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Dissertation/Thesis Abstract

Explosive Subaqueous Eruptions: The Influence of Volcanic Jets on Eruption Dynamics and Tephra Dispersal in Underwater Eruptions
by Cahalan, Ryan Cain, Ph.D., University of Oregon, 2020, 130; 28150103
Abstract (Summary)

Subaqueous eruptions are often overlooked in hazard considerations though they represent significant hazards to shipping, coastlines, and in some cases, aircraft. In explosive subaqueous eruptions, volcanic jets transport fragmented tephra and exsolved gases from the conduit into the water column. Upon eruption the volcanic jet mixes with seawater and rapidly cools. This mixing and associated heat transfer ultimately determines whether steam present in the jet will completely condense or rise to breach the sea surface and become a subaerial hazard. We develop a multiphase model with sub-grid calculations for in situ steam condensation to explore the relationship between eruption conditions (e.g. water depth, mass flux, eruption temperature) and the produced steam jet height and breach potential. We find that mass flux is the predominant control of jet height, more so than aspects of vent geometry.

After investigation of the controls of jet dynamics, we determine how jet dynamics affect mass transport and partitioning in the water column. Ultimately, this is the principle concern in studying eruptions, to determine when, where, why, and how tephra is deposited. We utilize the multiphase subaqueous eruption model to take the fundamental step in this investigation, to identify transport mechanisms that lead to different mass partitioning outcomes. The results of this investigation show trends in mass partitioning associated with varying eruption parameters (eruption temperature and vent velocity) and particle parameters (size, density, concentration). We compare mass partitioning results for eruptions with and without gas jets to define features specific to explosive eruptions. Finally, we aggregate the model results and observations into eruption column transport regimes. This work represents the first look at many of these dynamic processes.

Indexing (document details)
Advisor: Dufek, Josef
Commitee: Giachetti, Thomas, Wallace, Paul, Sutherland, Kelly
School: University of Oregon
Department: Department of Geological Sciences
School Location: United States -- Oregon
Source: DAI-B 82/9(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Geology, Environmental Geology
Keywords: Computational modeling, Eruption dynamics, Hydrous phase change, Subaqueous volcanology, Submarine volcanology, Volcanic jets, Underwater eruptions
Publication Number: 28150103
ISBN: 9798597074252
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