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Titel |
Coupling high-frequency measurement of ²²²Rn, ²²²Rn in soil gases with soil CO₂ efflux at Mt. Etna (Italy): a new strategy for active volcano monitoring |
VerfasserIn |
S. Giammanco, M. López, M. Neri, F. Murè |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250023983
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Zusammenfassung |
Concurrent measurement of soil radon, soil thoron and soil CO2 efflux is based on the
method developed by Giammanco et al. (Geochem. Geophys. Geosys., 8(10), Q 10001,
doi:10.1029/2007GC001644, 2007). An empirical relationship links the 222Rn/220Rn ratio to
the CO2 efflux: deep sources of gas are characterized by high 222Rn activity and high CO2
efflux, whereas shallow sources are indicated by high 220Rn activity and relatively low CO2
efflux. This relationship is more constraining on the type and depth of the gas source than
using the 222Rn/220Rn ratio alone. We studied the temporal variation of the ratio between
CO2 efflux and (222Rn/220Rn), that we define as a Soil Gas Disequilibrium Index (SGDI).
Since June 2006, periodical measurements of the SGDI were carried out in ten
sites located on the flanks of Mt. Etna, with sampling frequency of about ten days.
Remarkable variations in this parameter were recorded during the period 2006-2008 likely
associated with changes in the activity level of Mt. Etna. In particular, one of the sites
located in the area called Primoti (on the lower east flank of the volcano) has shown
significant anomalous changes of the SGDI in time, possibly correlated with the
eruptive/tectonic activity. For this reason, in this site we set up an automatic monitoring
station made of a Radon/Thoron monitor (model RTM 2100, SARAD GmbH, Germany)
coupled with a soil CO2 efflux station (model ACE, ADC BioScientific Ltd., UK).
The sampling frequency was set at 30 minutes, in order to allow for a sufficient
decay equilibration in the radon isotopes. Air temperature and barometric pressure
were recorded as well, with the same sampling rate as for the soil gases. The site
chosen for testing the monitoring station is located on the east flank of Mt. Etna at an
altitude of about 520 a.s.l., in an area known for widespread diffuse emissions of
CO2 and other gases of magmatic origin. The preliminary data acquired so far
showed an average soil CO2 efflux of 10 g m-2 d-1 (std dev of about 7 g m-2
d-1) and average 222Rn and 220Rn activities of about 3.3 Ã 103 Bq/m3 (std dev of
about 1140 Bq/m3) and about 2.0 Ã 103 Bq/m3 (std dev of about 620 Bq/m3),
respectively. The corresponding values of the SGDI thus obtained varied in the range
from about -1.5 to about 70.1, with an average of about 7 and standard deviation of
about 6.3. The apparent baseline of the parameter is around the value of 3, and daily
variations are clearly detected due to the combined influence of air temperature and
barometric pressure. No clear influence from rainfall was observed. Some spikes were
also detected, whose origin has to be studied by correlating the SGDI with other
environmental parameters as well as with changes in the volcanic/tectonic activity of Mt.
Etna. |
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