Dynamics of a powerful deep submarine eruption recorded in H2O contents and speciation in rhyolitic glass: the 2012 Havre eruption

Constraining the syn-eruptive volatile contents of magmatic melt is critical to understanding the intensities and styles of deep submarine volcanic eruptions, for which direct observations are scarce. Quantifying residual magmatic water contents in volcanic glass is complicated by rehydration, i.e., late-stage addition of molecular water. The 2012 deep submarine silicic eruption of Havre volcano provides an unusual opportunity to quantify glass water contents from a recent, well-sampled stratigraphic sequence. Fourier-transform infrared and microRaman spectroscopy measurements of water concentration and water speciation across the Havre 2012 eruptive sequence reveal an unanticipated range of excess molecular water within pumice. This excess water requires rapid timescales of diffusion that are inconsistent with our current understanding of low temperature secondary rehydration in both subaerial and subaqueous eruptive products. Diffusion models applied to enrichment profiles at vesicle edges confirm that low temperature rehydration is an unlikely cause. We instead support higher temperature, syn-eruptive pumice rehydration by condensed magmatic water and seawater in a submarine plume. Hydroxyl concentrations suggest shallow quenching depths of Havre pumice hundreds of meters above the 900-meter-deep main vent. Our data also support the presence of a vapor-rich plume and consequent modification of ocean pressure above the vent. We combine this novel volatile data with textural information and cooling rate calculations to explore the conditions that would cause slower, shallow cooling of clasts from a deep submarine eruption. By exploring the physical conditions for the interaction between pumice and submarine plumes, we emphasize fundamental differences between subaerial and submarine clast-producing eruptions.