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| Titel |
Diffuse CO2 degassing monitoring of the oceanic active volcanic island of El Hierro, Canary Islands, Spain |
| VerfasserIn |
Pedro A. Hernández, Janice Norrie, Yannick Withoos, Marta García-Merino, Gladys Melián, Eleazar Padrón, José Barrancos, German Padilla, Fátima Rodriguez, Nemesio M. Pérez |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143685
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| Publikation (Nr.) |
 EGU/EGU2017-7431.pdf |
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| Zusammenfassung |
| Even during repose periods, volcanoes release large amounts of gases from both visible
(fumaroles, solfataras, plumes) and non-visible emanations (diffuse degassing).
In the last 20 years, there has been considerable interest in the study of diffuse
degassing as a powerful tool in volcano monitoring programs, particularly in those
volcanic areas where there are no visible volcanic-hydrothermal gas emissions.
Historically, soil gas and diffuse degassing surveys in volcanic environments have focused
mainly on CO2 because it is, after water vapor, the most abundant gas dissolved
in magma. As CO2 travels upward by advective-diffusive transport mechanisms
and manifests itself at the surface, changes in its flux pattern over time provide
important information for monitoring volcanic and seismic activity. Since 1998,
diffuse CO2 emission has been monitored at El Hierro Island, the smallest and south
westernmost island of the Canarian archipelago with an area of 278 km2. As no visible
emanations occur at the surface environment of El Hierro, diffuse degassing studies
have become the most useful geochemical tool to monitor the volcanic activity in
this volcanic island. The island experienced a volcano-seismic unrest that began
in July 2011, characterized by the location of a large number of relatively small
earthquakes (M<2.5) beneath El Hierro at depths between 8 and 15 km. On October 12,
2011, a submarine eruption was confirmed during the afternoon of October 12,
2011 by visual observations off the coast of El Hierro, about 2 km south of the
small village of La Restinga in the southernmost part of the island. During the
pre-eruptive and eruptive periods, the time series of the diffuse CO2 emission released by
the whole island experienced two significant increases. The first started almost 2
weeks before the onset of the submarine eruption, reflecting a clear geochemical
anomaly in CO2 emission, most likely due to increasing release of deep seated
magmatic gases to the surface. The second one, between October 24 and November
27, 2011, before the most energetic seismic events of the volcanic-seismic unrest
(Melián et al., 2014. J. Geophys. Res. Solid Earth, 119, 6976–6991). The highest CO2
degassing rate measured in the last three years (1684 t/d) was observed during a
seismo-volcanic unrest. This value decreased until close to background value (∼422 t/d,
Melián et al., 2014) contemporaneously with the decline of the seismic activity
during the first half of 2013. The last diffuse CO2 degassing survey was carried out
in the summer of 2016, showing a emission rate of 854 t/d. Discrete surveys of
diffuse CO2 emission have provided important information to optimize the early
warning system in the volcano monitoring programs of El Hierro and to monitor the
evolution of an ongoing volcanic eruption, even though is a submarine eruption. |
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