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Outline of the 2022-2024 eruption at Ioto Island (Iwo-jima), Ogasawara, Japan : small subaqueous eruption associated with shallow magma intrusion towards theof caldera floor

Masashi Nagai 1, Takahiro Miwa1, Setsuya Nakada1, Hideki Ueda1, Hirochika Sumino2, Atsushi Yasuda3, Tomofumi Kozono1, Takashi Hirose4, Hiroki Minami5 and Tetsuo Kobayashi6

  • Affiliations: 1Research Division for Volcanic Disasters, National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan; 2Research Center for Advanced Science and Technology, the University of Tokyo, Tokyo, Japan; 3Earthquake Research Institute,The University of Tokyo, Tokyo, Japan; 4Graduate School of Science, Tohoku University, Sendai, Japan; 5Hydrographic and Oceanographic Department, Japan Coast Guard, Tokyo, Japan; 6Kagoshima University, Kagoshima, Japan

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 66

  • Programme No: 3.11.26

  • Theme 3 > Session 11

Abstract

Ioto Island is an active caldera volcano located in the Izu-Bonin-Mariana arc. Active uplift has continued since about 2011, suggesting that a shallow ring intrusioncontinues. From July 2022 to 2024, magma reached the seafloor off the coast of Okina-hama, resulting in frequent Surtseyan eruptions. While most eruptions occurred below sea level, a series of intense eruptions from late October to late November 2023 formed a new island. During this period, subaerial lava effusion accompanied by Vulcanian-like eruptions occurred briefly. The estimated eruption rate was relatively high at around 103 kg/s during island formation, compared to less than 102 kg/s during other periods. The whole-rock chemical composition of the essential materials was consistent, with a trachyte composition of about SiO2 = 61.3 wt%. The composition of quenched volcanic glass was in the range of SiO2 = 61.8-64.0 wt%, which tended to be low at the period of island formation. The eruption off Okina-hama, although small, showed a typical progression of shallow-water magma eruption. The estimated total erupted volume was only about 500,000 m3. Obvious crustal deformation, such as deflation, associated with the eruption was not detected. Therefore, the magma ascending to the shallow subsurface of the caldera was hardly consumed by the eruptions and continues to accumulate below. Temporal changes in the composition of volcanic glass indicate that crystallinity was lower when magma was erupted at higher rates. Under off Okina-hama conditions, monitoring the composition of volcanic glass in ejecta may allow us to estimate transitions in eruption rates.