Eruptive history of Usu volcano, Japan

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K03983
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17030:Human geosciences-related
• Research Institution: Muroran Institute of Technology
• Principal Investigator: Goto Yoshihiko 室蘭工業大学, 大学院工学研究科, 准教授 (20221252)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 有珠山 / 山体崩壊 / 洞爺カルデラ / 噴火史 / 防災

Outline of Final Research Achievements

Usu is a Quaternary basaltic to andesitic stratovolcano that has an amphitheater at the summit. The eruptive history of Usu as follows: (1) andesitic explosive eruption at 19 ka, (2) stratovolcano growth between 18 and 16 ka, (3) sector collapse at 16 ka, (4) hiatus in volcanic activity for 15,000 years, (5) rhyolitic Plinian eruption in AD 1663, and (6) dacitic dome-forming eruptions after AD 1663. This eruptive history indicates that the sector collapse occurred within ~3000 years of the onset of stratovolcano growth, much sooner than at other volcanoes where the timing of sector collapse is known. We infer that the sector collapse of such a young volcanic edifice was caused by a combination of dome-like uplifting/tilting (forced folding) of soft substratum, overloading of the volcanic edifice on the soft substratum, a NE-SW-trending fault system that deeply cuts the substratum, and possible magma intrusion within the edifice and associated earthquakes.

Free Research Field

火山地質学

Academic Significance and Societal Importance of the Research Achievements

有珠山の形成史と洞爺カルデラに関する多くの新知見が得られ，学術的な意義は大きい．有珠山は1万9千年前に活動を開始し，安山岩質成層火山を形成した後，約3000年以内に山体崩壊した．有珠山の崩壊は，有珠山の基盤をなす洞爺火砕流堆積物が脆弱であり，その上に成層火山が形成されていることに起因する．また，有珠山の東丸山潜在ドームが1663年の寛文噴火で形成されたことを解明できた．本研究は有珠山の防災を進める上で極めて重要である．洞爺カルデラ全体では，洞爺火砕流堆積物の下位から未知の火砕流堆積物を発見し立香火砕流堆積物と命名した．この立香火砕流堆積物は洞爺カルデラの長期的な進化を考える上で重要である．