Wallace, PaulLerner, Allan2020-12-082020-12-082020-12-08https://hdl.handle.net/1794/25883Interpreting volcanic behavior is challenging because the phenomena controlling volcano eruptibility occur at substantial crustal depths. However, volcanic gases are a measurable surface expression of subterranean magmatic processes. Consequently, tracking changes in rates and types of gas emissions is a principle method of monitoring volcanic unrest. The solubility and degassing of magmatic sulfur and other volatiles depend on physical (pressure, temperature) and geochemical parameters (melt composition, oxidation state) that vary widely among volcanoes and are often poorly constrained. Therefore, to better utilize gas emissions as a volcano monitoring tool, the physical and geochemical conditions of the magmatic system must be well characterized to create robust degassing models. My dissertation research aims to improve the physical and geochemical understanding of volcanic systems and how these properties affect volatile behavior. In chapter two, I compile a global database of geophysically imaged magma reservoirs at arc volcanoes. I assess the depth distribution of inferred magma bodies and their lateral locations relative to associated volcanic edifices. In chapter three, I present new techniques for correcting beam damage in silicate glasses during F-e and S-XANES measurements. These techniques enable more accurate measurements of redox states of a variety of melt compositions. In chapters four and five, I combine geophysical and petrologic data to better understand the behavior of magmatic volatiles at Kilauea (HI, USA), Augustine (AK, USA), and Mount St. Helens (WA, USA) volcanoes. I derive petrologic degassing frameworks for these volcanoes from analyses of major elements, volatiles, redox states, and sulfur isotopes that are measured in melt inclusions, matrix glasses, re-entrant channels, and silicate minerals. Petrologic gas budgets and degassing models for these volcanoes are compared to independently observed gas emissions, and will aid in the interpretation of future degassing signals at these active volcanoes. This dissertation includes both previously published and unpublished co-authored material. Supplemental data tables, a collection of volcanic edifice maps, and a Google Earth visualization database for Chapter II are available at the UO Libraries Scholars’ Bank (https://doi.org/10.7910/DVN/LHD1HY).en-USAll Rights Reserved.DegassingKilaueaMagma reservoirMelt inclusionsRedoxVolcanologyElectronic Thesis or Dissertation