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| Titel |
Diffuse H2 emission: a useful geochemical tool to monitor the volcanic activity at El Hierro volcano system |
| VerfasserIn |
Nemesio M. Pérez, Gladys Melián, Judit González-Santana, José Barrancos, German Padilla, Fátima Rodriguez, Eleazar Padrón, Pedro A. Hernández |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135833
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| Publikation (Nr.) |
 EGU/EGU2016-16744.pdf |
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| Zusammenfassung |
| The occurrence of interfering processes affecting reactive gases as CO2 during its ascent from
magmatic bodies or hydrothermal systems toward the surface environment hinders the
interpretation of their enrichments in the soil atmosphere and fluxes for volcano monitoring
purposes (Marini and Gambardella, 2005). These processes include gas scrubbing by
ground-waters and interaction with rocks, decarbonatation processes, biogenic production,
etc. Within the rest of the soil gases, particularly interest has been addressed to light and
highly mobile gases. They offer important advantages for the detection of vertical
permeability structures, because their interaction with the surrounding rocks or fluids
during the ascent toward the surface is minimum. H2 is one of the most abundant
trace species in volcano-hydrothermal systems and is a key participant in many
redox reactions occurring in the hydrothermal reservoir gas (Giggenbach, 1987).
Although H2 can be produced in soils by N2-fixing and fertilizing bacteria, soils
are considered nowadays as sinks of molecular hydrogen (Smith-Downey et al.,
2006). Because of its chemical and physical characteristics, H2 generated within the
crust moves rapidly and escapes to the atmosphere. These characteristics make H2
one of the best geochemical indicators of magmatic and geothermal activity at
depth.
El Hierro is the youngest and the SW-most of the Canary Islands and the scenario of the
last volcanic eruption of the archipelago, a submarine eruption that took place 2 km off the
southern coast of the island from October 2011 to March 2012. Since at El Hierro
Island there are not any surface geothermal manifestations (fumaroles, etc), we have
focused our studies on soil degassing surveys. Here we show the results of soil H2
emission surveys that have been carried out regularly since mid-2012. Soil gas samples
were collected in ∼600 sites selected based on their accessibility and geological
criteria. Soil gases were sampled at ∼40 cm depth using a metallic probe with a 60 cc
hypodermic syringes and stored in 10 cc glass vials for later laboratory analysis by a
VARIAN CP4900 micro-gas chromatograph. Soil H2 concentration data were used to
estimate the H2 emission assuming a pure diffusive mechanism. The emission ranged
between 12 and 25 kg d−1, showing a good relationship with the seismic energy
release during the period of study. However, spatial distribution of H2 emission
values did not show a clear relationship with main volcano-structures of El Hierro
Island. H2 emission studies are a promising volcano monitoring technique that
might help to detect early warning signals of volcanic unrest in oceanic volcanic
islands.
References
Marini and Gambardella, 2005. Ann Geophys 48, 739–753.
Giggenbach, 1987. Appl Geochem 2, 143–161.
Smith-Downey et al., 2006. Geophys Res Lett 33, L14813. |
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