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Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 190-205). Also available for download via the World Wide Web; free to University of Oregon users.

Eruption dynamics are sensitive to ash aggregation, and ash aggregates (e.g. accretionary lapilli) are commonly found in eruptive deposits, yet few experiments have been conducted on aggregation phenomena using natural materials. Experiments were developed to produce a probabilistic relationship for the efficiency of ash aggregation with respect to particle size, collision kinetic energy and atmospheric water vapor. The laboratory experiments were carried out in an enclosed tank designed to allow for the control of atmospheric water vapor. A synthetic ash proxy, ballotini, and ash from the 2006 eruption of Tungurahua, in Ecuador, were examined for their aggregation potential. Image data was recorded with a high speed camera and post-processed to determine the number of collisions, energy of collisions and probability of aggregation. Aggregation efficiency was dominantly controlled by collision kinetic energy and little to no dependence on atmospheric water vapor was seen in the range of relative humidity conditions tested, 20 to 80%. Equations governing the relationships between aggregation efficiency and collision kinetic energy and the related particle Stokes number, respectively, were determined for implementation into large scale numerical volcanic models.

abstract: Assessments for the threats posed by volcanic eruptions rely in large part on the accurate prediction of volcanic plume motion over time. That predictive capacity is currently hindered by a limited understanding of volcanic plume dynamics. While eruption rate is considered a dominant control on volcanic plume dynamics, the effects of variable eruption rates on plume rise and evolution are not well understood. To address this aspect of plume dynamics, I conducted an experimental investigation wherein I quantified the relationship between laboratory jet development and highly-variable discharge rates under conditions analogous to those which may prevail in unsteady, short-lived explosive eruptions. I created turbulent jets in the laboratory by releasing pressurized water into a tank of still water. I then measured the resultant jet growth over time using simple video images and particle image velocimetry (PIV). I investigated jet behavior over a range of jet Reynolds numbers which overlaps with estimates of Reynolds numbers for short-duration volcanic plumes. By analysis of the jet boundary and velocity field evolution, I discovered a direct relationship between changes in vent conditions and jet evolution. Jet behavior evolved through a sequence of three stages - jet-like, transitional, and puff-like - that correlate with three main injection phases - acceleration, deceleration and off. While the source was off, jets were characterized by relatively constant internal velocity distributions and flow propagation followed that of a classical puff. However, while the source was on, the flow properties - both in the flows themselves and in the induced ambient flow - changed abruptly with changes at the source. On the basis of my findings for unsteady laboratory jets, I conclude that variable eruption rates with characteristic time scales close to eruption duration have first-order control over volcanic plume evolution. Prior to my study, the significance of this variation was largely uncharacterized as the volcanology community predominately uses steady eruption models for interpretation and prediction of activity. My results suggest that unsteady models are necessary to accurately interpret behavior and assess threats from unsteady, short-lived eruptions. / Dissertation/Thesis / Ph.D. Geological Sciences 2012