A tsunami (from Japanese: 津波, lit. 'harbour wave';[1] English pronunciation: /suːˈnɑːmi/ soo-NAH-mee[2] or /tsuːˈnɑːmi/[3]) or tidal wave,[4], also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami.[5] Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.

Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer.[6] Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide.[7] For this reason, it is often referred to as a "tidal wave", although this usage is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis.[8] Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called "internal wave train".[9] Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.

The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes,[10][11] but the understanding of tsunamis remained slim until the 20th century and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do; accurately forecasting the passage of tsunamis across the oceans; and forecasting how tsunami waves interact with shorelines.

3D tsunami animation



Tsunami (Chinese characters)
"Tsunami" in kanji
Japanese name

The term "tsunami" is a borrowing from the Japanese tsunami 津波, meaning "harbour wave". For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese.[12] Some English speakers alter the word's initial /ts/ to an /s/ by dropping the "t", since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is /ts/.

Tidal wave

Tsunami 2004 aftermath. Aceh, Indonesia, 2005. Photo- AusAID (10730863873)
Tsunami aftermath in Aceh, Indonesia, December 2004.

Tsunamis are sometimes referred to as tidal waves.[13] This once-popular term derives from the most common appearance of a tsunami, which is that of an extraordinarily high tidal bore. Tsunamis and tides both produce waves of water that move inland, but in the case of a tsunami, the inland movement of water may be much greater, giving the impression of an incredibly high and forceful tide. In recent years, the term "tidal wave" has fallen out of favour, especially in the scientific community, because the causes of tsunamis have nothing to do with those of tides, which are produced by the gravitational pull of the moon and sun rather than the displacement of water. Although the meanings of "tidal" include "resembling"[14] or "having the form or character of"[15] the tides, use of the term tidal wave is discouraged by geologists and oceanographers.

A 1969 episode of the TV crime show Hawaii Five-O entitled "Forty Feet High And It Kills!" used the terms "tsunami" and "tidal wave" interchangeably.[16]

Seismic sea wave

The term seismic sea wave also is used to refer to the phenomenon, because the waves most often are generated by seismic activity such as earthquakes.[17] Prior to the rise of the use of the term tsunami in English, scientists generally encouraged the use of the term seismic sea wave rather than tidal wave. However, like tsunami, seismic sea wave is not a completely accurate term, as forces other than earthquakes – including underwater landslides, volcanic eruptions, underwater explosions, land or ice slumping into the ocean, meteorite impacts, and the weather when the atmospheric pressure changes very rapidly – can generate such waves by displacing water.[18][19]


While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people.[20] The Sumatran region is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island.[21]

Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. Of historical and current (with regard to risk assumptions) importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores–Gibraltar Transform Fault), the 1783 Calabrian earthquakes, each causing several tens of thousands of deaths and the 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the most deadly natural disasters in modern Europe. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves.

As early as 426 BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause.[10][11]

The cause, in my opinion, of this phenomenon must be sought in the earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen.[22]

The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15–19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria.[23][24]


The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea.[25] This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests.[26][27] The waves formed in this way are then sustained by gravity.


Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position.[28] More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal (extensional) faults can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the outer trench swell) cause enough displacement to give rise to a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events.[29][30]


Overriding plate bulges under strain, causing tectonic uplift.


Plate slips, causing subsidence and releasing energy into water.


The energy released produces tsunami waves.

Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres),[31] which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

On April 1, 1946, the 8.6 MwAleutian Islands earthquake occurred with a maximum Mercalli intensity of VI (Strong). It generated a tsunami which inundated Hilo on the island of Hawaii with a 14-metre high (46 ft) surge. Between 165 and 173 were killed. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.

Examples of tsunami originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before travelling transoceanic distances.

The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc.).

The 1960 Valdivia earthquake (Mw 9.5), 1964 Alaska earthquake (Mw 9.2), 2004 Indian Ocean earthquake (Mw 9.2), and 2011 Tōhoku earthquake (Mw9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (Mw 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only a few minutes at a time.


In the 1950s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant submarine landslides. These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 metres (over 1700 feet).[32] The wave did not travel far, as it struck land almost immediately. Two people fishing in the bay were killed, but another boat managed to ride the wave.

Another landslide-tsunami event occurred in 1963 when a massive landslide from Monte Toc entered the Vajont Dam in Italy. The resulting wave surged over the 262 m (860 ft) high dam by 250 metres (820 ft) and destroyed several towns. Around 2,000 people died.[33][34] Scientists named these waves megatsunamis.

Some geologists claim that large landslides from volcanic islands, e.g. Cumbre Vieja on La Palma in the Canary Islands, may be able to generate megatsunamis that can cross oceans, but this is disputed by many others.

In general, landslides generate displacements mainly in the shallower parts of the coastline, and there is conjecture about the nature of large landslides that enter the water. This has been shown to subsequently affect water in enclosed bays and lakes, but a landslide large enough to cause a transoceanic tsunami has not occurred within recorded history. Susceptible locations are believed to be the Big Island of Hawaii, Fogo in the Cape Verde Islands, La Reunion in the Indian Ocean, and Cumbre Vieja on the island of La Palma in the Canary Islands; along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on the flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are.[35]


Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths comparable to seismic tsunamis, but usually with lower energies. These are essentially dynamically equivalent to seismic tsunamis, the only differences being that meteotsunamis lack the transoceanic reach of significant seismic tsunamis and that the force that displaces the water is sustained over some length of time such that meteotsunamis can't be modelled as having been caused instantaneously. In spite of their lower energies, on shorelines where they can be amplified by resonance, they are sometimes powerful enough to cause localised damage and potential for loss of life. They have been documented in many places, including the Great Lakes, the Aegean Sea, the English Channel, and the Balearic Islands, where they are common enough to have a local name, rissaga. In Sicily they are called marubbio and in Nagasaki Bay, they are called abiki. Some examples of destructive meteotsunamis include 31 March 1979 at Nagasaki and 15 June 2006 at Menorca, the latter causing damage in the tens of millions of euros.[36]

Meteotsunamis should not be confused with storm surges, which are local increases in sea level associated with the low barometric pressure of passing tropical cyclones, nor should they be confused with setup, the temporary local raising of sea level caused by strong on-shore winds. Storm surges and setup are also dangerous causes of coastal flooding in severe weather but their dynamics are completely unrelated to tsunami waves.[36] They are unable to propagate beyond their sources, as waves do.

Man-made or triggered tsunamis

There have been studies of the potential of the induction of and at least one actual attempt to create tsunami waves as a tectonic weapon.

In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.[37]

There has been considerable speculation on the possibility of using nuclear weapons to cause tsunamis near an enemy coastline. Even during World War II consideration of the idea using conventional explosives was explored. Nuclear testing in the Pacific Proving Ground by the United States seemed to generate poor results. Operation Crossroads fired two 20 kilotonnes of TNT (84 TJ) bombs, one in the air and one underwater, above and below the shallow (50 m (160 ft)) waters of the Bikini Atoll lagoon. Fired about 6 km (3.7 mi) from the nearest island, the waves there were no higher than 3–4 m (9.8–13.1 ft) upon reaching the shoreline. Other underwater tests, mainly Hardtack I/Wahoo (deep water) and Hardtack I/Umbrella (shallow water) confirmed the results. Analysis of the effects of shallow and deep underwater explosions indicate that the energy of the explosions doesn't easily generate the kind of deep, all-ocean waveforms which are tsunamis; most of the energy creates steam, causes vertical fountains above the water, and creates compressional waveforms.[38] Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions.


Propagation du tsunami en profondeur variable
When the wave enters shallow water, it slows down and its amplitude (height) increases.
The wave further slows and amplifies as it hits land. Only the largest waves crest.

Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it, even with waves that do not appear to be large.

While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in the deep ocean has a much larger wavelength of up to 200 kilometres (120 mi). Such a wave travels at well over 800 kilometres per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft).[39] This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage.

The velocity of a tsunami can be calculated by obtaining the square root of the depth of the water in metres multiplied by the acceleration due to gravity (approximated to 10 m/s2). For example, if the Pacific Ocean is considered to have a depth of 5000 metres, the velocity of a tsunami would be the square root of √(5000 × 10) = √50000 = ~224 metres per second (735 feet per second), which equates to a speed of ~806 kilometres per hour or about 500 miles per hour. This is the formula used for calculating the velocity of shallow-water waves. Even the deep ocean is shallow in this sense because a tsunami wave is so long (horizontally from crest to crest) by comparison.

The reason for the Japanese name "harbour wave" is that sometimes a village's fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated by a huge wave.

As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its speed decreases below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its amplitude grows enormously – in accord with Green's law. Since the wave still has the same very long period, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break, but rather appears like a fast-moving tidal bore.[40] Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front.

When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a reference sea level.[40] A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run-up.[41]

About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. They are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and bolides.


Shallow water wave
An illustration of the rhythmic "drawback" of surface water associated with a wave. It follows that a very large drawback may herald the arrival of a very large wave.

All waves have a positive and negative peak; that is, a ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at the shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However, if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. The drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.

A typical wave period for a damaging tsunami is about twelve minutes. Thus, the sea recedes in the drawback phase, with areas well below sea level exposed after three minutes. For the next six minutes, the wave trough builds into a ridge which may flood the coast, and destruction ensues. During the next six minutes, the wave changes from a ridge to a trough, and the flood waters recede in a second drawback. Victims and debris may be swept into the ocean. The process repeats with succeeding waves.

Scales of intensity and magnitude

As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events.[42]

Intensity scales

The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean. The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula

where is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA[43] and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.

In 2013, following the intensively studied tsunamis in 2004 and 2011, a new 12-point scale was proposed, the Integrated Tsunami Intensity Scale (ITIS-2012), intended to match as closely as possible to the modified ESI2007 and EMS earthquake intensity scales.[44][45]

Magnitude scales

The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy.[42] Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale , calculated from,

where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicentre, a, b and D are constants used to make the Mt scale match as closely as possible with the moment magnitude scale.[46]

Tsunami heights

Tsunami run-up, height, and inundation
Diagram showing several measures to describe a tsunami size, including height, inundation and run-up.

Several terms are used to describe the different characteristics of tsunami in terms of their height:[47][48][49][50]

  • Amplitude, Wave Height, or Tsunami Height: Amplitude of Tsunami refers to its height relative to the normal sea level. It is usually measured at sea level, and it is different from the crest-to-trough height which is commonly used to measure other type of wave height.[51]
  • Run-up Height, or Inundation Height: The height reached by a tsunami on the ground above sea level, Maximum run-up height refers to the maximum height reached by water above sea level, which is sometimes reported as the maximum height reached by a tsunami.
  • Flow Depth: Refers to the height of tsunami above ground, regardless of the height of the location or sea level.
  • (Maximum) Water Level: Maximum height above sea level as seen from trace or water mark. Different from maximum run-up height in the sense that they are not necessarily water marks at inundation line/limit.

Warnings and predictions

Tsunami warning sign

Drawbacks can serve as a brief warning. People who observe drawback (many survivors report an accompanying sucking sound), can survive only if they immediately run for high ground or seek the upper floors of nearby buildings. In 2004, ten-year-old Tilly Smith of Surrey, England, was on Maikhao beach in Phuket, Thailand with her parents and sister, and having learned about tsunamis recently in school, told her family that a tsunami might be imminent. Her parents warned others minutes before the wave arrived, saving dozens of lives. She credited her geography teacher, Andrew Kearney.

In the 2004 Indian Ocean tsunami drawback was not reported on the African coast or any other east-facing coasts that it reached. This was because the wave moved downwards on the eastern side of the fault line and upwards on the western side. The western pulse hit coastal Africa and other western areas.

A tsunami cannot be precisely predicted, even if the magnitude and location of an earthquake is known. Geologists, oceanographers, and seismologists analyse each earthquake and based on many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and automated systems can provide warnings immediately after an earthquake in time to save lives. One of the most successful systems uses bottom pressure sensors, attached to buoys, which constantly monitor the pressure of the overlying water column.

Regions with a high tsunami risk typically use tsunami warning systems to warn the population before the wave reaches land. On the west coast of the United States, which is prone to Pacific Ocean tsunami, warning signs indicate evacuation routes. In Japan, the community is well-educated about earthquakes and tsunamis, and along the Japanese shorelines the tsunami warning signs are reminders of the natural hazards together with a network of warning sirens, typically at the top of the cliff of surroundings hills.[52]

The Pacific Tsunami Warning System is based in Honolulu, Hawaiʻi. It monitors Pacific Ocean seismic activity. A sufficiently large earthquake magnitude and other information triggers a tsunami warning. While the subduction zones around the Pacific are seismically active, not all earthquakes generate a tsunami. Computers assist in analysing the tsunami risk of every earthquake that occurs in the Pacific Ocean and the adjoining land masses.

Bamfield Tsunami Hazard Zone sign

Tsunami hazard sign at Bamfield, British Columbia

A tsunami warning sign in Kamakura, Japan

A tsunami warning sign in Kamakura, Japan

The monument to the victims of tsunami

The monument to the victims of the 1946 tsunami at Laupahoehoe, Hawaii

Tsunami Memorial Kanyakumari

Tsunami memorial in Kanyakumari beach

Zona de Inundabilidad

A Tsunami hazard sign (Spanish - English) in Iquique, Chile.

Tsunami Evacuation Route signage south of Aberdeen Washington

Tsunami Evacuation Route signage along U.S. Route 101, in Washington

As a direct result of the Indian Ocean tsunami, a re-appraisal of the tsunami threat for all coastal areas is being undertaken by national governments and the United Nations Disaster Mitigation Committee. A tsunami warning system is being installed in the Indian Ocean.

Dart tsunamicover
One of the deep water buoys used in the DART tsunami warning system

Computer models can predict tsunami arrival, usually within minutes of the arrival time. Bottom pressure sensors can relay information in real time. Based on these pressure readings and other seismic information and the seafloor's shape (bathymetry) and coastal topography, the models estimate the amplitude and surge height of the approaching tsunami. All Pacific Rim countries collaborate in the Tsunami Warning System and most regularly practise evacuation and other procedures. In Japan, such preparation is mandatory for government, local authorities, emergency services and the population.

Some zoologists hypothesise that some animal species have an ability to sense subsonic Rayleigh waves from an earthquake or a tsunami. If correct, monitoring their behaviour could provide advance warning of earthquakes, tsunami etc. However, the evidence is controversial and is not widely accepted. There are unsubstantiated claims about the Lisbon quake that some animals escaped to higher ground, while many other animals in the same areas drowned. The phenomenon was also noted by media sources in Sri Lanka in the 2004 Indian Ocean earthquake.[53][54] It is possible that certain animals (e.g., elephants) may have heard the sounds of the tsunami as it approached the coast. The elephants' reaction was to move away from the approaching noise. By contrast, some humans went to the shore to investigate and many drowned as a result.

Along the United States west coast, in addition to sirens, warnings are sent on television and radio via the National Weather Service, using the Emergency Alert System.

Forecast of tsunami attack probability

Kunihiko Shimazaki (University of Tokyo), a leading member of the Earthquake Research Committee at The Headquarters for Earthquake Research Promotion in Japan, has mentioned an idea for instituting a system of public education regarding the probability of tsunami risk; such a system was announced by Shimazaki at the Japan National Press Club in May 2011. The forecast would include a detection for environmental risk, including proposed tsunami height, danger areas prone to tsunamis, and overall occurrence probability. The forecast would integrate the scientific knowledge of recent interdisciplinarity with information gathered from the aftermath of the 2011 Tōhoku earthquake and tsunami. Per the announcement, a plan was due to be put in place by 2014; however, reliable forecasting of earthquake and tsunami probability is still unavailable. Shimazaki acknowledged that, given the current literature on the topic, tsunami probability warnings are just as, if not more, difficult to predict than earthquake risk probability.


Tsunami wall
A seawall at Tsu, Japan

In some tsunami-prone countries, earthquake engineering measures have been taken to reduce the damage caused onshore.

Japan, where tsunami science and response measures first began following a disaster in 1896, has produced ever-more elaborate countermeasures and response plans.[55] The country has built many tsunami walls of up to 12 metres (39 ft) high to protect populated coastal areas. Other localities have built floodgates of up to 15.5 metres (51 ft) high and channels to redirect the water from an incoming tsunami. However, their effectiveness has been questioned, as tsunami often overtop the barriers.

The Fukushima Daiichi nuclear disaster was directly triggered by the 2011 Tōhoku earthquake and tsunami, when waves exceeded the height of the plant's sea wall.[56] Iwate Prefecture, which is an area at high risk from tsunami, had tsunami barriers walls (Taro sea wall) totalling 25 kilometres (16 mi) long at coastal towns. The 2011 tsunami toppled more than 50% of the walls and caused catastrophic damage.[57]

The Okushiri, Hokkaidō tsunami which struck Okushiri Island of Hokkaidō within two to five minutes of the earthquake on July 12, 1993, created waves as much as 30 metres (100 ft) tall—as high as a 10-storey building. The port town of Aonae was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood-framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami, but it did not prevent major destruction and loss of life.[58]

See also


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Further reading

  • Boris Levin, Mikhail Nosov: Physics of tsunamis. Springer, Dordrecht 2009, ISBN 978-1-4020-8855-1.
  • Kontar, Y. A. et al.: Tsunami Events and Lessons Learned: Environmental and Societal Significance. Springer, 2014. ISBN 978-94-007-7268-7 (print); ISBN 978-94-007-7269-4 (eBook)
  • Kristy F. Tiampo: Earthquakes: simulations, sources and tsunamis. Birkhäuser, Basel 2008, ISBN 978-3-7643-8756-3.
  • Linda Maria Koldau: Tsunamis. Entstehung, Geschichte, Prävention, (Tsunami development, history and prevention) C.H. Beck, Munich 2013 (C.H. Beck Reihe Wissen 2770), ISBN 978-3-406-64656-0 (in German).
  • Walter C. Dudley, Min Lee: Tsunami! University of Hawaii Press, 1988, 1998, Tsunami! University of Hawai'i Press 1999, ISBN 0-8248-1125-9, ISBN 978-0-8248-1969-9.
  • Charles L. Mader: Numerical Modeling of Water Waves CRC Press, 2004, ISBN 0-8493-2311-8.

External links

1755 Lisbon earthquake

The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, occurred in the Kingdom of Portugal on the morning of Saturday, 1 November, Feast of All Saints, at around 09:40 local time. In combination with subsequent fires and a tsunami, the earthquake almost totally destroyed Lisbon and adjoining areas. Seismologists today estimate the Lisbon earthquake had a magnitude in the range 8.5–9.0 on the moment magnitude scale, with its epicentre in the Atlantic Ocean about 200 km (120 mi) west-southwest of Cape St. Vincent. Chronologically it was the third known large scale earthquake to hit the city (one in 1321 and another in 1531). Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the deadliest earthquakes in history.

The earthquake accentuated political tensions in the Kingdom of Portugal and profoundly disrupted the country's colonial ambitions. The event was widely discussed and dwelt upon by European Enlightenment philosophers, and inspired major developments in theodicy. As the first earthquake studied scientifically for its effects over a large area, it led to the birth of modern seismology and earthquake engineering.

1946 Aleutian Islands earthquake

The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1. The shock had a moment magnitude of 8.6 and a maximum Mercalli intensity of VI (Strong). It resulted in 165–173 casualties and over $26 million in damage. The seafloor along the fault was elevated, triggering a Pacific-wide tsunami with multiple destructive waves at heights ranging from 45–130 ft. The tsunami obliterated the Scotch Cap Lighthouse on Unimak Island, Alaska among others, and killed all five lighthouse keepers. Despite the destruction to the Aleutian Island Unimak, the tsunami had almost an imperceptible effect on the Alaskan mainland.Waves reportedly traveled across the ocean at 500 miles an hour and measured 55 feet high, crest to trough, according to the USGS. The wave reached Kauai, Hawaii 4.5 hours after the quake, and Hilo, Hawaii 4.9 hours later. In Hilo, the death toll was high: 173 were killed, 163 injured, 488 buildings were demolished and 936 more were damaged. Witnesses told of waves inundating streets, homes, and storefronts. Many victims were swept out to sea by receding water. The tsunami caused much damage in Maui as well. Waves there demolished 77 homes and many other buildings. The residents of these islands were caught off-guard by the onset of the tsunami due to the inability to transmit warnings from the destroyed posts at Scotch Cap, and the tsunami is known as the April Fools Day Tsunami in Hawaii because it happened on April 1st and many thought it to be an April Fool's Day prank. The effects of the tsunami also reached Washington, Oregon, and California.The tsunami was unusually powerful for the size of the earthquake. The event was classified as a tsunami earthquake due to the discrepancy between the size of the tsunami and the relatively low surface wave magnitude. The large-scale destruction prompted the creation of the Seismic Sea Wave Warning System, which became the Pacific Tsunami Warning Center in 1949.

1960 Valdivia earthquake

The 1960 Valdivia earthquake (Spanish: Terremoto de Valdivia) or the Great Chilean earthquake (Gran terremoto de Chile) on 22 May 1960 is the most powerful earthquake ever recorded. Various studies have placed it at 9.4–9.6 on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 15:11 local time), and lasted approximately 10 minutes. The resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia, and the Aleutian Islands.

The epicenter of this megathrust earthquake was near Lumaco, approximately 570 kilometres (350 mi) south of Santiago, with Valdivia being the most affected city. The tremor caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,200 mi) from the epicenter, and as far away as Japan and the Philippines.

The death toll and monetary losses arising from this widespread disaster are not certain.

Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, ranging between 1,000 and 7,000 killed. Different sources have estimated the monetary cost ranged from US$400 million to $800 million (or $3.39 billion to $6.78 billion today, adjusted for inflation).

1964 Alaska earthquake

The 1964 Alaskan earthquake, also known as the Great Alaskan earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday, March 27. Across south-central Alaska, ground fissures, collapsing structures, and tsunamis resulting from the earthquake caused about 131 deaths.Lasting four minutes and thirty-eight seconds, the magnitude 9.2 megathrust earthquake remains the most powerful earthquake recorded in North American history, and the second most powerful earthquake recorded in world history. Six hundred miles (970 km) of fault ruptured at once and moved up to 60 ft (18 m), releasing about 500 years of stress buildup. Soil liquefaction, fissures, landslides, and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles (320 km) southwest, some areas near Kodiak were permanently raised by 30 feet (9 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.

In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Washington, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas.

2004 Indian Ocean earthquake and tsunami

The 2004 Indian Ocean earthquake occurred at 00:58:53 UTC on 26 December, with an epicentre off the west coast of northern Sumatra. It was an undersea megathrust earthquake that registered a magnitude of 9.1–9.3 Mw, reaching a Mercalli intensity up to IX in certain areas. The earthquake was caused by a rupture along the fault between the Burma Plate and the Indian Plate.

A series of large tsunamis up to 30 metres (100 ft) high were created by the underwater seismic activity that became known collectively as the Boxing Day tsunamis. Communities along the surrounding coasts of the Indian Ocean were seriously affected, and the tsunamis killed an estimated 227,898 people in 14 countries. The Indonesian city of Banda Aceh reported the largest number of victims. The earthquake was one of the deadliest natural disasters in recorded history. The direct results caused major disruptions to living conditions and commerce particularly in Indonesia, Sri Lanka, India, and Thailand.

The earthquake was the third largest ever recorded and had the longest duration of faulting ever observed; between eight and ten minutes. It caused the planet to vibrate as much as 10 millimetres (0.4 inches), and it remotely triggered earthquakes as far away as Alaska. Its epicentre was between Simeulue and mainland Sumatra. The plight of the affected people and countries prompted a worldwide humanitarian response, with donations totaling more than US$14 billion. The event is known by the scientific community as the Sumatra–Andaman earthquake.

2009 Samoa earthquake and tsunami

The 2009 Samoa earthquake and tsunami took place on 29 September 2009 in the southern Pacific Ocean adjacent to the Kermadec-Tonga subduction zone. The submarine earthquake occurred in an extensional environment and had a moment magnitude of 8.1 and a maximum Mercalli intensity of VI (Strong). It was the largest earthquake of 2009.

A tsunami was generated which caused substantial damage and loss of life in Samoa, American Samoa, and Tonga. The Pacific Tsunami Warning Center recorded a 3-inch (76 mm) rise in sea levels near the epicenter, and New Zealand scientists determined that the waves measured 14 metres (46 ft) at their highest on the Samoan coast. The quake occurred on the outer rise of the Kermadec-Tonga subduction zone. This is part of the Pacific Ring of Fire, where tectonic plates in the Earth's lithosphere meet and earthquakes and volcanic activity are common.

Countries affected by the tsunami in the areas that were hit are American Samoa, Samoa and Tonga (Niuatoputapu) where more than 189 people were killed, especially children, most of them in Samoa.

Large waves with no major damage were reported on the coasts of Fiji, the northern coast of New Zealand and Rarotonga in the Cook Islands. People took precautions in the low-lying atolls of Tokelau and moved to higher ground. Niue was reported as reasonably safe because it is high. There were no reports of high waves from Vanuatu, Kiribati, New Caledonia and the Solomon Islands.

2010 Chile earthquake

The 2010 Chile earthquake (Spanish: Terremoto del 27F) occurred off the coast of central Chile on Saturday, 27 February at 03:34 local time (06:34 UTC), having a magnitude of 8.8 on the moment magnitude scale, with intense shaking lasting for about three minutes. It was felt strongly in six Chilean regions (from Valparaíso in the north to Araucanía in the south), that together make up about 80 percent of the country's population. According to the United States Geological Survey (USGS) the cities experiencing the strongest shaking—VIII (Severe) on the Mercalli intensity scale (MM)—were Concepción, Arauco and Coronel. According to Chile's Seismological Service Concepción experienced the strongest shaking at MM IX (Violent). The earthquake was felt in the capital Santiago at MM VII (Very strong) or MM VIII. Tremors were felt in many Argentine cities, including Buenos Aires, Córdoba, Mendoza and La Rioja. Tremors were felt as far north as the city of Ica in southern Peru (approx. 2,400 km (1,500 mi) away).The earthquake triggered a tsunami which devastated several coastal towns in south-central Chile and damaged the port at Talcahuano. Tsunami warnings were issued in 53 countries, and the wave caused minor damage in the San Diego area of California and in the Tōhoku region of Japan, where damage to the fisheries business was estimated at ¥6.26 billion (US$66.7 million). The earthquake also generated a blackout that affected 93 percent of the Chilean population and which went on for several days in some locations. President Michelle Bachelet declared a "state of catastrophe" and sent military troops to take control of the most affected areas. According to official sources, 525 people lost their lives, 25 people went missing and about 9% of the population in the affected regions lost their homes.On 10 March, Swiss Reinsurance Co. estimated that the Chilean quake would cost insurance companies between 4 and 7 billion dollars. The rival German-based Munich Re AG made the same estimate. Earthquake's losses to the economy of Chile are estimated at US$15–30 billion.

2011 Tōhoku earthquake and tsunami

The 2011 earthquake off the Pacific coast of Tōhoku (東北地方太平洋沖地震, Tōhoku-chihō Taiheiyō Oki Jishin) was a magnitude 9.0–9.1 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday 11 March 2011, with the epicentre approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 29 km (18 mi).

The earthquake is often referred to in Japan as the Great East Japan Earthquake (東日本大震災, Higashi nihon daishinsai) and is also known as the 2011 Tōhoku earthquake, the Great Sendai Earthquake, the Great Tōhoku Earthquake, and the 3.11 earthquake.

It was the most powerful earthquake ever recorded in Japan, and the fourth most powerful earthquake in the world since modern record-keeping began in 1900.

The earthquake triggered powerful tsunami waves that may have reached heights of up to 40.5 metres (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, traveled at 435 mph for up to 10 km (6 mi) inland. Residents of Sendai had only eight to ten minutes warning, and more than 19,000 were killed, many at the more than a hundred evacuation sites that washed away.The earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east, shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in), increased earth's rotational speed by 1.8 µs per day, and generated infrasound waves detected in perturbations of the low-orbiting GOCE satellite.

Initially, the earthquake caused sinking of part of Honshu's Pacific coast by up to roughly a metre, but after about three years, the coast rose back and kept on rising to exceed its original height.The tsunami swept the Japanese mainland and killed over ten thousand people, mainly through drowning, though blunt trauma also caused many deaths. The latest report from the Japanese National Police Agency report confirms 15,897 deaths, 6,157 injured, and 2,533 people missing across twenty prefectures, and a report from 2015 indicated 228,863 people were still living away from their home in either temporary housing or due to permanent relocation.A report by the National Police Agency of Japan on 10 September 2018 listed 121,778 buildings as "total collapsed", with a further 280,926 buildings "half collapsed", and another 699,180 buildings "partially damaged". The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Japanese Prime Minister Naoto Kan said, "In the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan." Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.The tsunami caused nuclear accidents, primarily the level 7 meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. Many electrical generators were taken down, and at least three nuclear reactors suffered explosions due to hydrogen gas that had built up within their outer containment buildings after cooling system failure resulting from the loss of electrical power. Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated.

Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the costliest natural disaster in history.

Crescent City, California

Crescent City (Chetco-Tolowa: Taa-’at-dvn, Yurok: Kohpey, Wiyot: Daluwagh ) is the county seat of, and only incorporated city in, Del Norte County, California. Named for the crescent-shaped stretch of sandy beach south of the city, Crescent City had a total population of 7,643 in the 2010 census, up from 4,006 in the 2000 census. The population includes inmates at Pelican Bay State Prison, also within the city limits, and the former census-designated place Crescent City North annexed to the city. The city is also the site of the Redwood National Park headquarters, as well as the historic Battery Point Light. Due to the richness of the local Pacific Ocean waters and the related catch, and ease of access, Crescent City Harbor serves as home port for numerous commercial fishing vessels.

The city is located on the Pacific coast in the upper northwestern part of California, about 20 miles (32 km) south of the Oregon border. Crescent City's offshore geography makes it unusually susceptible to tsunamis. Much of the city was destroyed by four tsunami waves generated by the Good Friday earthquake off Anchorage, Alaska in 1964. More recently, the city's harbor suffered extensive damage and destruction due to tsunamis generated by the March 11, 2011 earthquake off Sendai, Japan. Several dozen vessels and many of the docks they were moored to were destroyed as wave cycles related to the tsunamis exceeded 8 feet (2.4 m). Its climate is also very moderate, with very cool summers for its latitude as a result of intense maritime moderation. Nearby inland areas behind the mountains have significantly warmer summers.

Deep-ocean Assessment and Reporting of Tsunamis

Deep-ocean Assessment and Reporting of Tsunamis (DART) is a component of an enhanced tsunami warning system.

By logging changes in seafloor temperature and pressure, and transmitting the data via a surface buoy to a ground station by satellite, DART enables instant, accurate tsunami forecasts. In Standard Mode, the system logs the data at 15-minute intervals, and in Event Mode, every 15 seconds. A 2-way communication system allows the ground station to switch DART into Event Mode whenever detailed reports are needed.


An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.

At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.

In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.

Fukushima Daiichi nuclear disaster

The Fukushima Daiichi nuclear disaster (福島第一原子力発電所事故, Fukushima Dai-ichi (pronunciation) genshiryoku hatsudensho jiko) was an energy accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima Prefecture, started primarily by the tsunami following the Tōhoku earthquake on 11 March 2011. Immediately after the earthquake, the active reactors automatically shut down their sustained fission reactions. However, the ensuing tsunami flooded the emergency generators that were providing power to the pumps that cooled the reactors. The coolant loss led to three nuclear meltdowns, hydrogen-air explosions, and the release of radioactive material in Units 1, 2 and 3 between 12 and 15 March. Coolant loss also raised concerns over the recently loaded spent fuel pool of Reactor 4, which increased in temperature on 15 March due to decay heat from the freshly added spent fuel rods but did not boil down to exposure.On 5 July 2012, the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) found that the causes of the accident had been foreseeable, and that the plant operator, Tokyo Electric Power Company (TEPCO), had failed to meet basic safety requirements such as risk assessment, preparing for containing collateral damage, and developing evacuation plans. On 12 October 2012, TEPCO admitted for the first time that it had failed to take necessary measures for fear of inviting lawsuits or protests against its nuclear plants.The Fukushima disaster was the most significant nuclear incident since the 26 April 1986 Chernobyl disaster and the only other disaster to be given the Level 7 event classification of the International Nuclear Event Scale.Two TEPCO employees died of injuries from the earthquake, and six others received radiation exposure above the lifetime limit. As of September 2018, one cancer fatality had resulted in a financial settlement to the family of a former station workman. A report by the United Nations Scientific Committee on the Effects of Atomic Radiation and World Health Organization projected no increase in miscarriages, stillbirths or physical and mental disorders in babies born after the accident. More than 171,000 evacuees were still unable to return home as of March 2016. An estimated 1,600 deaths are believed to have occurred, primarily among elderly who had lived in nursing homes, due to poor evacuation conditions.An ongoing intensive cleanup program to both decontaminate affected areas and decommission the plant will take 30 to 40 years, plant management estimate. A frozen soil barrier, built in an attempt to prevent further contamination of seeping groundwater, slowed down the amount of contaminated water collected. The collected water is treated and all radioactive elements are removed, except for tritium.In February 2017, TEPCO released images taken inside Reactor 2 by a remote-controlled camera that show a 2-meter (6.5 ft) wide hole in the metal grating under the pressure vessel in the reactor's primary containment vessel, which could have been caused by fuel escaping the pressure vessel, indicating a meltdown/melt-through had occurred, through this layer of containment. Radiation levels of about 210 Sv per hour were subsequently detected inside the Unit 2 containment vessel. Undamaged spent fuel typically has values of 270 Sv/h, after ten years of cold shutdown with no shielding.

Johnny Tsunami

Johnny Tsunami is a 1999 Disney Channel Original Movie (DCOM). It was nominated in 2000 for the Humanitas Prize as Children's Live-Action Category. Johnny Tsunami is the predecessor to Johnny Kapahala: Back on Board, released in June 2007. The film focuses on a young surfer from Hawaii who must adapt to new challenges when his father's job forces the family to move to Vermont.

List of earthquakes in Japan

This is a list of earthquakes in Japan with either a magnitude greater than or equal to 7.0 or which caused significant damage or casualties. As indicated below, magnitude is measured on the Richter magnitude scale (ML) or the moment magnitude scale (Mw), or the surface wave magnitude scale (Ms) for very old earthquakes. The present list is not exhaustive, and reliable and precise magnitude data is scarce for earthquakes that occurred prior to the development of modern measuring instruments.

List of earthquakes in the United States

The following is a list of notable earthquakes and/or tsunamis which had their epicenter in areas that are now part of the United States with the latter affecting areas of the United States. Those in italics were not part of the United States when the event occurred.

Earthquake swarms which affected the United States:

1962–71 Denver earthquake swarm

Enola earthquake swarm

2008 Reno earthquakes

Guy-Greenbrier earthquake swarm

2009–present Oklahoma earthquake swarmsEarthquakes which affected the United States but whose epicenters were outside the United States borders:

1925 Charlevoix–Kamouraska earthquake – magnitude 6.2 earthquake, no injuries or fatalities anywhere

2010 Baja California earthquake (Mexico near S California) – magnitude 7.2 earthquake, 4 fatalities and 100 injuries, none in the United StatesEarthquakes which did not affect the United States directly, but caused tsunamis which did:

1960 Valdivia earthquake and tsunami – magnitude 9.5 earthquake, between 2200 and 6000 fatalities, including 61 in Hilo, HI

2006 Kuril Islands earthquake and tsunami – magnitude 8.3 earthquake, no injuries or fatalities anywhere

2009 Samoa earthquake and tsunami – magnitude 8.0 earthquake with an epicenter 120 miles (190 km) southwest of American Samoa generated tsunami waves up to 16 feet (5 m), killing 34 people in American Samoa and causing extensive damage

2010 Chile earthquake and tsunami – magnitude 8.8 earthquake, ~525 fatalities and unknown number of injuries, none in the United States

2011 Tohoku earthquake and tsunami – magnitude 9.0 earthquake, 15,850–28,000 fatalities and 6,011 injured, one fatality and unknown number of injuries in the United States

2012 Haida Gwaii earthquake – magnitude 7.8 earthquake with an epicenter on Moresby Island in British Columbia, the second largest Canadian earthquake ever recorded by a seismometer, over 100,000 people were evacuated to higher ground in the state of Hawai'i

List of tsunamis

This article lists notable tsunamis, which are sorted by the date and location that the tsunami occurred.

Because of seismic and volcanic activity associated with tectonic plate boundaries along the Pacific Ring of Fire, tsunamis occur most frequently in the Pacific Ocean, but are a worldwide natural phenomenon. They are possible wherever large bodies of water are found, including inland lakes, where they can be caused by landslides and glacier calving. Very small tsunamis, non-destructive and undetectable without specialized equipment, occur frequently as a result of minor earthquakes and other events.

Around 1600 BCE, a tsunami caused by the eruption of Thira devastated the Minoan civilization on Crete and related cultures in the Cyclades, as well as in areas on the Greek mainland facing the eruption, such as the Argolid.

The oldest recorded tsunami occurred in 479 BCE. It destroyed a Persian army that was attacking the town of Potidaea in Greece.As early as 426 BCE, the Greek historian Thucydides inquired in his book History of the Peloponnesian War (3.89.1–6) about the causes of tsunamis. He argued that such events could only be explained as a consequence of ocean earthquakes, and could see no other possible causes.


A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water.

Megatsunamis have quite different features from other, more usual types of tsunamis. Most tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquake and rise or fall in the sea floor, causing water to be displaced. Ordinary tsunamis have shallow waves out at sea, and the water piles up to a wave height of up to about 10 metres (33 feet) as the sea floor becomes shallow near land. By contrast, megatsunamis occur when a very large amount of material suddenly falls into water or anywhere near water (such as via a meteor impact), or are caused by volcanic activity. They can have extremely high initial wave heights of hundreds and possibly thousands of metres, far beyond any ordinary tsunami, as the water is "splashed" upwards and outwards by the impact or displacement. As a result, two heights are sometimes quoted for megatsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.

Modern megatsunamis include the one associated with the 1883 eruption of Krakatoa (volcanic eruption), the 1958 Lituya Bay megatsunami (landslide into a bay), and the wave resulting from the Vajont Dam landslide (caused by human activity destabilizing sides of valley). Prehistoric examples include the Storegga Slide (landslide), and the Chicxulub, Chesapeake Bay and Eltanin meteor impacts.

Natural disaster

A natural disaster is a major adverse event resulting from natural processes of the Earth; examples are floods, hurricanes, tornadoes, volcanic eruptions, earthquakes, tsunamis, and other geologic processes. A natural disaster can cause loss of life or damage property, and typically leaves some economic damage in its wake, the severity of which depends on the affected population's resilience, or ability to recover and also on the infrastructure available.An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population. In a vulnerable area, however, such as Nepal during the 2015 earthquake, an earthquake can have disastrous consequences and leave lasting damage, which can require years to repair.

Tsunami warning system

A tsunami warning system (TWS) is used to detect tsunamis in advance and issue warnings to prevent loss of life and damage to property. It is made up of two equally important components: a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms to permit evacuation of the coastal areas. There are two distinct types of tsunami warning systems: international and regional. When operating, seismic alerts are used to instigate the watches and warnings; then, data from observed sea level height (either shore-based tide gauges or DART buoys) are used to verify the existence of a tsunami. Other systems have been proposed to augment the warning procedures; for example, it has been suggested that the duration and frequency content of t-wave energy (which is earthquake energy trapped in the ocean SOFAR channel) is indicative of an earthquake's tsunami potential.

Ocean zones
Sea level

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