5:15 PM - 7:15 PM
[SVC36-P06] Petrography of white pumice observed near Torishima and arrived at the Nansei Islands: Towards the comparison with the proximal deposits of the possible source region
Keywords:submarine volcano, drift pumice, research cruise, mafic enclave
On October 8, 2023, swarm earthquakes occurred at the Sofu Seamount near Izu-Torishima in the Izu-Ogasawara (Bonin) Arc, Japan, followed by tsunamis arriving at a wide area of the Pacific coast of SW Japan (e.g., [1-3]). Immediately after the earthquakes, on October 20, aerial observation by Japan Coast Guard identified floating pumice rafts extending ~80 km at the nearby area, which were subsequently collected and reported to be white-colored rhyolite containing dark-colored patches [4]. After this event, in the summer and autumn of 2024, stranding of white pumice, which can be clearly distinguished from the pre-existing gray and black pumice, was observed at coasts of the Nansei Islands and Izu-Ogasawara Islands.
We investigated newly-stranded white pumice clasts collected at Okinawa, Hahajima, and Chichijima. The studied pumice clasts were rhyolitic composition. Some pumice clasts showed microlite-free white matrix with gray-colored frothy patches (possibly equivalent to the dark-colored patches reported by AIST), whose petrological characteristics along with the trace element characteristics are identical to those studied by AIST. Additionally, black enclaves containing less-differentiated minerals (Ol, high-Mg Cpx, Ca-Pl) are newly identified, which could retain the information about the deep magma plumping system of the source volcano. These observations clearly show the drifting of considerable amount of the pumice from the southern Izu Islands to the Nansei Islands (possibly via Hahajima) despite the small size of the initial raft.
Quick bathymetric surveys revealed abrupt morphological change in the Sofu Seamount where the epicenter of the swarm earthquakes were concentrated, and indicated the volcanic activities as the source of earthquakes [3,5]. However, drift simulation indicated the pumice originated from the north of the Sofu Seamount and in the back-arc rift zone near Sumisujima [6].
To investigate the relationship between these geological phenomena and the surface-observed signature, JAMSTEC would perform a research cruise targeting direct sampling of the volcanic rocks around the Sofu Seamount in March 2025 using R/V Kaimei (KM25-02 Leg2). In the presentation, we will show preliminary results of the geological survey around the Sofu Seamount to compare the characteristics of white drift pumice described above.
Funding information: ERCA Environment Research and Technology Development Fund (JPMEERF20244002); MEXT Volcano Practical Human Resource Development Support Program Japan (JPJ202414); TMU Ogasawara Research Committee; AJG Disaster Geography Research Grant
References:
1 Mizutani & Melgar https://doi.org/10.26443/seismica.v2i2.1160
2 Sandanbata et al. https://doi.org/10.1029/2023GL106949
3 Fujiwara et al. https://doi.org/10.1029/2024GL109766
4 AIST https://www.gsj.jp/hazards/volcano/torishima/index.html
5 Minami & Tani https://doi.org/10.1016/j.margeo.2024.107405
6 Kuwatani et al. https://doi.org/10.22541/essoar.172745007.73613799/v1
We investigated newly-stranded white pumice clasts collected at Okinawa, Hahajima, and Chichijima. The studied pumice clasts were rhyolitic composition. Some pumice clasts showed microlite-free white matrix with gray-colored frothy patches (possibly equivalent to the dark-colored patches reported by AIST), whose petrological characteristics along with the trace element characteristics are identical to those studied by AIST. Additionally, black enclaves containing less-differentiated minerals (Ol, high-Mg Cpx, Ca-Pl) are newly identified, which could retain the information about the deep magma plumping system of the source volcano. These observations clearly show the drifting of considerable amount of the pumice from the southern Izu Islands to the Nansei Islands (possibly via Hahajima) despite the small size of the initial raft.
Quick bathymetric surveys revealed abrupt morphological change in the Sofu Seamount where the epicenter of the swarm earthquakes were concentrated, and indicated the volcanic activities as the source of earthquakes [3,5]. However, drift simulation indicated the pumice originated from the north of the Sofu Seamount and in the back-arc rift zone near Sumisujima [6].
To investigate the relationship between these geological phenomena and the surface-observed signature, JAMSTEC would perform a research cruise targeting direct sampling of the volcanic rocks around the Sofu Seamount in March 2025 using R/V Kaimei (KM25-02 Leg2). In the presentation, we will show preliminary results of the geological survey around the Sofu Seamount to compare the characteristics of white drift pumice described above.
Funding information: ERCA Environment Research and Technology Development Fund (JPMEERF20244002); MEXT Volcano Practical Human Resource Development Support Program Japan (JPJ202414); TMU Ogasawara Research Committee; AJG Disaster Geography Research Grant
References:
1 Mizutani & Melgar https://doi.org/10.26443/seismica.v2i2.1160
2 Sandanbata et al. https://doi.org/10.1029/2023GL106949
3 Fujiwara et al. https://doi.org/10.1029/2024GL109766
4 AIST https://www.gsj.jp/hazards/volcano/torishima/index.html
5 Minami & Tani https://doi.org/10.1016/j.margeo.2024.107405
6 Kuwatani et al. https://doi.org/10.22541/essoar.172745007.73613799/v1