Дисертації: "Volcanic systems"

7

Wilson, Thomas McDonald. "Vulnerability of Pastoral Farming Systems to Volcanic Ashfall Hazards." Thesis, University of Canterbury. Geological Sciences, 2009. http://hdl.handle.net/10092/5978.

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Volcanic eruptions are powerful, spectacular, uncontrollable geophysical events which require management to mitigate loss of life and property. An essential part of volcanic risk management is to quantify the vulnerability of exposed elements of society to volcanic hazard. Agriculture takes advantage of the fertile soils of volcanic regions, but is vulnerable to damage and disruption from volcanic hazards, in particular ashfall. This thesis investigates the vulnerability of pastoral agriculture to volcanic ashfall by examining impacts on the resource base of pastoral farming (water supply, pasture and soil, and livestock) and explores mitigation and recovery strategies for ashfall hazards at varying levels. It provides a quantitative understanding of pastoral farming vulnerability to ashfall hazards, as part of probabilistic risk assessment. Surface farm water supplies are found to be more vulnerable to ashfall, through contamination and sedimentation, than groundwater supplies. After heavy ashfall, the physical impacts of ashfall overwhelm the more subtle chemical impacts on water supply systems, but even relatively thin ashfalls may cause potential toxic changes to water quality. Farm-scale assessment of water supplies was used to identify key areas of vulnerability to ash hazards. Modelling a large-scale evacuation of livestock following widespread, heavy ashfall found the logistical, time and cost requirements high and may make this action unrealistic. Perhaps most critically, it is doubtful that farms in surrounding regions have the capacity to accommodate the numbers of animals likely to be affected. Tunnel-house and field trials have shown pastures are relatively resilient to ashfalls of 10 mm, but this resilience rapidly reduces with increasing ashfall thickness and at .100 mm there is effectively no pasture recovery. Ashfall grain size, frequency, soluble salt volume, and different meteorological conditions also have a significant impact on pastures and soils. Pasture reestablishment will benefit from tillage of ash covered soils to mix ash and topsoil and break up the surface crust which may form on ash deposits. Targeted fertiliser treatments may also be required to buffer acidic soluble salts and remedy deficiencies of essential nutrients. Reworking of ash deposits was found to be highly disruptive to pasture re-establishment and in extreme cases may prolong and intensify the impacts following an ashfall. The majority of farmers impacted by ashfall will continue farming, albeit with varying levels of disruption. However real or perceived impacts to human health may result in farm evacuation in the short-term. Where ashfall thicknesses are too thick for a return to profitable farming, migration from impacted farms and agriculture-related industries will result in significant demographic changes to rural communities and potential social impacts. Stressed farming systems are most vulnerable to failure and psychosocial impacts.

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8

Wardman, John Blackburn. "Vulnerability of Electric Power Systems to Volcanic Ashfall Hazards." Thesis, University of Canterbury. Geological Sciences, 2013. http://hdl.handle.net/10092/8014.

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Volcanic eruptions are powerful natural events which impact strongly on society. As human populations grow and expand into volcanically active areas, their exposure and vulnerability to volcanic hazards is also increasing. Of all volcanic hazards, ashfall is the most likely to impact lifelines because of the large areas affected. The widespread dispersal of ash can cause large-scale disruption of vital infrastructure services, aviation, and primary production. Electric power supply is arguably the most crucial of modern infrastructure systems, especially considering the dependence of other sectors on electricity to maintain functionality. During and immediately after ashfalls, electric power systems are vulnerable to a number of impacts, but disruption from volcanic ash-induced insulator flashover (unintended, disruptive electrical discharge) is most common. This thesis investigates the vulnerability of electric power systems to volcanic ashfall by examining impacts to the different sectors of the modern power system and exploring appropriate mitigation strategies. Analogue laboratory trials using a pseudo (synthetic) ash are undertaken to verify the environmental, volcanological and electrical parameters that most affect electrical conductivity and therefore the flashover mechanism in these experiments. While dry ash is highly resistant to the flow of electric current, increasing moisture content, soluble salt load, and compaction (bulk density) will reduce this resistance and, in turn, increase the potential for flashover. Volcanic ash is an acute form of airborne pollution for areas downwind of active volcanoes. Results from laboratory experiments in this thesis suggest that insulator pollution (volcanic ash) performance (dielectric strength) is primarily dictated by (1) the conductivity of the ash, and (2) insulator material, profile (shape) and dimensioning. Composite polymer insulators tested herein effectively minimise sinusoidal leakage current and partial discharge activity and also exhibit higher pollution performance when compared to ceramic equivalents. Irrespective of insulator material, however, the likelihood of flashover increases significantly once the bottom surface of suspension insulator watersheds become contaminated in wet ash. The thesis investigates the vulnerability (hazard intensity/damage ratio) of electric power systems to volcanic ashfall hazards. Identification, analysis, and reduction of the risk of ashfall impacts to power networks is explored as a part of holistic volcanic risk assessment. The findings of the thesis contribute to the readiness, response and recovery protocols for large electric power systems in volcanic disasters; which directly affects the functional operation and economics of industrial and commercial society.

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9

Matoza, Robin S. "Seismic and infrasonic source processes in volcanic fluid systems." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3386569.

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Thesis (Ph. D.)--University of California, San Diego, 2009. Title from first page of PDF file (viewed January 19, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 219-246).

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10

Belien, Isolde L. M. B. (Leo Maria Beatrijs) 1985. "Gas Migration Through Crystal-Rich Mafic Volcanic Systems and Application to Stromboli Volcano, Aeolian Islands, Italy." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/12107.

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xvii, 171 p. : ill. (some col.) Crystals influence the migration of gas through magma. At low concentrations, they increase the bulk fluid properties, especially viscosity. At concentrations close to maximum packing, crystals form a rigid framework and magma cannot erupt. However, erupted pyroclasts with crystal contents close to the packing concentration are common at mafic volcanoes that exhibit Strombolian behavior. In this dissertation, I study the influence of solid particles on gas migration. I apply my results to Stromboli volcano, Italy, type locality of the normal Strombolian eruptive style, where gas moves through an essentially stagnant magma with crystallinity ∼50%. Specifically, I investigate the effect of crystals on flow regime, gas content (Chapter II), bubble concentration (number densities), bubble shapes, bubble sizes (Chapter III), and bubble rise velocities (gas flux) (Chapter IV). I find that gas-liquid flow regimes are not applicable at high particle concentrations and should be replaced by new, three-phase (gas-liquid-solid) regimes and that degassing efficiency increases with particle concentration (Chapter II). In Chapter III, I show that crystals modify bubble populations by trapping small bubbles and causing large bubbles to split into smaller ones and by modifying bubble shapes. In Chapter IV, I model Stromboli's crystal-rich magma as a network of capillary tubes and show that bubble rise velocities are significantly slower than free rise velocities in the absence of particles. In each chapter, I use analogue experiments to study the effect of different liquid and solid properties on gas migration in viscous liquids. I then apply my analogue results to magmatic conditions using simple parameterizations and/or numerical modeling or by comparing the results directly to observations made on crystal-rich volcanic rocks. Chapter V proposes a mechanism for Strombolian eruptions and gas migration through the crystalrich magma in which the effect of crystals is included. This model replaces the current twophase "slug" model, which cannot account for the high crystallinity observed at Stromboli. There are three appendices in this dissertation: a preliminary study of the influence of particles on gas expansion, image analysis methods, and the numerical code developed in Chapter IV. This dissertation includes previously published and unpublished co-authored material. Committee in charge: Katharine Cashman, Chairperson; Alan Rempel, Member; Mark Reed, Member; Raghuveer Parthasarathy, Outside Member

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11

Farquharson, James. "Permeability evolution in volcanic systems : field, laboratory, and numerical investigations." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH018/document.

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La perméabilité est une propriété essentielle notamment pour déterminer la nature explosive des volcans, ainsi que pour de nombreuses autres applications scientifiques et industrielles dans les environnements où l'écoulement du fluide est une préoccupation majeure. Combinant des méthodes expérimentales de déformation des roches en laboratoire, des approches de terrain, de la modélisation numérique, et des analyses systématiques de microstructure, ce travail a mis en évidence le caractère complexe de la formation et la destruction des réseaux poreux dans le magma et des roches volcaniques. La compétition entre les processus dilatants (qui augmentent la porosité) et compactants (qui la diminuent) exerce une influence sur les propriétés de transport des fluides à la fois dans le magma et dans la roche volcanique solidifiée. Ces processus incluent la vésiculation et la croissance des bulles dans le conduit, la rupture et la compression du magma, la fracturation issue du refroidissement et fracturation induite par le transport, ainsi que la déformation pendant ou après la mise en place des matériaux, et la densification par frittage The permeability of various volcanic materials is an essential parameter governing the explosive behaviour of volcanic systems, as well as being important in many other scientific and industrial applications in environments where fluid flow is a major concern. Combining experimental rock deformation methods with field measurements, numerical modelling, and systematic analyses of rock microstructure, this work explores the complexities involved in the formation and destruction of porous networks in magma and volcanic rocks, addressing how permeability can evolve in volcanic systems. Competition between dilatant processes (which increase porosity) and compactant processes (which decrease porosity) influences the fluid transport properties both in the conduit-dwelling magma and in solidified edifice rock. These processes include (but are not limited to) vesiculation and bubble growth in the conduit, fracture and compaction of magma, post-emplacement thermal or mechanical fracturing, strain-induced deformation, and viscous sintering

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12

Kent, Russell Malcolm. "Modelling fluid flow and heat transfer in some volcanic systems." Thesis, Lancaster University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306912.

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13

McLean, Charlotte Elizabeth. "Shallow magmatic plumbing systems and edifices of monogenetic volcanic fields." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8418/.

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Magmatic plumbing systems of monogenetic volcanic fields comprise an interconnected network of sills, dykes and inclined sheets; however, the morphology, distribution and emplacement mechanisms of these shallow plumbing systems are often overlooked due to the lack of observable field data. Using seismic data provides an opportunity to understand these systems and integrate seismic-scale features with macro-scale observations from the field. Using a seismic dataset from the Faroe-Shetland Basin, NW Scotland, the Ben Nevis Monogenetic Volcanic Field (BNVF), this research provides an insight into how monogenetic volcanic fields are fed, and how the distribution of edifices can be primarily influenced by the structure of the substrate. By comparing the seismic data with field observations from three separate field studies, this research focuses in on the shallow, ductile zone (< 1 km) between the feeding intrusion(s) and the volcanic edifice, in order to determine the processes that occur during emplacement at a sub-seismic scale. This study provides a comprehensive assessment of the features of very shallow plumbing systems (< 200 m) within a variety of water-saturated settings, including: passive and dynamic peperite (blocky and fluidal); R-T structures; clastogenic dykes; gas cavities; slurry cavities; protopillows and subsurface pillows; volcaniclastic injectites; and magma lobes and fingers. The range of features displayed within the four case studies demonstrates that a variety of processes affect the emplacement of magma in the ductile zone. These processes include: (1) exploiting preferential horizons by host-rock fluidisation; (2) exploiting boundaries in the host-rock by the rotation of principal stresses; (3) explosive magmatic degassing; (4) cooling–contraction fragmentation; (5) explosions caused by rapid vapourisation of porewater; (6) a variety of molten fuel-coolant interactions (non-explosive to highly explosive); and (7) density contrasts. Monogenetic volcanic fields and their plumbing systems have been identified in reflective seismic data in exploratory offshore sedimentary basins (e.g. Southern Australia Margin and the NE Atlantic Margin). This research presents unprecedented quantitative analysis of the thermal influence of diatremes using a range of techniques (vitrinite reflectance analysis, Raman spectroscopy and fluid inclusion techniques) to produce local isothermal models of the host-rock surrounding diatremes. This aims to provide a better understanding of the overall thermal effect of monogenetic plumbing systems on reservoir porosity and permeability, and source maturity.

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14

Darnell, Amii Rebecca. "Application of geographical information systems to lahar hazard assessment on an active volcanic system." Thesis, University of East Anglia, 2010. https://ueaeprints.uea.ac.uk/47533/.

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Lahars (highly dynamic mixtures of volcanic debris and water) have been responsible for some of the most serious volcanic disasters and have killed tens of thousands of people in recent decades. Despite considerable lahar model development in the sciences, many research tools have proved wholly unsuitable for practical application on an active volcanic system where it is difficult to obtain field measurements. In addition, geographic information systems are tools that offer a great potential to explore, model and map hazards, but are currently under-utilised for lahar hazard assessment. This research pioneered a three-tiered approach to lahar hazard assessment on Montserrat, West Indies. Initially, requirements of potential users of lahar information (scientists and decision-makers) were established through interview and evaluated against attainable modelling outputs (given flow type and data availability). Subsequently, a digital elevation model, fit for modelling lahars, was used by a path of steepest descent algorithm and a semi-empirical debris-flow model in the prediction of lahar routes and inundation areas. Limitations of these established geographical information system (GIS) based models, for predicting the behaviour of (relatively under-studied) dilute lahars, were used to inform key parameters for a novel model, also tightly coupled to a GIS, that simulated flow routes based on change in velocity. Importantly, uncertainty in model predictions was assessed through a stochastic simulation of elevation error. Finally, the practical utility of modelling outputs (visualisations) was assessed through mutual feedback with local scientists. The new model adequately replicated past flow routes and gave preliminary predictions for velocities and travel times, thus providing a short-term lahar hazard assessment. Inundation areas were also mapped using the debris-flow model to assist long-term planning. Ultimately, a GIS can support ‘on the ground’ planning decisions, but efficacy is limited by an active volcanic system which can restrict feedback to and from end-users.

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15

Faizy, Shelly Mardhia. "Assessing a Modeling Standard in Volcanic-Geothermal Systems: the Effects of the Lower System Boundary." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-438664.

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Geothermal energy consumption is projected to increase along with other renewable energy in the future. Therefore, it is important to have a better understanding on the evolution of geothermal systems to optimize the exploitation of such resources. Generally, numerical models are used as a fundamental tool to study a potential geothermal field. However, current modeling practices tend to focus on the shallow area around the heat source, while ignoring the deeper part below the heat source. The purpose of this project is to observe the influence of lower boundary at the bottom of intrusion towards the evolution of geothermal system, while changing the permeability and topography of host rock systematically, using a software from USGS called HYDROTHERM. Simulations differed in three main aspects: 1) having a layer below, or having the bottom boundary directly below intrusion, 2) different topographies with volcanic significance, and 3) varying permeabilities of the host rock. The study is based on a fossil geothermal system, the Cerro Bayo laccolith in Chachahuén volcanic complex (Neuquén Basin), Argentina. The input parameters were obtained in several ways. ILMAT Geothermometry analysis provide the temperature value related to the intrusion. The whole rock data is used to determined density of the intrusion by calculating partial molar volume of the oxides. The other parameters, e.g. densities of the host rock and the impermeable layer, permeability, porosity, and thermal conductivity were obtained from literature. The result from numerical modeling shows that the bottom boundary below intrusion strongly affect the entire system evolution. The added layer (with constant permeability) has strong influence on the life-span of the system. Additionally, while taking into account on the variation of topography and permeabilities, the models show two temperature anomalies: 1) A caldera volcano’s geometry “traps” heat below the caldera, whereas shield and strato-volcano geometries “push” heat away from below the volcanic edifice, and 2) a low temperature anomaly develops beneath the intrusion in all high permeability models with an added layer. Finally, this assessment could prove to be useful as prior knowledge for optimizing the extraction of heat from a given geothermal field, as well as future investigations towards geological applicability of numerical models of geothermal systems, hydrothermal alteration, and ore formation processes.

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16

Lamur, A. L. "Development, impact and longevity of fractures in magmatic, volcanic and geothermal systems." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3019206/.

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The migration of fluids in the Earth’s crust embodies the last stage of the internal heat release of our planet. Either spectacularly expressed at the surface through volcanic activity, or more subtly as internal hydrothermal circulation, this phenomenon involves the upwards motion of fluids and magmas that contribute to more efficient heat transfer. On one hand, volcanic eruptions result from the movement of buoyant magmatic liquids towards the surface. On their way up, these magmas cool down, crystallise and upon decompression, build up an internal pressure that dictate the eruptive style: Effusive when the internal pressure is released as it builds up; explosive when the internal pressure accumulates until it is able to fracture the magma. In nature, the shift from effusive to explosive activity is often periodic, reflecting cycles of pressure accumulation and relaxation in the conduit. On the other hand, hydrothermal circulation results from the infiltration of water, of meteoric or magmatic origin, into the rocks making up the crust. Higher temperatures at depth and/ or due to the presence of a magmatic body, trigger the formation of convective cells in which chilled, denser water percolates downwards then heats up, losing density before moving back upwards. Importantly, the circulation of both hydrothermal fluids and magmatic liquids is controlled by the presence of fractures in the crust and the permeability of the surrounding rocks. In this thesis, I first investigate how fractures affect the localisation of fluids in fractured porous rocks through permeability measurements, both at atmospheric pressure and at shallow confining conditions (< 30 MPa; ~1 km depth). I demonstrate that the impact of fractures is greater at lower porosities as the permeability is greatly increased. In more porous rocks, higher pore connectivity means that macro-fractures affect the permeability less significantly, as at least some of the fluid flows through the pre-existing connected porous network. I further demonstrate that, during confinement, most of the mechanical closure occurs at shallow conditions (< 5 MPa; ~200m depth) for the porosity range tested. In addition, I show that mechanically shutting a fracture does not seal the permeable pathways, and that the fractured system is unable to retrieve the same permeability as the intact system. I then develop an analytical solution for the permeability of variably porous, fractured systems as a function of depth before numerically solving it. I complement this work with two “case studies” in which tensile fractures form and open or heal, and link this to the system permeability evolution through time and the implications for magmatic, volcanic and geothermal systems. In the first scenario, tensile fractures open in a cooling magmatic body to form columnar joints in a basalt. Because the temperature at which cooling joints form remains elusive, causing a lingering scientific debate, I develop a novel type of mechanical testing and show for the first time that, in basaltic systems, these macro-fractures form purely in the elastic regime. This is further supported by the use of the rock’s thermo-mechanical characteristics (namely thermal expansion and tensile strength) to model the tensile stress build-up upon cooling and, once formed, the evolution of the fracture width between two columns. Applying the analytical solution for fractured systems permeability defined earlier, I further model the permeability evolution of a columnar jointing magmatic body, important for the understanding of fluid migration during drilling close to magmatic chambers. Finally, in magmas, the entrapment of exsolving gases, during ascent, force the accumulation of stress in the liquid, building pore pressure and potentially resulting in magmatic fragmentation. Consequently, the accumulated stresses can then be dissipated at times longer than the relaxation timescale of the melt, allowing fractures to heal and the system to recover strength lose permeability. Using synthetic glasses in a newly designed experimental setup, I show that the time required to start the healing process is proportional to the relaxation timescale of the melt. I further demonstrate that the kinetics of fracture healing involve two distinct stages. The first stage sees the fracture walls viscously deforming to dissipate excessive energy along the fracture plane (wetting regime), while the second stage consists of the diffusive exchange of elements across the fracture interface (diffusive regime). I finally surmise that the cyclic activity of persistently active silicic volcanoes could be explained by dynamic permeability and strength variations of material due to repeating fracture and healing cycles. Overall, I show that the development and longevity of fractures have significant impacts on the localisation of fluid flow, highlighting that fractures significantly contribute to the development of anisotropy in magmatic, volcanic and geothermal environments. A better understanding of the longevity of fractures in these systems is of prime importance in the mitigation of hazards associated to volcanic eruptions, but also in the development of cheaper, more efficient geothermal energy.

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17

Kushnir, Alexandra Roma Larisa. "Permeability development and evolution in volcanic systems : insights from nature and laboratory experiments." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2006/document.

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La transition entre le comportement effusif et explosif des volcans de magma riche en silice est en partie contrôlée par la capacité des surpressions gazeuses à se dissiper hors du magma. La libération efficace des gaz est associée aux éruptions effusives tandis que la rétention de ces gaz contribue aux processus explosifs. L’une des approches pour évaluer la facilité d’échappement des gaz est de considérer l’évolution et le développement de la perméabilité dans la colonne magmatique et dans l'édifice. J'évalue dans ce travail de thèse le rôle des changements post-mise en place sur la microstructure dans des andésites basaltiques du Merapi (Indonésie). La perméabilité de ces roches est principalement contrôlée par des fissures liées à leur mise en place. Malgré l’influence importante de ces fissures post-mise en place pour dégazer à travers l'édifice, elles ne contribuent pas au dégazage intrinsique du magma en cours d’ascension. Pour s’affranchir de l'influence des microstructures post-mise en place du magma, j'étudie le développement et l'évolution in situ des réseaux perméables en déformant des magmas à deux phases (bulles de gaz et liquide silicaté) en cisaillement simple dans une presse Paterson selon des viscosités et des vitesses de déformation réalistes pour la partie haute des conduits des strato-volcans. Le développement de la perméabilité est confirmé in situ et se développe à des vitesses de déformation supérieures à 4,5 x 10⁻⁴ s⁻¹. À des vitesses de déformation élevées (> 5 x 10⁻⁴ s⁻¹) le magma est fragile et l’échappement du gaz est lente, facilitée par l'interconnexion de courtes fractures de Mode I. À des vitesses de déformation < 5 × 10⁻⁴ s⁻¹, le magma se comporte à la fois de manière fragile et visqueuse et la perméabilité se développe lorsque la déformation est importante; le gaz s’échappe rapidement par de longues fractures de Mode I bien développées. Les fractures de Mode I sont idéalement orientées pour le dégazage du conduit central et sont, surtout, soumises à peu de déformation jusqu'à ce qu'elles soient réorientées dans la direction de cisaillement. Ces caractéristiques de dégazage peuvent, à long terme, favoriser un dynamisme éruptif effussif The transition from effusive to explosive behaviour at silicic volcanoes is, in part, governed by how efficiently gas overpressures are dissipated from the volcanic plumbing. Efficient gas release is associated with effusive eruptions while inadequate outgassing contributes to explosive processes. One approach to assessing the facility of gas escape is by considering how permeability develops and evolves in the magma column and surrounding edifice. Here, I appraise the role of post-emplacement changes to microstructure in edifice-forming basaltic andesites from Merapi (Indonesia). The permeability of these rocks is dominantly crack-controlled and while these features exert important controls on gas escape through the edifice, they do not represent the escape pathways available to gas within ascending magma. To avoid the influence of postemplacement microstructure, I investigate the development and evolution of permeable networks in magmas by deforming initially impermeable two-phase magmas in simple shear. This is done in a Paterson apparatus at viscosities and shear strain rates appropriate to upper conduits in stratovolcanoes. Permeability development is confirmed in situ and develops at moderate to high shear strain rates (> 4.5 × 10⁻⁴ s⁻¹). At very high strain rates (> 5 × 10⁻⁴ s⁻¹) the magma behaves in a brittle manner and gas egress is slow, facilitated by the interconnection of short, Mode I fractures. At moderate shear strain rates (< 5 × 10⁻⁴ s⁻¹), the magma displays both brittle and viscous behaviour and permeability develops at high strain; gas escape is rapid owing to long, well-developed, sample-length Mode I fractures. Mode I fractures are ideally oriented for outgassing of the central conduit and, critically, accommodate little deformation until they are rotated into the direction of shear, making them long-lived outgassing features that may favour volcanic effusion

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18

Sirinyildiz, Tunc. "Integration Of Geophysical - Geological Data Using Geographic Information Systems." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1206374/index.pdf.

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This study attempts to integrate geophysical data with other spatial data using Geographic Information Systems (GIS). The study is carried out in a part of Galatean Volcanic Province, north of Ankara. Gravity, magnetic, topographic, rock type and volcanic eruption center data are the data layers used in the study. All data layers are converted to raster format with a grid spacing of 100 m. The first step in the analysis is the pair-wise analyses of all data layers. For the geophysical data, different layers for the depths of 1 to 5 km are generated. All paired analyses indicate that geophysical and other data sets are correlative among each other but show no relationship for any two layers from different sets. In the second step of the analyses, two geophysical data are combined and overlaid with layers from the other set. These analyses indicate that relationship between geophysical data with other spatial data becomes more evident and that the geophysical data can be successfully integrated with other data sets. Accuracy of the results is highly dependent on the accuracy of both data sets. Analyses have shown GIS can contribute to the investigation of spatial distribution of buried planar structures using geophysical data.

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19

Budd, David A. "Characterising volcanic magma plumbing systems : A tool to improve eruption forecasting at hazardous volcanoes." Doctoral thesis, Uppsala universitet, Mineralogi, petrologi och tektonik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267473.

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This thesis attempts to develop our understanding of volcanic magma plumbing systems and the magmatic processes that operate within them, such as fractional crystallisation, crustal partial melting, assimilation, and magma mixing. I utilise petrology, rock and mineral geochemistry, and isotope systematics to seek to improve our ability to forecast the eruptive frequency and style of active volcanoes, an aspect often lacking in current volcano monitoring efforts. In particular, magma reservoir dynamics are investigated from a mineral scale at Katla volcano in Iceland, to a sub-mineral scale at Merapi, Kelud, and Toba volcanoes in Indonesia. The magma plumbing architecture of Katla volcano on Iceland is explored in the first part of this thesis. Crystalline components within tephra and volcanic rock preserve a record of the physical and chemical evolution of a magma, and are analysed through oxygen isotopic and thermobarometric techniques to temporally constrain changes in reservoir depth and decode the petrogenesis of the lavas. We find both prolonged upper crustal magma storage and shallow level assimilation to be occurring at Katla. The results generated from combining these analytical strands reveal the potential for unpredictable explosive volcanism at this lively Icelandic volcano. The second part of this thesis examines the magma plumbing systems of Merapi, Kelud and Toba volcanoes of the Sunda arc in Indonesia at higher temporal and petrological resolution than possible for Katla (e.g., due to the crystal poor character of the rocks). For this part of the thesis, minerals were analysed in-situ to take advantage of sub-crystal scale isotopic variations in order to investigate processes of shallow-level assimilation in the build-up to particular eruptions. We find that intra-crystal analyses reveal an otherwise hidden differentiation history at these volcanoes, and establish a better understanding as to how they may have rapidly achieved a critical explosive state. The outcomes of this thesis therefore deepen our knowledge of evolutionary trends in magma plumbing system dynamics, and highlight the importance of understanding the geochemical processes that can prime a volcano for eruption. Lastly, I emphasise the vital contribution petrology can make in current volcano monitoring efforts.

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20

Davidson, Jonathan Robert Joseph. "The Effect of Fractures on Fluid Flow in Geothermal Systems, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Department of Geological Sciences, 2014. http://hdl.handle.net/10092/9566.

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The goal of this thesis is to evaluate the effect of fractures on the bulk permeability of rocks. Several methods are used to address this problem: 1) surface radon gas measurements, 2) stress induced fracture permeability 3) fracture generation conditions. Each method was variably effective in providing answer to the initial question. The radioactive radon isotopes (220Rn and 222Rn) were measured in soil gas extracted from 1 m depth in two areas and the concentrations for both isotopes tended to be higher near mapped faults. Soil samples recovered from 1 m depth indicate that the isotopic anomalies are coincident with changes in soil colour and the emanation of 220Rn, but are unrelated to the 222Rn emanation. The lack of a relationship for the latter can be explained by small-scale (~1m) diffusion for >90% of the soil gas measurements. However, diffusion cannot explain all of the observed patterns in the data, and in some specific locations along the fault, 222Rn concentrations are more likely sensitive to advective flow of sub-surface gases, suggesting channelizing of flow along faults. Stress is estimated using Leak-off Tests, estimating overburden weigth, and using drilling induced features observable in boreholes to model stress conditions. The results of the stress interpretation in the Rotokawa Geothermal Field show a relationship between the differential stress and alteration zones containing smectite, where the presence of smectite lowers the differential stress in the crust. This confirms a well-recorded relationship between the friction of rocks, and the strength of the crust. The magnitude of the principal stress axes, which are determined in this thesis, are used to predict the fracture orientations prone to slip in the Rotokawa Reservoir. The precise range of fracture orientations prone to slip is critically dependent on the poorly constrained intermediate stress. However, analysis of stresses on fracture orientations observed in the Rotokawa Andesite, coupled with independent permeability estimates reveal a complex relationship between fracture slip, and permeability, suggesting that slip on fractures can have both a positive or negative effect on slip. This is will depend on the degree of alteration of the Rotokawa Andesite. Failure in the Rotokawa Andesite is a result of: 1) the constant tectonic strain and 2) the increase in fluid pressure. Mathematical models used in this thesis show that if failure occurs through increase in fluid pressure, it is unlikely that the overpressures required to induce rock mass failure are solely generated by porosity/permeability reduction in the Rotokawa geothermal reservoir, requiring a constant external flux of fluids to induce the overpressures. Large-scale failure of the Rotokawa Andesite is modelled as a rock mass using the Hoek-Brown failure criterion, and indicates that the current dominant mode of failure is for the Rotokawa Andesite is shear failure at depth. However, small scale changes in stress, or an increase in rock mass strength will favour tensile failure. High fracture densities observed in three wells of the Rotokawa Andesite are oriented consistent with fractures formed in shear mode, consistent with ‘Healy’ faulting being the main mode of fracture formation in the Rotokawa Andesite.

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21

AGOSTINI, CLAUDIA. "Crystallization kinetics: a probe of magmatic and eruptive processes for Stromboli and Pantelleria volcanic systems." Doctoral thesis, Università degli Studi di Camerino, 2013. http://hdl.handle.net/11581/401842.

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22

Riker, Jenny Michelle. "Experimental constraints on volatile-driven crystallisation in volcanic systems: A case study at Mount St. Helens." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629006.

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Degassing and crystallisation are concomitant processes in volcanic systems that together modulate the physico-chemical properties of magmas. The compositions and textures of crystal-bearing volcanic rocks therefore preserve valuable information about the degassing paths experienced by their host magmas. Accurate interpretation of the rock record, however, requires a detailed interpretive framework. This thesis presents the results of high-temperature, high-pressure experiments designed to clarify the mechanisms and manifestations of volatile-driven crystallisation in natural magmas. The well-characterised :Mount St. Helens volcanic system is taken as a case study. Isothermal phase equilibria experiments in P- XH20 space establish the fluid-composition dependence of phase relations in Mount St. Helens (Sugar Bowl) rhyodacite. Parameterisation of experimentally derived data enables simulation of magmatic properties across a wide range of parameter space. This approach has been applied to investigate the equilibrium evolution of phase assemblages, abundances, and compositions along different H20 - C02 degassing trajectories. Experimental decompression of magmas saturated with H20 and H20 -C0 2 fluids further demonstrates that plagioclase textures are strongly modulated by the isothermal decompression (PH20 - t) path. The presence of CO2 increases crystal nucleation rates relative to the pure-water case, while growth on pre-existing crystals contributes significantly to added crystallisation at a range of decompression conditions. Comparison of crystal textures in experimental samples and natural pyroclasts are used to interpret changing magma storage conditions during the summer 1980 explosive- effusion transition at Mount St. Helens. Finally, the behaviour of magmatic volatiles in the shallow crust is ultimately modulated by the nature and abundance of vapour exsolved at depth. To this end, this research presents new constraints on water solubility in silicic melts at lower crustal pressures, where experimental determinations are sparse. Together with data from lower pressures, these experiments define a continuous solubility curve in the Sugar Bowl rhyodacite from 0.1- 1.1 GPa. Saturation water contents suggest that the presence of fluid-saturated, evolved melts is likely in the deep crust.

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23

Raithatha, Bansri Gitesh. "The sealing potential of volcanic rocks in hydrocarbon systems : a case study from the Rosebank Field." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/11978/.

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Hydrocarbon exploration in frontier regions has resulted in a series of discoveries within intra- and sub-volcanic basins along the NE Atlantic margin. The majority of these basins are blanketed by varying thicknesses of subaerial lavas and volcaniclastic sequences that form the Paleogene-aged North Atlantic Igneous Province. During Exploratory drilling in 2004, the 213/27-1Z well encountered two oil and gas accumulation with a total pay thickness of 52 metres, within the Late Palaeocene-Early Eocene aged Colsay Member sandstones within the Rosebank Field. These hydrocarbon-bearing reservoir intervals comprise numerous fluvial clastic sequences that are inter-layered between sub-aerially erupted basaltic lavas and volcaniclastic sediments. This discovery gave rise to a new hydrocarbon play concept. In this study, the sealing potential of the volcanic and volcaniclastic sequences is investigated using multi-scale subsurface datasets (with a particular emphasis on the value of high resolution borehole image logs; FMI) and field analogues from the Faroe Islands. Through the combined use of wireline logs (Bivariate cross-plots) and high resolution FMI images, the volcanic and volcaniclastic rocks in the Rosebank Volcanic Formations (RVFs) were characterised, and a detailed volcanic stratigraphic section of the RVFs was constructed, to understand how these lithologies vary vertically and laterally between wells. Bivariate cross-plots (photoelectric factor versus bulk density) indicates that there are two distinct compositions of lava flows: (a) Lava Type I is characteristic of the Rosebank Lower Volcanics, and has a higher Iron/Magnesium variety, suggesting that it was emplaced during the initial phase of volcanism; and, (b) Lava Type II is characteristic in the Upper and Lower Rosebank Middle Volcanics (RMV_U and RMV_L) and the Rosebank Upper Volcanics, and is depleted in Iron and Magnesium. The FMI images revealed that the RVFs comprise a diverse and complex suite of volcanic and volcaniclastic rocks (e.g. pillow lavas, hyaloclastite, sub-aerial lavas and inter-basaltic rocks), some of which exhibit complex diagenetic overprints produced during post-volcanic process. Detailed interpretation of FMI images and integration with wireline logs showed that the ratio of volcanic, volcaniclastic and siliciclastic rocks varied between studied wells, for example the southernmost wells in Rosebank Main (205/1-1, 213/26-1, 213/26-1z and 213/27-1Z) comprise 57-62% sub-aerially erupted pahoehoe lava, ~25% volcaniclastic rocks, and ~15% siliciclastic rocks, while the wells in northern Rosebank Main (213/27-4 and 213/27-2) comprise ~35% sub-aerially erupted lava, ~50% volcaniclastic rocks, and ~20% siliciclastic rocks. These ratios indicate that the sub-aerially erupted lavas are thinning to the North of the field. Fractures interpreted in the volcanic rocks in the RVFs mainly occur in the more brittle units, for example, in the massive cores of sub-aerially erupted lava flows. Fractures distribution in the RVFs is strongly controlled by the type of lithology (e.g. simple lava flow, pillow lava, hyaloclastite etc.), their thickness and the degree of secondary degradation and alteration they have undergone. In comparison to the Colsay reservoir intervals, the RVFs are more brittle and highly fractured and thus much more prone to fracturing during drilling. Their sealing potential decreases from southern Rosebank Main to northern Rosebank Main, predominantly because the RVFs are much thinner to the North, and contain large, connected fractures. The inter-layering between volcanic and volcaniclastic rocks in southern Rosebank Main acts as an efficient vertical seal because the volcaniclastics tend to be clay-rich and do not fracture as easily. In terms of sealing potential, all the RVFs except RMV_U are low risk seals, suggesting that in some parts of the field, particularly in the northern most part of Rosebank Main, the Colsay 1 and 2 reservoir intervals may be connected. Evidence of faulting in the RVFs is infrequent in the FMI images, although where inferred, they tend to occur at contacts between lava and volcaniclastic rocks, usually at the transitional interface between the Colsay reservoir intervals and the RVFs. Similarly, faults were interpreted in the Ocean Bottom Node (OBN) seismic data, although they are generally small and discontinuous. It is therefore predicted that if faults are present in Rosebank, they are likely to be low-strain with minimal displacement. Integration of field analogues from the Faroe Islands with the subsurface datasets (FMI and recovered core) suggests that the majority of the fractures interpreted from the FMI images, and any possible faults within the RVFs, are likely to be sealing. Vein infill at the studied outcrops indicate that cementation rates were low, and therefore many fractures were still potential conduits. In Rosebank, however, due to high cementation rates, most of the fractures are completely healed. This also provides a significant clue on hydrocarbon migration within the Colsay reservoirs. It is evident that none of the fractures or the volcanic rocks recovered either through full core recovery, or side-wall cores, have any hydrocarbon shows, and therefore, the fractures present in the RVFs are likely to have been completely filled, during hydrocarbon migration into the Colsay reservoirs. It is therefore suggested that, hydrocarbons laterally migrated into the Colsay sands from the sands in the Flett Basin, and because the fractures in the RVFs did not act as conduits for fluid flow, the hydrocarbons were successfully trapped within their respective reservoirs.

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Atlas, Zachary D. "Volatiles in Melt Inclusions from Mexican and Nicaraguan Volcanoes: Implications for Complex Degassing Processes." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/142.

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The first section of this work examines melt inclusions in phenocrysts from Volcán Popocatépetl and Volcán de Colima within the Trans Mexican Volcanic Belt (TMVB). These inclusions are dacitic to rhyolitic. Trends in melt inclusion major element and water concentrations form the evolved extension of other Mexican volcanics including those presumably derived directly from primitive melts. Water concentrations in Popocatépetl and Colima melt inclusions are similar (0.3 to 3.4 weight percent Hsub2O). Melt-vapor equilibration pressures calculated from dissolved Hsub2O and COsub2 (Popocatépetl) or Hsub2O (Colima) in melt inclusions correspond to depths of entrapment of 12 km or less. Water and carbon dioxide concentrations correlate negatively with SiOsub2 and potassium. Normalized olivine-augite-quartz compositions are consistent with near cotectic crystallization under vapor-saturated conditions at pressures of 1.5 kb or less. Our results show that Popocatépetl and Colima magmas have undergone vapor-saturated crystallization during ascent in conjunction with varying degrees of mixing between degassed rhyo-dacitic and less degassed, mafic melts in the upper portions of the crust. These data suggest melt evolution occurred in conduits or inter-fingered dikes rather than a large stratified magma chamber. Part II looks at the Masaya caldera in Nicaragua. This volcano has erupted frequently in recorded history, producing lava lakes and very high gas emissions. Melt inclusions from Masaya are basaltic, with low Hsub2O (below 0.5 wt. %), low S (less than 300 ppm) and high COsub2 concentrations (up to approximately 6000 ppm). Relationships between water, sulfur, Cl and F in combination with Masaya's high COsub2 and Ba/Zr and Ba/Nb ratios suggest that Masaya has undergone a multi stage degassing process involving 1) shallow degassing, 2) recycling of magma into a deeper reservoir, and 3) fluxing of previously degassed magma with a nearly pure COsub2 vapor. Trace element signatures of melt inclusions are consistent with contributions that have been variably metasomatized by fluids generated by dehydration of subducted sediments and/or altered oceanic crust.

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25

Kraus, Stefan. "Magmatic dyke systems of the South Shetland Islands volcanic arc (West Antarctica) reflections of the geodynamic history /." Diss., [S.l.] : [s.n.], 2005. http://edoc.ub.uni-muenchen.de/archive/00003827/.

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26

Montanaro, Cristian [Verfasser], and Bettina [Akademischer Betreuer] Scheu. "A multidisciplinary approach to unravel the steam-driven eruptions in volcanic systems / Cristian Montanaro ; Betreuer: Bettina Scheu." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1114068195/34.

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27

Randazzo, Loredana Antonella. "The behaviour of trace elements during the volcanic ash-liquid interaction : example of marine and human systems." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10051.

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Les processus d’interaction solide-liquide régulent les mécanismes qui régissent la disponibilité des oligo-éléments en phase liquide. Dans cet article, ces processus ont été étudiés grâce à l'utilisation des éléments de terres rares (REE), car ils sont d'excellents traceurs des processus géochimiques. Le but de la première partie de ce travail était d'étudier la réactivité des particules volcaniques lors de l'interaction avec l'eau de la mer synthétique. Les résultats montrent que en dehors de la dissolution, qui est le processus principal, un procédé d'adsorption de surface se produit également, probablement sur la surface des cristaux nouvellement formé. La présence supposée de ces minéraux est suggéré par la variation temporelle de l'Y/Ho, des observations SEM et analyse XRD. Enfin, l'ajout des ligand dissous ne pas augmenter le taux de dissolution des particules volcaniques, mais modifiant la distribution de REE en phase liquide. Dans la deuxième partie de ce travail, l'étude des terres rares a été appliquée à un système humain. Ces éléments ont été utilisés, en fait, d'enquêter sur les fluides du poumon (BAL) chez les personnes exposées aux retombées de cendres volcaniques. Le résultat suggère que la co-précipitation du YLn-phosphates se produisent dans les poumons, à la suite de l'inhalation de particules volcaniques. Ce processus est confirmé par des simulations thermodynamiques et cinétiques indiquant que la cristallisation de YLn-phosphates et d'autres phases authigènes apparaît comme la conséquence de la dissolution de la fraction solubles de cendres The solid-liquid interaction processes regulate the mechanisms governing the availability of trace elements in liquid phase. In this paper, these processes have been studied through the use of the Rare Earth Elements (REE) since they are excellent tracers of geochemical processes. The purpose of the first part of this work was to study the reactivity of volcanic particulates during the interaction with synthetic seawater. The results show that apart from the dissolution, which is the main process, a surface adsorption process also occurs, probably on the surface of newly formed crystals. The supposed presence of these minerals is suggested by the temporal variation of the Y/Ho ratio, by SEM observations and XRD analysis. Finally the addition of ligand species to dissolved media does not increase dissolution rate of volcanic particles but modify the YLn distribution in liquid phase. In the second part of this work, the Rare Earth study was applied to a human system. These elements were used, in fact, to investigate the effects due to the interactions between the inhaled atmospheric particulate matter and the lung fluids (BAL), in people exposed to fallout of volcanic ash. The results suggest that YLn-phosphate co-precipitation occurs in lungs as a consequence of inhalation of volcanic particles and their interactions with lung fluids. This process is confirmed by thermodynamic and kinetic simulations indicating that crystallisation of YLn-phosphates and other authigenic phases occurs as a consequence of the soluble ash fraction dissolution. The combination of YLn fractionation in bronchial fluids can represent a potential tracer of exposure to atmospheric fallout

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Kaye, Grant David. "Volcanic hazard risk assessment for the RiskScape program, with test application in Rotorua, New Zealand, and Mammoth Lakes, USA." Thesis, University of Canterbury. Geological Sciences, 2008. http://hdl.handle.net/10092/1950.

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This thesis presents a new GIS-based scenario volcanic risk assessment model called RiskScape Volcano (RSV) that has been designed for the RiskScape program to advance the field of volcanic risk assessment. RiskScape is a natural hazards risk assessment software tool being developed in New Zealand by GNS Science and NIWA. When integrated into RiskScape, RSV will add proximal volcanic hazard risk assessment capability, and enhanced inventory design; it presently operates outside of RiskScape by combining volcanic hazard models’ output spatial hazard intensity (hazard maps) with inventory databases (asset maps) in GIS software to determine hazard exposure, which is then combined with fragility functions (relationships between hazard intensity and expected damage ratios) to estimate risk. This thesis consists of seven publications, each of which comprises a part of the development and testing of RSV: 1) results of field investigation of impacts to agriculture and infrastructure of the 2006 eruption of Merapi Volcano, Indonesia; 2) agricultural fragility functions for tephra damage in New Zealand based on the observations made at Merapi; 3) examination of wind patterns above the central North Island, New Zealand for better modeling of tephra dispersal with the ASHFALL model; 4) a description of the design, components, background, and an example application of the RSV model; 5) test of RSV via a risk assessment of population, agriculture, and infrastructure in the Rotorua District from a rhyolite eruption at the Okataina Volcanic Centre; 6) test of RSV via a comparison of risk to critical infrastructure in Mammoth Lakes, California from an eruption at Mammoth Mountain volcano versus an eruption from the Inyo craters; and 7) a survey of volcanic hazard awareness in the tourism sector in Mammoth Lakes. Tests of the model have demonstrated that it is capable of providing valid and useful risk assessments that can be used by local government and emergency management to prioritise eruption response planning and risk mitigation efforts. RSV has provided the RiskScape design team with a more complete quantitative volcanic risk assessment model that can be integrated into RiskScape and used in New Zealand and potentially overseas.

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Romero, Mujalli Gibran [Verfasser], and Jens [Akademischer Betreuer] Hartmann. "The role of temperature in processes controlling weathering rates of carbonate lithologies and volcanic systems / Gibran Romero Mujalli ; Betreuer: Jens Hartmann." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1187921734/34.

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30

Lupi, Matteo. "High-resolution simulations of fluid flow in active hydrothermal systems : applications to the Tjornes Fracture Zone and Askja Volcanic complex in Iceland." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2357.

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This study provides new insights into the transient uid ow dynamics that characterise high temperature hydrothermal systems. So far, these kind of studies have used process models that tend to over-simplify the geology and focus instead on the physical processes, hence not revealing the hidden behaviour that depends on the complex geological structures often encountered in hydrothermal systems. This study is one of the rst examples where high resolution numerical simulations in two and three dimensions have been applied to hydrothermal systems in order to preserve geological detail in the models explicitly. Two prime examples in Iceland for seismicity-induced uid ow and groundwater ow during volcanic eruptions, respectively, have been selected for this purpose. The rst example is the Tjörnes Fracture Zone, a heavily faulted transform zone o shore in North Iceland where most of the Icelandic earthquakes occur. The work demonstrated that a moderate permeability contrast between the shallow sedimentary basins and deep crustal basement causes two distinct uid ow regimes which are only connected during a seismic event. When such an event occurs, faults in the Tjörnes Fracture Zone in ate and connect the two uid ow systems, causing hot uids migrating from the basement into the basins at extreme ow rates. This explains key geochemical observations made in the Tjörnes Fracture Zone before and after a seismic event. The second study investigated the 1874 to 1875 volcano-tectonic episode at the Askja volcano, which is the third largest silicic eruption since settlement in Iceland. Here it was demonstrated how syn-eruptive groundwater ow inside the Askja caldera changed the eruptive style of the March 1875 eruption, causing a well-documented change from a wet to dry eruptive style. The results of this work provide some fundamental new insights into the transient dynamics of uid ow in active high temperature hydrothermal systems and suggest that these kind of simulations may be used to complement studies assessing the risk and hazard of future volcanic eruptions and seismic events.

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Konchi, Wakgari Furi. "Hydrogeology of complex volcanic systems in continental rifted zone : integrated geochimical, geophysical and hydrodynamic approach : Middle Awash basin, Main Ethiopian Rift, Ethiopia." Poitiers, 2010. http://theses.edel.univ-poitiers.fr/theses/2010/Konchi-Wakgari-Furi/2010-Konchi-Wakgari-Furi-These.pdf.

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Middle Awash basin, located in the complex volcanic centre of the Ethiopian Rift valley, is one of the drought prone areas marked by considerable water supply problems. Due to lack of surface waters, groundwater remains the sole resource supplying water for domestic and livestock. However, its effective use has been hampered due to the complex aquifer system of this basin. In this study, multidisciplinary method has been applied to characterize the hydrogeological system of this complex volcanic basin. The combined results from datasets show two distinct aquifer systems linked to geology and physiographic location. The Ca-alkaline rocks like basalt, ignimbrite, and trachybasalt form aquifers in the mountain regions whereas the Na-alkalne rocks which include scoria, pumice, tuff, and volcanoclastics are main aquifers in rift floor. Ground waters circulating in the highland areas are slightly mineralized and are Ca-Na-HCO3 type. On the other hand, ground waters in the rift floor are Na-HCO3-Cl types and are highly mineralized as well as contain high load of fluoride much higher than the permitted standard. Rivers hydrograph, hydrochemistry, environmental isotope, and 2D tomography are in good agreement showing fast percolation of rainfall and strong interaction between surface waters and ground waters. Result from numerical groundwater flow modeling further indicates the strong interaction between groundwater and surface waters in the form of losing and gaining Le bassin central d'Awash, situé dans le centre volcanique complexe de la Vallée du Rift éthiopien, est un des secteurs les plus touchés par la sécheresse et par des problèmes considérables d'approvisionnement en eau. En raison du manque d'eau de surface, l'eau souterraine reste la ressource unique fournissant l'eau potable. Cependant, l'exploitation effective de l'eau souterraine s'est heurtée à la méconnaissance du système hydrogéologique complexe de ce bassin. Dans cette étude, une approche pluridisciplinaire a été mise en oeuvre pour caractériser l'hydrogéologie de ce bassin volcanique complexe. Les résultats couplés de l'ensemble des données montrent deux systèmes aquifères distincts liés à la géologie et à la localisation physiographique. Les roches Ca-alcalines comme le basalte, l'ignimbrite et le trachybasalte forment des aquifères dans les régions de montagne tandis que les roches Na-alcalines qui incluent les scories, la pierre ponce, les tufs et les volcanoclastiques constituent les principaux aquifères au niveau du plancher du rift. Les eaux souterraines circulant dans les secteurs montagneux sont légèrement minéralisées et sont de type Ca-Na-HCO3. Par contre, les eaux souterraines du plancher du rift sont de type Na-HCO3-Cl, sont fortement minéralisées et contiennent une charge en fluorure beaucoup plus élevée que les normes permises. Les résultats de diverses approches (hydrogrammes des fleuves, hydrochimie, isotopes environnementaux et tomographie 2D) sont concordants et montrent une percolation rapide des eaux de pluie et une forte interaction entre les eaux de surface et les eaux souterraines. Les résultats de modélisation numérique confirment la forte interaction eau souterraine - eaux de surface

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32

Hernandez, Lindsey Danielle. "Magma Plumbing Systems along the Juan de Fuca Ridge." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587630136962186.

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33

Letham-Brake, Mark. "Geological constraints on fluid flow at Whakaari volcano (White Island)." Thesis, University of Canterbury. Department of Geological Sciences, 2013. http://hdl.handle.net/10092/8728.

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This study assesses the geological constraints on fluid flow within the main crater of Whakaari volcano (White Island) which is located in the Bay of Plenty, New Zealand. A review of the volcanological and morphological history, field mapping, and permeability experiments were used to propose a model for single-state (gas or liquid water) fluid flow in the volcano. Three structural scales were of most importance: (a) the elongate main crater (1.2 km by 0.5 km); which contains (b) three subcraters (~300-500 m in diameter); and (c) >14 historic eruption craters and crater complexes (30-300 m in diameter). A large (2.1x10⁸ m³) sector collapse formed the basic morphology and structure of the amphitheatre-like main crater ≤3.4 ka. Hot fluids are released from magma at ~1–2 km depth and circulated within a conduit-hosted volcano-hydrothermal system. The collapse event was likely to have removed low permeability cone lavas, significantly increasing meteoric water collection and lateral seawater infiltration within high permeability main crater fill above the magma conduit. It is proposed that this caused a susceptibility to ‘wet’ (i.e. phreatic and phreatomagmatic) eruptions which possibly formed three prehistoric subcraters and has been demonstrated in the last ~200 years of available historic record. The permeability of the remaining in-situ cone lavas is controlled by micro- (<1 mm) and macro- (>1 mm) cracks but despite these cracks, the cone lavas’ permeability is still sufficiently low to focus rising magmatic fluid flow through main crater fill. Low-to-high permeability lithified tuffs are inferred to fill the main crater at depth. Low permeability fine ash tuffs generally restrict vertical fluid flow put permit it when vertical trains of vesicles are present. Atmospheric steam and gas pluming is accommodated by a permeable zone of repeated and overlapping historic eruption crater-related discontinuities that extend to >250 m depth through highly permeable unlithified main crater fill in the west. It is likely to be this material into which the seawater infiltrates from the east. Throughout the main crater, fluid flow is focussed at subcrater margins due to steeply-dipping discontinuities between low permeability lava and low-to-high permeability crater fill deposits. The variable permeabilities of crater fill deposits are due to age-related factors of hydrothermal alteration, reworking/sorting, consolidation, and pore mineralisation. At shallow levels (<100 m depth), vertical fluid flow is diverted to historic eruption crater margins by very low permeability clay (reworked and altered tephra). High permeability coarse ash tuffs, Fe-rich lapilli tuffs, and surficial solfatara deposits do not appear to have much effect on the overall fluid flow system. The results of this study show that, within active volcanic craters, the spatial distributions of variably permeable lithologies are often related to discontinuous cratering structures. Together, these are significant geological constraints on fluid flow. Morphological changes to crater structure can directly impact the groundwater regime above the magma conduit and may strongly influence the occurrence of wet versus dry eruptions. This process is possibly a significant control on eruptive behaviour at volcanoes with similar fluid flow systems worldwide.

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34

Hartley, Margaret Elizabeth. "Post glacial volcanism and magmatism on the Askja volcanic system, North Iceland." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/5845.

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Postglacial activity on the Askja volcanic system, north Iceland, has been dominated by basaltic volcanism. Over 80% of Askja's postglacial basalts fall within a relatively narrow compositional range containing between 4 and 8 wt.% MgO. The 'main series' is further divided into two groups separated by a distinct compositional gap evident in major and trace element concentrations. The most evolved basalts formed by fractional crystallisation within shallow magma reservoirs, followed by the extraction of residual liquid from a semi-rigid, interconnected crystal network. This process is analogous to the formation of melt segregations within single lava flows, and was responsible for generating several small-volume, aphyric basaltic lavas erupted along caldera ring fractures surrounding the Oskjuvatn (Askja lake) caldera in the early 20th century. Further examples of evolved basalt are found throughout Askja's postglacial volcanic record. However, Askja's early postglacial output is dominated by more primitive compositions. Some of the most primitive basalts erupted within the Askja caldera are found in phreatomagmatic tuff cone sequences which crop out in the walls of Oskjuvatn caldera. one such tuff sequence has been dated at between 2.9 and 3.6 ka. This tuff cone shares geochemical source characteristics, such as Nb/La and Nb/Zr, with basaltic tephras erupted during precursory activity to the Plinian-phreatoplinian eruption of 28th-29th March 1875. It may therefore be considered to be compositionally representative of the primitive basaltic magmas supplied to Askja during the postglacial period. The predominance of relatively primitive basalt (6.8 wt.% MgO) within Askia's postglacial lava succession suggests that it did not have a permanent shallow magma chamber during the postglacial period. It is envisaged that the postglacial Askja magmas evolved by a process of polybaric factionation in transient, sill-like magma storage zones located at various levels in the crust. The most primitive magmas erupted directly from deeper reservoirs, while the more evolved magmas experienced longer crustal residence times. The buoyant rise of volatile-enriched melt from these sill-like bodies, without mobilising phenocryst phases, explains the observation that almost all lavas on Askja's eastern and southern lava aprons are essentially aphyric. The 28th-29th March 1975 eruption marked the climax of a volcanotectonic episode on the Askja volanic system lasting from late 1874 to early 1876. Fissure eruptions also occurred at the Sveinagja graben, 45-65 km north of Askja, between February and October 1875, producing the Nyjahraun lava. A strong similarity exists between whole-rock major element concentrations from Myjahraun and the Askja 20th century basalts. This has led to the suggestion that these basalts originated from a common shallow magma reservoir beneath Askja central volcano, with the Nyjahraun eruptions being fed by a lateral dyke extending northwards from Askja. This theory also offers an explanation for the observation that the volume of phyolitic ejecta from 28th-29th March 1875 is significantly less than the volume of Oskjuvatn caldera, which was formed as a result of this eruption. New major and trace element data from whole-rock and glass samples indicated that Nyjahraun and the Askja 20th century basalts did not share a common parental magma. A detailed investigation of historical accounts from explorers and scientists who visited Askja between 1875 and 1932 reveals that Oskjuvatn caldera took over 40 years to reach its current form, and that its size in 1876 was equal to the volume erupted on 28th-29th March 1875. Small injections of magma into an igneous intrusion complex beneath Askja, coupled with background deflation, are sufficient to provide the required accommodation space for continued caldera collapse after 1876. Lateral flow is therefore not required to explain the volume of Oskjuvatn caldera, nor the eruption of evolved basaltic magma on the Askja volcanic system in 1875. It has been conjectured that the Holuhraun lava, located at the southern tip of the Askja volcanic system, was also connected with the 1874-76 Askja volcanotectonic episode. However, major and trace element data from whole-rock samples, glass and melt inclusions receal the Holuhraun is geochemically more similar to basalts erupted on the Bardarbunga-Veidivotn volcanic system than to postglacial basalts from Askja. The division between the 'Askja' and 'Veidivotn' geochemical signatures appears to be linked to east-west-striking lineations in the region south of Askja. This indicates that a particular geochemical signature is not necessarily confined to the tectonic expression of a single volcanic system, and has important implications for the identification and delineation of individual volcanic systems beneath the northwest sector of Vatnajokull.

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Keith, Manuel [Verfasser], and Karsten [Akademischer Betreuer] Haase. "From active submarine vent systems to fossil volcanic-hosted massive sulphide deposits: an in-situ analytical study of hydrothermal sulphides / Manuel Keith. Gutachter: Karsten Haase." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2015. http://d-nb.info/1080362703/34.

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36

Needy, Sarah Katherine. "Tracking the Evolution of Mid Cenozoic Silicic Magma Systems in the Southern Chocolate Mountains Region, California Using Zircon Geochemistry and Quartz and Zircon Geothermometry." Thesis, Connect to resource online, 2009. http://hdl.handle.net/1805/1953.

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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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37

Syahbana, Davy Kamil. "Seismological study of volcanic activity at Papandayan volcano, West Java, Indonesia." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209395.

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Dans l'histoire des éruptions volcaniques, le Papandayan à l'Ouest de Java est considéré comme l'un des plus meurtriers après avoir causé la mort de 2957 personnes et des dégâts sérieux en 1772. L'éruption la plus récente de ce volcan a eu lieu en 2002 et était de type phréatique. Cette éruption a été précédée d'une augmentation soudaine de l'activité sismique moins de deux jours avant l'éruption. Aucune victime n'a été déplorée. La nature de cette éruption est indéfinie. Cette thèse regroupe plusieurs études utilisant différentes techniques en vue d'améliorer la prédictibilité des éruptions du volcan Papandayan, principalement via l'interprétation des signatures sismiques.Le monitoring sismique passif a débuté en décembre 2009 par l'installation d'une station sismique permanente à large bande dans le cratère du Papandayan. L'année suivante, une station météorologique a été installée pour compléter les mesures. La troisième année, 8 stations sismiques temporaires ont été déployées autour du volcan en réponse à une augmentation de l'activité sismique en 2011.Nous avons conduit différentes études; (1) Nous avons examiné l'évolution de l'activité volcanique par réalisation d'une revue complète de l'histoire éruptive du volcan, autant pour la période préhistorique qu'historique. (2) Nous avons réalisé une analyse temps-fréquence des événements sismiques, étudié leurs caractéristiques et proposé une nouvelle classification avec une description des processus physiques supposés les générer. (3) Nous avons étudié les signatures sismiques précurseur de l'éruption de 2002 et pendant la crise volcanique de 2011 en implémentant différentes méthodologies, dont: la détection automatique d'événements sismiques à l'aide de filtres récursifs STA/LTA, l'analyse spectrale des formes d'onde, la mesure continue de l'amplitude spectrale du signal (SSAM), la polarisation des ondes et l'analyse de la distribution fréquence/magnitude (b-value). Nous avons alors réalisé un modèle chronologique des séquences sismiques du Papandayan. (4) Pour améliorer la compréhension de la dynamique des fluides sous le volcan Papandayan, nous avons réalisé une analyse des fréquences complexes des événements longue période (LP) et leurs variations temporelles peuvent être utilisées pour estimer (a) la composition des fluides présents dans les fractures sous le volcan et/ou (b) l'évolution des dimensions de ces fractures. Ces variations des fréquences complexes des événements LP peuvent être interprétées comme les réponses dynamiques du système hydrothermal à des changements d'impulsions de chaleur transférées par les flux de gaz volcaniques du magma sous le volcan. (5) nous avons calculé l'évolution temporelle du rapport spectral horizontal-sur-vertical (HVSR) en utilisant le bruit sismique ambiant enregistré par une station unique pour estimer les variations de vitesse de propagation des ondes de cisaillement en lien avec l'activité dynamique du volcan. Nous avons trouvé une corrélation claire entre les variations de fréquence de résonnance HVSR et l'augmentation de la sismicité.Enfin, nous proposons des hypothèses sur les processus physiques qui se produisent sous le Papandayan. Cette étude est une première tentative d'utilisation de cette méthode pour surveiller l'activité volcanique en continu. Doctorat en Sciences info:eu-repo/semantics/nonPublished

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38

[Verfasser], Budi Joko Purnomo, Thomas [Akademischer Betreuer] Pichler, and Peter [Akademischer Betreuer] LaFemina. "Geothermal systems in the Sunda volcanic island arc : Investigations on the islands of Java and Bali, Indonesia / Budi Joko Purnomo. Gutachter: Thomas Pichler ; Peter LaFemina. Betreuer: Thomas Pichler." Bremen : Staats- und Universitätsbibliothek Bremen, 2015. http://d-nb.info/1072304244/34.

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39

Maussen, Katharine. "Carbon dioxide transport through Taal volcano’s hydrothermal system and Main Crater Lake (Philippines)." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/271649.

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The presence of a hydrothermal system at Taal volcano is evident from the presence of a craterlake (Main Crater Lake, MCL), a caldera lake (Lake Taal) and several hot springs on the flanksof Taal volcano island and in the crater. Taal MCL, covering an area of 1.2 km², is acidic (pH= 3), warm (T = 30-33 °C) and its composition is dominated by Cl, Na and SO4. This thesisaims at understanding the geochemistry of Taal volcano’s hydrothermal system and the wayCO2 is transported through the hydrothermal system and MCL towards the atmosphere.The long-term geochemical evolution of MCL indicates that the hydrothermal system is madeof two reservoirs, one being volcanic and one geothermal in origin. The geothermal componentin Taal MCL has stayed rather constant since 1991, while the volcanic component hasdecreased.The low pH makes Taal volcano the perfect natural laboratory to study the behaviour of CO2,because there is no dissociation of CO2. A combined approach of total CO2 flux measurementsvia accumulation chamber and gaseous CO2 flux measurements via echo sounder shows thatmore than 90% of the total CO2 output of Taal volcano is due to the influx of dissolved CO2,migrating from the hydrothermal system to MCL via thermal springs under the lake surface.After verification of both horizontal and vertical homogeneity of dissolved CO2 concentrations,a continuous monitoring station was installed in 2013, measuring dissolved CO2 using aninfrared gas analyser protected by an ePTFE membrane, as well as several meteorological andenvironmental parameters. Several environmental and lacustrine processes influence CO2transport in MCL, including stratification, solar heating and rainfall.Taal volcano regularly goes through periods of unrest, characterised by seismic swarms,ground deformation and increased carbon dioxide flux. In 1991-1994, this was accompaniedby geochemical changes in MCL, including pH decrease and F, Si and Fe concentrationincrease. These changes can be attributed to an intrusion of magma to shallow levels less thanone kilometre deep. More recent unrests do not show these geochemical changes and are likelycaused by pressure changes in the hydrothermal system. The permanent monitoring stationrecorded hourly data on the 2015 unrest and showed that abnormally high CO2 concentrationswere recorded before the start of seismic or deformation activity, which makes continuous CO2monitoring a very valuable addition to current monitoring activities at Taal volcano. La présence d’un système hydrothermal au volcan Taal se manifeste par la présence d’un lac de cratère (Main Crater Lake, MLC) ainsi qu’un lac de caldera (Lake Taal) et de multiples sources d’eau chaudes sur les flancs et dans le cratère. Le MCL, avec une surface de 1.2 km², est acide (pH = 3), chaud (T = 30-33 °C) et composé principalement de Cl, Na et SO4. Le but de cette thèse est de comprendre la géochimie du système hydrothermal du Taal et la manière dont le CO2 est transporté à travers de celui-ci ainsi qu’à travers le MCL vers l’atmosphère. L’évolution géochimique à long terme indique que le système hydrothermal est composé de deux réservoirs, un d’origine volcanique et un autre d’origine géothermale. Le composant géothermal est resté plutôt constant depuis 1991, tandis que le composant volcanique a diminué. Le pH plutôt bas fait que le volcan Taal est le laboratoire naturel parfait pour étudier le comportement du CO2, parce qu’il n’y a pas de dissociation de CO2. Une approche combinée du flux de CO2 total via chambre d’accumulation, et flux de CO2 gazeux via echo sondeur montre que plus que 90% du flux de CO2 total est dû au CO2 dissout, qui migre depuis le système hydrothermal au MCL via des sources thermales sous la surface du lac. Après vérification de l’homogénéité horizontale et verticale du CO2 dissout, une station de monitoring en continu a été installée en 2013. Cette station mesure le CO2 dissout à l’aide d’un analyseur de gaz infrarouge protégé par une membrane en ePTFE, ainsi que de multiples paramètres météorologiques et environnementaux. Le transport de CO2 dans le MCL est influencé par plusieurs processus environnementaux et lacustre, comprenant la stratification, l’échauffement solaire et la pluie. Le volcan Taal connait régulièrement des périodes de crises caractérisées par une activité sismique, par une déformation du sol et par un flux élevé du CO2. En 1991-1994, ceux-ci ont été accompagnés par des changements géochimiques du MCL, comprenant une diminution du pH et une augmentation de la concentration de F, Si et Fe. Ces changements peuvent être attribués à une intrusion superficielle de magma à moins d’un kilomètre de profondeur. Les crises plus récentes ne montrent pas ces changements en géochimie et sont probablement causés par des changements de pression dans le système hydrothermal. La station de monitoring en continu a enregistré des données toutes les heures pendant la crise en 2015 et a montré que des concentrations particulièrement élevées en CO2 dissout ont été enregistrées avant le début de l’activité sismique et de déformation. Ceci a montré que le monitoring en continu du CO2 est une addition très précieuse aux activités de monitoring du volcan Taal. Doctorat en Sciences info:eu-repo/semantics/nonPublished

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40

Peers, Justin, Ashleigh Reeves, Christopher Gregg, Michael K. Lindell, and Andrew Joyner. "Improving volcano risk communication at the Long Valley Caldera and Mono-Inyo Craters volcanic system, eastern California, USA." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/asrf/2018/schedule/4.

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Exposure to volcano hazards can lead to crises; with or without an eruptive event. Therefore, it is important to distinguish that volcanic events (unrest & eruptions) are physical phenomena while volcanic crises are social. Volcanic eruptions, unlike some other geologic hazards are often preceded by weeks or months of precursors, which offer the opportunity to reduce risk by early intervention. However, resistance to discussion of local hazards can hinder stakeholders’ (emergency managers, scientists, etc.) ability to mitigate volcano hazards and create well-informed protocols to respond when disaster strikes. The Long Valley Caldera (LVC) east of California’s Sierra Nevada Mountain Range, has experienced unrest since 1978, at which time a M5.6 earthquake ended 20 years of seismic quiet. Seismicity continued, followed by significant ground deformation and doming of the caldera floor, increased fumarolic activity, and CO2 degassing which has contributed to tree kills and human fatalities. Extensive research in volcano science provides an understanding of the physical phenomena behind the mechanics of volcanos, but limited resources have been dedicated to understanding human processes in response to volcano hazards and their corresponding disasters. Misconceptions and uncertainty surrounding organizational and physical communication of risk information can amplify economic consequences resulting from volcanic crises. This study will utilize two methods to obtain perceptions that local stakeholders and residents hold towards hazards in their region; and their confidence in the agencies that are responsible in responding to crises. A questionnaire sent to 1,200 households in February, 2018 asked head-of-households about their awareness of volcano hazards, preparedness for a volcano emergency, and perceptions of stakeholders responsible for decision making and warning systems. Mental model interviews conducted with stakeholders in summer, 2018 will provide insight on methods used by decision makers tasked with responding to disasters at LVC and the greater Long Valley Volcanic Region (LVVR). Mental models, i.e. schema, are a representation of how a person thinks about and mentally conceptualizes objects, events, and relationships in the real world. Robust to change, mental models are not easily altered; however, new information is either dismissed or made to fit within previous beliefs. Research suggests that the more discordant new information is with respect to existing beliefs, the more likely the information is to challenge those beliefs, providing opportunities for change. Together, these household and stakeholder studies will identify issues surrounding risk communication and risk management to improve tools that communicate the uncertainty of volcanic activity in the LVVR.

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Tambe-Ebot, Mathias Ashu Tako. "Proposing a Theoretical GIS Model for Landslides Analysis : The Case of Mount Cameroon." Thesis, Linköpings universitet, Institutionen för datavetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-65899.

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This study presents a theoretical GIS model to investigate the relative impacts of geomorphic and environmental factors that govern the occurrence of landslides on the slopes of Mount Cameroon and its surrounding areas. The study area is located along the Cameroon Volcanic Line (CVL), a major structural feature that originates from the south Atlantic and continues into the continental landmass. The quite frequent seismic activity, geologic character, humid tropical climate and high human pressure on hill slopes are the major factors behind the occurrence of landslides in Mount Cameroon. This paper, therefore, underscores the necessity of in-depth follow-up studies concerned with landslides prevention and management based on the relevance of sufficient reliable field methods in landform geomorphology and interpretation. As much is yet to be done to acquire data for structural and surface geology, hydrology, geomorphic processes and physiography of Mount Cameroon, it is difficult at this point in time to considerably apply suitable methods using GIS that would enable identifying and delineating the landslide-prone areas. In addition, the application of environmental surface monitoring instruments will not be meaningful without a clear presentation of which areas are a cause for concern (given that the employment of any slope stability monitoring and rehabilitation efforts will be only possible after appropriate problem-area identification has been done). Consequently, based on the writer’s previous work in the Mount Cameroon area and available related literature, a methodology using GIS is proposed, which provides the capability to demonstrate how the impact of individual or collective geomorphologic site-specific factors on landslides occurrence could be justified. Considering that digital data may not be readily available, a procedure for the creation of data and analysis of themes is proposed and illustrated. The factors analysis approach in landslides analysis may be cheaper and easier to employ in Mount Cameroon and similar problem regions in developing countries (given that there may be problems of limited financial resources and available expertise in GIS technology and applications). The study underscores and recommends the necessity for a later practical implementation with the availability of adequate resources.

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Rinaldi, Antonio Pio <1982&gt. "Modeling hydrothermal system: deriving observables and hydrothermal instability in volcanic and non-volcanic setting." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3321/1/Rinaldi_Antonio_tesi.pdf.

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Hydrothermal fluids are a fundamental resource for understanding and monitoring volcanic and non-volcanic systems. This thesis is focused on the study of hydrothermal system through numerical modeling with the geothermal simulator TOUGH2. Several simulations are presented, and geophysical and geochemical observables, arising from fluids circulation, are analyzed in detail throughout the thesis. In a volcanic setting, fluids feeding fumaroles and hot spring may play a key role in the hazard evaluation. The evolution of the fluids circulation is caused by a strong interaction between magmatic and hydrothermal systems. A simultaneous analysis of different geophysical and geochemical observables is a sound approach for interpreting monitored data and to infer a consistent conceptual model. Analyzed observables are ground displacement, gravity changes, electrical conductivity, amount, composition and temperature of the emitted gases at surface, and extent of degassing area. Results highlight the different temporal response of the considered observables, as well as the different radial pattern of variation. However, magnitude, temporal response and radial pattern of these signals depend not only on the evolution of fluid circulation, but a main role is played by the considered rock properties. Numerical simulations highlight differences that arise from the assumption of different permeabilities, for both homogeneous and heterogeneous systems. Rock properties affect hydrothermal fluid circulation, controlling both the range of variation and the temporal evolution of the observable signals. Low temperature fumaroles and low discharge rate may be affected by atmospheric conditions. Detailed parametric simulations were performed, aimed to understand the effects of system properties, such as permeability and gas reservoir overpressure, on diffuse degassing when air temperature and barometric pressure changes are applied to the ground surface. Hydrothermal circulation, however, is not only a characteristic of volcanic system. Hot fluids may be involved in several mankind problems, such as studies on geothermal engineering, nuclear waste propagation in porous medium, and Geological Carbon Sequestration (GCS). The current concept for large-scale GCS is the direct injection of supercritical carbon dioxide into deep geological formations which typically contain brine. Upward displacement of such brine from deep reservoirs driven by pressure increases resulting from carbon dioxide injection may occur through abandoned wells, permeable faults or permeable channels. Brine intrusion into aquifers may degrade groundwater resources. Numerical results show that pressure rise drives dense water up to the conduits, and does not necessarily result in continuous flow. Rather, overpressure leads to new hydrostatic equilibrium if fluids are initially density stratified. If warm and salty fluid does not cool passing through the conduit, an oscillatory solution is then possible. Parameter studies delineate steady-state (static) and oscillatory solutions.

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43

Rinaldi, Antonio Pio <1982&gt. "Modeling hydrothermal system: deriving observables and hydrothermal instability in volcanic and non-volcanic setting." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3321/.

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Анотація:

Hydrothermal fluids are a fundamental resource for understanding and monitoring volcanic and non-volcanic systems. This thesis is focused on the study of hydrothermal system through numerical modeling with the geothermal simulator TOUGH2. Several simulations are presented, and geophysical and geochemical observables, arising from fluids circulation, are analyzed in detail throughout the thesis. In a volcanic setting, fluids feeding fumaroles and hot spring may play a key role in the hazard evaluation. The evolution of the fluids circulation is caused by a strong interaction between magmatic and hydrothermal systems. A simultaneous analysis of different geophysical and geochemical observables is a sound approach for interpreting monitored data and to infer a consistent conceptual model. Analyzed observables are ground displacement, gravity changes, electrical conductivity, amount, composition and temperature of the emitted gases at surface, and extent of degassing area. Results highlight the different temporal response of the considered observables, as well as the different radial pattern of variation. However, magnitude, temporal response and radial pattern of these signals depend not only on the evolution of fluid circulation, but a main role is played by the considered rock properties. Numerical simulations highlight differences that arise from the assumption of different permeabilities, for both homogeneous and heterogeneous systems. Rock properties affect hydrothermal fluid circulation, controlling both the range of variation and the temporal evolution of the observable signals. Low temperature fumaroles and low discharge rate may be affected by atmospheric conditions. Detailed parametric simulations were performed, aimed to understand the effects of system properties, such as permeability and gas reservoir overpressure, on diffuse degassing when air temperature and barometric pressure changes are applied to the ground surface. Hydrothermal circulation, however, is not only a characteristic of volcanic system. Hot fluids may be involved in several mankind problems, such as studies on geothermal engineering, nuclear waste propagation in porous medium, and Geological Carbon Sequestration (GCS). The current concept for large-scale GCS is the direct injection of supercritical carbon dioxide into deep geological formations which typically contain brine. Upward displacement of such brine from deep reservoirs driven by pressure increases resulting from carbon dioxide injection may occur through abandoned wells, permeable faults or permeable channels. Brine intrusion into aquifers may degrade groundwater resources. Numerical results show that pressure rise drives dense water up to the conduits, and does not necessarily result in continuous flow. Rather, overpressure leads to new hydrostatic equilibrium if fluids are initially density stratified. If warm and salty fluid does not cool passing through the conduit, an oscillatory solution is then possible. Parameter studies delineate steady-state (static) and oscillatory solutions.

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44

Blacic, Tanya Marie. "Magma supply and storage in volcanic systems : shallow crustal emplacement processes and causes of the large axial high along the western Galápagos Spreading Center, and relation of earthquakes to tectonic and magmatic features near Lassen Peak, northern California /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.

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45

Arnott, Stuart K. "A seismic study of the Krafla volcanic system, Iceland." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6526/.

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Following a major crustal rifting episode centred on the Krafla volcanic system in Northeast Iceland, the local seismicity was monitored for three months using a dense network of single component seismometers. Initial earthquake locations were computed for 489 local events using a one-dimensional velocity model derived from seismic refraction data. Activity was concentrated in clusters beneath a geothermal area within the Krafla caldera and below the Bjarnarflag geothermal well field to the south, and in a narrow linear zone coincident with a site of recent dyke injection. Events of magnitudes -2.4 to 2.1 were located. The b-value for the entire dataset is 0.77±0.10, and is lower for events at Bjarnarflag than for events in the dyke injection zone. Seismicity was continuous. A simultaneous inversion of 1771 P-wave arrival times was carried out to calculate the 3-d velocity structure and refine hypocentral locations. The derivative weight sum was used to identify the well-resolved volume. High velocity bodies at depth beneath the rim of the caldera are high density intrusives, probably gabbros. Volumes of low velocity coincide with zones of geothermal exploitation within the caldera and beneath Bjarnarflag, and result from intense fracturing and hydrothermal alteration. After relocation through the three-dimensional velocity structure, the spatial distribution of hypocentres is more focussed and considerably shallower than before. This led to a closer correlation between zones of seismicity and detailed features within the source volumes, such as geothermal reservoirs, fault surfaces and zones of known recent magmatic intrusion. Focal mechanisms were determined using P-wave polarity data for 153 of the best located earth quakes, of which 139 have double couple solutions. Fourteen events were non-double couple, 4 of which could be solved as either opening or closing tensile cracks assuming small circle nodal lines. The biasing effect of using incorrect hypocentres and an over-simplified velocity structure were investigated by 3-d ray tracing. The effects on ray angles are large and variable. The impact of these effects on double couple solutions is generally small, but can be critical for the confident identification of non-double couple events. Seismicity in geothermal areas results from cooling and fracturing of hot intrusives at depth, and fault surfaces are marked by enhanced seismicity when they provide efficient migratory paths for geothermal fluids. Seismicity may be induced partially by geothermal mining. The stress field in the Krafla volcanic system at the time of the survey was variable along its length, as was the mode of fracturing. The stress field at Bjarnarflag was chaotic. In the geothermal area within the caldera σ(_3) was perpendicular to the plate boundary, and in the dyke injection zone σ(_1) was perpendicular to the plate boundary. Such heterogeneity in the stress field is contrary to what might be expected at a spreading axis, and is attributed to variation in regional extensional stress release during the recent rifting episode.

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46

Loughlin, Susan C. "The evolution of the Eyjafjöll volcanic system, southern Iceland." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/1456/.

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47

Kaikkonen, R. (Riina). "Evolution of basaltic lavas of the Kverkfjöll volcanic system, Northern Volcanic Zone, Iceland:evidence from in-situ LA-ICP-MS analyses." Master's thesis, University of Oulu, 2017. http://urn.fi/URN:NBN:fi:oulu-201704191514.

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This study deals with the evolution of the basaltic lavas of the Kverkfjöll volcanic system, which is located at the eastern edge of the Northern Volcanic Zone in central Iceland. The aim of this study is to model the melt and mineral evolution of the collected basaltic sample series by utilizing major and trace element data. The sample set consists of separated glass shards and plagioclase, olivine and clinopyroxene macrocrystals (d>500 µm). In addition, the glass shards contain microcrystals (d1 in specific minerals. Incompatible elements are enriched in evolved glasses and in general show higher concentrations in microcrystals than in earlier crystallized macrocrystals. Partitioning of V between olivine microcrystals and adjacent glass were used to determine the oxygen fugacity at 0–1 log units above the NNO buffer. This together with the appearance of titanomagnetite suggests the melts of the sample series were moderately oxidized. Stable ratios of incompatible element pairs analyzed from glass shards suggest that no remarkable contamination or magma mixing have disturbed the ratios between the most primitive and evolved samples. In the Zr/Y vs. Nb/Y diagram, the Kverkfjöll magmas plot in the high-ratio end of the Iceland array. This is consistent with the observed high incompatible element concentrations in the Kverkfjöll melts in comparison to the other volcanic centers nearby (i.e., Kistufell, Bárðarbunga and Grímsvötn). In addition, the volcanic rocks of Kverkfjöll are distinguishable from the other three volcanoes by its higher K₂O concentrations, resulting from a lower degree of partial melting.

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48

Lee, Sang Hee. "The responses of the respiratory system when exposed to volcanic ash." Thesis, Cardiff University, 2004. http://orca.cf.ac.uk/55387/.

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The toxicological investigations demonstrated quite clearly the different toxicological properties of the MA, CRS and ANR. The CRS proved to be fibrogenic in rat lung with a 5.0mg single instillation dose after long-term (1 year) exposure whereas ANR was minimally bioreactive. The MA did not cause inflammation in the lung until 49 weeks post-instillation even though size augmentation with granuloma formation in thoracic lymph nodes were recognised at 13 weeks. These findings suggested that the size and granuloma formation of thoracic lymph nodes were good early markers to assess the toxicity of crystalline silica containing volcanic ash. Histopathological and physicochemical investigations confirmed that the particles drained from the lung were deposited in mainly the granulomatous areas in the nodes. Furthermore, the crystalline silica content of the MA in the nodes was greater than that noted in the MA in the lung tissue and the original instillate. The macroarray technology has provided additional information on MA and CRS induced inflammation. A number of candidate inflammatory markers were identified

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49

Roberts, Katie Sarah. "Mud volcano systems : structure, evolution and processes." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/752/.

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Mud volcano systems erupt sediment and fluid onto the Earth’s surface producing edifices up to 25 km3 in volume however, little is known about how such volumes are transported through the Earth’s crust. This thesis investigates whether transport is through mud-dyke-sill complexes, or is diapiric. Structural field mapping of exhumed mud volcano intrusive domains onshore in Azerbaijan, shows that feeder complexes are 200-800 m wide and roughly circular. These complexes consist of various fracture networks and a megabreccia of country rock blocks tens-of-metres-across that have rotated up to 90° in a matrix of mud. A structural domain model categorises regions within the feeder complex which formed during stoping processes. Structural mapping is combined with nearest neighbour and 2-point-azimuth statistical analysis of vent distributions described from nine mud volcanoes in Azerbaijan and Lusi mud volcano, East Java. Vent distributions are non-random, showing alignments with: 1) anticline crestal faulting, 2) fractures 3) ring faults, and 4) detachment faults indicating that fracture systems and regional stresses significantly influence feeder complex architecture. Lusi’s vent alignments change orientation from 2006-2010 implying regions 10 km east and west of the main vent are more likely to be impacted by new vents due to the onset of elongate-caldera collapse. Kilometre-scale, elongate scarps are identified as ‘sector collapses’ on mud volcanoes in Azerbaijan due to morphological similarity to those on igneous volcanoes. Shape parameters distinguish sector collapses and eruptive mud breccia flows allowing identification in field and satellite-based mapping. The updip domains are characterised by vents showing there is linkage to deeper mud volcano fluid flow pathways. A model of a deflating mud chamber triggering ‘thin-skinned’ sector collapse is proposed. This sector collapse model, vent alignment orientation analysis and intrusive domain structural model are ultimately integrated into a comprehensive schematic model of the mud volcano system.

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50

Schmidt, Anja. "Modelling tropospheric volcanic aerosol : from aerosol microphysical processes to Earth system impacts." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540764.

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