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

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. 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. This observation and a recent InSAR analysis imply that the hydrothermal system of the volcano could be composed of multiple sub-systems, each of which can host earthquake swarm and show independent volume change. The 2015 eruption established routes for steam from the hydrothermal sub-system beneath the eruption center (≥ 150 m deep) to the surface through the cap-rock, allowing emission of super-heated steam (~ 160 ºC). This steam showed an increase in magmatic/hydrothermal gas ratios (SO2/H2S and HCl/H2S) in the 2019 unrest episode; however, no magma supply was indicated by seismic and geodetic observations. 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 and intensive seismic activity within the hydrothermal sub-system beneath the eruption center. 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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Volcanic unrest at Hakone volcano after the 2015 phreatic eruption: reactivation of a ruptured hydrothermal system?

Earth Planets and Space ◽

10.1186/s40623-021-01387-3 ◽

2021 ◽

Vol 73 (1) ◽

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 ◽

Eruption Center ◽

Brittle Ductile Transition ◽

Seismic Swarms ◽

Cap Rock

AbstractSince the beginning of the twenty-first 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. 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. This observation and a recent InSAR analysis imply that the hydrothermal system of the volcano could be composed of multiple sub-systems, each of which can host earthquake swarms and show independent volume changes. The 2015 eruption established routes for steam from the hydrothermal sub-system beneath the eruption center (≥ 150 m deep) to the surface through the cap-rock, allowing emission of super-heated steam (~ 160 ºC). This steam showed an increase in magmatic/hydrothermal gas ratios (SO2/H2S and HCl/H2S) in the 2019 unrest episode; however, no magma supply was indicated by seismic and geodetic observations. 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 and intensive seismic activity within the hydrothermal sub-system beneath the eruption center. 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–ductile 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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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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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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Structural controls on the 1998 volcanic unrest at Iwate volcano: Relationship between a shallow, electrically resistive body and the possible ascent route of magmatic fluid

Journal of Volcanology and Geothermal Research ◽

10.1016/j.jvolgeores.2009.08.009 ◽

2009 ◽

Vol 187 (1-2) ◽

pp. 131-139 ◽

Cited By ~ 13

Author(s):

Koki Aizawa ◽

Yasuo Ogawa ◽

Masaaki Mishina ◽

Kosuke Takahashi ◽

Shintaro Nagaoka ◽

...

Keyword(s):

Magmatic Fluid ◽

Volcanic Unrest ◽

Structural Controls

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Tectonic stress regime in the 2003–2004 and 2012–2015 earthquake swarms in the Ubaye Valley, French Alps

Pure and Applied Geophysics ◽

10.1007/s00024-018-1792-2 ◽

2018 ◽

Vol 175 (6) ◽

pp. 1997-2008 ◽

Cited By ~ 6

Author(s):

Lucia Fojtíková ◽

Václav Vavryčuk

Keyword(s):

Seismic Activity ◽

Joint Inversion ◽

Earthquake Swarm ◽

Active Faults ◽

Tectonic Stress ◽

Geological Mapping ◽

Earthquake Swarms ◽

Stress Regime ◽

French Alps ◽

Principal Axes

Abstract We study two earthquake swarms that occurred in the Ubaye Valley, French Alps within the past decade: the 2003–2004 earthquake swarm with the strongest shock of magnitude ML = 2.7, and the 2012–2015 earthquake swarm with the strongest shock of magnitude ML = 4.8. The 2003–2004 seismic activity clustered along a 9-km-long rupture zone at depth between 3 and 8 km. The 2012–2015 activity occurred a few kilometres to the northwest from the previous one. We applied the iterative joint inversion for stress and fault orientations developed by Vavryčuk (2014) to focal mechanisms of 74 events of the 2003–2004 swarm and of 13 strongest events of the 2012–2015 swarm. The retrieved stress regime is consistent for both seismic activities. The σ 3 principal axis is nearly horizontal with azimuth of ~ 103°. The σ 1 and σ 2 principal axes are inclined and their stress magnitudes are similar. The active faults are optimally oriented for shear faulting with respect to tectonic stress and differ from major fault systems known from geological mapping in the region. The estimated low value of friction coefficient at the faults 0.2–0.3 supports an idea of seismic activity triggered or strongly affected by presence of fluids.

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Episodic earthquake swarms in the Mineral Mountains, Utah driven by the Roosevelt hydrothermal system

10.5194/egusphere-egu21-1227 ◽

2021 ◽

Author(s):

Maria Mesimeri ◽

Kristine Pankow ◽

Ben Baker ◽

J. Mark Hale

Keyword(s):

Hydrothermal System ◽

Hot Springs ◽

Matched Filter ◽

Earthquake Swarm ◽

Earthquake Swarms ◽

Earthquake Catalog ◽

Spatial And Temporal Patterns ◽

University Of Utah ◽

South Central ◽

The University

The Mineral Mountains are located in south-central Utah within the transition zone from the Basin and Range to Colorado Plateau physiographic provinces, near the Roosevelt Hot Springs. First evidence of swarm-like activity in the area was found in 1981, when a six-station temporary network detected a very energetic swarm of ~1,000 earthquakes. More recently, in mid-2016, a dense local broadband seismic network was installed around the Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah, ~10 km west of the Mineral Mountains. Beginning in 2016, the University of Utah Seismograph Stations detected, located, and characterized 75 earthquakes beneath the Mineral Mountains. In this study, we build an enhanced earthquake catalog to confirm the episodic swarm-like nature of seismicity in the Mineral Mountains. We use the 75 cataloged earthquakes as templates and detect 1,000 earthquakes by applying a matched-filter technique. The augmented catalog reveals that seismicity in the Mineral Mountains occurs as short-lived earthquake swarms followed by periods of quiescence. Earthquake relocation of ~800 earthquakes shows that activity is concentrated in a <2 km long E-W striking narrow zone, ~4 km east of the Roosevelt hydrothermal system. Two fault orientations, both N-S and E-W parallel to the Opal Mound and Mag Lee faults, respectively, are observed after computing composite focal mechanisms of highly similar earthquakes. After examining the spatial and temporal patterns of the best recorded earthquake swarm in October 2019, we find that a complex mechanism of fluid diffusion and aseismic slip is responsible for the swarm evolution with migration velocities reaching 10 km/day. We hypothesize that these episodic swarms in the Mineral Mountains are primarily driven by migrating fluids that originate within the Roosevelt hydrothermal system.

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Trade-offs between deep (magmatic) and shallow (hydrological) forcings on volcanic unrest at La Soufrière de Guadeloupe (Lesser Antilles)

10.5194/egusphere-egu21-8761 ◽

2021 ◽

Author(s):

David Jessop ◽

Roberto Moretti ◽

Séverine Moune ◽

Vincent Robert

Keyword(s):

Time Series ◽

Hydrothermal System ◽

Temporal Variations ◽

Temperature Record ◽

Trade Offs ◽

External Forcings ◽

Seismic Swarms ◽

Long Time ◽

Deep Activity

Fumarolic gas composition and temperature record deep processes that generate and transfer heat and mass towards the surface. &#160;These processes are a result of the emplacement, degassing and cooling of magma and the overturning of the above hydrothermal system. &#160;A reasonable expectation, and too often an unproved assumption, is that fumarole temperatures and the deep heat sources vary on similar timescales. &#160;Yet signals from deep and shallow processes have vastly different temporal variations.&#160; This indicates that signals arising from deep activity may be masked or modified by intervening hydrothermal processes, such as fluid-groundrock reactions in which secondary minerals play a major role. &#160;Clearly, this complicates the interpretation of the signals such as the joint variation of fumarole vent temperature and geochemical ratios in terms of what is occurring at depth. &#160;So what do the differences between the timescales governing deep and shallow processes tell us about the intervening transport mechanisms?At the volcanic dome of La Soufri&#232;re de Guadeloupe, the Observatoire Volcanologique et Sismologique de la Guadeloupe has performed weekly-to-monthly in-situ vent gas sampling over many years. &#160;These analyses reliably track several geochemical species ratios over time, which provide important information about the evolution of deep processes. &#160;Vent temperature is measured as part of the in-situ sampling, giving a long time series of these measurements. &#160;Here, we look to exploit the temporal variations in these data to establish the common processes, and also to determine why these signals differ. &#160;By fitting sinusoids to the gas-ratio time series we find that several of the deep signals are strongly sinusoidal. &#160;For example, the He/CH4 and CO2/CH4 ratios, which involve conservative components and mark the injection of deep and hot magmatic fluids, oscillate on a timescale close to 3 years. We also analyse the frequency content of the temperature measurements since 2011 and find that such long signals are not seen. &#160;This may be due to internal buffering by the hydrothermal system, but other external forcings are also present. &#160;From these data we build up a more informed model of the heat-and-mass supply chain from depth to the surface. &#160;This will potentially allow us to predict future unrest (e.g. thermal crises, seismic swarms), and distinguish between sources of unrest.

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The Behavior of VLF/LF Variations Associated with Geomagnetic Activity, Earthquakes, and the Quiet Condition Using a Neural Network Approach

Entropy ◽

10.3390/e20090691 ◽

2018 ◽

Vol 20 (9) ◽

pp. 691 ◽

Cited By ~ 3

Author(s):

Irina Popova ◽

Alexandr Rozhnoi ◽

Maria Solovieva ◽

Danila Chebrov ◽

Masashi Hayakawa

Keyword(s):

Neural Network ◽

Radio Wave ◽

Seismic Activity ◽

Low Frequency ◽

Magnetic Storms ◽

Network Approach ◽

Neural Network Approach ◽

The Neural Network ◽

Different Types ◽

Parameters Of Seismicity

The neural network approach is proposed for studying very-low- and low-frequency (VLF and LF) subionospheric radio wave variations in the time vicinities of magnetic storms and earthquakes, with the purpose of recognizing anomalies of different types. We also examined the days with quiet geomagnetic conditions in the absence of seismic activity, in order to distinguish between the disturbed signals and the quiet ones. To this end, we trained the neural network (NN) on the examples of the representative database. The database included both the VLF/LF data that was measured during four-year monitoring at the station in Petropavlovsk-Kamchatsky, and the parameters of seismicity in the Kuril-Kamchatka and Japan regions. It was shown that the neural network can distinguish between the disturbed and undisturbed signals. Furthermore, the prognostic behavior of the VLF/LF variations indicative of magnetic and seismic activity has a different appearance in the time vicinity of the earthquakes and magnetic storms.

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