Product Code Database
A tsunami ( ; Entry: "tsunami" from , ) 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. , volcanic eruptions and underwater explosions (including detonations, , Ice calving, impact event and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal Wind wave, or , which are in turn generated by the gravitational pull of the Moon 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 Wind wave because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide. 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 packet". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.
The Ancient Greece historian Thucydides 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.
A tsunami which cannot be linked to an earthquake is sometimes termed an "orphan tsunami". This may happen in the case of tsunamis caused in the distant past, before international communications, by earthquakes far away, such as a tsunami in Japan caused by an earthquake in the Americas. General Information on Tsunami Waves, Seaquakes, and Other Catastrophic Phenomena in the Ocean
As early as 426 BC the Ancient Greece historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause.Thucydides: “A History of the Peloponnesian War”, 3.89.1–4 The oldest human record of a tsunami dates back to 479 BC, in the Greek colony of Potidaea, thought to be triggered by an earthquake. The tsunami may have saved the colony from an invasion by the Achaemenid Empire.
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: “A History of the Peloponnesian War”, 3.89.5
The Ancient Rome historian Ammianus Marcellinus ( Res Gestae 26.10.15–19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria.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 "
Tsunamis are an often underestimated hazard in the Mediterranean Sea and parts of Europe. Of historical and current (with regard to risk assumptions) importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores–Gibraltar transform fault), the 1783 Calabrian earthquakes, each causing several tens of thousands of deaths and the 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the deadliest natural disasters in modern Europe. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and , predominantly and less to earthquake-induced waves.
The destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. Indian Ocean tsunami anniversary: Memorial events held 26 December 2014, BBC News The region is also accustomed to tsunamis, due to earthquakes of varying magnitudes that occur regularly off the coast of the island. The 10 most destructive tsunamis in history , Australian Geographic, March 16, 2011.
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), Facts and figures: how tsunamis form , Australian Geographic, March 18, 2011. 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. It also destroyed the village in the Halawa Valley of
at time stamp 33:50 also 7:50 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 ( Mw 9.5), 1964 Alaska earthquake ( Mw 9.2), 2004 Indian Ocean earthquake ( Mw 9.2), and 2011 Tōhoku earthquake ( Mw9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller ( Mw 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can devastate stretches of coastline, but can do so in only a few minutes at a time.
In the 1950s, it was discovered that 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 .
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.
In general, landslides generate displacements mainly in the shallower parts of the coastline, and there is conjecture about the nature of large landslides that enter the water. This has been shown to subsequently affect water in enclosed bays and lakes, but a landslide large enough to cause a transoceanic tsunami has not occurred within recorded history. Susceptible locations are believed to be the Big Island of Hawaii, Fogo in the Cape Verde Islands, La Reunion in the Indian Ocean, and Cumbre Vieja on the island of La Palma in the Canary Islands; along with other volcanic ocean islands. This is because large masses of relatively unconsolidated volcanic material occurs on the flanks and in some cases detachment planes are believed to be developing. However, there is growing controversy about how dangerous these slopes actually are.
Debate has persisted over the origins and source mechanisms of such tsunamis as those generated by Krakatoa in 1883, 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 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.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 [10]
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.
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. They are unable to propagate beyond their sources, as waves do.
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'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.
There has been considerable speculation about the possibility of using 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 bombs were detonated, one in the air over and one underwater within the shallow waters of the deep lagoon at Bikini Atoll. The bombs detonated about from the nearest island, where the waves were no higher than 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 shallow and 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. Tsunamis are hallmarked by permanent large vertical displacements of very large volumes of water which do not occur in explosions.
While everyday have a wavelength (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 . Earthsci.org, Tsunamis 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 frequency, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not Breaking wave, but rather appears like a fast-moving tidal bore. 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 neighbouring island of Taiwan has registered only two, in 1781 and 1867.
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.
where is the "tsunami height" in metres, 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.Soloviev, S., & Go, N., 1974 (English transl. 1984), "Catalogue of tsunamis on the western shore of the Pacific Ocean", Canadian Translation of Fisheries and Aquatic Sciences, No. 5077, (310 p). 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:
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.Katsetsiadou, K.N., Andreadakis, E. and Lekkas, E., 2016. Tsunami intensity mapping: applying the integrated Tsunami Intensity Scale (ITIS2012) on Ishinomaki Bay Coast after the mega-tsunami of Tohoku, March 11, 2011. Research in Geophysics, 5(1).
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.
In 2004, ten-year-old Tilly Smith of Surrey, England, was on Maikhao beach in Phuket Province, 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. , , and 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, 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.
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.
can predict tsunami arrival, usually within minutes of the arrival time. Bottom pressure sensors can relay information in present. 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.
Japan, 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 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 and flooded the emergency generators.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 Okushiri, Hokkaidō tsunami, which struck within two to five minutes of the earthquake on July 12, 1993, created waves 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.
|
|
