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

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

Geochemistry plays a vital role in our understanding mechanisms behind major geological systems such as the Earth's crust and its oceans (Albarède, F. 2003). More recently, geo-chemistry has played a vital role in the field of forensic investigation and in period dating. Forensic soil samples have been traditionally analysed via examinations of colour, texture and mineral content by physical or chemical methods. However, these methods leave any organic or water-soluble fractions unexamined. Tephrochronology (the dating of sedimentary sequences using volcanic ash layers) is an important tool for the dating and correlation of sedimentary sequences containing archives and proxies of past environmental change. Its importance in this area has increased since the increased free carbon in out atmosphere has made radio-carbon dating unreliable. Tephrochronology requires successful geo-chemical identification of the tephras, a method reliant on electron probe micro-analysis (EPMA) to analyse major element composition. However, it is often impossible to differentiate key tephra layers using EPMA alone. Raman spectroscopy is commonly used in chemistry, since vibrational information is specific to the chemical bonds and symmetry of molecules, and can provide a fingerprint by which these can be identified. Here, we demonstrate how Raman spectroscopy can be used for the successful discrimination of mineral species in tephra through the analysis of individual glass shards. We further demonstrate how, with the use of oxidative preparation methods, Raman spectroscopy can be used to successfully discriminate between soil types using mineralogy as well as the organic and water-soluble fractions of soils.

The Caucasus is a land corridor between the Black and Caspian seas, linking Africa to Northern Eurasia, and is considered a migratory route for Neanderthals and Anatomically Modern Humans (AMH). Numerous cave sites in Armenia, Azerbaijan, Georgia and southwestern Russia indicate that Neanderthals and AMH occupied the region, but poor chronological control meant that the precise timing of the occupations was unknown. This work involved identifying and geochemically characterising volcanic ash layers (tephra) in archaeological cave and open air sites spanning approximately 125 ka to 30 ka to generate a tephrostratigraphic framework. This framework was used to correlate the sites and assess the synchronicity of Neanderthal and AMH occupation across the region. Tephra investigations were also carried out on a core (M72/5-25-GC1) from the southeast Black Sea (that spans the last ~ 60 ka), with the aim of linking the archaeological sites to this palaeoenvironmental archive, to investigate the impact changes in climate had on the archaeology in the region. Eleven of the archaeological sites investigated (Gubs rock shelter and Weasel Cave in Russia; Ortvale Klde, Ortvale Cave, Sakajia and Undo Cave in Georgia; Aghitue 3, Lusakert 1, Fantan and Kagasi in Armenia; and Azokh Cave in Azerbaijan) had tephra, 30 cryptotephras and 8 visible layers, preserved. Twenty-two tephra layers were identified in the Black Sea core, with distinct periods of frequent volcanic activity separated by long periods, up to 9 ka, of seemingly volcanic quiescence in the region. The glass chemistry of the tephra found in the archaeological sites and the core, determined using a wavelength-dispersive electron microprobe, was used to characterise and correlate the units between the sedimentary sequences. Although some widespread tephra from the major Mediterranean sources (3.6 ka Minoan eruption from Santorini, Greece and the ~39 ka Campanian Ignimbrite super eruption from Campi Flegrei, Italy) were identified in the Black Sea core, none of the archaeological sites contained Mediterranean tephra. Most of the tephra layers in the archaeological sites investigated and the Black Sea core are from sources in the Caucasus and Turkey. The limited information on the volcanic history and compositional data of these sources in the region does not allow most of the units to be correlated to particular eruptions or volcanoes. However, some of the cryptotephra units have been correlated to eruptions from Nemrut, Acigöl and Erciyes Dagi volcanoes in Turkey. Unfortunately, there are no tephra layers that are common to the Black Sea core and any of the archaeological sites, prohibiting direct correlation of the sites to this detailed palaeoenvironmental record. However, the ~30 ka Nemrut Formation (NF) eruption from Nemrut volcano, Turkey, is found in the Lake Van palaeoenvironmental record and in two of the archaeological sites. This allows the archaeological sites to be correlated to each other and palaeoclimate information can also be imported into these sites. More detailed characterisation of the proximal deposits may allow more units to be correlated to eruptions and will enable these distal records to be used to further constrain the tempo of explosive volcanic activity in the region. A few compositionally distinct tephra layers were found and a suite of new radiocarbon dates were obtained at various sites, allowing archaeological occupations to be dated and the synchronicity between sites to be assessed. A distinct rhyolitic tephra correlates a layer with an Upper Palaeolithic stone technology, associated with AMH, in Azokh Cave (Azerbaijan) to a layer in Sakajia cave (Georgia) that contains Neanderthal remains. This is clear evidence that AMH and Neanderthals were in the region (within 600 km) at the same time. Other sites have also been correlated with tephra. A dacitic tephra correlates a unit with an Upper Palaeolithic lithic and bone tool techno-complex in Ortvale Klde (Georgia) to a unit with a Middle Palaeolithic lithic assemblage in Lusakert 1 (Armenia). The Middle Paleolithic tool assemblage in Lusakert 1 is clearly different from the Upper Paleolithic assemblage that is clearly associated with AMH in Ortvale Klde, but it is not clear whether the other assemblage is associated with Neanderthals, archaic modern humans or AMH. This correlation between different lithic assemblages clearly indicates that there were different groups, with different technologies, occupying the region at the same time. The NF tephra is also found shallower in the sequences at both Lusakert 1 and Ortvale Klde. This time marker shows that the Middle Paleolithic assemblage is still being used in Lusakert 1 at ~30 ka, indicating that a less diverse stone techno-complex was used for a prolonged period of time in central Armenia. There does not appear to be any direct relationship between occupation in the region and the climate at the time, implying that this had little effect on the archaeological story in the region. A new radiocarbon based age model that combines new dates with published data for the sites within the Caucasus shows temporal overlap between AMH and Neanderthals in the region. This confirms the tephra correlations and clearly indicates both species co-existed in the Caucasus. The new radiocarbon data also suggest that AMH arrived in the region earlier than previously thought, at ~50-44 ka cal BP. The arrival of AMH in the Caucasus is now temporally similar to other early AMH sites in northern Eurasia.

As técnicas de sensoriamento remoto têm se mostrado fundamentais como ferramenta auxiliar no mapeamento geológico básico. O avanço tecnológico gerado pelos novos sensores permite o desenvolvimento de técnicas mais apuradas na integração de dados litológicos e estruturais de várias fontes. Este trabalho buscou avaliar a potencialidade das imagens do sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) para identificação dos diferentes litotipos da área do Cerro Chato, em especial as unidades vulcânicas e hipabissais relacionadas. O Cerro Chato é caracterizado como uma feição geomorfológica situada à cerca de 15 km ao norte do município de Herval, na microrregião denominada Serra do Sudeste na porção sudeste do estado do Rio Grande do Sul. É constituído principalmente por uma seqüência de rochas efusivas e piroclásticas de composição riolítica relacionada a sistemas do tipo alta-sílica, vinculadas ao magmatismo granítico tardio do Batólito Pelotas. O objetivo deste trabalho foi testar e avaliar diversas técnicas de geoprocessamento buscando a diferenciação litológica, a identificação de alvos e a definição de morfoestruturas da área do Cerro Chato. O processamento utilizando a técnica de Transformação por Componentes Principais forneceu os melhores resultados realçando diferenças entre as rochas vulcânicas e hipabissais e as rochas encaixantes. Foram selecionadas as CP2 das imagens CP's 2, 3 e 5 na geração de uma composição colorida que permitiu delimitar três principais domínios de ocorrências das rochas de origem vulcânica no Cerro Chato. / The remote sensing techniques have been a very important and auxiliary tool to basic geological mapping. The new orbital sensors carried out a technologic increment that possibility the development of refined methods applied in the integration with diverse geologic data as petrology and structural. In this work were utilized images obtained from the ASTER sensor (Advanced Spaceborne Thermal Emission and Reflection Radiometer) to identify the lithologies in the Cerro Chato area, giving emphasis to the volcanic and hypabissal units. The Cerro Chato can be characterized as geomorphologic feature situated about 15 km to north of Herval town, in the Southeast Sierra micro region of the Rio Grande do Sul state, southernmost Brazil. It is constituted mainly by an effusive and pyroclastic rocks sequence of rhyolitic composition related to high silica systems, which magma has been associated to the younger granitic magmastim of the Pelotas Batholith. The main objective of this work was to test and evaluate diverse techniques of geoprocessment to try identifying different lithologic units and morphologic structures in the Cerro Chato area. The selective principal component analysis technique was used in the digital image processing, because it provided the best results enhancing the existent spectral differences between volcanic and country rocks. In this processing were selected the PC's2 images of the PC's 2, 3, and 5 to generated a color composite image that permitted the individualization of three main dominions of volcanic rocks in the Cerro Chato.

The catastrophic eruption of the Indonesian volcano Mt. Tambora in April 1815, which ejected a cloud of sulfur dioxide into the upper atmosphere, plunged the world into a rapid temporary climate change event. A series of bizarre weather anomalies, including snowstorms in June and repeated heavy frosts throughout the rest of the summer, earned 1816 the moniker "the Year Without a Summer." This paper examines the various ways in which Americans reacted to the climate change--seeking causation explanations through science and superstition, political and religious responses, and the efforts to appreciate what the events meant in terms of the world's changing climate. Through these various reactions, a picture emerges of Americans' incomplete understanding of science and nature, as well as an uneasy reckoning with the impossibility of fully explaining their environment and the potential dangers it presented to them.

Processos diagenéticos controlam a porosidade e permeabilidade dos reservatórios de petróleo. Um estudo petrográfico sistemático de 71 arenitos e conglomerados da Formação Itabapoana (Aptiano), selecionadas de testemunhos de 13 poços na porção offshore da Bacia de Campos, Leste do Brasil, permitiu o reconhecimento dos principais constituintes primários, diagenéticos, tipos de poros e das relações temporais e espaciais entre eles. Essas rochas são contemporâneas aos extensos reservatórios lacustres do “Pré-Sal” atualmente em exploração. As rochas variam de arenitos muito finos a conglomerados, com predominância de arenitos muito grossos, e sua composição detrítica original corresponde a arcósios líticos e litarenitos feldspáticos, ricos em fragmentos de rochas vulcânicas (FRV). Argilominerais esmectíticos são os mais abundantes constituintes diagenéticos, relacionados principalmente à alteração de FRV, minerais pesados e biotita. A história térmica e de soterramento, e o fluxo de fluídos também exerceram um papel fundamental nos processos diagenéticos e na evolução da qualidade de reservatório. Os principais processos diagenéticos registrados foram a dissolução de FRV, feldspatos e minerais pesados, a autigênese de esmectitas, hematita, dolomita, calcita, zeolitas e óxidos de titânio cimentando e substituindo FRV, feldspatos, biotita e minerais pesados, a compactação mecânica e química, e a albitização dos feldspatos, principalmente dos plagioclásios. A porosidade primária intergranular foi fortemente reduzida pela compactação e cimentação por argilominerais esmectíticos, calcita, dolomita e zeolitas. Por outro lado, porosidade secundária foi gerada pela dissolução de constituintes primários e diagenéticos, e por faturamento. Futuros estudos específicos e detalhados, incluindo análises de microscopia eletrônica, difratometria de raios-X e isótopos estáveis, deverão contribuir para um melhor entendimento da distribuição espacial e temporal dos processos diagenéticos nessas rochas, de modo a embasar o desenvolvimento de modelos preditivos quanto à sua qualidade, que possam contribuir para reduzir os riscos envolvidos na sua exploração. / Diagenetic processes control the porosity and permeability of petroleum reservoirs. A systematic study of 71 sandstones and conglomerates of the Itabapoana Formation (Aptian), selected from the cores of 13 wells in the offshore portion of Campos Basin, eastern Brazil, allowed the recognition of the main primary and diagenetic constituents, pore types, and of the space and time relations among them. These rocks are contemporaneous to the extensive lacustrine Pre-Salt carbonate reservoirs under exploration. The rocks range from very fine-grained sandstones to conglomerates, with predominance of very coarse-grained sandstones, and their original detrital composition corresponds to lithic arkoses and feldspathic litharenites, rich in volcanic rock fragments (VFR). Smectitic clay minerals are the most abundant diagenetic constituents, related mostly to the alteration of VRF, heavy minerals and biotite. The burial and thermal history and the flow of fluids also exerted a fundamental role on the diagenetic processes and on the of reservoir quality. The main diagenetic processes recorded were the dissolution of volcanic fragments, feldspars and heavy minerals, the authigenesis of smectites, hematite, dolomite, calcite, zeolites and titanium oxides in intergranular pores and replacing VRF, feldspars, biotite and heavy minerals, mechanical and chemical compaction, and the albitization of feldspars, mostly plagioclase. Primary intergranular porosity was strongly reduced by compaction and smectite, calcite, dolomite and zeolite cementation. On the other hand, secondary porosity was generated by the dissolution of primary and diagenetic constituents, and by fracturing. Future specific and detailed studies, including electron microscopy, X-ray diffraction and stable isotope analyses, shall contribute to a better understanding of the space and time distribution of diagenetic processes in these rocks, in order to support the development of predictive models of their quality that may contribute to the reduction of risks involved in their exploration.

A busca por novas acumulações de hidrocarbonetos necessita de esforços exploratórios contínuos, gerando novas possibilidades e modelos geológicos e diminuindo os riscos associados à atividade exploratória. O interesse no entendimento da formação de armadilhas, migração e reservatórios de hidrocarbonetos, associado à halocinese motivou a realização deste trabalho. Apresenta-se como principal objetivo deste trabalho a caracterização e a descrição da evolução halocinética na porção centro-sul da bacia do Espírito Santo. Dados de poços, sísmicos e gravimetria foram utilizados com o intuito de gerar uma interpretação geológica integrada, possibilitando entender à influência do Complexo Vulcânico de Abrolhos (CVA) na evolução tectonossedimentar da área, por meio da técnica de restauração de seção geológica. Na área estudada, ocorreu uma intensa atividade halocinética, já a partir do Albiano, em resposta a distensão causada pela subsidência da bacia e a abertura do Atlântico Sul. Durante o Neocretáceo, cunhas clásticas do Rio Doce adentraram na bacia provocando um novo pulso halocinético, resultando num aumento da taxa de sedimentação nas mini-bacias. Em outras regiões esta progradação causou a migração da camada-mãe de sal para porções distais da bacia, acarretando uma deficiência no suprimento de sal. Isto ocasionou o colapso de alguns diápiros associados a uma quiescência tectônica na área. A principal fase tectônica na área ocorreu no Eoterciário, época em que ocorre a implantação do CVA, formando estilos estruturais característicos de terrenos compressivos, com falhas de empurrão, popups, dobras e gotas de sal. Esta nova configuração tectônica na área mudou os eixos dos principais depocentros, que passaram a ser controlados pelos altos estruturais gerados pela tectônica compressiva, e pelos seus baixos relativos, que passaram a receber os sedimentos sin-tectônicos. (As associações destas características de remobilização tectonossedimentar formou uma nova compartimentação, a saber: a) Zona de translação; b) Zona dobrada e c) Zona de Cavalgamento com falhas de empurrão . Esta nova configuração tectônica tem sua formação diretamente relacionada à implantação do CVA. / The search for new accumulations of hydrocarbons needs continuous exploratory efforts, in order to create new geological models and lessen the risks associated with exploratory activities. This work was motivated by the urge to understand the formation of traps, migration and reservoir properties, associated with halokinesis. The main goal of this work is the characterization and reporting of the halokinesis evolution in the south-central part of the Espirito Santo Basin. Seismic, gravity and well data incorporated in geological section reconstruction were used in the integrated geological interpretation, allowing a better understanding of the AVC (Abrolhos Volcanic Complex) in the tectonic and sedimentary evolution of the area. Intensive halokinesis activity was registered from Albian time, in response to an earlier stretching phase that resulted in subsidence of the basin and the opening to the South Atlantic ocean. During the Early Cretaceous, clastics of the Rio Doce were introduced in the basin provoking new haloknesis trigger, generating an increment of sedimentary rates in the sub-basins. In other regions, the progradation of the clastic wedge caused the migration of the mother salt layer to the distal portions of the basin, suppressing the supply of salt. The process created a collapse of some diapirs associated with a tectonic quiescence in the area. The main tectonic phase occurred in the Early Tertiary. The introduction of AVC occurred in this period, forming structural styles, typical of compressional tectonics, with thrust faults, pop-ups, folds, and salt canopies. This new tectonic configuration in the area has changed the axis of main sedimentary depocenter that became controlled by the high structures generated by the compressional tectonics, and by the associate low, that began to receive syntectonic sediments. The associations of these characteristics of tectonic and sedimentary remobilization formed a new compartmentalization in the basin, such as: a translation zone, b.Folded zone, c. Hangingwall thrust block zone. They are strongly connected to the emplacement of AVC. This new tectonic configuration has its formation directly related to the emplacement of AVC.

As técnicas de sensoriamento remoto têm se mostrado fundamentais como ferramenta auxiliar no mapeamento geológico básico. O avanço tecnológico gerado pelos novos sensores permite o desenvolvimento de técnicas mais apuradas na integração de dados litológicos e estruturais de várias fontes. Este trabalho buscou avaliar a potencialidade das imagens do sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) para identificação dos diferentes litotipos da área do Cerro Chato, em especial as unidades vulcânicas e hipabissais relacionadas. O Cerro Chato é caracterizado como uma feição geomorfológica situada à cerca de 15 km ao norte do município de Herval, na microrregião denominada Serra do Sudeste na porção sudeste do estado do Rio Grande do Sul. É constituído principalmente por uma seqüência de rochas efusivas e piroclásticas de composição riolítica relacionada a sistemas do tipo alta-sílica, vinculadas ao magmatismo granítico tardio do Batólito Pelotas. O objetivo deste trabalho foi testar e avaliar diversas técnicas de geoprocessamento buscando a diferenciação litológica, a identificação de alvos e a definição de morfoestruturas da área do Cerro Chato. O processamento utilizando a técnica de Transformação por Componentes Principais forneceu os melhores resultados realçando diferenças entre as rochas vulcânicas e hipabissais e as rochas encaixantes. Foram selecionadas as CP2 das imagens CP's 2, 3 e 5 na geração de uma composição colorida que permitiu delimitar três principais domínios de ocorrências das rochas de origem vulcânica no Cerro Chato. / The remote sensing techniques have been a very important and auxiliary tool to basic geological mapping. The new orbital sensors carried out a technologic increment that possibility the development of refined methods applied in the integration with diverse geologic data as petrology and structural. In this work were utilized images obtained from the ASTER sensor (Advanced Spaceborne Thermal Emission and Reflection Radiometer) to identify the lithologies in the Cerro Chato area, giving emphasis to the volcanic and hypabissal units. The Cerro Chato can be characterized as geomorphologic feature situated about 15 km to north of Herval town, in the Southeast Sierra micro region of the Rio Grande do Sul state, southernmost Brazil. It is constituted mainly by an effusive and pyroclastic rocks sequence of rhyolitic composition related to high silica systems, which magma has been associated to the younger granitic magmastim of the Pelotas Batholith. The main objective of this work was to test and evaluate diverse techniques of geoprocessment to try identifying different lithologic units and morphologic structures in the Cerro Chato area. The selective principal component analysis technique was used in the digital image processing, because it provided the best results enhancing the existent spectral differences between volcanic and country rocks. In this processing were selected the PC's2 images of the PC's 2, 3, and 5 to generated a color composite image that permitted the individualization of three main dominions of volcanic rocks in the Cerro Chato.

abstract: Among volcanic gases, sulfur dioxide (SO2) is by far the most commonly measured. More than a monitoring proxy for volcanic degassing, SO2 has the potential to alter climate patterns. Persistently active explosive volcanoes are characterized by short explosive bursts, which often occur at periodic intervals numerous times per day, spanning years to decades. SO2 emissions at those volcanoes are poorly constrained, in large part because the current satellite monitoring techniques are unable to detect or quantify plumes of low concentration in the troposphere. Eruption plumes also often show high concentrations of ash and/or aerosols, which further inhibit the detection methods. In this work I focus on quantifying volcanic gas emissions at persistently active explosive volcanoes and their variations over short timescales (minutes to hours), in order to document their contribution to natural SO2 flux as well as investigate the physical processes that control their behavior. In order to make these measurements, I first develop and assemble a UV ground-based instrument, and validate it against an independently measured source of SO2 at a coal-burning power plant in Arizona. I establish a measurement protocol and demonstrate that the instrument measures SO2 fluxes with < 20 % error. Using the same protocol, I establish a record of the degassing patterns at Semeru volcano (Indonesia), a volcano that has been producing cycles of repeated explosions with periods of minutes to hours for the past several decades. Semeru produces an average of 21-71 tons of SO2 per day, amounting to a yearly output of 8-26 Mt. Using the Semeru data, along with a 1-D transient numerical model of magma ascent, I test the validity of a model in which a viscous plug at the top of the conduit produces cycles of eruption and gas release. I find that it can be a valid hypothesis to explain the observed patterns of degassing at Semeru. Periodic behavior in such a system occurs for a very narrow range of conditions, for which the mass balance between magma flux and open-system gas escape repeatedly generates a viscous plug, pressurizes the magma beneath the plug, and then explosively disrupts it. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2015