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Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan

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Title: Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan
Authors: Narita, Shohei Browse this author
Murakami, Makoto Browse this author
Tanaka, Ryo Browse this author
Keywords: Phreatic eruption
Ground deformation
Discharge rate
Mass balance
Issue Date: 30-Dec-2019
Publisher: Springer (SpringerOpen)
Journal Title: Earth planets and space
Volume: 71
Issue: 1
Start Page: 145
Publisher DOI: 10.1186/s40623-019-1124-5
Abstract: The phreatic eruption of Mount Ontake in 2014 caused local-scale subsidence and a mass discharge of water-vapor plumes from vents. A previous study of InSAR data analysis modeled the local subsidence as a deflation of a shallow hydrothermal reservoir (similar to 500 m beneath the vents), and speculated that it was associated with plume emission continuing just after the eruption. In addition, combination of the InSAR and GNSS data implies that another, deeper deflation source similar to 3-6 km beneath the vents) contributes to the baseline contraction of the GNSS data. In this study, we estimated daily mass flux of the emitting plumes using photographed images, and compared the temporal behavior of the discharged mass with that of deflation of the two sources in order to clarify their association. The temporal profiles of the shallow deflation volume and the discharge mass both show evidence of decay, but with different characteristics; the deflation volume progress was approximated by a single exponential decay with a long relaxation time (379-641 days), whereas the discharge mass displayed a sum of a linear trend and an exponential decay with shorter relaxation time (47 days). This discrepancy, along with GNSS data, suggests the contribution of a deep deflation source with a short relaxation time (20-40 days). Estimation of mass balance between the emitting plume and fluids discharged from both shallow and deep sources revealed that more than 70% of the discharged mass came from the deep source. Based on the estimated mass balance, phase state of the shallow reservoir was estimated as a single-phase, liquid-rich reservoir. The fast decay of the deep deflation may reflect rapid depressurization due to violent fluid discharge at the onset of the eruption. In contrast, the slow decay of the shallow deflation suggests that it had a minor role in the eruption. However, such a wet reservoir has the potential to induce volcanic hazard such as snow-melting lahar for future eruptions, requiring monitoring the volcano, which will probably shift to pre-eruptive re-pressurized phase, until the future eruption.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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