To see the other types of publications on this topic, follow the link: Volcanic.
Dissertations / Theses on the topic 'Volcanic'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Volcanic.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Purdy, David John. "Volcanic stratigraphy and origin of the Wallangarra Volcanics, Wandsworth volcanic group, northern NSW, Australia." Thesis, Queensland University of Technology, 2003.
Find full text
2
Smith, R. T. "Eruptive and depositional models for units 3 and 4 of the 1.85 ka Taupo eruption: Implications for the nature of large-scale 'wet' eruptions." Thesis, University of Canterbury. Geological Science, 1998. http://hdl.handle.net/10092/5928.
Full textAbstract:
Phreatomagmatic eruptions result from the explosive interaction between magma and some external source of water, and produce deposits which are usually distinctive in nature from those of magmatic eruptions. The widespread deposits of large-scale phreatomagmatic eruptions (usually termed Phreatoplinian) are poorly studied relative to their magmatic counterparts and, consequently, current models for large-scale phreatomagmatic volcanism remain speculative. The Hatepe ash and Rotongaio ash (units 3 and 4 of the 1.85 ka Taupo eruption) are two classical widespread phreatomagmatic fall deposits. These have been examined in fine detail and sampled, for the first time, at a mm-scale, with the intention of quantifying vertical and lateral variations within these deposits and improving our understanding of the eruptive mechanisms and depositional processes during large-scale 'wet' eruptions.
The Hatepe ash (1.75 km3) is a widespread (>15 000 km2, individual subunit bt values = 4.4 to 5.5 km), multiple-bedded, poorly-sorted pumiceous fall deposit. The fines-rich character and widespread occurrence of ash aggregates in the proximal to medial dispersal areas are indicators of a phreatomagmatic origin. Subunits contain multiple layers with a wide range of dispersal and grain size characteristics, and a number of distinctive primary lithofacies have been defined which characterise the changes in eruptive conditions and main depositional modes during Hatepe volcanism. The
predominantly fine grained clasts (Mdø= 3.3-4.5), along with perhaps 20-25 wt.% liquid, were transported and deposited in the form of damp to wet 'mud lumps' and accretionary lapilli. Dispersal was from dense, 'wet' plumes which promoted the cohesion and aggregation of liquid-coated fine particles. This mode of transport and deposition was dominant during relatively long-lived episodes of relatively low discharge rate, with higher water/magma ratios at the vent and liquid/particle ratios in plumes. When magma discharge rate was relatively high and water/magma ratios low, fines-poor, plinian-style deposits (Mdø = -2.2 to 0.63) were produced by discrete particle fall from high (~25-30 km), relatively 'dry' plumes. Minor, short-lived fluctuations in discharge rate produced episodes of mixed discrete and ash aggregate fall which produced poly- and bimodal deposits (Mdø = 2.5-3) in proximal and inner-medial areas. Lateral emplacement by dilute, turbulent pyroclastic density currents was important in the proximal environment.
The range and indices of Hatepe ash juvenile clast vesicularities (50-90%, and 75% vesicles, respectively) indicate that fragmentation was driven by magmatic volatiles but that water played some part in quenching. The minimal variation in juvenile clast vesicularity through the deposit and between the facies types indicates that the state of the Hatepe magma remained a uniform foam, and that the mechanism of fragmentation (but not the water/magma ratio) was consistent throughout Hatepe volcanism.
Facies analysis and mapping of internal variations in ash dispersal confirm that the Hatepe ash is not the product of simple sustained magma discharge, but was actually the result of a continuous but highly irregular flux, with fluctuations in magma supply, sometimes over very short time intervals, resulting in a range of eruptive styles and depositional modes.
The Rotongaio ash (0.8 km3) is a widespread (>10 000 km2, subunit bt values = 2.9 to 5km), poorly-sorted fall deposit with abundant evidence for the important involvement of liquid water at the vent and in the plume. Modes of deposition were similar to the Hatepe ash; dominantly damp to wet mud lump fallout (Mdø= 3.9 to 5.5), but with minor episodes of discrete particle fall (Mdø = -1.1 to 1.9) and mixed discrete and aggregate fall (Mdø= 1.2 to 2.9) caused by fluctuations in discharge rate. An additional depositional mode in medial areas during Rotongaio volcanism was by dilute, turbulent density currents, derived from particle-laden downbursts from the umbrella region of dense, wet, convectively-unstable plumes. Such a process may account for occurrences of cross-stratification in the medial-distal parts of other widespread ash falls.
Secondary processes such as fluvial erosion and reworking, and soft-sediment deformation and slurry-flow were important depositional modes that operated syneruptively during Rotongaio (and Hatepe ash) volcanism. The very close association in time and space between primary and secondary lithofacies implies that there was a strong genetic link between the style of primary eruptive processes and the nature and extent of the secondary modification. In many cases the 'secondary' processes formed a continuum with primary depositional processes, influenced by the liquid/particle ratio of ash fallout and inherent to the mode of eruption. Throughout deposition of the Rotongaio ash a delicate balance always existed between primary accumulation, erosion and redeposition.
The Rotongaio ash differs from the Hatepe ash, and most other widespread ash fall deposits, in a number of important ways which indicate the Rotongaio ash is not a typical phreatoplinian deposit; 1) it is extremely finely laminated in proximal exposures and many of these beds cannot be traced into the medial environment indicating it is the product of multiple, discrete and non-sustained explosions which dispersed material along a number of axes and with a wide range of thinning rates, 2) juvenile clasts are mostly poorly- to non-vesicular and clast populations span a very wide range of densities (0-65% vesicles) indicating that the Rotongaio magma was partially degassed and heterogeneous (unlike the Hatepe ash and other pumiceous phreatoplinian deposits), and fragmentation was driven not by vesiculation, but largely by external volatiles, 3) the lack of any significant coarse component compared to the Hatepe ash at anyone site supports a fundamentally different mode of fragmentation for Rotongaio volcanism and vent processes which probably involved significant recycling of clasts through the vent.
Detailed analysis of the Hatepe ash and Rotongaio ash has provided some interesting insights into the nature of large-scale phreatomagmatic eruptions. Ash dispersal patterns for subunits of the two deposits indicate that 'wet' and 'dry' plumes, even of comparatively small magnitudes (0.02 to 0.8 km3 subunit volumes) behave in distinctive ways which hint at fundamentally different dynamics of dispersal. Assessment of lateral variations in clast size populations suggest the differences between proximal strongly fines-segregated 'dry' facies and the fines-rich 'wet' facies is an artefact controlled mostly by the initial liquid/solid ratio in the plume rather than the mechanism of fragmentation.
3
Bartolini, Stefania. "Volcanic hazard assessment in monogenetic volcanic fields." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284845.
Full textAbstract:
One of the most important tasks of modern volcanology, which represents a significant socio-economic implication, is to conduct hazard assessment in active volcanic systems. These volcanological studies are aimed at hazard that allows to constructing hazard maps and simulating different eruptive scenarios, and are mainly addressed to contribute to territorial planning, definition of emergency plans or managing volcanic crisis. The impact of a natural event, as a volcanic eruption, can significantly affect human life, property, infrastructures, and the environment. Long periods of quiescence are quite common in many volcanic areas and this often leads to a fall in the alert. The consequence is lack of preparation to deal with a volcanic crisis.
The present Ph.D. Thesis is focused on the development and application of different tools for the spatial and temporal analyses to assess volcanic hazard in monogenetic volcanic fields. Monogenetic volcanic fields are commonly not regarded as potentially dangerous and only a few studies concerning hazard assessment have been conducted in such environments. In the long-term hazard assessment, we assume that the future eruptive behaviour in the volcanic field could be similar to the last eruptive activity. First, we have developed a new tool, QVAST (QGIS for VolcAnic SuscepTibility), designed to carry out the spatial analysis. This tool allows to calculate the volcanic susceptibility of the area, i.e. the probability of new vent opening, using direct and indirect structural data. Second, we have developed a new tool, HASSET (Hazard Assessment Event Tree), to conduct temporal analysis. Combining both tools and the previous one, VORIS 2.0.1, that uses simulation models to predict the most probable eruptive scenarios and which areas could be affected by a future eruptive event, we can evaluate in a probabilistic way long-term hazard represented by a qualitative hazard map that allows us to identify different levels of hazard in the study area. In this thesis we present different case studies. The first example was carried out at El Hierro Island (Canary Islands), an island essentially characterized by basaltic volcanism with both Strombolian and Hawaiian activity. The last eruption on El Hierro occurred in 2011–2012 demonstrates the importance of reliable data and tools that can enable scientific advisors and decision-makers to consider possible future eruptive scenarios. The second case study was Deception Island (Southern Shetland Archipelago, Antarctica), which is the most active volcano in the South Shetland Islands and has been the scene of more than twenty eruptions over the past two centuries. We identified a number of significant scenarios using our GIS-based tools and evaluated the potential extent of the main volcanic hazards to be expected on the island. The last case study presented is La Garrotxa Volcanic Field (NE of Spain), which is a quaternary volcanic field, located in the Northeast of the Iberian Peninsula, and includes more than 50 well preserved volcanoes.
Finally, considering the importance of both quantity and quality of the available volcanic data and an optimum storage mechanism and as complement to the e-tools we have developed, we describe the design of a new spatial database structure, VERDI (Volcanic managEment Risk Database desIgn), which allows different types of data to be manipulated, organized, managed. The design of purpose-built databases should facilitate spatial and temporal analysis that will produce probabilistic hazard models for future vent opening, simulate volcanic hazards and assess their socio-economic impact, avoiding any duplication of information.
The methodologies described in this thesis establish the general guidelines of a procedure that facilitates undertaking volcanic hazard assessment in a systematic way, which can be easily applied to any volcanic area or system, and in particular to any monogenetic volcanic field.Una de las tareas más importantes de la vulcanología moderna, que representa una implicación socio-económica significativa, es llevar a cabo la evaluación de la peligrosidad en los sistemas volcánicos activos. Estos estudios vulcanológicos están enfocados a la elaboración de mapas de peligro y la simulación de diferentes escenarios eruptivos, y están dirigidas para contribuir a la planificación territorial, a la definición de los planes de emergencia o la gestión de crisis volcánicas. La presente Tesis doctoral está enfocada al desarrollo y aplicación de diferentes herramientas informáticas para los análisis espacial y temporal del peligro volcánico en campos volcánicos monogenéticos. En primer lugar, hemos desarrollado una nueva herramienta, QVAST, diseñada para llevar a cabo el análisis espacial, que permite calcular la susceptibilidad volcánica de la zona de estudio, utilizando datos estructurales directos e indirectos. En segundo lugar, hemos desarrollado una nueva herramienta, HASSET, para llevar a cabo el análisis temporal. La combinación de ambos instrumentos y una herramienta anterior, VORIS 2.0.1, que utiliza modelos de simulación para predecir los escenarios eruptivos más probables y aquellas áreas que podrían verse afectadas por un futuro evento eruptivo, nos permite evaluar de forma probabilística el peligro a largo plazo, representado por un mapa cualitativo que nos permite identificar los diferentes niveles de peligro en el área de estudio. En esta tesis se presentan diferentes casos de estudio en campos volcánicos monogenéticos: la isla de El Hierro (Islas Canarias), la isla Decepción (archipiélago de las Shetland del Sur, Antártida), el campo volcánico de La Garrotxa (NE de España). Por último, teniendo en cuenta la importancia de la cantidad y la calidad de los datos volcánologicos disponibles y un mecanismo de almacenamiento óptimo, se describe el diseño de una nueva estructura de base de datos espaciales, VERDI, que permite manipular, organizar y gestionar diferentes tipos de datos. Las metodologías descritas en esta tesis establecen líneas guía generales de un procedimiento que facilita la realización de la evaluación del peligro volcánico de forma sistemática, los cuales se pueden aplicar a cualquier zona volcánica o sistema, y en particular, a cualquier campo volcánico monogenético.
4
Wetie, Ngongang Ariane. "Seismic and Volcanic Hazard Analysis for Mount Cameroon Volcano." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/60871.
Full textAbstract:
Mount Cameroon is considered the only active volcano along a 1600 km long chain of volcanic complexes called the Cameroon Volcanic Line (CVL). It has erupted seven times during the last 100 years, the most recent was in May 2000. The approximately 500,000 inhabitants that live and work around the fertile flanks are exposed to impending threats from volcanic eruptions and earthquakes.
In this thesis, a hazard assessment study that involves both statistical modelling of seismic hazard parameters and the evaluation of a future volcanic risk was undertaken on Mount Cameroon. The Gutenberg-Richter magnitude-frequency relations, the annual activity rate, the maximum magnitude, the rate of volcanic eruptions and risks assessment were examined.
The seismic hazard parameters were estimated using the Maximum Likelihood Method on the basis of a procedure which combines seismic data containing incomplete files of large historical events with complete files of short periods of observations. A homogenous Poisson distribution model was applied to previous recorded volcanic eruptions of Mount Cameroon to determine the frequency of eruption and assess the probability of a future eruption.
Frequency-magnitude plots indicated that Gutenberg-Richter b-values are partially dependent on the maximum regional magnitude and the method used in their calculation. b-values showed temporal and spatial variation with an average value of 1.53 ± 0.02. The intrusion of a magma body generating the occurrence of relatively small earthquakes as observed in our instrumental catalogue, could be responsible for this high anomalous b-value.
An epicentre map of locally recorded earthquakes revealed that the southeastern zone is the most seismically active part of the volcano. The annual mean activity rate of the seismicity strongly depends on the time span of the seismic catalogue and results showed that on average, one earthquake event occurs every 10 days. The maximum regional magnitude values which had been determined from various approaches overlap when their standard deviations are taken into account. However, the magnitude distribution model of the Mt. Cameroon earthquakes might not follow the form of the Gutenberg-Richter frequency magnitude relationship.
The datations of the last eruptive events that have occurred on Mt. Cameroon volcanic complex are presented. No specific pattern was observed on the frequency of eruptions, which means that a homogenous Poisson distribution provides a suitable model to estimate the rate of occurrence of volcanic eruptions and evaluate the risk of a future eruption. Two different approaches were used to estimate the mean eruption rate (λ) and both yielded a value of 0.074. The results showed that eruptions take place on average once every 13 years and, with the last eruption occurring over 15 years ago, it is considered that there is at present a high risk of an eruption to occur.Dissertation (MSc)--University of Pretoria, 2016.
Geology
MSc
Unrestricted
5
Hellwig, Bridget M. "The viscosity of dacitic liquids measured at conditions relevant to explosive arc volcanism determing the influence of temperature, silicate composition, and dissolved volatile content /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4597.
Full textAbstract:
Thesis (M.S.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.
6
Vallejo, Vargas Silvia Ximena. "Numerical models of volcanic flows for an estimation and delimitation of volcanic hazards, the case of Reventador volcano (Ecuador)." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC100/document.
Full textAbstract:
Les coulées de laves sont les produits volcaniques les plus représentatifs des éruptions effusives. Elles sont formées quand le magma est extrudé et se répand à la surface de la Terre. Quand la lave arrive en surface, elle perd de la chaleur et refroidit. Le refroidissement affecte directement les propriétés rhéologiques de la lave, jusqu’à arrêter son écoulement. Les paramètres rhéologiques qui contrôlent la dynamique des coulées de laves sont la viscosité et le seuil de plasticité, qui dépendent eux-mêmes de la composition chimique, de la cristallinité et de la teneur en bulles. Il existe de nombreux modèles d’estimation de la rhéologie, la plupart développés pour les coulées de lave basaltiques et quelque uns pour les coulées de lave andésitiques. Les coulées de laves peuvent grandement affecter les régions peuplées, les infrastructures et l’environnement. Un moyen de prévoir les futurs dégâts est de développer des modèles numériques pour prévoir la propagation des coulées de laves sur des topographies volcaniques réelles. Cette méthode difficile combine la topographie, la rhéologie, la perte de chaleur et la dynamique de l’écoulement pour simuler l’emplacement d’une coulée de lave précise. Le code numérique VolcFlow, qui est basé sur une approche moyennée verticale, est capable de reproduire les caractéristiques principales des dépôts comme la morphologie, la longueur et l’épaisseur. Dans cette étude sont proposés trois modèles implémentés dans VolcFlow et ayant pour but de simuler des coulées de laves. Le premier est isotherme, le deuxième inclut le refroidissement et les variations rhéologiques associées, et le troisième prend en considération la déformation de la croûte à la surface de la coulée et son effet sur l’emplacement de la coulée. Afin de vérifier la validité des différentes approches, les modèles sont testés sur quatre cas d’étude : deux coulées de lave de composition basaltique (expérience de basalte fondu de Syracuse lava Project et la coulée de lave d’août novembre 2015 du Piton de la Fournaise, France) et deux de compositions andésitique (la coulée de lave du 4-5 décembre 2015 du Tungurahua et trois coulées de lave du Reventador, Equateur). Les résultats des simulations montrent que le modèle isotherme peut reproduire les coulées même s’il ne prend pas en compte les variations de rhéologie et le refroidissement. Le modèle incluant la cristallisation, induite par le refroidissement de la lave au cours de son écoulement, et les variations rhéologiques associées donne de très bons résultats mais est très sensible aux paramètres d’entrée, en particulier à la viscosité, elle-même très dépendante de la composition chimique et de la température. Enfin, le modèle prenant en compte le refroidissement et les variations de rhéologie par une loi synthétique sigmoïde montre une bonne cohérence dans tous les cas simulés, sauf pour le Piton de la Fournaise. Le modèle visant à simuler la formation d’une croûte à la surface de la lave et sa percée par l’écoulement sous-jacent amène uniquement à l’épaississement de la croûte. Le mécanisme de percée n’est pas reproduit avec VolcFlowLava flows are the most representative volcanic products of effusive eruptions and are formed whenthe magma is extruded and flows on the surface. When lava flows reach the surface they lose heat and cool.Cooling affects directly the rheology of the lava up to a point where it cannot flow anymore. Rheologicalparameters that control the dynamics of lava flows are the viscosity and the yield strength which in turndepends on the chemical composition, crystallinity and bubble content. There exist numerous models forthe rheology estimation, mostly developed for basaltic lava flows and few for andesitic ones.Lava flows can highly affect populated areas, infrastructures and environment. A way to forecastthe future damages is to developed numerical codes of the lava propagation on real volcanic topography.This challenging method combines the topography, the rheology, the heat loss, and flow dynamics tosimulate the emplacement of a particular lava flow. The numerical code VolcFlow which is based on thedepth-averaged approach is able to reproduce the main physical characteristics of the deposits likemorphology, length and thickness. Here 3 models are proposed for their implementation in VolcFlow withthe aim to simulate lava flows. One model is isothermal, the second includes cooling and the associatedrheological variations, and the third takes into account the crust formation and its effect on the flowemplacement. To check the validity of the different approaches, the models were tested with four studycases, two with basaltic compositions (molten basalt experiment of the Syracuse lava Project and the August-November, 2015 lava flow from Piton de la Fournaise, France) and two with andesitic compositions (theDecember 4th-5th lava flow from Tungurahua, Ecuador, and three lava flows from El Reventador,Ecuador). Results of the simulations shows that the isothermal model can reproduce the flows even if itdoes not consider the cooling and rheology variation. The model that includes rheological laws as functionof crystallization induced by cooling down flow can give very good results but is very sensitive to the inputdata, in particular to the fluid viscosity that is very dependent on chemical composition and temperature.Finally, the model that includes cooling and synthetic sigmoid rheological law shows good coherence for allthe cases except at Piton de la Fournaise. The model that aims to simulate the formation of a crust on thelava flow surface, lava flowing underneath and break-out mechanisms leads to the thickening of the crust.Hence, break-out mechanism is not reproduced with VolcFlow
7
Smith, Cassandra M. "Volcanic Electrification: A Multiparametric Case Study of Sakurajima Volcano, Japan." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7950.
Full textAbstract:
Electrical activity at volcanoes has been recently recognized as a potential new remote sensing technique for plume-forming eruptions. Volcanic electrical activity takes place in the conduit and plume and therefore has the benefit of being a direct indicator of surface activity. This is unlike seismic signals, which indicate magma/gas movement underground, and infrasound signals, which indicate a surface explosion but not necessarily the formation of an ash plume. There are two distinct types of volcanic electrical discharges: volcanic lightning and continual radio frequency (CRF) impulses. This dissertation explores the relationships between these two electrical signals and other commonly monitored volcanic parameters. For volcanic electrical activity to be widely adopted into monitoring platforms it is important to understand how electrical discharges at volcanoes are related to other monitored signals. I present a case study of the electrical activity at Sakurajima Volcano, Japan. The lightning mapping array (LMA) is used to record both lightning and CRF. I relate CRF to ash properties and show that CRF corresponds to eruptions containing more juvenile magma that has undergone milling as it is transported out of the conduit. Seismic, infrasound, and video data are used in conjunction with multivariable statistical methods on a suite of electrical parameters to show that high levels of volcanic electrical activity are related to eruptions with large infrasound signals (> 107 J), high initial velocities (> 55 m/s), and relatively tall plume heights (> 1 km). Finally, an examination of globally detected lightning at Bogoslof Volcano, AK shows the potential for volcanic lightning in plume tracking (0-100 km), even after the end of the explosive phase of the eruption.
8
Longobardi, Mariantonietta <1983>. "Locating the source of volcanic tremor at stromboli volcano, italy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5181/1/Tesi.pdf.
Full textAbstract:
We have developed a method for locating sources of volcanic tremor and applied it to a dataset recorded on Stromboli volcano before and after the onset of the February 27th 2007 effusive eruption. Volcanic tremor has attracted considerable attention by seismologists because of its potential value as a tool for forecasting eruptions and for better understanding the physical processes that occur inside active volcanoes. Commonly used methods to locate volcanic tremor sources are: 1) array techniques, 2) semblance based methods, 3) calculation of wave field amplitude. We have choosen the third approach, using a quantitative modeling of the seismic wavefield. For this purpose, we have calculated the Green Functions (GF) in the frequency domain with the Finite Element Method (FEM). We have used this method because it is well suited to solve elliptic problems, as the elastodynamics in the Fourier domain. The volcanic tremor source is located by determining the source function over a regular grid of points. The best fit point is choosen as the tremor source location. The source inversion is performed in the frequency domain, using only the wavefield amplitudes. We illustrate the method and its validation over a synthetic dataset. We show some preliminary results on the Stromboli dataset, evidencing temporal variations of the volcanic tremor sources.
9
Longobardi, Mariantonietta <1983>. "Locating the source of volcanic tremor at stromboli volcano, italy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5181/.
Full textAbstract:
We have developed a method for locating sources of volcanic tremor and applied it to a dataset recorded on Stromboli volcano before and after the onset of the February 27th 2007 effusive eruption. Volcanic tremor has attracted considerable attention by seismologists because of its potential value as a tool for forecasting eruptions and for better understanding the physical processes that occur inside active volcanoes. Commonly used methods to locate volcanic tremor sources are: 1) array techniques, 2) semblance based methods, 3) calculation of wave field amplitude. We have choosen the third approach, using a quantitative modeling of the seismic wavefield. For this purpose, we have calculated the Green Functions (GF) in the frequency domain with the Finite Element Method (FEM). We have used this method because it is well suited to solve elliptic problems, as the elastodynamics in the Fourier domain. The volcanic tremor source is located by determining the source function over a regular grid of points. The best fit point is choosen as the tremor source location. The source inversion is performed in the frequency domain, using only the wavefield amplitudes. We illustrate the method and its validation over a synthetic dataset. We show some preliminary results on the Stromboli dataset, evidencing temporal variations of the volcanic tremor sources.
10
NOGUEIRA, LAGES Joao Pedro. "Constrains on mantle, slab and crustal contributions to major volatiles and noble gases along the Andean Volcanic Belt." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/395502.
Full text
11
Milawski, James. "Quaternary Volcanic Ash Transformation in the Mayan Lowland." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377871595.
Full text
12
García, Pérez Olaya. "The explosive volcanism of Teide-Pico Viejo volcanic complex, Canary Island." Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/130923.
Full textAbstract:
The explosive events in Teide Pico Viejo (TPV) complex in Tenerife Island (Spain) have traditionally been restricted to the subplinian eruption of Montaña Blanca, which occurred about 2000 years ago. A recent revision of the stratigraphy of TPV shows that phonolitic explosive activity has been significant during the Holocene, with several distinct episodes related to eruptions ranging from Strombolian to sub-plinian. Using field, mineralogical and geochemical stratigraphic correlations, we have identified 11 phonolitic explosive eruptions related to the satellite domes present all around TPV complex. One of the most representative eruptions is that of El Boqueron (5,660 yBP), a dome that generated an explosive event of VEI 3 with a minimum volume of 4-6x107 m3 and produced a plume with a height of up to 9km above sea level (MER 6.9-8.2x105 kg/s, during 9-15 h). The occurrence of these explosive events in the recent eruptive record of TPV is of major importance in evaluating the risk imposed by the volcanic complex on Tenerife. These eruptions have generated a wide range of direct hazards, such as fallout, emplacement of pyroclastic density currents, debris flows, lahars, and rock avalanches, which could occur again in case of a renewal of volcanic activity. The results obtained in our study are relevant to define realistic and precise eruptive scenarios for TPV and to assess its associated hazard, a necessary step in the evaluation and mitigations of volcanic risk in TenerifeEl complejo volcánico Teide Pico Viejo (TPV) es un stratovolcano situado en la isla de Tenerife, Islas Canarias, y ha sido considerado por la UNESCO el sistema volcánico activo más peligroso en Europa. Los eventos explosivos en el complejo TPV se han limitado tradicionalmente a la erupción subplinian de Montaña Blanca, que ocurrió hace unos 2000 años. Una reciente revisión de la estratigrafía muestra que la actividad explosiva fonolítica asociada a TPV ha sido significativa durante el Holoceno, presentado distintos episodios relacionados con erupciones que varían en tamaño de estromboliano a sub-pliniano. A través de las correlaciones estratigráficas obtenidas mediante observaciones de campo y datos de mineralógicos y geoquímicos, se han identificado 11 erupciones explosivas fonolítica relacionados con los domos satélite presentes en todo complejo TPV. Una de las erupciones más representativa es El Boquerón (5660 YBP), un domo que generó un evento explosivo de VEI 3 con un volumen mínimo de 4-6x107 m3 y produjo una columna con una altura de hasta 9 kilometros sobre el nivel del mar ( MER 6.9-8.2x105 kg / s, durante 9-15 h). La ocurrencia de estos eventos explosivos en el reciente registro eruptivo del complejo TPV es de gran importancia para evaluar el riesgo impuesto por el complejo volcánico en Tenerife. Estas erupciones han generado una amplia gama de amenazas directas, como los depósitos de caida, emplazamiento de las corrientes piroclásticas densidad, flujo de derrubios, lahares y avalanchas de roca, lo que podría ocurrir de nuevo en caso de renovación de la actividad volcánica. Los resultados obtenidos en nuestro estudio son relevantes para definir escenarios eruptivos realista y precisos para el complejo TPV y para evaluar su riesgo asociado, un paso necesario en la evaluación y mitigación del riesgo volcánico en Tenerife
13
Watt, Sebastian F. L. "Records of volcanism and controls on volcanic processes in southern Chile." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:41cf206e-2cef-4108-9267-5e9217aee96d.
Full textAbstract:
This thesis describes volcanic records from the Andean southern volcanic zone, based on the collection of field data between Calbuco and Puyuhuapi volcanic centres, with a particular focus on the Hualaihue peninsula, combined with existing records from the region as a whole. These data, extending the understanding of the volcanic history of southern Chile, are examined for evidence of spatial or temporal variability, which may be used to explore underlying controls on volcanic processes. All three volcanoes on the Hualaihue peninsula have been active in the Holocene. A large mafic scoria unit from Apagado is unusually primitive, providing a potential window into primary magma generation in the arc. Dynamically similar eruptions occurred at Hornopirén and widely along the regional scale Liquiñe-Ofqui fault zone (LOFZ). Although the Hualaihue centres are closely related, petrological evidence indicates a complex magmatic storage system. Effusive activity is predominant at Yate and Hornopirén, and the tephrostratigraphy of the Hualaihue area is dominated by units from Calbuco volcano, to the north. The 2008 eruption of Chaitén provided an analogue for past large explosive eruptions in the region, with tephra deposition reflecting variable eruption intensity in a changing wind field. The regional tectonic setting and the LOFZ influence dyke ascent, volcano morphology and, as demonstrated at Yate, edifice stability, determining the orientation of collapse. Explosive eruption records over the post-glacial period also indicate a limited response of volcanism to deglaciation, suggesting a control on magma storage arising from changing crustal stress regimes, both at the arc front and along the LOFZ. On short timescales, large earthquakes are shown to influence eruption rate across the arc, implying a triggering role for dynamic seismic stresses. This work demonstrates the existence of a range of external forces affecting Chilean arc volcanism, but the degree to which these are quantifiable is strongly constrained by the quality of the available data.
14
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.
Full textAbstract:
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
15
Johnstone, Jade. "Rainfall induced volcanic activity on Soufriere Hills Volcano, Montserrat, West Indies." Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490615.
Full textAbstract:
Extremely hazardous volcanic dome collapse and pyroclastic flows can occur without warning and can be triggered by intense rainfall. Rainfall data collected on Soufriere Hills Volcano, Montserrat between 1998 and 2006 was analysed to assess the impact on primary volcanic activity, defined here as pyroclastic flows, dome collapse and explosions and to explore the utility of meteorological data as a predictive tool for active volcanoes. A statistical analysis of daily rainfall totals and volcanic activity, showed that if greater than 20 mm of rainfall fell on a particular day the probability of a dome collapse occurring on that day increased by a factor of 6.2 from 1.0% to 6.1%, similarly the probability of observing pyroclastic' flows and explosions increased by factors of 2.0 and 4.3 respectively. These statistically significant links increased as the rainfall threshold increased, and in some cases activity was observed up to 48 hrs after rainfall. The state of the volcano is important and an absence of a significant volume of material above the conduit removes the possibility that rainfall could trigger a collapse. An analysis of a network of 1 minute resolution rainfall and seismic data for the period 1 January 2001 - 31 December 2003 showed a correlation, statistically significant to the 99% level was found between rainfall and heightened activity; rockfalls, long period earthquakes, long period rockfalls and hybrid earthquakes. There were three prominent peaks in magnitUde, following a rainfall event of 5 mm hr-I at time lags of approximately 5, 14 and 25 hours. Over 50% of the heavy rainfall days were associated with synoptic scale weather systems which are potentially well predicted by current forecast models. However the remaining days were associated with localized and essentially unpredictable systems. There was significant variability between raingauges reflecting topographic variations and inherent variability within weather systems, hence any monitoring program is recommended to use a network rather than a single gauge. Incorporation of weather forecasting into hazard monitoring programs would help to improve the prediction of hazardous collapses.
16
Ebmeier, Susanna Kathryn. "InSAR measurements of volcano deformation on the Central American Volcanic Arc." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:c015fe2a-f4dc-49db-b150-a2ab00ba8f5b.
Full textAbstract:
Satellite measurements of volcano deformation have the potential to illuminate a wide range of volcanic processes and have provided us with the first opportunity to investigate volcano deformation as an arc-scale process. This thesis presents the results of an Interferometric Synthetic Aperture Radar (InSAR) survey of the Central American Volcanic Arc between 2007 and 2010. My measurements confirm a statistically significant absence of magmatic deformation in Central America relative to other well-studied volcanic arcs. I estimate a minimum detection threshold for deformation at 20 of the arc’s 26 active volcanoes using time series analysis of interferometric phase. I find that the majority (∼80%) of literature measurements of volcano deformation made at other arcs would have been possible with the average magnitude of noise in Central American volcanoes. The absence of measurable magmatic deformation in Central America may therefore be due to factors that limit the geodetic expression of magma movement, including the deep pooling of basalts and high parental melt volatile content. The quantification of measurement uncertainty also allows me to use the lack of deformation at specific erupting volcanoes to make order of magnitude estimations of the minimum depth for magma storage that would not result in measurable deformation. I present measurements and interpretation of non-magmatic deformation associated with edifice development at two Central American volcanoes: Arenal, Costa Rica and Santiaguito, Guatemala. At Arenal, I measure apparently steady slip (∼7 cm/yr) on the volcano’s western flanks, which I attribute to gravity-driven slip on the boundary between lavas emplaced over the past 50 years and older tephras and paleosols. At Santiaguito, I demonstrate the measurement of large-scale (∼10-200 m) topographic change from a small set of large baseline interferograms. Measurements of post-2000 lava fields allow me to estimate extrusion rate, map changes to flow morphology and make simultaneous measurements of lava flow thickness and subsidence rate.
17
Rawson, Harriet. "Volcanic history and magmatic evolution of Mocho-Choshuenco Volcano, southern Chile." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:05969e3b-4f38-4478-bc26-381ca13bce1d.
Full textAbstract:
Active volcanoes pose a significant natural hazard. In order to evaluate the hazard it is important to reconstruct the history of such volcanoes to understand the frequency, style of eruption and the areas typically affected by the explosive eruptions. This thesis focuses on deciphering the volcanic and magmatic record for one of the most productive volcanoes in southern Chile, Volcán Mocho-Choshuenco. Work presented in the thesis establishes a detailed record of the explosive activity during the last 18 kyrs, constructed using field observations and geochemical analyses of the eruption deposits. Using a multi-technique approach Mocho-Choshuenco is shown to be one of the most explosive, frequently active and hence hazardous volcanoes in Chile. This high-resolution eruptive record provides new constraints on the underlying causes of spatial and temporal variability in arc volcanism. Temporally, the record gives new understanding into the response of arc volcanoes to deglaciation; clear temporal variation in eruption flux, eruption size and magma composition are observed. This time-varying behaviour is hypothesised to reflect changes in the crustal plumbing system, and magma storage timescales in response to removal of an ice-load. It demonstrates that deglaciation can drive changes in eruption behaviour at arc volcanoes; however the response is more complex and subtle than settings where decompression melting dominates. Spatially, Mocho-Choshuenco has a high number and density of scoria cones that have erupted relatively primitive magmas but nonetheless with a wide range of magma compositions. For some of the 'classical' slab and mantle geochemical tracers the erupted magmas span the complete range seen in this part of the arc. The tight temporal and spatial constraints provided by the analysed samples, coupled with recent advances in numerical modelling of magma transport through subduction zones, enable new hypotheses for interpreting the signatures of mafic arc magmas to be defined.
18
Leonard, Graham S. "The evolution of Maroa Volcanic Centre, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geology, 2003. http://hdl.handle.net/10092/5437.
Full textAbstract:
Maroa Volcanic Centre (Maroa) is located within the older Whakamaru caldera, central Taupo Volcanic Zone, New Zealand. Dome lavas make up the majority of Maroa volume, with the large Maroa West and East Complexes (MWC and MEC, respectively) erupted mostly over a short 29 kyr period starting at 251 ± 17 ka. The five mappable Maroa pyroclastics deposits are discussed in detail. The Korotai (283 ± 11 ka), Atiamuri (229 ±12 ka), and Pukeahua (~229 -196 ka) pyroclastics are all s 1 km3 and erupted from (a) northern Maroa, (b) a vent below Mandarin Dome and (c) Pukeahua Dome Complex vents, respectively. The Putauaki (272 ± 10 ka) and Orakonui (256 ± 12 ka) pyroclastics total ~ 4 km3 from a petrologically and geographically very similar central Maroa source. The ~ 220 ka Mokai pyroclastics outcrop partly within Maroa but their source remains unclear, whereas the ~ 240 ka Ohakuri pyroclastics appear to have come from a caldera just north of Maroa. The ages of the Mamaku, Ohakuri and Mokai pyroclastics are equivocaL The Mamaku and Ohakuri pyroclastics appear to be older (~ 240 ka) than the age previously accepted for the Mamaku pyroclastics.
Maroa lavas are all plagioclase-orthopyroxene bearing, commonly with lesser quartz. Hornblende +/- biotite are sometimes present and their presence is correlated with geochemical variation. All Maroa deposits are rhyolites (apart from two high-silica dacite analyses) and are peraluminous and calcic. They all have the trace element signatures of arc-related rocks typical of TVZ deposits. Maroa deposits fall geochemically into three magma types based on Rb and Sr content: M (Rb 80-123 ppm,
Sr 65-88 ppm), T (Rb 80-113 ppm, Sr 100-175 ppm) and N (Rb 120-150 ppm, Sr 35- 100 ppm). The geochemical distinction of these types is also seen in the concentrations of most other elements. Based on the spatial, chronological and petrological similarities of the MWC/MEC and Pukeahua eastern magma associations (termed (1) and (2)) a further four magma associations are determined ((3) through (6)). These six associations account for almost all Maroa deposits. Two end-member models are proposed for the sources of each of the Maroa magma associations: (a) a single relatively shallow magma source feeding spatially clustered eruptions, and (b) a deeper source feeding multiple
shallower offshoots over a wider area. Sources for the Maroa magma associations probably lie on a continuum between these two model end members. The distinction between Maroa and Taupo Volcanic Centres is somewhat arbitrary and is best considered to be the easting directly north of Ben Lomond, north of which most volcanism is older than 100 ka and M and N type, and south of which most volcanism is younger than 100 ka and T type. The remaining boundaries (north to include Ngautuku, west to include Mokauteure and east to include Whakapapa domes) are arbitrary, and
include the farthest domes linked closely, spatially and magmatic ally, to the other Maroa domes.
From 230 to 64 ka there was a hiatus in caldera-forming ignimbrite eruptions. Maroa and the Western Dome Belt (WDB) constitute the largest concentrated volume of eruptions (as relatively gentle lava extrusion) during this period. The rate of Maroa volcanism has decreased exponentially from a maximum prior to 200 ka. In contrast volcanism at Taupo and Okataina has increased from ~ 64 ka to present. The oldest Maroa dome (305 ± 17 ka) constrains the maximum rate of infilling of Whakamaru
caldera as 39-17 km3/kyr. This highlights the extraordinarily fast rate of infilling common at silicic calderas and is in agreement with international case studies, except where post-collapse structural resurgence has continued for more than 100 kyr. The majority of caldera fill, representing voluminous eruption deposits in the first tens of thousands of years post collapse, is buried and only accessible via drilling. The WDB and Maroa are petrologically distinct from one another in terms of some or all of Rb, Sr, Ba and Zr content, despite eruption over a similar period. Magma sources for Maroa and
the WDB may have been partly or wholly derived from the Whakamaru caldera magma system(s), but petrological distinctions among all three mean that Maroa and the WDB cannot be considered as simple magmatic resurgence of the Whakamaru caldera.
Maroa's distinct Thorpe Rd Fault is in fact a fossil feature which hasn't been active in almost 200 kyr. In addition, the graben across Tuahu Dome was likely created by shallow blind diking. Several recent studies across TVZ show structural features with some associated dike intrusion/eruption. Such volcano tectonic interaction is rarely highlighted in TVZ but may be relatively common and lie on a continuum between dike-induced faulting and dikes following structural features. Although rates of
volcanism are now low in Maroa magmatic intrusion appears to remain high. This raises the possibility of a causative link between faulting and volcanism in contrast to traditional views of volcanism controlled by rates of magmatic ascent. Probable future eruptions from Maroa are likely to be of similar scale (<0.1 km3 ) and frequency (every ~ 14,000 years) to most of those over the last 100 ka. Several towns lie in a range of zones of Maroa volcanic hazard from total destruction to possible ash fall. However, the probability of a future eruption is only ~ 0.6 % in an 80 year lifetime.
19
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.
Full textAbstract:
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.
20
Spinks, Karl D. "Rift architecture and Caldera volcanism in the Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2005. http://hdl.handle.net/10092/4944.
Full textAbstract:
The Taupo Volcanic Zone (TVZ) is investigated to determine the interaction of regional structure and volcanism. A three-tiered approach is employed involving (i) analysis of rift geometry and segmentation in Modem TVZ(<300 ka) from remote sensing and digital topographic data; (ii) fault kinematic data collected along the length of TVZ; and (iii) combining new and existing volcanological data for TVZ. Modem TVZ is a NNE-SSW trending intra-arc rift zone, subject to dextral transtension, and characterised by a segmented axial rift zone with a number of offset and variably oriented rift segments. These segments are subject to varying degrees of extension, and a general correlation exists between the amount of extension and the volume and style of volcanism in each segment. Segments with the highest degrees of extension correspond to the Okataina and Taupo Caldera Complexes in the central rhyolitic zone of Modem TVZ, while segments with a higher degree of dextral transtension correspond to the volumetrically-subordinate andesitic extremities.
The influence of the structural framework on the shape and formation of calderas in Modem TVZ has been inferred from remote sensing and ground-based structural analysis. Detailed analysis of caldera structure and geometry in Modem TVZ indicates that caldera evolution is largely a function of caldera location relative to the axial rift zone. Calderas peripheral to the rift are simple, single-event structures, while those located within the axial rift zone are multiple-event caldera complexes with geometries dictated by their coincidence with rift faulting. These results show that in Modem TVZ the type, volume, and spatial distribution of magmatic activity is strongly influenced by rift structure and kinematics.
The inter-relationship between rift geometry and caldera-complex development is particularly clear at the intra-rift Okataina Caldera Complex (OCC). OCC is located at a step-over in the rift where local rotation of the extension direction accompanies the development of a major transfer zone. Three main collapse events are spatially concentrated in a zone of orthogonal extension within the transfer zone. The 28 x 22 km OCC is elongate parallel to the extension direction, with a complicated topographic margin largely controlled by regional faulting. Major embayments occur on each side of OCC where it is intersected by adjacent rift segments. These are contiguous with two intra-caldera dome complexes forming two overlapping linear vent zones, which transect the caldera complex. The development of volcanism at OCC records the progressive interaction between offset rift segments and the propagation of overlapping rift segment axes. As rift propagation proceeded, a diffuse zone of volcanism progressively concentrated in the centre of the transfer zone then divided into two spatially restricted eruptive centres as through-going faults became established.
Field investigations at OCC reveal a major revision to the eruptive stratigraphy that has implications for the development of the caldera and for hazard assessment in northern TVZ. Kawerau Ignimbrite is a partially welded pumice-rich ignimbrite that fills Puhipuhi Basin on the eastern side of the caldera complex and forms a thick terrace in and around the Kawerau township area. Within Puhipuhi Basin it is ~100 m thick, exposed on clear-felled knolls and locally forms jointed bluffs in thickest sections where it is valley ponded. Originally mapped as Kaingaroa Ignimbrite, it was subsequently considered distinct and renamed Kawerau Ignimbrite by Beresford & Cole (2000) with an accepted age of 240 ka.
In Puhipuhi basin the Kawerau Ignimbrite overlies both the ~280 ka Matahina and ~65 ka Rotoiti ignimbrites and also the older tephras of the 43-31 ka Mangaone Subgroup. Whole-rock and glass geochemistry tie the ignimbrite specifically to the 33 ka Unit I eruptive phase of the subgroup, vastly increasing the eruptive volume of that unit and implying caldera collapse in this recent phase of OCC activity. Two pumice compositions are identified, reflecting eruption of two distinct magma bodies.
Vertical variation in the ignimbrite records rapid depletion of a subordinate dacitic magma such that pumices of this composition are rare beyond proximal exposures. Lithic and pumice size distribution data indicate a source within OCC to the west of Puhipuhi basin. The residual volume of the ignimbrite is <15 km3, but estimates of the original volume approach 50 km3 when intra-caldera volumes are considered. Kawerau Ignimbrite thus represents the largest eruption from OCC in the last 65 ka since the Rotoiti event, and is the youngest partially-welded ignimbrite in TVZ.
21
Ritchie, Alistair B. H. "Volcanic geology and geochemistry of Waiotapu Ignimbrite, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geological Sciences, 1996. http://hdl.handle.net/10092/6588.
Full textAbstract:
Waiotapu Ignimbrite (0.710 ± 0.06 Ma) is a predominantly densely welded, purple-grey coloured, pumice rich lenticulite, which is exposed on both eastern and western flanks of Taupo Volcanic Zone. The unit is uniform in terms of lithology and mineralogy over its entire extent and has been deposited as a single flow unit. The unit contains abundant pumice clasts which are often highly attenuated (aspect ratios of c.1 :30) and are evenly distributed throughout the deposit. Lithic fragments are rare, never exceeding 1% of total rock volume at an outcrop and no proximal facies, such as lithic lag breccias, have been identified.
The deposit is densely welded to the base and only in more distal exposure does the ignimbrite become partially welded at the top of the deposit. Post-depositional devitrification is pervasive throughout the deposit, often destroying original vitroclastic texture in the matrix. Vapour phase alteration is extensive in welded and partially welded facies of the deposit.
Pumices within Waiotapu Ignimbrite appear to have been derived from two distinct magma batches, with differing Rb concentrations, that originated along different fractionation trends. Type-A pumices have significantly lower Rb than the subordinate type-B pumices. The presence of the pumices may represent the simultaneous evisceration of two spatially discrete magma chambers or the type-B chamber may have been intruded into type-A body, the magmas subsequently mingling prior to, or during, the eruption.
The source of Waiotapu Ignimbrite is poorly constrained, largely owing to the lack of meaningful maximum lithic data, and poor exposure of the unit. The distribution of the ignimbrite suggests that it was erupted from within Kapenga volcanic centre. If so the most proximal exposures of Waiotapu Ignimbrite are approximately 10km from the vent. Intensive and voluminous silicic volcanism, beginning with the eruption of the 0.33 Ma Whakamaru Group Ignimbrite eruptions, and extensive faulting within Kapenga volcanic centre will have obscured any intra-caldera Waiotapu Ignimbrite. The mechanism of eruption suggests that the source may not have been a caldera in the strictest sense, but instead a series of near linear fissures aligned with the trend of regional faulting.
Waiotapu Ignimbrite was generated in one sustained eruption and produced an energetic and high temperature pyroclastic flow. The lack of any recognised preceding plinian deposit, coupled with the energetic nature and paucity of lithics suggests eruption by an unusual mechanism. The eruption most likely resulted from the large scale collapse of a caldera block into the underlying chamber resulting in high discharge rates, which were no conducive to the development of a convecting column, and minimal vent erosion, resulting in negligible entrainment of lithics.
The density of welding and recrystallisation textures suggest that the flow retained heat to considerable distances which allowed the ignimbrite to weld densely to the base. The deposit was most likely progressively aggraded from the base, with material being supplied from an overriding particulate flow.
22
Emery, William Daniel. "Geology and Eruptive History of the Late Oligocene Nathrop Volcanics, Central Colorado Volcanic Field." Bowling Green State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1299733477.
Full text
23
Montelius, Cecilia. "The genetic relationship between rhyolitic volcanism and Zn-Cu-Au deposits in the Maurliden volcanic centre, Skellefte district, Sweden : volcanic facies, lithogeochemistry and geochronology /." Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1544/2005/17.
Full text
24
Maund, J. G. "The volcanic geology, petrology and geochemistry of Caldeira volcano, Graciosa, Azores, and its bearing on contemporaneous felsic-mafic oceanic island volcanism." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370121.
Full text
25
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.
Full textAbstract:
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.
26
Telling, Jennifer Whitney. "Microphysical processes of volcanic ash aggregation and their implications for volcanic eruption dynamics." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52925.
Full textAbstract:
Although numerous hazard models exist to assess possible ash fallout from explosive volcanic eruptions around the world, these models frequently neglect to consider ash aggregation or use a simple percent proxy to represent aggregation, without considering the varying processes at work throughout the volcanic flow. Eruption dynamics are sensitive to ash aggregation, and ash aggregates are commonly found in eruptive deposits, yet few experiments have been conducted on aggregation phenomena using natural materials. In this work, experiments were developed to produce both probabilistic and process-based relationships for the efficiency of ash aggregation with respect particle size, collision kinetic energy, atmospheric water vapor and residence time. A synthetic ash proxy, ballotini, and ash from the 2006 eruption of Tungurahua, Ecuador, and the 1980 eruption of Mount St. Helens, WA, were examined for their aggregation potential.
Two aggregation regimes, wet and dry, were identified based on their potential for aggregation. The wet flow regime occurs when particles are circulated in high relative humidity environments long enough to develop a water layer with a thickness that exceeds the particle roughness scale. Hydrodynamic forces control aggregation in the wet flow regime. The dry flow regime includes particles in low relative humidity environments as well as those that circulate too briefly in high humidity environments to fully develop a water layer. Electrostatic forces control aggregation in the dry flow regime. Aggregation efficiency in both regimes was dominantly controlled by collision kinetic energy; however, this effect is significantly dampened in the wet flow regime. Equations governing the relationships between aggregation efficiency, collision kinetic energy and the related forcings in the wet or dry flow regimes have been developed for implementation into large-scale numerical volcanic models.
The results of this experimental work have been developed into a probability distribution that has been integrated and incorporated into a multifluid numerical model. The numerical simulation was tested on a range of explosive depths and overpressure estimates from the 1790 eruption of Kilauea volcano, HI. The model output was compared to field data collected on the deposit thickness moving away from the source and the distribution, including both size and density, of aggregates. The mass fraction of ash removed from the eruption column in the form of aggregates was also calculated to examine how efficiently aggregation processes remove ash throughout the eruption. Cumulatively, the work presented here furthers our understanding of aggregation processes and the role they play in volcanic eruptions.
27
Galeazzo, Tommaso. "Tracking volcanic sulphate : modelling tropospheric volcanic sulphate formation and its oxygen isotopic signatures." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS300.
Full textAbstract:
Les émissions volcaniques sont une source importante de soufre. Le soufre volcanique est oxydé et forme des aérosols sulfatés qui influencent le climat en absorbant et en dispersant le rayonnement solaire incident. Les émissions de soufre dans la troposphère influencent le climat local et régional, mais de grandes incertitudes subsistent en ce qui concerne l’oxydation et sa conversion en aérosols de sulfate volcanique. L’oxydation du soufre dans une vaste gamme de panaches volcaniques et l’influence des halogènes volcaniques sur la chimie du panache sont étudiées à l’aide d’un modèle de boîte chimique. Parallèlement, la composition isotopique en oxygène du sulfate volcanique, à savoir l’excès de 17-O (∆17O), est à l’étude, ce qui peut limiter les voies d’oxydation du soufre. Les résultats suggèrent qu’en présence de gouttelettes d’eau et de cendres, l’oxydation du soufre dans les panaches est principalement due à l’oxydation en phase aqueuse avec de l’O2 catalysé par des ions de métaux de transition (TMI). Les émissions d’halogènes favorisent la dominance de l’O2 /TMI en induisant des phénomènes d’appauvrissement de la couche d’ozone (ODE). En l’absence de gouttelettes d’eau, la chimie du panache est largement déterminée par la chimie hétérogène des aérosols primaires sulfatés. Les oxydants dominants dans ces panaches sont OH et H2O2. Le taux d’oxydation du soufre est considérablement réduit par rapport aux panaches contenant des gouttelettes d’eau. Les résultats montrent que les isotopes de l’oxygène dans les sulfates exercent de fortes contraintes sur l’équilibre chimique du soufre dans les panaches volcaniques et sur le rôle des halogènes volcaniquesVolcanic emissions are a major source of sulphur. Volcanic sulphur is oxidized and forms sulphate aerosols that influence the climate by absorbing and dispersing incident solar radiation. Sulphur emissions in the troposphere influence local and regional climate, but large uncertainties remain regarding oxidation and its conversion into volcanic sulphate aerosols. The oxidation of sulphur in a wide range of volcanic plumes and the influence of volcanic halogens on plume chemistry are studied using a chemical box model. At the same time, the isotopic oxygen composition of volcanic sulphate, namely the excess of 17-O (∆17O), is being explored, which can provide constraints on sulphur oxidation pathways. The results suggest that in the presence of water droplets and ash, the oxidation of sulphur in plumes is mainly due to aqueous phase oxidation with O2 catalyzed by transition metal ions (TMI). Halogen emissions promote the domi- nance of O2 /TMI by inducing ozone depletion events (ODEs). In the absence of water droplets, plume chemistry is largely determined by heterogeneous chemistry on primary sulphate aerosols. The dominant oxidants in these plumes are OH and H2O2. The oxidation rate of sulphur is significantly reduced compared to plumes containing water droplets. The results show that oxygen isotopes in sulphates provide strong constraints on the chemical balance of sulphur in volcanic plumes and on the role of volcanic halogens
28
Dibben, Christopher J. L. "Looking beyond eruptions for an explanation of volcanic disasters : vulnerability in volcanic environments." Thesis, University of Bedfordshire, 1999. http://hdl.handle.net/10547/582569.
Full textAbstract:
'Natural' disasters have traditionally been viewed as the result of an extreme physical environment. A radical backlash against this dominant view, in the nineteen seventies and eighties, moved the debate to the opposite extreme and in doing so replaced physical with social determinism. Vulnerability analysis is proposed as a methodology that bridges these extremes. It takes into account individual decision making, social milieu and physical hazard when describing human habitation in areas of volcanic activity. It is argued that vulnerability should be defined in terms of universal human needs in order to avoid it simply being a measure of the chance of death and injury or losing its meaning in the uncertainty of cultural relativism. Once vulnerability is identified it is important to explore why it has come to exist. A contextual theory of vulnerability change is presented. Vulnerability to volcanic activity was explored in the area around Mt. Etna in Sicily (Italy) and Furnas volcano San Miguel in the Azores (Portugal) using a case study methodology. This included: collecting data through interviews (semistructured and structured) and field surveying, utilising census and other secondary data sources, and examining historical documents and texts. The volcanic hazard on Mt. Etna is related to regular (4-7 years) effusive lava flows which threaten property and land rather than people. Living in a European state, it is likely that a victim of Mt. Etna will have their basic needs provided for in the long-term and therefore they are not vulnerable. In contrast the irregular explosive eruptions of Furnas, last eruption 1630, not only damage property and land but also endanger lives. The limited ability of individuals to protect themselves in the event of an eruption and organisations to aid them in this means that, in spite of state insurance, many around Furnas are vulnerable. The production of vulnerability around Etna and Furnas is strongly related to the socio-economic nature of the region and wider European and global contexts. Opportunities and constraints that exist across socio-physical space encourage behaviour and forms of life which, in tum, produce various levels of vulnerability. Individuals seem to cognitively diminish their perceptions of this threat within a context of social representations of low risk. They, and society as a whole, rarely seem to engage directly with the risk itself.
29
Wilson, James Adams. "A New Volcanic Event Recurrence Rate Model and Code For Estimating Uncertainty in Recurrence Rate and Volume Flux Through Time With Selected Examples." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6435.
Full textAbstract:
Recurrence rate is often used to describe volcanic activity. There are numerous documented ex- amples of non-constant recurrence rate (e.g. Dohrenwend et al., 1984; Condit and Connor, 1996; Cronin et al., 2001; Bebbington and Cronin, 2011; Bevilacqua, 2015), but current techniques for calculating recurrence rate are unable to fully account for temporal changes in recurrence rate. A local–window recurrence rate model, which allows for non-constant recurrence rate, is used to calculate recurrence rate from an age model consisting of estimated ages of volcanic eruption from a Monte Carlo simulation. The Monte Carlo age assignment algorithm utilizes paleomagnetic and stratigraphic information to mask invalid ages from the radiometric date, represented as a Gaussian probability density function. To verify the age assignment algorithm, data from Heizler et al. (1999) for Lathrop Wells is modeled and compared. Synthetic data were compared with expected results and published data were used for cross comparison and verification of recurrence rate and volume flux calculations. The latest recurrence rate fully constrained by the data is reported, based upon data provided in the referenced paper: Cima Volcanic Field, 33 +55/-14 Events per Ma (Dohren- wend et al., 1984), Cerro Negro Volcano, 0.29 Events per Year (Hill et al., 1998), Southern Nevada Volcanic Field, 4.45 +1.84/-0.87 (Connor and Hill, 1995) and Arsia Mons, Mars, 0.09 +0.14/-0.06 Events per Ma (Richardson et al., 2015). The local–window approach is useful for 1) identifying trends in recurrence rate and 2) providing the User the ability to choose the best median recurrence rate and 90% confidence interval with respect to temporal clustering.
30
Clavero, Jorge Eduardo. "Evolution of Parinacota volcano and Taapaca Volcanic Complex, Central Andes of Northern Chile." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393075.
Full text
31
B, Jhon Macario Londoño. "A seismic model for the volcanic activity of Nevado del Ruiz Volcano, Colombia." 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149994.
Full text
32
Doherty, Angela Louise. "Blue-sky eruptions, do they exist? : implications for monitoring New Zealand's volcanoes." Thesis, University of Canterbury. Geological Sciences, 2009. http://hdl.handle.net/10092/2855.
Full textAbstract:
The term “blue-sky eruption” (BSE) can be used to describe eruptions which are unexpected or have no detected precursory activity. Case study analyses indicate that they have a diverse range of characteristics and magnitudes, providing both direct and indirect hazards and occur in both under-developed and developed countries. BSEs can be a result of physical triggers (e.g. the lack of physically detectable precursors or a lack of understanding of the eruption model of the volcano), social triggers (such as an inadequate monitoring network), or a combination of the two. As the science of eruption forecasting is still relatively young, and the variations between individual volcanoes and individual eruptions are so great, there is no effective general model and none should be applied in the absence of a site-specific model. Similarly, as methods vary between monitoring agencies, there are no monitoring benchmarks for effective BSE forecasting. However a combination of seismic and gas emission monitoring may be the most effective. The United States began a hazard and monitoring review of their volcanoes in 2005. While the general principles of their review would be beneficial in a monitoring review of New Zealand’s volcanoes, differences in styles of volcanism, geographic setting and activity levels mean changes would need to be review to fully appreciate the risk posed by New Zealand’s volcanoes. Similarly, the monitoring benchmarks provided in the U.S. review may not be fully applicable in New Zealand. While advances in technology may ultimately allow the effective forecasting of some BSEs, the immediate threat posed by unexpected eruptions means that effective management and mitigation measures may be the only tools currently at our disposal to reduce the risks from BSEs.
33
Wright, Heather Michelle. "Physical and chemical signatures of degassing in volcanic systems /." view abstract or download file of text, 2006. http://proquest.umi.com/pqdweb?did=1188873641&sid=1&Fmt=2&clientId=11238&RQT=309&VName=PQD.
Full textAbstract:
Thesis (Ph. D.)--University of Oregon, 2006.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 162-173). Also available for download via the World Wide Web; free to University of Oregon users.
34
McOwen, Lisa Kathryn 1968. "The Brock canyon volcanic complex, Grant County, New Mexico: volcanic evolution, alteration, and mineralization." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/558223.
Full text
35
Rinaldi, Antonio Pio <1982>. "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.
Full textAbstract:
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.
36
Rinaldi, Antonio Pio <1982>. "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/.
Full textAbstract:
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.
37
POLA, VILLASENOR ANTONIO. "Physical and Mechanical characterization of altered volcanic rocks for the stability of volcanic edifices." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/18917.
Full textAbstract:
Geomechanical characterisation of altered volcanic rocks and their role in flank volcanoes stability are evaluated in this study. Physical and mechanical properties and their variation with the degree of alteration are described in detailed. A series of multidisciplinary tests were performed to identify and quantify the progressive degradation of the properties. They are as follow: 1) petrographycal and chemical studies (thin-sections, x-ray diffractions and x-ray fluorescence); 2) effective and total porosity (standard test procedure, mercury intrusion porosimetry, pycnometer tests, two-dimensional and x-ray CT image analysis); 3) Ultrasonic pulse velocity measurements; 4) uniaxial compressive tests (with p-wave measurements, cyclic loading); tensile tests (with strain gauge measurements); and 5) triaxial tests (single-stage and multi-stage). Preliminary numerical modelling was mainly focus on the effect of altered rocks content and gravity effects, even if different perturbations such as pore water pressure (e.g. rainfall, vapour and gas), and regional or local tectonics (e.g. faults, earthquakes and dynamic loading) are presented in volcanoes nature.
Collected samples are representative of four different classes of volcanic deposits: i) trachytic lava with abundant crystals; ii) pyroclastic deposits, with lava clasts and pumice elements with different sizes; iii) Green tuff, constructed prevalently by pumice clasts; and iv) ignimbrite deposits characterized by low density. Petrographical and chemical characteristics, in particular weathering indexes reveal large differences not only between lithotypes, but also between samples. These differences are well quantified by physical properties, in particular porosity and shear wave velocity values. Decay of the properties, well represented by regression analysis with significant correlation parameter (R2>85), is observed when average values of the compressive strength, tensile strength and Young’s modulus are compared with the average porosity value, fractal dimension and grade of alteration. Failure of rocks were well documented by the evolution of elastic properties, differences between each lithotype are discussed. Post-failure reconstruction of samples reveals that the nature of deformation is controlled by textural properties (e.g. grains, pores, and cement) and the behaviour strongly influences the response of the specimen. Anisotropy of rocks is clear represented by triaxial tests post-failure reconstruction, abrupt differences between fresh and altered samples are observed. Finally, a simplified 2-D numerical stress‐strain modelling was carried out in order to visualize the effects of rock properties degradation in volcanic flank failure. Modelling was aimed at clarifying the role of the altered volcanic rocks in the evolution of volcano stability. The results, in terms of maximum computed values of shear strain and displacements, show that degradation of rock properties is capable of defining and controlling large zones of instability.
38
Mattsson, Hannes B. "Volcanism at the tip of a propagating rift : the Heimaey volcanic centre, south Iceland /." Stockholm : Institutionen för geologi och geokemi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-257.
Full text
39
Carmody, L. "Geochemical characteristics of carbonatite-related volcanism and sub-volcanic metasomatism at Oldoinyo Lengai, Tanzania." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348540/.
Full textAbstract:
The eruption of xenolithic material during large explosive eruptions, at any volcano, supply vital samples of the sub-surface lithologies upon which it is built, which in turn provides an indication of the evolution of the volcanic complex, in particular the volcanic conduit, magma storage zones and crustal / mantle lithologies. This is particularly important at alkaline-carbonatite complexes which are known to have “exotic” chemistries and also cause extensive zones of alteration through fenitisation processes. As the only active carbonatite volcano on Earth and also the unusual nature of Oldoinyo Lengai, Tanzania, it is an excellent study site to better understand the generation and chemical influence of carbonate-rich melts and fluids from source to surface. This study has attempted to better constrain the sub-volcanic environment, the source of the carbon within the material and the processes which lead to the formation of such unique rocks. Using geochemistry, isotopic studies and fluid inclusions, this thesis highlights the importance of fluid circulation within the volcanic system, both at the surface but also within the sub-volcanic mantle, leading to metasomatised material rich in carbon and alkali elements from which natrocarbonatite and potentially kimberlitic material could be derived. Almost all of the geochemical evidence and composition of fluid inclusions trapped within fenitised aureoles indicates a mantle derivation of carbonatitic material with isotopic signatures typical of the pre-defined “mantle-box”. The nature of the fluids is also investigated using trace element modelling and argued to be both carbonatitic and siliceous in origin, which have been circulating within the mantle beneath the Gregory Rift since before the establishment of Oldoinyo Lengai. These themes of research are discussed in terms of the genesis of natrocarbonatite, focussing upon the notion that it may be an evolutionary feature of Oldoinyo Lengai rather than a constant eruptive product.
40
Heslop, S. E. "Aspects of volcanic fluid dynamics." Thesis, Lancaster University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383570.
Full text
41
Matthews, C. "Fracture mechanics of volcanic eruptions." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/16280/.
Full textAbstract:
Seismology is a key tool in the forecasting of volcanic eruptions. The onset of an eruption is often preceded and accompanied by an increase in local seismic activity, driven by fracturing within the edifice. For closed systems, with a repose interval of the order of a century or more, this fracturing must occur in order to create a pathway for the magma to reach the surface. Time-to-failure forecasting models have been shown to be consistent with seismic acceleration patterns prior to eruptions at volcanoes in subduction zone settings. The aim of this research is to investigate the patterns in seismic activity produced by a failure model based on fundamental fracture mechanics, applied to a volcanic setting. In addition to the time series of earthquake activity, statistical measures such as seismic b-value are also analysed and compared with corresponding data from the field and laboratory studies. A greater understanding of the physical factors controlling fracture development and volcano-tectonic activity is required to enhance our forecasting capability. The one dimensional, fracture mechanics grid model developed in this work is consistent with the theory of growth and coalescence of multi-scale fractures as a controlling factor on magma ascent. The multi-scale fracture model predicts an initial exponential increase in the rate of seismicity, progressing to a hyperbolic increase that leads to eruption. The proposed model is run with variations in material and load properties, and produces exponential accelerations in activity with further development to a hyperbolic increase in some instances. In particular, the model reproduces patterns of acceleration in seismicity observed prior to eruptions at Mt. Pinatubo (1991) and Soufriere Hills (1995). The emergence of hyperbolic activity is associated with a mechanism of crack growth dominated by interaction and coalescence of neighbouring cracks, again consistent with the multi-scale fracture model. The model can also produce increasing sequences of activity that do not culminate in an eruption; an occurrence often observed in the field. Scaling properties of propagating fractures are also considered. The seismic bvalue reaches a minimum at the time of failure, similar to observations from the field and measurements of acoustic emissions in the laboratory. Similarly, the fractal dimension describing the fracture magnitude distribution follows trends consistent with other observations for failing materials. The spatial distribution of activity in the model emerges as a fractal distribution, even with an initially random location of fractures along the grid. Significant shifts in the temporal or spatial scaling parameters have been proposed as an indication of change in controlling factors on a volcanic system, and therefore represent a relatively unexplored approach in the art of eruption forecasting.
42
Simpson, Annika Emilia. "Microbial weathering of volcanic rocks." Thesis, Open University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607463.
Full textAbstract:
The aim of this thesis was to further the knowledge on microbial weathering, by looking at the effect of model organisms (AcidithiobacilIus ferrooxidans and Geobacter metallireducens) to natural microbial communities (from basaltic glass). It was found that the medium water-rock ratio (50: I) provided the optimum conditions for A. ferrooxidans growth, whilst the low water-rock ratio (1: I) had a lower release of iron because of pH. The pH affected the release of iron and REEs, with less released the higher the pH. In addition, it was found that, though localised areas of hematite were found on the treated rocks, there were also oxidised layers that did not correspond to specific mineralogy. The lack of specific mineral signatures on the rock surface, but the apparent oxidation of the surface, suggested that the surface had been passivated with Fe3+ binding to the mineral surface. In contrast, G. metallireducens did not affect the production of Fe2+ from basalt glass when compared to controls. However, when low water-rock ratios and hematite were tested, a difference was observed between abiotic and biotic flasks. It was suggested the low water ~rock ratio possibly allowed G. metallireducens to obtain the iron more easily by affecting the pH of the solution which in turn affected the stability of the bound iron. In terms of studying microbial communities on rocks, it was found that community structure in Icelandic basaltic glass changed over time, becoming more diverse, with a switch from r- to K-selected microorganisms over the course of the year, similarly to results obtained in the field. DGGE results showed each flask had a distinctive population - with no correlation between ratios, and replicates different in composition to each other. It is suggested that, though community does change over time (as shown by the clone libraries), the ratios do not have an effect and each flask is developing with its own 'microbial island'. However, the results of the chemistry of the flask solutions indicated that the biological experiments showed differences in pH and elemental release between ratios. Elemental release rates were faster in the biological experiments. 'the natural communities affected mineral dissolution, possibly through -- the release of organic acids, which would also account for the drop in pHs observed in the biological experiments. It was noted that there were differences in dissolution rates between the results reported in this thesis and previous literature. It is suggested that these are caused by the rock surface area as in previous studies the rocks have typically been crushed into powder and fine particles. This crushed powder would have provided fresh rock surface for the microorganisms and also greater surface area for reactions to take place, accounting for generally higher weathering rates in previous literature per unit weight of material.
43
Bower, S. M. "Models of explosive volcanic eruptions." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596823.
Full textAbstract:
This thesis describes the investigation of fluid dynamic processes involved in maintained explosive volcanic eruptions. The thesis is divided into chapters relating to dynamical processes in a volcanic system: evolution and evacuation of a reservoir of molten rock, flow in a narrow conduit to the Earth's surface, and subsequent transport in the atmosphere. In chapter 2, we calculate the mass erupted, prior to caldera collapse, from a chamber as the pressure changes from a certain overpressure to a specified underpressure at which wall collapse occurs. The compressibility of the magma increases significantly as the pressure falls and the magma becomes saturated in volatiles. Magma saturation exerts a dominant control on the amount of magma erupted. We also examine the effects on mass erupted of the chamber shape, size and depth beneath the Earth's surface, the magma composition and the strength of country rock. Finally, we demonstrate applications of our results to various historical eruptions, including the eruption at Vesuvius in 79A.D. and the eruption at Mt St Helens in 1980. During maintained explosive volcanic eruptions, fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10-100 atm and at the speed of sound of the mixture. In chapter 3, we review previous models of magma ascent up a conduit and identify some new scalings for the exit velocity as a function of the speed of sound of the mixture. In chapter 4, we combine models of evolution of the magma chamber with models of ascent of magma up the conduit to make estimates of the duration of the eruption and examine the rate of change in eruption rate with time under conditions of decreasing chamber pressure, changing magma volatile content and conduit widening due to erosion. Finally, we demonstrate an application of our results to the historical eruptions at Vesuvius in 79A.D. and at Mt St Helens in 1980. After decompression, the bulk of the material may ascend as a larger convecting eruption column or collapse to form a dense fountain which sheds ash flows around the vent. In chapter 5, we model the decompression of jets beyond the vent. We describe a jet freely decompressing into the atmosphere or into a crater, coupling our results with models of eruption column formation. We show that decompression through a crater may cause collapse at relatively small eruption rates, while it may promote formation of buoyant eruption columns at higher eruption rates. If a crater grows through erosion during an eruption, then typically a transition in eruption style may occur from an eruption column to column collapse.
44
Burt, Mary Louise. "Statistical modelling of volcanic hazards." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282730.
Full text
45
Harford, Chloe Linden. "The volcanic evolution of Montserrat." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343316.
Full text
46
Dingwell, Adam. "Atmospheric Dispersion Modellingof Volcanic Emissions." Licentiate thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-263081.
Full textAbstract:
Gases and particles released by volcanoes pose a serious hazard to humans and society. Emis-sions can be transported over long distances before being reduced to harmless concentrations.Knowing which areas are, or will be, exposed to volcanic emissions is an important part inreducing the impact on human health or society. In this thesis, the dispersion of volcanic emis-sions is studied using a set of atmospheric models. Two case studies have been performed, onestudying potential ash emission from future eruptions on Iceland, and a second covering SO2 emissions from Mt. Nyiragongo in D.R. Congo The first study covers long range (∼1,000 km) dispersion of fine ash from explosive erup-tions. Three years of meteorological data are used to repeatedly simulate five eruption scenarios.The resulting concentrations of airborne ash at different times relative the onset of each eruptionis compared to current and previous threshold concentrations used by air traffic controllers. Theash hazard showed a seasonal variation, with a higher probability of efficient eastward transportin winter, compared to summer; summer eruptions pose a more persistent hazard. In the second study, emissions of SO2 from passive degassing at Mt. Nyiragongo is studiedover a one–year period. The meteorological impact on the dispersion is studied by assigninga fixed emission source. Furthermore, flux measurements from the remote sensing data areused to improve the description of the emission source. Gases are generally transported to thenorth-west in June–August and to the south-west in December–January. A diurnal variation dueto land breeze around lake Kivu contributes to high concentrations of SO2 along the northernshore during the night. Daily averaged concentrations in the city of Goma (∼15 km SW of thesource) exceeded the European Union’s air quality standard (125 μg/m 3 ) for 120-210 days overa one year period.Gas- och partikelutsl ̈app fr ̊an vulkaner utg ̈or en fara för människor och för vårt samhälle. Utsläppen kan transporteras över långa avstånd innan de reduceras till ofarliga halter. Att kännatill vilka områden som utsätts, eller kommer utsättas, för utsläppen är ett viktigt verktyg för att minska påverkan påv folkhälsa och samhället. I den här avhandlingen studeras spridningen av utsläpp från vulkaner med hjälp av en uppsättning atmosfärsmodeller. Två fallstudier har utförts,en fokuserar på vulkanaska från potentiella framtida utbrott på Island, den andra studerar SO2 -ustl äpp fr ̊an Nyiragongo i Demokratiska Republiken Kongo. Den f ̈orsta studien beskriver l ̊angv ̈aga (∼1,000 km) transport av aska från explosiva utbrott.Tre är av meteorologiska data används för att modellera spridningen från fem olika utbrotts-scenarier för varierande vädersituationer. Koncentrationen av luftburen aska studeras vid olikatidpunkter relativt utbrottens starttid och j ̈amf ̈ors med tidigare samt befintliga gränsvärden för flygtrafik. Sannolikheten för skadliga halter aska varierar med årstid, med en högre sannolikhetför effektiv transport österut under vintermånaderna, jämfört med sommarmånaderna; sommar-utbrott är istället mer benägna att orsaka långvariga problem över specifika områden. I den andra studien modelleras utsl ̈app av SO 2 från passiva utsläpp vid Nyiragongo över en ettårsperiod. Den meteorologiska effekten på spridningen studeras genom att använda en konatant utsläppskälla. Dessutom studeras spridningen mer i detalj genom att använda fjärranalysdata för att bättre uppskatta utsläppen. Gaserna transporteras i regel mot nordväst i juni–augusti ochmot sydväst i december–februari. En sjö-/landbriscirkulation runt Kivusjön orsakar höga halterav SO2 längs sjöns norra strand nattetid. Dygnsmedelkoncentrationer av SO2 i provinshuvud-staden Goma (∼15 km sydväst om Nyiragongo) överskred EU-riktlinjer (125 μg/m3 ) under 120-210 dagar under en ettårsperiod.
47
Dingwell, Adam. "Dispersion modelling of volcanic emissions." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303959.
Full textAbstract:
Gases and particles released by volcanoes pose a serious hazard to humans and society. Emissions can be transported over long distances before being reduced to harmless concentrations. Knowing which areas are, or will be, exposed to volcanic emissions is an important part inreducing the impact on human health and society. In this thesis, the dispersion of volcanic emissions is studied using a set of atmospheric models. The work includes contribution to the development of the Lagrangian Particle Dispersion Model FLEXPART-WRF. Three case studies have been performed, one studying potential ash emissions from potential future eruptions on Iceland, a second covering SO2 emissions from Mt. Nyiragongo in D.R. Congo, and a third studying the SO2 emission rate of the Holuhraun eruption (Iceland) in 2014–2015. The first study covers volcanic ash hazard for air traffic over Europe. Three years of meteorological data are used to repeatedly simulate dispersion from different eruption scenarios. The simulations are used to study the probability of hazardous concentrations in ash in European airspace. The ash hazard shows a seasonal variation with a higher probability of efficient eastward transport in winter, while summer eruptions pose a more persistent hazard. In the second study, regional gas exposure around Mt. Nyiragongo is modelled using flux measurements to improve the description of the emission source. Gases are generally transported to the north-west in June–August and to the south-west in December–January. A diurnal variation due to land breeze around lake Kivu contributes to high concentrations of SO2 along the northern shore during the night. Potentially hazardous concentrations are occasionally reached in populated areas in the region, but mainly during the nights. The third study uses inverse dispersion modelling to determine the height and emission rates based on traverse measurements of the plume at 80–240 km from the source. The calculated source term yields better agreement with satellite observations compared to commonly used column sources. The work in this thesis presents improvements in dispersion modelling of volcanic emissions through improved models, more accurate representation of the source terms, and through incorporating new types of measurements into the modelling systems.Gas- och partikelutsläpp från vulkaner utgör en fara för människor och för vårt samhälle. Utsläppen kan transporteras över långa avstånd innan de reduceras till oskadliga halter. Att känna till vilka områden som utsätts för, eller kommer utsättas för, utsläppen är ett viktigt verktyg föratt minska påverkan på folkhälsa och samhälle. I avhandlingen studeras spridningen av utsläpp från vulkanutbrott med hjälp av en uppsättning numeriska atmosfärsmodeller. Den Lagrangiska Partikelspridningsmodellen FLEXPART-WRF har förbättrats och applicerats för spridningsmodellering av vulkanutbrott. Tre studier har utförts, en fokuserar på vulkanaska från potentiella framtida utbrott på Island, den andra studerar SO2-ustläpp från vulkanen Nyiragongo i Demokratiska Republiken Kongo, och den tredje studerar SO2-ustläpp från utbrottet i Holuhraun (Island) 2014–2015. Den första studien uppskattar sannolikheten för att vulkanaska från framtida vulkanutbrott på Island ska överskrida de gränsvärden som tillämpas för flygtrafik. Tre år av meteorologisk data används för att simulera spridningen från olika utbrottsscenarier. Sannolikheten för skadliga halter aska varierar med årstid, med en högre sannolikhet för effektiv transport österut under vintermånaderna, sommarutbrott är istället mer benägna att orsaka långvariga problem överspecifika områden. In den andra studien undersöks spridningen av SO2 från Nyiragongo över en ettårsperiod. Flödesmätningar av plymen används för att förbättra källtermen i modellen. Gaserna transporteras i regel mot nordväst i juni–augusti och mot sydväst i december–februari En dygnsvariation, kopplad till mesoskaliga processer runt Kivusjön, bidrar till förhöjda halter av SO2 nattetid längs Kivusjöns norra kust. Potentiellt skadliga halter av SO2 uppnås av och till i befolkade områden men huvudsakligen nattetid. Den tredje studien utnyttjar inversmodellering för att avgöra plymhöjd och gasutsläpp baserat på traversmätningar av plymen runt 80–240 km från utsläppskällan. Den beräknade källtermen resulterar i bättre överensstämmelse mellan modell- och satellitdata jämfört med enklare källtermer. Arbetet i den här avhandlingen presenterar flertalet förbättringar för spridningsmodellering av vulkanutbrott genom bättre modeller, nogrannare beskrivning av källtermer, och genom nya metoder för tillämpning av olika typer av mätdata.
48
Blower, Jonathan David. "Degassing processes in volcanic eruptions." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/30b2bc8c-2956-4a7a-a801-cdbef473ee1a.
Full text
49
Smith, Patrick John. "Attenuation of volcanic seismic signals." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1131/.
Full textAbstract:
Low frequency volcanic earthquakes, characterised by slowly decaying harmonic codas of 0.5-5Hz, have been observed on many volcanoes and are considered key tools in monitoring and eruption forecasting. The common element in a variety of models proposed for the origin of these earthquakes is resonance of a fluid body within a volcanic edifice. The source of the resonance is believed to consist of dispersive interface waves, trapped at the fluid-solid boundaries. The amplitude decay or attenuation of these earthquake signals can be decomposed into radiative and intrinsic components, and in this way yield information about both the geometry and fluid properties of the resonating source body. This thesis presents a study of the attenuation of low-frequency volcanic earthquakes, with particular emphasis on quantitatively linking seismic signals to magmatic processes and properties. The effect of the intrinsic attenuation of the fluid on the amplitude decay of low-frequency volcanic earthquakes is examined using a viscoelastic finite-difference model of seismic wave propagation. It is shown that the viscosity of the fluid contributes 23.6±2.26% less than previously thought to the apparent attenuation, and that its effect may have been substantially overestimated in previous studies. A physical explanation for this lies in understanding the fundamental differences between acoustic and interface waves. An analytical approach demonstrates that, for a set of realistic volcanic parameters, interface waves can be attenuated less than acoustic waves in a pure melt, if the longitudinal viscosity is at least 107 Pas. These results widen the set of possible resonators and imply that resonating volcanic conduits filled with high viscosity magma are viable sources for low-frequency seismicity. An automated method to measure the apparent attenuation of seismic signals is developed, tested, and applied to a dataset of low-frequency earthquakes from Soufri`ere Hills Volcano, Montserrat. Temporal trends in attenuation are observed and quantitatively interpreted as changes in magma viscosity. An estimate of the magma shear viscosity of 2.3 ± 2 × 105 Pas is obtained, demonstrating the ability of seismological data to place constraints on the magma properties.
50
Large, Adam M. "Silicic Volcanism at the Northern and Western Extent of the Columbia River Basalt Rhyolite Flare-up: Rhyolites of Buchanan Volcanic Complex and Dooley Mountain Volcanic Complex, Oregon." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/3122.
Full textAbstract:
Two mid-Miocene (16.5-15 Ma) rhyolite volcanic centers in eastern Oregon, the Buchanan rhyolite complex and Dooley Mountain rhyolite complex, were investigated to characterize eruptive units through field and laboratory analysis. Results of petrographic and geochemical analysis add to field observations to differentiate and discriminate the eruptive units. Additionally, new geochemical data are used to correlate stratigraphically younger and older basalt and ash-flow tuff units with regional eruptive units to constrain the eruptive periods with modern Ar-Ar age dates.
Previous work at the Buchanan rhyolite complex was limited to regional mapping (Piper et al., 1939; Greene et al., 1972) and brief mention of the possibility of multiple eruptive units (Walker, 1979). Observed stratigraphic relationships and geochemical analysis were used to identify eight distinct eruptive units and create a geologic map of their distribution. Slight differences in trace element enrichment are seen in mantle normalized values of Ba, Sr, P, Ti and Nd-Zr-Hf and are used to differentiate eruptive units. New geochemical analyses are used to correlate the overlying Buchanan ash-flow tuff (Brown and McLean, 1980) and two underlying mafic units to the Wildcat Creek ash-flow tuff (~15.9 Ma, Hooper et al., 2002) and flows of the Upper Steens Basalt (~16.57 Ma, Brueseke et al., 2007), respectively, bracketing the eruptive age of the Buchanan rhyolite complex to between ~16.5 and ~15.9 Ma (Brueseke et al., 2007; Hooper et al., 2002).
The Dooley Mountain rhyolite complex was thoroughly mapped by the U.S. Geological Survey (Evans, 1992) and geochemically differentiated in a previous Portland State University M.S. thesis (Whitson, 1988); however, discrepancies between published interpretations and field observations necessitated modern geochemical data and revisions to geologic interpretations. Field and laboratory studies indicate that the Dooley Mountain rhyolite complex consists of multiple eruptive units that were effusive domes and flows with associated explosive eruptions subordinate in volume. At least four geochemically distinct eruptive units are described with variations in Ba, Sr, Zr and Nb. Picture Gorge Basalt flows and Dinner Creek Tuff units found within the study area both overlay and underlie the Dooley Mountain rhyolite complex. These stratigraphic relationships are consistent with the one existing Ar-Ar age date 15.59±0.04 Ma (Hess, 2014) for the Dooley rhyolite complex, bracketing the eruptive period between ~16.0 and ~15.2 Ma (Streck et al., 2015; Barry et al., 2013).
The findings of this study indicate that the Buchanan rhyolite complex and the Dooley Mountain rhyolite complex are the westernmost and northernmost rhyolite complexes among the earliest (16-16.5 Ma) mid-Miocene rhyolites associated with initiation of Yellowstone hot spot related volcanism.