Long-term changes in quiescent degassing at Mount Baker Volcano, Washington, USA; Evidence for a stalled intrusion in 1975 and connection to a deep magma source

Journal of Volcanology and Geothermal Research
By: , and 

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Abstract

Long-term changes have occurred in the chemistry, isotopic ratios, and emission rates of gas at Mount Baker volcano following a major thermal perturbation in 1975. In mid-1975 a large pulse in sulfur and carbon dioxide output was observed both in emission rates and in fumarole samples. Emission rates of CO2 and H2S were ∼ 950 and 112 t/d, respectively, in 1975; these decreased to ∼ 150 and < 1 t/d by 2007. During the peak of the activity the C/S ratio was the lowest ever observed in the Cascade Range and similar to magmatic signatures observed at other basaltic–andesite volcanoes worldwide. Increases in the C/S ratio and decreases in the CO2/CH4 ratio since 1975 suggest a long steady trend back toward a more hydrothermal gas signature. The helium isotope ratio is very high (> 7 Rc/RA), but has declined slightly since the mid-1970s, and δ13C–CO2 has decreased by ≥ 1‰ over time. Both trends are expected from a gradually crystallizing magma. While other scenarios are investigated, we conclude that magma intruded the mid- to shallow-crust beneath Mount Baker during the thermal awakening of 1975. Since that time, evidence for fresh magma has waned, but the continued emission of CO2 and the presence of a long-term hydrothermal system leads us to suspect some continuing connection between the surface and deep convecting magma.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Long-term changes in quiescent degassing at Mount Baker Volcano, Washington, USA; Evidence for a stalled intrusion in 1975 and connection to a deep magma source
Series title Journal of Volcanology and Geothermal Research
DOI 10.1016/j.jvolgeores.2009.07.006
Volume 186
Issue 3-4
Year Published 2009
Language English
Publisher Elsevier
Contributing office(s) Volcano Science Center, Volcano Hazards Program
Description 8 p.
First page 379
Last page 386
Country United States
State Washington
Other Geospatial Mount Baker Volcano