V021-0009
The volcanic explosive-effusive transition explained by competing outgassing mechanisms

Thursday, 10 December 2020
Poster
Thomas Herbst1, Alan G Whittington2,3, Mattia Pistone4,5, James D. Schiffbauer2,6 and Tara Selly2,6, (1)University of Missouri Columbia, Columbia, MO, United States, (2)University of Missouri, Geological Sciences, Columbia, MO, United States, (3)University of Texas at San Antonio, Geological Sciences, San Antonio, TX, United States, (4)University of Georgia, Athens, GA, United States, (5)University of Lausanne, Earth Sciences, Lausanne, Switzerland, (6)University of Missouri, X-Ray Microanalysis Core Facility, Columbia, MO, United States
Abstract:
Lava dome-forming volcanoes commonly switch between effusive and explosive styles of eruption. Eruptions are driven by gas overpressure, which can be released through development of permeability, yet the least permeable magmas often erupt effusively. We studied gas exsolution and outgassing through experimental vesiculation of hydrous dacite glass samples containing crystal fractions between 0 and 0.8. Outgassing occurs rapidly via fracturing at crystal fractions ≥ 0.7, implying that crystal-rich effusive lavas are likely healed remains of fractured, initially more hydrous magmas. Fracturing and bubble coalescence are both inefficient at crystal fractions of 0.5–0.6, implying eruptive behavior of lava domes can fluctuate in response to minor changes in crystallinity or ascent rate. We delineate a critical permeability-porosity threshold separating effusive magmas from those with explosive potential.
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