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.

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Graduation date: 1997

Thesis (M.S.)--Oregon State University, 1975. / Includes bibliographical references (leaves 87-94).

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 138-146). Also available on the World Wide Web.

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This thesis studied the volcanic and geothermal source of arsenic (As) and its fate in shallow ground waters and upon entering the ocean by means of experimental and field measurements combined with geochemical modeling. Arsenic enters the atmosphere and hydrosphere from degassing magmas and during volcanic eruptions. The November 2004 eruption within the Vatnajökull Glacier, Iceland, provided an opportunity to study elemental fluxes from volcanic eruptions into the environment. According to geochemical modeling, lowering of pH due to magma gases during the eruption led to rapid tephra dissolution with corresponding change in flood water chemistry. Geochemical modeling of floodwater/seawater mixing indicated localised decrease in dissolved arsenic and sulphur due to adsorption on the suspended floodwater materials. As the floodwater was diluted the As desorbed and limited effect of the floodwater was predicted after thousand fold dilution. Laboratory experiments were carried out to generate and validate sorption coefficients for arsenite and arsenate in contact with basaltic glass at pH 3 to 10. The mobility of arsenite decreased with increasing pH. The opposite was true for arsenate, being nearly immobile at pH 3 to being highly mobile at pH 10. A 1D reactive transport model constrained by a long time series of field measurements of chemical composition of geothermal effluent fluids from a powerplant was constructed. Thioarsenic species were the dominant form of dissolved As in the waters exiting the power plant but converted to some extent to arsenite and arsenate before feeding into a basaltic lava field. Chloride, moved through the basaltic lava field (4100 m) in less than 10 yrs but arsenate was retarded considerably due to surface reactions and has entered a groundwater well 850 m down the flow path in accordance to prediction by the 1D model, which further predicted a complete breakthrough of arsenate in the year 2100 while arsenite will be retained for about 1000 yrs.

The Jurassic Ferrar large igneous province of Antarctica contains significant mafic volcaniclastic deposits, underlying the Kirkpatrick flood basalts. In South Victoria Land, the mafic volcaniclastics are referred to as the Mawson Formation. At Coombs Hills, the Mawson is interpreted as filling a large vent complex, which was re-examined in detail to better understand vent-forming processes. Two contrasting types of cross-cutting volcaniclastic bodies were found in the complex, both of which are interpreted to have been forcefully emplaced from below into existing, non-consolidated debris. The first type consists of country rock-rich lapilli-tuff pipes. These are interpreted as fossilized remnants of subterranean debris jets which originated when phreatomagmatic explosions occurred near the walls or floor of the vent complex, causing fragmentation of both magma and country rock. The second type of cross-cutting body consists of basalt-rich tuff-breccias and lapilli-tuffs, some of which could have been generated by explosions taking place within pre-existing basalt-bearing debris, well away from the vent walls. Other basalt-rich zones, accompanied by domains of in situ peperite and coherent basalt, are inferred to have originated by less violent processes. At nearby Allan Hills, the Mawson can be divided into two informal members, m₁ and m₂. Member m₁ is exposed only at central Allan Hills, consists essentially of sedimentary material from the underlying Beacon Supergroup, and is interpreted as a [less than or equal to]180 m-thick debris avalanche deposit. Most megablocks in m₁ were derived from the late Triassic Lashly Formation, parts of which were probably only weakly consolidated in the Jurassic. Sandstone breccias dominate volumetrically over megablocks within the deposits. This indicates pervasive and relatively uniform fragmentation of the moving mass, and probably reflects the weak and relatively homogeneous nature of the material involved. The avalanche flowed into a pre-existing topographic depression carved into the Beacon sequence, and flow indicators reveal a northeastward movement. Sparse globular basaltic megablocks suggest that Ferrar intrusions played a role in triggering the avalanche. Member m₂, which is exposed at both central and southern Allan Hills, consists predominantly of metre-thick basaltic volcaniclastic layers that fall into three broad categories: (1) poorly sorted, coarse lapilli-tuff and tuff-breccia; (2) block-rich layers; (3) tuff and fine lapilli-tuff. The former type is interpreted as the deposits of high-concentration pyroclastic density currents (PDCs), probably formed during the collapse of phreatomagmatic eruption plumes. Occasional block-rich layers probably were formed by both ballistic fall from local vents and pyroclastic flows, and the finer-grained layers were probably deposited by dilute PDCs. Dilute, moist turbulent currents were also likely responsible for the generation and deposition of large ([less than or equal to]4.5 cm) rim-type accretionary lapilli. The thick layers are locally underlain by or interbedded with thin tuff ring-style volcaniclastic layers, and all the layers are underlain and invaded by basalt-rich tuff-breccias and lapilli-tuffs. COMPLETE REFERENCE: Ross, P.-S. (2005) Volcanology of the Mawson Formation at Coombs and Allan Hills, South Victoria Land, Antarctica. PhD Thesis, University of Otago, Dunedin, New Zealand, 400 pages, 46 tables, 162 figures, plus appendices.

The Canary islands are formed by a slow moving hotspot, from Fuerteventura 20 Ma to el Hierro 1.2Ma years old and La Palma is in the shield building stage of evolution. La Palma had its last eruption 1971 and has had seven eruptions since 1430, which makes it the most active of the islands in our times. The samples consist of host lavas, basanites, and mafic/ultramafic and felsic xenoliths, alkali gabbros and syenites respectively. Minerals in the lavas and the alkali gabbro xenolith samples are clinopyroxene, olivine, amphibole and plagioclase, the clinopyroxenes are zoned. Forsterite content in the olivines increases at the rim for the xenoliths and decreases for the host lavas. While magnesium number in the clinopyroxenes decreases towards the rim. The Fe-Mg partitioning indicates that there were points of equilibrium between the clinopyroxenes and their host lavas, which was calculated to temperature, pressure and depth indicating 62-74km for the xenoliths and 23-35km for the host lavas. The temperatures and pressures were 1184-1205°C with 6-10 kbar for the host lavas compared to 1316-1341°C and 17-20 kbar for the xenoliths.

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