Experiment Vs Nature: Using Amphiboles To Test Models Of Magma Storage And Pre-Eruptive Magma Dynamics Preceding The 2006 Eruption Of Augustine Volcano, Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 2013This study investigates magmatic conditions preceding the 2006 eruption of Augustine Volcano through the use of amphibole compositions and textures. Due to their restricted stability region and common occurrence in calc-alkaline magmas, amphiboles are important for investigating pre-eruptive magmatic conditions at subduction zone volcanoes. Chapter 1 presents a study into geochemical and textural variations of natural amphibole phenocrysts in the erupted magmas. Magnesiohornblendes in the high- and low-silica andesites exhibit limited compositional variability. Intermediate-silica andesites and quenched mafic enclaves contain amphiboles that vary in composition and classification (magnesiohornblende-magnesiohastinsitetschermakite). Compositional variations are controlled by temperature-dependent substitutions. Both high-and low-silica andesites represent magmas that were stored in the shallow crust at 4-8 km depth, remaining distinct due to a complex sub-surface plumbing system. Intermediate-silica andesites and quenched mafic inclusions represent newly formed hybrids of resident high- and low-silica andesite magmas and an intruding basalt. Chapter 2 presents the results of a phase equilibria study the refines the model for high-silica andesite storage. The natural phase assemblage was reproduced between 860-880�C and 120-200 MPa. Experimental plagioclase and groundmass glass compositions most closely replicate natural samples at ~130-140 MPa. Estimated storage conditions fall within the ranges suggested by natural petrological data and modeled storage depths from geodetic data. The high temperature stability of experimental quartz and biotite (not identified in natural samples) may reflect the high f 02 of the Augustine system as well as the rapid kinetics associated with the crystal-poor sintered starting material of some experiments. Chapter 3 presents results of the first experimental study to target heating-induced amphibole reaction rim formation. Experiments show that reaction rims form on remarkably short timescales. They share mineralogical and textural features with natural reaction rims previously thought to represent decompression processes. Reaction rims cannot be simply classified on the basis of semi-quantitative observations. Rather, in-depth data collection (e.g. X-rap mapping), and the calculation of kinetic parameters (e.g. crystal nucleation rates), is necessary. Chapter 4 presents a new MATLABRTM based program that performs mineral formula recalculations and the associated propagation of analytical uncertainty

Perceptions of Stress, Mindfulness, and Occupational Engagement Among Graduate-level Occupational Therapy Students

Previous literature explored the concepts of stress, mindfulness, and occupational engagement, yet there is a substantial gap linking these terms within the field of occupational therapy (OT). The researchers identified a need to investigate the perceptions of these concepts among graduate-level OT students and its impact on their quality of life and occupational balance. Current research identified mindfulness and occupational engagement as healthy coping strategies for reducing stress and both concepts emphasized the action of being fully present and engaged. The exploratory mixed-methods study consisted of 490 students from graduate-level OT programs throughout the United States. Results revealed that the majority of participants experienced high levels of stress while in graduate school. The findings indicated that stress, academic responsibilities, and limited application of coping strategies impacted the ability to engage in meaningful activities. Participants identified mindfulness as an effective coping mechanism, which included strategies of deep breathing, journaling, and meditation in addition to the act of being mindful through self-reflection and self-awareness. Although participants reported positive views of mindfulness to decrease stress, the reported use did not appear to alter the participants’ perceptions of quality of life. Findings suggested a lack of occupational engagement in meaningful activities negatively impacted the participants’ perceived quality of life and occupational balance. The study provided support for strengthening the connection between the constructs of mindfulness and occupational engagement. The study has broad implications for the field of OT and its applicability to stress management in both academic and professional settings

Petrological architecture of a magmatic shear zone: A multidisciplinary investigation of strain localisation during magma ascent at Unzen volcano, Japan

Shearing of magma during ascent can promote strain localisation near the conduit margins. Anymechanical and thermal discontinuities associated with such events may alter the chemical, physicaland rheological stability of the magma and thus its propensity to erupt. Lava spines can record suchprocesses, preserving a range of macroscopic and microscopic deformation textures, attributed toshearing and friction, as magma ascends through the viscous-brittle transition. Here, we use a multi-disciplinary approach combining petrology, microstructures, crystallography, magnetics and experi-mentation to assess the evidence, role and extent of shearing across a marginal shear zone of the1994–1995 lava spine at Unzen volcano, Japan. Our results show that crystals can effectively moni-tor stress conditions during magma ascent, with viscous remobilisation, crystal plasticity and com-minution all systematically increasing towards the spine margin. Accompanying this, we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex-tural variations across the shear zone, from symplectitic to granular rims towards the spine margin.In addition, the compaction of pores, chemical and textural alteration of interstitial glass and mag-netic variations all change systematically with shear intensity. The strong correlation between thedegree of shearing, crystal deformation and disequilibrium features, together with distinct magneticproperties, implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent. This was accompanied by late-stage or post-emplacement fluid- andgas-induced alteration of the gouge, as well as oxidation and glass devitrification. Understandingand recognising evidence for strain localisation during magma ascent may, therefore, be vital whenassessing factors that regulate the style of volcanic eruptions, which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava dome

Spine growth and seismogenic faulting at Mt. Unzen, Japan

The concluding episode of activity during the recent eruption of Mt. Unzen (October 1994 to February 1995) was characterized by incremental spine extrusion, accompanied by seismicity. Analysis of the seismic record reveals the occurrence of two dominant long‐period event families associated with a repeating, nondestructive source mechanism, which we attribute to magma failure and fault‐controlled ascent. We obtain constraints on the slip rate and distance of faulting events within these families. That analysis is complemented by an experimental thermomechanical investigation of fault friction in Mt. Unzen dacitic dome rock using a rotary‐shear apparatus at variable slip rates and normal stresses. A power density threshold is found at 0.3 MW m−2, above which frictional melt forms and controls the shear resistance to slip, inducing a deviation from Byerlee's frictional law. Homogenized experimentally generated pseudotachylytes have a similar final chemistry, thickness, and crystal content, facilitating the construction of a rheological model for particle suspensions. This is compared to the viscosity constrained from the experimental data, to assess the viscous control on fault dynamics. The onset of frictional melt formation during spine growth is constrained to depths below 300 m for an average slip event. This combination of experimental data, viscosity modeling, and seismic analysis offers a new description of material response during conduit plug flow and spine growth, showing that volcanic pseudotachylyte may commonly form and modify fault friction during faulting of dome rock. This model furthers our understanding of faulting and seismicity during lava dome formation and is applicable to other eruption modes

Lesquin, Chemin de Merchin, Chemin des Loups. La nécropole mérovingienne du hameau de Merchin (fin Ve s. - déb. VIIIe s.)

Rapport de fouille archéologique, 906 p., 867 fig. et 27 tableaux

Lesquin (Nord), ZAC du Mélantois, Au Chemin Perdu : la nécropole mérovingienne du hameau de Merchin (zone 2) (fin Ve siècle-début VIIIe siècle) : rapport de fouilles

La construction d'un complexe d'entreprises au hameau de Merchin, au sein d'une zone sensible de découvertes archéologiques, a motivé plusieurs prescriptions de fouille qui se sont déroulées entre l'été 2008 et l'été 2009. Elles ont porté sur un ensemble de structures néolithiques, sur un complexe à vocation agro-pastoral protohistorique/antique, et, enfin, sur une nécropole du premier Moyen Âge. Inscrite dans un terroir occupé de manière plus ou moins continue depuis le Hallstatt jusqu'au bas Moyen Âge, la nécropole mérovingienne de Lesquin est localisée sur la frange orientale du plateau du Mélantois. Elle supplante une occupation débutée au Hallstatt au travers de l'élément structurant l'ensemble de ce terroir, un remarquable fossé reconnu sur 1,2 km, repris ensuite dans son tracé. L'occupation de La Tène ancienne livre un foyer et un rejet domestique, quant à l'occupation antique, elle est reconnue au travers de fosses d'extraction de la craie et des bordiers d'un cheminement. La nécropole livre 108 inhumations, 1 incinération et 3 fosses animales. Elle se situe à un peu moins de 100 m d'une occupation domestique qui a perduré jusqu'à l'époque carolingienne. Le champ de repos s'inscrit dans une aire d'environ 25 m de large et de plus de 40 m de long. Il s'organise selon un axe nord-ouest/sud-est, suivant un développement chrono-topographique, selon un déploiement depuis un point sommital sur la pente douce marquée dans le paysage. Il accueille une communauté villageoise sans sélection démographique apparente. L'impression de désordre dans l'implantation permet de supposer la présence de limites fortes malgré l'importance de la superficie probablement disponible en milieu rural. Six phases d'aménagement de l'espace funéraire sont observées avec des moments forts d'utilisation dès la phase MA 1 jusqu'à la phase MR 1, marquant ainsi l'accroissement démographique. Les phases MR 2 et MR 3 présentes de manière plus anecdotique permettent de supposer la chute brutale de la population et la fin de l'extension topographique. Ce schéma chronologique, somme toute ordinaire, indique le transfert de la nécropole à partir du milieu du VIIe s., traduisant ainsi le début de la fin du lien d'interdépendance avec l'habitat situé à 80 m. Les sépultures datées des phases MA 1 et MA 2 répondent majoritairement à une orientation ouest-sud-ouest/est-nord-est alors que celles des phases MA 3 et MR 1 sont plutôt orientées ouest-nord-ouest/est-sud-est. Aucune orientation préférentielle n'est toutefois relevée par phase. La différence d'orientation est également notable au sein de la typologie des sépultures. Les coffrages à traverses semblent faire leur apparition durant la phase MA 2 et se développent au cours de la phase suivante. Résultante de ce constat, les coffrages simples ont la faveur de la phase la plus ancienne. Nous remarquons que quelques fosses sépulcrales appartenant aux dernières périodes viennent contredire le constat d'un développement linéaire vers le sud. En effet, dès la phase MR 1 des sépultures se réimplantent au coeur de l'espace funéraire en superposition des phases plus anciennes. L'étude taphonomique a permis de restituer 76 contenants en bois assemblés ou cloués, reposant pour majorité sur des madriers transversaux, un cercueil monoxyle et deux chambres funéraires à double espace vide occupées par des immatures. Ces deux chambres attestent du statut social important accordé dès le plus jeune âge à certains individus de la communauté. Le reste des fosses sépulcrales a pu accueillir un individu dans une enveloppe souple, en \guillemotleft pleine terre \guillemotright. Quelques distinctions de rang, de position dans la communauté, de filiation intergénérationnelle, de regroupements familiaux sont perceptibles au sein de la nécropole. Les mobiliers sont présents dans 70 % des sépultures. L'absence frappante d'attributs dits \guillemotleft statutaires \guillemotright et une certaine modestie dans la qualité du dépôt sont les facteurs communautaires qui rassemblent la population. L'armement est particulièrement bien représenté. 28 sépultures à armes se répartissent quasi-uniformément sur l'ensemble du site entre la phase MA 1 et la phase MR 1, moments forts de l'utilisation par la communauté des vivants. Le dépôt de céramique concerne un tiers des sépultures. Il se localise le plus souvent aux pieds du défunt, plus rarement près de la tête. La nécropole de Lesquin s'insère dans la sphère géographique culturelle du nord. Chargée de tradition et de mélanges ethniques, multiculturelle par essence, elle mêle origine gallo-romaine et germanique avec ses chambres funéraires de type Morken, un tertre ?, des inhumations de chevaux\ldot