WHERE VOLCANISM AND THE ATMOSPHERE MEET: GAS COMPOSITIONS OF VOLCANIC PUMICE CLASTS
The Bishop Tuff was produced by a ~765,000 year old large-volume silicic volcanic eruption. Relatively mineral-free pumice clasts from the Bishop Tuff were placed under 1E-2 mbar vacuum prior to analysis to remove any atmospheric contamination or adsorbed water from the pumice clasts to ensure the gasses measured were those trapped within vesicles. These samples were then placed in stainless steel crushers and pumped to high vacuum (7E-7 mbar) for 2 days prior to being crushed on-line into a calibrated quadrupole mass spectrometer. Quantified major gas species include: H2O, CO2, O2, N2 and Ar. Binning these species in to atmospheric (N2, O2, Ar with minor CO2) and volcanic (H2O and CO2 with minor, un-quantified SO2) enables us to observe the composition of the atmosphere, the composition of volcanic volatiles during eruption, and the degree to which these components mix during eruption. This novel technique for analysis of gasses trapped in vesicles of pumice clasts has broad potential for elucidating climatic processes in the past as well as the events leading to the eruption of large-volume silicic volcanic systems.