Study of flow mechanism of low-aspect ratio ignimbrite which swept away the Jomon culture in the Southern Kyushu, Japan

2015 Fiscal Year Final Research Report

• Project/Area Number: 25400485
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Kobe University
• Principal Investigator: Suzuki Keiko 神戸大学, 理学(系)研究科(研究院), 准教授 (20192544)
• Co-Investigator(Kenkyū-buntansha): TATSUMI Yoshiyuki 神戸大学, 海洋底探査センター, 教授 (40171722) ; SATO eiichi 神戸大学, 大学教育推進機構, 助教 (40609848)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 鬼界カルデラ / 幸屋火砕流 / 拡散型火砕流

Outline of Final Research Achievements

Koya low-aspect ratio ignimbrite sourced from Kikai caldera 7.3 ka and traveled across the sea to reach the adjacent islands and the mainland of south Kyushu 30-80 km distant. Proximal facies of Koya ignimbrite comprises three flow units with a maximum thickness of 30 m, but the distal deposits are consist of one flow unit and are very thin.
Koya ignimbrite are underlain by pumice-fall deposits and overlain by Akahoya ash. These pyroclastic units represent 7.3 ka Akahoya eruption from the Kikai caldera and commonly contains highly silicic glass shards and pumice of c. 75 wt% SiO2. Koya ignimbrite and Akahoya ash-fall deposit characteristically contain glass shards and pumice fragments of lower silica content down to c. 65 wt%. In addition to the silicic glass fragments, reflecting contribution this mafic component increases upwards from the basal to middle level of the deposit, and this vertical variation likely indicates progressive aggradation of pyroclasts.

Free Research Field

火山地質学