Continuous monitoring of soil CO2 flux on Mt. Etna:The 2004–2005 eruption and the role of regional tectonics and volcano tectonics.

The soil CO2 flux on Mt. Etna as recorded by the ETNAGAS network (an automatic
system for measuring soil CO2 flux and meteorological parameters) started to increase
strongly about 5 months prior to the onset of the 2004–2005 eruption and decreased a few
months before the end of the eruption. Time delays in the occurrences of anomalies in soil
CO2 flux at different sites in the geochemical network constrain the relationship between
soil CO2 flux distributions and the tectonic framework of Etna volcano. The anomalies
observed before the 2004–2005 eruption support the intrusion of new undegassed magma
into the upper feeding system of the volcano (<20 km below sea level). Magma
subsequently rose slowly in the volcano conduits, thereby triggering the onset of the
2004–2005 eruption. The time delays in the occurrences of anomalies in combination
with spectral analysis indicate the importance of tectonic and volcanotectonic structures in
driving the ascent of deep gases within the crust. Moreover, greatest amplitude pulsations
of the low-frequency components of the CO2 flux signals were correlated with the
paroxystic activities of the 2004–2005 eruption. This study confirms that CO2 flux
variation is a useful indicator for volcanic activity in the surveillance of the Mt. Etna and
similar basaltic volcanoes.

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