ABSTRACT

Drifting pumices provide important clues for determining the activity of submarine volcanoes. On October 8, 2023, a tsunami hypothetically caused by a submarine eruption occurred near Izu-Torishima in the Izu-Bonin Arc. Later that month, two types of drifting pumice, white and gray, were found floating on the sea surface west of Izu-Torishima. The white pumices were also found on the coast of Izu-Torishima. The textural and geochemical characteristics of the gray pumice clasts indicate they were derived from the 2021 eruption of Fukutoku-Oka-no-Ba. The white pumice clasts have angular to subangular shapes with little evidence of abrasion. They contain plagioclase, pyroxenes, and Fe-Ti oxides as phenocrysts, and typically include dark enclaves. The composition of the white pumices is rhyolite to dacite, and their trace element characteristics resemble those of volcanic products from the back-arc rift zone of the Izu-Bonin Arc. These pumices are potentially associated with a recent submarine eruption in the back-arc region of the Izu-Bonin Arc.