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1
Smith, R. T. "Eruptive and depositional models for units 3 and 4 of the 1.85 ka Taupo eruption: Implications for the nature of large-scale 'wet' eruptions." Thesis, University of Canterbury. Geological Science, 1998. http://hdl.handle.net/10092/5928.
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Phreatomagmatic eruptions result from the explosive interaction between magma and some external source of water, and produce deposits which are usually distinctive in nature from those of magmatic eruptions. The widespread deposits of large-scale phreatomagmatic eruptions (usually termed Phreatoplinian) are poorly studied relative to their magmatic counterparts and, consequently, current models for large-scale phreatomagmatic volcanism remain speculative. The Hatepe ash and Rotongaio ash (units 3 and 4 of the 1.85 ka Taupo eruption) are two classical widespread phreatomagmatic fall deposits. These have been examined in fine detail and sampled, for the first time, at a mm-scale, with the intention of quantifying vertical and lateral variations within these deposits and improving our understanding of the eruptive mechanisms and depositional processes during large-scale 'wet' eruptions.
The Hatepe ash (1.75 km3) is a widespread (>15 000 km2, individual subunit bt values = 4.4 to 5.5 km), multiple-bedded, poorly-sorted pumiceous fall deposit. The fines-rich character and widespread occurrence of ash aggregates in the proximal to medial dispersal areas are indicators of a phreatomagmatic origin. Subunits contain multiple layers with a wide range of dispersal and grain size characteristics, and a number of distinctive primary lithofacies have been defined which characterise the changes in eruptive conditions and main depositional modes during Hatepe volcanism. The
predominantly fine grained clasts (Mdø= 3.3-4.5), along with perhaps 20-25 wt.% liquid, were transported and deposited in the form of damp to wet 'mud lumps' and accretionary lapilli. Dispersal was from dense, 'wet' plumes which promoted the cohesion and aggregation of liquid-coated fine particles. This mode of transport and deposition was dominant during relatively long-lived episodes of relatively low discharge rate, with higher water/magma ratios at the vent and liquid/particle ratios in plumes. When magma discharge rate was relatively high and water/magma ratios low, fines-poor, plinian-style deposits (Mdø = -2.2 to 0.63) were produced by discrete particle fall from high (~25-30 km), relatively 'dry' plumes. Minor, short-lived fluctuations in discharge rate produced episodes of mixed discrete and ash aggregate fall which produced poly- and bimodal deposits (Mdø = 2.5-3) in proximal and inner-medial areas. Lateral emplacement by dilute, turbulent pyroclastic density currents was important in the proximal environment.
The range and indices of Hatepe ash juvenile clast vesicularities (50-90%, and 75% vesicles, respectively) indicate that fragmentation was driven by magmatic volatiles but that water played some part in quenching. The minimal variation in juvenile clast vesicularity through the deposit and between the facies types indicates that the state of the Hatepe magma remained a uniform foam, and that the mechanism of fragmentation (but not the water/magma ratio) was consistent throughout Hatepe volcanism.
Facies analysis and mapping of internal variations in ash dispersal confirm that the Hatepe ash is not the product of simple sustained magma discharge, but was actually the result of a continuous but highly irregular flux, with fluctuations in magma supply, sometimes over very short time intervals, resulting in a range of eruptive styles and depositional modes.
The Rotongaio ash (0.8 km3) is a widespread (>10 000 km2, subunit bt values = 2.9 to 5km), poorly-sorted fall deposit with abundant evidence for the important involvement of liquid water at the vent and in the plume. Modes of deposition were similar to the Hatepe ash; dominantly damp to wet mud lump fallout (Mdø= 3.9 to 5.5), but with minor episodes of discrete particle fall (Mdø = -1.1 to 1.9) and mixed discrete and aggregate fall (Mdø= 1.2 to 2.9) caused by fluctuations in discharge rate. An additional depositional mode in medial areas during Rotongaio volcanism was by dilute, turbulent density currents, derived from particle-laden downbursts from the umbrella region of dense, wet, convectively-unstable plumes. Such a process may account for occurrences of cross-stratification in the medial-distal parts of other widespread ash falls.
Secondary processes such as fluvial erosion and reworking, and soft-sediment deformation and slurry-flow were important depositional modes that operated syneruptively during Rotongaio (and Hatepe ash) volcanism. The very close association in time and space between primary and secondary lithofacies implies that there was a strong genetic link between the style of primary eruptive processes and the nature and extent of the secondary modification. In many cases the 'secondary' processes formed a continuum with primary depositional processes, influenced by the liquid/particle ratio of ash fallout and inherent to the mode of eruption. Throughout deposition of the Rotongaio ash a delicate balance always existed between primary accumulation, erosion and redeposition.
The Rotongaio ash differs from the Hatepe ash, and most other widespread ash fall deposits, in a number of important ways which indicate the Rotongaio ash is not a typical phreatoplinian deposit; 1) it is extremely finely laminated in proximal exposures and many of these beds cannot be traced into the medial environment indicating it is the product of multiple, discrete and non-sustained explosions which dispersed material along a number of axes and with a wide range of thinning rates, 2) juvenile clasts are mostly poorly- to non-vesicular and clast populations span a very wide range of densities (0-65% vesicles) indicating that the Rotongaio magma was partially degassed and heterogeneous (unlike the Hatepe ash and other pumiceous phreatoplinian deposits), and fragmentation was driven not by vesiculation, but largely by external volatiles, 3) the lack of any significant coarse component compared to the Hatepe ash at anyone site supports a fundamentally different mode of fragmentation for Rotongaio volcanism and vent processes which probably involved significant recycling of clasts through the vent.
Detailed analysis of the Hatepe ash and Rotongaio ash has provided some interesting insights into the nature of large-scale phreatomagmatic eruptions. Ash dispersal patterns for subunits of the two deposits indicate that 'wet' and 'dry' plumes, even of comparatively small magnitudes (0.02 to 0.8 km3 subunit volumes) behave in distinctive ways which hint at fundamentally different dynamics of dispersal. Assessment of lateral variations in clast size populations suggest the differences between proximal strongly fines-segregated 'dry' facies and the fines-rich 'wet' facies is an artefact controlled mostly by the initial liquid/solid ratio in the plume rather than the mechanism of fragmentation.
2
Hellwig, Bridget M. "The viscosity of dacitic liquids measured at conditions relevant to explosive arc volcanism determing the influence of temperature, silicate composition, and dissolved volatile content /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4597.
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Thesis (M.S.)--University of Missouri-Columbia, 2006.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.
3
Watson, Sarah Penelope. "Hotspots and volcanism." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386840.
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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.
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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 Tenerife<br>El 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
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Watt, Sebastian F. L. "Records of volcanism and controls on volcanic processes in southern Chile." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:41cf206e-2cef-4108-9267-5e9217aee96d.
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This thesis describes volcanic records from the Andean southern volcanic zone, based on the collection of field data between Calbuco and Puyuhuapi volcanic centres, with a particular focus on the Hualaihue peninsula, combined with existing records from the region as a whole. These data, extending the understanding of the volcanic history of southern Chile, are examined for evidence of spatial or temporal variability, which may be used to explore underlying controls on volcanic processes. All three volcanoes on the Hualaihue peninsula have been active in the Holocene. A large mafic scoria unit from Apagado is unusually primitive, providing a potential window into primary magma generation in the arc. Dynamically similar eruptions occurred at Hornopirén and widely along the regional scale Liquiñe-Ofqui fault zone (LOFZ). Although the Hualaihue centres are closely related, petrological evidence indicates a complex magmatic storage system. Effusive activity is predominant at Yate and Hornopirén, and the tephrostratigraphy of the Hualaihue area is dominated by units from Calbuco volcano, to the north. The 2008 eruption of Chaitén provided an analogue for past large explosive eruptions in the region, with tephra deposition reflecting variable eruption intensity in a changing wind field. The regional tectonic setting and the LOFZ influence dyke ascent, volcano morphology and, as demonstrated at Yate, edifice stability, determining the orientation of collapse. Explosive eruption records over the post-glacial period also indicate a limited response of volcanism to deglaciation, suggesting a control on magma storage arising from changing crustal stress regimes, both at the arc front and along the LOFZ. On short timescales, large earthquakes are shown to influence eruption rate across the arc, implying a triggering role for dynamic seismic stresses. This work demonstrates the existence of a range of external forces affecting Chilean arc volcanism, but the degree to which these are quantifiable is strongly constrained by the quality of the available data.
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Buck, Adrian. "The Mt. Marcella volcanics : middle Triassic convergent margin volcanism in Southeast Queensland." Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/20171/1/Adrian_Buck_Thesis.pdf.
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Triassic igneous rocks in southeast Queensland show a number of subduction related geochemical characteristics. Extensive calc-alkalic granitoids chains characterise the region and define the ancient arc setting. Despite good evidence that an arc was present, Triassic volcanic rocks are relatively sparse in southeast Queensland. The Mt Marcella Volcanics, of the northern Esk Trough are a previously poorly understood piece of the Middle Triassic convergent margin of southeast Queensland. A three stage model is proposed for the eruptive development of the Middle Triassic (245- 230Ma) volcanic succession that involves; 1) The Middle Triassic basalt, comprising coalesced lava flows covering as much as 500km2 with an estimated eruptive volume in the order of 50km3. 2) The Penwhaupell Volcanic Centre, a concentration of inter-bedded lavas and pyroclastic rocks dominated by dacite that forms a volcanic pile exceeding 2km stratigraphic thickness and representing an eruptive volume of approximately 48km3. 3) The Ettiewyn Caldera, representing the catastrophic culmination of the Mt Marcella Volcanics event, with a sequence of caldera out-flow and in-fill andesite ignimbrites and post-caldera lavas with a total eruptive volume in the order of 130km3. The “Penwhaupell Volcanic Centre” and the “Ettiewyn Caldera” are two new sub-divisions and the proposed names, for the lower and upper sequences of the previously undifferentiated Mt Marcella Volcanics. The Mt Marcella Volcanics magma compositions show cogenetic characteristics that define three evolutionary pathways; 1) a mildly alkali series, from basaltic-andesite to trachy-dacite related through fractionation dominated by plagioclase and clinopyroxene 2) an amphibole series, basaltic-andesite to hornblende dacite through fractionation dominated by plagioclase and hornblende under hydrous conditions, and 3) a pyroxene series, from basaltic-andesite to pyroxene andesite through fractionation dominated by plagioclase and pyroxene. Quantitative petrogenetic models generally support the proposed fractional crystallisation pathway, however weaknesses are acknowledged, with good results for the major elements and REE off-set by generally poor results for the LILE. Despite the inconclusive trace element results for the modelled fractionation, strong geochemical similarities and cogenetic relationships have been established. A typical arc-like geochemical signature including a pronounced Nb depletion characterises the Mt Marcella Volcanics. However, the geochemical character within the Middle Triassic volcanic succession reveals an unusual transition from an OIB character of the Middle Triassic basalts, to the Andean arc character of later Mt Marcella Volcanics. The implications of this could have profound impact on our understanding of how southeast Queensland’s Triassic tectonic setting operated by providing support for hotspot activity rather than subduction-driven activity.
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Buck, Adrian. "The Mt. Marcella volcanics : middle Triassic convergent margin volcanism in Southeast Queensland." Queensland University of Technology, 2008. http://eprints.qut.edu.au/20171/.
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Triassic igneous rocks in southeast Queensland show a number of subduction related geochemical characteristics. Extensive calc-alkalic granitoids chains characterise the region and define the ancient arc setting. Despite good evidence that an arc was present, Triassic volcanic rocks are relatively sparse in southeast Queensland. The Mt Marcella Volcanics, of the northern Esk Trough are a previously poorly understood piece of the Middle Triassic convergent margin of southeast Queensland. A three stage model is proposed for the eruptive development of the Middle Triassic (245- 230Ma) volcanic succession that involves; 1) The Middle Triassic basalt, comprising coalesced lava flows covering as much as 500km2 with an estimated eruptive volume in the order of 50km3. 2) The Penwhaupell Volcanic Centre, a concentration of inter-bedded lavas and pyroclastic rocks dominated by dacite that forms a volcanic pile exceeding 2km stratigraphic thickness and representing an eruptive volume of approximately 48km3. 3) The Ettiewyn Caldera, representing the catastrophic culmination of the Mt Marcella Volcanics event, with a sequence of caldera out-flow and in-fill andesite ignimbrites and post-caldera lavas with a total eruptive volume in the order of 130km3. The “Penwhaupell Volcanic Centre” and the “Ettiewyn Caldera” are two new sub-divisions and the proposed names, for the lower and upper sequences of the previously undifferentiated Mt Marcella Volcanics. The Mt Marcella Volcanics magma compositions show cogenetic characteristics that define three evolutionary pathways; 1) a mildly alkali series, from basaltic-andesite to trachy-dacite related through fractionation dominated by plagioclase and clinopyroxene 2) an amphibole series, basaltic-andesite to hornblende dacite through fractionation dominated by plagioclase and hornblende under hydrous conditions, and 3) a pyroxene series, from basaltic-andesite to pyroxene andesite through fractionation dominated by plagioclase and pyroxene. Quantitative petrogenetic models generally support the proposed fractional crystallisation pathway, however weaknesses are acknowledged, with good results for the major elements and REE off-set by generally poor results for the LILE. Despite the inconclusive trace element results for the modelled fractionation, strong geochemical similarities and cogenetic relationships have been established. A typical arc-like geochemical signature including a pronounced Nb depletion characterises the Mt Marcella Volcanics. However, the geochemical character within the Middle Triassic volcanic succession reveals an unusual transition from an OIB character of the Middle Triassic basalts, to the Andean arc character of later Mt Marcella Volcanics. The implications of this could have profound impact on our understanding of how southeast Queensland’s Triassic tectonic setting operated by providing support for hotspot activity rather than subduction-driven activity.
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Hartley, Margaret Elizabeth. "Post glacial volcanism and magmatism on the Askja volcanic system, North Iceland." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/5845.
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Postglacial activity on the Askja volcanic system, north Iceland, has been dominated by basaltic volcanism. Over 80% of Askja's postglacial basalts fall within a relatively narrow compositional range containing between 4 and 8 wt.% MgO. The 'main series' is further divided into two groups separated by a distinct compositional gap evident in major and trace element concentrations. The most evolved basalts formed by fractional crystallisation within shallow magma reservoirs, followed by the extraction of residual liquid from a semi-rigid, interconnected crystal network. This process is analogous to the formation of melt segregations within single lava flows, and was responsible for generating several small-volume, aphyric basaltic lavas erupted along caldera ring fractures surrounding the Oskjuvatn (Askja lake) caldera in the early 20th century. Further examples of evolved basalt are found throughout Askja's postglacial volcanic record. However, Askja's early postglacial output is dominated by more primitive compositions. Some of the most primitive basalts erupted within the Askja caldera are found in phreatomagmatic tuff cone sequences which crop out in the walls of Oskjuvatn caldera. one such tuff sequence has been dated at between 2.9 and 3.6 ka. This tuff cone shares geochemical source characteristics, such as Nb/La and Nb/Zr, with basaltic tephras erupted during precursory activity to the Plinian-phreatoplinian eruption of 28th-29th March 1875. It may therefore be considered to be compositionally representative of the primitive basaltic magmas supplied to Askja during the postglacial period. The predominance of relatively primitive basalt (6.8 wt.% MgO) within Askia's postglacial lava succession suggests that it did not have a permanent shallow magma chamber during the postglacial period. It is envisaged that the postglacial Askja magmas evolved by a process of polybaric factionation in transient, sill-like magma storage zones located at various levels in the crust. The most primitive magmas erupted directly from deeper reservoirs, while the more evolved magmas experienced longer crustal residence times. The buoyant rise of volatile-enriched melt from these sill-like bodies, without mobilising phenocryst phases, explains the observation that almost all lavas on Askja's eastern and southern lava aprons are essentially aphyric. The 28th-29th March 1975 eruption marked the climax of a volcanotectonic episode on the Askja volanic system lasting from late 1874 to early 1876. Fissure eruptions also occurred at the Sveinagja graben, 45-65 km north of Askja, between February and October 1875, producing the Nyjahraun lava. A strong similarity exists between whole-rock major element concentrations from Myjahraun and the Askja 20th century basalts. This has led to the suggestion that these basalts originated from a common shallow magma reservoir beneath Askja central volcano, with the Nyjahraun eruptions being fed by a lateral dyke extending northwards from Askja. This theory also offers an explanation for the observation that the volume of phyolitic ejecta from 28th-29th March 1875 is significantly less than the volume of Oskjuvatn caldera, which was formed as a result of this eruption. New major and trace element data from whole-rock and glass samples indicated that Nyjahraun and the Askja 20th century basalts did not share a common parental magma. A detailed investigation of historical accounts from explorers and scientists who visited Askja between 1875 and 1932 reveals that Oskjuvatn caldera took over 40 years to reach its current form, and that its size in 1876 was equal to the volume erupted on 28th-29th March 1875. Small injections of magma into an igneous intrusion complex beneath Askja, coupled with background deflation, are sufficient to provide the required accommodation space for continued caldera collapse after 1876. Lateral flow is therefore not required to explain the volume of Oskjuvatn caldera, nor the eruption of evolved basaltic magma on the Askja volcanic system in 1875. It has been conjectured that the Holuhraun lava, located at the southern tip of the Askja volcanic system, was also connected with the 1874-76 Askja volcanotectonic episode. However, major and trace element data from whole-rock samples, glass and melt inclusions receal the Holuhraun is geochemically more similar to basalts erupted on the Bardarbunga-Veidivotn volcanic system than to postglacial basalts from Askja. The division between the 'Askja' and 'Veidivotn' geochemical signatures appears to be linked to east-west-striking lineations in the region south of Askja. This indicates that a particular geochemical signature is not necessarily confined to the tectonic expression of a single volcanic system, and has important implications for the identification and delineation of individual volcanic systems beneath the northwest sector of Vatnajokull.
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Spinks, Karl D. "Rift architecture and Caldera volcanism in the Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2005. http://hdl.handle.net/10092/4944.
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The Taupo Volcanic Zone (TVZ) is investigated to determine the interaction of regional structure and volcanism. A three-tiered approach is employed involving (i) analysis of rift geometry and segmentation in Modem TVZ(<300 ka) from remote sensing and digital topographic data; (ii) fault kinematic data collected along the length of TVZ; and (iii) combining new and existing volcanological data for TVZ. Modem TVZ is a NNE-SSW trending intra-arc rift zone, subject to dextral transtension, and characterised by a segmented axial rift zone with a number of offset and variably oriented rift segments. These segments are subject to varying degrees of extension, and a general correlation exists between the amount of extension and the volume and style of volcanism in each segment. Segments with the highest degrees of extension correspond to the Okataina and Taupo Caldera Complexes in the central rhyolitic zone of Modem TVZ, while segments with a higher degree of dextral transtension correspond to the volumetrically-subordinate andesitic extremities.
The influence of the structural framework on the shape and formation of calderas in Modem TVZ has been inferred from remote sensing and ground-based structural analysis. Detailed analysis of caldera structure and geometry in Modem TVZ indicates that caldera evolution is largely a function of caldera location relative to the axial rift zone. Calderas peripheral to the rift are simple, single-event structures, while those located within the axial rift zone are multiple-event caldera complexes with geometries dictated by their coincidence with rift faulting. These results show that in Modem TVZ the type, volume, and spatial distribution of magmatic activity is strongly influenced by rift structure and kinematics.
The inter-relationship between rift geometry and caldera-complex development is particularly clear at the intra-rift Okataina Caldera Complex (OCC). OCC is located at a step-over in the rift where local rotation of the extension direction accompanies the development of a major transfer zone. Three main collapse events are spatially concentrated in a zone of orthogonal extension within the transfer zone. The 28 x 22 km OCC is elongate parallel to the extension direction, with a complicated topographic margin largely controlled by regional faulting. Major embayments occur on each side of OCC where it is intersected by adjacent rift segments. These are contiguous with two intra-caldera dome complexes forming two overlapping linear vent zones, which transect the caldera complex. The development of volcanism at OCC records the progressive interaction between offset rift segments and the propagation of overlapping rift segment axes. As rift propagation proceeded, a diffuse zone of volcanism progressively concentrated in the centre of the transfer zone then divided into two spatially restricted eruptive centres as through-going faults became established.
Field investigations at OCC reveal a major revision to the eruptive stratigraphy that has implications for the development of the caldera and for hazard assessment in northern TVZ. Kawerau Ignimbrite is a partially welded pumice-rich ignimbrite that fills Puhipuhi Basin on the eastern side of the caldera complex and forms a thick terrace in and around the Kawerau township area. Within Puhipuhi Basin it is ~100 m thick, exposed on clear-felled knolls and locally forms jointed bluffs in thickest sections where it is valley ponded. Originally mapped as Kaingaroa Ignimbrite, it was subsequently considered distinct and renamed Kawerau Ignimbrite by Beresford & Cole (2000) with an accepted age of 240 ka.
In Puhipuhi basin the Kawerau Ignimbrite overlies both the ~280 ka Matahina and ~65 ka Rotoiti ignimbrites and also the older tephras of the 43-31 ka Mangaone Subgroup. Whole-rock and glass geochemistry tie the ignimbrite specifically to the 33 ka Unit I eruptive phase of the subgroup, vastly increasing the eruptive volume of that unit and implying caldera collapse in this recent phase of OCC activity. Two pumice compositions are identified, reflecting eruption of two distinct magma bodies.
Vertical variation in the ignimbrite records rapid depletion of a subordinate dacitic magma such that pumices of this composition are rare beyond proximal exposures. Lithic and pumice size distribution data indicate a source within OCC to the west of Puhipuhi basin. The residual volume of the ignimbrite is <15 km3, but estimates of the original volume approach 50 km3 when intra-caldera volumes are considered. Kawerau Ignimbrite thus represents the largest eruption from OCC in the last 65 ka since the Rotoiti event, and is the youngest partially-welded ignimbrite in TVZ.
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Carn, Simon Anthony. "Persistent volcanism in Indonesia." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624364.
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Nyland, Roseanne E. "Evidence for early-phase explosive basaltic volcanism at Mt. Morning from glass-rich sediments in the ANDRILL AND-2A core and possible response to glacial cyclicity." Bowling Green State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1308530267.
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Grindrod, Peter Martin. "Corona-related volcanism on Venus." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445531/.
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This thesis reports the results of a study of volcanic processes at coronae on Venus. The Aglaonice F-Map region has been mapped, and its geological history interpreted, at the full-resolution of Magellan SAR data. Volcanism at coronae is shown to have occurred repeatedly over a protracted period of time, supporting a non-directional style of resurfacing in the F-Map region, and suggesting that corona-related flows may be an important resurfacing mechanism on Venus. It is likely that the magma storage system varies between each corona, with eruption dependent on local conditions such as location of magma body and local stress regime. Numerous flows which can be sourced to coronae, and were previously mapped as plains units, have also been identified. A global survey has revealed 29 volcano/corona 'hybrids', features which resemble both coronae and large volcanoes. Age, magma supply, stress state, thermal gradient and eruption duration are all important factors in determining gross hybrid morphology. It is likely that not all hybrids follow a similar evolutionary path. A detailed study of four selected hybrids is presented and suggests that processes typical of both large volcanoes and coronae have occurred throughout their history, and does not imply evolution from one type of feature into another. The presence of large central depressions and/or topographic rims at the hybrids support the theory that some large volcanoes undergo a sagging process similar to coronae. Study of the depth and extension at large radial graben at four centres of radial fractures is also reported. The inferred levels of hoop strain are too large to be explained by previous models of plume uplift, and a newly applied magma chamber inflation model concludes that dike formation is responsible for the strain at the large radial graben, and that intrusion is an important process at early-phase coronae.
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Hardiman, J. C. "Quaternary volcanism on Nisyros, Greece." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603684.
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This thesis describes the volcanic deposits on Nisyros, Aegean sea, Greece and uses them to understand volcanic processes and the evolution of the island. Nisyros is a small (42 km<SUP>2</SUP> in area) symmetric stratovolcano which has evolved on the eastern end of the Aegean volcanic arc over the last 200 ka of the Quaternary. The first volcanic activity was submarine. This left a layer of pillow larvas of basaltic-andesite composition overlying the Tertiary sedimentary basement of the Aegean. Subsequent volcanic activity was subaerial, and over 20 lava and pyroclastic eruptions of basaltic-andesite to rhyolite composition led to the formation of a stratovolcano. The younger eruptions were rhyolitic and the magma emitted is estimated to be of the order of a few km<SUP>3</SUP> in volume. These eruptions led to the formation of a 10 km<SUP>2</SUP> in area caldera which now dominates the centre of the island. A suite of domes were extruded progressively on western side of the caldera floor with field appearances suggesting activity continuing into the Holocene. The activity documented in historical records and seen at the present day is entirely phreatic and is the expression of a geothermal reservoir at a shallow depth below the caldera floor. The aims of this project were to describe the volcanic stratigraphy, to use the xenolith suite to understand magmatic and vent erosion processes, and to use the deposits from the three rhyolite eruptions to understand the youngest volcanic history of the island and timing of the caldera formation. Fieldwork was used to deduce the stratigraphy of the island. The stratocone succession consists of 3 cycles that start with basaltic-andesite to andesite lavas (BA&AI, BA&AII. BA&AIII) and pyroclastic deposits (SPI, SPII, SPIII) and proceed to dacite to rhyolite lava extrusions (DI, DII and RI, DIII) and pyroclastics (MSP, PK, LP).
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Wiart, Pierre Alexandre Maurice. "Quarternary volcanism of northeast Afar." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621825.
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Nimmo, Walter Heron Francis. "Volcanism and tectonics on Venus." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627116.
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Mattsson, Hannes B. "Volcanism at the tip of a propagating rift : the Heimaey volcanic centre, south Iceland /." Stockholm : Institutionen för geologi och geokemi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-257.
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Carmody, L. "Geochemical characteristics of carbonatite-related volcanism and sub-volcanic metasomatism at Oldoinyo Lengai, Tanzania." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348540/.
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The eruption of xenolithic material during large explosive eruptions, at any volcano, supply vital samples of the sub-surface lithologies upon which it is built, which in turn provides an indication of the evolution of the volcanic complex, in particular the volcanic conduit, magma storage zones and crustal / mantle lithologies. This is particularly important at alkaline-carbonatite complexes which are known to have “exotic” chemistries and also cause extensive zones of alteration through fenitisation processes. As the only active carbonatite volcano on Earth and also the unusual nature of Oldoinyo Lengai, Tanzania, it is an excellent study site to better understand the generation and chemical influence of carbonate-rich melts and fluids from source to surface. This study has attempted to better constrain the sub-volcanic environment, the source of the carbon within the material and the processes which lead to the formation of such unique rocks. Using geochemistry, isotopic studies and fluid inclusions, this thesis highlights the importance of fluid circulation within the volcanic system, both at the surface but also within the sub-volcanic mantle, leading to metasomatised material rich in carbon and alkali elements from which natrocarbonatite and potentially kimberlitic material could be derived. Almost all of the geochemical evidence and composition of fluid inclusions trapped within fenitised aureoles indicates a mantle derivation of carbonatitic material with isotopic signatures typical of the pre-defined “mantle-box”. The nature of the fluids is also investigated using trace element modelling and argued to be both carbonatitic and siliceous in origin, which have been circulating within the mantle beneath the Gregory Rift since before the establishment of Oldoinyo Lengai. These themes of research are discussed in terms of the genesis of natrocarbonatite, focussing upon the notion that it may be an evolutionary feature of Oldoinyo Lengai rather than a constant eruptive product.
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NOGUEIRA, LAGES Joao Pedro. "Constrains on mantle, slab and crustal contributions to major volatiles and noble gases along the Andean Volcanic Belt." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/395502.
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Wooler, Dan Anthony. "Subsidence and volcanism in western Tethys." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307107.
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Gilbert, Jennie S. "Late-Hercynian volcanism of the Pyrenees." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302843.
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Tuffen, Hugh. "Subglacial rhyolite volcanism at Torfajokull, Iceland." Thesis, Open University, 2001. http://oro.open.ac.uk/54438/.
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Subglacial rhyolite eruptions at Torfajokull, Iceland have produced a variety of volcanic edifices during the last glacial period (115-11 ka). These range from small-volume (< 0.1 km3) volcanoes, such as Bhlhnukur and Dalakvislfell, to larger volume (-1 km3) flat-topped tuyas such as South-east Rauoufossafjoll. Lithofacies associations at each volcano record distinct phases of volcano-ice interaction beneath temperate glaciers at least 350 m thick. All eruptions began with the construction of a pile of glassy fragmental material within a subglacial cavity. Fragmentation at Bhlhnukur was primarily caused by quenching, when rising magma encountered meltwater. Fragmentation at Southeast Rauoufossafjoll was apparently more energetic, and generated phreatomagmatic ash over 300 m thick. Dalakvisl is intermediate between the other two localities. Most fragmental deposits are massive, suggesting that a sustained meltwater lake did not develop during eruptions, in contrast with evidence from many basaltic volcanoes. Instead, meltwater drained away in a number of discrete channels, some of which have been identified. The eruption at Blahnukur apparently terminated before the glacier surface had been pierced, whereas the eruption at South-east Rau6ufossafjoll produced a cap of flat-lying subaerial lava flows about 1.5 km in length. Numerical models are presented, in which simple patterns of ice melting and deformation are used to simulate the evolving size of subglacial cavities during eruptions. The radius of the cavity is compared to the radius of the growing subglacial volcano. The models predict that, at low magma discharge rates and beneath thick ice, cavities will become completely filled with volcanic debris and the eruption will be dominantly intrusive, forming the types of lithologies observed at Blahnukur. Cavities never become filled at higher magma discharge rates, and an explosive phreatomagmatic eruption is predicted, which would form the types of lithologies observed at South-east Rauoufossafjol1.
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Cassidy, Michael. "The evolution of volcanism on Montserrat." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/351278/.
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Montserrat is a small volcanic island located in the Lesser Antilles. It hosts an active volcano, the Soufriere Hills volcano, which has affected, and continues to significantly affect, the local population. The thesis aims to examine the history of volcanism and related hazards on this island, to further understand the periodicity of eruptions, magmatic processes and potential future hazards, such as landslides. Uniquely, this work combines samples collected and sequences logged in both the subaerial and submarine realms.
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Mazza, Sarah Elizabeth. "Understanding Non-Plume Related Intraplate Volcanism." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/83554.
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Intraplate volcanism is a worldwide phenomenon producing volcanoes away from active plate boundaries, a process that cannot yet be sufficiently explained by plate tectonic processes, and thus is still a missing piece in the understanding of the dynamics and evolution of our planet. Models for the formation of intraplate volcanism are dominated by mantle plumes, but alternative explanations, such as adiabatic decompression triggered by lithospheric delamination, and edge driven convection (EDC), could be responsible for magmatism. This dissertation explores intraplate volcanic locations that do not fit the mantle plume model, and presents geochemical evidence for lithospheric delamination and edge driven convection for the cause of volcanism.
I studied an Eocene volcanic swarm exposed in the Appalachian Valley and Ridge Province of Virginia and West Virginia, which are the youngest known igneous rocks along the Eastern North American Margin (ENAM). These magmas provide the only window into the most recent deep processes contributing to the post-rift evolution of this margin. This study presents the first high precision 40Ar/39Ar ages along with new geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions suggests that melting occurred under conditions slightly higher than average mantle beneath mid-ocean ridges. Asthenosphere upwelling related to localized lithospheric delamination is a possible process that can explain the intraplate signature of these magmas that lack evidence of a thermal anomaly.
The Virginia-West Virginia region of the ENAM also preserves a second post-rift magmatic event in the Late Jurassic. By studying both the Late Jurassic and Eocene magmatic events we can better understand the post-rift evolution of passive margins. This study presents a comprehensive set of geochemical data that includes new 40Ar/39Ar ages, major and trace-element compositions, and analysis of radiogenic isotopes to further constrain their magmatic history. Modeling suggests that the felsic volcanics from both the Late Jurassic and Eocene events are consistent with fractional crystallization. Lithospheric delamination is the best hypothesis for magmatism in Virginia/West Virginia, due to tectonic instabilities that are remnant from the long-term evolution of this margin, resulting in a 'passive-aggressive' margin that records multiple magmatic events long after rifting ended.
Finally, Bermuda is an intraplate volcano that has been historically classified as mantle plume related but evidence to support the plume model is lacking. Instead, geophysics have argued that EDC is the best model to explain Bermuda volcanism. This study presents the first geochemical analysis of Bermuda volcanism, and found that Bermuda was built by two different magmatic processes: melting of carbonated peridotite to produce silica under-saturated, trace element enriched volcanics and melting of an enriched upper mantle component that produced silica saturated volcanics. We attribute the cyclicity of silica under-saturated and silica saturated volcanics to EDC melting.<br>Ph. D.
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Miskovic, Aleksandar. "The connection between volcanism and plutonism in the Sifton Range volcanic complex, Northern Canadian Cordillera /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81363.
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The early Tertiary marked a period of intense magmatic activity in the Canadian Cordillera as a consequence of tectonic restructuring within the Kula-North American plate system from orthogonal to oblique convergence. Resultant calc-alkaline volcanism formed a discontinuous belt (Challis Arc) along the eastern margin of the Coast Plutonic Complex (CPC) from south-eastern Alaska through Yukon into west-central British Columbia and northern Washington State. The Sifton Range volcanic complex (SRVC) is the Yukon's largest Paleogene erosional remnant of volcanic rocks (240 km2), and represents the only coeval volcanic-plutonic suite within the Sloko-Skukum Group of southern Yukon Territory and northern British Columbia. It comprises a 900-m thick, shallow-dipping, volcanic succession dominated by intermediate to evolved lavas and abundant felsic pyroclastics deposited in a north-westerly trending half-graben. Three volcano-stratigraphic units are documented: (1) Lower Interbedded Unit, (2) Middle lavas, and (3) Upper Interbedded Unit. Locally, the volcanic sequence is intruded by biotite, hornblende, two-feldspar granites of the CPC's Nisling plutonic suite dated at 57.5 Ma. Felsite sills radiate from the main intrusive body, and together with numerous basaltic to dacitic dykes traverse the entire volcanic package. (Abstract shortened by UMI.)
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Manciati, Carla J. "Modélisation de l'interaction surface – souterrain du système aquifère Tumbaco - Cumbayá en Equateur, avec une approche hydrodynamique et géochimique." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20086/document.
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L'aquifère Tumbaco – Cumbayá, sujet de la présente étude, se situe dans le contexte typique des aquifères volcano-sédimentaires. Cet aquifère se localise dans la Vallée Interandine, à 15 Km à l'Est de Quito. L'aquifère principal est la formation volcano-sédimentaire Chiche. Il est limité par la rivière Chiche et San Pedro, la faille de Quito et le volcan Pasochoa. Le volcan Ilaló se trouve au milieu de la zone d'étude. Il forme un second aquifère essentiellement volcanique soumis à un géothermalisme lié au volcan, dont la partie enterrée du cône est apparemment au-dessous de la formation Chiche. La couche géologique en surface est appelée Cangahua. Elle recouvre toute la zone et elle est imperméable. L'exploitation des aquifères Chiche et Ilaló a été théoriquement suspendue à partir de 2006, quand des teneurs en arsenic supérieures à la norme de 10 microg/l ont été détectées. Notre objectif est d'améliorer la connaissance du fonctionnement intégral de ce système aquifère en utilisant trois axes principaux de recherche : i) l'hydrodynamique, ii) la géochimie et, iii) les isotopes stables, 18O et 2H, et radioactifs, 3H et 14C.L'hydrodynamique montre que le système aquifère a une saisonnalité très faible. Par ailleurs, les aquifères sont actuellement exploités par un usage industriel et domestique, contrairement à ce qui a été pensé au début. Le volcan sépare les parties Sud et Nord de l'aquifère Chiche et il fonctionne comme une barrière hydraulique du flux. Les rivières Chiche et San Pedro sont des axes de drainage de l'aquifère, au Nord et au Sud.L'analyse des paramètres physiques de l'eau ont mis en évidence deux aquifères bien différenciés : l'aquifère Chiche avec des CE et des températures plus basses que l'aquifère Ilaló. La chimie des ions majeurs a révélé un faciès de l'eau qui évolue d'un pôle Mg-HCO3 à un pôle Na-HCO3, dans l'aquifère Chiche et aussi dans l'aquifère Ilaló, alors que l'aquifère Chiche Sud est plus Mg-HCO3. Les teneurs en As sont plus élevées dans l'aquifère Ilaló que dans l'aquifère Chiche, où les teneurs baissent au fur et à mesure que l'on s'éloigne du volcan. Cet élément est d'origine naturelle, mais aucune corrélation significative n'a pas été trouvée pour l'aquifère Chiche. Cependant, dans l'aquifère Ilaló, une corrélation de 57% a été trouvée avec le fer, suggérant une interaction avec les oxydes de fer de la formation géologique.L'isotope radioactif 3H n'a pas été détecté dans l'eau des aquifères, à exception d'une source au Nord de la zone d'étude, dans la formation Chiche. Cette infiltration probable d'eaux récentes a été confirmée par le 14C, qui a des teneurs supérieures à 100%. Le reste des points de l'aquifère Chiche ont des activités 14C entre 45,4 et 87,4 pmc. Pour l'aquifère Ilaló les activités 14C sont < 20 pmc. L'âge de l'eau a été calculé et corrigée à partir du 13C qui montrait une contamination par le CO2 profond, qui donne des âges plus anciens qu'en réalité. Malgré la correction, les âges de l'eau continuent à se montrer très élevés, pour Chiche entre 400 et 4000 ans et Ilaló entre 11000 et 44000 ans. Les isotopes stables ont été utilisés pour identifier les zones de recharge. L'eau de l'aquifère Chiche a montré un comportement isotopique en 18O et 2H sous la droite météorique locale, avec une pente de 3,5, signal d'un fractionnement isotopique d'échange avec la roche chaude qui n'a pas été observé dans l'aquifère Ilaló. Le calcul de l'altitude de recharge a montré que l'aquifère Chiche s'alimente au pied du volcan Ilaló au Nord et au pied du volcan Pasochoa au Sud, en considérant des conditions climatiques similaires aux conditions actuelles. Pour l'aquifère Ilaló, la zone de recharge se trouverait sur les flancs du volcan, en supposant des conditions climatiques de recharge plus froides que les conditions actuelles. Mais cette zone ne serait plus fonctionnelle dû au dépôt de Cangahua.Les résultats suggèrent que les eaux de l'Ilaló se mélangent avec l'aquifère Chiche<br>The Tumbaco – Cumbayá aquifer is found in the context of volcano-sedimentary aquifers. This aquifer is located in the Interandean Valley, 15 km to the east of Quito. The principal aquifer is the volcano-sedimentary formation Chiche. It is limited by the Chiche and San Pedro rivers, the Quito fault and the Pasochoa volcano. The Ilaló volcano is in the middle of the study zone and constitutes a second essentially volcanic aquifer, and is therefore subject to geothermal influences. This volcanic formation appears to be below the Chiche formation. The geologic layer on the surface is called Cangahua, it covers the entire zone and is impermeable. The exploitation of the Chiche and Ilaló aquifers was theoretically suspended in 2006, when arsenic concentrations > the WHO standard of 10 microg/l were found. Our objective is to improve the knowledge of the functioning of this aquifer system using three main research methods: i) hydrodynamics, ii) geochemistry and iii) stable isotopes, 18O - 2H, and radioactive isotopes, 3H - 14C.Hydrodynamics showed that the aquifer system has a low seasonality. We revealed that the aquifers are currently exploited for industrial and domestic uses, contrary to what was known at the beginning. The Ilaló volcano divides the south and north parts of the Chiche aquifer, with the volcano apparently acting as a hydraulic barrier for flows. The Chiche and San Pedro rivers are the drainage axes of the Chiche aquifer in the north and south.The analyses of the waters' physical parameters differentiated the two aquifers, Chiche aquifer having lower EC and temperature than the Ilaló aquifer. Major ions analysis revealed waters that vary between Mg-HCO3 pole and a Na-HCO3 pole in both the Chiche and Ilaló aquifers. As concentrations are higher in the Ilaló aquifer than in the Chiche aquifer. In the Chiche aquifer, As concentrations also decrease as the distance from the volcano increases. Arsenic is of natural origin, but no significant correlations were found for the Chiche aquifer. In the Ilaló aquifer a 57% correlation with Fe was found, which suggests an interaction between As and Fe oxides present in the geologic formation.Radioactive isotope 3H was not detected in groundwater from either aquifer, except in one spring in the north of the study area in the Chiche formation. The likely infiltration from recent waters was confirmed by 14C analysis this spring, which showed concentrations > 100 pmc. Other sampling points in the Chiche aquifer have 14C activities between 45.4 - 87.4 pmc. The Ilaló aquifer has 14C activities < 20 pmc. Water ages were calculated and corrected using 13C, which reveal a contamination from geogenic CO2, making water seem older than it is in reality. Despite the age correction, groundwater ages remain very old: Chiche groundwaters are between 400 - 4,000 years old and Ilaló groundwaters are between 11,000 - 44,000 years old. Stable isotopes were used to identify recharge areas. Groundwaters from Chiche aquifer show an isotopic 18O and 2H signature below the Local Meteoric Water Line (slope=3.5). This was interpreted as isotopic fractionation from hot rock and water interactions, which was not observed in the Ilaló aquifer. Recharge altitude calculations show that the Chiche aquifer is fed on the Ilaló and Pasochoa volcano piedmonts, if we consider that climatic conditions over the recharge period are close to current conditions. However, for the Ilaló aquifer, recharge areas appear to be located on the flanks of the volcano, assuming colder recharge climatic conditions than today. This recharge area should no longer be functional because of the Cangahua deposits during the last volcanic events.Results suggest that Ilaló groundwaters are being mixed with Chiche groundwaters. This research is the first to have been done with this level of detail in Ecuador on this type of aquifer and will provide new opportunities for projects in others volcano-sedimentary aquifers in the country
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Hatter, Stuart James. "The long-term evolution of Montserrat volcanism." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/420908/.
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This thesis investigates the long-term geochemical trends of volcanism on Montserrat and Guadeloupe, islands in the northern Lesser Antilles arc, through both their terrestrial and marine (from International Ocean Discovery Program core U1396C) records, to examine the processes driving geochemical evolution in island arcs. Detailed mapping of the Silver Hills, the least studied volcanic centre on Montserrat, reveals activity was dominated by andesite dome growth and collapse. New 40Ar/39Ar ages from terrestrial samples, combined with new palaeomagnetic and biostratigraphic ages of tephra layers from marine sediment core U1396C, reveal the previously unrecognised overlap in volcanic activity between the Silver and Centre Hills, and Centre and Soufrière Hills. Pb-Nd-Sr isotope and major and trace element data for the Silver Hills show that lavas fall into two compositional groups; ‘normal’ lavas and ‘low Al2O3-high Fe2O3’ lavas. The latter group formed from parental magmas which experienced up to 25% greater plagioclase fractionation compared to the parent magmas of the normal lavas, likely as a result of lower magmatic H2O content. There is no systematic geochemical variation between lava domes of the Silver Hills, but there is an observed systematic shift in 143Nd/144Nd to progressively less radiogenic values with time, which is inferred to result from mantle heterogeneity. Tephra layers from core U1396C have been analysed for Pb-Nd-Sr isotope and major and trace element data, which provide a record of the geochemical evolution of volcanism on Montserrat and Guadeloupe over the past ~4.5 Ma; 2.3 and 1.7 Ma longer than their respective terrestrial records. The main geochemical change for the Montserrat source region occurred ~4.5–3.9 Ma, resulting from an increase in slab sediment contribution to the mantle wedge via an aqueous fluid. Tephra layers from Guadeloupe display greater temporal geochemical variation, driven by crustal assimilation of mid-ocean ridge basalt. Componentry, grain size and grain morphology analyses of the thickest tephra layer in core U1396C derived from Guadeloupe, T2.36, reveal it was formed by deposition from fallout from an eruption column, followed by a co-ignimbrite ash cloud from the same eruption. Eruption reconstructions suggest that this deposit likely formed from a VEI 6 eruption.
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Smedley, Pauline Lesley. "Petrochemistry of Dinantian volcanism in northern Britain." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/12975.
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Woodcock, Duncan Charles. "Magma-ice heat transfer in subglacial volcanism." Thesis, Lancaster University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730248.
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Subglacial explosive volcanism generates hazards resulting from magma-ice interaction, including meltwater flooding and fine-grained volcanic ash. The literature contains descriptions of some recent subglacial eruptions and suggests several heat transfer mechanisms but lacks a detailed study of heat transfer in the magma-water-ice system. Quantification of heat transfer processes allows further development of dynamic models of subglacial eruptions that may help to inform hazard management. 1 have quantified particle-water heat transfer with a model that couples intraparticle conduction with boiling on particle surfaces. In general, where magma is fragmented by explosion or granulation, much of the initial heat of the magma is transferred to water rapidly compared to eruption timescales. Within liquid-dominated subglacial eruption cavities, heat fluxes from water to ice of c. 0.6 MW m-2 can be obtained by single phase free convection. When local boiling occurs in the vent region heat fluxes of 3-5 MW m-2 , approaching those inferred for some recent subglacial eruptions, may be attained by two-phase free convection and may be increased by momentum transfer from the eruption jet. In vapour-dominated cavities, heat fluxes of 0.1-1 MW m-2 can be obtained by steam condensation during free convection, depending on cavity pressure and the concentration of non-condensable gases present. Forced convection reduces the effect of non-condensable gases; in this case a maximum heat flux of c. 2 MW m-2 may be attained. In a drained and depressurised cavity the resulting eruption jet may transfer heat by a combination of radiation, steam condensation and pyroclast impact. Heat fluxes from radiation and condensation are unlikely to exceed 0.5 MW m-2. An experimental study of pyroclast impact on ice, using sand at 300 °C, demonstrated heat fluxes of 0.4 MW in-2. The effects of higher particle temperature and damage from repeated impact of larger particles remain to be investigated.
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DI, CAPUA ANDREA. "Volcanism vs tectonics in the sedimentary record." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2015. http://hdl.handle.net/10281/75294.
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Il significato del materiale vulcaniclastico in bacini ricchi in sequence torbiditiche sembra essere assodato ed ambiguo nello stesso tempo. Il problema si pone quando il sistema area sorgente-bacino depositionale non risulta perfettamente preservato e/o differenti cicli magmatici sono registrati nel record stratigrafico, e risulta pragmaticamente difficile interpretare il segnale vulcaniclastico. Il problema principale riguarda discriminare la produzione di sedimento sin-magmatica da quella post-magmatica, tettonicamente controllata, nei depositi distali. In questo lavoro abbiamo preso in considerazione cinque formazioni esposte tra il bacino Giurassico continentale chiamato Cañadón Asfalto basin (Provincia del Chubut, Argentina), il bacino oligocenico degli Appennini settentrionali (Val d'Aveto, Piacenza – Italia), la Molassa Oligocenica Alpina (Francia e Svizzera) e l'avanfossa oligocenica alpina (Como – Italia). Le Formazioni considerate sono Las Leoneras e Lonco Trapial (Argentina), la Formazione della Val d'Aveto Formation (Appennini), le arenarie di Taveyanne (Francia e Svizzera) ed il Conglomerato di Villa Olmo (Como). Si è portato avanti un lavoro di terreno atto a misurare le colonne stratigrafiche nei bacini, effettuare il conteggio litologico dei clasti su conglomerati, correlare i depositi e ricostruirne le geometrie deposizionali. Più di 150 campioni sono stati selezionati tra strati arenitici e pelitici, clasti ignei, metamorfici e sedimentari, i quali sono stati tagliati per sezioni sottili, osservati al microscopio, analizzati mineralogicamente (diffrazione raggi X) e chimicamente (fluorescenza), minero-chimicamente tramite SEM-EDS e paleomagneticamente, in modo da ottenere qualsiasi tipo di indizio di attività sin-vulcanica della zona. Quando sono stati riconosciuti, depositi di flusso piroclastici primari preservati sott'acqua sono stati inoltre approfonditamente caratterizzati, per definire i possibili meccanismi che ne permettono la preservazione al passaggio aria/acqua. Le arenarie sono state composizionalmente analizzate tramite i metodi Folk e/o Gazzi-Dickinson, oppure tramite analisi XRD se di grana troppo minuta. La petrografia dei clasti ignei, sedimentari e metamorfici è stata utilizzata per studi di provenienza del detrito. Tutti i dati sono stati correlati a livello regionale prima, generale poi per considerazioni geodinamiche e sedimentologiche. Come mostrato nella tesi, il vulcanismo risulta dare vita ad un segnale molto forte, il quale cannibalizza il record stratigrafico, ma di breve durata, essendo legato all'attività dei centri vulcanici (media della vita 1 milione di anni). Il segnale tettonico, invece, pur avendo un impatto minore rispetto a quello vulcanico sul breve termine, è più duraturo ed ampio.
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Barnard, Scott Trevor. "The vulnerability of New Zealand lifelines infrastructure to ashfall." Thesis, University of Canterbury. Geological Sciences, 2010. http://hdl.handle.net/10092/3688.
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Risks posed by geohazards to urban centres are constantly increasing, due to the continuous increase in population and associated infrastructure. A major risk to North Island urban centres is impacts from volcanic ashfall. This study analyses the vulnerabilities of selected New Zealand lifelines infrastructure to volcanic ash, to better understand and mitigate these risks. Telecommunications and wastewater networks are assessed, as is the vulnerability of Auckland Airport and grounded aircraft. The ability of vehicles to drive on ash covered roads is also tested, to determine the extent to which emergency services, utility providers and the public will be able to travel during and immediately after ashfall. Finally, air-conditioners have been identified as a significant vulnerability during ashfall, due to the high dependence on cooling for infrastructure and lifelines providers. These are examined to quantify the effects of ashfall on their performance. Each of the selected infrastructure types is assessed through a review of past impacts of ashfall, and experimentation either in the field or under laboratory conditions. Where appropriate, mitigation options that reduce identified vulnerabilities are considered. In most cases these options are operational rather than physical engineering solutions, and indicate pre-planning and response requirements. Key recommended mitigation options include the acquirement or strategic relocation of resources prior to ashfall, regular cleaning and maintenance of essential air conditioners during ashfall to enable their continued use, access to appropriate vehicles for utility providers to reach infrastructure, and discharge of untreated wastewater into Waitemata harbour at Orakei during ashfall on Auckland, to preserve the ability to continue treating wastewater at the Mangere treatment plant
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Ruscitto, Daniel M. 1981. "Magmatic volatile contents and explosive cinder cone eruptions in the High Cascades: Recent volcanism in Central Oregon and Northern California." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11262.
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xvi, 182 p. : col. ill.<br>Volatile components (H 2 O, CO 2 , S, Cl) dissolved in magmas influence all aspects of volcanic activity from magma formation to eruption explosivity. Understanding the behavior of volatiles is critical for both mitigating volcanic hazards and attaining a deeper understanding of large-scale geodynamic processes. This work relates the dissolved volatile contents in olivine-hosted melt inclusions from young volcanics in the Central Oregon and Northern California Cascades to inferred magmatic processes at depth and subsequent eruptive activity at the surface.
Cinder cone eruptions are the dominant form of Holocene volcanism in the Central Oregon segment of the High Cascades. Detailed field study of deposits from three cinder cones in Central Oregon reveals physical and compositional similarities to explosive historic eruptions characterized as violent strombolian. This work has important implications for future hazard assessments in the region. Based on melt inclusion data, pre-eruptive volatile contents for seven calc-alkaline cinder cones vary from 1.7-3.6 wt.% H 2 O, 1200-2100 ppm S, and 500-1200 ppm Cl. Subarc mantle temperatures inferred from H 2 O and trace elements are similar to or slightly warmer than temperatures in other arcs, consistent with a young and hot incoming plate.
High-magnesium andesites (HMA) are relatively rare but potentially important in the formation of continental crust. Melt inclusions from a well-studied example of HMA from near Mt. Shasta, CA were examined because petrographic evidence for magma mixing has stimulated a recent debate over the origin of HMA magmas. High volatile contents (3.5-5.6 wt.% H 2 O, 830-2900 ppm S, 1590-2580 ppm Cl), primitive host crystals, and compositional similarities with experiments suggest that these inclusions represent mantle-derived magmas.
The Cascades arc is the global end member, warm-slab subduction zone. Primitive magma compositions from the Cascades are compared to data for arcs spanning the global range in slab thermal state to examine systematic differences in slab-derived components added to the mantle wedge. H 2 O/Ce, Cl/Nb, and Ba/La ratios negatively correlate with inferred slab surface temperatures predicted by geodynamic models. Slab components become increasingly solute-rich as slab surface temperatures increase from ∼550 to 950°C at 120 km depth.
This dissertation includes previously published and unpublished co-authored material.<br>Committee in charge: Dr. Paul J. Wallace, Chair and Advisor;
Dr. Katharine Cashman, Member;
Dr. Ilya Bindeman, Member;
Dr. Richard Taylor, Outside Member
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Carter, Catherine St John. "Communication of Lava Flow Hazards at the San Francisco Volcanic Field, Flagstaff, Arizona." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5655.
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This thesis examines different methods of communicating volcanic hazards to the population of Flagstaff, Arizona using the results of a recent lava flow hazard assessment of the nearby San Francisco Volcanic Field (SFVF). Harburger (2014) determined that given a lava flow originating in the SFVF, there is a statistical probability that it will inundate the city of Flagstaff or even originate from a vent within the city limits. Based on the recurrence rates for the most recent eruptions (3 x 10-4/year), the probability of lava flow inundation in Flagstaff is 1.1 x 10-5 per year.
This study considers the effects of three different communication methods on participants’ perceived risk. The methods were administered through a questionnaire and included a statement of probability of lava flow inundation per year, a statement of probability over a 100 year period, and an interactive lava flow map derived from the results of the lava flow hazard assessment. Each method was followed by questions gauging level of concern. Questionnaires were administered to 213 Flagstaff residents over a two week period in February 2015.
Results showed that levels of concern, rated from 1 (not concerned) to 5 (very concerned), varied based on each method of communication. The method with the greatest effect on perceived risk was the simulated lava flow map, while the first method with a one year odds resulted in a statistically lower mean rating of concern. It is suggested that the best way to change levels of perceived risk when communicating lava flow hazards includes a combination of comprehensible odds and visual aids. Further studies could also include visualization of the entire eruption scenario, including time scales and other volcanic hazards, which may have more effect on concern than a simplified visualization of lava flows.
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Roach, Angela Louise. "The evolution of silicic magmatism in the post-caldera volcanism of the Phlegrean Fields, Italy /." View online version; access limited to Brown University users, 2005. http://wwwlib.umi.com/dissertations/fullcit/3174665.
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Cáceres, Acevedo Francisco Andrés. "Magma storage conditions and eruptive dynamics of post-glacial effusive volcanism at Laguna del Maule Volcanic field." Tesis, Universidad de Chile, 2016. http://repositorio.uchile.cl/handle/2250/140208.
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Magíster en Ciencias, Mención Geología<br>Geólogo<br>La mayoría de los campos volcánicos monogenéticos están constituidos principalmente por productos piroclásticos de composición basáltica. Los volúmenes emitidos por cada centro eruptivo tienden a ser pequeños, menores a 1 km3, donde su actividad puede durar días a años, mientras que el campo volcánico completo se puede desarrollar y perdurar por millones de años, pudiendo superar en volumen a un volcán poligenético. En este sentido, el Campo Volcánico Laguna del Maule (CVLdM) representa un caso excepcional con más de 350 km3 de material basáltico a riolítico, eruptado mayormente de manera efusiva desde el Pleistoceno. En este trabajo se propone un modelo volcanológico-petrológico de la dinámica eruptiva de las lavas post-glaciales emplazadas en la parte Oeste del CVLdM, analizando la evolución del magma en profundidad, el ascenso de magma por los conductos eruptivos y el emplazamiento de lavas en superficie.
Se estudió la morfometría, mineralogía y química de seis lavas y un domo del CVLdM para modelar las condiciones termodinámicas pre-eruptivas del magma y su evolución, incluyendo posibles procesos magmáticos causantes de su migración y ascenso a la superficie. Las lavas analizadas tienen una composición química andesítica a riolítica, morfología de bloques, volúmenes de 0.03 a 1.16 km3, largos máximos de 10 km, anchos máximos de 5 km y espesores máximos de 140 m.
Los resultados indican la presencia de un sistema magmático formado en cuatro etapas, comenzando con la acumulación de magma andesítico basáltico a andesítico debido a múltiples intrusiones. Posteriormente, procesos de cristalización desarrollaron un reservorio tipo mush cristalino (13-17 km, 970-1025 °C) con extracción y ascenso de líquido intersticial. Una tercera etapa de estancamiento del magma en ascenso proveniente de la extracción más profunda (7-11 km, 900-970 °C), permitió la formación de un nuevo mush cristalino más evolucionado. Finalmente, una nueva extracción y ascenso del líquido intersticial riolítico formó un reservorio magmático riolítico pobre en cristales (~5 km, 760-800 °C) bajo el lago. El constante recalentamiento debido a múltiples intrusiones permitó al sistema magmático permanecer activo en el largo plazo, producto de variadas intrusiones de magma máfico en el caso del reservorio profundo y magma silícico en el caso del reservorio más somero.
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Branney, Michael John. "Subaerial explosive volcanism, intrusion, sedimentation and collapse in the Borrowdale Volcanic Group, SW Langdale, English Lake District." Thesis, University of Sheffield, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388778.
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Ukstins, Peate Ingrid Anne. "Volcanostratigraphy, geochronology and geochemistry of silicic volcanism in the Afro-Arabian flood volcanic province (Yemen and Ethiopia)." Thesis, Royal Holloway, University of London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411244.
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Cuppone, Tiberio. "Camp Volcanism: age, volcanic stratigraphy and origin of the magmas. Cases studies from Morocco and the U.S.A." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426069.
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During Triassic time, in the proto-North Atlantic area, the late Palaeozoic fracture system, inherited from the building of Pangea supercontinent, was reactivated. Rifting and breakup of Pangea, initiated during the early Triassic, continued and intensified at the beginning of the Norian. After few million years later, a massive magmatic event, namely CAMP (Central Atlantic Magmatic Province), occurred in the rifted and inside the cratonic areas, covering more than 10 millions kilometers square, leaving its products on 4 continents: North and South America, southwest Europe and west Africa. The main magmatic event occurred at ca 199-200 Ma near the Triassic-Jurassic boundary (Tr-J) with two minor secondary pulses al ca. 195 Ma and 192 Ma. The time spanned by the main magmatic event is very short, probably less than 1 Ma (ca. 610 Ka based on Milankovitch cyclostratigraphy), and the tight occurrence with one of great extinctions events in the Phanerozoic time and the climatic crisis and biotic turnover demarcating the Tr-J, led to the intriguing hypothesis that CAMP magmatism triggered these global events. At present the CAMP magmatism is represented by tholeiitic dikes, sills and minor amounts of lava flows, deeply eroded and in few places well preserved, being due to the subtropical palaeogeographic position of the basaltic outcrops which led to heavy weathering. Most of the CAMP basalts throughout circum-Atlantic domain have quite homogeneous compositions, with low-Ti (TiO<2wt.%) except for high-Ti dyke storms documented in Liberia, French Guyana and northern Brazil, strong Nb-Ta(PM) negative anomaly, enriched in light earth rare elements (LREE) and large ion lithophile elements (LILE) respect to the common normal mid-ocean ridge basalts. The purpose of this work is to describe and correlate 6 CAMP volcanic sequences in three different Morocco regions (three in the Central High Atlas, two in the Middle Atlas and one in the Western Meseta) on the base of a petrographic-mineralogic-geochemical-magneto-stratigraphic study in order to highlight similarities between the four basaltic units which made up the lava piles. Phase relationships, their major, minor and trace element compositions will be investigated to constrain crystallization order and conditions (T, P, H2O content and fO2) of basalts while the accurate chemo-magneto-stratigraphic correlation of five lava sequence allow to do new suppositions about feeding system of the Moroccan CAMP basalts. Finally new and accurate 40Ar/39Ar dating on plagioclase and biotite separates from 10 basaltic sample of the Eastern North America (Newark and Culpeper basins) will be presented, discussed and compared to both previous dating of the same province and a overall CAMP ages dataset.
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Albert, Mínguez Helena. "Processes, time scales and unrest of monogenetic volcanism." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/334689.
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Seismic, deformation, and gas activity (unrest) typically precedes volcanic eruptions. Successful volcanic event forecasting depends on the quality of the surveillance network for detecting any changes in volcano behaviour. To interpret the geochemical and geophysical precursors correctly it is important to understand the volcanic processes that occur prior and during volcanic eruptions. Detailed knowledge of the volcano internal structure, the rheology of the magmas, the time scales of the processes occurring at depth and the characteristics of past unrest episodes, must be combined with an adequate monitoring network to improve the volcanic hazard forecast. However, these aspects have received little attention in monogenetic volcanoes.
The aim of my PhD Thesis is to improve our understanding on monogenetic volcanism, its causes and dynamics, and to help anticipating the volcanic activity. I have focused on three main aspects of this problem. The first one is the calculation of the rheological properties of magmas during mixing. The second aspect I have addressed are the processes and time scales that lead to monogenetic eruptions with the aim to better interpret volcanic unrest and improve eruption forecasts. Finally, I have investigated the seismic unrest periods of historical monogenetic eruptions from a compilation of historical accounts worldwide. The results provide a conceptual framework for better anticipating monogenetic eruptions and should lead to improved strategies for mitigation of their associated hazards and risks.<br>Las erupciones volcánicas están generalmente precedidas por la actividad sísmica, la deformación y la desgasificación (unrest). El éxito en la predicción del evento volcánico depende de la calidad de la red de vigilancia para detectar cualquier cambio en el comportamiento del volcán. Para interpretar los precursores geoquímicos y geofísicos correctamente es importante entender los procesos volcánicos que ocurren antes y durante las erupciones volcánicas. El conocimiento en detalle de la estructura interna del volcán, la reología de los magmas, las escalas de tiempo de los procesos que ocurren en profundidad y las características de los episodios pasados de unrest, debe combinarse con una red de vigilancia adecuada para mejorar el pronóstico de los eventos volcánicos. Sin embargo, estos aspectos han recibido poca atención en los volcanes monogenéticos.
El objetivo de mi tesis doctoral es mejorar nuestra comprensión sobre el vulcanismo monogenético, sus causas y su dinámica, con el objetivo de mejorar la posibilidad de anticiparse a la actividad volcánica. Me he centrado en tres aspectos principales de este problema. El primero es el cálculo de las propiedades reológicas de los magmas durante los eventos de mezcla. El segundo aspecto es el estudio de los procesos, junto con sus escalas temporales, que llevan a erupciones monogenéticas con el fin de interpretar mejor la actividad volcánica y mejorar los pronósticos de una erupción. Por último, he investigado los períodos de unrest sísmico de erupciones monogenéticas históricas en todo el mundo mediante una compilación de documentos históricos. Los resultados proporcionan un marco conceptual que permite mejorar la predicción de erupciones monogenéticas y deberían conducir a mejores estrategias para mitigar sus peligros y riesgos asociados.
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Masoud, Abdelmoniem Ahmed Mohamed. "Composition and age of Cenozoic volcanism in Libya." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5517/.
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Libya has five major Cenozoic volcanic provinces (Garian, Jabal Al Haruj al Aswad, Jabal Al Hasawinah, Jabal as Sawda and Jabal Nuqay) that have a surface area of approximately 66,000 km2. These volcanic provinces are dominated by alkali to mildly alkali basalts. The provinces are aligned NNW-SSE, typically occurring where NE-SW trending structural features intersect the main regional uplift structures. Small volumes of phonolites are associated with the basaltic volcanism at Garian and Jabal Al Hasawinah. Despite their size and relative accessibility the Cenozoic volcanic provinces of Libya have been rarely studied. In the first part of this thesis I report a new study of the petrology, geochemistry (major and trace elements, REE, Sr-Nd isotopes) and geochronology (40Ar/39Ar) of basalts and phonolites from the Garian volcanic province in north Libya. These analyses indicate that the plateau and late basalts are not distinct basalt types produced from melting of different mantle regions at different times as proposed by earlier studies. They are the product of fractional crystallisation of a common parent. There is little indication of crustal contamination. Trace element and REE data support an origin in 2 to 12 % melts of heterogeneous sub-lithosphere mantle. Trace elements and Nd and Sr isotopic composition of the Garian basalts overlap values measured in metasomatised peridotite xenoliths in the GVP. They are compositionally similar to Cenozoic volcanism of northern Libya (e.g. Jabal Al Haruj) and southern Italy (e.g. Etna and Pantelleria; European asthenosphere mantle reservoir), and they lack the influence of enriched mantle present in other North African Cenozoic basalt provinces. Compositional variation in the Garian province phonolitic magmas is dominated by extensive fractional crystallisation (50-83%) of plagioclase and alkali feldspars combined with an unusual style of assimilation (2-45%) of old upper crust typical of Pan-African shield. The new high precision age determinations of the phonolites suggest that they were produced over a very short period at ~8.1 Ma. This contrasts strongly with previous age determinations that were 40-50 Ma. In the second half of the thesis I report new Ar/Ar chronology measurements for extrusive and intrusive rocks all the major Cenozoic volcanic fields in Libya. The major pulse of basaltic volcanism in Garian in the north (from 6 to 2 Ma) overlaps in time in Jabal Al Haruj province in southern Libya. Jabal Al Hasawinah and Jabal as Sawda basalts were erupted significantly earlier (23-10 Ma). Dykes and plugs at all provinces imply basaltic volcanism started in Miocene, followed by periods of erosion. There is no systematic trend of time in Cenozoic basaltic volcanism of Libya. It appears to be related to reactivation of ancient structures during the passive rifting that has been produced in response to interaction of African and European plates since the late Mesozoic.
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Airey, Martin Walter. "Volcanism as an active planetary process on Venus." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:c0ee4af9-b350-4ecf-8373-10c8af759fc3.
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Volcanism has been a crucial planetary process in the evolution of Venus, shaping the surface and contributing to the formation of the atmosphere and clouds. Some of the key outstanding questions are whether or not volcanism is active today, and what range of volcanic styles have occurred in the past or may occur in the future. This project uses three methods of investigating these questions. Firstly, computer modelling is used to simulate volcanic processes under Venusian conditions using a steady-state, isothermal, homogeneous flow model. It was found that the addition of CO2 to an H2O-driven eruption reduces the H2O requirement for explosive activity, and that eruptions possible on Venus may be detectable in Venus Express data. Next, radar datasets from both Venus and Earth were investigated with the aim of assessing relationships between differing volcanic deposits on Venus and their likely mode of formation, and using trends in the Earth radar data to inform us of what the Venus observations may be telling us. It was found that, in some cases, regional-scale radar observations may be useful in identifying deposit types, but the data used in the study were insufficient to define a globally applicable deposit identification scheme, pending further study. Finally, mapping and spatial analysis of volcanic features and rifts was performed to evaluate the nature of the interaction of volcanism within the global tectonic environment. Spatial relationships are consistent with aspects of the directional model of Venus' evolution, favouring a shift from globally dispersed, relatively small-scale, volcanism spread randomly across the planetary surface towards a gradually more rift-focused distribution indicative of a corresponding shift in global tectonic regime. These various strands are brought together here in order to contribute to our further understanding of volcanism as a fundamental Venusian planetary process.
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Alves, Ana. "Impact de l’éruption du volcan Toba sur le climat et la dynamique océan-atmosphère." Electronic Thesis or Diss., Sorbonne université, 2024. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2024SORUS060.pdf.
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Les éruptions volcaniques explosives tropicales, surtout si elles sont de nature stratosphérique, sont des phénomènes naturels qui peuvent influencer de manière significative le climat. Ce sont les émissions de soufre vers l'atmosphère qui jouent un rôle majeur. En effet, ce gaz précurseur d'aérosols, peut d'une part engendrer une modification de la température en diminuant le rayonnement solaire incident, et d'autre part, perturber la chimie des océans. L'éruption du volcan Toba (Younger Toba Tuff, YTT), s'est produite il y ~74 000 ans sur l'ile de Sumatra. Elle est actuellement considérée comme la plus grande éruption du Quaternaire. Ses émissions vers l'atmosphère sont estimées entre 3.5 x 1010 et 3.3 x 1012 kg de soufre, et ~8600 km3 de cendres qui se sont réparties sur près de ~40 millions de km2. De nombreuses incertitudes sur les paramètres clés de l'éruption (durée, dynamique éruptive, émissions) persistent et rendent difficile l'estimation de son impact sur le climat. Cependant, certaines études ont suggéré que l'éruption du Toba aurait eu un impact sur la mousson indienne. L'hypothèse est que le refroidissement global causé par les aérosols d'origine volcanique a pu altérer les gradients de température de surface et perturber la circulation atmosphérique et les vents de mousson. Cette thèse a pour objectif de (1) reconstruire la variabilité de la mousson indienne lors des derniers 150 000 ans, (2) étudier à très haute résolution la transition entre le stade isotopique marin 5 (interglaciaire) et le stade 4 (glaciaire) afin d'observer l'impact de l'éruption du Toba sur l'océan de surface et la dynamique océan-atmosphère. Pour réaliser cette étude, un analyse multi-proxy (isotopes du bore (δ11B) et de l'oxygène (δ18O), rapport Mg/Ca des foraminifères G. ruber, fluorescence de rayons X (XRF) et abondance des foraminifères G.bulloides et G. ruber) a été réalisée sur deux carottes marines provenant de l'océan Indien tropical. La carotte BAR94-25 a été prélevée en mer d'Andaman (~600 km du volcan Toba) et la carotte MD00-2355 en mer d'Arabie (~4500 km). Ces carottes sont idéalement situées dans deux régions fortement influencées par la mousson indienne. Plusieurs niveaux de téphra appartenant au volcan Toba ont été identifiés dans ces deux carottes et correspondent à plusieurs événements explosifs pendant la transition climatique MIS5-MIS4. Nos résultats ont montré que lors des dernier 150 000 ans, les variations de la salinité en mer d'Andaman sont en phases avec l'insolation d'automne à 6°N. Ceci a été interprété comme une influence de « El Niño-oscillation australe » (ENSO) et du dipôle de l'océan Indien (DOI) sur le régime de précipitations. En mer d'Arabie, nous avons observé une variabilité glaciaire-interglaciaire de la mousson indienne, avec un affaiblissement de la mousson d'été (Sud-Ouest) en période glaciaire.L'étude détaillé de la transition MIS 5/4 a mis en évidence une acidification de l'océan de surface en mer d'Andaman qui coïncide avec l'activité éruptive du volcan Toba. Nous avons également observé une augmentation graduelle de la salinité qui témoigne d'une diminution des précipitations dans cette région. Ainsi, l'activité volcanique du Toba aurait perturbé la circulation atmosphérique caractérisée par un état moyen semblable à El Niño et à un DOI-. En mer d'Arabie, nos résultats ont permis de voir que l'activité éruptive du volcan Toba a diminué, voire arrêté, la mousson d'été (Sud-Ouest)<br>Tropical explosive volcanic eruptions, especially the stratospheric ones, are natural phenomena that can have a significant influence on climate. Sulfur emissions into the atmosphere play a major role. This aerosol-precursor gas can both modify temperatures by reducing incident solar radiation, and disrupt ocean chemistry. The eruption of the Toba volcano (Younger Toba Tuff, YTT) occurred ~74,000 years ago on the island of Sumatra. It is currently considered the largest eruption of the Quaternary period. Its emissions of material into the atmosphere are estimated at between 3.5 x 1010 and 3.3 x 1012 kg of sulfur and ~8600 km3 of ash spread over nearly ~40 million km2. Numerous uncertainties about the eruption's key parameters (duration, eruptive dynamics, emissions) persist, making it difficult to estimate its impact on climate. However, some studies have suggested that the Toba eruption may have had an impact on the Indian Monsoon. The hypothesis is that the global cooling caused by the release of volcanic aerosols may have altered atmospheric conditions and Monsoon winds. The aim of this thesis is to reconstruct the variability of the Indian Monsoon during the last ice age (150 ka). Then, to study the impact of the Toba eruption on the surface ocean and ocean-atmosphere dynamics, by analyzing at very high resolution the transition between marine isotope stage 5 (interglacial) and stage 4 (glacial). To carry out this study, a multi-proxy analysis (boron (δ11B) and oxygen (δ18O) isotopes, G. ruber Mg/Ca ratio, X-ray fluorescence (XRF) and G.bulloides and G. ruber abundance) was carried out on two marine cores from the tropical Indian Ocean. Core BAR94-25 was taken from the Andaman Sea (~600 km from volcano Toba) and core MD00-2355 from the Arabian Sea (~4500 km). These cores are ideally located in two regions strongly influenced by the Indian Monsoon. Several tephra levels belonging to the Toba volcano were identified in these two cores, corresponding to several explosive events during the MIS5-MIS4 climatic transition. Our results show that during the last 150 ka, salinity variations in the Andaman Sea are in phase with autumn insolation at 6°N. This was interpreted as the influence of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (DOI) on the precipitation regime. In the Arabian Sea, we observed glacial-interglacial variability of the Indian Monsoon, with a weakening of the summer (southwest) Monsoon during the glacial period. A detailed study of the MIS 5/4 transition revealed acidification of the surface ocean in the Andaman Sea, coinciding with the Toba eruption. We also observed a gradual increase in salinity, reflecting a decrease in precipitation in this region. Thus, the volcanic activity of Toba would have disrupted the atmospheric circulation characterized by a mean state similar to El Niño and a DOI-. In the Arabian Sea, our results showed that the eruption of Toba reduced or even halted the summer Monsoon (Southwest)
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Stewart, Kathryn. "High temperature felsic volcanism and the role of mantle magmas in proterozoic crustal growth : the Gawler Range volcanic province /." Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phs8488.pdf.
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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.
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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.<br>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.
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Watson, Thomas LaPoint Dennis John. "Volcanism and sedimentation new insight into arc-related volcanism and sediment deposition in a synkinematic Paleoproterozoic basin, Rosebel Gold Mine, northeastern Suriname /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,1565.
Full textAbstract:
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2008.<br>Title from electronic title page (viewed Sep. 16, 2008). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Geological Sciences." Discipline: Geology; Department/School: Geological Sciences.
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Graham, David W. "Helium and lead isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic." Woods Hole, Mass. : Woods Hole Oceanographic Institution, 1987. http://catalog.hathitrust.org/api/volumes/oclc/17021004.html.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 1987.<br>Funding was provided by the National Science Foundation under grants OCE 15270 and OCE 16082.
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Renggli, Christian Josef. "Volcanic gases and the reaction of sulfur dioxide with aluminosilicate glasses." Phd thesis, Canberra, ACT : The Australian National University, 2018. http://hdl.handle.net/1885/147744.
Full textAbstract:
Volcanic gases are an important part of the volatile cycle in
active planetary systems and contribute significantly to the
mobilization and transport of metals to planetary surfaces. On
Earth, Venus, Mars and Io, SO2 is the most abundant corrosive
species in volcanic gases, and basalts are ubiquitous on these
planetary bodies. The reaction between SO2 and silicate rocks
forms oxidized sulfate and reduced sulfide. This reaction is a
key process in the formation of porphyry deposits. In volcanic
eruption plumes SO2 reacts with volcanic ash and is scavenged
onto the surface of the ash particles. Knowledge of the reaction
mechanisms between volcanic gas and rocks, minerals and glasses,
and processes controlling the metal mobilization and transport in
volcanic gas can constrain models of volatile and metal budgets
of planetary crusts and surfaces.
Using thermochemical modelling, I present a new model for the
composition of volcanic gas on the Moon and compare it to a
terrestrial volcanic gas from Erta Ale volcano (Ethiopia). The
main species in lunar volcanic gas are H2, S2 and CO. This
finding is in contrast to previous studies which suggested that
CO was the sole driver of explosive volcanic eruptions on the
Moon. This lunar volcanic gas has a lower capacity for metal
transport compared to the Cl- and H2O-rich volcanic gas from Erta
Ale volcano.
To identify how SO2-glass reactions occur at high temperature and
to investigate what might promote and limit these reactions, I
present results from an experimental study. Pure SO2 was reacted
with silicate glasses in the system anorthite-diopside-albite and
with Fe-bearing natural basaltic glasses.
The sulfate reaction products are relatively enriched in Ca
compared to the silicate glass composition, in particular in
experiments with Fe-free anorthite-diopside glasses. On these
Fe-free glasses CaSO4 is the sole observed phase in the coatings
at 800 °C, whereas at 600 °C minor amounts of MgSO4 were
detected. At 800 °C, the flux of Ca from the silicate glass to
the surface exceeds that of Mg by a factor of up to 330, whereas
at 600 °C this factor is only 3. The rate of reaction is not
constant, decreasing by an order of magnitude from 1 h to 24 h at
800 °C.
The reaction of SO2 with tholeiitic basalt glasses produces
coatings of CaSO4, MgSO4, Na2SO4 and oxides including Fe2O3 and
TiO2. In addition, the reaction modifies the basalt glass because
Ca, Mg and Na are lost to the coating. This results in the
nucleation of crystalline spherulites and needles including SiO2,
Al2O3, as well as Fe-Na-rich and Mg-rich pyroxenes.
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The results suggest that the structural properties of the
silicate glass substrate control the diffusive transport of Ca,
Na, Mg, Fe and Ti to the surface which in turn controls the
overall reaction rate and the formation of sulfates, oxides and
silicates. These findings can be applied to predicting reactions
on planetary surfaces and at shallow levels within their crusts.
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Pedrazzi, Dario. "Hydrmagmatic monogenetic volcanism in continental and oceanic island enronments." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/229382.
Full textAbstract:
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.<br>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.
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James, S. D. "Volcanism in sedimentary basins and its implications for mineralization." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379244.
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Mullis, Andrew martin. "Lunar volcanism and the thermal evolution of the moon." Thesis, University of York, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238687.
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Sloan, Roderick James. "Mid-Slurian sedimentation and volcanism in Dingle, southwest Ireland." Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361216.
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