Editing Tsunami (section)

==Causes==<!-- [[Ocean surface wave]] links here. -->
The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea.<ref>{{cite journal|doi=10.1016/j.marpetgeo.2004.10.016|last1=Haugen|first1=K|last2=Lovholt|first2=F|last3=Harbitz|first3=C|title=Fundamental mechanisms for tsunami generation by submarine mass flows in idealised geometries|journal=[[Marine and Petroleum Geology]]|date=2005|volume=22|issue=1–2|pages=209–217|bibcode=2005MarPG..22..209H}}</ref> This displacement of water is usually caused by earthquakes,<ref>{{cite web|title=Tsunami Locations & Occurrences|publisher=National Weather Service|url=https://www.weather.gov/jetstream/locations|access-date=16 January 2022}}</ref><ref>{{cite news|first=Lisa M.|last=Krieger|title=Volcanic tsunamis: Why they are so difficult to predict|date=15 January 2022|newspaper=The Mercury News|url=https://www.mercurynews.com/2022/01/15/volcanic-tsunamis-why-they-are-so-difficult-to-predict/|access-date=16 January 2022}}</ref><ref>{{cite news|title=Tsunamis|work=National Geographic|url=https://www.nationalgeographic.com/environment/article/tsunamis|archive-url=https://web.archive.org/web/20210412193722/https://www.nationalgeographic.com/environment/article/tsunamis|url-status=dead|archive-date=April 12, 2021|access-date=16 January 2022}}</ref> but can also be attributed to landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests.<ref>{{cite journal|last=Margaritondo|first=G|title=Explaining the physics of tsunamis to undergraduate and non-physics students|journal=European Journal of Physics|date=2005|volume=26|issue=3|doi=10.1088/0143-0807/26/3/007|pages=401–407|bibcode=2005EJPh...26..401M|s2cid=7512603|url=http://pdfs.semanticscholar.org/1b83/2dd51b201c4ee597b374780e359604e8b781.pdf|archive-url=https://web.archive.org/web/20190219220116/http://pdfs.semanticscholar.org/1b83/2dd51b201c4ee597b374780e359604e8b781.pdf|url-status=dead|archive-date=2019-02-19}}</ref><ref>{{cite journal|doi=10.1146/annurev.fl.19.010187.001245|last=Voit|first=S.S|title=Tsunamis|journal=Annual Review of Fluid Mechanics|date=1987|volume=19|issue=1|pages=217–236|bibcode=1987AnRFM..19..217V}}</ref> However, the possibility of a meteorite causing a tsunami is debated.<ref>{{cite news|title=Are Ocean Asteroid Impacts Really a Serious Threat?|author=Tia Ghose|date=2014|url=https://www.livescience.com/49298-asteroids-causing-tsunamis.html|archive-url=https://web.archive.org/web/20141231185338/https://www.livescience.com/49298-asteroids-causing-tsunamis.html|archive-date=December 31, 2014}}{{void|Fabrickator|comment|archive link is preferred to "live" link}}</ref>

===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.<ref>{{cite web|title=How do earthquakes generate tsunamis?|url=http://www.geophys.washington.edu/tsunami/general/physics/earthquake.html|publisher=University of Washington|archive-url=https://web.archive.org/web/20070203154326/http://www.geophys.washington.edu/tsunami/general/physics/earthquake.html|archive-date=2007-02-03}}</ref> More specifically, a tsunami can be generated when [[thrust fault]]s associated with [[convergent boundary|convergent]] or destructive [[plate boundaries]] move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on [[Fault (geology)#Dip-slip faults|normal (extensional) faults]] can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the [[outer trench swell]]) cause enough displacement to give rise to a significant tsunami, such as the [[1977 Sumba earthquake|1977 Sumba]] and [[1933 Sanriku earthquake|1933 Sanriku]] events.<ref>{{cite journal|title=Source Process of the Great 1977 Sumba Earthquake|url=http://www.es.ucsc.edu/~thorne/TL.pdfs/LL_Sumba_JGR1988.pdf|first1=C. S.|last1=Lynnes|first2=T.|last2=Lay|authorlink2=Thorne Lay|year=1988|journal=Geophysical Research Letters|publisher=[[American Geophysical Union]]|volume=93|issue=B11|pages=13, 407–413, 420|doi=10.1029/JB093iB11p13407|bibcode=1988JGR....9313407L}}</ref><ref name="Kanamori_1971">{{cite journal|title=Seismological evidence for a lithospheric normal faulting – the Sanriku earthquake of 1933|last=Kanamori|first=Hiroo|author-link=Hiroo Kanamori|journal=[[Physics of the Earth and Planetary Interiors]]|year=1971|volume=4|issue=4|pages=298–300|doi=10.1016/0031-9201(71)90013-6|bibcode=1971PEPI....4..289K}}</ref>

<gallery mode="packed">
File:Eq-gen1.svg|Drawing of [[tectonic plate boundary]] before [[earthquake]]
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.
</gallery>

Tsunamis have a small wave height offshore, and a very long [[wavelength]] (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres),<ref>[http://www.australiangeographic.com.au/journal/facts-and-figures-how-tsunamis-form.htm/ Facts and figures: how tsunamis form] {{Webarchive|url=https://web.archive.org/web/20131105033906/http://www.australiangeographic.com.au/journal/facts-and-figures-how-tsunamis-form.htm/ |date=2013-11-05 }}, Australian Geographic, March 18, 2011.</ref> which is why they generally pass unnoticed at sea, forming only a slight swell usually about {{convert|300|mm|in}} above the normal sea surface. They grow in height when they reach shallower water, in a [[wave shoaling]] process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

On April 1, 1946, the 8.6 {{M|w}} [[1946 Aleutian Islands earthquake|Aleutian Islands earthquake]] occurred with a maximum [[Mercalli intensity scale|Mercalli intensity]] of VI (''Strong''). It generated a tsunami which inundated [[Hilo, Hawaii|Hilo]] on the island of Hawaii with a {{convert|14|m|ft|adj=mid|high}} surge. Between 165 and 173 were killed. The area where the earthquake occurred is where the [[Pacific Ocean]] floor is [[subducting]] (or being pushed downwards) under Alaska.

Examples of tsunamis originating at locations away from convergent boundaries include [[Storegga]] about 8,000 years ago, [[Grand Banks]] in 1929, and [[Papua New Guinea]] 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]] ([[Moment magnitude scale|''M''<sub>w</sub>]] 9.5), [[1964 Alaska earthquake]] (''M''<sub>w</sub> 9.2), [[2004 Indian Ocean earthquake]] (''M''<sub>w</sub> 9.2), and [[2011 Tōhoku earthquake and tsunami|2011 Tōhoku earthquake]] (''M''<sub>w</sub>9.0) are recent examples of powerful [[megathrust earthquake]]s that generated tsunamis (known as [[teletsunamis]]) that can cross entire oceans. Smaller (''M''<sub>w</sub> 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]] was a large tsunami on [[Lake Geneva]] in 563 CE, caused by sedimentary deposits destabilised by a landslide.

{{Anchor|Tsunami generated by landslides}}
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 [[1958 Lituya Bay, Alaska earthquake and megatsunami|Lituya Bay]], Alaska, caused the highest wave ever recorded, which had a height of {{convert|524|m|ft|0}}.<ref name="drgeorgepc.com">{{cite web|url=http://www.drgeorgepc.com/Tsunami1958LituyaB.html|title=The Mega-Tsunami of July 9, 1958 in Lituya Bay, Alaska|author=George Pararas-Carayannis|date=1999|access-date=2014-02-27}}</ref> 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.<ref>{{cite web|url=https://alaskashipwreck.com/shipwrecks-a-z/alaska-shipwrecks-b/|title=alaskashipwreck.com Alaska Shipwrecks (B)}}</ref><ref>{{cite web|url=https://alaskashipwreck.com/shipwrecks-a-z/alaska-shipwrecks-s/|title=alaskashipwreck.com Alaska Shipwrecks (S)}}</ref><ref>{{cite web|url=https://earthquake.alaska.edu/60-years-ago-1958-earthquake-and-lituya-bay-megatsunami|title=Dickson, Ian, "60 Years Ago: The 1958 Earthquake and Lituya Bay Megatsunami," University of Alaska Fairbanks Alaska Earthquake Center, July 13, 2018 Retrieved December 2, 2018.}}</ref>

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 {{convert|262|m|ft|0|adj=on}}-high dam by {{convert|250|m|ft|0}} and destroyed several towns. Around 2,000 people died.<ref name=petley-blog-vajont>{{cite web|author=Petley, Dave (Professor)|url=http://www.landslideblog.org/2008/12/vaiont-vajont-landslide-of-1963.html|title=The Vaiont (Vajont) landslide of 1963|publisher=The Landslide Blog|date=2008-12-11|access-date=2014-02-26|url-status=dead|archive-url=https://web.archive.org/web/20131206033431/http://www.landslideblog.org/2008/12/vaiont-vajont-landslide-of-1963.html|archive-date=2013-12-06}}</ref><ref name=bbc-50th-anniv>{{cite web|last=Duff|first=Mark|url=https://www.bbc.co.uk/news/world-europe-24464867|title=Italy Vajont anniversary: Night of the 'tsunami'|publisher=BBC News|date=2013-10-10|access-date=2014-02-27}}</ref> Scientists named these waves [[megatsunami]]s.

Some geologists claim that large landslides from volcanic islands, e.g. [[Cumbre Vieja]] on [[La Palma]] ([[Cumbre Vieja tsunami hazard]]) in the [[Canary Islands]], may be able to generate megatsunamis that can cross oceans, but this is disputed by many others.
<!-- comment out pending translation
<gallery>
File:Tsunami4.JPG|Most tsunamis are caused by [[submarine earthquake]]s that dislocate the oceanic crust, pushing water upwards.
File:Tsunami3.JPG|Tsunami can be generated by erupting submarine volcanos ejecting magma into the ocean.
File:Tsunami5.JPG|A gas bubble erupting in a deep part of the ocean can also trigger a tsunami.
</gallery> -->

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 [[Hawaii (island)|Big Island]] of [[Hawaii]], [[Fogo, Cape Verde|Fogo]] in the [[Cape Verde Islands]], [[Réunion|La Reunion]] in the [[Indian Ocean]], and [[Cumbre Vieja]] on the island of [[La Palma]] in the [[Canary Islands]]; along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on the flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are.<ref>{{cite journal|journal=Science of Tsunami Hazards|volume=20|number=5|pages=251–277|url=http://news.bbc.co.uk/2/hi/science/nature/3963563.stm|access-date=7 September 2014|title=Evaluation of the threat of mega tsunami generation from postulated massive slope failures of the island volcanoes on La Palma, Canary Islands, and on the island of Hawaii|first=George|last=Pararas-Carayannis|date=2002}}</ref>

===Volcanic eruptions===
{{main|Volcanic tsunami}}

Other than by landslides or [[sector collapse]], volcanoes may be able to generate waves by [[pyroclastic flow]] submergence, caldera collapse, or underwater explosions.<ref name="Paris">{{cite journal|last1=Paris|first1=R.|date=2015|title=Source mechanisms of volcanic tsunamis|journal=Phil. Trans. R. Soc.|volume=373|issue=2053|doi=10.1098/rsta.2014.0380|pmid=26392617|bibcode=2015RSPTA.37340380P|s2cid=43187708|doi-access=free}}</ref> Tsunamis have been triggered by a number of volcanic eruptions. The best-known is perhaps the massive tsunami caused by the eruption of the [[Santorini]] volcano around 1600 BC, which is often mentioned as  driving the destruction of many harbours in the region and ultimately the decline of Minoan civilization - a question still subject to open debate. Others include the [[1883 eruption of Krakatoa#Tsunamis and distant effects|1883 eruption of Krakatoa]], and the [[2022 Hunga Tonga–Hunga Ha'apai eruption and tsunami|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 tsunami|volcanogenic]] tsunamis.<ref name="Latter">{{cite journal|last1=Latter|first1=J. H.|date=1981|title=Tsunamis of volcanic origin: Summary of causes, with particular reference to Krakatoa, 1883|url=https://link.springer.com/article/10.1007/BF02600578|journal=Bulletin Volcanologique|volume=44|issue=3|pages=467–490|doi=10.1007/BF02600578|bibcode=1981BVol...44..467L|s2cid=129637214}}</ref>

Debate has persisted over the origins and source mechanisms of such tsunamis as those generated by Krakatoa in 1883,<ref name="Latter" /> and they remain lesser understood than their seismic relatives. This poses the larger problem of awareness and preparedness, as exemplified by the eruption and collapse of [[2018 Sunda Strait tsunami|Anak Krakatoa in 2018]], which killed 426 and injured thousands when no warning was available. In all cases, developing better tsunami forecasting models and assessing the risks for densely populated coastal areas to be hit by severe tsunamis is a matter of global priority.<ref>Marine hazards and coastal vulnerabilities in the Mediterranean - realities and perceptions. 2024. pp. 5–25 in ’’ CIESM Monograph 52’’ (F. Briand, Ed.) ISSN 1726-5886 [https://www.researchgate.net/publication/388029017]</ref> 

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;<ref name="DayVolcano">{{cite encyclopedia|last=Day|first=Simon J.|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123859389000584|title=The Encyclopedia of Volcanoes|chapter=Volcanic Tsunamis|publisher=[[Elsevier]]|year=2015|pages=993–1009|doi=10.1016/B978-0-12-385938-9.00058-4|isbn=9780123859389|access-date=2022-03-21}}</ref> however, field investigation of the [[2022 Hunga Tonga–Hunga Ha'apai eruption and tsunami|Tongan event]], as well as developments in numerical modelling methods, currently aim to expand the understanding of the other source mechanisms.<ref name="Hayward">{{cite journal|last1=Hayward|first1=Matthew. W.|last2=Whittaker|first2=C. N.|last3=Lane|first3=E. M.|last4=Power|first4=W. L.|last5=Popinet|first5=S.|last6=White|first6=J.D.L.|date=2022|title=Multilayer modelling of waves generated by explosive subaqueous volcanism|url=https://nhess.copernicus.org/articles/22/617/2022/|journal=[[Natural Hazards and Earth System Sciences]]|volume=22|issue=2|pages=617–637|doi=10.5194/nhess-22-617-2022|bibcode=2022NHESS..22..617H|doi-access=free}}</ref><ref name="Battershill">{{cite journal|last1=Battershill|first1=L.|date=2021|title=Numerical Simulations of a Fluidized Granular Flow Entry into Water: Insights into Modeling Tsunami Generation by Pyroclastic Density Currents|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022855|archive-url=https://web.archive.org/web/20230603121655/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022855|url-status=dead|archive-date=June 3, 2023|journal=[[Journal of Geophysical Research: Solid Earth]]|volume=126|issue=11|doi=10.1029/2021JB022855|bibcode=2021JGRB..12622855B|s2cid=243837214}}</ref>

===Meteorological===
{{main|Meteotsunami}}
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.<ref name="Monserrat">{{cite journal|last1=Monserrat|first1=S.|last2=Vilibíc|first2=I.|last3=Rabinovich|first3=A. B.|date=2006|title=Meteotsunamis: atmospherically induced destructive ocean waves in the tsunami frequency band|journal=Natural Hazards and Earth System Sciences|volume=6|pages=1035–1051|doi=10.5194/nhess-6-1035-2006|bibcode=2006NHESS...6.1035M|issue=6|doi-access=free}}</ref>

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

=== Human-made or triggered tsunamis ===
{{see also|Tsunami bomb}}

The accidental [[Halifax Explosion]] in 1917 triggered an {{convert|18|metre|adj=on}} high tsunami in the harbour at [[Halifax, Nova Scotia]], Canada.<ref>{{Cite book|last=Mac Donald|first=Laura|title=Curse of the Narrows: The Halifax Explosion of 1917|publisher=HarperCollins|year=2005|isbn=978-0-00-200787-0|page=66|url=https://archive.org/details/curseofnarrowsth00macd}}</ref><ref>{{cite book|last1=Krehl|first1=Peter|title=History of shock waves, explosions and impact a chronological and biographical reference|date=2007|publisher=Springer|isbn=978-3-540-30421-0|page=459}}</ref>

There have been studies of the potential for the use of explosives to induce tsunamis as a [[tectonic weapon]]. As early as [[World War II]] (1939–1945), consideration of the use of conventional explosives was explored, and [[New Zealand Defence Force|New Zealand's military forces]] initiated [[Project Seal]], which attempted to create small tsunamis with explosives in the area of what is now [[Shakespear Regional Park]] at the tip of the [[Whangaparāoa Peninsula]] in the [[Auckland Region]] of [[New Zealand]]; the attempt failed.<ref name="PART2-P9">{{cite news|title=The Hauraki Gulf Marine Park, Part 2|date=3 March 2010|work=Inset to [[The New Zealand Herald]]|page=9}}</ref>

There has been considerable speculation about the possibility of using [[nuclear weapon]]s to cause tsunamis near an enemy coastline.  Nuclear testing in the [[Pacific Proving Ground]] by the United States generated poor results. In [[Operation Crossroads]] in July 1946, two {{convert|20|ktTNT|abbr=on|adj=on}} bombs were detonated, one in the air over and one underwater within the shallow waters of the {{convert|50|m|0|adj=on}} deep [[lagoon]] at [[Bikini Atoll]]. The bombs detonated about {{convert|6|km|mi nmi|abbr=on}} from the nearest island, where the waves were no higher than {{convert|3|to|4|m|abbr=on}} when they reached the shoreline. Other underwater tests, mainly [[Operation Hardtack I]]/Wahoo in deep water and Operation Hardtack I/Umbrella in shallow water, confirmed the results. Analysis of the effects of [[underwater explosion#shallow underwater explosions|shallow]] and [[underwater explosion#deep underwater explosions|deep]] underwater explosions indicate that the energy of the explosions does not easily generate the kind of deep, all-ocean waveforms typical of tsunamis because most of the energy creates [[steam]], causes vertical fountains above the water, and creates compressional waveforms.<ref>{{cite book|last1=Glasstone|first1=Samuel|author-link1=Samuel Glasstone|last2=Dolan|first2=Philip J.|date=1977|title=Shock effects of surface and subsurface bursts (in ''The effects of nuclear weapons'')|edition=third|publisher=U.S. Department of Defense; Energy Research and Development Administration|url=https://www.atomicarchive.com/resources/documents/effects/glasstone-dolan/chapter6.html}}</ref> Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions.