Understanding of a tsunami generated by the 7.3 ka eruption of the Kikai caldera: geological record and numerical approach

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K14577
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Shinshu University
• Principal Investigator: Yamada Masaki 信州大学, 学術研究院理学系, 助教 (40806402)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 津波堆積物 / 鬼界アカホヤ噴火 / 火山性津波 / 大規模カルデラ / 津波シミュレーション / 火山ガラス含有率

Outline of Final Research Achievements

In this study, we inferred the tsunami factor associated with the 7.3 ka eruption of the Kikai caldera from stratigraphic relationship between the co-ignimbrite ash-fall deposit (K-Ah ash) and Akahoya tsunami deposit preserved in sediment cores at coastal lowlands far from the caldera. The presence of K-Ah volcanic glass beneath the sandy tsunami deposit in the sediment cores ensures that the K-Ah ash fell before the arrival of the tsunami. Considering that the ash, which takes longer to move than tsunami, reached these areas before or at the same time as the tsunami, it is inferred that the tsunami occurred at the end of the eruption process. Since caldera collapse occurred at the end of the eruption process, we suggest that the tsunami generated by this eruption was more likely to be mainly caused by caldera collapse.

Free Research Field

堆積学，自然災害科学

Academic Significance and Societal Importance of the Research Achievements

カルデラを形成するような破局噴火は極めて低頻度で発生するイベントであるため，実際に観測することは難しい．本研究では，7300年前の鬼界カルデラ噴火に伴って発生した巨大津波の発生要因を，堆積物コアに含まれる津波堆積物と火山灰の層序関係および津波数値計算から明らかにした．海底火山は世界中に多く存在しており，本研究の成果は浅海域で発生する破局噴火に伴う巨大津波のリスク評価に貢献すると言える．