Textural Constraints on Pumice Formation and the Development of Permeability in Silicic Magmas

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9418008 Cashman Processes of volatile exsolution and gas expansion strongly influence eruptive styles of volcanoes. For this reason, rates and mechanisms of magmatic vesiculation have long been a fundamental question in volcanology. The relationship between pumice clast vesicularity, vesicle structure, permeability, and eruptive style will be determined by (1) making detailed structural measurements of pumice clasts; (2) developing techniques for determination of pumice permeability in both the solid and the liquid state, and (3) making experimental measurements of rates of bubble coalescence through use of a microscope-based heating stage and video recorder. This work will provide critical new data that are necessary input to rapidly-developing models of magma ascent, fallout of tephra eruption columns and magmatic fragmentation.