From Rhyolite to Basalt and Conduit Flow to Lava Flow: How Good are Our Models?

deGraffenried, Rebecca
Shea, Thomas
Earth and Planetary Sciences
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Volcanic eruptions impact human lives in a multitude of ways, mainly dependent on eruption intensity and style. Broadly speaking, powerfully explosive eruptions produce large plumes of ash and pyroclastic density currents, whereas effusive to weakly explosive eruptions can produce scoria cones and ramparts, as well as lava domes and flows, depending on the fluidity of the lava. On either end of this explosivity spectrum, unique hazards exist that disaster management agencies must mitigate to keep nearby populations safe. As our understanding of volcanic eruptions and their underlying processes has been refined, our ability to forecast volcanic hazards has begun to improve. In this dissertation, I examine two key processes that are used to forecast impacts of volcanic eruptions: magma decompression and lava flow propagation. Magma decompression rate is a critical parameter that influences whether a magma will erupt explosively, and thus it requires accurate determination. A new, promising technique to calculate magma decompression rate utilizes small pockets of magma trapped within crystals that remained open to the host magma, called melt embayments. These embayments develop concentration gradients in dissolved volatiles (e.g., H2O, CO2) during decompression that can be measured. Assuming the concentration gradients are formed purely through diffusive loss of the volatiles from the embayment to the host magma, the decompression timescale (and by extension decompression rate) that the embayments experienced can be calculated. This technique is gaining use due to its relative ease of implementation, the prevalence of embayments, and the wide range of decompression rates that can be resolved, provided an appropriate diffusing volatile species is present and measured. However, this technique has not undergone any testing to verify that the current modeling standard is not introducing its own error. Therefore, I quantify the amount of error introduced into calculated timescales by modeling simplifications numerically. Other decompression rate meters can be used in conjunction with diffusion modeling to quantify the range of decompression rates during the course of a volcanic eruption. However, this is a relatively new approach, so I conduct decompression experiments that use two decompression rate meters in the same experimental charge to evaluate whether these meters are compatible with each other. Additionally, the experiments provide insights into the assumptions needed to recover a known decompression rate. Once lava erupts on the surface, it can produce lava flows that are destructive to nearby communities, as in the 2018 eruption of Kīlauea, HI. Forecasting the path and velocity of lava flows is a crucial step to issue accurate warnings and implement effective evacuations. The 2018 Kīlauea eruption is an excellent natural laboratory to test previous forecasting methods as the data on the flows is exceptional in its temporal resolution, with daily overflights by the response team with both helicopters and drones, as well as daily overflights by commercial photographers. I utilize equations from two complimentary studies that predict lava flow length through time by calculating the evolution of various lava properties that serve to slow the flow. This study focuses on three flows during the eruption that span a range of lava composition, crystallinity, and duration to test the applicability of equations that require limited a priori knowledge of flow conditions. Altogether, this dissertation provides new insights to implementation of simulations of volcanic processes that will aid future modelers.
Geology, Geochemistry, Diffusion modeling, Magma decompression, Rheology, Volcanology
153 pages
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