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1
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.
Анотація:
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
2
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.
3
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.
Анотація:
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.
4
Sigmarsson, Olgeir. "Geochimie isotopique du thorium des iles oceaniques (islande, canaries) et des zones de subduction (indonesie et chili)." Clermont-Ferrand 2, 1990. http://www.theses.fr/1990CLF21284.
Анотація:
La geochimie isotopique du thorium, associee a celle de l'o, du sr et du nd et a des mesures precises des teneurs en u et th dans les roches volcaniques actuelles, permet d'etudier la genese et l'evolution des magmas dans plusieurs contextes geodynamiques. Les resultats essentiels de ce travail sont les suivants: 1) la mise en evidence, en islande, de l'importance des phenomenes de contamination crustale: l'assimilation de croute profonde se produit aussi bien dans les zones de rift (produisant des tholeiites a quartz normatif a partir de tholeiites a olivine), que dans la zone laterale sud de l'islande ou l'extension est quasi inexistante et ou les basaltes primaires sont des basaltes alcalins donnant apres contamination crustale des basaltes riches en fe, ti; 2) l'origine des roches acides en islande est a rechercher dans la fusion de la croute metabasique, parfois prealablement alteree par l'hydrothermalisme. Ce modele pourrait s'appliquer a la formation de la croute continentale primitive; 3) le volcan hekla, etudie en detail, montre les roles respectifs de la fusion crustale et de la cristallisation fractionnee dans la formation des laves, allant des andesites basiques aux rhyolites; 4) dans l'archipel des canaries, les magmas primaires derivent d'un melange de magmas venant d'une source appauvrie et d'une source de type tristan de cunha; 5) l'importance d'un composant sedimentaire dans les sources des magmas de zones de subduction a ete mise en evidence dans l'arc de la sonde, en indonesie et au chili. Dans ce dernier cas, une correlation entre l'enrichissement des magmas en u et #1#0be montre que ces deux elements sont apportes dans les magmas par des fluides issus de la deshydration des sediments subductes, quelques 20000 ans avant leur eruption a la surface
5
Belien, Isolde L. M. B. (Leo Maria Beatrijs) 1985. "Gas Migration Through Crystal-Rich Mafic Volcanic Systems and Application to Stromboli Volcano, Aeolian Islands, Italy." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/12107.
Анотація:
xvii, 171 p. : ill. (some col.)Crystals influence the migration of gas through magma. At low concentrations, they increase the bulk fluid properties, especially viscosity. At concentrations close to maximum packing, crystals form a rigid framework and magma cannot erupt. However, erupted pyroclasts with crystal contents close to the packing concentration are common at mafic volcanoes that exhibit Strombolian behavior. In this dissertation, I study the influence of solid particles on gas migration. I apply my results to Stromboli volcano, Italy, type locality of the normal Strombolian eruptive style, where gas moves through an essentially stagnant magma with crystallinity ∼50%. Specifically, I investigate the effect of crystals on flow regime, gas content (Chapter II), bubble concentration (number densities), bubble shapes, bubble sizes (Chapter III), and bubble rise velocities (gas flux) (Chapter IV). I find that gas-liquid flow regimes are not applicable at high particle concentrations and should be replaced by new, three-phase (gas-liquid-solid) regimes and that degassing efficiency increases with particle concentration (Chapter II). In Chapter III, I show that crystals modify bubble populations by trapping small bubbles and causing large bubbles to split into smaller ones and by modifying bubble shapes. In Chapter IV, I model Stromboli's crystal-rich magma as a network of capillary tubes and show that bubble rise velocities are significantly slower than free rise velocities in the absence of particles. In each chapter, I use analogue experiments to study the effect of different liquid and solid properties on gas migration in viscous liquids. I then apply my analogue results to magmatic conditions using simple parameterizations and/or numerical modeling or by comparing the results directly to observations made on crystal-rich volcanic rocks. Chapter V proposes a mechanism for Strombolian eruptions and gas migration through the crystalrich magma in which the effect of crystals is included. This model replaces the current twophase "slug" model, which cannot account for the high crystallinity observed at Stromboli. There are three appendices in this dissertation: a preliminary study of the influence of particles on gas expansion, image analysis methods, and the numerical code developed in Chapter IV. This dissertation includes previously published and unpublished co-authored material.
Committee in charge: Katharine Cashman, Chairperson; Alan Rempel, Member; Mark Reed, Member; Raghuveer Parthasarathy, Outside Member
6
Dávila, Harris Pablo. "Explosive ocean-island volcanism : the 1.8–0.7 Ma explosive eruption history of Cañadas volcano recorded by the pyroclastic successions around Adeje and Abona, southern Tenerife, Canary Islands." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/9931.
Анотація:
The 1.8 to 0.7 Ma explosive eruption history of Las Cañadas volcano is recorded by the pyroclastic stratigraphy of southern Tenerife. A large pyroclastic apron is well exposed in the Bandas del Sur. It is divided into two regions, Adeje (southwest) and Abona (southeast). The lower stratigraphy of both successions is described here for the first time, and is divided into soil-bound eruption-units. The lithofacies record repeated phonolite explosive eruptions involving Plinian eruption columns and ignimbrite emplacement, with sedimentary reworking and soilification during repose intervals. The southwestern pyroclastic apron of Cañadas, around Adeje, includes eleven eruption-units, with one explosive eruption every 24,300–31,200 years. Two major unconformities are identified in this region, each representing ~0.6 myr hiatuses. The southeastern pyroclastic apron, around Abona, reveals nine newly discovered phonolitic eruption-units, eight of which are dated by 40Ar/39Ar. The eruptions span 1.6 Ma, and occurred with frequencies averaging one per 21,000 years to one per 79,556 years. The deposits include welded and non-welded ignimbrites and numerous fallout layers. Documentation of the ‘lower’ Bandas del Sur Group allows the entire pyroclastic record of southeast Tenerife to be constrained for the first time: over 18 explosive eruptions occurred during the past 1.6 myr, of which 7 may have been caldera-forming. Eruption frequencies cluster and are separated by unconformities that span from 184,000–563,000 years. A debris-avalanche deposit was discovered on the southeast flank of Cañadas. It records a catastrophic landslide, the Abona landslide, triggered by a phonolite explosive eruption 735 ± 5 ka ago. The Abona debris-avalanche deposit is enclosed between pyroclastic units of the Helecho Formation, and represents a single eruptionunit. Debris avalanche block and mixed facies, and a hummocky topography that dammed small ephemeral perched lakes, are exceptionally well-preserved. Limited disruption and mixing, and a general absence of clast segregation within the deposit, indicate that the landslide did not move as a rapid granular flow. The debris-block characteristics indicate that pervasive shattering and microbrecciation occurred progressively during transport, and were accompanied by limited shear, mixing and substrate erosion during predominantly laminar emplacement of a dilated, but essentially solid, shearing mass. The deposit is the only precisely dated giant landslide on Tenerife and provides the first unequivocal evidence of an eruption trigger on an ocean-island volcano.
7
Grunewald, Uwe. "Measuring and modelling of volcanic pollutants from White Island and Ruapehu volcanoes assessment of related hazard in the North Island /." Thesis, University of Canterbury. Geological Sciences, 2007. http://hdl.handle.net/10092/1428.
Анотація:
White Island and Ruapehu are currently the most active volcanoes in New Zealand. During non-eruptive periods, intense quiescent degassing through fumaroles can occur. The current project studies the quiescent degassing plumes, including aerosol sampling on White Island and dispersion modelling of SO₂ and PM₁₀ from White Island and Ruapehu volcanoes. Aerosol sampling from fumaroles at the crater floor on White Island volcano was carried out on 9 February and 6 April 2005. The exposed filters were analysed for various anions and cations and the particle mass concentration and molar concentration determined. Major elemental constituents were sodium and chlorine (Na⁺: 413 µg m⁻³, Cl⁻: 1520 µg m⁻³), which show best correlation at both sampling sessions. Other ions detected, with little correlation, are Ca²⁺, PO₄³⁻ and to a certain extent Mg²⁺. Other constituents found, which cannot correlate explicitly to other ions, are K⁺, NH₄⁺, NO₃⁻, and SO₄²⁻. SEM study of one exposed filter was performed and mainly NaCl particles could be distinguished due to their well-defined cubic shape. The Air Pollution Model (TAPM) was used for dispersion modelling of SO₂ (models 1-4) and PM₁₀ (models 5 and 6) from White Island and Ruapehu volcanoes. Annual modelling was performed using different parameters of emission rate, exit temperature and exit velocity. The resulting plume dispersions show relatively low concentrations at ground level ≤10 m), particularly for the models of PM₁₀ dispersion. TAPM calculated the highest SO₂ ground level concentrations with model 4, where the NES values of 350 and 570 µg m⁻³ were exceeded several times. The data was then used for detailed hazard assessment of urban population in the North Island. The meteorological data from annual modelling was used for model evaluation and compared with observation data from different weather stations by statistical calculations. Overall, TAPM performed well with most good and very good results. To evaluate SO₂ dispersion modelling, airborne plume measurements were carried out on 22 November 2006 by plume traverses at 3, 10 and 20 km. Although there is some variation, the calculated correlation coefficients indicate good model results for two plume traverses at 3 and 20 km and one plume traverse at 10 km. The meteorological data was also used for model evaluation, and the results indicate good model performance. TAPM is therefore suggested for future studies when more observation data are available to verify the calculated model data.
8
Hevia, Cruz Francisco. "Climatic and landscape evolution of the Azores over the past million years." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASJ035.
Анотація:
L'évolution des îles volcaniques résulte d'interactions complexes entre croissance des volcans et processus de destruction (éruptions explosives, glissements de terrain, érosion fluviale, altération). Les changements climatiques peuvent influencer ces processus sur des échelles variées. A l’échelle événementielle, des précipitations intenses peuvent engendrer des épisodes érosifs extrêmes. Sur le long-terme, des variations des taux d'altération, sensibles aux précipitations et à la température, peuvent impacter la fertilité des sols et le cycle global du carbone.Les îles volcaniques des Açores offrent un cadre idéal pour étudier ces interactions, avec une grande importance scientifique et sociétal, en particulier dans le contexte actuel du réchauffement climatique. Au centre de l'Atlantique Nord, elles sont influencées par des facteurs climatiques majeurs. Ces îles ont eu des pulses d'activité volcanique au cours du dernier million d'années (Ma), une période marquée par d’importants changements climatiques liés aux cycles glaciaires-interglaciaires. Si les variations des conditions globales ont été bien documentées sur cette période, la reconstruction paléoclimatique aux échelles locales/régionales reste un défi. Les paléosols (PSs) sont des anciens sols inclus dans le registre géologique. Leur géochimie fournit des informations précieuses sur les conditions paléo-environnementales, et la géochronologie des produits volcaniques les encadrant permet leur contrainte temporelle.Dans ce travail, nous avons reconstruit les conditions moyennes annuelles de précipitation (MAP) et de température de l’air (MAAT) aux Açores au cours du dernier Ma. Deux proxies basés sur la composition en éléments majeurs des PSs ont été utilisés : l’indice d'altération CIA-K et l’argilosité, tous deux validés dans d'autres milieux volcaniques. La datation précise des unités volcaniques par K-Ar sur mésostase séparée (laves) et par ⁴⁰Ar/³⁹Ar sur monocristaux de feldspath potassique (dépôts pyroclastiques), révèle des «pulses» d‘altération sur quelques milliers d’années, notamment après les terminaisons glaciaires (MIS 21, 19, 11, 9e, 5e et 1). La géochimie des PSs montre des changements environnementaux rapides et des MAATs (12-28 ᵒC) en accord avec les données de température marine de surface établies à partir d’archives océaniques. Cette concordance indique une étroite relation océan-atmosphère. Ces «pulses» suggèrent en outre des phases d'affaiblissement de l'anticyclone des Açores, permettant aux courants d'air humides d'atteindre des secteurs plus au sud.Les taux moyens de formation des sols (3-180 mm/kyr) ont été influencés par la structure et la texture du substrat rocheux. Des PSs se sont formés lors de MAPs plus faibles dans les dépôts pyroclastiques que dans les coulées de lave (seuils de ~500 et ~800 mm/an). Cette différence supporte une cinétique favorisée par la fragmentation et une surface spécifique élevée. L’altération accrue en surface et le long des discontinuités géologiques de sub-surface peut avoir favorisé l'érosion par glissements de terrain. Des MAPs élevées (jusqu'à 1500 mm/an) sont notamment obtenues autour du stade interglaciaire de l’Eemien, qui coïncide avec l’initiation d’un glissement complexe sur le flanc Sud de Pico. Des MAPs intenses ont pu accélérer l’infiltration des eaux et favoriser les interactions hydromagmatiques. L’augmentation associée de pression interstitielle a ainsi pu déclencher la mise en mouvement du flanc le long de failles listriques toujours actives. Les conditions actuelles aux Açores sont plus humides et légèrement plus chaudes qu’au cours du dernier Ma, ce que pourrait favoriser le détachement du flanc externe de Pico, avec des conséquences potentiellement drastiques.Plus généralement, l’altération accrue favorise l’évolution rapide du paysage sur de telles îles et engendre des flux élémentaires et une absorption de CO₂ atmosphérique croissantes, ce qui a impacts locaux, régionaux et globauxLandscape evolution on volcanic islands is driven by complex interactions between volcano growth and destruction by a variety of processes (explosive eruptions, landslides, riverine erosion, weathering). Major climate changes, may impact the dynamics of degradation processes at different spatial and temporal scales. For example, extreme rain can produce an immediate hydrological response causing important destruction. Changes in weathering rates, sensitive to precipitation and temperature, can trigger changes in soil fertility but also modify global carbon cycling.The Azores volcanic islands provide an ideal setting to study these interactions, with both scientific and societal significance, especially in the context of ongoing global warming. Located in the Central North Atlantic, they are under the influence of major climatic drivers. Most of them had pulses of volcanic activity over the past 1 Myr, a period characterized by high-amplitude glacial-interglacial transitions with major climatic changes. While global climatic variations have been relatively well-studied for this period, reconstructing the atmospheric paleoclimate and its effects at local/regional scales remains challenging. Paleosols (PSs) are fossil soils formed by weathering at surface, and later incorporated into the geological record. Their geochemistry provides valuable insights into past environmental conditions, while the geochronology of volcanic products “bracketing” PSs allows their temporal constraint.In this work, we reconstructed mean annual precipitations (MAP) and air temperature (MAAT) over the last 1 Myr in the Azores region through a combined geochemical-geochronological study of PSs. Two proxies based on PSs’ major element were used: the weathering index (CIA-K) and the Clayeyness, both validated in other volcanic settings. The precise dating of volcanic units by either unspiked K-Ar on lava flow groundmass separates or ⁴⁰Ar/³⁹Ar on single K-feldspar of trachytic fallout evidence “pulses” of soil-formation within only a few kyr. This occurred especially after glacial terminations (MIS 21, 19, 11, 9e, 5e and 1), under wet and warm conditions. Fast paleoenvironmental changes were recorded in PSs’ geochemistry, and MAAT reconstructions (12-28 ᵒC) agree with previously published Sea Surface Temperatures, pointing to a tight ocean-atmosphere teleconnection. Those “pulses” suggest sustained weakening phases for the Azores High, allowing humid air currents (Westerlies) to reach further to the south.Our data also show contrasted rates of vertical soil development (3-180 mm/kyr). Weathering was favored by the structure and texture of parental materials, as PSs formed under lower MAP in pyroclastic deposits than in lava flows (~500 and ~800 mm/yr thresholds). This highlights the influence of fragmentation on weathering’s kinetics due to higher specific surface area. Enhanced weathering at surface and along geological discontinuities may have promoted mechanical weakening, favoring erosion and landslides. Notably, high MAPs (up to 1500 mm/yr) obtained around the Eemian interglacial stage are coincident in time with the initiation of a large slide complex on the southern flank of Pico. Intense precipitation may have led to increased water infiltration favoring enhanced hydromagmatic interactions. Drastic increase in pore pressure may then have triggered the initiation of the flank movement along listric faults that are still active. Current conditions in the Azores are wetter and slightly warmer than during the last Myr. Increased infiltration along faults could partly control subsequent movement and yield to detachment of the outer flank of Pico, with potentially dramatic consequences.More generally, present temperature and humidity increase on volcanic islands points to intense weathering, resulting in fast landscape evolution, increased lixiviation and elementary export and high atmospheric CO₂ uptaking, with local, regional and global impacts
9
Meletlidis, Tsiogalos Stavros. "Eruptive dynamics and petrological evolution of recent volcanism on the El Hierro Island : Implications for volcanic hazard assessment." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/461582.
Анотація:
The Canarian archipelago, extends over approximately 500 km in total along the passive continental margin off NW Africa, comprises seven major and four minor islands, and it is part of the so called Macaronesia region, together with the archipelagos of Azores, Madeira, Salvajes and Cape Verde.
Within the oceanic geodynamic context, the Canary archipelago is located on oceanic crust of the big African plate, specifically upon the passive continental margin, with thickness exceeding 20 km. It is a good example of oceanic intraplate alkaline volcanism.
According the radioisotopic data available (Carracedo et al., 1998) the archipelago has been formed during the last 60 Ma and is still volcanically active. Multiple periods of volcanic activity accompanied with extreme range in magma compositions and eruptive styles have been exhibited during the evolution.
A wide variety of models have been proposed for the origin of the Canary Islands, such as, hot spot, decompressing fusion, Atlas generated propagating fracture, or the "block" model based on regional fractures that helped elevate the islands.
Holocene sub-aerial activity has occurred on all islands, except La Gomera, with 18 eruptions in the last 520 years (historic activity) on Tenerife, La Palma, Lanzarote and El Hierro. All these eruptive events consist of monogenetic basaltic eruptions along structures or zones identified as rifts (only the 1798 of Montaña Chahorra in Tenerife, expulsed intermediate composition magma and was located at the base of the Teide-Pico Viejo volcanic complex).
Although monogenetic volcanism is the most extended type of volcanic activity on the planet (Walker 2000) and is characterized by a large diversity of eruptive styles and products, it is generally associated to low level volcanic hazard and many times it is underestimated in the hazard assessment.
The main structures generated by these type of eruptions (concentrated as volcanic fields or long rift zones) are cinder cones, formed by the pyroclastic products and lava flows, that can reach several kilometres length. Eventually, can generate phreatomagmatic deposits, when an interaction between magma and water occurs (shallow submarine volcanism or littoral cones).
These eruptions, traditionally, are associated with a single batch and pulse of magma and are greatly influenced by local and regional stress fields. Other parameters that can be important in the evolution
of the activity, as in any other volcanic activity, are magma composition, volume, and rheological contrast beneath the surface.
Recent studies have revealed that, even in a monogenetic eruption, an internal geochemical evolution could be possible, mainly because of the multiple batches involved and the importance of the local stress controls in the migration and finally eruption of magma.
Complexity, derived from these internal and external conditions in combination with the depth where magmas are stored and transported, is reflected in the difficulty to anticipate and forecast these types of eruptions and their evolution, especially, for areas with long quiescent periods and a variety of magmas as in the Canary Islands, where a new volcano could come up in any location.
The reconstruction of the structure, geometry, composition and plumbing system conditions of pre- existed monogenetic eruptions on the Canary Islands along with the data obtained (petrological, seismological, geodetical, etc.) of an eruption in course such was the 2011 El Hierro eruption will help us obtain a significant progress in understanding the processes that take place, improve our knowledge on monogenetic eruptions and as a consequence enhance hazard assessment and reduce the risk to human lives.a última erupción en la isla de El Hierro (2011-12) representa una excelente oportunidad para estudiar el volcanismo monogenético basáltico. La comparación de los productos emitidos durante esa erupción con los emitidos en erupciones anteriores y la interpretación de los resultados petrológicos junto con los datos obtenidos por la red multiparamétrica de vigilancia volcánica del IGN de vigilancia (estaciones sísmicas, GNSS, gravimétricas,…) nos ha permitido lograr un conocimiento integral de los procesos que ocurren antes y durante este tipo de erupciones basáticas monogenéticas, que son las más probables a corto y medio plazo en Canarias. Este enfoque multidisciplinar nos ha proporcionado nueva información sobre el ascenso del magma, las condiciones y procesos internos, los mecanismos de las erupciones basálticas, los mecanismos de deposición y los escenarios de interacción. La interpretación conjunta de todos los datos obtenidos permitirá una mejor evaluación del riesgo volcánico, no solo para la isla de El Hierro, sino para todo el archipiélago canario. En esta tesis, junto con el estudio de la erupción de 2011-12, se han estudiado dos más erupciones; la que ha dado el depósito de productos evolucionados en el centro de la isla (área del Malpaso) donde la dinámica y evolución de ella se ha ligado en la interacción magma/agua y la erupción de Chinyero (1909, Tenerife) que con rasgos similares a la de El Hierro (basáltica) pero con menor volumen de magma involucrado, ha tenido una dinámica más explosiva de lo que se había creído hasta hoy. Por lo tanto, las evaluaciones de riesgo volcánico a largo y corto plazo para el conjunto de las islas Canarias deben tener en cuenta posibles escenarios que no solo incluyen la erupciones basálticas submarinas, como es el caso de 2011-2012, sino también las erupciones sub-aéreas de corta vida como la del Chinyero o las erupciones como la del Malpaso, donde la intrusión basáltica y la interacción con el agua son procesos que aumentan la explosividad de una erupción y como consecuencia, al área afectado de sus productos.
10
Palmiotto, Camilla <1985>. "Transform Tectonics and Non-Volcanic Oceanic Islands." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6472/1/Palmiotto_Camilla_Tesi.pdf.
Анотація:
Oceanic islands can be divided, according to their origin, in volcanic and tectonic. Volcanic islands are due to excess volcanism. Tectonic islands are mainly formed due to vertical tectonic motions of blocks of oceanic lithosphere along transverse ridges flanking transform faults at slow and ultraslow mid-ocean ridges. Vertical tectonic motions are due to a reorganization of the geometry of the transform plate boundary, with the transition from a transcurrent tectonics to a transtensive and/or transpressive tectonics, with the formation of the transverse ridges. Tectonic islands can be located also at the ridge–transform intersection: in this case the uplift is due by the movement of the long-lived detachment faults located along the flanks of the mid-ocean ridges.
The "Vema" paleoisland (equatorial Atlantic) is at the summit of the southern transverse ridge of the Vema transform. It is now 450 m bsl and it is capped by a carbonate platform 500 m-thick, dated by 87Sr/86Sr at 10 Ma. Three tectonic paleoislands are on the summit of the transverse ridge flanking the Romanche megatrasform (equatorial Atlantic). They are now about 1,000 m bsl and they are formed by 300 m-thick carbonate platforms dated by 87Sr/86Sr, between 11 and 6 Ma. The tectonic paleoisland “Atlantis Bank" is located in the South-Western Indian Ridge, along the Atlantis II transform, and it is today 700 m bsl. The only modern example of oceanic tectonics island is the St. Paul Rocks (equatorial Atlantic), located along the St. Paul transform. This archipelago is the top of a peridotitic massif that it is now a left overstep undergoing transpression.
Oceanic volcanic islands are characterized by rapid growth and subsequent thermal subsidence and drowning; in contrast, oceanic tectonic islands may have one or more stages of emersion related to vertical tectonic events along the large oceanic fracture zones.
11
Palmiotto, Camilla <1985>. "Transform Tectonics and Non-Volcanic Oceanic Islands." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6472/.
Анотація:
Oceanic islands can be divided, according to their origin, in volcanic and tectonic. Volcanic islands are due to excess volcanism. Tectonic islands are mainly formed due to vertical tectonic motions of blocks of oceanic lithosphere along transverse ridges flanking transform faults at slow and ultraslow mid-ocean ridges. Vertical tectonic motions are due to a reorganization of the geometry of the transform plate boundary, with the transition from a transcurrent tectonics to a transtensive and/or transpressive tectonics, with the formation of the transverse ridges. Tectonic islands can be located also at the ridge–transform intersection: in this case the uplift is due by the movement of the long-lived detachment faults located along the flanks of the mid-ocean ridges.
The "Vema" paleoisland (equatorial Atlantic) is at the summit of the southern transverse ridge of the Vema transform. It is now 450 m bsl and it is capped by a carbonate platform 500 m-thick, dated by 87Sr/86Sr at 10 Ma. Three tectonic paleoislands are on the summit of the transverse ridge flanking the Romanche megatrasform (equatorial Atlantic). They are now about 1,000 m bsl and they are formed by 300 m-thick carbonate platforms dated by 87Sr/86Sr, between 11 and 6 Ma. The tectonic paleoisland “Atlantis Bank" is located in the South-Western Indian Ridge, along the Atlantis II transform, and it is today 700 m bsl. The only modern example of oceanic tectonics island is the St. Paul Rocks (equatorial Atlantic), located along the St. Paul transform. This archipelago is the top of a peridotitic massif that it is now a left overstep undergoing transpression.
Oceanic volcanic islands are characterized by rapid growth and subsequent thermal subsidence and drowning; in contrast, oceanic tectonic islands may have one or more stages of emersion related to vertical tectonic events along the large oceanic fracture zones.
12
Knill, R. "Isotopic age studies from the Cape Verde Islands." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377450.
13
Finney, Benjamin Mark. "Magmatic differentiation at an island-arc caldera : a stratigraphically constrained multi-isotope study of Okmok Volcano, Aleutian Islands, Alaska." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417639.
14
Svensson, Anna. "Determining the depth of magma storage by investigation of samples from the eruption on La Palma 1971." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-206827.
Анотація:
The Canary islands are formed by a slow moving hotspot, from Fuerteventura 20 Ma to el Hierro 1.2Ma years old and La Palma is in the shield building stage of evolution. La Palma had its last eruption 1971 and has had seven eruptions since 1430, which makes it the most active of the islands in our times. The samples consist of host lavas, basanites, and mafic/ultramafic and felsic xenoliths, alkali gabbros and syenites respectively. Minerals in the lavas and the alkali gabbro xenolith samples are clinopyroxene, olivine, amphibole and plagioclase, the clinopyroxenes are zoned. Forsterite content in the olivines increases at the rim for the xenoliths and decreases for the host lavas. While magnesium number in the clinopyroxenes decreases towards the rim. The Fe-Mg partitioning indicates that there were points of equilibrium between the clinopyroxenes and their host lavas, which was calculated to temperature, pressure and depth indicating 62-74km for the xenoliths and 23-35km for the host lavas. The temperatures and pressures were 1184-1205°C with 6-10 kbar for the host lavas compared to 1316-1341°C and 17-20 kbar for the xenoliths.
15
Schwandner, Florian Maximilian. "The organic chemistry of volcanic gases at Vulcano (Aeolian Islands, Italy) /." [Zürich] : [s.n.], 2002. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14706.
16
Woodhead, J. D. "Geochemistry of volcanic rocks from the Northern Mariana islands, West Pacific." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379957.
17
Storey, Michael. "Petrology of volcanic rocks from Sao Miguel and Faial, Azores Islands." Thesis, Royal Holloway, University of London, 1985. http://repository.royalholloway.ac.uk/items/ac799f4c-b4d1-45c1-bf74-c9c54fa5822d/1/.
Анотація:
Volcanic rocks from Sao Miguel form two distinct alkaline (potassic) magma series. Recent eruptives comprise Ne-normative basalts and derivatives (Main Series). Older basalts associated with the extinct stratovolcano Povoacao are either Ne or Hy-normative (Povoacao Series ) and have lower P/Zr, Ba/Zr and Sr/Zr ratios. Faial volcanic rocks form a single series, basaltic compositions being Ne-normative. Differentiates on both islands range through intermediate compositions to metaluminous and peralkaline trachytes. The latter are strongly enriched in the incompatible elements (eg Th, Rb, Ta, Nb, Zr and the rare-earths) and are depleted in Mg, Ni, Cr, V, Ti, P, Sr, Eu and Ba. Fractional crystallization of the observed phenocryst assemblages can account for most chemical variations, incompatible element abundances indicating that the trachytes result from some 60--85% solidification of a parental basalt. Mixed-magma lavas occur on both Faial and Sao Miguel. They form two distinct groups. (1) M-type lavas. These have high Ni, Cr and MgO and low CaO, Sr, P2 O5, TiO2 and V. Modelling suggests they are a mix of trachyte (70%) and MgO-rich basalt (30%). (2). AM-type lavas. They show similar geochemical features but also have high Ba and Eu and large K/Rb ratios. They are best modelled by mixing hawaiite, trachyte and alkali feldspar. AM-type lavas and geochemically heterogeneous pumice deposits suggest compositionally zoned (basalt-intermediate-trachyte) magma chambers beneath both islands. Compositional variations in recent pumice deposits from Agua de Pau volcano show temporal control. Trends up the succession include the depletion of Sr, Ba and Eu coupled with stepwise enrichment in the incompatible elements. These suggest the deposits represent successive samples of an evolving body of trachytic magma. The lack of similar variations in the Furnas pumice succession is attributed to a high magma viscosity, inhibiting crystal/liquid fractionation. Pre-eruptive temperatures for trachytic pumice deposits, from coexisting magnetite and ilmenite, ranged between 960°C--880°C. fO 2 varied between 10-10.9--10-13.4. Thermodynamic-based estimates of magnetic water contents were between 6.5--7.2 wt.%. These values are compatible with field data. Estimates of S2, H2S, SO2, SO3, H2, CO2, HCl and HF suggest they are several orders of magnitude less abundant than H2O. Lastly, Azores basalts exhibit inter and intra-island compositional heterogeneity. Relative to N type m.o.r.b., they are characterized by high La/Yb, Ba/La, 87Sr/86Sr ratios and low 143Nd/ 144Nd, Zr/Nb, Zr/Ta and K/Rb ratios. Sao Miguel shows a systematic increase in 87Sr/86Sr ratios from west to east (up to 0.70522). Most of these features represent source characteristics and suggest a complexly heterogeneous mantle.
18
Pedrazzi, Dario. "Hydrmagmatic monogenetic volcanism in continental and oceanic island enronments." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/229382.
Анотація:
Monogenetic volcanism is characterized by a large diversity of eruptive styles, morphologies and deposits. Monogenetic landforms are the result of a complex merging of internal (magma composition, vesiculation) and external (geological setting, fracturation, hydrogeology, substrate stratigraphy, etc) parameters that govern the physics of the eruptions. Changes in these parameters may cause variations in the eruption style several times during the course of such short-lived volcanoes. Monogenetic volcanoes may form in any type of geological environment with scoria cones being the most common volcano type and hydrovolcanic tuff rings, tuff cones, and maars as the second in abundance. These small-volume volcanoes are generally the result of short-lived eruptions but the activity in a monogenetic volcanic field might exceed the total life of composite volcanoes.
The attention of this work was focused on the relation between monogenetic volcanic landforms and the external variables that influenced the dynamics of the eruptions (i.e. magmatism vs phreatomagmatism) through a multidisciplinary perspective, in marine and continental geological settings under which monogenetic volcanism may develop.
Different case studies representative of this type of activity and of these different environments have been considered. The first one corresponds to the La Crosa De Sant Dalmai volcano (Garrotxa Volcanic Field, southern sector of the Catalan Volcanic Zone), a roughly circular asymmetrical maar-diatreme volcano, which is one of the most characteristic volcanic edifices of this continental monogenetic volcanic field and the largest Quaternary volcanic crater on the Iberian Peninsula. This edifice is an example of monogenetic landform, mostly composed of phreatomagmatic deposits with subordinate Strombolian phases, constructed on a mixed basement made of hard Paleozoic granites and schists rocks and soft Plio-Quaternary deposits. Here, I reconstructed the hydrogeological conditions of the substrate and the implication for the eruptive dynamics. As a second case study, I carried out detailed stratigraphic and sedimentological studies of the succession of El Golfo tuff cone (Lanzarote, Canary Islands). The main objective of the work was to describe in detail the structure and association of facies of this edifice and use this information to infer changes in eruption style and depositional processes. Another type of eruption was studied in the same archipelago at El Hierro, an island essentially characterized by basaltic volcanism with both Strombolian and Hawaiian activity. Here I reported the stratigraphic, lithological, sedimentological and petrographic characteristics of a felsic hydrovolcanic episode in order to discuss, transport/depositional mechanisms, dynamics, relative age and implications for hazard assessment on the island. Finally, the same type of methodology was applied at Deception Island (Southern Shetland Archipelago, Antarctica), determining the lithological and sedimentological characteristics, and clasts distribution (isopach and isopleth maps) of the eruption of 1970. This information was, then, used to determine depositional processes, eruption style and physical parameters (i.e. plume height, erupted volume, VEI) of the eruption in order to compare this episode with the previous 1967 episode, and to deduce their implications to conduct hazard assessment at the island.
Each work represents a diverse aspect of hydrovolcanism and the results obtained helped to better understand the eruptive behavior of this type of volcanoes, which is a fundamental task in order to understand the possible future hazards associated with this type of volcanism. The results obtained can be applied to monogenetic volcanic fields worldwide and are, therefore, useful to reconstruct the evolution of a certain volcanic fields, through the study of single monogenetic volcanoes, and to evaluate the possible volcanic hazards, as similar eruptions represent a serious threat, which is often underestimated. A more systematic study is, thus, needed in order to understand the role of shallow-level conditions in the formation of specific volcano types in such complex volcanic fields.El vulcanismo monogenético se caracteriza por una gran diversidad de estilos eruptivos, morfologías y depósitos. Los tipos de edificios que se forman son el resultado de una compleja combinación de parámetros que rigen la física de la erupción. La atención de este trabajo se centra en la relación entre los edificios volcánicos monogenéticos y las variables externas que influyen en la dinámica de las erupciones (es decir, magmatismo vs freatomagmatismo) a través de un punto de vista multidisciplinar, en ambientes continentales y marinos en los que el vulcanismo puede desarrollar. Diferentes estudios, representativos de este tipo de actividad en diferentes entornos geográficos y geológicos, se han llevado a cabo. El primer ejemplo corresponde al volcán de La Crosa de Sant Dalmai (Campo Volcánico de La Garrotxa) donde se han reconstruido las condiciones hidrogeológicas del sustrato y la implicación para la dinámica eruptiva. Como segundo caso de estudio, se ha realizado una estratigrafía de detalle del cono de toba de El Golfo (Lanzarote, Islas Canarias), donde se han estudiado los mecanismos de emplazamiento de los depósitos para inferir cambios en la interacción magma/agua. Otro tipo de erupción se ha investigado en el mismo archipiélago, en la Isla de El Hierro, determinando las características físicas de un episodio félsico de origen hidrovolcánico ocurrido en una isla que se caracteriza esencialmente por el vulcanismo basáltico tanto Estromboliano como Hawaiiano. Por último, este mismo tipo de metodología se ha aplicado a la Isla Decepción (archipiélago de las Shetland del Sur, Antártida), estableciendo los parámetros físicos de la erupción del 1970 con el fin de comparar este episodio con el evento anterior del 1967, y deducir sus consecuencias para llevar a cabo la evaluación de peligrosidad en la isla. Los resultados obtenidos pueden ser aplicados a campos volcánicos monogenéticos en todo el mundo y, por tanto, son útiles para reconstruir la evolución de ciertos campos volcánicos, a través del estudio de volcanes monogenéticos individuales, para evaluar los posibles riesgos volcánicos, teniendo en cuenta como erupciones similares representan una grave amenaza, que es a menudo subestimada.
19
Saunders, Katharine Emma. "Micro-analytical studies of the petrogenesis of silicic arc magmas in the Taupo Volcanic Zone and southern Kermadec Arc, New Zealand : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy in Geology /." ResearchArchive@Victoria e-Thesis, 2009. http://hdl.handle.net/10063/943.
20
Olin, Paul Hessel. "Magma dynamics of the phonolitic Diego Hernández Formation, Tenerife, Canary Islands." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/p_olin_112607.pdf.
21
Pryet, Alexandre. "Hydrogeology of volcanic islands : a case-study in the Galapagos Archipelago (Ecuador)." Paris 6, 2011. http://www.theses.fr/2011PA066563.
Анотація:
La population de l’Archipel des Galápagos est croissante, tandis que les ressources en eau sont limitées et inégalement réparties. Dans le cadre de ce travail, une approche intégrée combinant géophysique, géologie structurale, suivis hydro-climatologique et piézométrique est utilisée pour caractériser les modèles conceptuels hydrogéologiques d’une île à l’autre et identifier d’éventuelles ressources complémentaires. La géophysique permet d’identifier des zones d’intérêt hydrogéologique. Les données acquises lors de la mission géophysique SkyTEM réalisée en 2006 sur les îles de Santa Cruz et San Cristóbal ont été mises en perspective avec une nouvelle technique d'interprétation. Avec des outils géostatistiques, cette méthode a permis la construction d'une grille 3D de la résistivité électrique pour chacune des deux îles. Des zones d'intérêts ont été cartographiées en 3D et confrontées aux observations structurale, géomorphologiques et hydrologiques. Un paramètre déterminant en hydrogéologie est la recharge des aquifères. Sur les principales îles de l'Archipel, la présence semi-permanente de brouillard pendant six mois de l'année présente un apport supplémentaire aux précipitations classiques. Pour quantifier cet apport, un réseau de suivi hydrométéorologique a été mis en place sur le versant au vent de l'île de Santa Cruz. L’apport du brouillard a été quantifié avec une méthode basée sur un modèle d'interception à base physique. La vitesse du vent est identifiée comme un facteur déterminant pour l’interception du brouillard. A Santa Cruz, un suivi hydrogéologique de l'aquifère de base a été réalisé. Affecté par l’intrusion saline, cet aquifère est soumis aux variations du niveau de la mer et à la dynamique de recharge. La cartographie de la fracturation a été réalisée sur des affleurements sélectionnés. Combinée à l'analyse de la propagation du signal de marée, elle a permis de caractériser les propriétés hydrodynamiques des basaltes.
22
Ricchi, Alessandro <1988>. "Insular shelves as a tool for reconstructing the evolution of volcanic islands." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amsdottorato.unibo.it/8943/1/Ricchi_Alessandro_tesi.pdf.
Анотація:
The erosion by waves, accomplished at different elevations due to glacio-eustatic sea-level fluctuations and islands’ vertical movements, carves the flanks of volcanic islands resulting in the formation of insular shelves, features long known in literature since the early paper of Menard (1983). However, a systematic study of their morphometric parameters and evolution has seldom been carried out. This Ph.D project, based on high-resolution multibeam bathymetric data and seismic reflection profiles collected in the last decades by the University of Bologna, University of Rome “La Sapienza”, CNR-IGAG Rome and by the Hydrographic Institute of the Portuguese Navy, explores the geomorphologic and structural features of the shelves surrounding the volcanic islands of Salina, Lipari and Vulcano in the Central Aeolian Archipelago and Santa Maria in the Azores Archipelago, respectively. The main aim is to increment our knowledge regarding the processes that influence the formation and the evolution of insular shelves and how these features might help us to better constraint the volcanic history of such islands. The study of insular shelves helps to improve the evolutionary models of the studied volcanic islands, which were previously developed only from the knowledge of the onshore geology. The information derived from the measured morphometric parameters (mainly the shelf width and the erosive edge depth) were integrated with field studies, allowing to infer, in some cases, the possible location of their earlier evolutionary stages, as well as to improve the overall geological evolution of studied volcanic islands.In the Central Aeolian sector, we thus document the occurrence of presently submerged and largely dismantled volcanic edifices predating the oldest complexes located onshore. At Santa Maria we adopted the same integrated approach to relate the morphologic characteristics of the shelf with the geology onshore.
23
Sykes, Mark A. "The petrology and tectonic significance of the James Ross Island volcanic group, Antarctica." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238294.
24
So, Chak-tong Anthony. "Petrology and geochemistry of volcanic rocks of the Lantau Peak Area, Lantau Island, Hong Kong /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21375549.
25
Ribeiro, Luisa Joubert Chaves Pinto. "Petrologic and geochemical characterization of São Jorge island volcanism, Azores." Doctoral thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/7993.
Анотація:
Doutoramento em GeociênciasThe island of São Jorge (38º 45’ 24’’ N - 28º 20’ 44’’W and 38º 33’ 00’’ N - 27º 44’ 32’’ W) is one of the nine islands of the Azores Archipelago that is rooted in the Azores Plateau, a wide and complex region which encompasses the triple junction between the American, Eurasia and Nubia plates. São Jorge Island has grown by fissural volcanic activity along fractures with the regional WNW-ESE trend, unveiling the importance of the regional tectonics during volcanic activity. The combination of the volcanostratigraphy (Forjaz & Fernandes, 1975; and Madeira, 1998) with geochronological data evidences that the island developed during two main volcanic phases. The first subaerial phase that occurred between 1.32 and 1.21 Ma ago (Hildenbrand et al. 2008) is recorded on the lava sequence forming the cliff at Fajã de São João, while the second phase started at 757 ka ago, is still active, and edified the rest of the island. This second phase edified the east side of the island that corresponds to Topo Volcanic Complex, in the period between 757 and 543 ka ago, while the west side named Rosais Volcanic Complex, started at 368 ka ago (Hildenbrand et al. 2008) and was still active at 117 ka ago. After the onset of Rosais, volcanic activity migrates to the center of São Jorge edifying Manadas Volcanic Complex. The volcanism on São Jorge is dominantly alkaline, with a narrow lithological composition ranging between the basanites/tefrites through the basaltic trachyandesites, in spite of this the two volcanic phases show distinct mineralogical, petrographic and geochemical characteristics that should be related with different petrogenetic conditions and growth rates of the island. Abstract viii During the first volcanic phase, growth rates are faster (≈3.4 m/ka), the lavas are slightly less alkaline and plagioclase-richer, pointing to the existence of a relative shallow and dynamic magma chamber where fractional crystallization associated with gravitational segregation and accumulation processes, produced the lavas of Fajã de São João sequence. The average growth rates during the second volcanic phase are lower (≈1.9 m/ka) and the lavas are mainly alkaline sodic, with a mineralogy composed by olivine, pyroxene, plagioclase and oxide phenocrysts, in a crystalline groundmass. The lavas are characterized by enrichment in incompatible trace element and light REE, but show differences for close-spaced lavas that unveil, in some cases, slight different degrees of fertilization of the mantle source along the island. These differences might also result from higher degrees of partial melting, as observed in the early stages of Topo and Rosais volcanic complexes, of a mantle source with residual garnet and amphibole, and/or from changing melting conditions of the mantle source as pressure. The subtle geochemical differences of the lavas contrast with the isotopic signatures, obtained from Sr-Nd-Pb-Hf isotopes, that São Jorge Island volcanism exhibit along its volcanic complexes. The lavas from Topo Volcanic Complex and from the submarine flank, i.e. the lavas located east of Ribeira Seca Fault, sample a mantle source with similar isotopic signature that, in terms of lead, overlaps Terceira Island. The lavas from Rosais and Manadas volcanic complexes, the western lavas, sample a mantle source that becomes progressively more distinct towards the west end of the island and that, in terms of lead isotopes, trends towards the isotopic composition of Faial Island. The two isotopic signatures of São Jorge, observed from the combination of lead isotopes with the other three systems, seem to result from the mixing of three distinct end-members. These end-members are (1) the common component related with the Azores Plateau and the MAR, (2) the eastern component with a FOZO signature and possibly related with the Azores plume located beneath Terceira, and (3) the western component, similar to Faial, where the lithosphere could have been entrained by an ancient magmatic liquid, isolated for a period longer than 2Ga. The two trends observed in the island reinforce the idea of small-scale mantle heterogeneities beneath the Azores region, as it has been proposed to explain the isotopic diversity observed in the Archipelago.
A ilha de São Jorge (38º 45’ 24’’ N - 28º 20’ 44’’W e 38º 33’ 00’’ N - 27º 44’ 32’’ W) é uma das nove ilhas do Arquipélago dos Açores que integram uma extensa e complexa estrutura, a Plataforma dos Açores, onde convergem as placas Americana, Eurasiática e Núbia que definem a junção tripla dos Açores. A ilha de São Jorge exibe características próprias, dentro do contexto açoriano, que evidenciam um vulcanismo fissural ao longo da direcção WNW-ESE, indicando uma importante interacção entre a actividade tectónica e a actividade vulcânica. A conjunção entre dados de natureza vulcanoestratigráfica (Forjaz & Fernandes, 1975; and Madeira, 1998) e geocronológica, revelam que a formação da ilha deverá ter decorrido fundamentalmente durante duas fases vulcânicas distintas. Durante a primeira fase vulcânica, entre 1,31 e 1,21 Ma (Hildenbrand et al. 2008) ter-se-á formado o empilhamento lávico sobranceiro à Fajã de São João e, há cerca de 757 Ka, provavelmente, iniciou-se a segunda fase vulcânica que foi responsável pela edificação da restante parte da ilha e que se tem mantido activa até aos nossos dias. Durante a segunda fase vulcânica, no período compreendido entre os 757 e 543 ka, terá sido edificado o Complexo Vulcânico do Topo, constituindo a zona este da ilha; enquanto que a parte oeste, englobando o Complexo Vulcânico dos Rosais, deverá ter-se começado a formar à cerca 368 ka e mantido em actividade até, pelo menos, há aproximadamente 117 ka. Depois da edificação do Complexo Vulcânico dos Rosais a actividade Resumo iv vulcânica parece ter migrado para a zona central da ilha o que conduziu à formação do Complexo Vulcânico das Manadas. O vulcanismo em São Jorge é predominantemente alcalino, apresentando uma diversidade litológica que varia entre os basanitos/tefritos e os traquiandesitos basálticos. Apesar deste pequeno espectro litológico, as duas fases vulcânicas apresentam diferentes características mineralógicas, petrográficas e geoquímicas que deverão derivar de distintas condições petrogenéticas e taxas efusivas diversas e, consequentemente, de velocidades de crescimento dos empilhamentos lávicos distintos. Durante a primeira fase vulcânica, em que a velocidade média de crescimento da ilha foi mais elevada (≈3.4 m/ka), as lavas apresentam-se ligeiramente menos alcalinas e mais enriquecidas em plagioclase. Tais factos sugerem a existência de uma câmara magmática, possivelmente, pouco profunda e bastante dinâmica, sob o empilhamento lávico da Fajã de São João, à qual estarão associados processos de cristalização fraccionada, segregação gravítica e acumulação. A velocidade média de crescimento das sequências lávicas, durante a segunda fase vulcânica, foi mais baixa (≈1.9 m/ka) e as lavas apresentam uma composição, maioritariamente, alcalina sódica em que a paragénese é representada por fenocristais de olivina, piroxena, plagioclase e óxidos. As lavas são caracterizadas por um enriquecimento em elementos traço incompatíveis e terras raras leves mas evidenciam, para lavas geograficamente próximas, diferentes níveis de enriquecimento que poderão indicar pequenas heterogeneidades na fonte mantélica. Outros factores a considerar, que eventualmente contribuem para estas assimetrias, poderão ser: (1) a ocorrência de taxas de fusão ligeiramente mais elevadas, como observado nas lavas mais antigas dos complexos vulcânicos do Topo e Rosais; (2) a presença na fonte mantélica de granada e anfíbola residuais e/ou (3) a variação nas condições de fusão da fonte, tais como, a pressão. As subtis diferenças geoquímicas acima referenciadas contrastam com as assinaturas isotópicas obtidas através dos isótopos de Sr-Nd-Pb-Hf, estando claramente impressas nas lavas dos vários complexos vulcânicos da ilha de São Jorge. As lavas do Complexo Vulcânico do Topo e do flanco submarino, i.e. as lavas localizadas a este da falha da Ribeira Seca, amostram uma fonte mantélica com uma assinatura isotópica, que em termos de chumbo é semelhante à ilha Terceira. Por outro lado, as lavas dos complexos vulcânicos dos Rosais e das Manadas, i.e. as lavas do lado oeste de São Jorge, mostram que a Petrologic and Geochemical Characterization of São Jorge Island Volcanism, Azores v fonte mantélica se torna progressivamente mais diferenciada em termos de isótopos de chumbo, sobrepondo-se à assinatura isotópica da ilha do Faial. As duas assinaturas isotópicas de São Jorge, verificada pelos isótopos de chumbo, em conjugação com os outros três sistemas isotópicos (Sr- Nd-Hf), evidenciam a contribuição de três reservatórios/componentes mantélicos para a formação das composições observadas. Estes componentes mantélicos são (1) o Componente Comum, relacionado com a Plataforma dos Açores e a Crista Média Atlântica, (2) o Componente Este, com uma assinatura FOZO e, possivelmente, relacionado com o ponto quente dos Açores localizado sob a ilha Terceira, e (3) o Reservatório Oeste, semelhante ao encontrado sob a ilha do Faial, onde a litosfera poderá ter sido impregnada por um líquido magmático antigo e isolado no manto por mais de 2Ga. Neste contexto, parece poder-se concluir que as duas assinaturas isotópicas observadas reforçam a existência de pequenas heterogeneidades sob a Região dos Açores, como tem sido proposto, por alguns autores, para explicar a diversidade isotópica observada nas ilhas do Arquipélago.
26
Schmitt, Susanne F. "Disturbance and succession on the Krakatau Islands, Indonesia." Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:a2b3257d-0a00-4286-a38a-01e3016da708.
Анотація:
This thesis set out to investigate the influence of disturbance on the succession of the Krakatau islands (Rakata, Sertung, Panjang). The hierarchical model of succession by S. Pickett and colleagues (1987) was adopted as a research framework, and provided the basis for an alternative model of succession on Krakatau that focuses on processes rather than successional pathways. Investigations were conducted on (i) the meso-scale, and (ii) the patch-scale, (i) quantified the recent disturbance regime, and inter- and intra-island differences in diversity, (ii) compared sapling performance (growth, mortality and recruitment), and species compositional patterning in space and time for saplings and the seed bank with respect to island, gap size and severity of disturbance. Multivariate techniques were used, and amongst other attempts at characterising the light environment, hemispherical photography was employed. For the first time the effect of a continuous period of volcanic activity (1992-1995) of Anak Krakatau could be directly quantified and compared between Panjang and Sertung (ash-affected) and Rakata (receiving no ash). Increased rates of gap formation in the volcanically active period in comparison to the previous decade were found for all islands. This supports the disturbance-driven model of Whittaker and colleagues. However, an extension is required, because, contrary to expectation, Rakata also experienced more disturbance. This increase is argued to be a result of more severe weather conditions, and an increased number of earth tremors, during times of volcanic activity. The disturbance factors of extreme climatic events (e.g. ENSO events) and human impact are also proposed for inclusion in the alternative model. Drought associated with the 1994 El Niño is of relevance to short-term and potential long-term impact on regeneration dynamics and succession. Attention was drawn to the local human influence of pumice mining on the coastal forests. Supporting previous findings on the plot- and whole island scales, data from species presence/absence transects established that species richness and beta-diversity on the ash- affected islands was also lower on the meso-scale. Panjang's canopy composition is less uniform, and locally more species-rich than Sertung's. More evidence of the suggested decline of the mono-dominant species Neonauclea calycina and Timonius compressicaulis was gathered. The third dominant, Dysoxylum gaudichaudianum, is expanding in the lowlands of all islands. This is aided by its ability to regenerate in moderate shade, to grow rapidly in gap environments, and its tolerance of ash-fall, drought and herbivory. However, on Rakata, it is not expected to become generally mono-dominant because a considerable number of other potential canopy species are present. Sapling performance and species composition and its changes were in general strongly affected by ash-fall and drought. These factors tended to override effects of gap size and severity of disturbance. Advance regeneration, and the composition of the local forest type were identified as important factors influencing the composition of the early stages of gap-fill. The local forest type also seemed to contribute most to seed bank composition. As rarer species tended to have clumped distributions, and 'safe sites' for regeneration seemed not to be limiting, dispersal constraints were argued to be the most likely factors slowing diversification, unless further severe volcanic disturbance leads to successional set-back. The latter also strongly limits the predictability of succession on Krakatau.
27
Hürlimann, Marcel. "Geotechnical analysis of large volcanic landslides: The La Orotava events on Tenerife,Canary Islands." Doctoral thesis, Universitat Politècnica de Catalunya, 1999. http://hdl.handle.net/10803/6217.
Анотація:
Los grandes deslizamientos volcánicos son uno de los procesos geológicos más devastadores y pueden representar un importante peligro para la población de las zonas volcánicas. Este tipo de deslizamientos puede sobrepasar volúmenes de decenas o incluso centenares de kilómetros cúbicos. En Tenerife, siete grandes deslizamientos han afectado durante los últimos ~6 millones de años la morfología subaérea y submarina de la isla.En este estudio se ha realizado un extenso análisis de los eventos que han formado el valle de "La Orotava" en la parte Norte de Tenerife. El estudio incluye una investigación de campo, ensayos de laboratorio y análisis de estabilidad. En el laboratorio, las propiedades mecánicas de un suelo residual han sido investigadas mediante cortes directos y ensayos triaxiales. Durante el análisis de estabilidad, los resultados de los ensayos de laboratorio han sido incorporados a diferentes tipos de modelos de estabilidad. Finalmente, las condiciones mecánicas de los modelos dos y tres dimensionales han sido estudiados mediante el método de equilibrio límite y métodos de elementos finitos.
Los resultados de los análisis revelan que la estabilidad de las laderas volcánicas puede ser reducida debido a diversos factores, como geológicos, morfológicos, climáticos y volcánicos. Los suelos residuales - bastante comunes en Tenerife - pueden haber actuado como superficie de rotura a causa de su débil comportamiento mecánico. Por otra parte, los estrechos y profundos barrancos han definido los límites laterales de los deslizamientos. Además de ello, los acantilados, el clima húmedo y especialmente la constante intrusión de diques, han llevado la ladera a condiciones de estabilidad críticas. Finalmente, una aceleración sísmica causada por un seísmo fuerte y cercano provocó muy probablemente el deslizamiento catastrófico.
En Tenerife, se ha observado una relación temporal entre los colapsos de caldera y los grandes deslizamientos, lo que permite suponer que los fuertes terremotos asociados a los colapsos de caldera hayan provocado los deslizamientos.
Large volcanic landslides are one of the most hazardous of geological processes. They have occurred about once every 25 years during the last 500 years, and are a serious risk for the population due to their great volume and mobility. In spite of their destructive potential there are few comprehensive studies analysing large landslides on volcano flanks, and the mechanisms of such mass movements are not yet resolved. Within the last few years, several hypotheses concerning the potential causes of volcanic landslides have been proposed including processes such as dike intrusion, volcanic spreading, hydrothermal alteration, seismic shocks and caldera collapse events.
Tenerife exhibits three large subaerial valleys originated by giant flank failures with ages ranging from Upper Pliocene to Middle Pleistocene. The northern submarine flank of the island is characterised by a voluminous apron of landslide debris. The La Orotava valley has been selected for analysis due to the amount of available data concerning its structure and evolution, and has been used as a test site to validate new assumptions that could be applied to other volcanic areas.
The site investigation has revealed that the present morphology of the La Orotava valley was formed by two different failures: one in the western sector and the other in the eastern sector. The mechanical stability of the preslide volcano flank was strongly reduced by geologic, morphologic, climatic and volcanological factors which play a fundamental role in the initiation of the landslides. Widespread residual soils (paleosols) might have acted as potential slip surfaces, while deep erosive canyons probably evolved into the lateral limits of the failures. A high coastal cliff and a humid climate have also contributed to the critical stability conditions. The location of the landslide amphitheatre is perpendicular to the active Dorsal rift zone and adjacent to the Las Cañadas caldera, both important influences on the stability of the volcano slopes. On Tenerife, the relationship between large volcanic landslides and vertical caldera collapses is supported by a temporal coincidence of at least two failures with caldera collapse events.
The mechanical behaviour of a residual soil sampled in the La Orotava valley has been analysed. Red coloured residual soils are generally located at the top of phonolitic pyroclastic deposits and are proposed as potential slip surfaces due to their very weak behaviour and their flat, homogeneous characteristics. They represent the only planar surface within the succession making up the volcano slopes. Their weak mechanical behaviour is characterised by volumetric collapse during shearing, a substantial reduction of shear strength for high normal stresses, and a significant increase of pore water pressure during undrained loading. The last feature is fundamental to the stability of volcano flanks since it strongly reduces the soil strength. Earthquakes, common processes in active volcanic areas, and saturated conditions can generate high excess pore pressures indicating the importance of regional climate and seismicity.
The stability analysis has considered three different mechanisms: 1) ground acceleration due to seismicity - including both tectonic earthquakes and volcano-tectonic seismic shocks produced by caldera collapse; 2) horizontal stress due to dike intrusion, and; 3) vertical shear stress due to caldera collapse. The results indicate that ground acceleration principally decreases the mechanical stability of volcano flanks, enabling failure. Horizontal stresses due to dike intrusion can also influence slope stability, but preferably act as a preparing factor destabilising the slope, and not as a final triggering mechanism. The 3D numerical simulations show the significant effect of deeply incised canyons creating high shear stress at their base.
Applying the results to the La Orotava events, the following scenario is assumed: First, deep narrow canyons, weak residual soils, humid climate, coastal cliff and persistent dike intrusion have significantly reduced the mechanical stability of the volcano slope and determined the limits of the failing mass. Then, seismicity generated by the caldera collapse episode at the end of the Guajara cycle at ~0.56 Ma triggered the catastrophic landslides.
The results of the mobility analysis show the important influence of water on the runout distances of landslides. Subaqueous drag forces reduce the velocity, while hydroplaning effects strongly increase the runout distance. For Tenerife, the model indicates that a sliding mass can advance great distances, tens of kilometres away from the island, at water depths exceeding 3000 m, as can be observed in the bathymetric data.
28
Oladottir, Bergrun Arna. "Holocene eruption history and magmatic evolution of the subglacial volcanoes, Grimsvötn, Bárdarbunga and Kverkfjöll beneath Vatnajökull, Iceland." Clermont-Ferrand 2, 2009. http://www.theses.fr/2009CLF21940.
Анотація:
Dans le but d'étudier l'activité volcanique et l'évolution magmatique des volcans sous-glaciaires de Grimsvötn, Bárdarbunga et Kverkfjöll, des téphras ont été systématiquement échantillonnés au sein de profils établis dans les sols autour du glacier de Vatnajökull en Islande. La composition en éléments majeurs de 921 échantillons de téphra a été analysée par microsonde, ce qui a permis, par comparaison avec la composition chimique des différents produits émis par ces systèmes volcaniques, de déterminer leur provenance. Les nouveaux résultats indiquent 3 groupes de composition distincts, présentant chacun des variations cohérentes avec une évolution cotectique. Si l'identification de ces groupes améliore la distinction compositionnelle entre les produits émis par les 3 systèmes volcaniques étudiés, une légère superposition des compositions demeure néanmoins entre ces différents groupes. L'analyse in situ des teneurs en éléments traces par ICP-MS à ablation laser permet toutefois d'affiner leur distinction. Ensemble, l'analyse des teneurs en éléments majeurs et traces permet d'améliorer significativement l'identification de la provenance des téphras basaltiques holocène qui peuvent avoir des compositions en éléments majeurs similaires autour de Vatnajökull. Régionalement, les profils étudiés dans les sols sont corrélés les uns avec les autres en utilisant des niveaux de téphras marqueurs clefs, et les unités intermédiaires sont corrélées grâce à des outils stratigraphiques et à leur composition chimique. Approximativement, 70% des couches de téphras viennent de Grimsvötn, Bárdarbunga ou Kverkfjöll. La fréquence éruptive de Grimsvötn indique que c'est le système volcanique le plus actif, suivi de Bárdabunga. En revanche, Kverkfjöll présente une activité épisodique avec des périodes de repos supérieures au millier d'années. La diminution de la fréquence éruptive observée il y a 2000-5000 ans dans les 3 systèmes volcaniques, est liée à une diminution de l'activité volcanique et non à des facteurs environnementaux. Pendant la préhistoire, une différence d'âge de 1000-3000 ans a été observée entre les pics d'activité à l'aplomb du panache mantellique (Grimsvötn et Bardarbunga) et les pics d'activité des volcans localisés au sud-ouest, dans la partie hors-rift de la Zone Volcanique Est (ZVE ; e. G. Kalta). Ceci suggère qu'une importante augmentation de l'activité volcanique dans cette partie du ZVE est attendue dans un futur proche car la fréquence éruptive maximum a été observée il y a 1000-2000 ans à Grimsvötn et Bárdarbung. L'évolution magmatique des 3 systèmes volcaniques étudiés est contrôlée par les processus de cristallisation fractionnée et de contamination crustale. Les teneurs en éléments traces indiquent des minéralogies similaires dans les différentes sources magmatiques sous les 3 volcans. Ceci permet alors d'accéder aux conditions relatives de fusion partielle du manteau source : Bárdarbunga à l'aplomb du centre du panache mantellique islandais produit des basaltes issus de plus forts degrés de fusion alors que les plus faibles degrés de fusion sont atteints sous Kverkfjöll, plus loin du centre du panache. Une source magmatique profonde semble avoir joué un rôle important dans l'activité de Grimsvötn et Bárdarbunga, avec un système de sills et dykes plus actif sous le système volcanique de Grimsvötn pendant la période de plus forte fréquence éruptive. Ce système a évolué en chambre magmatique il y a environ 1000 ans, ce qui explique les plus faibles fréquences éruptives observées à cette période. Un lien direct semble lié la fréquence éruptive à l'architecture de la chambre magmatique. Les variations de composition des basaltes issus de Grimsvötn et Bárdarbunga sont consistantes avec la présence d'une chambre magmatique active en profondeur
29
Ellam, R. M. "The transition of calc-alkaline to potassic volcanism in the Aeolian Islands, southern Italy." Thesis, Open University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377343.
30
Ablay, Giray Jan. "Evolution of the Teide-Pico Viejo volcanic complex and magmatic system, Tenerife, Canary Islands." Thesis, University of Bristol, 1997. http://hdl.handle.net/1983/34b7cffc-09b2-4fc7-8f8b-f331abccd9ad.
31
Paulson, Benjamin D. DeBari Susan M. "Magmatic processes in the Jurassic Bonanza arc : insights from the Alberni region of Vancouver Island, Canada /." Online version, 2010. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=331&CISOBOX=1&REC=3.
32
Milluzzo, Vincenzo. "Seismic chacterization of Vulcano island and Aeolian area by tectonic and seismo-volcanic events." Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1330.
Анотація:
We investigated the relationship between seismo-volcanic events, recorded at La Fossa crater of Vulcano (Aeolian Islands, Italy) during 2004-2009, and the dynamics of the hydrothermal system. During the period of study, six episodes of increasing numbers of seismo-volcanic events took place at the same time as geothermal and geochemical anomalies were observed. These geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids. Four classes of seismic events (long period, high frequency, monochromatic and tornillos events), characterised by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly below La Fossa crater area at depths of 0.5 1.1 km b.s.l., were space-distributed according to the classes. Based on their features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms, the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed, such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system.
After careful analysis of the seismo-volcanic events of the Aeolian Islands area, the attention was paid to the tectonic events, in order to find possible relationships with the volcanic activity in the area. The aim of this part of the thesis was to identify spatial clusters of earthquakes, locate active seismogenic zone and their relationships with the volcanic activity in the Aeolian Islands.
High precision locations were performed in the present thesis, by applying the concept of the velocity model-hypocentres joint inversion and earthquake relocations, along with an analysis of the fault plane solutions. In order to improve our knowledge on the active seismo-tectonics areas we exploited a dataset encompassing 351 events recorded during a 17 year period (1993-2010). Overall, our results show that part of the seismicity is clustered along active seismogenic structures that concur with the main regional tectonic trends whose activity furnishes new elements to better understand the dynamics of the area.
A cluster of 24 events in the northern part of Vulcano, NE-SW oriented, marks the presence of a structure that seems to play a key role in magma uprising at Vulcano. These earthquakes suggest the existence of a seismogenic structure (passing just below Vulcanello), which could be interpreted as a discontinuity linking the two magma accumulation zones, thereby representing a possible preferential pathway along which magma may intrude as well as being responsible for fluid migration toward the surface.
The results presented in this thesis suggest that the comparison of seismic, ground deformation and temperature data can be useful for better understanding the dynamics of a complex volcano-hydrothermal system, including a better definition of the origin of a volcano unrest, and hence for improving the estimation of the level of the local volcanic hazard.
33
[Verfasser], Budi Joko Purnomo, Thomas [Akademischer Betreuer] Pichler, and Peter [Akademischer Betreuer] LaFemina. "Geothermal systems in the Sunda volcanic island arc : Investigations on the islands of Java and Bali, Indonesia / Budi Joko Purnomo. Gutachter: Thomas Pichler ; Peter LaFemina. Betreuer: Thomas Pichler." Bremen : Staats- und Universitätsbibliothek Bremen, 2015. http://d-nb.info/1072304244/34.
34
Crosweller, Helen Sian. "An analysis of factors influencing volcanic risk communication on two islands in the Lesser Antilles." Thesis, University of East Anglia, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514282.
Анотація:
This thesis presents a comparative study into factors influencing volcanic risk communication on the islands of St Vincent and Dominica in the Lesser Antilles. A strong focus was placed on inter-island differences that could be attributed to variations in hazard experience. Communication about volcanic hazards is currently focused on awareness raising and encouraging preparedness in an attempt to minimise the impact of future eruptions. This is often a one-way `top-down' process with the content being determined by what the `experts' believe the public need to know. This approach has been found to be ineffective in communicating information about a range of hazards as the expert view of the lay person's knowledge is often inaccurate. The mental models approach provides a structured methodology for identifying and comparing expert and lay views to target future information more effectively. This research constitutes the first use of the mental models approach to volcanic hazards to date. A mixed methods approach was used, with qualitative data from semi-structured interviews used to initially explore the issues, followed by a quantitative questionnaire to investigate these issues in further detail and test for their prevalence within the populations. A wide range of topics were covered including the behaviour of volcanic systems and associated hazards, sources of communication, and levels of trust in a range of actors. This thesis finds that the populations on these islands have a reasonable idea of the volcanic hazards and the expected safest locations during an eruption. They are aware of uncertainties involved in predicting volcanic activity. However, this has not had a detrimental effect on trust in scientists and hazard managers; this remains high on both islands. Personal sources are afforded greater trust and utilised more often on St Vincent. A number of `risky beliefs' exist in the population, which could have dangerous consequences during a crisis. Many of these appear to be related to hazard experience. Recommendations as to how these issues should be tackled in future campaigns are discussed. Significant inter-island differences suggest that volcanic hazards information should be context specific in order for it to be most effective
35
Martin, Erwan. "Etude géochimique des magmas acides d'Islande : mode de genèse, implications sur l'évolution géodynamique islandaise et sur la formation de la proto-croûte continentale." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2006. http://tel.archives-ouvertes.fr/tel-00717368.
Анотація:
L'approche principalement géochimique menée (éléments majeurs et en trace, 87Sr/86Sr, 143Nd/144Nd, etdelta 18O) a montré que : tout au long de l'histoire de l'Islande, le gradiant géothermique résultant de l'interaction ride-panache mantellique favorise la genèse des magmas acide par fusion partielle de la croûte métabasaltique au centre de l'île et par cristallisation fractionnée en périphérie. En se basant sur le point précédent et des échantillons datés, un modèle d'évolution géodynamique de l'Islande a pu être établit afin de rendre compte de la largeur anormalement élevée de l'île. La comparaison des roches acides (roches "continentales") émises en Islande, à Hawaï et à Kerguelen, avec celles de la croûte continentale primitive (TTG) a montré que les plateaux océaniques n'ont pas été un environnement favorable lors de la genèse de la croûte primitive.
36
Wainwright, Alan John. "Volcanostratigraphic framework and magmatic evolution of the Oyu Tolgoi porphyry Cu-Au district, South Mongolia." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2760.
Анотація:
The super-giant Oyu Tolgoi porphyry copper-gold deposits in the South Gobi
desert, Mongolia, consist of multiple discrete porphyry centers aligned within a north-northeast trending, >6.5 km long, arc-transverse mineralized corridor. The porphyries are linked to a tectono-magmatic event at ~372 Ma within a Devonian to Carboniferous volcanic arc, and U-Pb (zircon) geochronology records magmatic activity from ~390 Ma to ~320 Ma. The Oyu Tolgoi district underwent at least three discrete periods of syn- to post-mineral shortening and there is evidence for at least three unconformities within the Paleozoic sequence. Although the deposits were formed in an active orogenic
environment characterized by rapid uplift, their preservation is a reflection of climactic effects as well insulation from erosion by rapid burial under mass-wasted and pyroclastic material in the volcaniclastic apron of late-mineral dacitic volcanoes.
The porphyry copper-gold deposits are spatially and temporally related to
medium- to high-K calc-alkaline quartz monzodiorite (~372 Ma) and granodiorite (~366
Ma) intrusive phases that comprise the Late Devonian Oyu Tolgoi Igneous Complex
(OTIC). Adakite-like wholerock compositions as well as zircon grains with high
CeN/CeN*, EuN/EuN* and Yb/Gd in the sample populations from syn- and late-mineral
porphyry intrusions are different from younger intrusions that are not related to porphyry Cu-Au deposit formation. Moreover, mixed zircon populations within OTIC intrusions indicate that efficient assimilation of material from different host rocks by a convecting magma chamber occurred.
Mafic to intermediate volcanic units evolved from tholeiitic to calc-alkaline compositions, which is interpreted to be a reflection of marine arc maturation and
thickening. Felsic rock suites are dominantly high-K calc-alkaline, regardless of age.
Nd-isotopic geochemistry from all suites is consistent with magma derivation from
depleted mantle in an intra-oceanic volcanic arc and lead isotopic compositions indicate
that the sulfides in the porphyry Cu-Au deposits are genetically linked to the Late
Devonian magmas.
Magma mixing, adakite-like magmatism and rapid uplift and erosion in a juvenile
marine arc setting differentiate the ore-stage geologic environment at Oyu Tolgoi from other settings in active and fossil volcanic arcs.
37
Scotney, Philip M. "The geology and genesis of massive sulphide, barite-gold deposits on Wetar Island, Indonesia." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273876.
38
De, Joux Alexandra. "Cosmos greenstone terrane : insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistry." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8918.
Анотація:
The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.
39
Meschiari, Sara <1992>. "Eruptive and depositional processes of widely dispersed volcanic ash: Insights from the Brown Tuffs (Aeolian Islands)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9970/1/Meschiari_Sara_tesi.pdf.
Анотація:
This is a multidisciplinary study of the Brown Tuffs (BT) ash deposits of the Aeolian Islands in northern Sicily and representing the most voluminous and widely distributed tephra deposit in this region. A large dataset of major and minor elements of the BT glass has defined a range from K-series basaltic-andesites and trachy-andesites through to tephri-phonolites and trachytes that is consistent with the Vulcano magmatic system. Combined with stratigraphic information and new radiocarbon ages, four stratigraphic macro-units are defined: the Lower (80-56 ky; LBT), Intermediate (56-27 ky; IBT), Intermediate-upper (26-24 ky; IBT-upper) and Upper BT (24-6 ky; UBT). Glass compositional data provide constraints on proximal-distal correlations of the BT with deep-sea tephra layers in the Tyrrhenian and Adriatic Seas and new insights on the definition of the dispersal area of the BT eruptions. Sedimentological evidence of massive to stratified deposits and shear-related structures, coupled with grain-size and componentry analyses, have allowed to interpret the BT as the result of laterally-spreading, concentrated ash-rich PDCs, with a high potential of erosion of the substratum. Shear-structures similar to those observed in the field in the BT deposits have been reproduced by small-medium scale laboratory experiments carried out on ash granular flows, which have also allowed to describe the behaviour of ash-rich PDcs and their mobility depending on variations of slope-ratio, grain size and flow channelization. The resulting integrated dataset provides a contribution to the knowledge of the BT eruptions and insights on long-term hazard assessment in the study area. The eruptive dynamics of the BT may have a role in characterizing the whole magmatic system of the La Fossa Caldera on Vulcano, in the light of the geochemical link highlighted between the UBT macrounit and the early products of the La Fossa cone.
40
Smith, Daniel James. "From slab to sinter : the magmatic-hydrothermal system of Savo Volcano, Solomon Islands." Thesis, University of Leicester, 2008. http://hdl.handle.net/2381/8207.
Анотація:
This PhD was made possible by funding from the Natural Environment Research Council and the British Geological Survey. Additional funds came from the Society of Economic Geologists, Robert’s Skills Fund, Whitaker Fund, the Mineralogical Society and the Geochemical Society.
41
Scott, Craig Russell. "Physical volcanology, stratigraphy, and lithogeochemistry of an archean volcanic arc : evolution from plume-related volcanism to arc rifting within the SE Abitibi Greenstone Belt, Val d'Or, Quebec, Canada." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2005. http://theses.uqac.ca.
42
Gilbert, Ian Michael. "Volcaniclastic sedimentation associated with active and ancient island volcanoes : White Island, New Zealand and Snowden, North Wales." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358934.
43
Tsoukalas, Nikolaos. "Stratigraphy of the Upper Miocene volcanic rocks of the Island of Kos, Greece : geodynamic implications /." Halifax, N.S. : Saint Mary's University, 2008.
44
Thomas, Kelly Jean. "Volcanology and petrology of submarine volcanoes of the New Hebrides island arc." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/45480/1/Kelly_Thomas_Thesis.pdf.
Анотація:
The New Hebrides Island Arc, an intra-oceanic island chain in the southwest Pacific, is formed by subduction of the Indo-Australian Plate beneath the Pacific Plate. The southern end of the New Hebrides Island Arc is an ideal location to study the magmatic and tectonic interaction of an emerging island arc as this part of the island chain is less than 3 million years old. A tectonically complex island arc, it exhibits a change in relative subduction rate from ~12cm/yr to 6 cm/yr before transitioning to a left-lateral strike slip zone at its southern end. Two submarine volcanic fields, Gemini-Oscostar and Volsmar, occur at this transition from normal arc subduction to sinistral strike slip movement. Multi-beam bathymetry and dredge samples collected during the 2004 CoTroVE cruise onboard the RV Southern Surveyor help define the relationship between magmatism and tectonics, and the source for these two submarine volcanic fields. Gemini-Oscostar volcanic field (GOVF), dominated by northwest-oriented normal faults, has mature polygenetic stratovolcanoes with evidence for explosive subaqueous eruptions and homogeneous monogenetic scoria cones. Volsmar volcanic field (VVF), located 30 km south of GOVF, exhibits a conjugate set of northwest and eastwest-oriented normal faults, with two polygenetic stratovolcanoes and numerous monogenetic scoria cones. A deep water caldera provides evidence for explosive eruptions at 1500m below sea level in the VVF. Both volcanic fields are dominated by low-K island arc tholeiites and basaltic andesites with calcalkalic andesite and dacite being found only in the GOVF. Geochemical signatures of both volcanic fields continue the along-arc trend of decreasing K2O with both volcanic fields being similar to the New Hebrides central chain lavas. Lavas from both fields display a slight depletion in high field strength elements and heavy rare earth elements, and slight enrichments in large-ion lithophile elements and light rare earth elements with respect to N-MORB mantle. Sr and Nd isotope data correlate with heavy rare earth and high field strength element data to show that both fields are derived from depleted mantle. Pb isotopes define Pacific MORB mantle sources and are consistent with isotopic variation along the New Hebrides Island Arc. Pb isotopes show no evidence for sediment contamination; the subduction component enrichment is therefore a slab-derived enrichment. There is a subtle spatial variation in source chemistry which sees a northerly trend of decreasing enrichment of slab-derived fluids.
45
Andrew, Anne. "Lead and strontium isotope study of five volcanic and intrusive rock suites and related mineral deposits, Vancouver Island, British Columbia." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26953.
Анотація:
Lead isotope compositions have been obtained from five major volcanic and intrusive rock suites and several ore deposits on Vancouver Island. Lead, uranium and thorium concentrations and strontium isotope ratios have been obtained for a subset of these samples. The rock suites examined are the Paleozoic Sicker Group, Triassic Karmutsen Formation, Jurassic Island Intrusions and Bonanza Group volcanic rocks, and the Eocene Catface intrusions.
Isotope geochemistry of the Sicker Group is consistent with the interpretation that it formed as an island arc. Relatively high 207pb/204pb ratios indicate sediment involvement in the subduction process, which suggests that the Sicker Group formed close to a continent. Buttle Lake ore deposits display decreasingly radiogenic lead isotope ratios with time, suggesting that the associated magmas become increasingly primitive. This supports the hypothesis that these deposits formed during the establishment of rifting in a back-arc environment.
Karmutsen Formation flood basalts display isotopic mixing between an ocean island-type mantle source and average crust. Isotopic evidence is used to support a Northern Hemisphere origin for these basalts.
Mixing is apparent in the lead and strontium isotope signatures of the Island Intrusions and Bonanza Group volcanic rocks, between depleted mantle and crustal (possibly trench sediments) components. This is consistent with formation of these rocks in an island arc environment.
Eocene Catface intrusions have relatively high 207pb/204pb indicating that crustal material was involved in their formation. There are two groups of plutons corresponding to an east belt and west belt classification. Galena from the Zeballos mining camp related to the Eocene Zeballos pluton indicates that the mineralization was derived from the pluton.
Galena lead isotope data from Vancouver Island may be interpreted in a general way by comparison with data from deposits elsewhere of known age and origin. No single growth curve model can be applied. Lead isotope characteristics of Vancouver Island are clearly different from those of the North American craton, reflecting the oceanic affinities of this terrane.
A new technique has been developed to compare 207pb/204pb ratios between samples with differing 206pb/204pb ratios. The procedure projects 207pb/204pb ratios along suitable isochrons until they intersect a reference value of 206pb/204pb. This technique can be used for interpreting lead isotope data from old terranes, in which lead and uranium may have undergone loss or gain, and if lead and uranium abundances have not been measured.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
46
Kraus, Stefan. "Magmatic dyke systems of the South Shetland Islands volcanic arc (West Antarctica) reflections of the geodynamic history /." Diss., [S.l.] : [s.n.], 2005. http://edoc.ub.uni-muenchen.de/archive/00003827/.
47
Moore, Lowell. "The volatile contents of melt inclusions and implications for mantle degassing and ocean island evolution." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/93345.
Анотація:
The amount of volatile elements dissolved in silicate melts is a controlling factor in a range of geologic processes, which include hazardous volcanic eruptions, economically-significant ore-forming systems, and global-scale volatile fluxes, which contribute to planetary evolution. While melt volatile contents are important, estimating the origin and fate of volatiles distributed within magmas is challenging because volatiles exsolve from the melt during eruption and are transferred into the atmosphere. Therefore, the stratigraphic record of volcanic and intrusive deposits does not contain direct information regarding the pre-eruptive volatile content of the melt. However, melt inclusions trapped within growing phenocrysts present an opportunity to sample the melt before it has completely degassed. Analysis of melt inclusions is challenging owing to a range of processes which occur after the melt inclusion is trapped and which overprint the original texture and composition of the inclusion at the time of entrapment. Thus, efforts to accurately determine the current composition of the melt inclusion sample and then infer the original composition of the trapped melt which that inclusion represents require a combination of microanalytical, numerical, and/or experimental methods.
In Chapter 1, we present a pedagogical approach for estimating the processes that affect the CO2 content of a magma from its origin during melting a C-bearing source material to its exsolution into a free fluid phase during crystallization and degassing. In Chapter 2, we explore different experimental, microanalytical, and numerical methods which may be used to estimate the CO2 contents of melt inclusions that contain fluid bubbles and describe the advantages and disadvantages of each approach. In Chapter 3, we apply some of the methods discussed in the previous chapters to estimate the pre-eruptive volatile content of Haleakala Volcano (Maui) and assess different melting mechanisms that may be active in the Hawaiian plume.Doctor of Philosophy
Volcanoes are features which form on the Earth’s surface and are located above regions where material melts tens of kilometers (or more) below the surface. The process of melting is studied through laboratory experimentation, and therefore it is possible to estimate the composition of deep subsurface material based on the compositions of volcanic rocks which can be sampled on the Earth's surface. This sub-discipline of geologic research is called "igneous petrology." A fundamental problem in igneous petrology is estimating the volatile content of the Earth's deep interior. Volatile elements are those elements such as hydrogen and carbon, which are stable as gasses in the atmosphere rather than in the mineral components of a rock. It is thought that the gasses produced from volcanic vents, of which the compositions are well known, represent volatile elements which were originally present as dissolved components in the melt. Experiments performed on volcanic rocks have demonstrated that volatile elements can be dissolved in melts at high pressures corresponding to depths within the Earth's crust, and these elements exsolve from the melt when it approaches the surface -- similar to how CO2 can be dissolved in a carbonated beverage, which bubbles out when the beverage is opened. The only geologically-persistent features which preserves the pre-eruptive volatile content of a melt (i.e. how much gas was dissolved before eruption) are droplets of melt which are accidentally trapped within crystals that grow from the melt as it cools near the Earth's surface -- these are called "melt inclusions." While melt inclusions are useful in this regard, they are challenging to apply to geologic problems because they undergo a range of physical and chemical changes after they are trapped, which can alter their composition from the original composition of the melt that was trapped. This dissertation concerns the theory used to infer how volatile elements are distributed within the deep Earth, analytical and numerical methods used to gather relevant information from melt inclusion samples, and an application of these methods to investigate the volatile content of the mantle below Hawaii. Chapter 1 describes a framework for systematically determining the amount of CO2 distrubuted within a given volcanic setting. Chapter 2 compares different methods used to estimate the original volatile content of melt inclusions from Kamchatka, which have formed fluid bubbles -- a common feature present in melt inclusions. Chapter 3 applies the methods described in the first two chapters to estimate how volatile elements are distributed within the Earth's mantle below Hawaii, and how the process of melting transfers them to the Earth's atmosphere.
48
Win, Noel Antony. "Formation of Fe-rich subsurface precipitate layers on White Island, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2014. http://hdl.handle.net/10092/9660.
Анотація:
White Island is a highly active volcano with an acidic, S-rich hydrothermal system in the Bay of Plenty, North Island, New Zealand. In this acidic environment a series of subsurface Fe-rich layers are ubiquitous in the crater sediments at shallow depth and are capable of modifying the flow and gas flux dynamics in the system. The mineralogy of the subsurface Fe-rich layer(s) and the processes leading to their formation are unknown. Here the mineralogy and formation of the subsurface Fe-rich layers in relation to the surface and subsurface environment(s) within the Main Crater at White Island are assessed. Based on geochemical analyses, subsurface Fe-rich crusts are composed of a mix of jarosite and goethite, cementing crater fill sediments into cohesive layers. Saturation index (SI) and Eh/pH assessments identify that fluids evolved at White Island are undersaturated with respect to the mineral phases present in the Fe-rich subsurface layers. Formation of the Fe-rich subsurface layers is most likely related to the transition between atmospheric gases and/or meteoric water mixing with hydrothermal fluids. This transition zone creates an environment conducive to forming jarosite and goethite forming in the same layer. Additionally, subsurface sediments including the Fe-rich layers show a consistent organic carbon isotopic signature of -23 ‰. Microscopic investigations confirm diatoms and microbes are present in the subsurface Fe-rich layers. The full extent of microbial activity in relation to the Fe-rich layers at White Island still requires further investigation. Based on chemical extractions for isotopic analyses, Fe-rich layers are shown to preserve δ¹³C signatures indicative of microbial life. Interface zones such as those identified in the hydrothermal environment at White Island can create metal-rich deposits and habitable/preservative microbial environments as well as affecting the macroscopic dynamics of volcanic and epithermal systems.
49
Henriot, Olivier. "La déformation actuelle au nord de l'Islande, à la jonction entre un rift et une transformante : mesure par InSAR et modélisation d'un système volcano-tectonique actif." Chambéry, 2003. http://www.theses.fr/2003CHAMS018.
Анотація:
Ce travail consiste en une étude de déformation portant sur le Nord de l'Islande, en employant la méthode InSAR DIAPASON, sur la période post-rifting (92-02) qui fait suite à l'épisode de rifting majeur de Krafla (75-94). Deux types de signaux ont été identifiés : - un signal local, autour du volcan Krafla, affectant une zone de 10 x 30 km, et marqué par un mouvement essentiellement subsidant de vitesse constante (3 cm. An-1 au maximum). Ce signal posséderait une source peu profonde (entre 6 et 3 km) composée d'une chambre magmatique prolongée au Nord et au Sud par des sills. - un signal régional affectant l'ensemble de la zone étudiée (100 x 10 km) révélé au premier ordre dans les interférogrammes radar par des franges parallèles en direction N20ʿE. Le nombre de franges augmente linéairement avec le temps. Celles ci pourraient correspondre à des vitesses de déplacement avec composante horizontale et verticale, dont les modèles de croûte purement élastique ne peuvent rendre compteThis work consists of a study of North Iceland using the DIAPASON InSAR method over the 1992-2002 post-rifting period which immediately follows the Krafla 1975-1984 major rifting episode. Two types of signal have been identified : - A local signal, around Krafla volcano, affecting a 10 x 30 km area, essentially marked by a vertical subsidence signal at a constant rate (3 cm/y maximum). The signal source appears to be shallow (3 to 6 km depth) and made up of a magma chamber prolonged north and south by sills. - A regional signal affecting the whole of the studied area (100 x 10 km) revealed to the first order by parallel N 20ʿE fringes in the interferograms. The number of fringes increases linearly with time. This signal may represent displacements with both horizontal and vertical components which purely elastic crust models cannot properly account for
50
Bullard, Elizabeth. "Compositional variability of Pleistocene land snail assemblages preserved in a cinder cone volcano from Tenerife, Canary Islands." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470744125.