World Ocean. Sea waves
IN Atlantic Ocean There was a strong magnitude 6.7 earthquake off the coast of Brazil in a very shallow depth of only 6 miles, and it is impossible to determine whether it caused a TSUNAMI because all but one of the Atlantic tsunami warning buoys are OFFLINE and cannot issue warnings.
The East Coast could be at risk if such a wave were to bypass, but we couldn't be warned because the US Commerce Department couldn't repair the buoys.
The earthquake occurred at 1:33 a.m. East Coast time, at a depth of only 6 miles.
According to the Tsunami Warning Center, there is "no tsunami danger" for the US East Coast. I wonder how they can make this assessment given the fact that our tsunami warning buoys are INOPAL.
Here is the Statement issued by the Tsunami Warning Center:
WEXX32 PAAQ 300646
TIBATE
Tsunami Information Statement Number 1
NWS National Tsunami Warning Center Palmer AK
146 AM EST Thu Nov 30 2017
…THIS IS A TSUNAMI INFORMATION STATEMENT FOR THE U.S. EAST COAST,
GULF OF MEXICO STATES, AND EASTERN CANADA…
* Based on the earthquake location near the Mid-Atlantic Ridge,
a damaging tsunami is not expected.
* An earthquake has occurred with parameters listed below.
PRELIMINARY EARTHQUAKE PARAMETERS
———————————
* The following parameters are based on a rapid preliminary
assessment and changes may occur.
* Magnitude 6.5
* Origin Time 0133 EST Nov 30 2017
0033 CST Nov 30 2017
0233 AST Nov 30 2017
0633 UTC Nov 30 2017
* Coordinates 1.1 South 23.5 West
* Depth 6 miles
*Location near the central Mid-Atlantic Ridge
ADDITIONAL INFORMATION AND NEXT UPDATE
————————————–
* Refer to the internet site tsunami.gov for more information.
* Caribbean coastal regions should refer to the Pacific
Tsunami Warning Center messages at tsunami.gov.
* This will be the only U.S. National Tsunami Warning Center
message issued for this event unless additional information
becomes available.
If they are true, we have nothing to worry about. If they are NOT right, the tsunami travels through the open ocean at about 600 mph. It will hit the northern coast of Brazil first. IF WE HEAR THAT BRAZIL HAS BEEN SUFFERED IN THE NEXT TWO HOURS, THEN WE WILL BE HIT IN ABOUT FOUR HOURS.
First by North Carolina. Minutes later, southern Delaware and New Jersey would be hit. Minutes after that, New York and Long Island. Around the same time that New York City comes under attack, the entire Southeast will also be attacked.
The National Data Buoy Center (NDBC) is part of the National Oceanic and Atmospheric Administration (NOAA), which is part of the U.S. Department of Commerce.
According to the NDBC, the following tsunami warning buoys (listed from south to north as the southernmost buoy will be closest to the earthquake) in the Atlantic, OFFLINE:
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 tsunami generation. 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 smaller shelf areas, the wave rises and turns into a 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 the open waters of the Pacific Ocean, which is about 4–5 km deep, 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 a speed jet plane.
Tsunamis naturally occur more often where earthquakes occur more often, that is, in the area of the Pacific Ocean trenches. These earthquakes create waves that crash onto the shores of Japan, Kuril Islands and other island arcs. Earthquakes in the area Aleutian Islands cause tsunamis that sweep across the Pacific Ocean and flood the coasts 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 largest natural disaster of the historical era, which had a direct impact on the death 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 |
Interesting descriptions of eyewitnesses of this natural phenomenon. 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.
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 globe, most susceptible 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 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 nearby islands South-East 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 washed away, 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 inhabitants of the archipelago. Tsunami waves spread throughout the 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, 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 South America
The Pacific coast within Peru and Chile is susceptible frequent earthquakes. Changes occurring in the bottom topography of the coastal part of the Pacific Ocean lead to the formation 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 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 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 to seven big waves, the maximum height of one of which was 30 m. The waves completely washed away the city of Minko, destroyed 1 building and caused the death of 27 people. And 10 years later, during the earthquake of 1906, on east coast country, when the tsunami struck again, about 3 people died.
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, located 12 km south of Yokohama naval base Japan's Yokosuka 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. 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 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
A wave 300 meters high literally washed away one of the Cape Verde islands - Santiago Island, located in the Atlantic Ocean about 620 kilometers from west coast Africa. This happened a very long time ago - 73 thousand years ago. But the traces are still preserved. They were found by scientists from the UK, USA, Portugal and Japan, as reported in the scientific journal Science Advances. According to the head of the research group, Ricardo Ramalho from the Columbia University Observatory, the monstrous wave shot up as a result of a volcanic eruption on the island of Fogo, located 55 kilometers from the island of Santiago. Part of the crater wall collapsed into the ocean - a block with a volume of several cubic kilometers fell into the water. The resulting water shaft reached almost 300 m in height - more precisely, 266 m. And rolled across the ocean. And the piece that fell off sank to the bottom - it is still there.
Scientists determined the height of the wave by finding traces of sea water, sea sand and giant boulders high in the mountains of Santiago Island - 49 pieces weighing from 50 to 200 tons. These blocks, thrown into the mountains, testify to the monstrous power of the wave.
Scientists warn that a kilometer-high wave - the so-called megatsunami - may rise in the Atlantic Ocean. It can be created by rocky rock that collapses into the water as a result of volcanic eruptions in Canary Islands. The most dangerous in this sense are the active vents of the Cumbre Vieja volcanic ridge on the island of La Palma. According to calculations by Simon Day from University College London, the wave will reach the west coast of Africa within an hour. And spreading in the opposite direction, it will pour into America. Off the coast of Africa, the wave height will be 100 m, off the coast of the USA - 50 m.
By the way, megatsunamis have formed in our time. In 1958, as a result of an earthquake in Alaska, a glacier weighing 90 million tons came down from the mountain and fell into the water. The collapse created a wave 525 m high in Lituya Bay - just below the Ostankino TV tower, which is 540 m high. This wave was the highest of all officially recorded.
SAVE YOURSELF WHO CAN!
A rogue wave in the Mediterranean could affect 130 million people.
It would seem that people vacationing at the resorts of the Mediterranean - essentially inland - sea have nothing to fear. As well as local residents, inhabiting coastal areas. Unless a storm blows up sometimes. So it’s not scary - it’s even beautiful. It won't wash away. You can serenely sip a mojito while continuing to admire the turquoise waves...
The ocean is a different matter - tsunamis of destructive force occur there. In 2004 huge waves struck Indonesia and Thailand, and in 2011 - Japan. However, as Italian scientists have found, walls of water can also rise in the Mediterranean.
Modeling carried out by Dr. Achilles Samaras from the University of Bologna demonstrated that earthquakes of magnitude 7-8 that occurred in Sicily and the island of Crete will definitely cause a tsunami. The waves will travel throughout the sea at a speed of about 600 kilometers per hour. Their height near the coast will reach 20 meters. This will allow water in some places to penetrate several kilometers deep into the coast. That is, the danger of being washed away from the beach really exists. Estimates show that 130 million people in coastal areas could be affected.
Scientists claim that tsunamis in the Mediterranean Sea occur approximately once every hundred years. They hint that the time for another cataclysm is approaching. After all, the previous one happened in 1908. Then an earthquake in Sicily generated waves that killed thousands of people in the Messina area.
It could be worse: in 365 AD, an earthquake in Crete caused waves that reached Greece, Italy and Egypt. And in Alexandria alone, 5 thousand people were drowned.
Samaras is echoed by German researchers Rainer Kind and Dieter Kelletat from the University of Duisburg-Essen, who also do not exclude the possibility of a strong tsunami in the Mediterranean.
No one can predict a cataclysm yet - there are no reliable means in the world to predict earthquakes - the source of tsunamis. But there is an opportunity to insure yourself. Scientists propose equipping the Mediterranean Sea with a tsunami early warning system, similar to the one that operates, for example, in Southeast Asia. Of course, it will not prevent destruction, but it will give people a chance to escape or go to a higher place.
Tsunami is one of the most terrifying natural phenomena. It is a wave formed as a result of “shaking” of the entire thickness of water in the ocean. Tsunamis are most often caused by underwater earthquakes.
Approaching the shore, the tsunami grows into a huge shaft tens of meters high and hits the shore with millions of tons of water. The largest tsunami in the world caused colossal destruction and led to the death of millions of people.
Krakatoa, 1883
This tsunami was not caused by an earthquake or landslide. The explosion of the Krakatoa volcano in Indonesia generated a powerful wave that swept along the entire coast of the Indian Ocean.Residents of fishing villages within a radius of about 500 km from the volcano had virtually no chance of survival. Victims were observed even in South Africa, on the opposite shore of the ocean. In total, 36.5 thousand people are considered dead from the tsunami itself.
Kuril Islands, 1952
The tsunami, triggered by a magnitude 7 earthquake, destroyed the city of Severo-Kurilsk and several fishing villages. Then the residents had no idea about the tsunami and after the earthquake stopped they returned to their homes, becoming victims of a 20-meter water shaft. Many were caught up in the second and third waves because they did not know that a tsunami is a series of waves. About 2,300 people died. Authorities Soviet Union decided not to report the tragedy in the media, so the disaster became known only decades later. 
The city of Severo-Kurilsk was subsequently moved to a higher place. And the tragedy became the reason for the organization of a tsunami warning system in the USSR and more active scientific research in seismology and oceanology.
Lituya Bay, 1958
An earthquake with a magnitude of more than 8 provoked a huge landslide with a volume of more than 300 million cubic meters, consisting of stones and ice from two glaciers. To these were added the waters of the lake, the shore of which collapsed into the bay. 
As a result, a gigantic wave was formed, reaching a height of 524 m! It swept across the bay, licking the vegetation and soil on the slopes of the bay like a tongue, completely destroying the spit that separated it from Gilbert Bay. This is the highest tsunami wave in history. The banks of Lituya were not inhabited, so only 5 fishermen became victims.
Chile, 1960
On May 22, the consequences of the Great Chilean Earthquake with a magnitude of 9.5 were a volcanic eruption and a tsunami 25 m high. Almost 6 thousand people died. 
But the rogue wave did not calm down there. At the speed of a jet plane, it crossed the Pacific Ocean, killing 61 people in Hawaii, and reached the shores of Japan. Another 142 people became victims of the tsunami, which occurred at a distance of more than 10 thousand km. After this, it was decided to warn about the danger of a tsunami even in the most remote areas of the coast that may be in the path of a deadly wave.
Philippines, 1976
The powerful earthquake caused a wave, the height of which seems to be unimpressive - 4.5 m. Unfortunately, the tsunami hit the low-lying coast for more than 400 miles. But the residents were not prepared for such a threat. The result is more than 5 thousand dead and about 2.5 thousand missing without a trace. Almost 100 thousand residents of the Philippines were left homeless, and many villages along coastline were simply completely washed away along with the residents. 
Papua New Guinea, 1998
The consequence of the earthquake on July 17 was a gigantic underwater landslide, which caused a 15-meter wave. And so the poor country suffered several natural disasters, more than 2,500 people died or went missing. And more than 10 thousand residents lost their homes and livelihoods. The tragedy became the impetus for studying the role of underwater landslides in causing tsunamis. 
Indian Ocean, 2004
December 26, 2004 is forever inscribed in blood in the history of Malaysia, Thailand, Myanmar and other countries on the Indian Ocean coast. On this day, the tsunami claimed the lives of about 280 thousand people, and according to unofficial data - up to 655 thousand. 
The underwater earthquake caused waves 30 m high that hit coastal areas within 15 minutes. The large number of deaths is due to several reasons. This is a high degree of population of the coast, lowland areas, a large number of tourists on the beaches. But the main reason is the lack of an established tsunami warning system and poor awareness of people about safety measures.
