Bubble Nucleation in Magmas: Experimental Constraints on the Influences of Gas and Melt Composition

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Intellectual Merit. Understanding how magmas degas and erupt is a key goal for volcanologists. The critical step for degassing and eruption is bubble nucleation, and so addressing how the gas budget controls the onset of nucleation will further progress towards reaching that goal. For eruptions driven by escaping volatiles (e.g., CO2, H2O) as propellants, the mechanisms of fluid escape, or vesiculation, provide critical control. This process depends on surface tension and other properties of the melts, which in turn depend on melt composition and even the relative proportions of CO2 and H2O. Because existing data are too limited to fully predict these relations, the PI proposes a systematic study that will ultimately lead to a formal expression relating these various parameters to predict volatile solubilities and degassing, Using various melts saturated with mixed volatile contents will make results applicable to diverse volcanic systems ranging from mid-ocean ridges to subduction zones. Critical questions to be addressed include: [1] How does CO2 influence bubble nucleation in different silicate melts?, and [2] Can variations in surface tension be predicted from gas solubilities? These questions will be addressed via decompression experiments designed to constrain rates and magnitudes of bubble nucleation in various melts.Broader Impacts. This project is designed to educate a M.S. graduate student (Kathy Goepfert) and a Ph.D. graduate student (TBA) in the planning, collection, analysis, and presentation of data from experimental petrology and quantitative analytical techniques, including electron microprobe and Fourier Transform Infrared (FTIR) spectroscopy. This project will also support an undergraduate honors student who will gain valuable insight into carrying out scientific investigations from mentorship by the PI and the graduate students.