Tidal influence on seismic activity during the 2011‐2013 El Hierro volcanic unrest

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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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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Changes in the Diffuse CO2 Emission and Relation to Seismic Activity in and around El Hierro, Canary Islands

Terrestrial Fluids, Earthquakes and Volcanoes: The Hiroshi Wakita Volume III ◽

10.1007/978-3-7643-8738-9_7 ◽

2008 ◽

pp. 95-114 ◽

Cited By ~ 4

Author(s):

Eleazar Padrón ◽

Gladys Melián ◽

Rayco Marrero ◽

Dácil Nolasco ◽

José Barrancos ◽

...

Keyword(s):

Canary Islands ◽

Seismic Activity ◽

Co2 Emission ◽

El Hierro ◽

Diffuse Co2 Emission

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Changes in the Diffuse CO2 Emission and Relation to Seismic Activity in and around El Hierro, Canary Islands

Pure and Applied Geophysics ◽

10.1007/s00024-007-0281-9 ◽

2008 ◽

Vol 165 (1) ◽

pp. 95-114 ◽

Cited By ~ 30

Author(s):

Eleazar Padrón ◽

Gladys Melián ◽

Rayco Marrero ◽

Dácil Nolasco ◽

José Barrancos ◽

...

Keyword(s):

Canary Islands ◽

Seismic Activity ◽

Co2 Emission ◽

El Hierro ◽

Diffuse Co2 Emission

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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/v2 ◽

2021 ◽

Author(s):

Kazutaka Mannen ◽

Yuki Abe ◽

Yasushi Daita ◽

Ryosuke Doke ◽

Masatake Harada ◽

...

Keyword(s):

Hydrothermal System ◽

Seismic Activity ◽

Earthquake Swarm ◽

Low Frequency ◽

Magmatic Fluid ◽

Volcanic Unrest ◽

Hakone Volcano ◽

Eruption Center ◽

Seismic Swarms ◽

Cap Rock

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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The time lag between deformation process and seismic activity in El Hierro Island during the eruptive process (2011–2014): a functional phased approach

Earth Planets and Space ◽

10.1186/s40623-021-01514-0 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Sonia Pérez-Plaza ◽

Manuel Berrocoso ◽

Belén Rosado ◽

Gonçalo Prates ◽

Fernando Fernández-Palacín

Keyword(s):

Volcanic Activity ◽

Seismic Activity ◽

Deformation Process ◽

Time Lag ◽

Deformation Curve ◽

Reference Station ◽

Correlation Measure ◽

Cumulative Energy ◽

El Hierro ◽

Long Period

AbstractOn 10 October 2011, a submarine eruption occurred in El Hierro island. Thus, the eruptive process in the Canary islands was reactivated after 40 years of inactivity. The main objective of this work is to evaluate, using Functional Data Analysis, how the surface deformation phenomenon explains the seismic–volcanic activity in the island. The GNSS-GPS data are from the FRON (GRAFCAN) station, located in Frontera. These data measure, each 4 h, the distance between the FRON station and the reference station LPAL (La Palma island) from August, 2010 to December, 2013. In this study a functional correlation measure is employed to establish the relation between the deformation curve and the curve of cumulative energy released. The period of time analysed has been divided into four phases to avoid the mix of phenomena. For each phase, the correlation measure and the time lag between deformation curve and the curve of cumulative energy released have been estimated. These values show a strong relation between these curves. With respect to time lag period, the only significant lag, of about 1 month, occurred in Phase 1, which was after a long period without seismic activity. The later phases had very short, insignificant, lags. After a long period without seismic and volcanic activity in El Hierro island, the time lag between the deformation process and the beginning of the seismic activity takes approximately 1 month. In a similar situation a method to predict in real time the beginning of the seismic activity is proposed. This method, based on the changes produced in the derivative curves when there is a rapid descent in the deformation curve, could activate a warning system approximately 13 days before the beginning of seismicity.

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