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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Geochemical and isotopic investigation of the rate and pathway of fluid flow in partially-welded fractured unsaturated tuff

Davidson, Gregg Randall, 1963- January 1995 (has links)
Fluid flow rates and pathways in partially-welded, fractured, unsaturated tuff are investigated in a sloping borehole (DSB-1) cored from the surface to a perched aquifer at the Apache Leap near Superior, Arizona. Suspected water-bearing fractures were identified in the borehole using video and geophysical logs. Pore water extracted from cores associated with these fractures proved to have elevated ¹⁴C activity relative to pore waters from intermediate depths. Pore water from the deepest fracture interval contained post-bomb ¹⁴C. Low tritium concentrations in most samples indicates imbibition from each flow is small relative to the volume of water in the pores, but cumulative imbibition over time is significant based on ¹⁴C distribution through the unsaturated zone. The saturated zone beneath DSB-1 is a mixture of fracture flows with older aquifer water. Estimates based on ¹⁴C and ³H data indicate half of the water in the local aquifer originated from fractures near DSB-1. Geochernical models incorporating pore-water, surface-runoff, aquifer-water and mineral chemistry suggest that fracture flow may also be the predominant source of recharge for the older aquifer water. Water and carbon are extracted from core samples using uni-axial compression and a new vacuum distillation technique. Distillation is shown to be an effective method when carbon extraction is not possible by other methods. Mass yields from distillation provide evidence that there may be a substantial reservoir of carbon adsorbed to mineral phases. Carbon-14 activity of formation air samples from intervals with low air permeability reflect the composition of water imbibed from fracture flows at those depths. In zones of higher permeability, atmospheric contamination is suspected even though SF₆ (injected as a tracer during drilling) concentrations had not diminished. An independent investigation on the carbon isotopic composition of soil-zone CO₂ demonstrates the need to correct soil-respired CO₂ samples for CO₂ contamination in base reagents and for fractionation during sample collection. The minimum δ¹³C-shift from soil CO₂ to soil-respired CO₂ is also shown to be a function of the δ¹³C of soil organic material rather than a fixed 4.4%₀ as previously thought.
102

Petrology and geochemistry of volcanic rocks of the Lantau Peak Area, Lantau Island, Hong Kong

So, Chak-tong, Anthony., 蘇澤棠. January 1999 (has links)
published_or_final_version / Earth Sciences / Master / Master of Philosophy
103

Filtering out the Ash: Mitigating Volcanic Ash Ingestion for Generator Sets

Hill, Daniel John January 2014 (has links)
Volcanic eruptions produce a range of hazards which can impact society. The most widespread of these hazards is volcanic ash fall which can impact a range of critical infrastructure. Power systems are particularly vulnerable to ash fall hazards and the resulting impacts may lead to power supply disruption. This can lead to cascading disruption of dependent systems, such as hospitals, water and wastewater treatment plants, telecommunications and emergency services. Typically, large emergency power generator sets are used to provide emergency power supply for essential services during electrical power outages. There has been little study of what impact ash fall exposure will have on generator performance. International experience suggests large generators can experience rapid performance reduction when exposed to high concentrations of suspended or falling ash due to obstruction of air filters and radiators, causing overheating of the engine and shut down of the generator system. However, it is not clear at what ash fall thresholds generators are likely to be disrupted. This research uses custom designed empirical laboratory experiments to investigate the performance of large generators subjected to a range of volcanic ash fall types and intensities, simulating both proximal and distal ash fall exposure from a range of eruptive styles. It also investigates the application of temporary external filters to minimise the ingestion of volcanic ash into generator housings. The results are used to inform recommendations on the likely impacts of ash to generators and the most effective type of mitigation, which maximises filtration whilst maintaining generator performance. Control tests recorded high particle concentrations (~0.006 mg/m3) which indicate substantial ash contamination is possible. Multiple factors were considered to determine the best mitigation measure including the lowest particle concentration, highest air speed and the ease with which the measure could be fitted. The study found material filtration to be the most effective measure; however as the quality of filtration increased, the air speed was reduced and thus so was the volume of air available to the generator engine. Therefore, the type of filtration required is dependent the ash fall intensity. The study also found that a deflection hood is an effective mitigation measure; maintaining airspeed while reducing particle concentrations within the generator. This research informs risk management strategies for critical infrastructure organisations to reduce the risk of generator disruption during volcanic ash falls.
104

Dynamic and cyclic properties in shear of tuff specimens from Yucca Mountain, Nevada

Jeon, Seong Yeol, 1972- 11 September 2012 (has links)
Yucca Mountain was designated as the proposed high-level radioactive waste repository by the U.S. Government in 1987. The proposed repository design requires high safety for a long maintenance period of 10,000 years. To satisfy this requirement, evaluation of the influence of earthquakes on the repository is necessary. Prediction of earthquake-induced ground motions around the repository requires knowledge of the dynamic properties of the geologic materials around the repository. The main geologic materials in the vicinity of Yucca Mountain are tuffs (ignimbrites) which are formed by the deposition of volcanic ash mixed with erupted volcanic gas, water vapor and pyroclastic material. Two types of dynamic tests, (1) the free-free, unconfined, resonant column and direct arrival test (freefree URC test) and (2) the fixed-free resonant column and torsional shear test (fixed-free RCTS test), were used to measure the dynamic properties of tuffs. The emphasis in this dynamic testing was evaluation of shear modulus (G) and material damping ratio (D) of the tuffs in the small-strain (linear) and mildly nonlinear (to strains of about 0.02 %) ranges. To evaluate the influence of various parameters on G and D of tuffs, correlations with other features such as total unit weight, porosity and stratigraphic unit were performed and general relationships between them are proposed. In addition, an unconfined, slow-cyclic torsional shear (CTS) device was developed and used to measure the cyclic shear properties of the tuffs from Yucca Mountain at larger strain amplitudes than possible in the fixed-free RCTS tests. Additionally, the CTS device was also used to determine the shear failure strength of the tuffs. By combining the cyclic shear properties of the tuffs from the CTS tests and the dynamic properties of the tuffs from the fixed-free RCTS tests, complete dynamic property curves from small-strain to failure strain were evaluated.
105

Volcanologie physique et sédimentologie du groupe volcanique de Piché et relations stratigraphiques avec les groupes sédimentaires encaissants de Pontiac et de Cadillac /

Landry, Jacques. January 1991 (has links)
Mémoire (M.Sc.T.)-- Université du Québec à Chicoutimi, 1991. / Bibliogr.: f. 83-86. Document électronique également accessible en format PDF. CaQCU
106

Étude volcanologique du centre volcanique felsique du lac des Vents, région de Chibougamau /

Potvin, Robin. January 1991 (has links)
Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 1991. / Document électronique également accessible en format PDF. CaQCU
107

Étude de la genèse des pépérites et de leur contexte volcano-sédimentaire, formation de Blondeau, Chibougamau, Québec /

Lefebvre, Christian. January 1991 (has links)
Mémoire (M.Sc.T.)-- Université du Québec à Chicoutimi, 1991. / "Mémoire présenté en vue de l'obtention de la maîtrise en sciences de la terre" CaQCU Bibliogr.: f. 166-171. Document électronique également accessible en format PDF. CaQCU
108

The Quaternary geology and sequence stratigraphy of Lake Bonneville deposits in the Matlin quadrangle, Box Elder County, northwestern Utah /

Cavas, Matthew P. January 2003 (has links)
Thesis (M.S.)--Ohio University, November, 2003. / Includes bibliographical references (p. 73-77).
109

Petrology and geochemistry of volcanic rocks of the Lantau Peak Area, Lantau Island, Hong Kong /

So, Chak-tong, Anthony. January 1999 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 123-128).
110

Tracking the evolution of mid cenozoic silicic magma systems in the southern Chocolate Mountains region, California using zircon geochemistry and quartz and zircon geothermometry /

Needy, Sarah Katherine. January 2009 (has links)
Thesis (M.S.)--Indiana University, 2009. / Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Andrew P. Barth, Gabriel Filippelli, Jeffery Wilson. Includes vitae. Includes bibliographical references (leaves 62-64).

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