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dc.contributor.authorAlmberg, Leslie D.
dc.date.accessioned2022-03-09T20:32:57Z
dc.date.available2022-03-09T20:32:57Z
dc.date.issued2010-05
dc.identifier.urihttp://hdl.handle.net/11122/12719
dc.descriptionThesis (Ph.D.) University of Alaska Fairbanks, 2010en_US
dc.description.abstract"Conduit samples from Unzen Volcano, obtained a decade after the 1991-1995 eruption, exhibit important physical and mineralogical differences, and subtle differences in bulk chemistry from erupted samples. These differences reflect emplacement confining pressures, maintenance at hypersolidus temperature, and subsequent subsolidus hydrothermal alteration. In contrast, extruded lava underwent decompression to ~1 atm., ~complete loss of magmatic water and rapid cooling. The resulting hypabyssal conduit texture is distinct from both eruptive and plutonic rocks. The low temperature of the conduit, <200°C when sampled by drilling, requires swift post-emplacement textural development. Significant changes in bulk composition were Mg, Fe and Na depletion and C and S enrichment. Trace-element concentrations of the conduit and the last-emplaced lava of the spine indicate a common derivation. Investigating three aspects of magma transport and post-emplacement evolution at Unzen, in conjunction with observations from comparable dome-forming volcanoes, quantifies the processes working in concert to produce the resultant textures. First, we constrain magmatic ascent rates and crystallization depth of the Unzen dacite via decompression crystallization experiments. Our results indicate that slow effusion rates (<̲20 m/hr) are required for both spine and conduit. Second, we present mineralogical evidence for extremely rapid alteration beneath Unzen, related to temperature, permeability within and volatile flux through the volcanic edifice. We describe meter-scale variations in alteration conditions, and conclude that maintenance of permeability to low porosity allows basalt-derived volatiles to traverse the conduit zone promoting extremely rapid alteration, orders of magnitude greater than predicted by models for larger/deeper intrusions. This suggests that despite convective hydrothermal heat removal, chemical effects were limited to early loss of magmatic water and later addition of magmatic volatiles. The extensive alteration within Unzen's conduit contrasts the minimal alteration beneath Obsidian Dome, considered as a 'control'. Finally, we present anisotropy measurements and three-dimensional visualizations of degassing structures from four volcanoes: Bezymianny, Unzen, Mount St. Helens and Obsidian Dome. Our novel approach, employing X-ray computed tomography and percolation models, indicates that gas loss at depth is more efficient in sheared regions (anisotropic), than in those that contain no evidence for shearing (isotropic)"--Leaves iii-iven_US
dc.description.sponsorshipNational Science Foundation grants EAR-0310406 and INT-0530278, Alaska Volcano Observatory, Geophysical Institute Director’s Office, Commonwealth Scientific and Industrial Research Organisationen_US
dc.description.tableofcontents1. Comparison of eruptive and intrusive samples from Unzen Volcano, Japan : effects of contrasting pressure -- temperature -- time paths -- 2. Experimental decompression crystallization -- final emplacement conditions in the 1995 Unzen conduit and spine -- 3. Influence of emplacement temperature, hydrothermal alteration and time on the permeability of shallow silicic conduit systems : Unzen, Japan and Inyo Domes, USA -- 4. Three-dimensional degassing structures in the upper conduit of silicic volcanic systems -- Bezymianny, Russia, Unzen, Japan, Inyo Domes and Mount St. Helens, USA -- Summary.en_US
dc.language.isoen_USen_US
dc.subjectMagmasen_US
dc.subjectVolcanic ashen_US
dc.subjectMount Unzenen_US
dc.subjectMount Saint Helensen_US
dc.subjectObsidianen_US
dc.subject.otherDoctor of Philosophy in Geophysicsen_US
dc.titleTemporal-spatial micro-scale investigations of shallow silicic conduits: late-stage degassing, crystallization, and alterationen_US
dc.typeThesisen_US
dc.type.degreephden_US
dc.identifier.departmentDepartment of Geology and Geophysicsen_US
refterms.dateFOA2022-03-09T20:32:59Z


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Appendices 3.A, 3.C, amd 4.A

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