A plethora of magmatic processing occurs in magma reservoirs, where melts are stored prior to eruption. Magma reservoirs are complex, open systems, and often multiple reservoirs are partially inter-connected from source to surface, giving rise to the term 'volcanic plumbing system'. Parental melts feeding these reservoirs can have diverse and distinct geochemical and petrological characteristics, and be variably evolved or enriched. These melts can also bring with them a crystal cargo that may remain in equilibrium in the magma reservoir, but may also be modified by reaction, resorption, crystallisation and diffusion. Melts and crystals can be transported between reservoirs, from the upper mantle and through the crust, leading to melt mixing, reactions and volatile exsolution. Basaltic volcanic systems are fed by primitive melts, and due to the rapid ascent of melts and short magma storage times, these volcanoes provide the best means of unravelling the mantle and crustal contribution to geochemical heterogeneity observed in erupted samples. Despite the potential chemical complexity of a magma reservoir, evidence for magma processing and reaction can be preserved in melt inclusion suites and the compositional structure of their host crystals. Magmatic processes during storage and transport at two basaltic volcanoes are investigated using two carefully selected eruptions: the 1669 eruption at Mt. Etna, and the 2007 Father's Day eruption at Kīlauea. A suite of diverse geochemical, petrological and petrographical observations, made at a range of length-scales, are combined and interpreted in tandem with geophysical monitoring data. The conclusions of these studies shed light on the architecture of each volcano's plumbing systems and basaltic plumbing systems in general. This thesis is divided into two parts. The first study unravels the crustal and mantle processes controlling melt geochemical heterogeneity at Mt. Etna, Sicily, during the 1669 eruption, the largest eruption in historical times. The 1669 melt inclusion suite arises from the mixing of two basaltic melts with similar major element compositions but very different trace and volatile element compositions. The melt geochemistry suggests that at least one end-member melt has been heavily influenced by assimilation of carbonate in the crust. The elevation in alkalis, caused by carbonate assimilation, enhances carbon and sulfur solubility in one end member. The melt inclusion suite indicates that mixing of these melts occurred in the shallow crust shortly before eruption and this mixing may be the cause of the enhanced $CO_{2}$ fluxes prior to eruptions at Mt. Etna. The second study is split into two parts. Each uses the eruptive products of the Father's Day eruption at Kīlauea and aims to unravel the connectivity of the plumbing system between the summit and East Rift Zone, with a focus on timescales of storage and transport. The first part investigates the melt geochemistry in terms of heterogeneity and volatile composition, and the second investigates the crystal cargo in terms of features of the macro-scale crystal cargo distribution and the micro-scale geochemical zoning of individual crystals. The integration of observations and models from these two studies constrains the pressure, temperature and composition of source magma feeding the Father's Day eruption. The eruption is investigated in the context of the "magma surge'' event that preceded the intrusion, as well as within the context of the longer-term trends in Kīlauea geochemistry at the summit and East Rift Zone. Melt inclusion and matrix glass volatile systematics provide insights into the degassing path of the magma and the duration of magma transport to the surface is constrained by diffusion modelling. Estimated timescales for ascent by diffusion modelling of macrocryst major element composition, melt inclusion water content and the melt Fe$^{3+}$/Fe$_{tot}$ ratio are in agreement with timescales observed from the geophysical data of $< $8 hours from reservoir depth to eruption. Both studies emphasise how petrological observations can supplement geophysical monitoring datasets collected at the surface to aid our interpretation of volcanic behaviour and eruption forecasting.

It is clear that ecosystems are devastated after a volcanic eruption coats the landscape with a layer of ash; however, the ecological recovery of mammalian communities after eruptions is poorly understood. Volcanic eruptions vary with magnitude and type and only a fraction of them have been analyzed for effects on mammalian communities. To better understand mammalian community recovery, I investigated three different lines of evidence. First, I created a new numeric metric for statistically analyzing reproductive strategies in mammals and tested the impact of diet and body size on reproductive strategies within a phylogenetic framework as proof of concept. The trend of lower reproductive rates and larger body size hold true for herbivores and omnivores, but different trajectories exist for carnivores. Second, I investigated how species richness, evenness, and similarity change across volcanic boundaries in the 1980 Mount St. Helens (MSH), Washington, and 1914-1917 Mount Lassen, California, eruptions. Richness and evenness remain unchanged in Lassen. MSH saw an immediate drop in richness followed by an increase over five years to pre-eruptive levels. Chord distance analysis suggests no long-term change in the Lassen fauna. The pre- and post-MSH fauna are different from one another. The post-eruptive fauna was more similar to neighboring regions. Lastly, I tested whether the Oligocene horse Miohippus demonstrated morphological changes across the volcanic Picture Gorge ignimbrite (PGI; 29.069 Ma) in the John Day Formation of Oregon. Variation in upper and lower teeth was first tested to define a single species in the assemblage. Length, width, and wear of teeth were compared across the PGI and there were no significant differences between pre- and post-PGI assemblages. It is clear from my results that larger eruptions tend to have a greater impact on mammalian community recovery than smaller eruptions, but ultimately, mammalian populations are robust and the presence of neighboring communities is important for recolonizing devastated areas. There are two supplemental files associated with this dissertation, a CSV file of raw data downloaded for Chapter III and an excel file of raw data and coefficient of variation calculations for Chapter IV. This dissertation includes both unpublished and co-authored material.

The Little Drum Mountains represent a deeply eroded Eocene-Oligocene volcano, consisting of a vent complex which erupted mafic flows and flow breccias, accompanied by lahars. Flows are dominated by members of the shoshonite suite and contain up to 3.95 percent K2O, mainly occult in K-rich glass, with K2O/Na2O ratios greater than 1.0. In a few interbedded flows, apparently of the calc-alkaline series, pyroxene with varying amounts of plagioclase in a fine-grained groundmass of plagioclase, mafic minerals, and interstitial glass. An ash-flow tuff of the Oligocene Needles Range Formation unconformably overlies the volcanic sequence. Contemporaneous eruptions of calc-alkaline and shoshonitic lavas are possibly related to different depths of magna derivation corresponding to two mid-Cenozoic imbricate subduction zones beneath the western United States.

Recent ocean sediments collected offshore Chile by Ocean Drilling Program Leg 202 contained layers of volcanic ash of unknown origin. These deposits may have originated from sources in the Southern Volcanic Zone (SVZ) within the Andean Volcanic Belt to the east, or from explosive volcanoes in the southwestern Pacific transported by westerly prevailing winds. In this study, mineral and glass textures and compositions of Leg 202 ashes were evaluated to try to determine the sources of the ash layers. Ash fragments were imaged and analyzed for major elements using an SEM with X-Ray detector and for trace elements using LA-ICPMS. Results show that the ash samples are rhyolitic and that they formed in a subduction zone setting or a continental margin. The ash samples have distinct physical and geochemical features that can be used in the future to identify their source(s) by comparison to databases of Pleistocene Recent explosive volcanic eruptions.

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.

This thesis examines different methods of communicating volcanic hazards to the population of Flagstaff, Arizona using the results of a recent lava flow hazard assessment of the nearby San Francisco Volcanic Field (SFVF). Harburger (2014) determined that given a lava flow originating in the SFVF, there is a statistical probability that it will inundate the city of Flagstaff or even originate from a vent within the city limits. Based on the recurrence rates for the most recent eruptions (3 x 10-4/year), the probability of lava flow inundation in Flagstaff is 1.1 x 10-5 per year. This study considers the effects of three different communication methods on participants’ perceived risk. The methods were administered through a questionnaire and included a statement of probability of lava flow inundation per year, a statement of probability over a 100 year period, and an interactive lava flow map derived from the results of the lava flow hazard assessment. Each method was followed by questions gauging level of concern. Questionnaires were administered to 213 Flagstaff residents over a two week period in February 2015. Results showed that levels of concern, rated from 1 (not concerned) to 5 (very concerned), varied based on each method of communication. The method with the greatest effect on perceived risk was the simulated lava flow map, while the first method with a one year odds resulted in a statistically lower mean rating of concern. It is suggested that the best way to change levels of perceived risk when communicating lava flow hazards includes a combination of comprehensible odds and visual aids. Further studies could also include visualization of the entire eruption scenario, including time scales and other volcanic hazards, which may have more effect on concern than a simplified visualization of lava flows.

Αντικείμενο της παρούσας εργασίας είναι η ανάλυση και ερμηνεία των θαλάσσιων γεωλογικών – γεωφυσικών δεδομένων τα οποία έχουν συλλεχθεί από το υποθαλάσσιο τμήμα της Καλδέρας της Σαντορίνης. Σκοπός της εργασίας είναι: • να μελετηθεί η υποθαλάσσια μορφολογική και γεωλογική δομή της Καλδέρας, • να αναλυθεί η σεισμική στρωματογραφία των ηφαιστειακών αποθέσεων κάτω από τον πυθμένα και ιδιαίτερα των αποθέσεων που προέκυψαν από την Μινωική έκρηξη • να συσχετισθούν οι σεισμικοί ορίζοντες με αντίστοιχες ηφαιστειακές αποθέσεις και ορίζοντες που έχουν χαρτογραφηθεί στην Σαντορίνη και τέλος • να γίνει προσπάθεια αναπαράστασης της μορφολογίας της καλδέρας πριν την Μινωική έκρηξη. Στη παρούσα εργασία χρησιμοποιήθηκαν γεωφυσικά δεδομένα που συλλέχθηκαν από το Ω/Κ ΑΙΓΑΙΟ του Ελληνικού Κέντρου Θαλάσσιων Ερευνών με τη χρήση συστημάτων υποθαλάσσιας γεωφυσικής διασκόπησης (σεισμικά ανάκλασης) και πολυδιαυλικής βυθομέτρησης στα πλαίσια του ερευνητικού προγράμματος THERA 2006, σε συνεργασία με το University of Rhodes Island, USA και με χρηματοδότηση από το National Science Foundation. / The object of this work is the analysis and interpretation of marine geological - geophysical data which has been collected from the offshore part of the caldera of Santorini. The purpose of this paper is: • To study the underwater geological and morphological structure of Caldera • To analyze the seismic stratigraphy of the volcanic deposits under the bottom and especially the deposits obtained from the Minoan eruption • To compare the seismic horizons with the corresponding deposits and volcanic horizons that have been mapped to Santorini and finally • To attempt representation of the morphology of the caldera before the Minoan eruption The present study includes geophysical data collected by the Oceanographic vessel AEGEAN of the Hellenic Centre for Marine Research with the use of underwater geophysical ( seismic reflection ) and multiplexer sounding of the research program THERA 2006, in collaboration with the University of Rhodes Island, USA and funded by the National Science Foundation.

This presentation contains photographs taken during the Little Springs Ethnographic Investigation. These photographs are meant to supplement the information presented in the report entitled: Unav~Nuquaint: Little Springs Lava Flow Ethnographic Investigation (Van Vlack et al. 2013).

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