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In situ X-ray tomographic microscopy observations of vesiculation of bubble-free and bubble-bearing magmas

Pistone, Mattia
Fife, Julie
Mader, Kevin
Ulmer, Peter
Published in Bulletin of volcanology. 2015, vol. 77, no. 108
Abstract Magma degassing is thought to play a major role in magma fractionation, transport, storage, and volcanic eruption dynamics. However, the conditions that determine when and how magma degassing operates prior to and during an erup- tion remain poorly constrained. We performed experiments to explore if the initial presence of gas bubbles in magma influ- ences the capability of gas to escape from the magma. Vesic- ulation of natural H2O-poor (<<1 wt.%) silicic obsidian glasses was investigated by in situ, high temperature (above the glass transition) experiments using synchrotron-based X- ray tomographic microscopy with high spatial (3 μm/pixel) and temporal resolution (1 second per 3D dataset). As a vali- dation, a second set of experiments was performed on identi- cal starting materials using a Karl-Fisher titration setup toquantify the amount of extracted gas that escapes via volatile diffusion and/or bubble coalescence during vesiculation. In both sets of experiments, vesiculation was triggered by heating the samples at room pressure. Our results suggest that the presence of pre-existing gas bubbles during a nucleation event significantly decreases the tendency of bubbles to coa- lesce and inhibits magma outgassing. In contrast, in initially bubble-free samples, the nucleation and growth of bubbles is accompanied by significant coalescence and outgassing. We infer that volatile-undersaturated (i.e. bubble-free) magmas in the reservoirs are more likely to erupt effusively, while the presence of excess gas already at depth (i.e. bubble-bearing systems) increases the likelihood of explosive eruptions.
Keywords MagmasVesiculationBubblesDegassingOutgassingSynchrotronX-rayExperimentsVolcanic eruption style
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Research group Petrology and Volcanology
Swiss National Science Foundation: 200020–120221
Swiss National Science Foundation: 200021_150204
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PISTONE, Mattia et al. In situ X-ray tomographic microscopy observations of vesiculation of bubble-free and bubble-bearing magmas. In: Bulletin of volcanology, 2015, vol. 77, n° 108. doi: 10.1007/s00445-015-0992-1 https://archive-ouverte.unige.ch/unige:78386

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Deposited on : 2015-12-08

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