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 tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquakes and the subsequent rise or fall in the sea floor 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 run-up height of around 30m (100feet) in the cases of the most powerful earthquakes.[1] By contrast, megatsunamis occur when a large amount of material suddenly falls into water or anywhere near water (such as via a landslide, meteor impact, or volcanic eruption). They can have extremely large initial wave heights in the hundreds of metres, far beyond the height of any ordinary tsunami. These giant wave heights occur because the water is "splashed" upwards and outwards by the displacement.
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 524m (1,719feet)), and 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.
A megatsunami is a tsunami with an initial wave amplitude (height) measured in many tens or hundreds of metres. 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 30cm (10inches) 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 .[2] [3]
By contrast, megatsunamis are caused by landslides and other impact events 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 earthquakes or volcanic eruptions do not normally generate megatsunamis, but landslides 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.[4]
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 "run-up height" can be several times larger than the wave's height just before reaching shore.[5] While there is currently no minimum or average height classification for megatsunamis that is broadly accepted by the scientific community, the limited number of observed megatsunami events in recent history have all had run-up heights that exceeded 100m (300feet). The megatsunami in Spirit Lake, Washington, USA that was caused by the 1980 eruption of Mount St. Helens reached 853feet, while the tallest megatsunami ever recorded (Lituya Bay in 1958) reached a run-up height of 1720feet.[6] It is also possible that much larger megatsunamis occurred in prehistory; researchers analyzing the geological structures left behind by prehistoric asteroid impacts have suggested that these events could have resulted in megatsunamis that exceeded 1500metres in height.[7]
See main article: 1958 Lituya Bay earthquake and 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. 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, 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 July 9, 1958, a 7.8 strike-slip earthquake in southeast Alaska caused 90000000ST 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 520m (1,710feet), 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.
The mechanism giving rise to megatsunamis was analysed for the Lituya Bay event in a study presented at the Tsunami Society in 1999;[8] 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. 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:
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.[9]
See main article: Minoan eruption.
See main article: 1674 Ambon earthquake and megatsunami. On February 17, 1674, between 19:30 and 20:00 local time, an earthquake struck the Maluku Islands. Ambon Island received run-up heights of 100m (300feet), 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.[41]
At 10:00 p.m. on January 8, 1731, a landslide with a volume of possibly 6000000m2 fell from the mountain Skafjell from a height of 500m (1,600feet) into the Storfjorden opposite Stranda, Norway. The slide generated a megatsunami 30m (100feet) in height that struck Stranda, flooding the area for 100m (300feet) inland and destroying the church and all but two boathouses, as well as many boats. Damaging waves struck as far away as Ørskog. The waves killed 17 people.[42]
See main article: 1741 eruption of Oshima–Ōshima and the Kampo tsunami. An eruption of Oshima-Ōshima occurred that lasted from 18 August 1741 to 1 May 1742. On 29 August 1741, a devastating tsunami occurred.[43] It killed at least 1,467 people along a 120km (80miles) section of the coast, excluding native residents whose deaths were not recorded. Wave heights for Gankakezawa have been estimated at 34m (112feet) based on oral histories, while an estimate of is derived from written records. At Sado Island, over 350km (220miles) away, a wave height of 2to has been estimated based on descriptions of the damage, while oral records suggest a height of 8m (26feet). Wave heights have been estimated at 3to even as far away as the Korean Peninsula.[44] 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.[45] [46] [47] [48] The event reduced the elevation of the peak of Hishiyama from 850mto722mm (2,790feetto2,369feetm). An estimated 2.4km3 section of the volcano collapsed onto the seafloor north of the island; the collapse was similar in size to the 2.3km3 collapse which occurred during the 1980 eruption of Mount St. Helens.[49]
Just before 8:00 p.m. on February 22, 1756, a landslide with a volume of 12000000m215000000m2 travelled at high speed from a height of 400m (1,300feet) on the side of the mountain Tjellafjellet into the Langfjorden about 1km (01miles) west of Tjelle, Norway, between Tjelle and Gramsgrø. The slide generated three megatsunamis in the Langfjorden and the Eresfjorden with heights of 40mto50mm (130feetto160feetm). The waves flooded the shore for 200m (700feet) inland in some areas, destroying farms and other inhabited areas. Damaging waves struck as far away as Veøy, 25km (16miles) from the landslide – where they washed inland 20m (70feet) above normal flood levels – and Gjermundnes, 40km (30miles) from the slide. The waves killed 32 people and destroyed 168 buildings, 196 boats, large amounts of forest, and roads and boat landings.[50]
See main article: 1792 Unzen landslide and tsunami. 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 100m (300feet), but when they hit the other side of Ariake Bay, they were only 10mto20mm (30feetto70feetm) in height, though one location received 57m (187feet) waves due to seafloor 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.[51]
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 run-up height of 120m (390feet), flooding the coast of the bay up to 750feet inland.[52]
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 run-up height of 800NaN0, flooding the coast of the bay up to 21000NaN0 inland.[53]
The massive explosion 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.[54] 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.[55] Groups of human skeletons were found floating on pumice numerous times, up to a year after the event.[56] The eruption also generated what is often called the loudest sound in history, which was heard 4800km (3,000miles) away on Rodrigues in the Indian Ocean.
On January 15, 1905, a landslide on the slope of the mountain Ramnefjellet with a volume of 350000m2 fell from a height of 500m (1,600feet) into the southern end of the lake Lovatnet in Norway, generating three megatsunamis of up to 40.5m (132.9feet) 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 boathouses, and 70 to 80 boats, one of which – the tourist boat Lodalen – was thrown 300m (1,000feet) inland by the last wave and wrecked. At the northern end of the 11.71NaN1 long lake, a wave measured at almost 6m (20feet) destroyed a bridge.[57]
On July 4, 1905, an overhanging glacier – since known as the Fallen Glacier – broke loose, slid out of its valley, and fell 1000sigfig=1NaNsigfig=1 down a steep slope into Disenchantment Bay in Alaska, clearing vegetation along a path 0.51NaN1 wide. When it entered the water, it generated a megatsunami which broke tree branches 1100NaN0 above ground level 0.51NaN1 away. The wave killed vegetation to a height of 650NaN0 at a distance of 30NaN0 from the landslide, and it reached heights of 50to at different locations on the coast of Haenke Island. At a distance of 150NaN0 from the slide, observers at Russell Fjord reported a series of large waves that caused the water level to rise and fall 15to for a half-hour.[58]
On April 7, 1934, a landslide on the slope of the mountain Langhamaren with a volume of 3000000m2 fell from a height of about 730m (2,400feet) into the Tafjorden in Norway, generating three megatsunamis, the last and largest of which reached a height of between 62and on the opposite shore. Large waves struck Tafjord and Fjørå. At Tafjord, the last and largest wave was 17m (56feet) tall and struck at an estimated speed of 160kph, flooding the town for 300m (1,000feet) inland and killing 23 people. At Fjørå, waves reached 13m (43feet), destroyed buildings, removed all soil, and killed 17 people. Damaging waves struck as far as 50km (30miles) away, and waves were detected at a distance of 100km (100miles) from the landslide. One survivor suffered serious injuries requiring hospitalization.[59]
On September 13, 1936, a landslide on the slope of the mountain Ramnefjellet with a volume of 1000000m2 fell from a height of 800m (2,600feet) into the southern end of the lake Lovatnet in Norway, generating three megatsunamis, the largest of which reached a height of 74m (243feet). 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 grain mills, a restaurant, a schoolhouse, and all boats on the lake. A 12.60NaN0 wave struck the southern end of the 11.71NaN1 long lake and caused damaging flooding in the Loelva River, the lake's northern outlet. The waves killed 74 people and severely injured 11.[57]
On October 27, 1936, a megatsunami occurred in Lituya Bay in Alaska with a maximum run-up height of 490feet 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 100and high. The maximum inundation distance was 2000feet inland along the north shore of the bay. The cause of the megatsunami remains unclear, but may have been a submarine landslide.[60]
See main article: 1958 Lituya Bay earthquake and megatsunami and Lituya Bay.
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 elevation of 520m (1,710feet) at the entrance of Gilbert Inlet.[61] The wave surged over the headland, stripping trees and soil down to bedrock, and surged along the fjord which forms Lituya Bay, destroying two fishing boats anchored there and killing two people.[62] This was the highest wave of any kind ever recorded. The subsequent study of this event led to the establishment of the term "megatsunami," to distinguish it from ordinary tsunamis.
See main article: Vajont Dam. On October 9, 1963, a landslide above Vajont Dam in Italy produced a 250m (820feet) 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.[63]
See main article: Spirit Lake (Washington), 1980 eruption of Mount St. Helens and Mount St. Helens. On May 18, 1980, the upper 400m (1,300feet) 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 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 260m (850feet) above the pre-eruption water level (about ASL). 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.[64]
On November 21, 2000, a landslide composed of 90000000m2 of rock with a mass of 260,000,000 tons fell from an elevation of 1000mto1400mm (3,000feetto4,600feetm) at Paatuut on the Nuussuaq Peninsula on the west coast of Greenland, reaching a speed of 140kph. About 30000000m2 of material with a mass of 87,000,000 tons entered Sullorsuaq Strait (known in Danish as Vaigat Strait), generating a megatsunami. The wave had a run-up height of 50m (160feet) near the landslide and 28m (92feet) at Qullissat, the site of an abandoned settlement across the strait on Disko Island, 20km (10miles) away, where it inundated the coast as far as 100m (300feet) 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.[65]
See main article: Icy Bay (Alaska).
At 8:19 p.m. Alaska Daylight Time on October 17, 2015, the side of a mountain collapsed, at the head of Taan Fiord, a finger of Icy Bay in Alaska.[66] [67] [68] Some of the resulting landslide came to rest on the toe of Tyndall Glacier,[66] [69] but about 180000000sigfig=3NaNsigfig=3 of rock with a volume of about 50000000m2 fell into the fjord.[68] [66] [70] [71] The landslide generated a megatsunami with an initial height of about 100abbr=offNaNabbr=off[69] [72] that struck the opposite shore of the fjord, with a run-up height there of 1930NaN0.[66] [67]
Over the next 12 minutes,[67] the wave travelled down the fjord at a speed of up to 60sigfig=2NaNsigfig=2,[71] with run-up heights of over 100m (300feet) in the upper fjord to between 30and or more in its middle section, and 20m (70feet) or more at its mouth.[66] [67] Still probably 40abbr=offNaNabbr=off tall when it entered Icy Bay,[72] the tsunami inundated parts of Icy Bay's shoreline with run-ups of 4to before dissipating into insignificance at distances of 5km (03miles) from the mouth of Taan Fiord,[67] although the wave was detected 1400NaN0 away.[66]
Occurring in an uninhabited area, the event was unwitnessed, and several hours passed before the signature of the landslide was noticed on seismographs at Columbia University in New York City.[67] [73]
On June 17, 2017, 35000000m258000000m2 of rock on the mountain Ummiammakku fell from an elevation of roughly 1000m (3,000feet) 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 100m (300feet) wave. The settlement of Nuugaatsiaq, away, saw 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 100km (100miles) away.[74] [75] [76] [77] [78]
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.[79]
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.[80] The size and power of a wave generated by such means could produce devastating effects, travelling across oceans and inundating up to 25km (16miles) inland from the coast. This research was later found to be flawed. 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.
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).[81]
See main article: Cumbre Vieja tsunami hazard.
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. Day and Ward hypothesize that if such an eruption causes the western flank to fail, a megatsunami could be generated.
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 2.5km (01.6miles) 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 2m (07feet) downwards and 1m (03feet) westwards towards the Atlantic Ocean.[82]
In 1971, an eruption occurred at the Teneguía vent at the southern end of the sub-aerial 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.[83]
Cumbre Vieja remained dormant until an eruption began on September 19, 2021.[84]
It is likely that several eruptions would be required before failure would occur on Cumbre Vieja. The western half of the volcano has an approximate volume of 500km3 and an estimated mass of 1.5e12MT. If it were to catastrophically slide into the ocean, it could generate a wave with an initial height of about at the island, and a likely height of around 50m (160feet) 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. The likelihood of this happening is a matter of vigorous debate.
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 nowthe region conjectured as prone to collapse is too small and too stable to collapse within the next 10,000 years.[85] A closer study of deposits left in the ocean from previous landslides suggests that a landslide would likely occur as a series of smaller collapses rather than a single landslide. 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 41to above sea level between 32,000 and 1.75 million years ago.[86] 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.[87] A 2008 study examined this scenario and concluded that while it could cause a megatsunami, it would be local to the Canary Islands and would diminish in height, becoming a smaller tsunami by the time it reached the continents as the waves interfered and spread across the oceans.[88]
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.[89] [90] [91] A tsunami event is also possible, with the tsunami potentially reaching up to about 1km (01miles) in height[92] According to the documentary National Geographic's Ultimate Disaster: Tsunami, if a big landslide occurred at Mauna Loa or the Hilina Slump, a 30m (100feet) 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 25km (16miles) inland. Also, the West Coast of America and the entire Pacific Rim could potentially be affected.
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."[93]
In the same article, geologist Mika McKinnon stated:[93]
Another volcanologist, Janine Krippner, added:[93]
Despite this, evidence suggests that catastrophic collapses do occur on Hawaiian volcanoes and generate local tsunamis.[94]
Although known earlier to the local population, a crack 2m (07feet) wide and 500m (1,600feet) in length in the side of the mountain Åkerneset in Norway was rediscovered in 1983 and attracted scientific attention. It since has widened at a rate of 4cm (02inches) per year. Geological analysis has revealed that a slab of rock 62m (203feet) thick and at an elevation stretching from 150to is in motion. Geologists assess that an eventual catastrophic collapse of 18000000m254000000m2 of rock into Sunnylvsfjorden is inevitable and could generate megatsunamis of 35to in height on the fjord′s opposite shore. The waves are expected to strike Hellesylt with a height of 35to, Geiranger with a height of 30to, Tafjord with a height of 14m (46feet), 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.[95]