A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water.
Megatsunamis have different features from ordinary . Ordinary tsunamis are caused by underwater plate tectonics (movement of the earth's plates) and therefore occur along plate boundaries and as a result of and the subsequent rise or fall in the seabed that displaces a volume of water. Ordinary tsunamis exhibit shallow waves in the deep waters of the open ocean that increase dramatically in height upon approaching land to a maximum Wave run-up height of around in the cases of the most powerful earthquakes.
Examples of modern megatsunamis include the one associated with the 1883 eruption of Krakatoa (volcanic eruption), the 1958 Lituya Bay megatsunami (a landslide which caused an initial wave of ), and the 1963 Vajont Dam landslide (caused by human activity destabilizing sides of valley). Prehistoric examples include the Storegga Slide (landslide), and the Chicxulub crater, Chesapeake Bay, and Eltanin impact meteor impacts.
Overview
A megatsunami is a tsunami with an initial
wave amplitude (
wave height) measured in many tens or hundreds of metres. The term "megatsunami" has been defined by media and has no precise definition, although it is commonly taken to refer to tsunamis over high.
A megatsunami is a separate class of event from an ordinary tsunami and is caused by different physical mechanisms.
Normal tsunamis result from displacement of the sea floor due to movements in the Earth's crust (plate tectonics). Powerful earthquakes may cause the sea floor to displace vertically on the order of tens of metres, which in turn displaces the water column above and leads to the formation of a tsunami. Ordinary tsunamis have a small wave height offshore and generally pass unnoticed at sea, forming only a slight swell on the order of above the normal sea surface. In deep water it is possible that a tsunami could pass beneath a ship without the crew of the vessel noticing. As it approaches land, the wave height of an ordinary tsunami increases dramatically as the sea floor slopes upward and the base of the wave pushes the water column above it upwards. Ordinary tsunamis, even those associated with the most powerful strike-slip earthquakes, typically do not reach heights in excess of .
By contrast, megatsunamis are caused by landslides and other that displace large volumes of water, resulting in waves that may exceed the height of an ordinary tsunami by tens or even hundreds of metres. Underwater or volcanic eruptions do not normally generate megatsunamis, but next to bodies of water resulting from earthquakes or volcanic eruptions can, since they cause a much larger amount of water displacement. If the landslide or impact occurs in a limited body of water, as happened at the Vajont Dam (1963) and in Lituya Bay (1958) then the water may be unable to disperse and one or more exceedingly large waves may result.
Submarine landslides can pose a significant hazard when they cause a tsunami. Although a variety of different types of landslides can cause tsunami, all the resulting tsunami have similar features such as large run-ups close to the tsunami, but quicker attenuation compared to tsunami caused by earthquakes. An example of this was the 17 July 1998, Papua New Guinean landslide tsunami where waves up to 15 m high impacted a 20 km section of the coast killing 2,200 people, yet at greater distances the tsunami was not a major hazard. This is due to the comparatively small source area of most landslide tsunami (relative to the area affected by large earthquakes) which causes the generation of shorter wavelength waves. These waves are greatly affected by coastal amplification (which amplifies the local effect) and radial damping (which reduces the distal effect).
The size of landslide-generated tsunamis depends both on the geological details of the landslide (such as its Froude number) and also on assumptions about the hydrodynamics of the model used to simulate tsunami generation, thus they have a large margin of uncertainty. Generally, landslide-induced tsunamis decay more quickly with distance than earthquake-induced tsunamis, as the former, often having a dipole structure at the source,
Recent findings show that the nature of a tsunami is dependent upon volume, velocity, initial acceleration, length and thickness of the contributing landslide. Volume and initial acceleration are the key factors which determine whether a landslide will form a tsunami. A sudden deceleration of the landslide may also result in larger waves. The length of the slide influences both the wavelength and the maximum wave height. Travel time or run out distance of slide will also influence the resulting tsunami wavelength. In most cases the submarine landslides are noticeably subcritical, that is the Froude number (the ratio of slide speed to wave propagation) is significantly less than one. This suggests that the tsunami will move away from the wave generating slide preventing the buildup of the wave. Failures in shallow waters tend to produce larger tsunamis because the wave is more critical as the speed of propagation is less here. Furthermore, shallower waters are generally closer to the coast meaning that there is less radial damping by the time the tsunami reaches the shore. Conversely tsunamis triggered by earthquakes are more critical when the seabed displacement occurs in the deep ocean as the first wave (which is less affected by depth) has a shorter wavelength and is enlarged when travelling from deeper to shallower waters.
Determining a height range typical of megatsunamis is a complex and scientifically debated topic. This complexity is increased due to the fact that two different heights are often reported for tsunamis – the height of the wave itself in open water, and the height to which it surges when it encounters land. Depending upon the locale, this second or so-called "Wave run-up height" can be several times larger than the wave's height just before reaching shore.
Recognition of the concept of megatsunami
Before the 1950s, scientists had theorized that tsunamis orders of magnitude larger than those observed with earthquakes could have occurred as a result of ancient geological processes, but no concrete evidence of the existence of these "monster waves" had yet been gathered.
searching for oil in
Alaska in 1953 observed that in
Lituya Bay, mature tree growth did not extend to the shoreline as it did in many other bays in the region. Rather, there was a band of younger trees closer to the shore. Forestry workers, glaciologists, and geographers call the boundary between these bands a
trim line. Trees just above the trim line showed severe scarring on their seaward side, while those from below the trim line did not. This indicated that a large force had impacted all of the elder trees above the trim line, and presumably had killed off all the trees below it. Based on this evidence, the scientists hypothesized that there had been an unusually large wave or waves in the deep inlet. Because this is a recently deglaciated
fjord with steep slopes and crossed by a major fault (the Fairweather Fault), one possibility was that this wave was a landslide-generated tsunami.
On 9 July 1958, a 7.8 strike-slip earthquake in southeast Alaska caused of rock and ice to drop into the deep water at the head of Lituya Bay. The block fell almost vertically and hit the water with sufficient force to create a wave that surged up the opposite side of the head of the bay to a height of , and was still many tens of metres high further down the bay when it carried eyewitnesses Howard Ulrich and his son Howard Jr. over the trees in their fishing boat. They were washed back into the bay and both survived.
Analysis of mechanism
The mechanism giving rise to megatsunamis was analysed for the Lituya Bay event in a study presented at the Tsunami Society in 1999;
[ "The Mega-Tsunami of July 9, 1958 in Lituya Bay, Alaska: Analysis of Mechanism" – George Pararas-Carayannis, Excerpts from Presentation at the Tsunami Symposium of Tsunami Society of 25–27 May 1999, in Honolulu, Hawaii, US] this model was considerably developed and modified by a second study in 2010.
Although the earthquake which caused the megatsunami was considered very energetic, it was determined that it could not have been the sole contributor based on the measured height of the wave. Neither water drainage from a lake, nor a landslide, nor the force of the earthquake itself were sufficient to create a megatsunami of the size observed, although all of these may have been contributing factors.
Instead, the megatsunami was caused by a combination of events in quick succession. The primary event occurred in the form of a large and sudden impulsive impact when about 40 million cubic yards of rock several hundred metres above the bay was fractured by the earthquake, and fell "practically as a monolithic unit" down the almost-vertical slope and into the bay.
A 2010 model that examined the amount of infill on the floor of the bay, which was many times larger than that of the rockfall alone, and also the energy and height of the waves, and the accounts given by eyewitnesses, concluded that there had been a "dual slide" involving a rockfall, which also triggered a release of 5 to 10 times its volume of sediment trapped by the adjacent Lituya Glacier, as an almost immediate and many times larger second slide, a ratio comparable with other events where this "dual slide" effect is known to have happened.
Examples
Prehistoric
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An astronomical object between wide traveling at per second struck the Earth 3.26 billion years ago east of what is now Johannesburg, South Africa, near South Africa's border with Eswatini, in what was then an Archean ocean that covered most of the planet, creating a crater about wide. The impact generated a megatsunami that probably extended to a depth of thousands of meters beneath the surface of the ocean and rose to the height of a skyscraper when it reached shorelines. The resultant event created the Barberton Greenstone Belt.
-
The asteroid linked to the extinction of dinosaurs, which created the Chicxulub crater in the Yucatán Peninsula approximately 66 million years ago, would have caused a megatsunami over tall. The height of the tsunami was limited due to relatively shallow sea in the area of the impact; had the asteroid struck in the deep sea the megatsunami would have been tall. Among the mechanisms triggering megatsunamis were the direct impact, shockwaves, returning water in the crater with a new push outward and with a magnitude up to ~11.
-
During the Messinian (ca. 7.25–ca. 5.3 million years ago) various megatsunamis likely struck the coast of northern Chile.
-
Reservoir-induced seismicity at the end of or shortly after the Zanclean Flood (ca. 5.33 million years ago), which rapidly filled the Mediterranean Basin with water from the Atlantic Ocean, created a megatsunami with a height of nearly which struck the coast of Spain near what is now Algeciras.
-
A megatsunami affected the coast of Zona Sur in the Pliocene as evidenced by the sedimentary record of the Ranquil Formation.
-
The Eltanin impact in the southeast Pacific Ocean 2.5 million years ago caused a megatsunami that was over high in southern Chile and the Antarctic Peninsula; the wave swept across much of the Pacific Ocean.
-
The northern half of the East Molokai Volcano on Molokai in Hawaii suffered a catastrophic collapse about 1.5 million years ago, generating a megatsunami, and now lies as a debris field scattered northward across the ocean bottom,
[Culliney, John L. (2006) Islands in a Far Sea: The Fate of Nature in Hawaii. Honolulu: University of Hawaii Press. p. 17.] The megatsunami may have reached a height of near its origin and reached California and Mexico.
-
The existence of large scattered in only one of the four of Herradura Bay south of the Chilean city of Coquimbo has been interpreted by Roland Paskoff as the result of a mega-tsunami that occurred in the Pleistocene.
-
In Hawaii, a megatsunami at least in height deposited marine at a modern-day elevation of – above sea level at the time the wave struck – on Lanai about 105,000 years ago. The tsunami also deposited such sediments at an elevation of on Oahu, Molokai, Maui, and the island of Hawaii.
-
The collapse of the ancestral Mount Amarelo on Fogo in the Cape Verde Islands about 73,000 years ago triggered a megatsunami which struck Santiago, away, with a height of and a Wave run-up height of over . The wave swept boulders inland and deposited them above sea level
-
A major collapse of the western edge of the Lake Tahoe basin, a landslide with a volume of which formed McKinney Bay between 21,000 and 12,000 years ago, generated megatsunamis/seiche with an initial height of probably about and caused the lake's water to slosh back and forth for days. Much of the water in the megatsunamis washed over the lake's outlet at what is now Tahoe City, California, and flooded down the Truckee River, carrying house-sized boulders as far downstream as the California-Nevada border at what is now Verdi, California.
[ Alden, Andrew, "The 'Tahoe Tsunami': New Study Envisions Early Geologic Event," kqed.org, 31 July 2014, Retrieved 23 June 2020]
-
In the North Sea, the Storegga Slide caused a megatsunami approximately 8,200 years ago.
-
Around 6370 BCE, a landslide on the eastern slope of Mount Etna in Sicily into the Mediterranean Sea triggered a megatsunami in the Eastern Mediterranean with an initial wave height along the eastern coast of Sicily of . It struck the Neolithic village of Atlit Yam off the coast of Israel with a height of , prompting the village's abandonment.
-
Around 5650 B.C., a landslide in Greenland created a megatsunami with a Wave run-up height on Alluttoq Island of .
-
Around 5350 B.C., a landslide in Greenland created a megatsunami with a Wave run-up height on Alluttoq Island of .
[
]
Historic
c. 2000 BC: Réunion
c. 1600 BC: Santorini
-
The Thera volcano erupted, the force of the eruption causing megatsunamis which affected the whole Aegean Sea and the eastern Mediterranean Sea.
c. 1100 BC: Lake Crescent
-
An earthquake generated the Sledgehammer Point Rockslide, which fell from Mount Storm King in what is now Washington in the United States and entered waters at least deep in Lake Crescent, generating a megatsunami with an estimated maximum Wave run-up height of .
Modern
1674: Ambon Island, Banda Sea
On 17 February 1674, between 19:30 and 20:00 local time, an earthquake struck the Maluku Islands. Ambon Island received
Wave run-up heights of , making the wave far too large to be caused by the quake itself. Instead, it was probably the result of an underwater landslide triggered by the earthquake. The quake and tsunami killed 2,347 people.
1731: Storfjorden, Norway
At 10:00 p.m. on 8 January 1731, a
landslide with a volume of possibly fell from the mountain Skafjell from a height of into the Storfjorden opposite Stranda,
Norway. The slide generated a megatsunami in height that struck Stranda, flooding the area for inland and destroying the church and all but two
, as well as many boats. Damaging waves struck as far away as Ørskog. The waves killed 17 people.
[ Hoel, Christer, "The Skafjell Rock Avalanche in 1731," fjords.com Retrieved 23 June 2020]
1741: Oshima-Ōshima,Sea of Japan
An eruption of Oshima-Ōshima occurred that lasted from 18 August 1741 to 1 May 1742. On 29 August 1741, a devastating tsunami occurred.
It killed at least 1,467 people along a section of the coast, excluding native residents whose deaths were not recorded. Wave heights for Gankakezawa have been estimated at based on oral histories, while an estimate of is derived from written records. At Sado Island, over away, a wave height of has been estimated based on descriptions of the damage, while oral records suggest a height of . Wave heights have been estimated at even as far away as the
Korean Peninsula.
There is still no consensus in the debate as to what caused it but much evidence points to a landslide and debris avalanche along the flank of the volcano. An alternative hypothesis holds that an earthquake caused the tsunami.
The event reduced the elevation of the peak of Hishiyama from . An estimated section of the volcano collapsed onto the
Sea bed north of the island; the collapse was similar in size to the collapse which occurred during the 1980 eruption of Mount St. Helens.
1756: Langfjorden, Norway
Just before 8:00 p.m. on 22 February 1756, a landslide with a volume of travelled at high speed from a height of on the side of the mountain Tjellafjellet into the Langfjorden about west of
Tjelle, Norway, between Tjelle and Gramsgrø. The slide generated three megatsunamis in the Langfjorden and the
Eresfjorden with heights of . The waves flooded the shore for inland in some areas, destroying farms and other inhabited areas. Damaging waves struck as far away as Veøya, from the landslide – where they washed inland above normal flood levels – and
Gjermundnes, from the slide. The waves killed 32 people and destroyed 168 buildings, 196 boats, large amounts of forest, and roads and boat landings.
1792: Mount Unzen, Japan
On 21 May 1792, a flank of the Mayamaya dome of
Mount Unzen collapsed after two large earthquakes. This had been preceded by a series of earthquakes coming from the mountain, beginning near the end of 1791. Initial wave heights were , but when they hit the other side of Ariake Bay, they were only in height, though one location received waves due to
Seabed topography. The waves bounced back to Shimabara, which, when they hit, accounted for about half of the tsunami's victims. According to estimates, 10,000 people were killed by the tsunami, and a further 5,000 were killed by the landslide. As of 2011, it was the deadliest known volcanic event in Japan.
1853–1854: Lituya Bay, Alaska
Sometime between August 1853 and May 1854, a megatsunami occurred in
Lituya Bay in what was then
Russian America. Studies of Lituya Bay between 1948 and 1953 first identified the event, which probably occurred because of a large landslide on the south shore of the bay near Mudslide Creek. The wave had a maximum
Wave run-up height of , flooding the coast of the bay up to inland.
[Lander, pp. 39–41.]
1874: Lituya Bay, Alaska
A study of Lituya Bay in 1953 concluded that sometime around 1874, perhaps in May 1874, another megatsunami occurred in
Lituya Bay in
Alaska. Probably occurring because of a large landslide on the south shore of the bay in the Mudslide Creek Valley, the wave had a maximum
Wave run-up height of , flooding the coast of the bay up to inland.
[Lander, pp. 44–45.]
1883: Krakatoa, Sunda Strait
The massive explosion of
Krakatoa created
which generated megatsunamis when they hit the waters of the
Sunda Strait on 27 August 1883. The waves reached heights of up to 24 metres (79 feet) along the south coast of
Sumatra and up to 42 metres (138 feet) along the west coast of
Java.
[ Bryant, Edward, Tsunami: The Underrated Hazard, Springer: New York, 2014, , pp. 162–163.] The tsunamis were powerful enough to kill over 30,000 people, and their effect was such that an area of land in
Banten had its human settlements wiped out, and they never repopulated. (This area rewilded and was later declared a national park.) The
steamship Berouw, a colonial
gunboat, was flung over a mile (1.6 km) inland on Sumatra by the wave, killing its entire crew. Two thirds of the island collapsed into the sea after the event.
Groups of human skeletons were found floating on pumice numerous times, up to a year after the event.
The eruption also generated what is often called the loudest sound in history, which was heard away on
Rodrigues in the
Indian Ocean.
1905: Lovatnet, Norway
On 15 January 1905, a landslide on the slope of the mountain Ramnefjellet with a volume of fell from a height of into the southern end of the lake
Lovatnet in Norway, generating three megatsunamis of up to in height. The waves destroyed the villages of Bødal and
Nesdal near the southern end of the lake, killing 61 people – half their combined population – and 261 farm animals and destroying 60 houses, all the local
, and 70 to 80 boats, one of which – the tourist boat
Lodalen – was thrown inland by the last wave and wrecked. At the northern end of the long lake, a wave measured at almost destroyed a bridge.
[ Hoel, Christer, "The Loen Accidents in 1905 and 1936," fjords.com Retrieved 22 June 2020]
1905: Disenchantment Bay, Alaska
On 4 July 1905, an overhanging glacier – since known as the Fallen Glacier – broke loose, slid out of its valley, and fell down a steep slope into Disenchantment Bay in
Alaska, clearing vegetation along a path wide. When it entered the water, it generated a megatsunami which broke tree branches above ground level away. The wave killed vegetation to a height of at a distance of from the landslide, and it reached heights of at different locations on the coast of
Haenke Island. At a distance of from the slide, observers at
Russell Fjord reported a series of large waves that caused the water level to rise and fall for a half-hour.
[Lander, p. 57.]
1934: Tafjorden, Norway
On 7 April 1934, a landslide on the slope of the mountain Langhamaren with a volume of fell from a height of about into the
Tafjorden in Norway, generating three megatsunamis, the last and largest of which reached a height of between on the opposite shore. Large waves struck
Tafjord and Fjørå. At Tafjord, the last and largest wave was tall and struck at an estimated speed of , flooding the town for inland and killing 23 people. At Fjørå, waves reached , destroyed buildings, removed all soil, and killed 17 people. Damaging waves struck as far as away, and waves were detected at a distance of from the landslide. One survivor suffered serious injuries requiring hospitalization.
[ Hoel, Christer, "The Tafjord Accident in 1934," fjords.com Retrieved 22 June 2020]
1936: Lovatnet, Norway
On 13 September 1936, a landslide on the slope of the mountain Ramnefjellet with a volume of fell from a height of into the southern end of the lake
Lovatnet in Norway, generating three megatsunamis, the largest of which reached a height of . The waves destroyed all farms at Bødal and most farms at
Nesdal – completely washing away 16 farms – as well as 100 houses, bridges, a
power station, a
workshop, a
sawmill, several
, a restaurant, a schoolhouse, and all boats on the lake. A wave struck the southern end of the long lake and caused damaging flooding in the
Loelva River, the lake's northern outlet. The waves killed 74 people and severely injured 11.
[
]
1936: Lituya Bay, Alaska
On 27 October 1936, a megatsunami occurred in Lituya Bay in Alaska with a maximum Wave run-up height of in Crillon Inlet at the head of the bay. The four eyewitnesses to the wave in Lituya Bay itself all survived and described it as between high. The maximum inundation distance was inland along the north shore of the bay. The cause of the megatsunami remains unclear, but may have been a submarine landslide.[Lander, pp. 61–64.]
1958: Lituya Bay, Alaska, US
On 9 July 1958, a giant landslide at the head of Lituya Bay in Alaska, caused by an earthquake, generated a wave that washed out trees to a maximum elevation of at the entrance of Gilbert Inlet.
1963: Vajont Dam, Italy
On 9 October 1963, a landslide above Vajont Dam in Italy produced a surge that overtopped the dam and destroyed the villages of Longarone, Pirago, Rivalta, Villanova, and Faè, killing nearly 2,000 people. This is currently the only known example of a megatsunami that was indirectly caused by human activities.[ Vaiont Dam photos and virtual field trip (University of Wisconsin), retrieved 1 July 2009]
1964: Valdez Arm, Alaska
On 27 March 1964, the 1964 Alaska earthquake triggered a landslide that generated a megatsunami which reached a height of in the Valdez Arm of Prince William Sound in Southcentral Alaska.
1980: Spirit Lake, Washington, US
On 18 May 1980, the upper of Mount St. Helens collapsed, creating a landslide. This released the pressure on the magma trapped beneath the summit bulge which exploded as a lateral eruption, which then released the pressure on the magma chamber and resulted in a plinian eruption.
One lobe of the avalanche surged onto Spirit Lake, causing a megatsunami which pushed the lake waters in a series of surges, which reached a maximum height of [[7]USGS Website. Geology of Interactions of Volcanoes, Snow, and Water: Tsunami on Spirit Lake early during 18 May 1980 eruption]
2000: Paatuut, Greenland
On 21 November 2000, a landslide composed of of rock with a mass of 260,000,000 tons fell from an elevation of at Paatuut on the Nuussuaq Peninsula on the west coast of Greenland, reaching a speed of . About of material with a mass of 87,000,000 tons entered Sullorsuaq Strait (known in Danish language as Vaigat Strait), generating a megatsunami. The wave had a Wave run-up height of near the landslide and at Qullissat, the site of an abandoned settlement across the strait on Disko Island, away, where it inundated the coast as far as inland. Refracted energy from the tsunami created a wave that destroyed boats at the closest populated village, Saqqaq, on the southwestern coast of the Nuussuaq Peninsula from the landslide.
2007: Chehalis Lake, British Columbia, Canada
On 4 December 2007, a landslide composed of of rock and debris fell from an elevation of on the slope of Mount Orrock on the western short of Chehalis Lake. The landslide entered the deep lake, generating a megatsunami with a Wave run-up height of on the opposite shore and at the lake's exit point away to the south. The wave then continued down the Chehalis River for about .[
]
2015: Taan Fiord, Alaska, US
At 8:19 p.m. Alaska Time on 17 October 2015, the side of a mountain collapsed at the head of Taan Fiord, a finger of Icy Bay in Alaska.[ researchgate.net "The 2015 Landslide and Tsunami in Taan Fiord, Alaska"][ Higman, Bretwood, et al., "The 2015 landslide and tsunami in Taan Fiord, Alaska," nature.com, 6 September 2018 Retrieved 16 June 2020][ nps.gov National Park Service, "Taan Fjord Landslide and Tsunami," nps.gov, Retrieved 16 June 2020] Some of the resulting landslide came to rest on the toe of Tyndall Glacier,[ Rozell, Ned, "The giant wave of Icy Bay," alaska.edu, 7 April 2016 Retrieved 16 June 2020] but about of rock with a volume of about fell into the fjord.[ Underwood, Emily, "Study of Alaskan Landslide Could Improve Tsunami Modeling," eos.org, 26 April 2019 Retrieved 16 June 2020][ Mooney, Chris, "One of the biggest tsunamis ever recorded was set off three years ago by a melting glacier," washingtonpost.com, 6 September 2018 Retrieved 16 June 2020] The landslide generated a megatsunami with an initial height of about [ Stolz, Kit, "Why Scientists Are Worried About a Landslide No One Saw or Heard," atlasobscura.com, 17 March 2017 Retrieved 16 June 2020] that struck the opposite shore of the fjord, with a Wave run-up height there of .[
]
Over the next 12 minutes,[ the wave travelled down the fjord at a speed of up to ,][ with run-up heights of over in the upper fjord to between or more in its middle section, and or more at its mouth.][ Still probably tall when it entered Icy Bay,][ the tsunami inundated parts of Icy Bay's shoreline with run-ups of before dissipating into insignificance at distances of from the mouth of Taan Fiord,][ although the wave was detected away.][
]
Occurring in an uninhabited area, the event was unwitnessed, and several hours passed before the signature of the landslide was noticed on at Columbia University in New York City.[ Morford Stacy, "Detecting Landslides from a Few Seismic Wiggles," columbia.edu, 18 December 2015 Retrieved 16 June 2020]
2017: Karrat Fjord, Greenland
On 17 June 2017, of rock on the mountain Ummiammakku fell from an elevation of roughly into the waters of the Karrat Fjord. The event was thought to be caused by melting ice that destabilised the rock. It registered as a magnitude 4.1 earthquake and created a wave. The settlement of Nuugaatsiaq, away, saw Wave run-up heights of . Eleven buildings were swept into the sea, four people died, and 170 residents of Nuugaatsiaq and Illorsuit were evacuated because of a danger of additional landslides and waves. The tsunami was noted at settlements as far as away.
2020: Elliot Creek, British Columbia, Canada
On 28 November 2020, unseasonably heavy rainfall triggered a landslide of into a glacial lake at the head of Elliot Creek. The sudden displacement of water generated a high megatsunami that cascaded down Elliot Creek and the Southgate River to the head of Bute Inlet, covering a total distance of over . The event generated a magnitude 5.0 earthquake and destroyed over of salmon habitat along Elliot Creek.
2023: Dickson Fjord, Greenland
On 16 September 2023 a large landslide originating above sea level entered Dickson Fjord, triggering a tsunami exceeding in run-up. Run-up of was observed along a stretch of coast. There was no major damage and there were no casualties. The tsunami was followed by a seiche that lasted for a week.
Potential future megatsunamis
In a BBC television documentary broadcast in 2000, experts said that they thought that a landslide on a volcanic ocean island is the most likely future cause of a megatsunami.[ The documentary was produced before the experts' scientific paper was published and before responses were given by other geologists. There have been megatsunamis in the past,][ and future megatsunamis are possible but current geological consensus is that these are only local. A megatsunami in the Canary Islands would diminish to a normal tsunami by the time it reached the continents.][ Also, the current consensus for La Palma is that the region conjectured to collapse is too small and too geologically stable to do so in the next 10,000 years, although there is evidence for past megatsunamis local to the Canary Islands thousands of years ago. Similar remarks apply to the suggestion of a megatsunami in Hawaii.][
]
British Columbia
Some geologists consider an unstable rock face at Mount Breakenridge, above the north end of the giant fresh-water fjord of Harrison Lake in the Fraser Valley of southwestern British Columbia, Canada, to be unstable enough to collapse into the lake, generating a megatsunami that might destroy the town of Harrison Hot Springs (located at its south end).
Canary Islands
Geologists Dr. Simon Day and Dr. Steven Neal Ward consider that a megatsunami could be generated during an eruption of Cumbre Vieja on the volcanic ocean island of La Palma, in the Canary Islands, Spain.
In 1949, an eruption occurred at three of the volcano's ventsDuraznero, Hoyo Negro, and Llano del Banco. A local geologist, Juan Bonelli-Rubio, witnessed the eruption and recorded details on various phenomenon related to the eruption. Bonelli-Rubio visited the summit area of the volcano and found that a fissure about long had opened on the east side of the summit. As a result, the western half of the volcanowhich is the volcanically active arm of a triple-armed rifthad slipped approximately downwards and westwards towards the Atlantic Ocean.[Bonelli-Rubio, J. M. (1950). Contribucion al estudio de la erupcion del Nambroque o San Juan. Madrid: Inst. Geografico y Catastral, 25 pp.]
In 1971, an eruption occurred at the Teneguía vent at the southern end of the subaerial section of the volcano without any movement. The section affected by the 1949 eruption is currently stationary and does not appear to have moved since the initial rupture.[As per Bonelli Rubio]
Cumbre Vieja remained dormant until an eruption began on 19 September 2021.
It is likely that several eruptions would be required before failure would occur on Cumbre Vieja.
Geologists and are in general agreement that the initial study was flawed. The current geology does not suggest that a collapse is imminent. Indeed, it seems to be geologically impossible right nowthe region conjectured as prone to collapse is too small and too stable to collapse within the next 10,000 years.
Day and Ward have admitted that their original analysis of the danger was based on several worst case assumptions.
Hawaii
Sharp cliffs and associated ocean debris at the Kohala Volcano, Lanai and Molokai indicate that landslides from the flank of the Kilauea and Mauna Loa volcanoes in Hawaii may have triggered past megatsunamis, most recently at 120,000 Before Present.
Other research suggests that such a single large landslide is not likely. Instead, it would collapse as a series of smaller landslides.
In 2018, shortly after the beginning of the 2018 lower Puna eruption, a National Geographic article responded to such claims with "Will a monstrous landslide off the side of Kilauea trigger a monster tsunami bound for California? Short answer: No."
In the same article, geologist Mika McKinnon stated:[
]
Another volcanologist, Janine Krippner, added:[
]
Despite this, evidence suggests that catastrophic collapses do occur on Hawaiian volcanoes and generate local tsunamis.
Norway
Although known earlier to the local population, a crack wide and in length in the side of the mountain Åkerneset in Norway was rediscovered in 1983 and attracted scientific attention. Located at (62°10'52.28"N, 6°59'35.38"E), it since has widened at a rate of per year. Geology analysis has revealed that a slab of rock thick and at an elevation stretching from is in motion. Geologists assess that an eventual catastrophic collapse of of rock into Sunnylvsfjorden is inevitable and could generate megatsunamis of in height on the fjord′s opposite shore. The waves are expected to strike Hellesylt with a height of , Geiranger with a height of , Tafjord with a height of , and many other communities in Norway's Sunnmøre district with a height of several metres, and to be noticeable even at Ålesund. The predicted disaster is depicted in the 2015 Norwegian film The Wave.[ Hole, Christer, "The Åkerneset Rock Avalanche," fjords.com Retrieved 23 June 2020]
See also
Footnotes
Bibliography
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target="_blank" rel="nofollow"> Lander, James F. Tsunamis Affecting Alaska 1737–1996. Boulder, Colorado: NOAA National Geophysical Data Center, September 1996.
Further reading
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BBC 2 TV; 2000. Transcript "Mega-tsunami; Wave of Destruction", Horizon. First screened 21.30 hrs, Thursday, 12 October 2000.
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Rihm, R; Krastel, S. & CD109 Shipboard Scientific Party; 1998. "Volcanoes and landslides in the Canaries". National Environment Research Council News. Summer, 16–17.
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Sandom, J.G., 2010, The Wave – A John Decker Thriller, Cornucopia Press, 2010. A thriller in which a megatsunami is intentionally created when a terrorist detonates a nuclear bomb on La Palma in the Canary Islands.
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Ortiz, J.R., Bonelli Rubio, J.M., 1951. La erupción del Nambroque (junio-agosto de 1949). Madrid: Talleres del Instituto Geográfico y Catastral, 100 p., 1h. pleg.;23 cm
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