Total mass estimate of the January 23, 2018, phreatic eruption of Kusatsu-Shirane Volcano, central Japan

Kametani, Nobuko; Ishizaki, Yasuo; Yoshimoto, Mitsuhiro; Maeno, Fukashi; Terada, Akira; Furukawa, Ryuta; Honda, Ryo; Ishizuka, Yoshihiro; Komori, Jiro; Nagai, Masao; Takarada, Shinji

doi:10.1186/s40623-021-01468-3

Cited by 6 publications

(1 citation statement)

References 14 publications

(25 reference statements)

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“…As far as we know, a phreatic eruption at Ontake volcano in 2014 is the only event we can compare our results (the tilt onset, VLP, and the total inflation volume) and eruption scales (Table S3 in Supporting Information S1). The 2014 Ontake eruption is greater than the 2018 Motoshirane eruption in terms of the total precursory inflation volume (Maeda et al., 2017; Terada et al., 2021), the total ash emission amount (Kametani et al., 2021; Takarada et al., 2016), the maximum cloud height (E. Sato et al., 2016; Terada et al., 2021), post‐eruptive fumarole activities (JMA, 2018; Narita et al., 2019), and post‐eruptive ground deformations (Himematsu et al., 2020; Narita et al., 2019). On the other hand, the inflation rate and VLP intensity are not correlated with the eruption scales defined by other observables.…”

Section: Discussionmentioning

confidence: 99%

The Onset, Middle, and Climax of Precursory Hydrothermal Intrusion of the 2018 Phreatic Eruption at Kusatsu‐Shirane Volcano

Yamada,

Terada,

Noguchi

et al. 2023

JGR Solid Earth

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Triggering intrusions of phreatic eruptions are often observed as seismic and ground deformation signals on a time scale of minutes. The current understanding of hydrothermal intrusions still needs improvement to obtain insight into the eruption scale from the observables. We examine local geophysical data from the precursory hydrothermal intrusion of the 2018 phreatic eruption of Kusatsu‐Shirane volcano. To achieve an integrated intrusion model, we divide analyzing time window into the onset, middle, and climax. Focusing on the transient response of tilt data for the sudden pressurization, we estimate a vertical tensile opening (1.7 × 103 m3/s in 40 s) at 1.1 km depth for the intrusion onset. Pressurization can represent the start of vapourization. Very long period (VLP, 0.033–0.1 Hz) seismic signals are adopted to constrain the middle and climax phases. We obtained two sequential semi‐horizontal tensile crack oscillation sources with peak volume changes of 3.6 × 104–1.9 × 105 m3 at 0.3–0.6 km depths. The second VLP source acted as a final trigger of the eruption to cause depressurization in the shallow portion of the intruded region, which is constrained as having reached 0.1 km depth by surface deformation. Simultaneously, we find another depressurization originated from depth in the climax due to a decrease in the hydrothermal intrusion rate. Through comparison with the 2014 Ontake phreatic eruption, the total inflation volume may correlate with eruption scales. Intruded hydrothermal fluid and local structure characteristics also may have to be considered to evaluate the eruptions scales from inferred signal source intensity.

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Section: Discussionmentioning

confidence: 99%

The Onset, Middle, and Climax of Precursory Hydrothermal Intrusion of the 2018 Phreatic Eruption at Kusatsu‐Shirane Volcano

Yamada,

Terada,

Noguchi

et al. 2023

JGR Solid Earth

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The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

Terada

Kanda

Ogawa

et al. 2021

Earth Planets Space

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We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the strike of the crack modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 × 105 and 3.6 × 105 m3, respectively, meaning that 1.5 × 105 m3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥ 1014 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 year. Although the ejecta mass of the 2018 phreatic eruption was small, the eruption at Mt. Motoshirane was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 × 107 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

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Crisis hazard assessment for snow-related lahars from an unforeseen new vent eruption: the 2018 eruption of Kusatsu-Shirane volcano, Japan

Kataoka

Tsunematsu

Matsumoto

et al. 2021

Earth Planets Space

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Two-thirds of the 111 active volcanoes in Japan are covered with snow for several months during winter and demonstrate high hazard and risk potentials associated with snow-related lahars during and after eruptions. On 23 January 2018, a sudden phreatic eruption occurred at the ski field on Kusatsu-Shirane (Mt. Motoshirane) volcano, Japan. This new vent eruption from the snow-clad pyroclastic cone required forecasting of future snow-related lahars and crisis hazards zonation of downslope areas including Kusatsu town, a popular tourist site for skiing and hot springs. In order to achieve a prompt hazard assessment for snow-related lahars, a multidisciplinary approach was carried out involving characterization of proximal tephra deposits, snow surveys, and numerical lahar flow simulations using the Titan2D model. To determine the input parameters for the flow model, the consideration of snow water equivalent (SWE) immediately after the eruption (on 29 January) and in the post-eruptive period (on 12 March), was significant. In the case of Kusatsu-Shirane volcano during the winter of 2018, linear relationships between altitude and SWE, obtained at different elevations, were used to estimate the snow volume around the new vents. Several scenarios incorporating snow and snowmelt (water), with or without the occurrence of a new eruption, were simulated for the prediction of future lahars. Three lahar scenarios were simulated, including A) rain-on-snow triggered, B) ice/snow slurry, and C) full snowmelt triggered by a new eruption, and indicated the flow paths (inundation areas) and travel distances. These were useful for lahar hazard zonation and identification of potential high-risk areas. Since the input parameters required for the Titan2D flow model can be relatively easily determined, the model was suitable for the 2018 eruption at Motoshirane where historical and geological lahar records are not available for calibration. The procedure used in the study will enable rapid lahar prediction and hazard zonation at snow-clad volcanoes. Further consideration for simulating a cohesive-type flow, which was predicted by the primary deposits containing large amounts of clay minerals and could not be expressed in the Titan2D flow model, is necessary.

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Total mass estimate of the January 23, 2018, phreatic eruption of Kusatsu-Shirane Volcano, central Japan

Cited by 6 publications

References 14 publications

The Onset, Middle, and Climax of Precursory Hydrothermal Intrusion of the 2018 Phreatic Eruption at Kusatsu‐Shirane Volcano

The Onset, Middle, and Climax of Precursory Hydrothermal Intrusion of the 2018 Phreatic Eruption at Kusatsu‐Shirane Volcano

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

Crisis hazard assessment for snow-related lahars from an unforeseen new vent eruption: the 2018 eruption of Kusatsu-Shirane volcano, Japan

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