A tsunami ( ; from ja, 津波, lit=harbour 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.

Earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...

s and other

underwater explosion An underwater explosion (also known as an UNDEX) is a chemical or nuclear explosion that occurs under the surface of a body of water. While useful in anti-ship and submarine warfare, underwater bombs are not as effective against coastal facilities. ...

s (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide t ...

s, which are in turn generated by the gravitational pull of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, a tsunami is generated by the displacement of water from a large event. Tsunami waves do not resemble normal undersea currents or

sea waves In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction of ...

because their

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

is far longer. Rather than appearing as a

breaking wave In fluid dynamics, a breaking wave or breaker is a wave whose amplitude reaches a critical level at which large amounts of wave energy transform into Wave turbulence, turbulent kinetic energy. At this point, simple physical models that describ ...

, a tsunami may instead initially resemble a rapidly rising

. 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. Tsunamis generally consist of a series of waves, with

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

s ranging from minutes to hours, arriving in a so-called "

wave train In physics, a wave packet (or wave train) is a short "burst" or "envelope" of localized wave action that travels as a unit. A wave packet can be analyzed into, or can be synthesized from, an infinite set of component sinusoidal waves of diff ...

". 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 Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

. The

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

historian

Thucydides Thucydides (; grc, , }; BC) was an Athenian historian and general. His ''History of the Peloponnesian War'' recounts the fifth-century BC war between Sparta and Athens until the year 411 BC. Thucydides has been dubbed the father of "scientifi ...

suggested in his 5th century BC ''

History of the Peloponnesian War The ''History of the Peloponnesian War'' is a historical account of the Peloponnesian War (431–404 BC), which was fought between the Peloponnesian League (led by Sparta) and the Delian League (led by Athens). It was written by Thucydides, an ...

'' that tsunamis were related to

submarine earthquake A submarine, undersea, or underwater earthquake is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean. They are the leading cause of tsunamis. The magnitude can be measured scientifically by the use of the ...

s, 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. This ongoing research is designed to help accurately forecast the passage of tsunamis across oceans as well as how tsunami waves interact with shorelines.

Terminology

Tsunami

The term "tsunami" is a borrowing from the Japanese ''tsunami'' , 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. Some English speakers alter the word's initial to an by dropping the "t," since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is .

Tidal wave

Tsunamis are sometimes referred to as ''tidal waves''. This once-popular term derives from the most common appearance of a tsunami, which is that of an extraordinarily high

tidal bore Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...

. 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

s, 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" or "having the form or character of" tides, use of the term ''tidal wave'' is discouraged by geologists and oceanographers. A 1969 episode of the TV crime show ''

Hawaii Five-O Hawaii Five-O or Hawaii Five-0 may refer to: * ''Hawaii Five-0'' (2010 TV series), an American action police procedural television series * ''Hawaii Five-O'' (1968 TV series), an American police procedural drama series produced by CBS Productio ...

'' entitled "Forty Feet High and It Kills!" used the terms "tsunami" and "tidal wave" interchangeably.

Seismic sea wave

The term ''seismic sea wave'' is also used to refer to the phenomenon because the waves most often are generated by

seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

activity such as earthquakes. 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

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

s, volcanic eruptions, underwater explosions, land or ice

slumping Slumping is a technique in which items are made in a kiln by means of shaping glass over molds at high temperatures. The slumping of a pyrometric cone is often used to measure temperature in a kiln. Technique Slumping glass is a highly techni ...

into the ocean,

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...

impacts, and the weather when the atmospheric pressure changes very rapidly—can generate such waves by displacing water.

History

While Japan may have the longest

recorded history Recorded history or written history describes the historical events that have been recorded in a written form or other documented communication which are subsequently evaluated by historians using the historical method. For broader world hist ...

of tsunamis, the sheer destruction caused by the

2004 Indian Ocean earthquake and tsunami An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time (UTC+7) on 26 December 2004, with an epicentre off the west coast of northern Suma ...

event mark it as the most devastating of its kind in modern times, killing around 230,000 people. The Sumatran region is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island. Tsunamis are an often underestimated hazard in the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

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 Azores–Gibraltar Transform Fault (AGFZ), also called a fault zone and a fracture zone, is a major seismic zone in the Eastern Atlantic Ocean between the Azores and the Strait of Gibraltar. It is the product of the complex interaction between ...

), the

1783 Calabrian earthquakes The 1783 Calabrian earthquakes were a sequence of five strong earthquakes that hit the region of Calabria in southern Italy (then part of the Kingdom of Naples), the first two of which produced significant tsunamis. The epicenters form a clear a ...

, each causing several tens of thousands of deaths and the

1908 Messina earthquake The 1908 Messina earthquake (also known as the 1908 Messina and Reggio earthquake) occurred on 28 December in Sicily and Calabria, southern Italy with a moment magnitude of 7.1 and a maximum Mercalli intensity of XI (''Extreme''). The epicen ...

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 The three Storegga Slides ( no, Storeggaraset) are amongst the largest known submarine landslides. They occurred at the edge of Norway's continental shelf in the Norwegian Sea, approximately 6225–6170 BCE. The collapse involved an estimated ...

in the Norwegian Sea and some examples of

tsunamis affecting the British Isles Tsunamis affecting the British Isles are extremely uncommon, and there have only been two confirmed cases in recorded history. Meteotsunamis (displacements due to atmospheric pressure, rather than seismic shock) are somewhat more common, especially ...

refer to landslide and

meteotsunami A meteotsunami or meteorological tsunamiTsunami Glossary 2008
, UNESCO is a

As early as 426 BC the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

historian

inquired in his book ''

'' about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause.

“A History of the Peloponnesian War”, 3.89.1–4
/ref> The oldest human record of a tsunami dates back to 479 BC, in the Greek colony of

Potidaea __NOTOC__ Potidaea (; grc, Ποτίδαια, ''Potidaia'', also Ποτείδαια, ''Poteidaia'') was a colony founded by the Corinthians around 600 BC in the narrowest point of the peninsula of Pallene, the westernmost of three peninsulas at ...

, thought to be triggered by an earthquake. The tsunami may have saved the colony from an invasion by the

Achaemenid Empire The Achaemenid Empire or Achaemenian Empire (; peo, 𐎧𐏁𐏂, , ), also called the First Persian Empire, was an ancient Iranian empire founded by Cyrus the Great in 550 BC. Based in Western Asia, it was contemporarily the largest em ...

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.
Thucydides Thucydides (; grc, , }; BC) was an Athenian historian and general. His ''History of the Peloponnesian War'' recounts the fifth-century BC war between Sparta and Athens until the year 411 BC. Thucydides has been dubbed the father of "scientifi ...

“A History of the Peloponnesian War”, 3.89.5
/ref>

The

Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a letter ...

historian

Ammianus Marcellinus Ammianus Marcellinus (occasionally Anglicisation, anglicised as Ammian) (born , died 400) was a Roman soldier and historian who wrote the penultimate major historical account surviving from Ancient history, antiquity (preceding Procopius). His w ...

(''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 Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, Alexandria ...

.Stanley, Jean-Daniel & Jorstad, Thomas F. (2005),
The 365 A.D. Tsunami Destruction of Alexandria, Egypt: Erosion, Deformation of Strata and Introduction of Allochthonous Material
"

Causes

The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually caused by earthquakes, but can also be attributed to landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. However, the possibility of a meteorite causing a tsunami is debated.

Seismicity

Tsunamis 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. More specifically, a tsunami can be generated when

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s associated with convergent or destructive

plate boundaries Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

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 The outer trench swell, outer trench high, or outer rise is a subtle ridge on the seafloor near an oceanic trench, where a descending plate begins to flex and fault in preparation for its descent into the mantle at a subduction zone. The lithosph ...

) cause enough displacement to give rise to a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events. File:Eq-gen1.svg, Drawing of

tectonic plate boundary Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

before

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

File:Eq-gen2.svg, Over-riding plate bulges under strain, causing

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thick ...

. File:Eq-gen3.svg, Plate slips, causing

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...

and releasing energy into water. File:Eq-gen4.svg, The energy released produces tsunami waves. Tsunamis have a small wave height offshore, and a very long

(often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), which is why they generally pass unnoticed at sea, forming only a slight swell usually about above the normal sea surface. They grow in height when they reach shallower water, in a

wave shoaling In fluid dynamics, wave shoaling is the effect by which surface waves, entering shallower water, change in wave height. It is caused by the fact that the group velocity, which is also the wave-energy transport velocity, changes with water depth ...

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 Aleutian Islands earthquake occurred with a maximum

Mercalli intensity The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

of VI (''Strong''). It generated a tsunami which inundated

Hilo Hilo () is a census-designated place (CDP) and the largest settlement in Hawaii County, Hawaii, Hawaii County, Hawaii, United States, which encompasses the Hawaii (island), Island of Hawaii. The population was 44,186 according to the 2020 United ...

on the island of Hawaii with a surge. Between 165 and 173 were killed. The area where the earthquake occurred is where the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

floor is

subducting Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

(or being pushed downwards) under Alaska. Examples of tsunamis originating at locations away from convergent boundaries include Storegga about 8,000 years ago,

Grand Banks The Grand Banks of Newfoundland are a series of underwater plateaus south-east of the island of Newfoundland on the North American continental shelf. The Grand Banks are one of the world's richest fishing grounds, supporting Atlantic cod, swordf ...

in 1929, and

Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

in 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 The 1960 Valdivia earthquake and tsunami ( es, link=no, Terremoto de Valdivia) or the Great Chilean earthquake (''Gran terremoto de Chile'') on 22 May 1960 was the most powerful earthquake ever recorded. Various studies have placed it at 9.4– ...

( ''M''_w 9.5), 1964 Alaska earthquake (''M''_w 9.2),

2004 Indian Ocean earthquake An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time (UTC+7) on 26 December 2004, with an epicentre off the west coast of northern Suma ...

(''M''_w 9.2), and 2011 Tōhoku earthquake (''M''_w9.0) are recent examples of powerful

megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthqua ...

s that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (''M''_w 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.

Landslides

The

Tauredunum event The Tauredunum event (german: Tauredunum-Ereignis) of 563 AD was a tsunami on Lake Geneva (then under the Frankish territory of the Kingdom of Orleans), triggered by a massive landslide which caused widespread devastation and loss of life along ...

was a large tsunami on

Lake Geneva , image = Lake Geneva by Sentinel-2.jpg , caption = Satellite image , image_bathymetry = , caption_bathymetry = , location = Switzerland, France , coords = , lake_type = Glacial lak ...

in 563 CE, caused by sedimentary deposits destabilized by a landslide. In the 1950s, it was discovered that tsunamis larger than had previously been believed possible can be caused by giant submarine landslides. These large volumes of rapidly displaced water transfer energy at a faster rate than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in

Lituya Bay Lituya Bay (; Tlingit: ''Ltu.aa'',. Spelled L'tua in translation of Tebenkov's log. meaning 'lake within the point') is a fjord located on the coast of the south-east part of the U.S. state of Alaska. It is long and wide at its widest point ...

, Alaska, caused the highest wave ever recorded, which had a height of . The wave did not travel far as it struck land almost immediately. The wave struck three boats—each with two people aboard—anchored in the bay. One boat rode out the wave, but the wave sank the other two, killing both people aboard one of them. Another landslide-tsunami event occurred in 1963 when a massive landslide from

Monte Toc Monte Toc, nicknamed the walking mountain by locals due to its tendency to experience landslides, is a mountain on the border between Veneto and Friuli-Venezia Giulia in Northern Italy best known for the Vajont Dam, which was built at the mountai ...

entered the reservoir behind the

Vajont Dam The Vajont Dam (or Vaiont Dam) is a disused dam in northern Italy. It is one of the tallest dams in the world, with a height of . It is in the valley of the Vajont River under Monte Toc, in the municipality of Erto e Casso, north of Venice ...

in Italy. The resulting wave surged over the -high dam by and destroyed several towns. Around 2,000 people died. Scientists named these waves

megatsunami 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 ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movemen ...

s. Some geologists claim that large landslides from volcanic islands, e.g.

Cumbre Vieja The Cumbre Vieja (; meaning "Old Summit") is an active volcanic ridge on the island of La Palma in the Canary Islands, Spain. The spine of Cumbre Vieja trends in an approximate north–south direction, comprising the southern half of La Palma, ...

La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...

( Cumbre Vieja tsunami hazard) in the

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

, 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 Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

, Fogo in the

Cape Verde Islands , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...

, La Reunion in the

, and

on the island of

in the

; 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.

Volcanic eruptions

Other than by landslides or

sector collapse A sector collapse is the collapse of a portion of a volcano due to a phreatic eruption, an earthquake, or the intervention of new magma. Occurring on many volcanoes, sector collapses are generally one of the most hazardous volcanic events, and will ...

, volcanoes may be able to generate waves by

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of bu ...

submergence, caldera collapse, or underwater explosions. Tsunamis have been triggered by a number of volcanic eruptions, including the

1883 eruption of Krakatoa The 1883 eruption of Krakatoa ( id, Letusan Krakatau 1883) in the Sunda Strait occurred from 20 May until 21 October 1883, peaking in the late morning hours of 27 August when over 70% of the island of Krakatoa and its surrounding archipelago w ...

, and the 2022 Hunga Tonga–Hunga Ha'apai eruption. Over 20% of all fatalities caused by volcanism during the past 250 years are estimated to have been caused by volcanogenic tsunamis. Debate has persisted over the origins and source mechanisms of these types of tsunamis, such as those generated by Krakatoa in 1883, and they remain lesser understood than their seismic relatives. This poses a large problem of awareness and preparedness, as exemplified by the eruption and collapse of Anak Krakatoa in 2018, which killed 426 and injured thousands when no warning was available. It is still regarded that lateral landslides and ocean-entering pyroclastic currents are most likely to generate the largest and most hazardous waves from volcanism; however, field investigation of the Tongan event, as well as developments in numerical modelling methods, currently aim to expand the understanding of the other source mechanisms.

Meteorological

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. These are comparable to seismic tsunamis, but usually with lower energies. Essentially, they are dynamically equivalent to seismic tsunamis, the only differences being 1) that meteotsunamis lack the transoceanic reach of significant seismic tsunamis, and 2) that the force that displaces the water is sustained over some length of time such that meteotsunamis cannot 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. 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 Coastal flooding normally occurs when dry and low-lying land is submerged by seawater. The range of a coastal flooding is a result of the elevation of floodwater that penetrates the inland which is controlled by the topography of the coastal land ...

in severe weather but their dynamics are completely unrelated to tsunami waves. 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 A tectonic weapon is a hypothetical device or system which could trigger earthquakes, volcanic eruptions, or other seismic events in specified locations by interfering with the Earth's natural geological processes. It was defined in 1992 by Aleksey ...

. In World War II, the

New Zealand Military Forces , image = New Zealand Army Logo.png , image_size = 175px , caption = , start_date = , country = , branch = ...

initiated

Project Seal The tsunami bomb was an attempt during World War II to develop a tectonic weapon that could create destructive tsunamis. The project commenced after US Navy officer E.A. Gibson noticed small waves generated by explosions used to clear coral reef ...

, which attempted to create small tsunamis with explosives in the area of today's

Shakespear Regional Park Shakespear Regional Park is a nature park in the Auckland Region of New Zealand. It is located at the tip of the Whangaparaoa Peninsula, and is named after the Shakespear family which bought the land in the 1880s from local Maori. ...

; the attempt failed. There has been considerable speculation on the possibility of using

nuclear weapons A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb ...

to cause tsunamis near an enemy coastline. Even during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

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 bombs, one in the air and one underwater, above and below the shallow () waters of the

Bikini Atoll Bikini Atoll ( or ; Marshallese: , , meaning "coconut place"), sometimes known as Eschscholtz Atoll between the 1800s and 1946 is a coral reef in the Marshall Islands consisting of 23 islands surrounding a central lagoon. After the Second ...

lagoon. Fired about from the nearest island, the waves there were no higher than upon reaching the shoreline. Other underwater tests, mainly ''

Hardtack I Operation Hardtack I was a series of 35 nuclear tests conducted by the United States from April 28 to August 18 in 1958 at the Pacific Proving Grounds. At the time of testing, the Operation Hardtack I test series included more nuclear detonatio ...

/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 does not 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. Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions.

Characteristics

Propagation du tsunami en profondeur variable

Tsunamis are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and

bolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a ...

s. They 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 wave In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction of t ...

s have a

(from crest to crest) of about and a height of roughly , a tsunami in the deep ocean has a much larger wavelength of up to . Such a wave travels at well over , 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 . 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 = ≈ , which equates to a speed of about . 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 A fisher or fisherman is someone who captures fish and other animals from a body of water, or gathers shellfish. Worldwide, there are about 38 million commercial and subsistence fishers and fish farmers. Fishers may be professional or recreat ...

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,

compresses the wave and its speed decreases below . Its wavelength diminishes to less than and its amplitude grows enormously—in accord with Green's law. Since the wave still has the same very long

, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not

break Break or Breaks or The Break may refer to: Time off from duties * Recess (break), time in which a group of people is temporarily dismissed from its duties * Break (work), time off during a shift/recess ** Coffee break, a short mid-morning res ...

, but rather appears like a fast-moving

. 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. 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. About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. However, tsunami interactions with shorelines and the seafloor topography are extremely complex, which leaves some countries more vulnerable than others. For example, the Pacific coasts of the United States and Mexico lie adjacent to each other, but the United States has recorded ten tsunamis in the region since 1788, while Mexico has recorded twenty-five since 1732. Similarly, Japan has had more than a hundred tsunamis in recorded history, while the neighboring island of Taiwan has registered only two, in 1781 and 1867.

Drawback

All

wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (res ...

s 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.

Intensity scales

The first scales used routinely to measure the intensity of tsunamis were the '' Sieberg-Nicholas Ambraseys, Ambraseys scale'' (1962), used in the

and the ''Imamura-Iida intensity scale'' (1963), used in the Pacific Ocean. The latter scale was modified by Soloviev (1972), who calculated the tsunami intensity "''I''" according to the formula: :

\mathit = \frac + \log_ \mathit_

where

\mathit_

is the "tsunami height" in meters, averaged along the nearest coastline, with the tsunami height defined as the rise of the water level above the normal tidal level at the time of occurrence of the tsunami. This scale, known as the ''Soloviev-Imamura tsunami intensity scale'', is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami. This formula yields: * ''I'' = 2 for

\mathit_

= 2.8 metres * ''I'' = 3 for

\mathit_

= 5.5 metres * ''I'' = 4 for

\mathit_

= 11 metres * ''I'' = 5 for

\mathit_

= 22.5 metres * etc. 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 Environmental Seismic Intensity scale, ESI2007 and European Macroseismic Scale, EMS earthquake intensity scales.

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. Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the ''tsunami magnitude scale

\mathit_

'', calculated from, :

\mathit_ =  \log h +  \log R + \mathit

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 M_t scale match as closely as possible with the moment magnitude scale.

Tsunami heights

Several terms are used to describe the different characteristics of tsunami in terms of their height: *Amplitude, Wave Height, or Tsunami Height: Refers to the height of a tsunami relative to the normal sea level at the time of the tsunami, which may be tidal High Water, or Low Water. It is different from the crest-to-trough height which is commonly used to measure other type of wave height. *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

Calculated Travel Time Map for 1964 Alaska Tsunami

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 Province, 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 earthquake, 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 initial wave moved downwards on the eastern side of the megathrust 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 tsunamis from the Pacific Ocean, warning signs indicate evacuation routes. In Japan, the populace is well-educated about earthquakes and tsunamis, and along Japanese shorelines, tsunami warning signs remind people of the natural hazards along with a network of warning sirens, typically at the top of the cliffs of surrounding hills. The Pacific Tsunami Warning Center, Pacific Tsunami Warning System is based in Honolulu, Hawaii, Hawaii. 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. File:Bamfield Tsunami Hazard Zone sign.jpg, Tsunami hazard sign at Bamfield, British Columbia File: A tsunami warning sign in Kamakura, Japan.jpg, A tsunami warning sign in Kamakura, Kanagawa, Kamakura, Japan File:Zona de Inundabilidad.jpg, A Tsunami hazard sign (Spanish - English) in Iquique, Chile. File:Tsunami Evacuation Route signage south of Aberdeen Washington.jpg, alt=Photo of evacuation sign, Tsunami Evacuation Route signage along U.S. Route 101 in Washington, U.S. Route 101, in Washington (state), 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

Computer models can predict tsunami arrival, usually within minutes of the arrival time. Bottom pressure sensors can relay information in present, 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. 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.

Possible animal reaction

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 and tsunamis. However, the evidence is controversial and is not widely accepted. There are unsubstantiated claims about the 1755 Lisbon earthquake, 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

. 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.

Mitigation

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 1896 Sanriku earthquake, disaster in 1896, has produced ever-more elaborate countermeasures and response plans. The country has built many tsunami walls of up to high to protect populated coastal areas. Other localities have built floodgates of up to high and channels to redirect the water from an incoming tsunami. However, their effectiveness has been questioned, as tsunamis 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.Phillip Lipscy, Kenji Kushida, and Trevor Incerti. 2013.
The Fukushima Disaster and Japan’s Nuclear Plant Vulnerability in Comparative Perspective
". ''Environmental Science and Technology'' 47 (May), 6082–6088. Iwate Prefecture, which is an area at high risk from tsunami, had tsunami barriers walls (Taro sea wall) totalling long at coastal towns. The 2011 tsunami toppled more than 50% of the walls and caused catastrophic damage. The Historic tsunami#1993: Okushiri, Hokkaido, Japan (北海道南西沖地震), Okushiri, Hokkaidō tsunami which struck Okushiri, Hokkaidō, Okushiri Island of Hokkaidō within two to five minutes of the 1993 Okushiri earthquake, earthquake on July 12, 1993, created waves as much as 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.

Footnotes

References

IOC Tsunami Glossary
by the Intergovernmental Oceanographic Commission (IOC) at th
International Tsunami Information Centre
(ITIC) of UNESCO
Tsunami Terminology
at NOAA *In June 2011, the VOA Special English service of the Voice of America broadcast a 15-minute program on tsunamis as part of its weekly Science in the News series. The program included an interview with an NOAA official who oversees the agency's tsunami warning system. A transcript and MP3 of the program, intended for English learners, can be found a
The Ever-Present Threat of Tsunamis.

abelard.org.
''tsunamis: tsunamis travel fast but not at infinite speed''. retrieved March 29, 2005. * Dudley, Walter C. & Lee, Min (1988: 1st edition) ''Tsunami!''

* Iwan, W.D., ''editor'', 2006, Summary report of the Great Sumatra Earthquakes and Indian Ocean tsunamis of December 26, 2004 and March 28, 2005: Earthquake Engineering Research Institute, EERI Publication #2006-06, 11 chapters, 100-page summary, plus CD-ROM with complete text and supplementary photographs, EERI Report 2006–06.
website
* Kenneally, Christine (December 30, 2004). "Surviving the Tsunami." ''Slate''
website
* Lambourne, Helen (March 27, 2005). "Tsunami: Anatomy of a disaster." ''BBC News''
website
* Macey, Richard (January 1, 2005). "The Big Bang that Triggered A Tragedy," ''The Sydney Morning Herald'', p 11—quoting Dr Mark Leonard, seismologist at Geoscience Australia.
Interactive Map of Historical Tsunamis
from NOAA National Centers for Environmental Information * Tappin, D; 2001. Local tsunamis. Geoscientist. 11–8, 4–7.

''Telegraph.co.uk''
Philippines warned to prepare for Japan's tsunami
''Noypi.ph''

External links

World's Tallest Tsunami
– geology.com
Tsunami Data and Information
– National Centers for Environmental Information
IOC Tsunami Glossary
– International Tsunami Information Center (UNESCO)
Tsunami & Earthquake Research at the USGS
– United States Geological Survey
Intergovernmental Oceanographic Commission
– Intergovernmental Oceanographic Commission
Tsunami
– National Oceanic and Atmospheric Administration
Wave That Shook The World
– ''Nova (American TV series), Nova''
Recent and Historical Tsunami Events and Relevant Data
– Pacific Marine Environmental Laboratory
Raw Video: Tsunami Slams Northeast Japan
– Associated Press
Tsunami alert
page (in English) from Japan Meteorological Agency
Tsunami status page
from United States Geological Survey, USGS-run Pacific Tsunami Warning Center
Tsunami animation – Geoscience Australia
{{Authority control Tsunami, Articles containing video clips

Terminology

Tsunami

Tidal wave

Seismic sea wave

History

Causes

Seismicity

Landslides

Volcanic eruptions

Meteorological

Man-made or triggered tsunamis

Characteristics

Drawback

Scales of intensity and magnitude

Intensity scales

Magnitude scales

Tsunami heights

Warnings and predictions

Possible animal reaction

Mitigation

See also

Footnotes

References

Further reading

External links