This thesis deals with the study of flow through tailings dams. Examination of the current practices led to the construction of a valid experimental model. A unique system of instrumentation was developed, which was employed successfully to measure pore water pressures accurately and thus provide the necessary information to locate the position of the phreatic surface. Using the developed technique, models of tailings dams were constructed and monitored and it was discovered that a major deviation in the expected position of the phreatic surface occurred in a tailings dam. Further investigation by the construction of various types of dams led to the redefining of the phreatic surface and thus the flow regime. A computer programme based on the use of the finite difference technique was applied to water retention dams and found to locate the position of the phreatic surface accurately.

Phreatic and hydrothermal eruptions often occur with little or no warning representing a significant hazard within geothermal regions. These violent eruptions occur at a range of temperatures and pressures within varying rock types. A range of mechanisms including heating or decompression, allows hydrothermal/supercritical fluid to rapidly flash to steam, expanding and shattering the surrounding rock to produce an eruption, with no direct magmatic influence. These eruptions are highly variable resulting in the current wide ranging classification schemes, many of which are based on characteristics that are hard to observe and define. This has resulted in confusing nomenclature with many different terms used to describe the same eruptive phenomena. Here a new classification scheme is presented, based on the easily definable features of eruption size, trigger type (natural or anthropogenic) and geological setting (volcanic or hydrothermal). This ultimately produces a classification dividing the eruptions into either phreatic, where magma interacts with cold water but no juvenile material is erupted; or hydrothermal where eruption occurs from an already heated hydrothermal system. Examples are then provided for each classification type. Previous studies have focused exclusively on either physical characteristics of eruptions, small scale experimental modelling of trigger processes or mathematical modelling of various eruption characteristics. Here, a new experimental procedure has been developed to model phreatic fragmentation, based on shock tube experiments for magmatic fragmentation by Alidibirov and Dingwell (1996). Water saturated samples are fragmented from a combination of argon gas overpressure and steam flashing within vesicles. In this thesis, these experimental results have been integrated with the physical characteristics of porosity, permeability and mineralogy to create two new models of phreatic fragmentation. Firstly a generalised model to explain fragmentation processes and secondly a specific model describing the eruption forming Lake Okaro, within the Taupo Volcanic Zone of New Zealand. These models were developed with the overall aim to improve understanding of these eruption types, ultimately improving future hazard modelling. Experiments were performed on Rangitaiki ignimbrite, through which the Okaro eruption occurred. In order to evaluate alteration effects, both unaltered ignimbrite and hydrothermally altered ignimbrite samples were analysed. Experiments were performed at room temperature and 300°C with pressures from 4 to 15 MPa, to reflect likely geothermal conditions while also assessing the effect of liquid water on fragmentation. Results indicate that within these samples 5 to 8 MPa of decompression is required to trigger an eruption, fitting well with the previously identified trend between decompression and porosity for magmatic samples. The fragmentation front propagates through the sample at speeds ranging between 14 m/s to 42 m/s, increasing with higher applied pressures and higher sample porosity. Most importantly, grain size analysis from these experiments show a clear shift to smaller grain sizes when liquid water flashes to steam (independent of pressure or sample type), reflecting the greater energy involved with steam flashing. Previous grain size analysis of the Okaro breccia deposits have indicated that the highest weight percentage of fragments fall between -3.5 and 1.5 phi, with our experimentally produced fragments fitting right within this range at -0.5 to 1.0 phi. Here the first parameterisation of conditions for phreatic and hydrothermal eruptions is presented creating a general fragmentation model along with a case study on Lake Okaro. These models describe how eruptions occur, with stages from initial system priming and overpressure development through to the last stages of eruption and crater formation.

Amostras de diferentes espécies de Phreatobius foram coletadas para obtenção de dados moleculares potencialmente informativos do gene nuclear RAG-2 para resolver as relações filogenéticas do gênero. Apresento resultados de sequências. Os dados de Phreatobius foram combinados com sequências equivalentes de representantes de várias outras famílias de Siluriformes, e analisados via máxima parcimônia (total de 966 pares de base de RAG-2 para 176 táxons). As análises resultaram em 172 árvores com 5213 passos. O resultado do consenso estrito indica fortemente que Phreatobius forma um grupo monofilético (sustentado por 33 sinapomorfias moleculares) com Pseudopimelodidae e Pimelodidae, e Conorhynchos + Heptapteridae. Hipóteses anteriores posicionando Phreatobius exclusivamente com Heptapteridae não foram sustentadas. Os resultados apresentados requerem que Phreatobius seja alocado na sua própria família, Phreatobiidae (disponível em nível subfamiliar). Uma revisão taxonômica de Phreatobiidae mostra que existem ao menos sete espécies, das quais apenas três descritas: Phreatobius cisternarum, Phreatobius dracunculus, Phreatobius sanguijuela, Phreatobius sp. "Anapixi", Phreatobius sp. "Jaú", Phreatobius sp. Tarumanzinho", Phreatobius sp. "Viruá". A hipótese de relações filogenéticas dentro de Phreatobiidae mostra que Phreatobius cisternarum é grupo-irmão do clado composto por (Phreatobius sp. "Viruá" (P. dracunculus + Phreatobius sp. "Tarumanzinho")). O mapeamento filogenético demonstra que o hábito subterrâneo evoluiu uma única vez na família e o ambiente freático foi invadido duas vezes. / Samples from different species of Phreatobius were collected in order to obtain molecular data from nuclear RAG-2 gene sequence potentially informative to resolve phylogenetic relationships of the genus. The data on Phreatobiidae were combined with equivalent sequence information from representatives of several other siluriform families, and analyzed by maximum parsimony (a total of 966 bp RAG-2 for 176 taxa). The analyses resulted in 172 trees, with 5213 steps. The strict consensus results strongly indicate that Phreatobius forms a monophyletic group (supported by 33 molecular synapomorphies) with Pseudopimelodidae, Pimelodidae, and Conorhynchos + Heptapteridae. Previous hypotheses aligning Phreatobius exclusively with Heptapteridae were not supported. Results herein presented requires that Phreatobius be allocated in its own family, as Phreatobiidae (already available at subfamilial level). A taxonomic revision of Phreatobiidae shows that at least seven species exist, only three of which currently described: Phreatobius cisternarum, Phreatobius dracunculus, Phreatobius sanguijuela, Phreatobius sp. "Anapixi", Phreatobius sp. "Jaú", Phreatobius sp. Tarumanzinho", Phreatobius sp. "Viruá". A hypothesis of relationships within Phreatobiidae shows that P. cisternarum is sister-group of a clade composed of (P. sp. "Viruá" (P. dracunculus + P. sp. "Tarumanzinho")). Phylogenetic mapping shows that subterranean habit has evolved once in the family and the phreatic environment was invaded twice.

Telica Volcano, Nicaragua, is a persistently restless volcano with high rates of seismicity that can vary from less than ten events to over a thousand events per day. Low-frequency (LF) events dominate the seismic catalogue and seismicity rates at Telica show little clear correlation with periods of eruption. As such, traditional methods of forecasting of volcanic activity based on increases in seismicity and recognition of LF activity are not applicable. A single seismic station has been operating at Telica since 1993, and in 2010 we installed a broadband seismic and continuous GPS network (TESAND network) at Telica. In this study we investigate the seismic characteristics surrounding a nine-month period of phreatic to phreatomagmatic explosions in 1999, and also from the initial three-and-a-half year deployment of the TESAND network, including a three-month phreatic vulcanian eruptive period in 2011. We demonstrate that pertinent information can be obtained from analysis of single-station data, and while large seismic networks are preferable when possible, we note that for many volcanoes this is not possible. We find unusual patterns of seismicity before both eruptive periods; rather than a precursory increase in seismicity as is observed prior to many volcanic eruptions, we observe a decrease in seismicity many months prior to eruption. We developed a new program for cross-correlation of large seismic data catalogues and analysed multiplet activity surrounding both eruptive periods. We observed that the formation of new multiplets corresponds to periods of high event rates (during inter-eruptive periods) and high percentages of daily events that belong to a multiplet. We propose a model for the seismicity patterns observed at Telica, where changes in seismicity are related to a cyclic transition between open-system degassing and closed-system degassing. Periods of open-system degassing occur during non-eruptive episodes and are characterised by high event rates, a broad range of frequency content of events and high degrees of waveform correlation. A transition to closed-system degassing could be due to sealing of fluid pathways in the magmatic and/or hydrothermal system, or due to magma withdrawal. Periods of closed-system degassing are characterised by low event rates, higher frequency contents and low degrees of waveform correlation. Eruptive periods may then represent a transition from closed-system degassing to open-system degassing, however the system must also be capable of transitioning to open-system degassing without eruption. These observations have important implications for volcano monitoring and eruption forecasting at persistently restless volcanoes. Rather than a precursory increase in seismicity as is often observed prior to eruption at other volcanoes, our observations indicate that phreatic eruptions at Telica occur after a decrease in seismicity, a corresponding change in the frequency content of events, and a decrease in waveform correlation. These changes may represent a period of closed-system degassing that could culminate in phreatic eruptions. The inclusion of real-time analysis of variations in frequency content and multiplet activity provides critical information for volcano monitoring institutions.

La presente tesis titulada “Instrumentación geotécnica para monitorear el nivel freático y calidad del agua con sensores eléctricos en piezómetros de tubo abierto”, planteará las nuevas propuestas y actividades que se realizan para el monitoreo de las aguas subterráneas, que tiene como objetivo principal preservar los recursos hídricos y el ecosistema. La obtención de la serie de datos del nivel freático, permitirá conocer las variaciones bruscas de los niveles de agua durante el tiempo de operación; a su vez nos permitirá determinar si existen flujos de agua que alteren el comportamiento del mismo. Además en función a la información obtenida de los resultados de los ensayos físico-químicos y de los resultados de los ensayos de determinación de metales pesados realizados en laboratorios. Estos indicadores fueron comparados y nos permitieron conocer cuál es el estado de las aguas subterráneas en el momento de su evaluación. La metodología empleada es del tipo explicativa y cuantitativa, el diseño de la investigación será descriptivo, observacional y de corte longitudinal. Por ello la presente tesis pretende establecer una metodología de monitoreo de aguas subterráneas, que permita mejorar el comportamiento ambiental de las zonas de operación de una empresa dedica a la explotación de materia prima para el sector construcción; por lo cual se procesaron parámetros asociados a los aspectos ambientales establecidos en las herramientas de gestión y la legislación ambiental aplicable. Los resultados obtenidos respecto al nivel freático permitieron establecer aquellas épocas de incremento y disminución de los niveles de agua; además se lograron identificar posibles focos de contaminación del agua subterránea, presente en el área de influencia de las unidades de operación de una empresa cementera, concluyendo con la aceptación de las hipótesis planteadas. This thesis entitled as "Geotechnical instrumentation to monitor the phreatic level and water quality sensors in electrical piezometers open tube", raise new proposals and activities undertaken for monitoring groundwater, whose main objective is to preserve the water resources and the ecosystem. Obtaining the data series of the phreatic level, will reveal the abrupt changes in water levels during the time of operation; in turn will allow us to determine if water flows that alter behavior of the same. Also, according to information obtained from the results of the physicochemical and the results of tests of heavy metal determination tests conducted in laboratories. These indicators were compared and let us know what the status of groundwater at the time of evaluation. The methodology used is the explicative and quantitative type, the research design is descriptive and longitudinal. Therefore this thesis aims to establish a methodology for groundwater monitoring, which improves environmental performance of operational areas of a company engaged in the exploitation of raw materials for construction sector; whereby parameters associated with the environmental aspects set out in the management tools and the applicable environmental legislation is processed. The results regarding the phreatic level allowed to establish those periods of rising and falling water levels, they were also able to identify potential sources of groundwater contamination present in the area of influence of the operating units of a cement company, concluding with the acceptance of the hypotheses.

Amostras de diferentes espécies de Phreatobius foram coletadas para obtenção de dados moleculares potencialmente informativos do gene nuclear RAG-2 para resolver as relações filogenéticas do gênero. Apresento resultados de sequências. Os dados de Phreatobius foram combinados com sequências equivalentes de representantes de várias outras famílias de Siluriformes, e analisados via máxima parcimônia (total de 966 pares de base de RAG-2 para 176 táxons). As análises resultaram em 172 árvores com 5213 passos. O resultado do consenso estrito indica fortemente que Phreatobius forma um grupo monofilético (sustentado por 33 sinapomorfias moleculares) com Pseudopimelodidae e Pimelodidae, e Conorhynchos + Heptapteridae. Hipóteses anteriores posicionando Phreatobius exclusivamente com Heptapteridae não foram sustentadas. Os resultados apresentados requerem que Phreatobius seja alocado na sua própria família, Phreatobiidae (disponível em nível subfamiliar). Uma revisão taxonômica de Phreatobiidae mostra que existem ao menos sete espécies, das quais apenas três descritas: Phreatobius cisternarum, Phreatobius dracunculus, Phreatobius sanguijuela, Phreatobius sp. "Anapixi", Phreatobius sp. "Jaú", Phreatobius sp. Tarumanzinho", Phreatobius sp. "Viruá". A hipótese de relações filogenéticas dentro de Phreatobiidae mostra que Phreatobius cisternarum é grupo-irmão do clado composto por (Phreatobius sp. "Viruá" (P. dracunculus + Phreatobius sp. "Tarumanzinho")). O mapeamento filogenético demonstra que o hábito subterrâneo evoluiu uma única vez na família e o ambiente freático foi invadido duas vezes. / Samples from different species of Phreatobius were collected in order to obtain molecular data from nuclear RAG-2 gene sequence potentially informative to resolve phylogenetic relationships of the genus. The data on Phreatobiidae were combined with equivalent sequence information from representatives of several other siluriform families, and analyzed by maximum parsimony (a total of 966 bp RAG-2 for 176 taxa). The analyses resulted in 172 trees, with 5213 steps. The strict consensus results strongly indicate that Phreatobius forms a monophyletic group (supported by 33 molecular synapomorphies) with Pseudopimelodidae, Pimelodidae, and Conorhynchos + Heptapteridae. Previous hypotheses aligning Phreatobius exclusively with Heptapteridae were not supported. Results herein presented requires that Phreatobius be allocated in its own family, as Phreatobiidae (already available at subfamilial level). A taxonomic revision of Phreatobiidae shows that at least seven species exist, only three of which currently described: Phreatobius cisternarum, Phreatobius dracunculus, Phreatobius sanguijuela, Phreatobius sp. "Anapixi", Phreatobius sp. "Jaú", Phreatobius sp. Tarumanzinho", Phreatobius sp. "Viruá". A hypothesis of relationships within Phreatobiidae shows that P. cisternarum is sister-group of a clade composed of (P. sp. "Viruá" (P. dracunculus + P. sp. "Tarumanzinho")). Phylogenetic mapping shows that subterranean habit has evolved once in the family and the phreatic environment was invaded twice.

Made available in DSpace on 2015-03-26T13:28:17Z (GMT). No. of bitstreams: 1 texto completo.pdf: 5059501 bytes, checksum: 170c2825c5239225e0e73b8816f33b5b (MD5) Previous issue date: 2013-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / It is estimated that 35% of Brazil s population are supplied by groundwater and its use increases continuously. Some states, such as São Paulo, Maranhão and Piauí have most of its municipalities served by groundwater sources. Therefore it is necessary not only acquire knowledge about the country's underground water availability, but also the protection of its aquifers and the understanding of their behavior, allowing the management of those resource. The hydrogeological modeling is one of the most used tools in this process. This is the context related to the present work, which consists of the hydrogeological modeling of the Palmital watershed, located in Viçosa, Zona da Mata, Minas Gerais. The modeling process was based on a detailed characterization of the watershed comprising the basis of the area s hydrogeological conceptual model. The characterization included several field activities like six GPR tests, ten survey boreholes, several collections of soil samples for tactile-visual analysis, allocation and monitoring of water level in 6 wells and slug tests in 4 of them. The water balance calculation and estimation of recharge through the hydrographs of monitoring wells were also part of the characterization of the area. This data helped in determined the initial and boundary conditions and the characteristics of the model´s mesh, among other relevant information, allowing the generation of the computational hydrogeological model throughout Visual Modflow® software. Once created, the numerical model went through a calibration process involving WinPest® software, resulting in a normalized standard deviation of 7.1 % and refinement of some hydraulic conductivity parameters. This method has resulted in a good correlation between simulated head data and observed head data (in the field) at the 10 references (wells and springs) used in the calibration. After calibration, the model was validated throughout others 9 springs on the watershed, resulting in a normalized standard deviation of 8.0 %. The simulated aquifer, characterized as porous and free, is widespread, covering much of the basin until a depth of 30 m, which is the lower modeling for the present work. The groundwater flow occurs from areas of higher elevation to the drainage network or to the lower areas of the sub-basin. Once calibrated and validated, the model had its parameters sensitivity evaluated and was found that the hydraulic conductivity and recharge parameters strongly influence the model while conductance of drains have little influence on it. Finally, two hypothetical scenarios were simulated. In each one of them pumping wells were entered into the model, working all with the same flow rate. All wells were installed with 12 m depth, the 2 final meters being its screened interval. The simulations ran with flow rates of 1 and 3 m3·d-1. It was observed that for simulated scenarios, impacts on the aquifer were stronger for higher flow rates, causing the most visible changes of equipotentials curves. Although, insignificant changes in the direction or magnitude of the underground water flow were noted. The changes caused by simulations were easily noticed in places of higher height due to proximity to the edges of the aquifer. / Estima-se que 35% da população brasileira são abastecidos por águas subterrâneas e o seu uso aumenta a cada década. Alguns estados, como São Paulo, Maranhão e Piauí possuem a maioria de seus municípios abastecidos por mananciais subterrâneos. Logo, é necessário não apenas o conhecimento acerca das disponibilidades hídricas subterrâneas do país, mas também a proteção dos aquíferos e a compreensão de seu comportamento, permitindo que a gestão desses recursos possa ser realizada de forma adequada. A modelagem hidrogeológica é uma das ferramentas mais utilizadas neste processo. Esse é o contexto em que se insere o presente trabalho, que consiste na modelagem hidrogeológica da sub-bacia hidrográfica do Córrego Palmital, localizada no município de Viçosa, Zona da Mata de Minas Gerais. A caracterização desenvolvida compreendeu diversas atividades de campo como seis seções de levantamentos com GPR (Radar de Penetração do Solo), dez furos de sondagem, várias coletas de amostras de solo para análise táctil-visual, alocação e monitoramento do nível da água em 6 poços e ensaio de slug test em 4 deles. A caracterização também se baseou em outros trabalhos realizados na área, principalmente nos de Andrade (2010) e Betim (2013). O cálculo do balanço hídrico e a estimativa da recarga através dos hidrogramas do monitoramento dos poços também fizeram parte da caracterização da área, compondo também o modelo conceitual da sub-bacia. De posse desses dados, foram determinadas as condições iniciais, condições de contorno e as características da malha do modelo, dentre outras informações pertinentes, gerando-se o modelo hidrogeológico computacional por intermédio do software Visual Modflow®. Depois de criado, o modelo numérico passou por um processo de calibração envolvendo o software WinPest®, resultando em um desvio padrão normalizado de 7,1 % e no refinamento das condutividades hidráulicas iniciais. Também se obteve uma boa correlação entre os dados de carga simulados e os dados de carga observados em campo nas 10 referências utilizadas, entre poços e nascentes. Após a calibração, o modelo foi validado com base na localização de outras 9 nascentes existentes na bacia, o que gerou um desvio padrão normalizado de 8,0 %. O aquífero simulado, caracterizado como poroso e livre, é extenso, cobrindo grande parte da bacia até uma profundidade máxima em torno de 30 m, sendo este o limite inferior de modelagem, nesta pesquisa. O fluxo subterrâneo ocorre dos locais de maior cota para a rede de drenagem ou para as áreas mais baixas da sub-bacia. Uma vez calibrado e validado, o modelo teve a sensibilidade de seus parâmetros analisada, tendo sido constatado que os parâmetros condutividade hidráulica e recarga influenciam fortemente o modelo, enquanto que a condutância dos drenos exerce pouca influência. Por fim, foram simulados dois cenários hipotéticos em que foram inseridos poços de bombeamento que trabalhavam com a mesma vazão, todos com 12 m de profundidade, com seção filtrante localizada nos 2 m finais. Nos cenários 1 e 2, as vazões usadas nas simulações foram de 1 e 3 m3·d-1, respectivamente. Observou-se nos cenários simulados que os impactos ao aquífero são mais fortes para a maior vazão provocando alterações mais visíveis das equipotenciais. Não se obervaram mudanças significativas na direção ou na magnitude do fluxo hídrico subterrâneo. As alterações provocadas pelas simulações são facilmente notadas nos locais de maiores cotas devido à proximidade com as bordas do aquífero.