From the cold seal to the Cook Inlet: advancing the petrological tools used to understand magma storage and ascent in explosive volcanic eruptions

Abstract

Explosive volcanic eruptions pose significant societal and economic risks, making it critical to understand the processes that govern eruption dynamics. This dissertation investigates the role of magmatic volatiles (H 2O, CO 2, S, Cl, F) in the storage, ascent, and eruption of magma, focusing on records preserved within two key petrological tools: melt inclusions and melt embayments within erupted phenocrysts. Melt inclusions provide snapshots of volatile contents at different depths, while melt embayments record changing volatile conditions during magma decompression and ascent. However, both tools have limitations that need to be addressed. The research proceeds with three main objectives: (1) to refine the use of melt embayments as geospeedometers, (2) to develop improved models for extracting magma decompression rates from melt embayments, and (3) to expand the application of melt inclusions in intermediate magmatic compositions that are associated with frequently active and high threat volcanic systems. Chapter 2 presents the first experimental decompression study of quartz-hosted melt embayments, validating the fidelity of this petrologic tool to record constant-rate decompression over a range of rates. Chapter 3 introduces a new two-stage decompression model, EDiTS, which successfully reproduces multi-stage magma ascent conditions as simulated through an experimental approach. EDiTS further reconciles embayment-based ascent rates with independent estimates, as evidenced by a case study of the May 18th, 1980 eruption of Mount St. Helens (Washington). Chapter 4 shifts to the application of melt inclusions in intermediate composition eruptions, focusing on the 2009 eruption of Redoubt Volcano in the Cook Inlet (Alaska). This chapter demonstrates that plagioclase- and pyroxene-hosted melt inclusions, if appropriately analyzed, can reliably reconstruct pre-eruptive volatile contents and magma staging conditions that agree with independent records. Importantly, these volatiles provide valuable context for observed surface gas emissions. Overall, this work advances the application of melt inclusions and melt embayments in understanding magma storage and transport conditions, thus improving our ability to leverage these tools in volcanic systems and offering new insights into eruption dynamics.