Tsunamis of volcanic origin: Summary of causes, with particular reference to Krakatoa, 1883
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Submarine volcano
Caldera
Phreatomagmatic eruption
Submarine landslide
Peléan eruption
Vulcanian eruption
The Kikai caldera volcano located under water in East China Sea is one of the most gigantic calderas in southern Kyushu. At the caldera, a violent eruption occurred from the submarine vent, at ca. 70-80 ka. The eruption is interpreted to have been phreatomagmatic throughout. Each eruptive phase of the eruption sequence generated its own characteristic deposits. The sequence of the events can be summarized as fallows ; (1) a small phreatomagmatic eruption, which generated the fine grained ash including accretionary lapilli, (2) the catastrophic pyroclastic-flow eruption, which formed a large-scale pyroclastic flow (the Nagase pyroclastic flow), two pyroclastic surges (Nishinoomote-1 member : Ns-1, Nishinoomote-3 member : Ns-3), and a wide-spread co-ignimbrite ash fall (Nishinoomote-2 member : Ns-2).The Nagase pyroclastic flow came down from the rim of the caldera, and entered the sea. Then, the flow body, which included a large amount of large pumice blocks and heavy lithic fragments, was disintegrated as gas-particle flow by violent phreatomagmatic explosions, or continued subaqueously as water-supported mass flow. Dilute and fine-particle-rich pyroclastic surges, probably with a density much less than that of water, 1.0 g/cm3, generated off the top or head of subaerial Nagase pyroclastic flow. They could cross on the smooth surface of the sea, becoming water-cooled, vaporish and depleted in large clasts which dropped into the sea. Eventually, the cool and wet pyroclastic surges attacked the islands around the caldera, and deposited as Ns-1 and Ns-3.Ns-2 co-ignimbrite ash fall, composing of glass shards were generated from the upper convective part of the eruption column of the Nagase pyroclastic flow. Included accretionary lapilli indicate that the eruption column was very moisture because of much sea water flash-out subaerially for very violent explosions from the submarine vent. Ns-2 is probably correlated with the Kikai-Tozurahara ash which was found in central Japan more than 500 km off the source.
Phreatomagmatic eruption
Pyroclastic fall
Peléan eruption
Caldera
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Phreatomagmatic eruption
Peléan eruption
Dense-rock equivalent
Volcanic hazards
Effusive eruption
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Phreatic eruption
Caldera
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The mechanisms controlling the transport of pyroclasts in a plinian-type eruption column are discussed. An estimate is made of the density of the magmatic gas in the vent, and initial (‘muzzle’) velocities are deduced for 18 eruptions using the a real distribution of pyroclasts in the resulting air-fall deposits. A model of the physical properties of the lower part of an eruption column is presented, and used to deduce the heights to which plinian eruption columns should commonly extend. It is demonstrated that column collapse to form ignimbrites may be a common result of the change, with time, of the volatile content of the erupted material as progressively deeper levels in a magma chamber are tapped. Vent radii are estimated for those eruptions for which the duration of the eruption is known.
Peléan eruption
Phreatomagmatic eruption
Vulcanian eruption
Pyroclastic fall
Dense-rock equivalent
Effusive eruption
Magma chamber
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A Classic Period agricultural village in El Salvador was partially destroyed and encased in pyroclastic debris during the eruption of Loma Caldera about A.D. 590. The eruption was phreatomagmatic in nature, depositing alternating units of “muddy” pyroclastic surge beds and units of air fall lapilli, pumice, and volcanic bombs. This ephemeral eruptive left only a partially eroded collapsed tephra ring. The eruption began with earth tremors and possible steam explosions, giving enough warning to allow the inhabitants of the nearby village to flee, but violent enough that they left behind many of their most valuable personal items. The low temperature of wet ash surge units, which were likely emplaced as “ash hurricanes,” preserved much of the vegetation and other botanical remains surrounding the village. Analysis of the maturity of maize preserved in agricultural fields, and the presence or absence of blossoming and fruiting plants indicates that the eruption occurred in the mid-rainy season, probably late August or September. The placement of artifacts within buildings indicate that the eruption occurred in the early evening, after the inhabitants had returned from their agricultural fields and eaten an evening meal, but before retiring for the night. Although the exact year of the eruption can only be estimated within the uncertainty of radiocarbon dating, the season of the year and the time of day can be identified with unusual precision. © 1996 John Wiley & Sons, Inc.
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Volcanic ash
Phreatomagmatic eruption
Phreatic eruption
Subaerial
Vulcanian eruption
Volcanic hazards
Peléan eruption
Effusive eruption
Dense-rock equivalent
Submarine volcano
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The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production.
Pumice
Submarine volcano
Effusive eruption
Dense-rock equivalent
Silicic
Vulcanian eruption
Peléan eruption
Seafloor Spreading
Lateral eruption
Volcanology
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The climactic phase of the 2011 eruption at Shinmoe-dake was a mixture of subplinian and vulcanian eruptive events, successive lava accumulation (lava dome) within the crater, and repetition of vulcanian events after the dome growth. It was preceded by inflation and elevated seismicity for about one year and by phreatomagmatic explosions of one week before. Small pyroclastic flows and ash-cloud surges formed during the subplinian events, when the eruption column reached the highest level and the vent was widened. A lava dome, which was extruded close to the vent of subplinian events, grew by swelling upward and filling the crater. After the vent was covered by the lava, an intense vulcanian event occurred from the base of the dome and the swelled dome became deflated. After that, vulcanian events were repeated for three months. Simultaneous eruption styles in the crater (vulcanian events, continuous ash emission and dome growth) and some phreatomagmatic events in the vulcanian stage probably are due to a complex upper-conduit system developed in water-saturated country rock.
Phreatomagmatic eruption
Lava dome
Strombolian eruption
Vulcanian eruption
Dome (geology)
Effusive eruption
Peléan eruption
Phreatic eruption
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