, and a large amount of water rose from the ocean floor, which, at a speed reaching one kilometer per hour, began to move rapidly throughout the Indian Ocean.

As a result, thirteen countries were affected, about a million people were left without a “roof over their heads”, and more than two hundred thousand died or went missing. This disaster turned out to be the worst in the history of mankind.

Tsunamis are long and high waves that appear as a result of a sharp displacement of the lithospheric plates of the ocean floor during underwater or coastal earthquakes (the length of the shaft is from 150 to 300 km). Unlike ordinary waves, which appear as a result of exposure to water surface strong wind(for example, storms), a tsunami wave affects the water from the bottom to the surface of the ocean, because of which even low-raised water can often lead to disasters.

Interestingly, these waves are not dangerous for ships in the ocean at this time: most of the agitated water is in its bowels, the depth of which is several kilometers - and therefore the height of the waves above the water surface is from 0.1 to 5 meters. Approaching the coast, the back of the wave catches up with the front, which at this time slows down slightly, grows to a height of 10 to 50 meters (the deeper the ocean, the larger the shaft) and a crest appears on it.

It should be taken into account that the impending shaft develops the highest speed in the Pacific Ocean (it ranges from 650 to 800 km/h). As for the average speed of most waves, it ranges from 400 to 500 km / h, but cases have been recorded when they accelerated to a speed of a thousand kilometers (the speed usually increases after the wave passes over a deep trench).

Before crashing on the coast, the water suddenly and quickly moves away from the coastline, exposing the bottom (the further it retreated, the higher the wave will be). If people do not know about the approaching elements, instead of moving as far as possible from the coast, on the contrary, they run to collect shells or pick up fish that did not have time to go to sea. And just a few minutes later, a wave that arrived here at great speed does not leave them the slightest chance of salvation.

It must be borne in mind that if a wave rolls on the coast from the opposite side of the ocean, then the water does not always recede.

Ultimately, a huge mass of water floods the entire coastal line and goes inland to a distance of 2 to 4 km, destroying buildings, roads, piers and leading to the death of people and animals. In front of the shaft, clearing the way for water, there is always an air shock wave, which literally blows up buildings and structures that are in its path.

It is interesting that this deadly natural phenomenon consists of several waves, and the first wave is far from the largest: it only wets the coast, reducing the resistance for the waves following it, which often do not come immediately, and at intervals of two to three hours. Fatal mistake people is their return to the shore after the departure of the first attack of the elements.

Reasons for education

One of the main reasons for the displacement of lithospheric plates (in 85% of cases) are underwater earthquakes, during which one part of the bottom rises and the other falls. As a result, the ocean surface begins to oscillate vertically, trying to return to the initial level, forming waves. It is worth noting that underwater earthquakes do not always lead to the formation of a tsunami: only those where the source is located at a small distance from the ocean floor, and the shaking was at least seven points.

The reasons for the formation of a tsunami are quite different. The main ones include underwater landslides, which, depending on the steepness of the continental slope, are able to overcome huge distances - from 4 to 11 km strictly vertically (depending on the depth of the ocean or gorge) and up to 2.5 km - if the surface is slightly inclined.

Large waves can cause huge objects that have fallen into the water - rocks or blocks of ice. Thus, the largest tsunami in the world, whose height exceeded five hundred meters, was recorded in Alaska, in the state of Lituya, when, as a result of a strong earthquake, a landslide descended from the mountains - and 30 million cubic meters of stones and ice fell into the bay.

Volcanic eruptions (about 5%) can also be attributed to the main causes of tsunamis. During strong volcanic explosions, waves are formed, and water instantly fills the vacated space inside the volcano, as a result of which it forms and begins its journey. huge size shaft.

For example, during the eruption of the Indonesian volcano Krakatoa in late XIX Art. "killer wave" destroyed about 5 thousand sea ​​vessels and caused the death of 36 thousand people.

In addition to the above, experts identify two more possible reasons occurrence of a tsunami. First of all, it is a human activity. So, for example, in the middle of the last century, Americans made an underwater atomic explosion at a depth of sixty meters, causing a wave about 29 meters high, however, it did not last long and fell, breaking 300 meters as much as possible.

Another reason for the formation of a tsunami is the fall into the ocean of meteorites with a diameter of more than 1 km (the impact of which is strong enough to cause a natural disaster). According to one version of scientists, several thousand years ago, it was meteorites that caused the strongest waves that caused the largest climatic disasters in the history of our planet.

Classification

When classifying tsunamis, scientists take into account a sufficient number of factors of their occurrence, among which are meteorological disasters, explosions, and even ebb and flow, while the list includes low wave surges about 10 cm high.
Shaft strength

The strength of the shaft is measured, taking into account its maximum height, as well as how catastrophic it caused and, according to the international IIDA scale, 15 categories are distinguished, from -5 to +10 (than more casualties, the higher the category).

By intensity

According to the intensity of the “killer wave”, they are divided into six points, which make it possible to characterize the consequences of the elements:

1. Waves with a category of one point are so small that they are recorded only by instruments (most do not even know about their presence).
2. Double-point waves are capable of slightly flooding the coast, therefore only specialists can distinguish them from fluctuations of ordinary waves.
3. The waves, which are classified as three-point, are strong enough to throw small boats onto the coast.
4. Four-point waves can not only wash large sea vessels ashore, but also throw them ashore.
5. Five-point waves are already acquiring the scale of a catastrophe. They are able to destroy low buildings, wooden buildings, and lead to human casualties.
6. As for the six-point waves, the waves that have washed over the coast completely devastate it along with the adjacent lands.

By the number of victims

According to the number of deaths, there are five groups of this dangerous phenomenon. The first includes situations where deaths were not recorded. To the second - waves that resulted in the death of up to fifty people. Shafts belonging to the third category cause the death of fifty to one hundred people. The fourth category includes "killer waves" that killed from a hundred to a thousand people.

The consequences of a tsunami belonging to the fifth category are catastrophic, since they entail the death of more than a thousand people. Typically, such disasters are characteristic of the deepest ocean in the world, the Pacific, but often occur in other parts of the planet. This applies to the disasters of 2004 near Indonesia and 2011 in Japan (25,000 deaths). “Killer waves” were also recorded in history in Europe, for example, in the middle XVIII century a thirty-meter shaft hit the coast of Portugal (during this disaster, from 30 to 60 thousand people died).

Economic damage

As for the economic damage, it is measured in US dollars and calculated taking into account the costs that must be allocated for the restoration of the destroyed infrastructure (lost property and destroyed houses are not taken into account, because they are related to the country's social expenditures).

According to the size of losses, economists distinguish five groups. The first category includes waves that did not cause much harm, the second - with losses up to $ 1 million, the third - up to $ 5 million, the fourth - up to $ 25 million.

The damage from the waves, related to the fifth group, exceeds 25 million. For example, the losses from two major natural disasters in 2004 near Indonesia and in 2011 in Japan amounted to about $250 billion. It is also worth considering environmental factor, because the waves that caused the death of 25 thousand people damaged in Japan nuclear power plant causing an accident.

Natural disaster identification systems

Unfortunately, "killer waves" often appear so unexpectedly and move at such a high speed that it is extremely difficult to determine their appearance, and therefore seismologists often fail to cope with the task assigned to them.

Basically, disaster warning systems are built on the processing of seismic data: if there is a suspicion that an earthquake will have a magnitude of more than seven points, and its source will be on the ocean (sea) floor, then all countries that are at risk receive warnings of the approach of huge waves.

Unfortunately, the disaster of 2004 happened because almost all the neighboring countries did not have an identification system. Despite the fact that about seven hours passed between the earthquake and the surge, the population was not warned about the approaching disaster.

To determine the presence of dangerous waves in the open ocean, scientists use special hydrostatic pressure sensors that transmit data to the satellite, which allows you to fairly accurately determine the time of their arrival at a particular point.

How to survive during the elements

If it so happens that you find yourself in an area where there is a high probability of deadly waves, you must definitely remember to follow the forecasts of seismologists and remember all the warning signals of an approaching disaster. It is also necessary to know the boundaries of the most dangerous zones and the shortest roads by which you can leave the dangerous territory.

If you hear a signal warning of approaching water, you should immediately leave danger zone. Experts will not be able to say exactly how much time there is for evacuation: maybe a couple of minutes or several hours. If you do not have time to leave the area and live in a multi-storey building, then you need to go up to the top floors, closing all windows and doors.

But if you are in a one- or two-story house, you must immediately leave it and run to a tall building or climb any hill (in extreme cases, you can climb a tree and cling to it tightly). If it so happened that you did not have time to leave a dangerous place and ended up in the water, you need to try to free yourself from shoes and wet clothes and try to cling to floating objects.

When the first wave subsides, it is necessary to leave the dangerous area, since the next one will most likely come after it. You can return only when there are no waves for about three to four hours. Once at home, check walls and ceilings for cracks, gas leaks, and electrical conditions.

Tsunamis have been a nightmare for the inhabitants of the islands for all ages. These multi-meter waves swept away everything in their path with tremendous destructive force, leaving behind only bare ground and trash. The statistics of monstrous waves has been conducted by scientists since the nineteenth century, during this period more than a hundred tsunamis of various power were recorded. Do you know what the most big tsunami in the world?

Tsunami: what is it?

It is not surprising that the term "tsunami" was first introduced by the Japanese. They suffered from giant waves most often, because the Pacific Ocean gives rise to the largest number of destructive waves than all other seas and oceans combined. This is due to the peculiarities of the relief of the ocean floor and the high seismicity of the region. AT Japanese the word "tsunami" consists of two hieroglyphs meaning a bay and a wave. Thus, the very meaning of the phenomenon is revealed - a wave in the bay, sweeping away all life on the coast.

When was the first tsunami recorded?

Of course, tsunamis have always suffered. Ordinary island residents came up with their own names for the killer waves and believed that the gods of the seas punish people by sending destructive waves at them.

For the first time, a tsunami was officially recorded and explained at the end of the sixteenth century. This was done by a monk of the Jesuit church, Jose de Acosta, he was in Peru, when a wave about twenty-five meters high hit the shore. She swept away all the settlements around in a few seconds and advanced ten kilometers deep into the continent.

Tsunami: causes and consequences

Tsunamis are most often caused by earthquakes and underwater volcanic eruptions. The closer the epicenter of the earthquake is to the coast, the stronger the killer wave will be. The largest tsunamis in the world that were recorded by mankind could reach speeds of up to one hundred and sixty kilometers per hour and exceed three hundred meters in height. Such waves do not leave a chance to survive for any of the living beings that are on their way.

If we consider the nature of this phenomenon, then briefly it can be explained as the simultaneous displacement of a large amount of water masses. Eruptions or earthquakes raise the ocean floor sometimes by several meters, which causes water vibrations and forms several waves that diverge from the epicenter in different directions. Initially, they do not represent something terrible and deadly, but as they approach the coast, the speed and height of the wave increases, and it turns into a tsunami.

In some cases, tsunamis are formed as a result of giant landslides. During the twentieth century, about seven percent of all gigantic waves arose for this reason.

The consequences of the devastation left behind by the largest tsunamis in the world are terrible: thousands human casualties and hundreds of kilometers of land filled with debris and mud. In addition, in the disaster area, there is a high probability of the spread of infectious diseases due to the lack of drinking water and rotting of the bodies of the dead, the search for which is not always possible to organize in the shortest possible time.

Tsunami: is it possible to escape?

Unfortunately, world system tsunami warnings are still imperfect. AT best case people learn about the danger a few minutes before the wave hits, so it is necessary to know the signs of impending disaster and the rules for survival during a cataclysm.

If you are on the sea or ocean coast, then carefully follow the reports of earthquakes. A shaking of the earth's crust with a magnitude of about seven on the Richter scale that occurred somewhere nearby could serve as a warning of a possible tsunami strike. The approach of a killer wave gives out a sudden ebb - the ocean floor is quickly exposed for several kilometers. This is a clear sign of a tsunami. And the further the water will go away, the stronger and more destructive the incoming wave will be. Often such natural disasters animals anticipate: a few hours before the cataclysm, they whine, hide, try to go deep into the island or mainland.

To survive during a tsunami, you need to leave the dangerous area as soon as possible. Do not take a lot of things with you, drinking water, food and documents will be enough. Try to get as far away from the coast as possible or climb to the roof of a multi-storey building. All floors after the ninth are considered safe.

If the wave still overtakes you, then find an object that you can hold on to. According to statistics, most people die when the wave begins to return back to the ocean and takes away all the objects that have come across. Keep in mind that tsunamis almost never end in one wave. Most often, the first will be followed by a series of two or even three new ones.

So, when was the biggest tsunami in the world? And how much destruction did they bring?

This catastrophe does not fit any of the previously described incidents on the sea coast. To date, the Lituya Bay megatsunami has become the most gigantic and destructive in the world. Eminent luminaries in the field of oceanology and seismology are still arguing about the possibility of a repetition of such a nightmare.

Lituya Bay is located in Alaska and extends inland for eleven kilometers, its maximum width does not exceed three kilometers. Two glaciers descend into the bay, which became the unwitting creators of a huge wave. The 1958 tsunami in Alaska was caused by an earthquake on July 9th. The power of the shocks exceeded eight points, which caused a huge landslide to descend into the waters of the bay. Scientists calculated that thirty million cubic meters of ice and stones fell into the water in a few seconds. Parallel to the landslide, an under-ice lake sank thirty meters, from which the released water masses rushed into the bay.

A huge wave rushed to the coast and circled the bay several times. The height of the tsunami wave reached five hundred meters, the raging elements completely demolished the trees on the rocks along with the ground. At the moment, this wave is the highest in the history of mankind. Surprising fact is that as a result powerful tsunami only five people died. The fact is that there are no residential settlements in the bay; at the time the wave arrived in Lituya, there were only three fishing boats. One of them, together with the crew, immediately sank, and the other was raised by a wave to its maximum height and carried out into the ocean.

2004 Indian Ocean avalanche

The tsunami in Thailand in 2004 shocked all people on the planet. As a result of the destructive wave, more than two hundred thousand people died. The cause of the disaster was an earthquake in the Sumatra region on December 26, 2004. The tremors lasted no more than ten minutes and exceeded nine on the Richter scale.

A thirty-meter wave swept at great speed throughout the Indian Ocean and circled it, stopping near Peru. Almost all island states, including India, Indonesia, Sri Lanka and Somalia, suffered from the tsunami.

After killing hundreds of thousands of people, the 2004 Thailand tsunami left behind destroyed houses, hotels and several thousand local residents who died as a result of infections and poor-quality drinking water. At the moment, this tsunami is considered the largest in the twenty-first century.

Severo-Kurilsk: tsunami in the USSR

The list of "The biggest tsunamis in the world" should include the wave that hit the Kuriles in the middle of the last century. An earthquake in the Pacific Ocean caused a twenty-meter wave. The epicenter of the tremors of magnitude seven was located one hundred and thirty kilometers from the coast.

The first wave arrived in the city about an hour later, but most of the locals were in hiding on the high ground away from the city. No one warned them that a tsunami was a series of waves, so all the townspeople returned to their homes after the first one. A few hours later, the second and third waves hit Severo-Kurilsk. Their height reached eighteen meters, they almost completely destroyed the city. More than 2,000 people died as a result of the cataclysm.

Killer wave in Chile

In the second half of the last century, the inhabitants of Chile faced a terrifying tsunami, which killed more than three thousand people. The cause of the giant waves was the most powerful earthquake in the history of mankind, its magnitude exceeded nine and a half points.

A twenty-five-meter high wave covered Chile fifteen minutes after the first shocks. During the day, she covered several thousand kilometers, destroying the coast of Hawaii and Japan.

Despite the fact that humanity has been "familiar" with the tsunami for quite a long time, this natural phenomenon is still among the little-studied. Scientists have not learned how to predict the appearance of killer waves, therefore, most likely, in the future the list of their victims will be replenished with new deaths.