Megatsunami

A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water.

Megatsunamis have quite different features from other, more usual types of tsunamis. Most tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquake and rise or fall in the sea floor, causing water to be displaced. Ordinary tsunamis have shallow waves out at sea, and the water piles up to a wave height of up to about 10 metres (33 feet) as the sea floor becomes shallow near land. By contrast, megatsunamis occur when a very large amount of material suddenly falls into water or anywhere near water (such as via a meteor impact), or are caused by volcanic activity. They can have extremely high initial wave heights of hundreds and possibly thousands of metres, far beyond any ordinary tsunami, as the water is "splashed" upwards and outwards by the impact or displacement. As a result, two heights are sometimes quoted for megatsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.

Modern megatsunamis include the one associated with the 1883 eruption of Krakatoa (volcanic eruption), the 1958 Lituya Bay megatsunami (landslide into a bay), and the wave resulting from the Vajont Dam landslide (caused by human activity destabilizing sides of valley). Prehistoric examples include the Storegga Slide (landslide), and the Chicxulub, Chesapeake Bay and Eltanin meteor impacts.

Lituya Bay megatsunami diagram (English)
Diagram of the 1958 Lituya Bay megatsunami, which proved the existence of megatsunamis.

Overview

A megatsunami is a tsunami – a large wave due to displacement of a body of water – with an initial wave amplitude (height) measured in several tens, hundreds, or possibly thousands of metres.

Normal tsunamis generated at sea result from movement of the sea floor. They have a small wave height offshore, are very long (often hundreds of kilometres), and generally pass unnoticed at sea, forming only a slight swell usually of the order of 30 cm (12 in) above the normal sea surface. When they reach land, the wave height increases dramatically as the base of the wave pushes the water column above it upwards.

By contrast, megatsunamis are caused by giant landslides and other impact events. This could also refer to a meteorite hitting an ocean. Underwater earthquakes or volcanic eruptions do not normally generate such large tsunamis, but landslides next to bodies of water resulting from earthquakes can, since they cause a large amount of displacement. If the landslide or impact occurs in a limited body of water, as happened at the Vajont Dam (1963) and Lituya Bay (1958) then the water may be unable to disperse and one or more exceedingly large waves may result.

A way to visualize the difference, is that an ordinary tsunami is caused by sea floor changes, somewhat like pushing up on the floor of a large tub of water to the point it overflows, and causing a surge of water to "run-off" at the sides. In this analogy, a megatsunami would be more similar to dropping a large rock from a considerable height into the tub, at one end, causing water to splash up and out, and overflow at the other end.

Two heights are sometimes quoted for megatsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.

Recognition of the concept of megatsunami

Geologists 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, whilst those from below the trim line did not. 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, one possibility was a landslide-generated tsunami.[1]

On 9 July 1958, a 7.8 Mwstrike-slip earthquake in southeast Alaska caused 90 million tonnes 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 1720 feet (524 m), 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.[1]

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;[2] this model was considerably developed and modified by a second study in 2010.

Although the earthquake which caused the megatsunami was considered very energetic, and involving strong ground movements, several possible mechanisms were not likely or able to have caused the resulting megatsunami. Neither water drainage from a lake, nor landslide, nor the force of the earthquake itself led to the megatsunami, although all of these may have contributed.

Instead, the megatsunami was caused by a massive and sudden impulsive impact when about 40 million cubic yards of rock several hundred metres above the bay was fractured from the side of the bay, by the earthquake, and fell "practically as a monolithic unit" down the almost vertical slope and into the bay.[2] The rockfall also caused air to be "dragged along" due to viscosity effects, which added to the volume of displacement, and further impacted the sediment on the floor of the bay, creating a large crater. The study concluded that:

The giant wave runup of 1,720 feet (524 m.) at the head of the Bay and the subsequent huge wave along the main body of Lituya Bay which occurred on July 9, 1958, were caused primarily by an enormous subaerial rockfall into Gilbert Inlet at the head of Lituya Bay, triggered by dynamic earthquake ground motions along the Fairweather Fault.

The large mass of rock, acted as a monolith (thus resembling high-angle asteroid impact), struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth. The displaced water and the displacement and folding of the sediments broke and uplifted 1,300 feet of ice along the entire front of the Lituya Glacier at the north end of Gilbert Inlet. Also, the impact and the sediment displacement by the rockfall resulted in an air bubble and in water splashing action that reached the 1,720 foot (524 m.) elevation on the other side of the head of Gilbert Inlet. The same rockfall impact, in combination with the strong ground movements, the net vertical crustal uplift of about 3.5 feet, and an overall tilting seaward of the entire crustal block on which Lituya Bay was situated, generated the giant solitary gravity wave which swept the main body of the bay.

This was the most likely scenario of the event – the "PC model" that was adopted for subsequent mathematical modeling studies with source dimensions and parameters provided as input. Subsequent mathematical modeling at the Los Alamos National Laboratory (Mader, 1999, Mader & Gittings, 2002) supported the proposed mechanism – as there was indeed sufficient volume of water and an adequately deep layer of sediments in the Lituya Bay inlet to account for the giant wave runup and the subsequent inundation. The modeling reproduced the documented physical observations of runup.

A 2010 model 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.[3]

List of megatsunamis

Prehistoric

  • The asteroid linked to the extinction of dinosaurs, which created the Chicxulub crater in Yucatán approximately 66 million years ago, would have caused an over 100 metres (330 ft) tall megatsunami. The height of the tsunami was limited due to relatively shallow sea in the area of the impact; in deep sea it would be 4.6 kilometres (2.9 mi) tall.[4] A more recent simulation of the global effects of the megatsunami showed initial wave height of 1.5 kilometres (0.93 mi), with later waves up to 100 metres (330 ft) height in the Gulf of Mexico, and up to 14 metres (46 ft) in the North Atlantic and South Pacific.[5]
  • A series of megatsunamis were generated by the bolide impact that created the Chesapeake Bay impact crater, about 35.5 million years ago.[6]
  • During the Messinian the coasts of northern Chile were likely struck by various megatsunamis.[7]
  • A megatsunami affected the coast of south–central Chile in the Pliocene as evidenced by the sedimentary record of Ranquil Formation.[8]
  • The Eltanin impact in the southeast Pacific Ocean 2.5 million years ago caused a megatsunami that was over 200 m (660 ft) 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 suffered a catastrophic collapse and likely megatsunami about 1.5 million years ago and now lies as a debris field scattered northward across the ocean bottom,[9] while what remains on the island are the highest sea cliffs in the world.[10]
  • The existence of large scattered boulders in only one of the four marine terraces 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 Middle Pleistocene.[11]
  • A massive collapse of the western edge of the Lake Tahoe basin, which formed McKinney Bay around 50,000 years ago, is thought to have generated a tsunami/seiche wave with a height approaching 330 ft (100 m).[12]
  • In the North Sea, the Storegga Slide caused a megatsunami approximately 8,200 years ago.[13] It is estimated to have completely flooded the remainder of Doggerland.[14]
  • Approximately 8,000 years ago, a massive volcanic landslide off Mt. Etna, Sicily caused a megatsunami which devastated the eastern Mediterranean coastline on three continents. Wave heights on the coast of Calabria are estimated to have reached a maximum of 40m.[15]

Historic

c. 2000 BC: Réunion

c. 1600 BC: Santorini

Modern

1792: Mount Unzen, Japan

In 1792, Mount Unzen in Japan erupted, causing part of the volcano to collapse into the sea. The landslide caused a megatsunami that reached 100 metres (330 ft) high and killed 15,000 people in the local fishing villages.

1883: Krakatoa

The eruption of Krakatoa created pyroclastic flows 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.[17]

1958: Lituya Bay, Alaska, US

Lituya-Bay-overview-with-arrows
Damage from the 1958 Lituya Bay megatsunami can be seen in this oblique aerial photograph of Lituya Bay, Alaska as the lighter areas at the shore where trees have been stripped away. The red arrow shows the location of the landslide, and the yellow arrow shows the location of the high point of the wave sweeping over the headland.

On July 9, 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 altitude of 520 metres (1,710 ft) at the entrance of Gilbert Inlet.[18] The wave surged over the headland, stripping trees and soil down to bedrock, and surged along the fjord which forms Lituya Bay, destroying a fishing boat anchored there and killing two people.[1]

1963: Vajont Dam, Italy

On October 9, 1963, a landslide above Vajont Dam in Italy produced a 250 m (820 ft) surge that overtopped the dam and destroyed the villages of Longarone, Pirago, Rivalta, Villanova and Faè, killing nearly 2,000 people.[19]

1980: Spirit Lake, Washington, US

On May 18, 1980, the upper 460 metres (1,509 feet) of Mount St. Helens collapsed, creating a massive landslide. This released the pressure on the magma trapped beneath the summit bulge which exploded as a lateral blast, 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 260 metres (853 feet)[20] above the pre-eruption water level (~975 m asl/3,199 ft). Above the upper limit of the tsunami, trees lie where they were knocked down by the pyroclastic surge; below the limit, the fallen trees and the surge deposits were removed by the megatsunami and deposited in Spirit Lake.[21]

Potential future megatsunamis

In a BBC television documentary broadcast in 2000, experts said that they thought that a massive landslide on a volcanic ocean island is the most likely future cause of a megatsunami.[22] The size and power of a wave generated by such means could produce devastating effects, travelling across oceans and inundating up to 25 kilometres (16 mi) inland from the coast. This research, however, was later found to be flawed.[23] 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,[24] 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.[25] 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 Isles thousands of years ago. Similar remarks apply to the suggestion of a megatsunami in Hawaii.[26]

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).[27]

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.[28][29]

In 1949, this volcano erupted at its Duraznero, Hoyo Negro and Llano del Banco vents, and there was an earthquake with an epicentre near the village of Jedey. The next day Juan Bonelli Rubio, a local geologist, visited the summit area and found that a fissure about 2.5 kilometres (1.6 mi) long had opened on the east side of the summit. As a result, the west half of the volcano (which is the volcanically active arm of a triple-armed rift) had slipped about 2 metres (6.6 ft) downwards and 1 metre (3.3 ft) westwards towards the Atlantic Ocean.[30]

Cumbre Vieja is currently dormant, but will almost certainly erupt again. Day and Ward hypothesize[28][29] that if such an eruption causes the western flank to fail, a mega-tsunami could be generated.

La Palma is currently the most volcanically active island in the Canary Islands Archipelago. It is likely that several eruptions would be required before failure would occur on Cumbre Vieja.[28][29] However, the western half of the volcano has an approximate volume of 500 cubic kilometres (120 cu mi) and an estimated mass of 1.5 trillion metric tons (1.7×1012 short tons). If it were to catastrophically slide into the ocean, it could generate a wave with an initial height of about 1,000 metres (3,300 ft) at the island, and a likely height of around 50 metres (164 ft) at the Caribbean and the Eastern North American seaboard when it runs ashore eight or more hours later. Tens of millions of lives could be lost in the cities and/or towns of St. John's, Halifax, Boston, New York, Baltimore, Washington, D.C., Miami, Havana and the rest of the Eastern Coasts of the United States and Canada, as well as many other cities on the Atlantic coast in Europe, South America and Africa.[28][29] The likelihood of this happening is a matter of vigorous debate.[31]

The last eruption on the Cumbre Vieja occurred in 1971 at the Teneguia vent at the southern end of the sub-aerial section without any movement. The section affected by the 1949 eruption is currently stationary and does not appear to have moved since the initial rupture.[32]

Geologists and volcanologists 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 now, the region conjectured as prone to collapse is too small and too stable to collapse within the next 10,000 years.[23] They also concluded that a landslide is likely to happen as a series of smaller collapses rather than a single landslide from closer study of deposits left in the ocean by previous landslides. A megatsunami does seem possible locally in the distant future as there is geological evidence from past deposits suggesting that a megatsunami occurred with marine material deposited 41 to 188 meters above sea level between 32,000 and 1.75 million years ago.[24] This seems to have been local to Gran Canaria.

Day and Ward have admitted that their original analysis of the danger was based on several worst case assumptions.[33][34] A 2008 paper looked into this very worst-case scenario, the most massive slide that could happen (though unlikely and probably impossible right now with the present day geology). Although it would be a megatsunami locally in the Canary Isles, it would diminish in height to a regular tsunami when it reaches the continents as the waves interfere and spread across the oceans.[25]

For more details see Cumbre Vieja#Criticism

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 BP.[35][36][37] A tsunami event is also possible, with the tsunami potentially reaching up to about 1 kilometre (3,300 ft) in height[38] According to the documentary National Geographic's Ultimate Disaster: Tsunami, if a big landslide occurred at Mauna Loa or the Hilina Slump, a 30-metre (98 ft) tsunami would take only thirty minutes to reach Honolulu. There, hundreds of thousands of people could be killed as the tsunami could level Honolulu and travel 25 kilometres (16 mi) inland. Also, the West Coast of America and the entire Pacific Rim could potentially be affected.

However, other research suggests that such a single large landslide is not likely. Instead, it would collapse as a series of smaller landslides.[39]

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."[26]

In the same article, geologist Mika McKinnon stated:[26]

there are submarine landslides, and submarine landslides do trigger tsunamis, but these are really small, localized tsunamis. They don't produce tsunamis that move across the ocean. In all likelihood, it wouldn't even impact the other Hawaiian islands.

Another volcanologist, Janine Krippner, added:[26]

People are worried about the catastrophic crashing of the volcano into the ocean. There's no evidence that this will happen. It is slowly—really slowly—moving toward the ocean, but it's been happening for a very long time.

Despite this, evidence suggests that catastrophic collapses do occur on Hawaiian volcanoes and generate massive, yet local tsunamis.[40]

Cape Verde Islands

Steep cliffs on the Cape Verde Islands have been caused by catastrophic debris avalanches. These have been common on the submerged flanks of ocean island volcanoes and more can be expected in the future.[41]

See also

References

  1. ^ a b c Miller, Don J. "Giant Waves in Lituya Bay, Alaska". uwsp.edu. p. 3. Archived from the original on 13 October 2013.
  2. ^ a b 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 May 25–27, 1999, in Honolulu, Hawaii, USA
  3. ^ Ward, Steven N.; Day, Simon (2010). "Lituya Bay Landslide and Tsunami — A Tsunami Ball Approach" (PDF). Journal of Earthquake and Tsunami. 4 (4): 285–319. doi:10.1142/S1793431110000893.
  4. ^ Bryant, Edward (June 2014). Tsunami: The Underrated Hazard. Springer. p. 178. ISBN 978-3-319-06133-7.
  5. ^ "Dinosaur-Killing Asteroid Created A Mile-High Tsunami That Swept Through The World's Oceans". iflscience.com. January 8, 2019.
  6. ^ Poag, C. W. (1997). "The Chesapeake Bay bolide impact: A convulsive event in Atlantic Coastal Plain evolution". Sedimentary Geology. 108 (1–4): 45–90. Bibcode:1997SedG..108...45P. doi:10.1016/S0037-0738(96)00048-6.
  7. ^ Le Roux, Jacobus P. (2015). "A critical examination of evidence used to re-interpret the Hornitos mega-breccia as a mass-flow deposit caused by cliff failure". Andean Geology. 41 (1): 139–145.
  8. ^ Le Roux, J.P.; Nielsen, Sven N.; Kemnitz, Helga; Henriquez, Álvaro (2008). "A Pliocene mega-tsunami deposit and associated features in the Ranquil Formation, southern Chile" (PDF). Sedimentary Geology. 203 (1): 164–180. Bibcode:2008SedG..203..164L. doi:10.1016/j.sedgeo.2007.12.002. Retrieved 11 April 2016.
  9. ^ "Hawaiian landslides have been catastrophic". mbari.org. Monterey Bay Aquarium Research Institute. 2015-10-22.
  10. ^ Culliney, John L. (2006) Islands in a Far Sea: The Fate of Nature in Hawaii. Honolulu: University of Hawaii Press. p. 17.
  11. ^ Paskoff, Roland (1991). "Likely occurrence of mega-tsunami in the Middle Pleistocene near Coquimbo, Chile". Revista geológica de Chile. 18 (1): 87–91. Retrieved 17 July 2016.
  12. ^ Gardner, J.V. (July 2000). "The Lake Tahoe debris avalanche". 15th Annual Geological Conference. Geological Society of Australia.
  13. ^ Bondevik, S.; Lovholt, F.; Harbitz, C.; Mangerud, J.; Dawsond, A.; Svendsen, J. I. (2005). "The Storegga Slide tsunami—comparing field observations with numerical simulations". Marine and Petroleum Geology. 22 (1–2): 195–208. doi:10.1016/j.marpetgeo.2004.10.003.
  14. ^ Rincon, Paul (1 May 2014). "Prehistoric North Sea 'Atlantis' hit by 5m tsunami". BBC News. Retrieved 22 February 2017 – via www.bbc.com.
  15. ^ Pareschi, M. T.; Boschi, E.; Favalli, M. (2006). "Lost tsunami". Geophysical Research Letters. 33 (22): L22608. Bibcode:2006GeoRL..3322608P. doi:10.1029/2006GL027790.
  16. ^ "Mega-tsunami: Wave of Destruction". BBC Two. 12 October 2000.
  17. ^ Bryant, Edward, Tsunami: The Underrated Hazard, Springer: New York, 2014, ISBN 978-3-319-06132-0, pp. 162–163.
  18. ^ Mader, Charles L.; Gittings, Michael L. (2002). "Modeling the 1958 Lituya Bay Mega-Tsunami, II" (PDF). Science of Tsunami Hazards. 20 (5): 241–250.
  19. ^ "Archived copy". Archived from the original on 2009-07-29. Retrieved 2009-07-29.CS1 maint: archived copy as title (link) Vaiont Dam photos and virtual field trip (University of Wisconsin), retrieved 2009-07-01
  20. ^ Voight et al. 1983
  21. ^ USGS Website. Geology of Interactions of Volcanoes, Snow, and Water: Tsunami on Spirit Lake early during 18 May 1980 eruption
  22. ^ Mega-tsunami: Wave of Destruction. Transcript. BBC Two television programme, first broadcast 12 October 2000
  23. ^ a b New Research Puts 'Killer La Palma Tsunami' At Distant Future, Science Daily, September 21, 2006, based on materials from the Delft University of Technology
  24. ^ a b Pérez-Torrado, F. J; Paris, R; Cabrera, M. C; Schneider, J-L; Wassmer, P; Carracedo, J. C; Rodríguez-Santana, A; & Santana, F; 2006. Tsunami deposits related to flank collapse in oceanic volcanoes: The Agaete Valley evidence, Gran Canaria, Canary Islands. Marine Geol. 227, 135–149
  25. ^ a b Løvholt, F., G. Pedersen, and G. Gisler. "Oceanic propagation of a potential tsunami from the La Palma Island." Journal of Geophysical Research: Oceans 113.C9 (2008).
  26. ^ a b c d "No, Hawaii's Volcano Won't Trigger a Mega-Tsunami", National Geographic, Sarah Gibbons, May 17, 2018
  27. ^ Evans, S.G.; Savigny, K.W. (1994). "Landslides in the Vancouver-Fraser Valley-Whistler region" (PDF). Geological Survey of Canada. Ministry of Forests, Province of British Columbia. pp. 36 p. Retrieved 2008-12-28.
  28. ^ a b c d Day et al. 1999
  29. ^ a b c d Ward & Day 2001
  30. ^ Bonelli 1950
  31. ^ Pararas-Carayannis 2002
  32. ^ As per Bonelli Rubio
  33. ^ Ali Ayres (2004-10-29). "Tidal wave threat 'over-hyped'". BBC NEWS.
  34. ^ Pararas-Carayannis, George (2002). "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" (PDF). Science of Tsunami Hazards. 20 (5): 251–277. Retrieved 7 September 2014.
  35. ^ McMurtry, Gary M.; Fryer, Gerard J.; Tappin, David R.; Wilkinson, Ian P.; Williams, Mark; Fietzke, Jan; Garbe-Schoenberg, Dieter; Watts, Philip (1 September 2004). "Megatsunami deposits on Kohala volcano, Hawaii, from flank collapse of Mauna Loa". Geology. 32 (9): 741. Bibcode:2004Geo....32..741M. doi:10.1130/G20642.1.
  36. ^ McMurtry, Gary M.; Fryer, Gerard J.; Tappin, David R.; Wilkinson, Ian P.; Williams, Mark; Fietzke, Jan; Garbe-Schoenberg, Dieter; Watts, Philip (September 1, 2004). "A Gigantic Tsunami in the Hawaiian Islands 120,000 Years Ago". Geology. SOEST Press Releases. Retrieved 2008-12-20.
  37. ^ McMurtry, G. M.; Tappin, D. R.; Fryer, G. J.; Watts, P. (December 2002). "Megatsunami Deposits on the Island of Hawaii: Implications for the Origin of Similar Deposits in Hawaii and Confirmation of the 'Giant Wave Hypothesis'". AGU Fall Meeting Abstracts. 51: OS51A–0148. Bibcode:2002AGUFMOS51A0148M.
  38. ^ Britt, Robert Roy (14 December 2004). "The Megatsunami: Possible Modern Threat". LiveScience. Retrieved 2008-12-20.
  39. ^ Pararas-Carayannis, George (2002). "Evaluation of the threat of mega tsunami generation from postulated massive slope failures of island volcanoes on La Palma, Canary Islands, and on the island of Hawaii". drgeorgepc.com. Retrieved 2008-12-20.
  40. ^ https://earthweb.ess.washington.edu/tsunami2/deposits/downloads/posters/fryer05worksmall.pdf
  41. ^ Le Bas, T.P. (2007). "Slope Failures on the Flanks of Southern Cape Verde Islands". In Lykousis, Vasilios (ed.). Submarine mass movements and their consequences: 3rd international symposium. Springer. ISBN 978-1-4020-6511-8.

Further reading

External links

1792 Unzen earthquake and tsunami

The 1792 Unzen earthquake and tsunami resulted from the volcanic activities of Mount Unzen (in the Shimabara Peninsula of Nagasaki Prefecture, Japan) on 21 May. This caused the collapse of the southern flank of the Mayuyama dome in front of Mount Unzen, resulting in a tremendous megatsunami, killing 15,000 people altogether. It was also called Shimabara erupted, Higo affected (島原大変肥後迷惑), (Shimabara means the central mountain of the Shimabara Peninsula) since many people were killed by this tsunami in Higo (Kumamoto Prefecture, situated 20 km away across the Ariake Sea).

1958 Lituya Bay, Alaska earthquake and megatsunami

The 1958 Lituya Bay earthquake occurred at July 9 at 22:15:58 with a moment magnitude of 7.8 and a maximum Mercalli intensity of XI (Extreme). The strike-slip earthquake took place on the Fairweather Fault and triggered a rockslide of 40 million cubic yards (30 million cubic meters and about 90 million tons) into the narrow inlet of Lituya Bay, Alaska. The impact was heard 50 miles (80 km) away, and the sudden displacement of water resulted in a megatsunami that washed out trees to a maximum elevation of 1,720 feet (520 m) at the entrance of Gilbert Inlet. This is the largest and most significant megatsunami in modern times; it forced a re-evaluation of large-wave events and the recognition of impact events, rockfalls, and landslides as causes of very large waves.

A 2010 model 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. Scientists 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, a ratio comparable with other events where this "dual slide" effect is known to have happened. Lituya Bay has a history of megatsunami events, but the 1958 event was the first for which sufficient data was captured at the time.

Burckle Crater

Burckle crater is an undersea feature that is hypothesized to be an impact crater by the Holocene Impact Working Group. They considered that it likely was formed by a very large-scale and relatively recent (c. 3000–2800 BCE) meteorite impact event, possibly resulting from a comet. Burckle crater is estimated to be about 29 kilometres (18 mi) in diameter, about 25 times wider than Meteor Crater in Arizona. The Russian Academy of Sciences lists the crater as a potential impact crater.

Chicxulub crater

The Chicxulub crater (; Mayan: [tʃʼikʃuluɓ]) is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. It was formed by a large asteroid or comet about 11 to 81 kilometres (6.8 to 50.3 miles) in diameter, the Chicxulub impactor, striking the Earth. The date of the impact coincides precisely with the Cretaceous–Paleogene boundary (K–Pg boundary), slightly less than 66 million years ago, and a widely accepted theory is that worldwide climate disruption from the event was the cause of the Cretaceous–Paleogene extinction event, a mass extinction in which 75% of plant and animal species on Earth became extinct, including all non-avian dinosaurs.

The crater is estimated to be 150 kilometres (93 miles) in diameter and 20 km (12 mi) in depth, well into the continental crust of the region of about 10–30 km (6.2–18.6 mi) depth. It is the second largest confirmed impact structure on Earth and the only one whose peak ring is intact and directly accessible for scientific research.The crater was discovered by Antonio Camargo and Glen Penfield, geophysicists who had been looking for petroleum in the Yucatán during the late 1970s. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. Evidence for the impact origin of the crater includes shocked quartz, a gravity anomaly, and tektites in surrounding areas.

In 2016, a scientific drilling project drilled deep into the peak ring of the impact crater, hundreds of meters below the current sea floor, to obtain rock core samples from the impact itself. The discoveries were widely seen as confirming current theories related to both the crater impact and its effects.

Cumbre Vieja

Cumbre Vieja (Spanish: Old Summit) is an active although dormant volcanic ridge on the volcanic ocean island of La Palma in the Canary Islands, Spain, that erupted twice in the 20th century – in 1949, and again in 1971.

The ridge of the Cumbre Vieja trends in an approximate north-south direction and covers the southern two-thirds of the island. Several volcanic craters are located on the summit ridge and flanks.

Fenambosy Chevron

The Fenambosy Chevron is one of four chevron-shaped land features on the southwest coast of Madagascar, near the tip of Madagascar, 180 meters (590 ft) high and 5 kilometres (3.1 mi) inland. Chevrons such as Fenambosy have been hypothesized as providing evidence of "megatsunamis" caused by comets or asteroids crashing into Earth. However, the megatsunami origin of the Fernambosy and other chevrons has been challenged by other geologists and oceanographers.A feature called the Burckle crater lies about 1,700 kilometres (1,100 mi) east-southeast of the Madagascar chevrons and in deep ocean. it is hypothesized to be an impact crater by the Holocene Impact Working Group. Although its sediments have not been directly sampled, cores from the area contain high levels of nickel and magnetic components that are argued to be associated with impact ejecta. Abbott estimates the age of this feature to be about 4,500 to 5,000 years old.

Harrison Hot Springs

The Village of Harrison Hot Springs is a small community at the southern end of Harrison Lake in the Fraser Valley of British Columbia. It is a member of the Fraser Valley Regional District; its immediate neighbour is the District of Kent and included in it, the town of Agassiz. It is a resort community known for its hot springs, and has a population of just over 1500 people. It is named after Benjamin Harrison, a former deputy governor for the Hudson's Bay Company.

Impact event

An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect. When large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry. Impact craters and structures are dominant landforms on many of the Solar System's solid objects and present the strongest empirical evidence for their frequency and scale.

Impact events appear to have played a significant role in the evolution of the Solar System since its formation. Major impact events have significantly shaped Earth's history, have been implicated in the formation of the Earth–Moon system, the evolutionary history of life, the origin of water on Earth and several mass extinctions. The famous prehistoric Chicxulub impact, 66 million years ago, is believed to be the cause of the Cretaceous–Paleogene extinction event.Throughout recorded history, hundreds of Earth impacts (and exploding bolides) have been reported, with some occurrences causing deaths, injuries, property damage, or other significant localised consequences. One of the best-known recorded events in modern times was the Tunguska event, which occurred in Siberia, Russia, in 1908. The 2013 Chelyabinsk meteor event is the only known such incident in modern times to result in numerous injuries, excluding the 1490 Ch'ing-yang event in China. The Chelyabinsk meteor is the largest recorded object to have encountered the Earth since the Tunguska event.

The Comet Shoemaker–Levy 9 impact provided the first direct observation of an extraterrestrial collision of Solar System objects, when the comet broke apart and collided with Jupiter in July 1994. An extrasolar impact was observed in 2013, when a massive terrestrial planet impact was detected around the star ID8 in the star cluster NGC 2547 by NASA's Spitzer space telescope and confirmed by ground observations. Impact events have been a plot and background element in science fiction.

In April 2018, the B612 Foundation reported "It’s 100 per cent certain we’ll be hit [by a devastating asteroid], but we’re not 100 per cent certain when." Also in 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.

La Palma

La Palma (Spanish pronunciation: [la ˈpalma]), also San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of 708 square kilometres (273 sq mi) making it the fifth largest of the seven main Canary Islands. The total population at the start of 2018 was 81,863, of which 15,674 lived in the capital, Santa Cruz de la Palma and about 20,171 in Los Llanos de Aridane. La Palma has "sister city" status with El Dorado Hills, California. Its highest mountain is the Roque de los Muchachos, at 2,423 metres (7,949 ft), being second among the peaks of the Canaries only to the peaks of the Teide massif on Tenerife.

In 1815, the German geologist Leopold von Buch visited the Canary Islands. It was as a result of his visit to Tenerife, where he visited the Las Cañadas caldera, and then later to La Palma, where he visited the Taburiente caldera, that the Spanish word for cauldron or large cooking pot – "caldera" – was introduced into the geological vocabulary. In the center of the island is the Caldera de Taburiente National Park; one of four national parks in the Canary Islands.

List of earthquakes in Alaska

This is an incomplete list of earthquakes in Alaska.

List of tsunamis

This article lists notable tsunamis, which are sorted by the date and location that the tsunami occurred.

Because of seismic and volcanic activity associated with tectonic plate boundaries along the Pacific Ring of Fire, tsunamis occur most frequently in the Pacific Ocean, but are a worldwide natural phenomenon. They are possible wherever large bodies of water are found, including inland lakes, where they can be caused by landslides and glacier calving. Very small tsunamis, non-destructive and undetectable without specialized equipment, occur frequently as a result of minor earthquakes and other events.

Around 1600 BCE, a tsunami caused by the eruption of Thira devastated the Minoan civilization on Crete and related cultures in the Cyclades, as well as in areas on the Greek mainland facing the eruption, such as the Argolid.

The oldest recorded tsunami occurred in 479 BCE. It destroyed a Persian army that was attacking the town of Potidaea in Greece.As early as 426 BCE, the Greek historian Thucydides inquired in his book History of the Peloponnesian War (3.89.1–6) about the causes of tsunamis. He argued that such events could only be explained as a consequence of ocean earthquakes, and could see no other possible causes.

Lituya Bay

Lituya Bay (; Tlingit: Ltu.aa, meaning 'lake within the point') is a fjord located on the coast of the Southeast part of the U.S. state of Alaska. It is 14.5 km (9.0 mi) long and 3.2 km (2.0 mi) wide at its widest point. The bay was noted in 1786 by Jean-François de La Pérouse, who named it Port des Français. Twenty-one of his men perished in the tidal current in the bay.

Lituya Glacier

Lituya Glacier is a tidewater glacier in the U.S. state of Alaska. Located at 58°43′25″N 137°29′33″W inside Glacier Bay National Park and Preserve, its source is in the Fairweather Range and it feeds into Lituya Bay on the gulf coast of Southeast Alaska.

It is partially responsible for creating the 1958 Lituya Bay megatsunami. The glacier, which has receded over the years, carved Lituya Bay into a unique topographic phenomenon with steep walls, a very deep submerged bottom, and a very narrow entrance to the ocean which created the opportunity for a megatsunami to occur.

The glacier is also the namesake of the Alaska Marine Highway ferry M/V Lituya.

Monte Toc

Monte Toc, nicknamed the walking mountain by locals due to its tendency to landslide, is a mountain on the border between Veneto and Friuli-Venezia Giulia in Northern Italy best known for the Vajont Dam, which was built at the mountain's base in 1960.

On October 9, 1963, 260 million cubic metres of rock slid down the side of Mount Toc and plunged into the reservoir created by the Vajont Dam, causing a megatsunami 250 metres high over the dam wall and destroying the town of Longarone and its suburbs. 1,918 people were killed, 1,450 of whom were in Longarone.

Mount Breakenridge

Mount Breakenridge, 2,395 m or 7,858 ft, is a mountain in the Lillooet Ranges of southwestern British Columbia, Canada, located on the east side of upper Harrison Lake in the angle of mountains formed by that lake and the Big Silver River.

N'Quatqua

This article is about the community and location of N'Quatqua, British Columbia. For the First Nations government of N'Quatqua, see N'Quatqua First Nation.N'Quatqua, variously spelled Nequatque, N'quat'qua, is the proper historic name in the St'at'imcets language for the First Nations village of the Stl'atl'imx people of the community of D'Arcy, which is at the upper end of Anderson Lake about 35 miles southeast of Lillooet and about the same distance from Pemberton. The usage is synonymous with Nequatque Indian Reserve No. 1, which is 177 ha. in size and located adjacent to the mouth of the Gates River (see N'Quatqua First Nation for a list of other reserves administered by the band, some of which are also named Nequatque).

The village and its beach were at the end of pavement northeast of Vancouver and Whistler until the opening of the Duffey Lake Road stretch of Hwy 99, which runs on the south side of the Cayoosh Range which rises above N'Quatqua on the south and east. Beyond D'Arcy towards Seton Portage, at the other end of Anderson Lake, there is only a rough powerline road thousands of feet above the lake, known as the High Line Road, that is not recommended for the unwary or unsure, or the feeble of engine or nerve.

First Nations people have resided at N'Quatqua "since time immemorial" and there is little doubt that there has been human habitation at this sheltered, food-rich spot soon after the catastrophic collapse of the Cayoosh Range 8-20,000 BP that created Seton Portage and separated Anderson and Seton Lakes (the catastrophe would have created a huge wave - see megatsunami - wiping out all human populations in the valley). Prior to the diversion of the Bridge River into the Seton watershed, the salmon runs coming up the lake were as typically large as on other tributaries of the Fraser.

There were other villages in the Gates Valley, southwest from D'Arcy and up Blackwater Creek towards Birkenhead Lake, as well as at Birken but between the ravages of smallpox, an early 19th-century war with the Tsilhqot'in, the effects of the gold rush and Oblate evangelization and the Indian Act, today there is only N'Quatqua.

The N'Quatqua people were part of the Lakes Lillooet group of the St'at'imc, which included today's Seton Lake Band as well as other villages and single residences along Anderson and Seton Lakes. In the 19th century, the paramount chief of the Lakes Lillooet, or the closest thing there was to such a title, was Chief Hunter Jack (In-Kick-Tee in St'at'imcets, whose principal residence was at D'Arcy, although he often lived at Shalalth and was a habitué of the Bridge River goldfields over which he claimed suzerainty).

During the gold rush N'Quatqua was busy as a shipping and transference point on the Douglas Road and went by the name Port Anderson. The name D'Arcy was conferred in honour of Thomas D'Arcy McGee when the Pacific Great Eastern Railway was built, and that name was also applied to the alpine peak just south of "town".

N'Quatqua/D'arcy today has a mix of non-native housing and there are large recreational subdivisions in between D'Arcy and Birken. At Devine, two miles from D'Arcy, a sawmill operated in World War II by a Frank Devine employed Japanese Canadians who had been relocated from the coast to a relocation centre at McGillivray Falls, a few miles farther northeast along the north side of Anderson Lake.

Tollmann's bolide hypothesis

Tollmann's bolide hypothesis is a hypothesis presented by Austrian paleontologist Edith Kristan-Tollmann and geologist Alexander Tollmann in 1994. The hypothesis postulates that one or several bolides (asteroids or comets) struck the Earth around 7640 ± 200 years BCE, with a much smaller one approximately 3150 ± 200 BCE. The hypothesis tries to explain early Holocene extinctions and possibly legends of the Universal Deluge.The claimed evidence for the event includes stratigraphic studies of tektites, dendrochronology, and ice cores (from Camp Century, Greenland) containing hydrochloric acid and sulfuric acid (indicating an energetic ocean strike) as well as nitric acids (caused by extreme heating of air).

Christopher Knight and Robert Lomas in their book, Uriel's Machine, argue that the 7640 BCE evidence is consistent with the dates of formation of a number of extant salt flats and lakes in dry areas of North America and Asia. They argue that these lakes are the remains of multiple-kilometer-high waves that penetrated deeply into continents as the result of oceanic strikes that they proposed occurred. Research by Quaternary geologists, palynologists and others has been unable to confirm the validity of the hypothesis and proposes more frequently occurring geological processes for some of the data used for the hypothesis. Dating of ice cores and Australasian tektites has shown long time span differences between the proposed impact times and the impact ejecta products.

Vajont Dam

The Vajont Dam (or Vaiont Dam) is a disused dam, completed in 1959 in the valley of the Vajont River under Monte Toc, in the municipality of Erto and Casso, 100 km (60 miles) north of Venice, Italy. One of the tallest dams in the world, it is 262 metres (860 ft) high, 27 metres (89 ft) wide and 22.11 metres (72 ft 6 in) thick at the base and 191 metres (627 ft) wide and 3.4 metres (11 ft 2 in) thick at the top.The dam was conceived in the 1920s, designed by Carlo Semenza, and eventually built between 1957 and 1960 by Società Adriatica di Elettricità ("SADE", or "EDIS") (English: Adriatic Energy Corporation), the electricity supply and distribution monopoly in northeastern Italy, which was owned by Giuseppe Volpi di Misurata. In 1962 the dam was nationalized and came under the control of ENEL as part of the Italian Ministry for Public Works. It was described as 'the tallest dam in the world', intended to meet the growing demands of industrialization, and as of 2010 is still one of the tallest in the world.

On 9 October 1963, during initial filling, a massive landslide caused a man-made megatsunami in the lake in which 50 million cubic metres of water overtopped the dam in a 250 metres (820 ft) wave, leading to the complete destruction of several villages and towns, and 1,917 deaths. This event occurred when the company and the Italian government dismissed evidence and concealed reports describing the geological instability of Monte Toc on the southern side of the basin, and other early warning signs reported prior to the disaster. Numerous warnings, signs of danger, and negative appraisals had been disregarded, and the eventual attempt to safely control the landslide into the lake by lowering its level came when the landslide was almost imminent and was too late to prevent it. Although the dam itself remained almost intact, and two thirds of the water was retained behind it, the landslide was much larger than expected and the impact brought massive flooding and destruction to the Piave valley below. Although the wave only contained a third of the dam's contents, it was still ten times higher than calculations had predicted.

Wave base

The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.

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