In total, volcanically generated tsunamis are responsible for about 20% of all fatalities related to volcanic eruptions. Other historically recorded examples include the 1929 Grand Banks earthquake, the 1958 Lituya Bay tsunami, a 2002 tsunami at Stromboli that caused severe damage to coastal settlements, the 1888 tsunami caused by the Ritter Island collapse which killed about 3000 people and is the largest historical tsunami-forming collapse with a volume of 5 cubic kilometres (1.2 cu mi), and the 1792 Shimabara collapse of Unzen volcano in Japan which claimed 4,000 or 14,538 victims. The possibility of a large collapse of this volcano causing a tsunami was known already before the 2018 event. The most recent such tsunami is the 2018 Sunda Strait tsunami, which was caused by a flank collapse of Anak Krakatau and caused at least 437 fatalities. The 1998 Papua New Guinea earthquake in particular drew attention to this hazard.
Large collapses on volcanoes have generated tsunamis, of which about 1% relates to volcanic collapse both small collapses and earthquake-linked landslides that took place in historical times generated tsunamis. Finally, the mechanical stability both of the volcanic edifice and the underlying basement and the influence of climate and sea level changes play a role in volcano stability. Shield volcanoes have different mechanical properties than stratovolcanoes as well as flatter slopes and undergo larger collapses than the latter. Periodic collapses have been found at some volcanoes, such as at Augustine and Volcan de Colima. Mechanisms that destabilize volcanic edifices to the point of collapse include inflation and deflation of magma chambers during the entry of new magma, intrusion of cryptodomes and dykes, and instability of slopes under loading from lava flows and oversteepened lava domes. Many processes are involved in the onset of volcano instability and the eventual failure of the edifice. The most recent such event took place at El Hierro 15,000 years ago and was later re-dated to have occurred between 87,000☘,000 (margin of uncertainty) and 39,000☑3,000 years ago. They do not appear to form through individual collapses multi-stage failures lasting hours or days appear to be more common as has been inferred from the patterns of landslide-generated turbidite deposits in the Agadir Basin north of the Canary Islands. They mostly take the form of debris flows with volumes of 50–200 cubic kilometres (12–48 cu mi) that emanate from an amphitheatre-shaped depression on the volcanic island and come to rest on the seafloor at 3,000–4,000 metres (9,800–13,100 ft) depth. Ī number of such landslides have been identified in the Canary Islands, especially in the more active volcanoes El Hierro, La Palma and Tenerife where about 14 such events are recorded through their deposits. In the Hawaiian Islands, collapses with volumes of over 5,000 cubic kilometres (1,200 cu mi) have been identified. As volcanoes grow in size they eventually become unstable and collapse, generating landslides and collapses such as the failure of Mount St. Giant landslides and collapses of ocean island volcanoes were first described in 1964 in Hawaii and are now known to happen in almost every ocean basin. Sector collapses and tsunamis caused by them
Other volcanoes across the world are at risk of causing such tsunamis. The recurrence rate of similar collapses is extremely low, about one every 100,000 years or less in the case of the Canary Islands. Evidence indicates that most collapses in the Canary Islands took place as multistage events that are not as effective at creating tsunamis, and a multi-stage collapse at La Palma likewise would result in smaller tsunamis. Later research has debated whether the tsunami would still have a significant size far away from La Palma, as the tsunami wave may quickly decay in height away from the source and interactions with the continental shelves could further reduce its size.
They estimated that such a collapse could cause tsunamis across the entire North Atlantic and severely impact areas as far away as North America. Ward and Simon Day in a 2001 research article proposed that a Holocene change in the eruptive activity of Cumbre Vieja volcano and a fracture on the volcano that formed during an eruption in 1949 may be the prelude to a giant collapse. A recent example is Anak Krakatau, which collapsed to cause the 2018 Sunda Strait tsunami.
Volcanic islands and volcanoes on land frequently undergo large landslides/collapses, which have been documented in Hawaii for example. The island of La Palma in the Canary Islands is at risk of undergoing a large landslide, which could cause a tsunami in the Atlantic Ocean. The island of La Palma in the Atlantic Ocean
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