Bindeman, IlyaHudak, Michael2021-11-232021-11-232021-11-23https://hdl.handle.net/1794/26855The goal of my dissertation is to expand the application of H2O, δD, and δ18O in silicic volcanic glass to a greater diversity of pyroclast cooling, degassing, and rehydration histories. All pyroclasts must cool from magmatic temperatures and those at Earth’s surface, which can affect the distribution of H2O and its constituent isotopes in glass. Vapor hydration experiments of silicic glass constrain H2O solubility and diffusivity in glass between 175°C and 375°C. Modeling of the experimental data demonstrates that H2O diffusivities approximate extrapolations of high temperature relationships, but H2O solubility in glass is at least 1.5 wt% higher than predicted by extrapolating H2O solubilities in melts. Next, I evaluate the time evolution of δD in experimental glasses with an isotope reaction-diffusion model. Below 250°C, the δD fractionation between glass and H2O vapor (103lnαg-v) is between −25‰ and −33‰, overlapping with low temperature D/H 103lnαglass-H2O values. The boundary composition of the model controls the bulk glass composition rather than reactions of H2Om to OH− internal to the glass during hydration. These results enable interpretation of H2O, δD, and δ18O in natural samples over a large range of temperature conditions, which I first apply to cooling ignimbrites from the 7700 BP Mt. Mazama eruption and the 1912 Novarupta eruption. This work also highlights that glass hydration of pumaceous can occur rapidly over days to months and lock in a δD value that records local meteoric waters as a paleoclimate proxy. Finally, I show that glass rehydration can occur even more rapidly on the timescales in eruptive volcanic plumes with meteoric water sources using H2O–δD compositions in a suite of tephras from the 2009 eruption of Redoubt volcano. Waning influence of a summit glacier has no effect on tephra compositions, suggesting moist air entrainment is the rehydration source. Furthermore, H2O diffusion modeling illustrates that the temperatures at which erupted material comes into contact with an H2O is more important than the quench rate of the pyroclast as rehydration can occur at the fastest quench rates if H2O is available. Tephra H2O–δD compositions therefore record water-glass interactions in multiple volcanic environments.en-USAll Rights Reserved.glass hydrationH2O diffusionhydrogen isotopespaleoclimateVolcanic glassvolcanologyElectronic Thesis or Dissertation