EAR-PF: Does eruption trigger mechanism ultimately control eruption style at arc volcanoes?

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Dr. Rebecca deGraffenried has been granted an EAR Postdoctoral Fellowship to carry out research and education plans at the Arizona State University. Dr. deGraffenried’s project is designed to to understand the underlying factors that dictate how explosive a volcanic eruption will be in order to accurately forecast volcanic hazards when a volcano shows signs of activity. Recent work shows that the specific reason a magma begins traveling to the surface (the “eruption trigger”) influences how explosive the eventual eruption will be, although it is unclear why this is true. Both the eruption trigger and rate at which magma rises to the surface (magma ascent rate) are thought to be related to the amount of internal pressure in a given magma body. Therefore, this project aims to test whether different eruption triggers produce different magma ascent rate and will determine the ascent rates and trigger mechanisms from a range of eruption styles at Mt. St. Helens and Mt. Hood, two high threat volcanoes in the United States. Not only will this study shed light on an underlying process that controls eruption style, but it will also advance knowledge about the behavior and hazards of two very active volcanoes that threaten communities in the Pacific Northwest. The work has implications for volcanic risk and hazard assessment and will train an undergraduate in research methods. Additionally, Dr. deGraffenried will partner with Arizona State University’s “Ask an Earth and Space Scientist” to communicate with the broader community about the results of this project. This project is a petrologic investigation of two volcanoes in the Cascades volcanic arc. Subduction zone volcanoes in particular are hazardous to communities due to the range of magma compositions and eruption styles possible. Therefore, understanding the factors that influence volcanic eruption style is particularly critical for these volcanoes. Mt. St. Helens and Mt. Hood are both poised to threaten communities in the event of eruption, though they have vastly different eruptive histories. This study will utilize diffusion modeling of Fe-Mg concentration gradients in orthopyroxene to determine the timescale of ascent from storage to the surface. Additionally, eruption trigger mechanism for each eruption of interest will be determined by crystal/melt equilibrium, thermobarometers, and hygrometers. Altogether, these data will provide insights into a range of eruption styles and magma compositions represented by the two volcanoes of interest and elucidate a previously unexplored connection between eruption initiation and eruption outcome. The results of these studies could be useful in hazard forecasts as geophysical monitoring data can be used to identify certain eruption triggers. As a part of the broader impacts of this study, Dr. deGraffenried will contribute articles on volcanic processes to the “Ask an Earth and Space Scientist” series on the Arizona State University School of Earth and Space Exploration website. This series is geared towards K-12 students and answers questions these students have about how the Earth works.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.