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Paper No. 241-3
Presentation Time: 10:35 AM

THE VOLCANIC EXPLOSIVE-EFFUSIVE TRANSITION EXPLAINED BY COMPETING OUTGASSING MECHANISMS


HERBST, Thomas, Geological Sciences, University of Missouri, 101 Geological Sciences Bldg, Columbia, MO 65211, WHITTINGTON, Alan, Department of Geological Sciences, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249; Department of Geological Sciences, University of Missouri, 101 Geology Building, Columbia, MO 65211, PISTONE, Mattia, University of Lausanne, Lausanne, Switzerland; Department of Geology, University of Georgia, Athens, GA 30602, SCHIFFBAUER, James D., Department of Geological Sciences, University of Missouri, Columbia, MO 65211; X-ray Microanalysis Core, University of Missouri, 101 Geological Sciences Building, Columbia, MO 65211 and SELLY, Tara, X-ray Microanalysis Core, University of Missouri, 101 Geological Sciences Building, Columbia, MO 65211; Geological Sciences, University of Missouri, 101 Geological Sciences Building, Columbia, MO 65211

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.

Session No. 241

T36. Experimental and Petrologic Investigation of Halogens, Sulfur, and Other Volatile Species in Igneous Systems: In Honor of Jim Webster
Friday, 30 October 2020: 10:00 AM-2:00 PM
Geological Society of America Abstracts with Programs. Vol 52, No. 6
doi: 10.1130/abs/2020AM-359881
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