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Slug formation in basaltic eruptions driven by rapid coalescence of bubbles

Takafumi Maruishi1, Atsushi Toramaru2

  • Affiliations: 1Volcano Disaster Resilience Research Division, National Research Institute for Earth Science and Disaster Resilience, Ibaraki, Japan 2Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan

  • Presentation type: Poster

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

  • Poster Board Number: 212

  • Programme No: 3.6.16

  • Theme 3 > Session 6

Abstract

Bursts of decameter-sized bubbles are commonly observed during basaltic eruptions. These giant bubbles are thought to form through the coalescence of smaller bubbles within the volcanic conduit, driven by buoyancy forces resulting from the low viscosity of basaltic magma. Understanding the dynamics of buoyancy-driven bubble coalescence is thus essential for estimating the explosivity of basaltic eruptions. In this study, we investigate the evolution of the bubble volume distribution by considering both buoyancy-driven coalescence and bubble expansion due to decompression. Our findings reveal that, at lower decompression rates, the bubble volume distribution quickly evolves into a power-law form, where the number of bubbles scales with the inverse square of the bubble volume. This suggests that repeated bubble coalescence in basaltic magma can generate large bubbles within a timescale of 45 minutes to 3 days. Furthermore, we analyze the occurrence of eruption styles, specifically Strombolian and Hawaiian, under the assumption that slug bursts drive Strombolian eruptions. From this analysis, we identify a critical magma ascent velocity that governs the transition between these eruption styles, aligning well with observed style transitions at Izu-Oshima and Kilauea.