[S-VC34] Volcanic and igneous activities, and these long-term forecasting

[SVC34-P12] The Holocene eruption history of Makushin Volcano, Unalaska Island, Aleutian Islands

Ryo Kataoka¹, *Eiichi Sato¹, Mitsuru Okuno², Toshio Nakamura³, Virginia Hatfield⁴ (1.Hokkaido University of Education at Asahikawa, 2.Osaka Metropolitan University, 3.Nagoya University, 4.Museum of the Aleutians)

Keywords:Aleutian Islands, Unalaska Island, Makushin Volcano, Eruption history

Unalaska Island is located in the eastern Aleutian Islands of Alaska. Makushin Volcano, which has a caldera (2.4 km x 3.2 km), is lacated on the north side of Unalaska Island. Makshin Volcano has erupted at least 26 times since 1768 (Miller et al., 1998), making it one of the most active volcanoes in the Aleutian Islands. The caldera of Makshin Volcano was formed at 8900 calBP (Bean, 1999), and small to medium-sized eruptions have occurred intermittently since the caldera formation. However, the eruption style and intervals of these eruptions are unclear. In this study, we conducted field surveys and collected volcanic ash samples to clarify the eruption history of Makshin Volcano during the Holocene. We conducted composition analysis, volcanic glass composition analysis, and ¹⁴C dating of the volcanic ashes. As a result, we found that Makshin Volcano has had at least 23 medium-sized eruptions in the last 10,000 years. Additionally, while the range of SiO₂ content in volcanic glass was wide from 10,000 to 7,000 years ago, the range of SiO₂ content became narrower from 7,000 years ago to the present, and the SiO₂ content has been trending downwards. From 10,000 to 7,000 years ago, high-SiO₂ magma and low-SiO₂ magma were mixed, but after 7,000 years ago, the high-SiO₂ magma was consumed, and activity transitioned to low-SiO₂ magma only.