6. Sea waves.
© Vladimir Kalanov,
"Knowledge is power".
The surface of the sea is always moving, even with complete calm. But then the wind blew, and ripples immediately appeared on the water, which turned into waves the faster the stronger the wind blew. But no matter how strong the wind is, it cannot cause waves larger than a certain maximum. large sizes.
Waves generated by wind are considered short. Depending on the strength and duration of the wind, their length and height range from several millimeters to tens of meters (in a storm, the length of wind waves reaches 150-250 meters).
Observations of the sea surface show that waves become strong even at wind speeds of more than 10 m/s, while the waves rise to a height of 2.5-3.5 meters, crashing onto the shore with a roar.
But then the wind turns storm, and the waves reach enormous sizes. There are many places on the globe where very strong winds blow. For example, in the northeastern part of the Pacific Ocean east of the Kuril and Commander Islands, as well as east of the main Japanese island of Honshu, in December-January maximum wind speeds are 47-48 m/s.
In the South Pacific, maximum wind speeds are observed in May in the area northeast of New Zealand (49 m/s) and near the Antarctic Circle in the area of Balleny and Scott Islands (46 m/s).
We perceive speeds expressed in kilometers per hour better. So the speed of 49 m/s is almost 180 km/h. Already at a wind speed of more than 25 m/s, waves 12-15 meters high rise. This degree of excitement is rated 9–10 points as a severe storm.
Measurements have established that the height of the storm wave in the Pacific Ocean reaches 25 meters. There are reports that waves up to 30 meters high have been observed. True, this assessment was made not on the basis of instrumental measurements, but approximately, by eye.
In the Atlantic Ocean, the maximum height of wind waves reaches 25 meters.
The length of storm waves does not exceed 250 meters.
But the storm stopped, the wind died down, but the sea still did not calm down. Like the echo of a storm on the sea arises swell. Swell waves (their length reaches 800 meters or more) move over enormous distances of 4-5 thousand km and approach the shore at a speed of 100 km/h, and sometimes higher. In the open sea, low and long swell waves are invisible. When approaching the shore, the speed of the wave decreases due to friction with the bottom, but the height increases, the front slope of the wave becomes steeper, foam appears at the top, and the crest of the wave crashes onto the shore with a roar - this is how the surf appears - a phenomenon equally colorful and majestic, as dangerous as it is. The force of the surf can be colossal.
When faced with an obstacle, the water rises to a great height and damages lighthouses, port cranes, breakwaters and other structures. Throwing stones from the bottom, the surf can damage even the highest and most distant parts of lighthouses and buildings. There was a case when the surf tore a bell from one of the English lighthouses from a height of 30.5 meters above sea level. The surf on our Lake Baikal sometimes in stormy weather throws stones weighing up to a ton at a distance of 20-25 meters from the shore.
During storms in the Gagra region, the Black Sea eroded and swallowed up a 20-meter-wide coastal strip over 10 years. When approaching the shore, the waves begin their destructive work from a depth equal to half their length in the open sea. Thus, with a storm wave length of 50 meters, characteristic of seas such as the Black or Baltic, the impact of waves on the underwater coastal slope begins at a depth of 25 m, and with a wave length of 150 m, characteristic of the open ocean, such impact begins already at a depth of 75 m.
Current directions affect the size and strength of sea waves. With countercurrents, the waves are shorter but higher, and with countercurrents, on the contrary, the height of the waves decreases.
Near the boundaries of sea currents, waves of unusual shapes, resembling a pyramid, and dangerous whirlpools often appear, which suddenly appear and just as suddenly disappear. In such places, navigation becomes especially dangerous.
Modern ships have high seaworthiness. But it happens that, having traveled many miles across a stormy ocean, ships find themselves in even greater danger than at sea when they arrive in their home bay. The mighty surf, breaking the multi-ton reinforced concrete breakwaters of the dam, is capable of turning even capital ship into a pile of metal. In a storm, it is better to wait until entering the port.
To combat the surf, specialists in some ports tried to use air. A steel pipe with numerous small holes was laid on the seabed at the entrance to the bay. Air under high pressure was supplied into the pipe. Escaping from the holes, streams of air bubbles rose to the surface and destroyed the wave. This method has not yet found widespread use due to insufficient efficiency. Rain, hail, ice and thickets of marine plants are known to calm waves and surf.
Sailors have long noticed that fat poured overboard smoothes the waves and reduces their height. Animal fat, such as whale blubber, works best. The effect of vegetable and mineral oils is much weaker. Experience has shown that 50 cm 3 of oil is enough to reduce disturbances over an area of 15 thousand square meters, that is, 1.5 hectares. Even a thin layer of oil film noticeably absorbs the energy of vibrational movements of water particles.
Yes, that's all true. But, God forbid, we under no circumstances recommend that captains sea vessels Before the voyage, stock up on fish or whale oil in order to then pour these fats into the waves to calm the ocean. After all, things can reach such an absurdity that someone will start pouring oil, fuel oil, and diesel fuel into the sea in order to appease the waves.
It seems to us that The best way combating waves consists of a well-organized weather service that notifies ships in advance about the expected place and time of the storm and its expected strength, good navigational and pilot training of sailors and coastal personnel, as well as constant improvement of the design of ships in order to improve their seaworthiness and technical capabilities. reliability.
For scientific and practical purposes, it is necessary to know the full characteristics of the waves: their height and length, the speed and range of their movement, the power of an individual water shaft and the wave energy in a particular area.
The first measurements of waves were made in 1725 by the Italian scientist Luigi Marsigli. At the end of the 18th – beginning of the 19th centuries, regular observations of waves and their measurements were carried out by Russian navigators I. Kruzenshtern, O. Kotzebue and V. Golovin during their voyages across the World Ocean. The technical basis for measurements in those days was very weak; of course, there were no special instruments for measuring waves on the sailing ships of that time.
Currently, for these purposes, there are very complex and precise instruments that are equipped with research vessels that carry out not only measurements of wave parameters in the ocean, but also much more complex scientific work. The ocean still holds many secrets, the disclosure of which could bring significant benefits to all of humanity.
When they talk about the speed of movement of waves, that waves run up and roll onto the shore, you need to understand that it is not the water mass itself that moves. The water particles that make up the wave practically do not move forward. Only the wave form moves in space, and water particles in a rough sea perform oscillatory movements in the vertical and, to a lesser extent, in the horizontal plane. The combination of both oscillatory movements leads to the fact that the water particles in the waves actually move in circular orbits, the diameter of which is equal to the height of the wave. The oscillatory movements of water particles quickly decrease with depth. Precise instruments show, for example, that with a wave height of 5 meters (storm wave) and a length of 100 meters, at a depth of 12 meters the diameter of the wave orbit of water particles is already 2.5 meters, and at a depth of 100 meters - only 2 centimeters.
Long waves, unlike short and steep ones, transmit their motion to great depths. In some photographs of the ocean floor down to a depth of 180 meters, researchers noted the presence of sand ripples formed under the influence of oscillatory movements of the bottom layer of water. This means that even at such a depth, the surface waves of the ocean make themselves felt.
Is it necessary to prove what danger a storm wave poses to ships?
In the history of navigation, there are countless tragic incidents at sea. Small longboats and high-speed sailing ships, along with their crews, perished. Modern ocean liners are not immune to the insidious elements.
On modern ocean-going ships, among other devices and instruments that ensure safe navigation, pitch stabilizers are used, which prevent the ship from getting an unacceptably large roll on board. In some cases, powerful gyroscopes are used for this, in others, retractable hydrofoils are used to level the position of the ship’s hull. Computer systems on ships are in constant communication with meteorological satellites and other spacecraft, telling navigators not only the location and strength of storms, but also the most favorable course in the ocean.
In addition to surface waves, there are also internal waves in the ocean. They form at the interface between two layers of water of different densities. These waves travel slower than surface waves, but can have greater amplitude. Internal waves are detected by rhythmic changes in temperature at different depths of the ocean. The phenomenon of internal waves has not yet been sufficiently studied. It has only been established that waves arise at the boundary between layers with lower and higher densities. The situation may look like this: there is complete calm on the surface of the ocean, but at some depth a storm is raging; along the length, internal waves are divided, like ordinary surface ones, into short and long. For short waves, the length is much less than the depth, while for long waves, on the contrary, the length exceeds the depth.
There are many reasons for the appearance of internal waves in the ocean. The interface between layers with different densities can be thrown out of balance by a moving large vessel, surface waves, or sea currents.
Long internal waves manifest themselves, for example, in this way: a layer of water, which is a watershed between more dense (“heavy”) and less dense (“light”) water, first rises slowly, for hours, and then suddenly falls by almost 100 meters. Such a wave is very dangerous for submarines. After all, if a submarine sank to a certain depth, it means it was balanced by a layer of water of a certain density. And suddenly, unexpectedly, a layer of less dense water appears under the hull of the boat! The boat immediately falls into this layer and sinks to the depth where the less dense water can balance it. But the depth may be such that the water pressure exceeds the strength of the hull of the submarine, and it will be crushed in a matter of minutes.
According to the conclusion of American experts who investigated the causes of the death of the nuclear submarine Thresher in 1963 in the Atlantic Ocean, this submarine found itself in exactly this situation and was crushed by enormous hydrostatic pressure. Naturally, there were no witnesses to the tragedy, but the version of the cause of the disaster is confirmed by the results of observations carried out by research ships in the area where the submarine sank. And these observations showed that internal waves with a height of more than 100 meters often arise here.
A special type are the waves that arise on the sea when there is a change atmospheric pressure. They're called seiches And microseiches. Oceanology studies them.
So, we talked about both short and long waves at sea, both surface and internal. Now let us remember that long waves arise in the ocean not only from winds and cyclones, but also from processes occurring in the earth’s crust and even in the deeper regions of the “interior” of our planet. The length of such waves is many times greater than the longest ocean swell waves. These waves are called tsunami. The height of tsunami waves is not much higher than large storm waves, but their length reaches hundreds of kilometers. The Japanese word "tsunami" roughly translates to "harbour wave" or "coastal wave" . To some extent, this name conveys the essence of the phenomenon. The point is that in open ocean a tsunami poses no danger. At a sufficient distance from the coast, the tsunami does not rage, does not cause destruction, and cannot even be noticed or felt. All tsunami disasters occur on the shore, in ports and harbors.
Tsunamis occur most often from earthquakes caused by the movement of tectonic plates earth's crust, as well as from strong volcanic eruptions.
The mechanism for the formation of a tsunami is most often as follows: as a result of the displacement or rupture of a section of the earth's crust, a sudden rise or fall of a significant section of the seabed occurs. As a result, a rapid change in the volume of the water space occurs, and elastic waves appear in the water, propagating at a speed of about one and a half kilometers per second. These powerful elastic waves generate tsunamis on the ocean surface.
Having arisen on the surface, tsunami waves scatter in circles from the epicenter. At the point of origin, the height of the tsunami wave is small: from 1 centimeter to two meters (sometimes up to 4-5 meters), but more often in the range from 0.3 to 0.5 meters, and the wave length is huge: 100-200 kilometers. Invisible in the ocean, these waves, approaching the shore, like wind waves, become steeper and higher, sometimes reaching a height of 10-30 and even 40 meters. Having hit the shore, tsunamis destroy and destroy everything in their path and, worst of all, bring death to thousands, and sometimes tens and even hundreds of thousands of people.
The speed of tsunami propagation can be from 50 to 1000 kilometers per hour. Measurements show that the speed of a tsunami wave varies in proportion to the square root of the sea depth. On average, a tsunami rushes across the open ocean at a speed of 700-800 kilometers per hour.
Tsunamis are not regular events, but they are no longer rare.
In Japan, tsunami waves have been recorded for more than 1,300 years. On average, destructive tsunamis hit the Land of the Rising Sun every 15 years (small tsunamis that did not have serious consequences are not taken into account).
Most tsunamis occur in the Pacific Ocean. Tsunamis raged in the Kuril, Aleutian, Hawaiian, and Philippine islands. They also attacked the coasts of India, Indonesia, Northern and South America, as well as to European countries located on the Atlantic coast and in the Mediterranean.
The last most destructive tsunami attack was the terrible flood of 2004 with enormous destruction and loss of life, which had seismic causes and originated in the center of the Indian Ocean.
In order to have an idea of the specific manifestations of a tsunami, you can refer to numerous materials that describe this phenomenon.
We will give just a few examples. This is how the results of the earthquake that occurred in the Atlantic Ocean not far from the Iberian Peninsula on November 1, 1755 were described in the press. It caused terrible destruction in the capital of Portugal, Lisbon. The ruins of what once once stood still stand in the center of the city. majestic building convent Karmo that was never restored. These ruins remind the people of Lisbon of the tragedy that struck the city on November 1, 1755. Shortly after the earthquake, the sea receded, and then a wave 26 meters high hit the city. Many residents, fleeing the falling debris of buildings, left the narrow streets of the city and gathered on the wide embankment. The surging wave washed away 60 thousand people into the sea. Lisbon was not completely flooded because it is located on several high hills, but in low-lying areas the sea flooded the land up to 15 kilometers from the coast.
August 27, 1883 occurred powerful eruption Kratau volcano, located in the Sunda Strait of the Indonesian archipelago. Clouds of ash rose into the sky, a strong earthquake arose, generating a wave 30-40 meters high. In a few minutes, this wave washed away all the villages located on the low shores of western Java and southern Sumatra into the sea, killing 35 thousand people. At a speed of 560 kilometers per hour, tsunami waves swept through the Indian and Pacific oceans, reaching the shores of Africa, Australia and America. Even in the Atlantic Ocean, despite its isolation and remoteness, in some places (France, Panama) a certain rise in water was noted.
On June 15, 1896, the incoming tsunami waves destroyed 10 thousand houses on the eastern coast of the Japanese island of Honshu. As a result, 27 thousand inhabitants died.
It is impossible to fight a tsunami. But it is possible and necessary to minimize the damage they cause to people. Therefore, now in all seismically active areas where there is a threat of tsunami waves, special warning services have been created, equipped with the necessary equipment that receives signals about changes in the seismic situation from sensitive seismographs located in different places on the coast. The population of such areas is regularly instructed on the rules of behavior in the event of a threat of tsunami waves. Tsunami warning services in Japan and the Hawaiian Islands have repeatedly given timely warning signals about the approach of a tsunami, thereby saving more than one thousand human lives.
All types of currents and waves are characterized by the fact that they carry colossal energy - thermal and mechanical. But humanity is not able to use this energy, unless, of course, we count attempts to use the energy of ebbs and flows. One of the scientists, probably a lover of statistics, calculated that the power of sea tides exceeds 1000000000 kilowatts, and all rivers globe– 850000000 kilowatts. Energy of one square kilometer stormy sea is estimated at billions of kilowatts. What does this mean for us? Only that a person cannot use even a millionth part of the energy of tides and storms. To some extent, people use wind energy to generate electricity and other purposes. But that, as they say, is another story.
© Vladimir Kalanov,
"Knowledge is power"
Causes of tsunamis
The distribution of tsunamis is usually associated with areas of strong earthquakes. It is subject to a clear geographical pattern, determined by the connection of seismic areas with areas of recent and modern mountain building processes.
It is known that most earthquakes are confined to those belts of the Earth within which the formation continues. mountain systems, especially young ones belonging to the modern geological era. The purest earthquakes occur in areas close to large mountain systems and depressions of seas and oceans.
In Fig. Figure 1 shows a diagram of folded mountain systems and areas of concentration of earthquake epicenters. This diagram clearly identifies two zones of the globe that are most prone to earthquakes. One of them occupies a latitudinal position and includes the Apennines, Alps, Carpathians, Caucasus, Kopet-Dag, Tien Shan, Pamir and Himalayas. Within this zone, a tsunami is observed on the coasts of the Mediterranean, Adriatic, Aegean, Black and Caspian seas and the northern part of the Indian Ocean. The other zone is located in the meridional direction and runs along the shores of the Pacific Ocean. The latter is, as it were, surrounded by underwater mountain ranges, the peaks of which rise in the form of islands (Aleutian, Kuril, Japanese islands and others). Tsunami waves are generated here as a result of gaps between rising mountain ranges and deep-sea trenches descending parallel to the ridges, separating island chains from the sedentary area of the Pacific Ocean floor.
The direct cause of the occurrence of tsunami waves is most often changes in the topography 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 were noted in the telegraph cable laid at the bottom of the sea at a depth of four hundred meters. After the earthquake, one of the ends of the broken cable was discovered at a depth of more than 600 m. Consequently, the earthquake caused a sharp subsidence of a section of the seabed to a depth of about 200 m. A few years later, as a result of another earthquake, a cable laid on a flat bottom broke again, and its ends found themselves at a depth that differed from the previous one by several hundred meters. Finally, another year after the new tremors, the sea depth at the rupture site increased by 400 m.
Even greater disturbances of the bottom topography occur during earthquakes in the Pacific Ocean. Thus, during an underwater earthquake in Sagami Bay (Japan), about 22.5 cubic meters were displaced when a section of the ocean floor suddenly rose. km of water, which hit the shore in the form of tsunami waves.
In Fig. Figure 2a shows the mechanism of tsunami generation as a result of an earthquake. At the moment of a sharp subsidence of a section of the ocean floor and the appearance of a depression on the seabed, the pod rushes to the center, overflows the depression and forms a huge bulge on the surface. When a section of the ocean floor rises sharply, significant masses of water are revealed. At the same time, tsunami waves arise on the surface of the ocean, quickly spreading in all directions. They usually 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.
Another reason that causes tsunamis is volcanic eruptions that rise above the sea surface in the form of islands or are located on the ocean floor (Fig. 2b). The most striking example in this regard is the formation of a tsunami during the eruption of the 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 nearby islands South-East Asia. On August 27 at 10 o'clock in the morning, a gigantic explosion destroyed the volcanic island. At this moment, tsunami waves arose, spreading across all oceans and devastating many islands of the Malay Archipelago. In the narrowest part of the Sunda Strait, the wave height reached 30–35 m. In some places, the waters penetrated deep into Indonesia and caused terrible destruction. Four villages were destroyed on Sebezi Island. The cities of Angers, Merak and Bentham were destroyed, forests and railways washed away, and fishing vessels abandoned on land at a distance of 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 disaster 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 the Pacific Ocean they reached Alaska and San Francisco.
Cases of tsunamis during volcanic eruptions are also known in Japan. So, on September 23 and 24, 1952, there was a strong eruption of an underwater volcano on the Meijin Reef, several hundred kilometers from Tokyo. The resulting waves reached Hotidze Island, northeast of the volcano. During this disaster, the Japanese hydrographic vessel Kaiyo-Maru-5, from which observations were carried out, was lost.
The third reason for a tsunami is the fall of huge rock fragments into the sea, caused by the destruction of rocks by groundwater. The height of such waves depends on the mass of material that has fallen into the sea and the height of its fall. So, in 1930, on the island of Madeira, a block fell from a height of 200 m, which caused the appearance of a single wave 15 m high.
Tsunami off the coast of South America
The Pacific coast within Peru and Chile is prone to frequent earthquakes. Changes occurring in the bottom topography of the coastal part of the Pacific Ocean lead to the formation of large tsunamis. Greatest height(27 m) tsunami waves reached the Callao area during the Lima earthquake in 1746.
If usually the decrease in sea level that precedes the onset of tsunami waves on the coast lasts from 5 to 35 minutes, then during the earthquake in Pisco (Peru) the receding sea waters returned only after three hours, and at Santa even after a day.
Often the onset and retreat of tsunami waves occur here several times in a row. Thus, in Iquique (Peru) on May 9, 1877, the first wave hit the coast half an hour after the main shock of the earthquake, and then within four hours the waves arrived five more times. During this earthquake, the epicenter of which was located 90 km from the Peruvian coast, tsunami waves reached the coasts of New Zealand and Japan.
On August 13, 1868, on the coast of Peru in Arica, 20 minutes after the earthquake began, a wave several meters high surged, but soon receded. With an interval of a quarter of an hour, it was followed by several more waves, smaller in size. After 12.5 hours, the first wave reached the Hawaiian Islands, and 19 hours later - the coast of New Zealand, where 25,000 people became victims. average speed tsunami waves between Arica and Valdivia at a depth of 2200 m were 145 m/sec, between Arica and Hawaii at a depth of 5200 m – 170-220 m/sec, and between Arica and the Chatham Islands at a depth of 2700 m – 160 m/sec.
The most frequent and powerful earthquakes characterize the area of the Chilean coast from Cape Concepcion to the island of Chiloe. It is known that since the disaster of 1562, the city of Concepción suffered 12 strong earthquakes, and the city of Valdivia suffered 7 earthquakes from 1575 to 1907. The January 24, 1939 earthquake killed 1,000 people and left 70,000 homeless in and around Concepcion.
Destruction caused by the 1960 tsunami waves in the city of Puerto Monte
On May 21, 1960, a new earthquake shook the Chilean coast near Cape Concepcion, and then shook the entire southern part countries over 1500 km. During this time, about a thousand people died and about 350,000 people were left homeless. In the cities of Concepción, Puerto Monte, Temuco and the island of Chiloe, 65,000 buildings were completely destroyed and 80,000 were seriously damaged. The strongest shock was on May 22, when the maximum amplitude of soil vibrations in Moscow was 1500 microns. This is three times the amplitude of the vibrations caused by the 1948 Ashgabat earthquake, the epicenter of which was located six times closer to Moscow.
The catastrophic shaking on May 22 generated tsunami waves that spread across the Pacific Ocean and beyond at a speed of 650-700 km/h. On the Chilean coast, fishing villages and port facilities were destroyed; hundreds of people were carried away by the waves. On the island of Chiloe, waves destroyed four-fifths of all buildings.
Consequences of the 1960 tsunami in the Hawaiian Islands
The giant shaft not only devastated pacific coast up to California, but also crossed the Pacific Ocean, hitting Hawaii and the Philippines, the coasts of Australia and New Zealand, the Kuril Islands and Kamchatka. In Hawaii, in the city of Hilo, dozens of people died during the tsunami, many residents went missing and were injured.
Consequences of the 1960 tsunami off the coast of Japan
On the Japanese islands, 36,000 houses were flooded, 900 ships and fishing boats were capsized. On the island of Okinawa, 180 people died or went missing, and in the village of Momoishi, 150 residents died. Never before has it been observed that tsunami waves, having traveled such a huge distance, retained their destructive power.
At about 6 a.m. on May 24, tsunami waves, having traveled 16,000 km, reached the Kuril Islands and the shores of Kamchatka. A five-meter-high wave rushed onto the shore. However, measures to evacuate the population were taken in a timely manner and there were no casualties. On the island of Paramushir, where the ramparts were the highest, the berths of the local fishing collective farm were slightly damaged.
Tsunami off the coast of Japan
Tsunamis are usually accompanied by the most powerful, catastrophic earthquakes that occur on the Japanese Islands on average every seven years. Another reason that causes the formation of a tsunami off the coast of Japan is volcanic eruptions. It is known, for example, that as a result of a volcanic explosion on one of the Japanese islands in 1792, rocks with a volume of about 1 cubic meter were thrown into the sea. km. A sea wave about 9 m high, formed as a result of the fall of eruption products into the sea, demolished several coastal villages and caused the death of more than 15,000 residents.
The tsunami was particularly powerful during the 1854 earthquake, which destroyed Largest cities countries - Tokyo and Kyoto. First, a nine-meter-high wave came ashore. However, it soon flowed away, drying up the coastal area at a great distance. Over the next 4-5 hours, five or six more large waves hit the shore. And after 12.5 hours, tsunami waves, moving at a speed of more than 600 km/h, reached the coast of North America in the San Francisco area.
After this terrible disaster, stone walls were erected on some parts of the coast of the island of Honshu to protect the coast from destructive waves. However, despite the precautions taken, during the earthquake of June 15, 1896, the island of Honshu was again severely damaged by devastating waves. An hour after the earthquake began, six or seven large waves hit the shore at intervals of 7 to 34 minutes, the maximum height of one of which was 30 m. The waves completely washed away the city of Minco, destroyed 10,000 buildings and killed 27,000 people. And 10 years later, during the earthquake of 1906, about 30,000 people again died on the east coast of the country during the onset of a tsunami.
During the famous catastrophic earthquake of 1923, which completely destroyed the Japanese capital, tsunami waves caused devastation on the coast, although they did not reach particularly large sizes, at least in Tokyo Bay. IN southern regions country, the consequences of the tsunami were even more significant: several villages in this part of the coast were completely washed away, and the Yokosuka Japanese naval base, located 12 km south of Yokohama, was destroyed. The city of Kamakura, located on the shores of Sagami Bay, was also severely damaged by sea waves.
On March 3, 1933, 10 years after the 1923 earthquake, a new strong earthquake occurred in Japan, not much inferior to the previous one. The tremors swept the entire eastern part Honshu Islands. The greatest disasters for the population during this earthquake were associated with the onset of tsunami waves, which swept over the entire northern region 40 minutes after the earthquake began. East Coast Honshu. The wave destroyed the port city of Komaishi, where 1,200 houses were destroyed. A large number of villages on the coast were demolished. According to newspaper reports, about 3,000 people were killed or missing during this disaster. In total, more than 4,500 houses were destroyed by the earthquake and washed away by the waves, and more than 6,600 houses were partially damaged. More than 50,000 people were left homeless.
Destruction in the city of Komami after the tsunami in March 1933
Tsunami off the Pacific coast of Russia
The shores of Kamchatka and the Kuril Islands are also susceptible to tsunamis. Initial information about catastrophic waves in these places dates back to 1737. The famous domestic traveler and geographer S.P. Krasheninnikov wrote: “... the shaking began and continued in waves for about a quarter of an hour, so strong that many Kamchadal yurts collapsed and the booths fell. Meanwhile, there was a terrible noise and excitement on the sea, and suddenly water surged onto the shore to a height of three fathoms, which, without standing still, ran into the sea and moved away from the shore to a considerable distance. Then the earth shook a second time, the water came in opposite to the previous one, but at low tide it ran so far that it was impossible to see the sea. At the same time, rocky mountains appeared on the bottom of the sea in the strait between the first and second Kuril Islands, which had never been visible before, although earthquakes and floods had occurred before.
A quarter of an hour after all this, the shocks of a terrible earthquake, incomparable in its strength, followed, and then a wave thirty fathoms high rushed onto the shore, which still quickly ran back. Soon the water entered its banks, fluctuating at long intervals, sometimes covering the banks, sometimes escaping into the sea.”
During this earthquake, massive rocks collapsed, and the incoming wave threw blocks of stone weighing several pounds onto the shore. The earthquake was accompanied by various optical phenomena in the atmosphere. In particular, Abbot Prevost, another traveler who observed this earthquake, wrote that fiery “meteors” could be seen on the sea, scattered over a wide area.
S.P. Krasheninnikov noticed all the most important features of a tsunami: an earthquake, a drop in ocean level preceding the flood, and, finally, the onset of huge destructive waves.
Enormous tsunamis on the coasts of Kamchatka and the Kuril Islands took place in 1792, 1841, 1843, 1918. A series of earthquakes during the winter of 1923 caused repeated onsets of catastrophic waves. There is a well-known description of the tsunami of February 4, 1923, when “three waves rushed onto the land of the eastern coast of Kamchatka one after another, tore off the coastal ice (fast ice a fathom thick), rushed along with it over the coastal spit, and flooded low places. The ice in a low place near Semyachik was thrown out almost 1 verst 400 fathoms from the shore; at higher elevations the ice remained at a height of three fathoms above sea level. In the sparsely populated areas of the east coast, this unprecedented phenomenon caused some damage and destruction.” The natural disaster affected a vast coastal zone with a length of 450 km.
On April 13, 1923, renewed tremors caused tsunami waves up to 11 m high, which completely destroyed the coastal buildings of fish canning factories, some of which were cut off by hummocky ice.
Strong tsunamis were reported on the coast of Kamchatka and the Kuril Islands in 1927, 1939 and 1940.
On November 5, 1952, an earthquake occurred on the eastern coast of Kamchatka and the Kuril Islands, reaching 10 points and accompanied by a tsunami of exceptional consequences, which caused severe destruction in Severo-Kurilsk. It began at 3:57 a.m. local time. At 4 hours 24 minutes, i.e. 26 minutes after the earthquake began, the sea level quickly dropped and in some places the water retreated from the shore by 500 m. Then strong tsunami waves hit the section of the Kamchatka coast from Sarychev Island to the Kronotsky Peninsula. Later they reached the Kuril Islands, capturing a strip of coast about 800 km long. The first wave was followed by a second, even stronger one. After her arrival, all buildings located no higher than 10 m above sea level were destroyed on the island of Paramushir.
One of the houses in the city of Severo-Kurilsk, transported by a wave to port part city during the tsunami in November 1952
Tsunami in Hawaii
The coasts of the Hawaiian Islands are often subject to tsunamis. Over the past half century alone, destructive waves have struck the archipelago 17 times. The tsunami in Hawaii in April 1946 was very powerful.
From the area of the earthquake's epicenter near Unimak Island (Aleutian Islands), the waves moved at a speed of 749 km/h. The distance between the crests of the waves reached approximately 150 km. The famous American oceanologist, who witnessed this natural disaster, F. Shepard, noted a gradual increase in the height of the waves that hit the shore at intervals of 20 minutes. The tide gauge readings were successively 4, 5, 2 and 6.8 m above the high tide level.
The damage caused by the sudden onset of the waves was very great. Much of the city of Hilo on the island of Hawaii was destroyed. Some houses collapsed, others were carried by water over a distance of more than 30 m. The streets and embankments were cluttered with debris, blocked by barricades of mangled cars; Here and there the ugly hulks of small ships stood abandoned by the waves. Bridges and railways were destroyed. On the coastal plain, among the crushed, uprooted vegetation, numerous blocks of coral were scattered, and the corpses of people and animals could be seen. The disaster claimed 150 lives and caused a loss of $25 million. This time, waves of prices reached the shores of North and South America, and the largest wave was noted near the epicenter - in the western part of the Aleutian Islands. The Scotu Cap lighthouse, which stood at an altitude of 13.7 m above sea level, was destroyed, and the radio mast was also demolished.
A boat washed ashore during the 1946 tsunami in Hawaii
Application
Rice. 1. Areas of tsunami occurrence near the coasts of seas and oceans (1) and distribution of epicenters of the largest earthquakes (2)
Rice. Fig. 2. Scheme of the occurrence of tsunami waves during a displacement of a section of the seabed (a) and during an underwater eruption (b)
Literature:
1. Babkov A., Koshechkin B. Tsunami. – Leningrad: 1964
2. Murthy T. Seismic sea waves at prices. – Leningrad: 1981
3. Ponyavin I. D. Waves in prices. – Leningrad: 1965
4. The tsunami problem. Digest of articles. – M.: 1968
5. Solovyov S. L., Go Ch. N. Catalog of tsunamis on the eastern coast of the Pacific Ocean. – M.: 1975
6. Solovyov S.L., Go Ch.N. Catalog of tsunamis on west coast Pacific Ocean. – M.: 1974
A tide gauge is a device that records sea level fluctuations.
MINISTRY OF EDUCATION OF THE RUSSIAN FEDERATION
FAR EASTERN STATE ACADEMY
ECONOMY AND GOVERNMENT
DEPARTMENT OF GENERAL AND
HUMANITIES DISCIPLINES
on the topic of Tsunamis and their manifestation in the Pacific Ocean
Plan:
Causes of tsunamis
Causes of tsunamis
The distribution of tsunamis is usually associated with areas of strong earthquakes. It is subject to a clear geographical pattern, determined by the connection of seismic areas with areas of recent and modern mountain building processes.
It is known that most earthquakes are confined to those zones of the Earth within which the formation of mountain systems continues, especially young ones dating back to the modern geological era. The purest earthquakes occur in areas close to large mountain systems and depressions of seas and oceans.
In Fig. Figure 1 shows a diagram of folded mountain systems and areas of concentration of earthquake epicenters. This diagram clearly identifies two zones of the globe that are most prone to earthquakes. One of them occupies a latitudinal position and includes the Apennines, Alps, Carpathians, Caucasus, Kopet-Dag, Tien Shan, Pamir and Himalayas. Within this zone, a tsunami is observed on the coasts of the Mediterranean, Adriatic, Aegean, Black and Caspian seas and the northern part of the Indian Ocean. The other 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 (Aleutian, Kuril, Japanese islands and others). Tsunami waves are generated here as a result of gaps between rising mountain ranges and deep-sea trenches descending parallel to the ridges, separating island chains from the sedentary area of the Pacific Ocean floor.
The direct cause of the occurrence of tsunami waves is most often changes in the topography 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 were noted in the telegraph cable laid at the bottom of the sea at a depth of four hundred meters. After the earthquake, one of the ends of the broken cable was discovered at a depth of more than 600 m. Consequently, the earthquake caused a sharp lowering of a part of the seabed to a depth of about 200 m. A few years later, as a result of another earthquake, a cable laid on a flat bottom was broken again, and its ends found themselves at a depth that differed from the previous one by several hundred meters. Finally, another year after the new tremors, the depth of the sea at the rupture site increased by 400 m.
Even greater disturbances of the bottom topography occur during earthquakes in the Pacific Ocean. Thus, during an underwater earthquake in Sagami Bay (Japan), about 22.5 cubic meters were displaced when a part of the ocean floor suddenly rose. km of water, which hit the shore in the form of tsunami waves.
In Fig. Figure 2a shows the mechanism of tsunami generation as a result of an earthquake. At the moment of a sharp subsidence of a part of the ocean floor and the appearance of a depression on the bottom of the sea, the pod rushes to the center, overflows the depression and forms a huge bulge on the surface. When a portion of the ocean floor rises sharply, significant masses of water are revealed. At the same time, tsunami waves arise on the surface of the ocean, quickly spreading in all directions. Usually they form a series of 3-9 waves, the distance between the crests of which is 100-300 km, the heights when the waves approach the shore reach 30 m or more.
Another reason that causes tsunamis is volcanic eruptions that rise above the sea surface in the form of islands or are located on the ocean floor (Fig. 2b). The most striking example in this regard is the formation of a tsunami during the eruption of the 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 a.m., a gigantic explosion destroyed the volcanic island. At this moment, tsunami waves arose, spreading across all oceans and devastating many islands of the Malay Archipelago. In the narrowest part of the Sunda Strait, wave heights 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, 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 disaster brought the death of 36 inhabitants of the archipelago. Tsunami waves spread throughout the Indian Ocean from the coast of India in the north to the Cape of Good Hope in the south. In the Atlantic Ocean they reached the Isthmus of Panama, in the Pacific Ocean they reached Alaska and San Francisco.
Cases of tsunamis during volcanic eruptions are also known in Japan. So, on September 23 and 24, 1952, there was a strong eruption of an underwater volcano on the Meijin Reef, several hundred kilometers from Tokyo. The resulting waves reached Hotidze Island, northeast of the volcano. During this disaster, the Japanese hydrographic vessel Kaiyo-Maru-5, from which observations were carried out, was lost.
The third reason for a tsunami is the fall of huge rock fragments into the sea, caused by the destruction of rocks by groundwater. The height of such waves depends on the mass of material that has fallen into the sea and the height of its fall. So, in 1930, on the island of Madeira, a block fell from a height of 200 m, which caused the appearance of a single wave 15 m high.
Tsunami off the coast of South America
The Pacific coast within Peru and Chile is prone to frequent earthquakes. Changes occurring in the bottom topography of the coastal part of the Pacific Ocean lead to the formation of large tsunamis. The tsunami waves reached their highest height (27 m) in the Callao area during the Lima earthquake in 1746.
If usually the decrease in sea level that precedes the onset of tsunami waves on the shore lasts from 5 to 35 minutes, then during the earthquake in Pisco (Peru) the receding sea waters returned only after three hours, at Santa - even after a day.
Often the onset and retreat of tsunami waves occur here several times in a row. Thus, in Iquique (Peru) on May 9, 1877, the first wave hit the coast half an hour after the main shock of the earthquake, then within four hours the waves arrived five more times. During this earthquake, the epicenter of which was located 90 km from the Peruvian coast, tsunami waves reached the coasts of New Zealand and Japan.
On August 13, 1868, on the coast of Peru in Arica, 20 minutes after the earthquake began, a wave several meters high surged, but soon receded. With an interval of a quarter of an hour, it was followed by several more waves, smaller in size. After 12.5 hours, the first wave reached the Hawaiian Islands, and 19 hours later - the coast of New Zealand, where 25 people became victims. The average speed of tsunami waves between Arica and Valdivia at a depth of 2200 m was 145 m/sec, between Arica and Hawaii at a depth of 5200 m - 170-220 m/sec, between Arica and the Chatham Islands at a depth of 2700 m - 160 m/sec.
The most frequent and powerful earthquakes characterize the area of the Chilean coast from Cape Concepcion to the island of Chiloe. It is known that since the disaster of 1562, the city of Concepcion suffered 12 strong earthquakes, the city of Valdivia during the period from 1575 to 1907 - 7 earthquakes. During the earthquake of January 24, 1939, 1 person died and 7 people were left homeless in Concepción and its surroundings.
Tsunami off the coast of Japan
Tsunamis are usually accompanied by the most powerful, catastrophic earthquakes that occur on the Japanese Islands on average every seven years. Another reason that causes the formation of a tsunami off the coast of Japan is volcanic eruptions. It is known, for example, that as a result of a volcanic explosion on one of the Japanese islands in 1792, rocks with a volume of about 1 cubic meter were thrown into the sea. km. A sea wave about 9 m high, formed as a result of the fall of eruption products into the sea, demolished several coastal villages and killed more than 15 residents.
The tsunami was especially powerful during the 1854 earthquake, which destroyed the country's largest cities - Tokyo and Kyoto. First, a nine-meter-high wave came ashore. However, it soon flowed away, drying up the coastal area at a great distance. Over the next 4-5 hours, five or six more large waves hit the shore. And after 12.5 hours, tsunami waves, moving at a speed of more than 600 km/h, reached the coast of North America in the San Francisco area.
After this terrible disaster, stone walls were erected on some parts of the coast of Honshu to protect the coast from destructive waves. However, despite the precautions taken, during the earthquake of June 15, 1896, the island of Honshu was again severely damaged by devastating waves. An hour after the earthquake began, six or seven large waves hit the shore at intervals of 7 to 34 minutes, the maximum height of one of which was 30 m. The waves completely washed away the city of Minco, destroyed 1 building and killed 27 people. And 10 years later, during the earthquake of 1906, about 3 people again died when a tsunami struck on the east coast of the country.
During the famous catastrophic earthquake of 1923, which completely destroyed the Japanese capital, tsunami waves caused devastation on the coast, although they did not reach particularly large sizes, at least in Tokyo Bay. In the southern regions of the country, the consequences of the tsunami were even more significant: several villages in this part of the coast were completely washed away, and the Yokosuka Japanese naval base, located 12 km south of Yokohama, was destroyed. The city of Kamakura, located on the shores of Sagami Bay, was also severely damaged by sea waves.
On March 3, 1933, 10 years after the 1923 earthquake, a new strong earthquake occurred in Japan, little compared to the previous one. Tremors affected the entire eastern part of the island of Honshu. The greatest disasters for the population during this earthquake were associated with the onset of tsunami waves, which engulfed the entire northeastern coast of Honshu 40 minutes after the earthquake began. The wave destroyed the port city of Komaishi, where 1,200 houses were destroyed. A large number of villages on the coast were demolished. Judging by newspaper reports, about 3 people were killed or missing during this disaster. In total, more than 4,500 houses were destroyed by the earthquake and washed away by the waves, and more than 6,600 houses were partially damaged. More than 5 people were left homeless.
Tsunami off the Pacific coast of Russia
The shores of Kamchatka and the Kuril Islands are also susceptible to tsunamis. Initial information about catastrophic waves in these places dates back to 1737. The famous domestic traveler - geographer S.P. Krasheninnikov wrote: l... the shaking began and continued in waves for about a quarter of an hour, so strong that many Kamchadal yurts collapsed and the booths fell. Meanwhile, there was a terrible noise and excitement on the sea, and suddenly water surged onto the shore to a height of three fathoms, which, without standing still, ran into the sea and moved away from the shores at a considerable distance. Then the earth shook a second time, the water came in opposite to the previous one, but at low tide it ran so far that it was impossible to see the sea. At the same time, rocky mountains appeared on the bottom of the sea in the strait between the first and second Kuril Islands, which had never been visible before, although earthquakes and floods had occurred before.
A quarter of an hour after all this, the shocks of a terrible earthquake, incomparable in its strength, followed, then a wave thirty fathoms high rushed onto the shore, which still quickly ran back. Soon the water entered its banks, fluctuating at long intervals, sometimes covering the banks, sometimes escaping into the sea.
During this earthquake, massive rocks collapsed, and the incoming wave threw blocks of stone weighing several pounds onto the shore. The earthquake was accompanied by various optical phenomena in the atmosphere. In particular, Abbot Prevost, another traveler who observed this earthquake, wrote that fiery meteors could be seen on the sea, scattered over a wide area.
S.P. Krasheninnikov noticed all the most important features of a tsunami: an earthquake, a decrease in the level of the ocean preceding the flood, and, finally, the onset of huge destructive waves.
Enormous tsunamis on the coasts of Kamchatka and the Kuril Islands took place in 1792, 1841, 1843, 1918. A series of earthquakes during the winter of 1923 caused repeated onsets of catastrophic waves. There is a well-known description of the tsunami on February 4, 1923, when three waves rushed onto the land of the eastern coast of Kamchatka one after another, tore off the coastal ice (fast ice a fathom thick), threw it over the coastal spit, and flooded low places. The ice in a low place near Semyachik was thrown out almost 1 verst 400 fathoms from the shore; at higher elevations the ice remained at a height of three fathoms above the level of the sea. In the sparsely populated areas of the east coast, this unprecedented phenomenon caused some damage and destruction. The natural disaster affected a vast coastal zone with a length of 450 km.
On April 13, 1923, renewed tremors caused tsunami waves up to 11 m high, which completely destroyed the coastal buildings of fish canning factories, some of which were cut off by hummocky ice.
Strong tsunamis were reported on the coast of Kamchatka and the Kuril Islands in 1927, 1939 and 1940.
On November 5, 1952, an earthquake occurred on the eastern coast of Kamchatka and the Kuril Islands, reaching 10 points and accompanied by a tsunami of exceptional consequences, which caused severe destruction in Severo-Kurilsk. It began at 3:57 a.m. local time. At 4 hours 24 minutes, i.e. 26 minutes after the earthquake began, the level of the ocean quickly fell and in some places the water retreated from the shore by 500 m. Then strong tsunami waves hit a part of the Kamchatka coast from Sarychev Island to the Kronotsky Peninsula. Later they reached the Kuril Islands, capturing a strip of coast about 800 km long. The first wave was followed by a second, even stronger one. After her arrival on the island of Paramushir, all buildings located no higher than 10 m above the ocean level were destroyed.
Tsunami in Hawaii
The coasts of the Hawaiian Islands are often subject to tsunamis. Over the past half century alone, destructive waves have struck the archipelago 17 times. The tsunami in Hawaii in April 1946 was very powerful.
From the area of the earthquake's epicenter in the area of Nimak Island (Aleutian Islands), the waves moved at a speed of 749 km/h. The distance between the crests of the waves reached approximately 150 km. The famous American oceanologist, who witnessed this natural disaster, F. Shepard, noted a gradual increase in the height of the waves that hit the shore at intervals of 20 minutes. The tide gauge readings were successively 4, 5, 2 and 6.8 m above the tide level.
The damage caused by the sudden onset of the waves was very great. Much of the city of Hilo on the island of Hawaii was destroyed. Some houses collapsed, others were carried by water over a distance of more than 30 m. Faces and embankments were cluttered with debris, blocked by barricades of mangled cars; Here and there, abandoned by the waves, towered the macabre hulks of small ships. Bridges and railways were destroyed. On the coastal plain, among the crushed, uprooted vegetation, numerous blocks of coral were scattered, and the corpses of people and animals could be seen. The disaster claimed 150 human lives and caused a loss of 25 million dollars. This time, waves of prices reached the shores of North and South America, but the largest wave was noted near the epicenter - in the western part of the Aleutian Islands. The Skotu-Kap lighthouse, which stood at an altitude of 13.7 m above sea level, was destroyed, and the radio mast was also demolished.
Application
1. Babkov A., Koshechkin B. Tsunami. - Leningrad: 1964
2. Murthy T. Seismic sea waves at prices. - Leningrad: 1981
3. Ponyavin I. D. Waves in prices. - Leningrad: 1965
4. The tsunami problem. Digest of articles. - M.: 1968
5. Solovyov S. L., Go Ch. N. Catalog of tsunamis on the eastern coast of the Pacific Ocean. - M.: 1975
6. Solovyov S. L., Go Ch. N. Catalog of tsunamis on the western coast of the Pacific Ocean. - M.: 1974
A tide gauge is a device that records fluctuations in sea level
Tsunami is a word of Japanese origin and literally means “long waves in the port.” Later, the scope of this concept was expanded, and today it means any long destructive waves. A lot is said and written about the tsunami, but it is very difficult to imagine. Probably the most correct idea of what a tsunami looks like at sea is the one who has seen the film “The Adventures of Poseidon”, in which the tsunami is depicted truly magnificently. According to the plot of the film, the tsunami was caused by an earthquake off the island of Crete. Underwater earthquakes are indeed the most common cause of tsunamis. However, it can be caused by an underwater volcanic eruption or coastal collapse.
Rice. 23. Scheme of earthquakes in the Eastern Mediterranean. Symbols indicate the epicenters of earthquakes that occurred in 1961–1967, taking into account the depths of their sources. In the Aegean basin, earthquakes are particularly frequent, but mostly shallow. On the contrary, deep earthquakes predominate around Sicily. Based on the data on the depths of earthquake sources, a tectonic map of the Mediterranean was reconstructed (it is shown in Fig. 21). In the Aegean Basin we see an arc of young volcanoes characteristic of this area. (After D. Stanley, 1972)
Tsunamis are very long and high waves, and the wave height in the open ocean is not that great, only a few meters. But when the wave front penetrates into shallower shelf areas, the wave rises and turns into huge wall, the height of which can reach several tens of meters. The greater the depth of the ocean, the greater the speed of the tsunami. For example, in open waters The Pacific Ocean, whose depth is about 4–5 km, the theoretically possible wave speed is almost incredible - 716 km/h. After all, it's essentially speed. transport aircraft. In reality, the speed of a tsunami is much slower. However, the maximum recorded speed turned out to be even higher, approximately 1000 km/h, and this is already the speed of a jet aircraft.
Tsunamis naturally occur more often where earthquakes occur more often, that is, in the area of the Pacific Ocean trenches. These earthquakes generate waves that crash onto the shores of Japan, the Kuril Islands and other island arcs. Earthquakes in the Aleutian Islands region cause tsunamis that sweep across the Pacific Ocean, flood the coasts of the Hawaiian Islands and even reach California. Tsunamis caused by earthquakes in the Peru-Chile Trench hit the coast of Chile with devastating force. And even in the Mediterranean Sea, earthquakes generate tsunamis. The most significant of them took place off the coast of Corsica and Sicily. In the Atlantic Ocean, tsunamis occur mainly as a result of earthquakes in the Azores-Gibraltar ridge. And then they flood the Portuguese coast.
Rice. 24. Map of the so-called “earthquake risk” in the Eastern Mediterranean. Isolines connect points with the same earthquake energy. The numbers express the energy in 1015 erg km -2 - year -1. (After K. Lomnitz, 1974)
A classic example of a tsunami resulting from a volcanic explosion is the tsunami generated by the eruption of the Krakatoa volcano in Indonesia. This happened in 1883. A wave 36–40 m high was formed due to the collapse of part of the island. A few minutes later she reached the coast of Java and Sumatra. The wave traveled across all oceans and was recorded even in Panama, 18,350 km from the point of origin.
And now we should once again mention the small island of Thira in the Cyclades archipelago, where a tsunami of 100 m in height may have occurred around 1500 BC (see p. 91). However, there are no eyewitness accounts of this phenomenon, and the height and consequences of the tsunami were calculated only by comparing the magnitudes of the Krakatoa and Thira calderas. In half an hour, a wave of terrible force was supposed to reach Crete and mainland Greece, and an hour later Egypt. As we have already mentioned, some authors believe that this was the greatest natural disaster of the historical era, which had a direct impact on the death of the Minoan civilization. According to some atlantologists, it was she who could have caused the death of Atlantis. We discuss many controversial issues related to this topic on p. 93–95.
The third reason for a tsunami is coastal collapse. And although this phenomenon is not so frequent, and most importantly, not so large-scale, it can still cause a wave that reaches impressive proportions. Here is one example of many. In Lituya Bay in Alaska, 30 million m3 of soil slid into the sea, as a result of which the water surface rose 600 m and a huge breaking wave crashed onto the opposite shore of the bay. At this height, traces of its destructive effects are still visible.
In table 8 contains data on some of the most famous tsunamis of the historical era.
| Table 8. Some of the largest tsunamis of the historical era (according to various sources) | |||
| Year | Place | Cause of occurrence | Wave speed and height |
| Around 1500 BC | O. Thira | Volcanic explosion and caldera formation | Using the extrapolation method, it was calculated that the wave could reach a height of 100 m and a speed of 200 km/h; it captured the entire Eastern Mediterranean region |
| 1737 | Kamchatka, Kuril Islands, Sakhalin | Wave height 17–35 m, speed probably 700 km/h | |
| 1854 | Japan | Earthquake in the Japan Trench | A 9 m high wave traveled across the entire Pacific Ocean in 12.5 hours; in San Francisco a height of 0.5 m was recorded |
| 1872 | Bay of Bengal | Causes unknown, possibly as a result of storm surge | Wave height 20 m (200,000 victims) |
| 1883 | Krakatoa | Volcanic explosion, caldera formation | Wave height 35–40 m in Java and Sumatra; speed about 200 km/h; noted even 18,000 km from the explosion site |
| 1908 | Messina | Earthquake in the Messina Trench | Wave height 23 m |
| 1946 | Hawaiian Islands | Earthquake in the Aleutian Trench | Wave height in Hawaii is 10 m, speed in the open ocean is 700 km/h |
| 1952 | Kamchatka and Kuril Islands | Earthquake in the Kuril-Kamchatka Trench | Wave height 8–18 m, speed about 500 km/h |
| 1953 | Alaska | Earthquake in the Aleutian Trench | Wave height 17–35 m, speed about 700 km/h |
| 1960 | Chile | Earthquake in the Peru-Chile Trench | Three cycles of waves; the highest is about 11 m at a speed of 700 km/h; a wave 8 m high hit Hawaii, the same wave off Hokkaido had a height of 6 m |
The descriptions of eyewitnesses of this natural phenomenon are interesting. Among them is even such an authoritative specialist as one of the founders of modern marine geology, American Francis Shepard. By chance, he was on vacation in the Hawaiian Islands just when a destructive wave hit them in 1946. Eyewitness accounts are important for concluding how rapidly such a catastrophe is developing, as well as whether it can be compared with the destruction of Atlantis described by Plato. If we compare the testimony of authoritative experts, we can draw the following conclusions: at first, the sea seems to recede and the water level drops. Then the first wave, several meters high, comes in. After a few minutes it subsides and after 5-10 minutes a second wave arrives, sometimes the same height as the first, sometimes a little lower. After 10–20 minutes it subsides, and then, usually an hour later, sometimes after a longer period of time, the third, highest and most destructive wave rolls in. If a wave enters the bay, its height increases significantly. Waves throw very heavy loose objects ashore, tear off rocks, sweep away houses and even the concrete foundations of lighthouses.
We now have a clear idea of what a tsunami can do and how long it will last. The whole disaster lasts no more than an hour or two. During this time, the entire coastal zone of a mainland or island, or even an entire island, can be completely destroyed. As we have already said, many historians are confident that a large share of the blame for the death of the Minoan culture on the island of Crete lies with the tsunami. Some Atlantologists also believe that the tsunami was to blame for the destruction of Atlantis. And this would not require “one terrible day,” as Plato claims. An hour would be enough. Thus, a tsunami is a catastrophe that theoretically, given the appropriate scale, could easily destroy Atlantis.
Tsunamis produced by earthquakes and volcanic eruptions are considered the most dangerous natural phenomena on Earth. In the last two decades alone, giant waves and tremors have combined to kill 55% of the 1.35 million people killed in natural disasters. Throughout its history, humanity has experienced many similar disasters, but in this article we bring to your attention the ten most destructive and deadly tsunamis ever recorded on our planet.
1. Sumatra (Indonesia), December 24, 2004
At the end of December 2004, off the coast of Sumatra, at a depth of about 30 km, a powerful earthquake with a magnitude of 9.1 occurred, caused by a vertical displacement of the seabed. As a result of a seismic event, a a big wave about 1300 km wide, which reached a height of 15 meters as it approached the coast. A giant wall of water hit the shores of Indonesia, Thailand, India, Sri Lanka and several other countries, leaving behind between 225,000 and 300,000 dead. Many people were swept into the ocean, so the exact numbers of deaths are unlikely to ever be known. According to general estimates, the damage from the disaster amounted to about 10 billion US dollars.
2. Pacific Northwest Coast (Japan), March 11, 2011
In 2011, on March 11, a huge 10-meter wave, moving at a speed of 800 km/h, swept the east coast of Japan and led to the death or disappearance of over 18,000 people. The reason for its appearance was an earthquake of magnitude 9.0 that occurred at a depth of 32 km east of the island Honshu. About 452,000 Japanese survivors were moved to temporary shelters. Many still live there today. An earthquake and tsunami caused an accident at the Fukushima nuclear power plant, after which significant radioactive releases occurred. Total damage amounted to $235 billion.
3. Lisbon (Portugal), November 1, 1755
An earthquake of magnitude 8.5 that occurred in the Atlantic caused a series of three huge waves that covered the Portuguese capital and a number of coastal cities in Portugal, Spain and Morocco. In some places the tsunami height reached 30 meters. The waves crossed Atlantic Ocean and reached Barbados, where their height was 1.5 meters. Overall, the quake and subsequent tsunami killed about 60,000 people.
4. Krakatoa (Indonesia), August 27, 1883
The volcanic eruption in 1883 was one of the largest in history. modern history humanity. The giant's explosions were so powerful that they caused high waves that flooded the surrounding islands. After the volcano split and fell into the ocean, the largest tsunami was generated, 36 meters high, destroying over 160 villages on the islands of Sumatra and Java. Of the more than 36,000 people killed in the eruption, over 90% of people were victims of the tsunami.
5. Nankaido (Japan), September 20, 1498
According to general estimates, the earthquake that shook the islands in southeastern Japan had a magnitude of at least 8.4. The seismic event led to a tsunami that hit the Japanese provinces of Kii, Awaji and the coast of Shikoku island. The waves were strong enough to destroy the isthmus that previously separated Lake Hamana from the ocean. Flooding was observed throughout the historical Nankaido region, and the death toll was estimated to have reached between 26,000 and 31,000 people.
6. Nankaido (Japan), October 28, 1707
Another devastating tsunami, caused by a magnitude 8.4 earthquake, hit Nankaido, Japan in 1707. The wave height was 25 meters. Settlements on the coast of Kyushu, Shikoku and Honshu were damaged, and the large Japanese city of Osaka was also damaged. The disaster resulted in the destruction of more than 30,000 homes and the death of approximately 30,000 people. It is estimated that about a dozen tsunamis hit Japan in just 1 hour that day, some of them traveling several kilometers deep into the islands.
7. Sanriku (Japan), June 15, 1896
The tsunami in the northeastern part of the island of Honshu was caused by an earthquake of magnitude 7.2, caused by a shift of lithospheric plates in the area of the Japan Trench. After the earthquake, two waves rushed into the Sanriku region one after another, rising to a height of up to 38 meters. Since the arrival of the water coincided with the tide, the damage from the disaster was incredibly high. More than 22,00 people were killed and over 9,000 buildings were destroyed. The tsunamis also reached the Hawaiian Islands, but here their height was much lower - about 9 meters.
8. Northern Chile, August 13, 1868
The tsunami in northern Chile (at that time off the coast of Arica in Peru) was caused by a series of two large earthquakes with a magnitude of 8.5. Waves up to 21 meters high flooded the entire Asia-Pacific region and reached Sydney, Australia. The waters washed over the shores for 2 or 3 days, ultimately causing 25,000 deaths and $300 million in damage.
9. Ryukyu (Japan), April 24, 1771
Boulders thrown up by the tsunami
A magnitude 7.4 earthquake caused a tsunami that flooded many Japanese islands. The hardest hit areas were Ishigaki and Miyako, where wave heights ranged from 11 to 15 meters. The disaster resulted in the destruction of 3,137 houses and the death of about 12,000 people.
10. Ise Bay (Japan), January 18, 1586
Ise Bay today
The earthquake that caused the tsunami in Ise Bay on the island of Honshu received a magnitude of 8.2. Waves rose to a height of 6 meters, causing damage settlements on the coast. The city of Nagahama suffered not only from water, but also from fires that broke out after the earthquake and destroyed half of the buildings. The Gulf tsunami killed more than 8,000 people.
