UBC Theses and Dissertations
Shallow subaqueous and subglacial explosive eruptions : quantifying controls on the dynamics, stability, evolution, and stratospheric injection of water-rich eruption columns Rowell, Colin Richard
Explosive eruptions impact global climate through stratospheric injection of SO₂ to form sulfate aerosols. The stratospheric delivery and life time of sulfur is sensitive to eruption height and cloud chemistry which are, in turn, influenced by plume water and fine ash concentration. Diverse processes that result from the interaction of magma with surface water give rise to ash columns that are abundant in water and fine ash, have characteristically unsteady source conditions, and are prone to gravitational collapse. All of these effects have significant consequences for plume rise height, stratospheric delivery, and the chemical and microphysical evolution of SO₂ and aerosols, but associated relationships have not been systematically explored and the climate impacts of hydrovolcanic eruptions remain poorly constrained. To address this knowledge gap, I build a novel 1-dimensional model for hydrovolcanic eruptions simulating magma ascent in the conduit, magma-water interaction in a subaqueous pyroclastic jet, and subaerial plume rise. Critically, I make predictions of the water depths through which eruptions of a given magnitude can penetrate to form buoyant, ash-laden eruption columns, as well as the abundance of fine ash and water mass in the resulting eruption clouds. A water layer of 50 to 70 m thickness overlying a volcanic vent is sufficient to increase by an order of magnitude the mass eruption rate required for buoyant stratospheric plumes. Next, I apply the hydrovolcanic model to reconstruct the 1918 subglacial eruption of Katla volcano. Combined with a model governing the ice melt and drainage from the subglacial eruption site and constrained by eyewitness accounts, I show that the timing of emergence of the subaerial eruption column required early drainage of the englacial cauldron by subglacial pathways. Finally, I develop a machine learning algorithm to track coherent vortices in thermal imagery of unsteady eruption plumes from Sabancaya Volcano, Peru, quantifying their time-evolving thermal mixing behavior. Tracking results demonstrate evolution of entrainment and mixing behavior between predictions for sustained and instantaneous plume sources. Analysis of unsteady plume sources leads to a preliminary framework for quantitative definitions of source unsteadiness and its impact on hydrovolcanic and other unsteady explosive eruption plumes.
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