Elucidation of occurrence conditions and disaster prediction of peculiar Plinian eruption that ejected a large amount of high-density basaltic pyroclastic material

Research Project

Project/Area Number	16K01315
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Natural disaster / Disaster prevention science
Research Institution	University of Toyama
Principal Investigator	Ishizaki Yasuo 富山大学, 学術研究部都市デザイン学系, 教授 (20272891)
Project Period (FY)	2016-04-01 – 2020-03-31
Project Status	Completed (Fiscal Year 2019)
Budget Amount *help	¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000) Fiscal Year 2018: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2017: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000) Fiscal Year 2016: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000)
Keywords	プリニー式噴火 / 玄武岩質火砕物 / マグマ溜り / 火砕物密度 / 災害予測 / 男体火山 / 玄武岩質マグマ / 玄武岩質プリニー式噴火 / 火山 / 防災
Outline of Final Research Achievements	The Plinian eruption that occurred about 30,000 years ago at Nantai Volcano was a peculiar eruption in which a large amount of high-density basaltic pyroclastic material erupted at the end of the eruption. Material elucidation of the ejecta of this eruption (Nt-Og tephra) revealed that (1) the magma reservoir before the eruption was a layered, and dacite magma, andesite magma, and basalt magma coexisted, and (2) each magma was formed by removal and addition of phenocryst minerals from a single parent magma with assimilation of granitic crustal material. There is no other example of a plinian eruption that ejected a large amount of high-density pyroclastic material such as Nt-Og. If a similar eruption occurs, serious human damage is highly likely to occur within 10 km downwind of the crater.
Academic Significance and Societal Importance of the Research Achievements	本課題では、高密度火砕物噴出型玄武岩質プリニー式噴火というこれまで報告例のない特異な噴火様式の実態を、主に噴出物の地質学的・岩石学的解析から明らかにした。この噴火様式では、火口の 10 km 以上遠方でも粗大な高密度火砕物が噴煙から降下することから、国内外の玄武岩質活火山でのプリニー式噴火堆積物の見直しやハザードマップの再検討などの波及効果が予想される。また、本課題で着目した、火砕物密度という新たなパラメータを用いることにより、従来の噴火様式分類を見直すきっかけになる可能性もある。