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Sequential triggers of Plinian eruptions at Sakurajima Volcano inferred from multi-diffusion analyses

Naoki Araya 1, Michihiko Nakamura1, Keiko Matsumoto2, and Satoshi Okumura1

  • Affiliations: 1Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Japan; 2Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan 

  • Presentation type: Poster

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

  • Poster Board Number: 263

  • Programme No: 1.3.11

  • Theme 1 > Session 3

Abstract

Understanding the triggering mechanisms of Plinian eruptions remains an important scientific challenge. Mafic magma recharge and subsequent mixing are often considered direct triggers of eruptions. However, despite the geodetic detection of frequent recharge in active volcanoes, such processes rarely result in Plinian eruptions, making their roles as triggers ambiguous. To enhance our understanding of these mechanisms, we conducted diffusion modeling on multiple mineral phases and investigated the magmatic processes leading to historical Plinian eruptions at Sakurajima Volcano, Japan, over various timescales. The reverse zoning of orthopyroxene phenocrysts commonly indicates diffusion timescales of years or more following recharge-and-mixing, which may represent the ultimate triggers of the eruptions (cf. Putirka, 2017). By contrast, almost all magnetite phenocrysts, where elemental diffusion is much faster, lack zoning. Given that the mixed magmas after recharge were stored in a shallow, thick conduit before the eruptions (conduit pre-charge; Araya et al., 2019), the pre-charged magma body had been reposed for longer than the diffusive re-equilibration time of magnetite (several tens of days). This shallow stagnation may be related to precursory phenomena, as early as six months before the latest AD 1914 eruption. The timescales of magma ascent to the surface after this stagnation period are up to tens of hours, as inferred from the zoned magnetites which occurred rarely. Crystallization-driven vesiculation during the pre-charge, which can produce sufficient overpressure to cause an eruption, could act as the immediate trigger (cf. Putirka, 2017). The Sakurajima case demonstrates the hierarchical timescales of trigger processes