Open AccessVariation of H 2 O/CO 2 and CO 2 /SO 2 ratios of volcanic gases discharged by continuous degassing of Mount Etna volcano, Italy
Author(s) -
Shinohara H.,
Aiuppa A.,
Giudice G.,
Gurrieri S.,
Liuzzo M.
Publication year - 2008
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jb005185
Subject(s) - volcano , magma , geology , magma chamber , bubble , impact crater , volcanic gases , gas composition , petrology , mineralogy , geochemistry , astrobiology , thermodynamics , physics , parallel computing , computer science
We applied the Multi‐GAS technique to measure compositions of the volcanic plumes continuously discharged from summit craters of Voragine, Northeast and Bocca Nuova at Mount Etna, in an attempt to estimate compositions of the source volcanic gases. The estimated CO 2 /SO 2 and H 2 O/CO 2 ratios of the volcanic gases show a large variation ranging from 0.6 to 30 and from 1 to 18, respectively. This variability overlaps with the compositional range of dissolved volatiles in melt inclusions and their coexisting bubbles in a magma chamber and can be caused by the low‐pressure degassing of a magma with variable bubble content ranging from 0.3 to 15 wt.%. The variable bubble content in the magma is likely a result of supply of deep‐derived CO 2 ‐rich gas phase to the chamber and subsequent bubble‐magma differentiation by bubble ascent in the magma chamber. In contrast, the variation of volcanic gas composition can also be caused by changes of degassing pressure (gas–magma separation pressure), ranging from 0 to 100 MPa, as a result of changes in the depth of the top of the convecting magma in volcanic conduits. Both mechanisms can cause similar compositional variations. However, the two mechanisms will result in contrasting correlations between the SO 2 emission rates and the gas compositions that can be examined by parallel observations of the emission rates and compositions in the future.