Volcanic Tsunamis
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A volcanic tsunami, also called a volcanogenic tsunami, is a
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
produced by volcanic phenomena. About 20–25% of all fatalities at volcanoes during the past 250 years have been caused by volcanic tsunamis. The most devastating volcanic tsunami in recorded history was that produced by the
1883 eruption of Krakatoa The 1883 eruption of Krakatoa ( id, Letusan Krakatau 1883) in the Sunda Strait occurred from 20 May until 21 October 1883, peaking in the late morning hours of 27 August when over 70% of the island of Krakatoa and its surrounding archipelago w ...
. The waves reached heights of and killed 36,000 people.


Causes

A wide variety of volcanic processes can produce tsunamis. This includes volcanic earthquakes,
caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber ...
collapse, explosive submarine eruptions, the effects of pyroclastic flows and lahars on water, base surges with accompanying
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
s,
lava Lava is molten or partially molten rock ( magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...
avalanching into the sea, air waves from explosive subaerial eruptions, avalanches of cold rock, and avalanches of hot material. Volcanic tsunamis produced by large lateral collapse
landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...
s and ocean-entering pyroclastic flows are the largest and most hazardous.


Volcanic eruptions

Pyroclastic flows can cause tsunamis as a result of them interacting with waterbodies, although the conditions required to generate a tsunami and the mechanisms of interaction between pyroclastic flows and water remain partially elusive. This is because theoretical studies of this complex phenomenon are rare and observations by the scientific community are scarce. It has been demonstrated by Watts and Waythomas (2003) that the dense, basal
debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented Rock (geology), rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. ...
component of a pyroclastic flow produces the most energetic and coherent water waves. Smaller waves are theoretically generated by pressure impulses and steam explosions, as well as flow pressure and shear. Discharge rate, transport distance from a volcanic vent, angle of incidence, bulk density of the flow and its preservation or disaggregation underwater are important parameters controlling the interactions between pyroclastic flows and bodies of water. Pyroclastic flow-induced tsunamis occurred during the 1815 eruption of Mount Tambora, the 1871 eruption of Mount Ruang, the 1883 eruption of Krakatoa, the 1902 eruption of Mount Pelée and the 1994 eruption of Rabaul Volcano. Tsunamis generated by underwater volcanic explosions depend on the energy and water depth of the explosion. An underwater explosion resulting in the formation of a crater can cause subsequent expansion, rise and gravitational collapse to create tidal bores as well as smaller waves. Most waves caused by underwater volcanic explosions have small amplitudes, an exception being those produced by the 1996 eruption of Karymsky Lake in Russia which reached heights of up to or more. Although underwater volcanic explosions can generate tsunamis, many are not tsunamigenic. This is especially true for Surtseyan-type phreatomagmatic eruptions, which are the result of complex
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
-water interactions. Potentially more tsunamigenic are violent steam explosions that result in the formation of maars and tuff rings. Tsunamis produced by volcanic shock waves is a rare phenomenon, involving pressure from an explosive eruption that must be high enough to excite free waves in the atmosphere. Such volcanic tsunamis took place during the 1883 eruption of Krakatoa, the 1956 eruption of Bezymianny and the 2022 eruption of Hunga Tonga–Hunga Ha'apai. Shock wave-induced volcanic tsunamis may have also occurred during the Hatepe eruption of Taupō Volcano around 200 CE. Underwater caldera collapse resulting from large explosive eruptions can cause tsunamis due to subsidence of the water surface. Volcanic tsunamis caused by caldera collapse may have occurred during the
Minoan eruption The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera (also called Santorini) circa 1600 BCE. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on nea ...
of
Santorini Santorini ( el, Σαντορίνη, ), officially Thira (Greek: Θήρα ) and classical Greek Thera ( English pronunciation ), is an island in the southern Aegean Sea, about 200 km (120 mi) southeast from the Greek mainland. It is th ...
in 1638 BC, the 1650 eruption of Kolumbo and the 1883 eruption of Krakatoa.


Volcanic earthquakes

Tsunamis caused by earthquakes preceding or during volcanic eruptions are poorly documented. Such earthquakes can be volcano-tectonic or purely tectonic in origin. Volcano-tectonic earthquakes are caused by the movement of magma beneath the surface, which results in pressure changes where the rock around the magma has experienced stress. They occur as earthquake swarms and are capable of producing small-magnitude tsunamis. Volcano-tectonic earthquakes typically have magnitudes of less than 6 on the surface-wave scale and often precede volcanic eruptions. The 1878 and 1937 eruptions of Rabaul Volcano in Papua New Guinea were reportedly preceded by tsunamis caused by an initial earthquake. Tsunamis caused by volcano-tectonic earthquakes have also occurred at Mount Yasur in 1878, Mount Okmok in 1878 and
Kharimkotan Kharimkotan (russian: Харимкотан); Japanese 春牟古丹島; Harimukotan-tō, alternatively Harumukotan-tō or 加林古丹島; Karinkotan-tō) is an uninhabited volcanic island located from Onekotan near the northern end of the K ...
in 1933. Earthquakes caused by tectonic processes at volcanoes are also known to cause tsunamis. Such earthquakes can reach magnitudes greater than 6 and may occur on large
thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...
s at the base of volcanic edifices. For example, a Ms 7.2 earthquake in
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...
associated with large-scale
slumping Slumping is a technique in which items are made in a kiln by means of shaping glass over molds at high temperatures. The slumping of a pyrometric cone is often used to measure temperature in a kiln. Technique Slumping glass is a highly techni ...
of
Kīlauea Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. Located along the southeastern shore of the Big Island of Hawaii, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago. Hi ...
's southern submarine flank caused the 1975 Kalapana tsunami.


Slope instabilities

The slopes of many volcanoes are naturally unstable due to magmatic intrusions, structural discontinuities, high lava accumulation rates and hydrothermal alteration. Slope failures of volcanic edifices produce a wide spectrum of instability phenomena ranging from
rockfall A rockfall or rock-fallWhittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, 1984. . is a quantity/sheets of rock that has fallen freely from a cliff face. The term is also used for collapse of rock from roof or walls of mi ...
s and small landslides to large debris avalanches. The impact of debris sweeping into a waterbody can produce an impulsive wave which then propagates away from the source. Slope instabilities at volcanoes have accounted for 1% of tsunamis observed since the 17th century. Tsunamis caused by slope instabilities occurred at
Hokkaido Koma-ga-take , also , , or just is a andesitic stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are chara ...
in 1640, Mount Unzen in 1792, Augustine Volcano in 1883, Ritter Island in
1888 In Germany, 1888 is known as the Year of the Three Emperors. Currently, it is the year that, when written in Roman numerals, has the most digits (13). The next year that also has 13 digits is the year 2388. The record will be surpassed as late ...
, Paluweh in 1928,
Iliwerung Iliwerung or Illiwerung is a complex volcano forming a prominent south-facing peninsula on Lembata Island in southern Indonesia. It contains north-south and northwest-southeast trending lines of craters and lava domes, with the summit dome having ...
in 1979, Mount St. Helens in 1980,
Vulcano Vulcano ( scn, Vurcanu) or Vulcan is a small volcanic island belonging to Italy in the Tyrrhenian Sea, about north of Sicily and located at the southernmost end of the seven Aeolian Islands. The island is known for its volcanic activity and c ...
in 1988, Stromboli in 2002 and Anak Krakatoa in 2018. Some geologists claim that large landslides from volcanic islands may be able to generate megatsunamis that can cross oceans, e.g. Cumbre Vieja on
La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...
(
Cumbre Vieja tsunami hazard 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. Volcanic islands and volcanoes on land frequently undergo large landslides/collapses, which have been do ...
) in the
Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Mo ...
, but this is disputed by many others.


See also

*
List of natural disasters by death toll A natural disaster is a sudden event that always causes widespread destruction, major collateral damage or loss of life, brought about by forces other than the acts of human beings. A natural disaster might be caused by earthquakes, flooding, vo ...
* List of tsunamis * Tsunamis in lakes


References

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