Akahoya Ash-A Holocene Widespread Tephra Erupted from the Kikai Caldera, South Kyushu, Japan

Machida, Hiroshi; Arai, Fusao

doi:10.4116/jaqua.17.143

Cited by 129 publications

(43 citation statements)

References 3 publications

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“…In the base of the Koya-Takeshima ignimbrite in Satsuma Iwojima, poorly vesicular obsidian clasts, bombs with chilled cracks, and boulders are included. In addition, in southern Kyushu, there are armored lapilli and accretionary lapilli concentrated at the base of co-ignimbrite ash-fall deposits (Machida and Arai, 1978). This evidence indicates that magma-water interactions have occurred during the climactic pyroclastic flow phase (Maeno, 2006) (Fig.…”

Section: Interpretation Of Tsunami Traces In Each Coastalmentioning

confidence: 85%

“…The intraplinian phase and climactic ignimbrite phase were thought to be accompanied with phreatomagmatic explosions (Maeno, 2006;Maeno and Taniguchi, submitted). The topmost layer is composed of more than 100 km 3 of co-ignimbrite ash-fall deposits (Akahoya Ash; Machida and Arai, 1978), which are widely dispersed throughout Japan and are of a critical age for understanding the environmental changes associated with postglacial sea-level changes (Arai et al, 1981). The sea level in this area at the time of the eruption was almost the same as at present (Ōki, 2002).…”

Section: Geological Setting and The 73 Ka Eruptionmentioning

confidence: 99%

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Numerical simulation of tsunamis generated by caldera collapse during the 7.3 ka Kikai eruption, Kyushu, Japan

2006

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The relationship between tsunamis and scales of caldera collapse during a 7.3 ka eruption of the Kikai volcano were numerically investigated, and a hypothetical caldera collapse scale was established. Wave height, arrival time, and run-up height and distance were determined at some locations along the coastline around Kikai caldera, using non-linear long-wave equations and caldera collapse models using parameters showing the difference in geometry between pre-and post-collapse and the collapse duration. Whether tsunamis become large and inundations occur in coasts is estimated by the dimensionless collapse speed. Computed tsunamis were then compared with geological characteristics found in coasts. The lack of evidence of tsunami inundation at Nejime, 65 km from the caldera, suggests that any tsunamis were small; indicating that the upper limit of dimensionless caldera collapse speed was 0.01. On the other hand, on the coast of the Satsuma Peninsula, 50 km from the caldera, geological characteristics suggests that tsunamis did not inundate, or that even if tsunamis inundated the area, the traces of a tsunami have been eroded by a climactic pyroclastic flow or the tsunami itself and they have not been left. In numerical computations, when a dimensionless caldera collapse speed is more than 0.003, tsunami can inundate this area.

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Section: Interpretation Of Tsunami Traces In Each Coastalmentioning

confidence: 85%

Section: Geological Setting and The 73 Ka Eruptionmentioning

confidence: 99%

Numerical simulation of tsunamis generated by caldera collapse during the 7.3 ka Kikai eruption, Kyushu, Japan

2006

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“…These layers are dated as 7.3 and 28.5 kya, and coincide with major eruption events recorded in the northern volcanoes of Kikai and Aira on Kyushu Island, Japan (Machida and Arai 1976;Machida and Arai 1978;Machida 1999;Machida 2002). …”

Section: Core Descriptions and Age Modelsmentioning

confidence: 99%

Millennial-Scale Planktic Foraminifer Faunal Variability in the East China Sea during the Past 40000 Years (IMAGES MD012404 from the Okinawa Trough)

Chang¹,

Wang²,

Yokoyama³

et al. 2008

Terr. Atmos. Ocean. Sci.

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High resolution planktic foraminifer fauna assemblage data are used to reconstruct the millennial-scale sea surface temperature (SST) variability of the past 40000 years at an IMAGES core site (MD012404) in the Okinawa Trough in the East China Sea (ECS). The fauna assemblages in core MD012404 are dominated by five species -Globigerinoides ruber, Globigerina bulloides, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globigerinita glutinata, which account for > 70% in relative abundance. Our Q-mode factor analysis decomposed the fauna abundance data into three factors, which indicate cold water mass, warm water mass, and possibly coastal water flow with low salinity in the ECS. The MD012404 fauna data show abrupt changes at~16 kya, suggesting a return to a warmer climate or warm water intrusion of the Kuroshio into the Okinawa Trough since the Last Glacial Maximum (LGM). SST estimates based on the fauna assemblages of planktic foraminifers indicate a LGM cooling of 1 -2°C. A maximum cooling by 3 -4°C is observed in episodic, millennial-scale events in the glacial stages of the record. The SST record displays variability that closely tracks the structure of oxygen isotopes of stalagmites from Hulu Cave and ice cores from GISP 2 Dansgaard/Oeschger cycles and Heinrich events. Low salinity in the ECS is inferred based on MD012404 fauna SST and planktic foraminifer oxygen isotope records for the cold millennial-scale intervals, pointing to the Intertropical Convergence Zone (ITCZ) and/or East Asian monsoon as important factors driving SST and salinity in the subtropical western Pacific, both on orbital and suborbital time scales.

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“…Pyroclastic products of the caldera-forming eruption (Koabiyama and Takeshima pyroclastic ow deposits) are preserved in the northwest part of the island. The eruption that accompanied the Takeshima pyroclastic deposit also ejected "Akahoya" about 6300 years ago, a well-known ne air-fall ash that is used as a standard tephra in Japan (Machida and Arai, 1978). Post-caldera units include the basaltic Inamuradake volcano and rhyolitic Iwodake volcano.…”

Section: Geological Settingmentioning

confidence: 99%

Volcanic-related alteration and geochemistry of Iwodake volcano, Satsuma-Iwojima, Kyushu, SW Japan

Hamasaki

2014

Earth Planet Sp

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Satsuma-Iwojima is located near the northwestern margin of Kikai caldera, and active Mt. Iwodake is one of the post-caldera cones. Inside the summit crater of about 300 m diameter and 50 m depth, volcanic gas with maximum temperature >800• C is discharged. At Iwodake, the rhyolite is strongly altered by volcanic vapor and acid hydrothermal solution inside and around the summit crater. The main alteration mineral assemblages at surface include quartz-tridymite-cristobalite, tridymite-cristobalite-alunite and cristobalite-(alunite) inside the summit crater and on the ank. Molybdenum blue sublimates are forming at the surface around high-temperature fumaroles inside the summit crater. The ground surface is commonly cemented by amorphous silica or cristobalite. The original rhyolite with SiO 2 = 71-72 wt% has been leached, resulting in a rock with maximum SiO 2 = 97 wt%. All major elements are leached except for TiO 2 . Although LIL (large-ion lithophile) elements have leached, HFS (high eld-strength) elements appear to be immobile. Rare earth elements are considered to have been soluble as a complex with sulfate mainly in the low pH hydrothermal uid during the silici cation of the rhyolite. There is abundant Mo, Pb, Zn, Bi, Sn and much lower As in the volcanic sublimates and altered rocks inside the summit crater. By contrast, the rocks near the acid springs at the foot of the cone are As-rich, but with lower Pb, Zn, Bi and little Mo in comparison with the summit. The fractures and fumarole locations around Iwodake summit and erosional ridges on the anks re ects a NE-SW trend that is parallel to the trace of the outer ring of Kikai caldera. In addition, this is the same direction as the alignment of Shin-Iwojima, Iwodake and Inamuradake, all of which are post-caldera cones. Zones of structural weakness parallel to the caldera rim may exist, acting as pathways for the ascending volcanic gases and hydrothermal solutions. Fumarolic activity appears to be shifting gradually to the eastern part of the summit crater.

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Akahoya Ash-A Holocene Widespread Tephra Erupted from the Kikai Caldera, South Kyushu, Japan

Cited by 129 publications

References 3 publications

Numerical simulation of tsunamis generated by caldera collapse during the 7.3 ka Kikai eruption, Kyushu, Japan

Numerical simulation of tsunamis generated by caldera collapse during the 7.3 ka Kikai eruption, Kyushu, Japan

Millennial-Scale Planktic Foraminifer Faunal Variability in the East China Sea during the Past 40000 Years (IMAGES MD012404 from the Okinawa Trough)

Volcanic-related alteration and geochemistry of Iwodake volcano, Satsuma-Iwojima, Kyushu, SW Japan

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