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| Titel |
Diffuse He degassing from Cumbre Vieja volcano, La Palma, Canary Islands |
| VerfasserIn |
María Asensio-Ramos, Marli E. De Jongh, Kristen R. Lamfers, Mar Alonso, Cecilia Amonte, Eleazar Padrón, Pedro A. Hernández, 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 |
250143610
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| Publikation (Nr.) |
 EGU/EGU2017-7347.pdf |
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| Zusammenfassung |
| Helium is considered as an ideal geochemical tracer due to its geochemical properties:
chemical inertness, physical stability and practical insolubility in water under normal
conditions. These characteristics, together with its high mobility on the crust, make the
presence of helium anomalies on the surface environment of a volcanic system to be related
to deep fluid migration controlled by volcano-tectonic features, also providing valuable
information about the location and characteristics of the gas source and the fracturing of the
crust. The recent results reported by Padrón et al. (2013) clearly show importance of helium
emission studies for the prediction of major volcanic events and the importance of continuous
monitoring of this gas in active volcanic regions. La Palma Island (708.32 km2) is
located at the northwestern end of the Canarian Archipelago. Subaerial volcanic
activity on this island started ∼2.0 My ago and has taken place exclusively at the
southern part in the last 123 ka. Cumbre Vieja volcano, the most active basaltic
volcano of the Canary Islands, was built in this zone, including a main north-south
rift area 20 km long and up to 1,950 m in elevation, with vents located also at the
northwest and northeast. Padrón et al., (2012) showed that helium is mainly emitted
along both N-S and N-W rift of Cumbre Vieja, being, therefore, zones of enhanced
permeability for deep gas migration and preferential routes for degassing. This work
represents a continuation of the results obtained by Padrón et al. (2012) until the
year 2016. Each study covered the 220 km2 of Cumbre Vieja with an average of
570 homogenously distributed sampling points. At each sampling site, soil gas
samples were collected at 40 cm depth by withdrawing the gas aliquots into 60
cc hypodermic syringes. He content in the soil gases was analyzed by means of
quadrupole mass spectrometry (QMS). Atmospheric gas was used periodically to
calibrate the instrument. To estimate the helium emission rate at each sampling point, a
pure diffusive model was applied following the Fick’s law. Thus, assuming a pure
diffusive mechanism, the helium emission was estimated between 18 and 38 kg d−1
in the studied period (2002-2016). Helium efflux contour maps were constructed
using sequential Gaussian simulation (sGs) as interpolation method. In most of the
surveys, helium enrichments in the soil layer with respect to the air concentration
measured on Cumbre Vieja indicate a strong structural control in the degassing
processes of the volcano and the excess helium seems to be emitted mainly along
both N–S and N–W rifts of the volcano. This work reinforce the importance of
performing helium emission studies as an important volcano monitoring technique that
might help to detect early warning signals of volcanic unrest in oceanic volcanic
islands.
References:
Padrón et al., (2012). Chem. Geol. 312–313, 138–147.
Padrón et al. (2013). Geology 41(5), 539–542. |
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