Publication Date:
2017-04-04
Description:
This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–
January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with
changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack
methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume
S/Cl ratios increased by a factor of f10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late
November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl = 0.1) typical of
the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is
proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a
volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed
melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254–255]. According to this model, degassing of Etnean
basaltic melt at high pressures and depths (〉100 MPa, 3 km) is likely to release a CO2+H2O-rich vapor phase with S/Cl molar
ratios f1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth ( P 〈 20 MPa, 0.6 km),
with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and
volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased
degassing due to depressurization of a basaltic magma batch ascending toward the surface.
Description:
Published
Description:
469-483
Description:
partially_open
Keywords:
magmatic degassing
;
volcanic plume
;
basaltic eruption
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
532 bytes
Format:
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Format:
text/html
Format:
application/pdf
