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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, fr ...
s, 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. 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 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 tables ...
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, a tsunami is generated by the displacement of water from a large event. Tsunami waves do not resemble normal undersea currents or sea waves 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, tr ...
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 turbulent kinetic energy. At this point, simple physical models that describe wave dynam ...
, a tsunami may instead initially resemble a rapidly rising
tide Tides are the rise and fall of sea levels caused by the combined effects of the 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 tables ...
. 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 periods ranging from minutes to hours, arriving in a so-called " wave train". 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 ...
. 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 pe ...
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 " scienti ...
suggested in his 5th century BC '' History of the Peloponnesian War'' that tsunamis were related to submarine earthquakes, 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 (se ...
. 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
tide Tides are the rise and fall of sea levels caused by the combined effects of the 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 tables ...
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'' 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 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 landslides, 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 moon. When the original object ...
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 his ...
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 ...
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 ...
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 betwee ...
), 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 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 refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves. As early as 426 BC the Greek 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 " scienti ...
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.
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 " scienti ...

“A History of the Peloponnesian War”, 3.89.1–4
/ref> The oldest human record of a tsunami dates back to
479 BC __NOTOC__ Year 479 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Vibulanus and Rutilus (or, less frequently, year 275 ''Ab urbe condita''). The denomination 479 BC for this year has ...
, 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 a ...
, 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 " scienti ...

“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 lett ...
historian
Ammianus Marcellinus Ammianus Marcellinus (occasionally anglicised as Ammian) (born , died 400) was a Roman soldier and historian who wrote the penultimate major historical account surviving from antiquity (preceding Procopius). His work, known as the ''Res Gestae ...
(''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, Alexandri ...
.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 te ...
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 lithosp ...
) 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 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, fr ...
File:Eq-gen2.svg, Over-riding plate bulges under strain, causing tectonic uplift. File:Eq-gen3.svg, Plate slips, causing subsidence 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
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, tr ...
(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 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 of VI (''Strong''). It generated a tsunami which inundated Hilo 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 conti ...
floor is subducting (or being pushed downwards) under Alaska. Examples of tsunamis originating at locations away from convergent boundaries include
Storegga 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 ...
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, sword ...
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 ( ''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 ...
(''M''w 9.2), and
2011 Tōhoku earthquake Eleven or 11 may refer to: *11 (number), the natural number following 10 and preceding 12 * one of the years 11 BC, AD 11, 1911, 2011, or any year ending in 11 Literature * ''Eleven'' (novel), a 2006 novel by British author David Llewellyn *''E ...
(''M''w9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as
teletsunamis A teletsunami (also called an ocean-wide tsunami, distant tsunami, distant-source tsunami, far-field tsunami, or trans-ocean tsunami) is a tsunami that originates from a distant source, defined as more than away or three hours' travel from the a ...
) 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, 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 entered the reservoir behind the Vajont Dam in Italy. The resulting wave surged over the -high dam by and destroyed several towns. Around 2,000 people died. Scientists named these waves megatsunamis. Some geologists claim that large landslides from volcanic islands, e.g. Cumbre Vieja on La Palma ( Cumbre Vieja tsunami hazard) in the
Canary Islands The Canary Islands (; es, :es:Canarias, Canarias, ), also known informally as the Canaries, are a Spanish Autonomous communities of Spain, autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to ...
, 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, La Reunion in 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 ...
, and Cumbre Vieja on the island of La Palma in the
Canary Islands The Canary Islands (; es, :es:Canarias, Canarias, ), also known informally as the Canaries, are a Spanish Autonomous communities of Spain, autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to ...
; 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, 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 b ...
submergence, caldera collapse, or underwater explosions. Tsunamis have been triggered by a number of volcanic eruptions, including the 1883 eruption of Krakatoa, 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 Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
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 A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the no ...
, 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. 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. There has been considerable speculation on the possibility of using nuclear weapons 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 World War II by country, vast majority of the world's countries—including all of the great power ...
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 lagoon. Fired about from the nearest island, the waves there were no higher than 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 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

Tsunamis are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and bolides. 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 waves have a
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, tr ...
(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 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 . 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 period, 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 rest ...
, but rather appears like a fast-moving
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 (se ...
. 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 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.


Intensity scales

The first scales used routinely to measure the intensity of tsunamis were the '' Sieberg- Ambraseys scale'' (1962), used 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 ...
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 ESI2007 and 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 Mt 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

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 Tilly Smith (born 1994) is an English woman who has been credited with saving the lives of about 100 beachgoers at Mai Khao Beach in Thailand by warning them minutes before the arrival of the tsunami caused by the 2004 Indian Ocean earthquake. S ...
of
Surrey Surrey () is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in South East England, bordering Greater London to the south west. Surrey has a large rural area, and several significant ur ...
, England, was on Maikhao beach in
Phuket Phuket (; th, ภูเก็ต, , ms, Bukit or ''Tongkah''; Hokkien:普吉; ) is one of the southern provinces (''changwat'') of Thailand. It consists of the island of Phuket, the country's largest island, and another 32 smaller islands o ...
, 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 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.
Geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s, 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 System is based in
Honolulu Honolulu (; ) is the capital and largest city of the U.S. state of Hawaii, which is in the Pacific Ocean. It is an unincorporated county seat of the consolidated City and County of Honolulu, situated along the southeast coast of the isla ...
,
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 ...
. 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 Bamfield is a community that is surrounded by Crown Land, First Nation Lands belonging to the Huu-ay-aht Nations, and portions of the Pacific Rim National Park, located on Barkley Sound, Vancouver Island in British Columbia. The community, wit ...
,
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
File: A tsunami warning sign in Kamakura, Japan.jpg, A tsunami warning sign in Kamakura, Japan File:Zona de Inundabilidad.jpg, A Tsunami hazard sign (Spanish - English) in Iquique,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...
. File:Tsunami Evacuation Route signage south of Aberdeen Washington.jpg, alt=Photo of evacuation sign, Tsunami Evacuation Route signage along
U.S. Route 101 U.S. Route 101, or U.S. Highway 101 (US 101), is a north–south United States Numbered Highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States. It is also known as (The Royal Roa ...
, in
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
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. 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 Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...
) and coastal
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...
, 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 The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
, using the
Emergency Alert System The Emergency Alert System (EAS) is a national warning system in the United States designed to allow authorized officials to broadcast emergency alerts and warning messages to the public via cable, satellite, or broadcast television, and bot ...
.


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 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 Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
in the
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 ...
. It is possible that certain animals (e.g.,
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...
s) 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 Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, where tsunami science and response measures first began following a 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 The occurred at 14:46 Japan Standard Time, JST (05:46 UTC) on 11 March. The Moment magnitude scale, magnitude 9.0–9.1 (M) Submarine earthquake, undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peni ...
, 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 Taro () (''Colocasia esculenta)'' is a root vegetable. It is the most widely cultivated species of several plants in the family Araceae that are used as vegetables for their corms, leaves, and petioles. Taro corms are a food staple in Africa ...
) totalling long at coastal towns. The 2011 tsunami toppled more than 50% of the walls and caused catastrophic damage. The Okushiri, Hokkaidō tsunami which struck Okushiri Island of
Hokkaidō is Japan, Japan's Japanese archipelago, second largest island and comprises the largest and northernmost Prefectures of Japan, prefecture, making up its own List of regions of Japan, region. The Tsugaru Strait separates Hokkaidō from Honshu; th ...
within two to five minutes of the 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.


See also

* * * * * * * * * * * * * * * *


Footnotes


References


IOC Tsunami Glossary
by the Intergovernmental Oceanographic Commission (IOC) at th
International Tsunami Information Centre
(ITIC) of
UNESCO The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...

Tsunami Terminology
at NOAA *In June 2011, the VOA Special English service of the
Voice of America Voice of America (VOA or VoA) is the State media, state-owned news network and International broadcasting, international radio broadcaster of the United States, United States of America. It is the largest and oldest U.S.-funded international br ...
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 BBC News is an operational business division of the British Broadcasting Corporation (BBC) responsible for the gathering and broadcasting of news and current affairs in the UK and around the world. The department is the world's largest broadc ...
''
website
* Macey, Richard (January 1, 2005). "The Big Bang that Triggered A Tragedy," ''
The Sydney Morning Herald ''The Sydney Morning Herald'' (''SMH'') is a daily compact newspaper published in Sydney, New South Wales, Australia, and owned by Nine. Founded in 1831 as the ''Sydney Herald'', the ''Herald'' is the oldest continuously published newspaper ...
'', 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 ''The Daily Telegraph'', known online and elsewhere as ''The Telegraph'', is a national British daily broadsheet newspaper published in London by Telegraph Media Group and distributed across the United Kingdom and internationally. It was fou ...
''
Philippines warned to prepare for Japan's tsunami
''Noypi.ph''


Further reading

* Boris Levin, Mikhail Nosov: ''Physics of tsunamis''. Springer, Dordrecht 2009, . * Kontar, Y. A. et al.: ''Tsunami Events and Lessons Learned: Environmental and Societal Significance.'' Springer, 2014. (print); (eBook) * Kristy F. Tiampo: ''Earthquakes: simulations, sources and tsunamis''. Birkhäuser, Basel 2008, . *
Linda Maria Koldau Linda Maria Koldau (born October 28, 1971) is a German musicologist and was Chair of Musicology and Cultural History (formerly Knud Jeppesen's Chair of Musicology) at Aarhus University in Denmark. Since 2013 she has been director of the Coastal A ...
: Tsunamis. Entstehung, Geschichte, Prävention, (Tsunami development, history and prevention) C.H. Beck, Munich 2013 (C.H. Beck Reihe Wissen 2770), (in German). * Walter C. Dudley, Min Lee: ''Tsunami!'' University of Hawaii Press, 1988, 1998, Tsunami! University of Hawai'i Press 1999, , . * Charles L. Mader: ''Numerical Modeling of Water Waves'' CRC Press, 2004, .


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 The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...
)
Tsunami & Earthquake Research at the USGS
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

Intergovernmental Oceanographic Commission
Intergovernmental Oceanographic Commission
Tsunami
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditi ...

Wave That Shook The World
– '' Nova''
Recent and Historical Tsunami Events and Relevant Data
Pacific Marine Environmental Laboratory
Raw Video: Tsunami Slams Northeast Japan
Associated Press The Associated Press (AP) is an American non-profit news agency headquartered in New York City. Founded in 1846, it operates as a cooperative, unincorporated association. It produces news reports that are distributed to its members, U.S. new ...

Tsunami alert
page (in English) from
Japan Meteorological Agency The , abbreviated JMA, is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation an ...

Tsunami status page
from
USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
-run Pacific Tsunami Warning Center
Tsunami animation – Geoscience Australia
{{Authority control Articles containing video clips