HR: 09:00h
AN: V11F-05 INVITED    [Abstracts]
TI: Inferring gas transport mechanisms through volcanic gas measurements
AU: * Edmonds, M
EM: medm06@esc.cam.ac.uk
AF: University of Cambridge, Earth Sciences Department, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AB: The composition of volcanic gases is controlled by a number of factors, such as the initial concentration of volatiles in the magma; the rate of volatile diffusion through the melt with respect to decompression rate; the depth and style of melt-vapour separation; the degree of equilibration between ascending gases and resident shallow magma; and the extent to which the vapour phase interacts with a hydrothermal system. All of these processes influence the proportions and fluxes of the major species in volcanic gases. Measurements of volcanic gas species from both basaltic and silicic systems allow insight into the mechanisms of gas transport, from its exsolution to its escape into the atmosphere. At Kilauea Volcano, the composition of gas (measured by FTIR) emitted during different styles of activity constrains the depth and mode of vapour-melt separation that occurs in the conduit. Distinct degassing regimes can be identified: gas accumulation at depth followed by rapid ascent is associated with the emission of CO₂-rich gases; ascent and growth of large bubbles through relatively stagnant magma is accompanied by H₂O-rich gases. At the andesitic Soufriere Hills Volcano, SO₂ flux is measured by UV spectrometers (DOAS) during dome-building and during explosive activity. Observations suggest that an S-rich vapour phase may flow through a shear zone at the conduit walls, derived from a mafic, unerupted magma, thus bypassing shallow bubble networks. Volcanic gas measurements are thus a valuable addition to the existing pool of observational, experimental, numerical and theoretical observations elucidating gas transport through magma.
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8419 Volcano monitoring (7280)
DE: 8425 Effusive volcanism
DE: 8430 Volcanic gases
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting