[S-VC36] Volcanoes in the sea

[SVC36-P05] Physical properties, pore structure, and lithofacies of submarine lava flows at Nishinoshima

*Yuya Akamatsu¹, Kenta K. Yoshida¹, Tomoki Sato¹, Noriko Tada¹ (1.Research Institute for Marine Geogynamics, JAMSTEC)

Keywords:Nishinoshima, Physical property, Seismic velocity, Resistivity

Nishinoshima, located in the Izu–Ogasawara Arc, has shown intermittent volcanic activity with varying eruption styles since its re-eruption in 2013. Understanding the internal pore structure (e.g., vesicles and fractures) of erupted materials is crucial for evaluating processes of degassing within the volcanic edifice and seawater infiltration, and the physical conditions during lava emplacement. Akamatsu et al. (2025, JVGR) conducted a comprehensive laboratory measurement of the physical properties of andesitic lava samples collected during past land surveys on Nishinoshima, revealing the following key findings regarding the relationship between pore structure and physical properties: 1. The physical property trends with porosity differ significantly across lithofacies (vesicular, dense, foliated) and are associated with distinct pore structures of each lithofacies. 2. Pores in foliated lava tend to be flattened and highly connected, leading to significant reductions in resistivity and seismic velocity even at low porosity. 3. Variations in pore geometry likely reflect shear deformation during lava flow and cooling rates, suggesting that physical properties and geophysical data can be used to infer the internal structure of the volcanic edifice and eruption conditions. However, the majority of Nishinoshima’s edifice is submerged, and understanding the current pressure conditions within the edifice, fluid circulation patterns, and pore structures in lavas from past eruptions requires a comparison with the subaerial and submarine lava samples. In this presentation, we report the results of porosity, density, and seismic velocity measurements of lava samples dredged from the seafloor during the research cruise YK22-15 in 2022. The results are compared with those of subaerial lava samples from Nishinoshima to discuss the influence of seawater during eruption on the pore structure and physical properties of the lava.

Acknowledgments
We express our gratitude to the crew and onboard scientists of the R/V Yokosuka during the YK22-15 cruise for their support in collecting submarine samples from Nishinoshima.