Relationship between soil CO2 flux and volcanic tremor at Mt. Etna: Implications for magma dynamics

Large variations of the CO2 flux through the soil
were observed between November 2002 and January 2006 at
Mt. Etna volcano. In many cases, the CO2 flux was strongly
influenced by changes in air temperature and atmospheric
pressure. A new filtering method was then developed to
remove the atmospheric influences on soil CO2 flux and, at
the same time, to highlight the variations strictly related to
volcanic activity. Successively, the CO2 corrected data were
quantitatively compared with the spectral amplitude of the
volcanic tremor by cross correlation function, cross-wavelet
spectrum and wavelet coherence. These analyses suggested
that the soil CO2 flux variations preceded those of volcanic
tremor by about 50 days. Given that volcanic tremor is
linked to the shallow (a few kilometer) magma dynamics
and soil CO2 flux related to the deeper (*12 km b.s.l.)
magma dynamics, the ‘‘delayed similarity’’ between the
CO2 flux and the volcanic tremor amplitude was used to
assess the average speed in the magma uprising into the
crust, as about 170–260 mper day. Finally, the large amount
of CO2 released before the onset of the 2004–2005 eruption
indicated a deep ingression of new magma, which might
have triggered such an eruption.