Source constraints for the 2015 phreatic eruption of Hakone volcano, Japan, based on geological analysis and resistivity structure

AbstractOn June 29, 2015, a small phreatic eruption occurred in the most intensively steaming area of Hakone volcano, Japan. A previous magnetotelluric survey for the whole volcano revealed that the eruption center area (ECA) was located near the apex of a bell-shaped conductive body (resistivity < 10 Ωm) beneath the volcano. We performed local, high-resolution magnetotelluric surveys focusing on the ECA before and after the eruption. The results from these, combined with our geological analysis of samples obtained from a steam well (500 m deep) in the ECA, revealed that the conductive body contained smectite. Beneath the ECA, however, the conductive body intercalated a very local resistive body located at a depth of approximately 150 m. This resistive body is considered a vapor pocket. For the 2 months prior to eruption, a highly localized uplift of the ECA had been observed via satellite InSAR. The calculated depth of the inflation source was coincident with that of the vapor pocket, implying that enhanced vapor flux during the precursory unrest increased the porosity and vapor content in the vapor pocket. In fact, our magnetotelluric survey indicated that the vapor pocket became inflated after the eruption. The layer overlaying the vapor pocket was characterized by the formation of various altered minerals, and mineral precipitation within the veins and cracks in the layer was considered to have formed a self-sealing zone. From the mineral assemblage, we conclude that the product of the 2015 eruption originated from the self-sealing zone. The 2015 eruption is thus considered a rupture of the vapor pocket only 150 m below the surface. Even though the eruption appeared to have been triggered by the formation of a considerably deeper crack, as implied by the ground deformation, no geothermal fluid or rocks from significantly deeper than 150 m were erupted.

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Monitoring ground deformation of eruption center by ground-based interferometric synthetic aperture radar (GB-InSAR): a case study during the 2015 phreatic eruption of Hakone volcano

Earth Planets and Space ◽

10.1186/s40623-018-0951-0 ◽

2018 ◽

Vol 70 (1) ◽

Cited By ~ 4

Author(s):

Senro Kuraoka ◽

Yuichi Nakashima ◽

Ryosuke Doke ◽

Kazutaka Mannen

Keyword(s):

Synthetic Aperture Radar ◽

Ground Deformation ◽

Phreatic Eruption ◽

Synthetic Aperture ◽

Interferometric Synthetic Aperture Radar ◽

Hakone Volcano ◽

Eruption Center ◽

Aperture Radar

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The nature and source of the volcanic ash during the 2015 small phreatic eruption at Hakone volcano, central Japan

GEOCHEMICAL JOURNAL ◽

10.2343/geochemj.2.0560 ◽

2019 ◽

Vol 53 (3) ◽

pp. 209-217 ◽

Cited By ~ 4

Author(s):

Muga Yaguchi ◽

Takeshi Ohba ◽

Masakazu Sago

Keyword(s):

Volcanic Ash ◽

Phreatic Eruption ◽

Central Japan ◽

Hakone Volcano

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Observing posteruptive deflation of hydrothermal system using InSAR time series analysis: An application of ALOS-2/PALSAR-2 data on the 2015 phreatic eruption of Hakone volcano, Japan

10.1002/essoar.10507409.1 ◽

2021 ◽

Author(s):

Ryosuke Doke ◽

Kazutaka Mannen ◽

Kazuhiro Itadera

Keyword(s):

Time Series ◽

Time Series Analysis ◽

Hydrothermal System ◽

Phreatic Eruption ◽

Hakone Volcano ◽

Series Analysis

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Thaw subsidence and frost heave caused by 2018-20 forest fires around Batagay: validation with multiple InSAR data and field observation

10.5194/egusphere-egu21-14093 ◽

2021 ◽

Author(s):

Kazuki Yanagiya ◽

Masato Furuya ◽

Go Iwahana ◽

Petr Danilov

Keyword(s):

Forest Fires ◽

Field Observation ◽

Ground Deformation ◽

Frost Heave ◽

The Arctic ◽

Maximum Temperature ◽

Daily Maximum Temperature ◽

Fire Scar ◽

Before And After ◽

Surface Vegetation

<p>The Arctic has experienced numerous fires in last year, and from June to August 2020, satellite data showed record carbon dioxide emissions from forest fires. Peatland in the Arctic contains large amounts of organic carbon, and their release into the atmosphere can create positive feedbacks for further increase of air temperature. In addition, forest fires burn the surface vegetation layer that has been acting as a heat insulator, which will accelerate the thawing of permafrost on scales of years to decades. Although the thaw depth can recover together with the recovery of surface vegetation, the massive segregated ice is not recoverable once it melted. Our study area is around the Batagay, Sakha Republic, Eastern Siberia. In June 2020, Verkhoyansk, located about 55 km west of Batagay, recorded the highest daily maximum temperature of 38.0 degrees Celcius. The Sentinel-2 optical satellite images showed a number of forest fires in 2019-20. We detected the surface deformation signals at each fire site with the remote-sensing method called InSAR (Interferometric Synthetic Aperture Radar). Also, we conducted a field observation in September 2019 for validations: 1) installed a soil thermometer and soil moisture meter; 2) established a reference point for leveling and first survey; 3) measured the thawing depth with a frost probe.</p><p>&#160;For seasonal ground deformations immediately after the fire, we mainly analyzed Sentinel-1 images. Sentinel-1 is the ESA's C-band SAR satellite, which has a short imaging interval of 12 days. As the short wavelength, vegetation changes lost coherence, and some pairs failed to detect ground deformation signals immediately after the fire. However, after the end of September, we detected displacements toward the satellite line-of-sight direction at all the fire sites. It indicates uplift signals due presumably to frost heave at the fire scar. For long-term deformations over one year, we used ALOS2 imaged derived by JAXA's L band SAR satellite. In the previous studies in Alaska, the ground deformation signal immediately after a fire could not be detected due to the coherence loss in the pairs derived from pre-fire and post-fire SAR images. Indeed, we could not detect deformation signals at the fire scars from the June pairs derived before and after the fire. However, the January pairs and March pairs, both of which were acquired before and after the fire, showed relatively high coherence even in the fire scar and indicated clear subsidence signals by as much as 15 cm. We interpret that, because the studied Verkhoyansk Basin is very dry and has little snow cover, the microwaves could penetrate the snow layer, which allowed us to detect deformation signals even in winter. Yanagiya and Furuya (2020) validated the consistency of the winter uplift signal for the 2014 fire site. We also analyzed the SM1 high spatial resolution mode (3 m) ALOS2 InSAR to investigate the specific ground deformation at each fire site.</p>

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Analyzing the continuous volcanic tremors detected during the 2015 phreatic eruption of the Hakone volcano

Earth Planets and Space ◽

10.1186/s40623-017-0751-y ◽

2017 ◽

Vol 69 (1) ◽

Cited By ~ 17

Author(s):

Yohei Yukutake ◽

Ryou Honda ◽

Masatake Harada ◽

Ryosuke Doke ◽

Tatsuhiko Saito ◽

...

Keyword(s):

Phreatic Eruption ◽

Hakone Volcano

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Volcanic Unrest at Hakone Volcano after the 2015 phreatic eruption — Reactivation of a Ruptured Hydrothermal System?

10.21203/rs.3.rs-86165/v1 ◽

2020 ◽

Author(s):

Kazutaka Mannen ◽

Yuki Abe ◽

Yasushi Daita ◽

Ryosuke Doke ◽

Masatake Harada ◽

...

Keyword(s):

Hydrothermal System ◽

Seismic Activity ◽

Low Frequency ◽

Magmatic Fluid ◽

Volcanic Unrest ◽

Hakone Volcano ◽

Seismic Swarms ◽

Cap Rock ◽

Sealing Zone ◽

Eruptive Period

Abstract Since the beginning of the 21st century, volcanic unrest has occurred every 2–5 years at Hakone volcano. After the 2015 eruption, unrest activity changed significantly in terms of seismicity and geochemistry. In this paper, characteristics of the post-eruptive volcanic unrest that occurred in 2017 and 2019 are described, and changes in the hydrothermal system of the volcano caused by the eruption are discussed. Like the pre- and co-eruptive unrest, each post-eruptive unrest episode was detected by deep inflation below the volcano (~ 10 km) and deep low frequency events, which can be interpreted as reflecting supply of magma or magmatic fluid from depth. The seismic activity during the post-eruptive unrest episodes also increased; however, seismic activity beneath the eruption center during the unrest episodes was significantly lower, especially in the shallow region (~2 km), while sporadic seismic swarms were observed beneath the caldera rim, ~3 km away from the center. The 2015 eruption established routes for steam from the hydrothermal system (≥ 150 m deep) to the surface through the cap-rock, allowing emission of super-heated steam (~ 160 ºC), which was absent before the eruption. This steam showed an increase in magmatic/hydrothermal gas ratios (SO2/H2S and HCl/H2S) in the 2019 unrest, which may be interpreted as magmatic intrusion at shallow depth; however, no indicative seismic and geodetic signals were observed. Net SO2 emission during the post-eruptive unrest episodes, which remained within the usual range of the post-eruptive period, is also inconsistent with shallow intrusion. We consider that the post-eruptive unrest episodes were also triggered by newly derived magma or magmatic fluid from depth; however, the breached cap-rock was unable to allow subsequent pressurization of the hydrothermal system beneath the volcano center and suppressed seismic activity significantly. The heat released from the newly derived magma or fluid dried the vapor-dominated portion of the hydrothermal system and inhibited scrubbing of SO2 and HCl to allow a higher magmatic/hydrothermal gas ratio. The 2015 eruption could have also breached the sealing zone near the brittle–plastic transition and the subsequent self-sealing process seems not to have completed based on the observations during the post-eruptive unrest episodes.

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Preliminary results of ground deformation measurements near the CANNIKIN explosion

Bulletin of the Seismological Society of America ◽

10.1785/bssa0620061505 ◽

1972 ◽

Vol 62 (6) ◽

pp. 1505-1518 ◽

Cited By ~ 2

Author(s):

D. D. Dickey ◽

F. A. McKeown ◽

R. C. Bucknam

Keyword(s):

High Speed ◽

Nuclear Explosion ◽

Ground Deformation ◽

Motion Pictures ◽

Ground Surface ◽

Underground Nuclear Explosion ◽

Geological Structures ◽

Level Lines ◽

Before And After ◽

Principal Strains

abstract Ground deformation around the CANNIKIN underground nuclear explosion was studied by means of geodetic measurements, observation of tilt in lakes, and analysis of high-speed motion pictures. The lengths of 53 lines of the order of 1 km long located as many as 7 km from ground zero (GZ) were measured before and after the explosion. Principal strains calculated from the observed changes in length indicate northeast-oriented extension, which is interpreted as reflecting, in part, the release of tectonic strain. Information from an incomplete remeasurement of level lines indicates as much as about 1 m of residual uplift along nearly 2 km of the Bering coast adjacent to the explosion site. Measurements of tilt at six lakes differ in magnitude and direction from the values expected to be produced by expansion of the explosion cavity, but seem to be related to the influence of geological structures near the lakes. High-speed motion pictures indicate that the ground surface in the GZ area had risen vertically about 8 m by 1.4 sec after the explosion and had returned to within about 1 m of its original elevation by 4 sec after the explosion.

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