Eruptive History of Ikeda Volcano, Ibusuki Area, Southern Kyushu, Japan(＜Special Section＞Determination of the Construction of an Outcrop Database to Reveal Eruptive History)

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  • INAKURA Hirohito
    Survey and Analysis Department, West Japan Engineering Consultants Incorporation
  • NARUO Hideto
    Takeokadai Senior High School
  • OKUNO Mitsuru
    Department of Earth System Science, Faculty of Science, Fukuoka University:AIG Collaborative Research Institute for International Study on Eruptive History and Informatics (ACRIFIS-EHAI), Fukuoka University
  • KOBAYASHI Tetsuo
    Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University

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Other Title
  • 南九州,池田火山の噴火史(＜特集＞火山噴火史解明のための露頭データベース構築の検討)
  • 南九州,池田火山の噴火史
  • ミナミキュウシュウ,イケダ カザン ノ フンカシ

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Abstract

We made a detailed geological study to understand the eruptive history of the Ikeda volcano, which includes the Ikeda caldera, maars and lava domes. The pre-caldera activity began at about 20 cal kBP with the Iwamoto ash fall deposit. The Senta lava was also effused before the Kikai-Akahoya tephra (7.3 cal kBP). The caldera-forming eruption began at 6.4 cal kBP with a phreatic explosion that produced the Ikezaki ash fall and surge deposits. This was soon followed by the magmatic eruptions that produced the Osagari and Mizusako scoria fall deposits and the Ikeda pumice fall deposit. During the climactic stage, the Ikeda ignimbrite was erupted and covered portions of the coastal area. Immediately after the caldera-forming event, four maars were formed along the fissure vent southeast of the caldera. The Yamagawa maar, which is the largest and is located at the southeastern end of the fissure vent, erupted a pumiceous base surge (the Yamagawa base surge), while the other maars ejected small amounts of accessory or accidental materials. During the late stage of the Ikeda eruption, a phreatomagmatic eruption occurred at the bottom of the caldera floor, which formed the widespread Ikedako ash fall deposit. The central lava dome was formed during the late stage of this eruption. After the Ikedako ash fall, secondary explosions of the Ikeda ignimbrite occurred mainly along the coastal area, generating small base surge deposits. About 2,000 years after the caldera-forming eruption at 4.8 cal kBP, new magmatic activity began on the margin of the caldera rim, and formed the Nabeshimadake lava dome.

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