Temporal Geochemical Variations In Volatile Emissions From Mount St Helens, Usa, 1980-1994

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Journal Article: Temporal Geochemical Variations In Volatile Emissions From Mount St Helens, Usa, 1980-1994

Abstract
Fumarole discharges (95-560°C) collected from the dacite dome inside Mount St. Helens crater show temporal changes in their isotopic and chemical compositions. A ΔD vs. Δ18O plot shows that condensed waters from the gases are mixtures of meteoric and magmatic components, but that the apparent magmatic end-member in 1994 was depleted by about 7‰ in ΔD relative to the apparent end-member in 1980. Based on ΔD modeling, approximately 63% of shallow, post-1980 magma has yet to degas. Surprisingly, Cl and F contents in the 1994 samples were only 0.47 and 3.8%, respectively, of the concentrations determined for end-member magmatic fluid in 1980. The data indicate that Cl (and F and B) is degassed from magma relatively quickly compared to water and/or that most of the Cl degassed in later years is dissolved into the shallow Mount St. Helens hydrothermal system. Because metals are often transported in magmatic and hydrothermal fluids as Cl complexes, rapid changes in surface volatile compositions may have implications for the timing and location of metals transport and deposition in some volcanoes.

Authors 
L. Shevenell and F. Goff








Published Journal 
Journal of Volcanology and Geothermal Research, 2000





DOI 
Not Provided
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Citation

L. Shevenell,F. Goff. 2000. Temporal Geochemical Variations In Volatile Emissions From Mount St Helens, Usa, 1980-1994. Journal of Volcanology and Geothermal Research. (!) .