L’objectif de notre étude est de modéliser un réservoir géothermique. Si nous supposons que le réservoir géothermique n’est composé que d’eau pure le transfert de matière et d’énergie est classiquement décrit par deux équations de conservation : la conservation de la matière et la conservation de l’énergie. À ces deux équations vient s’ajouter la vitesse du fluide classiquement donnée par la loi de Darcy tandis que les propriétés thermodynamiques, obtenues grâce à des équations théoriques ou empiriques (les équations d’état), ferment le modèle mathématique. Dès lors, ce modèle fermé, il existe différents schémas de résolution. Le premier est de résoudre en pression et température puis de procéder à un changement de variables lors du passage de monophasique à diphasique ou de diphasique à monophasique. TOUGH2 utilise le couple pression-saturation dans la zone diphasique.La seconde approche est de résoudre en pression et enthalpie afin d’accroître la stabilité lors de la transition entre l’état monophasique et l’état diphasique (voir Hydrotherm). Nous avons adopté la seconde option, résoudre en pression et enthalpie. De plus la résolution spatiale est faite avec les volumes finis.La modélisation d’un réservoir géothermique fait intervenir des équations fortement dépendantes l’une de l’autre. Cependant nous avons fait le choix de découpler la résolution afin de se libérer de la complexité de la résolution du système couplé. En effet, cette méthode possède l’avantage d’être moins consommatrice de mémoire puisque nous travaillons toujours avec le même nombre de données, mais dans une matrice deux fois moins importante. Nous montrerons que cette méthode demeure suffisamment précise pour une utilisation aussi bien dans le domaine industriel que dans celui de la recherche.Nous offrons à l’utilisateur une grande liberté grâce à l’implémentation de plusieurs méthodes : Euler implicite, explicite, Runge-Kutta ou BDF2 pour les solveurs temporels ou GMRES et BICGSTAB pour les solveurs linéaires. Nous pouvons gérer des conditions aux limites très variées telles que des flux nuls (décrivant une frontière qui n’échange pas de matière avec l’extérieur) ou une condition mixte (un Dirichlet sur la pression et un Dirichlet ou condition « sortie libre » sur la température… Cette dernière situation décrit une zone de recharge ou de décharge. Nous avons développé un outil multilangage : Python,Fortran et C++ (une implémentation de l’IAPWS provenant du projet freesteam incluant la zone supercritique). Tous ces langages sont orientés objet. L’IAPWS est l’outil permettant de calculer les propriétés physiques inconnues et par conséquent il ferme le système.Enfin nous avons appliqué le modèle sur le bassin parisien, France, sur plusieurs systèmes 1D et un autre système 2D réalisés par Coumou avec la plateforme CSMP++. Le bassin parisien est un réservoir exploité pour produire de la chaleur par le biais du pompage d’une eau à 70 _C et réinjecté à 40 _C. Les simulations 1D permettent de visualiser le déplacement d’un front de chaleur en haute enthalpie. La simulation 2D montre la convection naturelle de l’eau dans une faille. Chaque simulation a été comparée aux résultats obtenus avec un autre code (CSMP++, HYDROTHERM ou TOUGH2) et les résultats sont en accord. / The purpose of our study is to model a geothermal reservoir. When geothermal reservoirs are assumed to be composed of pure water, the transfer of mass and energy is classically described by two balance equations: the mass balance equation and the energy balance equation. In addition to those equations, fluid velocity is classically given by the Darcy law while thermodynamic properties, inferred from theoretical or empirical equations of state, are used to close the mathematical system. Once this system is closed, there exist different solutions. The first one is to solve for pressure and temperature with a variable switch to saturation in the two-phase region (e.g. TOUGH2). The second one is to solve for pressure and enthalpy to increase the stability of phase transition between single and two-phase states (e.g. Hydrotherm). We adopted the second option. We solve the system by using a splitting method — to get rid of the complexity of coupling equations — and a finite volume method for the spatial discretization. We offer some freedom to users thanks to the implementation of several methods like explicit or implicit Euler, Runge-Kutta or BDF2 for time solvers or GMRES and BICGSTAB for the linear solver. We can handle several boundary conditions like no-flow — describing a boundary which cannot exchange matter withthe exterior — or like a mixed-therm condition — a Dirichlet condition to the pressure and a Dirichlet or an outflow condition to the temperature in order to describe a recharge or a discharge zone — …Selecting object-oriented languages, we developed a multi-language framework, combining Python, Fortran and a C++ implementation of IAPWS (from the freesteam project) including the supercritical equations. To close the system physical propertiesare determined by the IAPWS- IF97 thermodynamic formulation. We’ve applied this simulation model to the dogger in Paris, France, to several onedimensional systems and a two-dimensional one made by Coumou with the CSMP++platform. The dogger is a reservoir exploited to produce heat by pumping water at 70 _C and reinjecting it in the reservoir at 40 _C. In the one-dimensional systems we wanted to observe the process of heat transfer from a higher temperature boundary to a smaller one in a high-energy domain. The last simulation shows the natural convection of water in a fault. For every simulation we compared the solutions we found with another code (TOUGH2 or CSMP++) and they agreed.

Dans l'histoire des éruptions volcaniques, le Papandayan à l'Ouest de Java est considéré comme l'un des plus meurtriers après avoir causé la mort de 2957 personnes et des dégâts sérieux en 1772. L'éruption la plus récente de ce volcan a eu lieu en 2002 et était de type phréatique. Cette éruption a été précédée d'une augmentation soudaine de l'activité sismique moins de deux jours avant l'éruption. Aucune victime n'a été déplorée. La nature de cette éruption est indéfinie. Cette thèse regroupe plusieurs études utilisant différentes techniques en vue d'améliorer la prédictibilité des éruptions du volcan Papandayan, principalement via l'interprétation des signatures sismiques.<p>Le monitoring sismique passif a débuté en décembre 2009 par l'installation d'une station sismique permanente à large bande dans le cratère du Papandayan. L'année suivante, une station météorologique a été installée pour compléter les mesures. La troisième année, 8 stations sismiques temporaires ont été déployées autour du volcan en réponse à une augmentation de l'activité sismique en 2011.<p>Nous avons conduit différentes études; (1) Nous avons examiné l'évolution de l'activité volcanique par réalisation d'une revue complète de l'histoire éruptive du volcan, autant pour la période préhistorique qu'historique. (2) Nous avons réalisé une analyse temps-fréquence des événements sismiques, étudié leurs caractéristiques et proposé une nouvelle classification avec une description des processus physiques supposés les générer. (3) Nous avons étudié les signatures sismiques précurseur de l'éruption de 2002 et pendant la crise volcanique de 2011 en implémentant différentes méthodologies, dont: la détection automatique d'événements sismiques à l'aide de filtres récursifs STA/LTA, l'analyse spectrale des formes d'onde, la mesure continue de l'amplitude spectrale du signal (SSAM), la polarisation des ondes et l'analyse de la distribution fréquence/magnitude (b-value). Nous avons alors réalisé un modèle chronologique des séquences sismiques du Papandayan. (4) Pour améliorer la compréhension de la dynamique des fluides sous le volcan Papandayan, nous avons réalisé une analyse des fréquences complexes des événements longue période (LP) et leurs variations temporelles peuvent être utilisées pour estimer (a) la composition des fluides présents dans les fractures sous le volcan et/ou (b) l'évolution des dimensions de ces fractures. Ces variations des fréquences complexes des événements LP peuvent être interprétées comme les réponses dynamiques du système hydrothermal à des changements d'impulsions de chaleur transférées par les flux de gaz volcaniques du magma sous le volcan. (5) nous avons calculé l'évolution temporelle du rapport spectral horizontal-sur-vertical (HVSR) en utilisant le bruit sismique ambiant enregistré par une station unique pour estimer les variations de vitesse de propagation des ondes de cisaillement en lien avec l'activité dynamique du volcan. Nous avons trouvé une corrélation claire entre les variations de fréquence de résonnance HVSR et l'augmentation de la sismicité.<p>Enfin, nous proposons des hypothèses sur les processus physiques qui se produisent sous le Papandayan. Cette étude est une première tentative d'utilisation de cette méthode pour surveiller l'activité volcanique en continu.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Neste trabalho estudamos um controlador denominado rastreador linear quadrático (RLQ) com custo médio de longo prazo (CMLP) para sistemas lineares com saltos markovianos (SLSM). Mostramos que o conceito de detetabilidade uniforme, juntamente com a hipótese de que o regulador linear quadrático associado ao RLQ tenha custo uniformemente limitado, são suficientes para que o controle obtido seja estabilizante em um certo sentido. A partir deste resultado, e considerando as mesmas hipóteses, demonstramos a existência do CMLP. Com isto, estendemos os resultados dispostos na literatura desde que consideramos um sistema variante no tempo e uma estrutura mais geral para a cadeia deMarkov. Além disto, avaliamos a aplicação deste controlador no planejamento da operação de um sistema hidrotérmico. Para isto, utilizamos o sistema de usinas do rio São Francisco, em dois casos de estudo, para comparar o desempenho do controlador estudado em relação à solução ótima para o problema, encontrada com o uso da programação dinâmica estocástica, e em relação à solução obtida via programação dinâmica determinística. Os resultados sugerem que o RLQ pode representar uma alternativa interessante para o problema de planejamento hidrotérmico / In the present work we study the reference tracking controller (RTC) for the long run average cost (LRAC) problem for Markov jump linear systems. We show that uniform detectability and an hypothesis that the linear quadratic regulator associated with the RTC has uniformly bounded cost, together, are sufficient conditions for the obtained control be exponentially stabilizing in a certain sense. This result allows us to demonstrate the existence of the LTAC under the same hypotheses. The results can be regarded as an extension of previous works, since we have considered a more general framework with time-varying systems and quite general Markov chains. As an applicatioin, we consider the operational planning of hydrothermal systems. We have considered some power plants of the Sao Francisco river, in two different scenarios, and we have compared the performances of the RTC and standard controls obtained by deterministic and stochastic dynamic programming, indicating that the RTC may be an interesting alternative for the hydrothermal planning problem

The thesis presents research on recent hydrothermal discharge features in a shallow marine hydrothermal system. It aims to clarify their occurrence, genesis, and preservation potential. A facies model is developed, being based on the processes involved in the formation and the prevailing lithofacies. It describes six major groups: channels, fractures, tubes, cones, bowls, and lineaments. Each of these groups subdivides into numerous facies types according to the cements or mineral precipitates prevailing. To clarify the rather complex formation processes of hydrothermal discharge features, genetic models for each facies are proposed. An integrated evolutionary model is developed considering the temporal evolution of the major types of hydrothermal discharge features in the Panarea system and their preservation potential. Confirming presumptions of former, preliminary data, the first documentation of secure paleo-evidences of such hydrothermal discharge features is presented.:1. Introduction ....11 1.1. Preamble .....11 1.2. Research questions, objectives, and hypotheses ......................................... 12 2. State of research - seafloor hydrothermal systems ................................ 15 2.1. Hydrothermal deposits in general ................................................................. 15 2.2. Deep-sea environments ............................................................................... 16 2.3. Shallow-water systems and their preservation potential ............................... 17 3. Panarea Island - the area of investigation ................................................ 20 3.1. The hydrothermal system of Panarea Island ................................................ 20 3.2. Fluid discharge features in Panarea ............................................................. 30 3.3. Study sites .................................................................................................... 34 4. Materials and methods ............................................................................... 40 4.1. Underwater research .................................................................................... 40 4.2. Field methods ............................................................................................... 41 4.3. Laboratory methods ..................................................................................... 44 5. Results ........................................................................................................ 47 5.1. Prevailing lithologies ..................................................................................... 47 5.1.1. Hardrocks ..................................................................................................... 47 5.1.2. Sedimentary rocks ........................................................................................ 51 5.1.3. Sediments .................................................................................................... 54 5.1.4. Cements ....................................................................................................... 58 5.2. Underwater investigation sites and findings ................................................. 66 HYDROTHERMAL FLUID DISCHARGE FEATURES IN PANAREA, ITALY PAGE 10 | 174 5.2.1. Area 26 ......................................................................................................... 66 5.2.2. Basiluzzo ...................................................................................................... 75 5.2.3. Black Point ................................................................................................... 77 5.2.4. Bottaro North ................................................................................................ 79 5.2.5. Bottaro West ................................................................................................. 81 5.2.6. Cave ............................................................................................................. 84 5.2.7. Fumarolic Field ............................................................................................. 87 5.2.8. Hot Lake ....................................................................................................... 89 5.2.9. La Calcara .................................................................................................... 92 5.2.10. Point 21 ........................................................................................................ 98 5.2.11. Subaerial locations ..................................................................................... 100 5.3. Summarizing tables .................................................................................... 104 6. Interpretation ............................................................................................ 106 6.1. Discharge features and secondary processes ............................................ 106 6.1.1. Complex genesis and development of discharge features and their occurrence throughout the system ............................................................. 119 6.1.1.1. Cones, bowls, and lineament structures ..................................................... 119 6.1.1.2. Tubes ......................................................................................................... 128 6.2. Preservation potential and paleo-record ..................................................... 138 7. Conclusion and Discussion .................................................................... 141 7.1. General context of the formation of hydrothermal discharge features in Panarea ...................................................................................................... 141 7.2. Evolution of hydrothermal discharge features in Panarea .......................... 142 7.3. Comprehensive summary ........................................................................... 145

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-03-20T13:40:45Z No. of bitstreams: 1 wellingtoncarlosdaconceicao.pdf: 4259949 bytes, checksum: 52410bbb422df8d4e80e7f6956efc71e (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-03-21T13:12:55Z (GMT) No. of bitstreams: 1 wellingtoncarlosdaconceicao.pdf: 4259949 bytes, checksum: 52410bbb422df8d4e80e7f6956efc71e (MD5) / Made available in DSpace on 2017-03-21T13:12:55Z (GMT). No. of bitstreams: 1 wellingtoncarlosdaconceicao.pdf: 4259949 bytes, checksum: 52410bbb422df8d4e80e7f6956efc71e (MD5) Previous issue date: 2016-12-12 / O sistema de produção de energia elétrica brasileiro é um sistema hidrotérmico de grande porte com forte predominância de usinas hidrelétricas. O planejamento e operação do sistema é realizado considerando diversos fatores, tais como, estocasticidade das afluências, usinas hidrelétricas em cascata e acoplamento temporal da operação. A resolução deste tipodeproblemaéfeitaconsiderandodiversoshorizontesdeplanejamento. Oplanejamento da operação de médio prazo compreende um período de 5 anos de estudo, e este período é discretizado em base mensal. O presente trabalho apresenta uma metodologia alternativa para resolução do problema de planejamento da operação de médio prazo de sistemas hidrotérmicos utilizando a Programação Dinâmica Estocástica (PDE) com discretização dointercâmbiodeenergiaentreossubsistemas(PDE-INT).Alémdisso, utiliza-seatécnica de sistemas equivalentes de energia e o algoritmo de fechos convexos (convex hull) para obtenção da função de custo futuro a partir dos pontos obtidos pela PDE-INT. Nesta abordagem, para cálculo da política energética, os subsistemas são considerados isolados, e desta forma, as variáveis que compõem o espaço de estados que são discretizadas são a energia armazenada e o intercâmbio líquido entre os subsistemas. Inicialmente, para análise e avaliação da metodologia proposta na resolução do problema de planejamento hidrotérmico, criou-se um sistema tutorial, composto por dois subsistemas. Em seguida, a metodologia foi utilizada considerando todo o sistema elétrico brasileiro, representado por quatro subsistemas ou submercados. Os resultados mostraram que com a técnica de separação dos subsistemas há uma redução significativa no tempo computacional quando comparados com as técnicas tradicionais que utilizam programação dinâmica. Desta forma, a metodologia proposta pode ser utilizada para uma análise rápida e inicial do caso em estudo, servindo como base para estudos e refinamentos posteriores. / The Brazilian power production system is a large scale hydrothermal system with a strong predominance of hydroelectric power plants. The electric power system operation planning must take into consideration several factors, such as uncertainty of the water inflows, hydroelectric plants in cascade and temporal coupling. This problem is solved considering different planning horizon. The long-term operation planning problem is generally solved by a chain of computational models that consider a period of 5 years ahead with monthly discretization. This work presents an alternative strategy to solve hydrothermalsystemsoperationplanningbyStochasticDynamicProgramming(SDP)with discretization of energy interchange between subsystems (SDP-INT). Under the presented approach, the hydroelectric plants are grouped into energy equivalent subsystems and the expected operation cost functions are modeled by a piecewise linear approximation, by means of the convex hull algorithm. Also, under this methodology, the subsystems are solved isolated, but the net energy interchange (export – import) between subsystems is set as a state variable of the cost function, together with the energy storage Initially, for the analysis and evaluation of the proposed methodology applied on solving the hydrothermalplanningproblem, themethodologyisusedinatutorialsystem, composedof two subsystems. Next, a simulation with the whole Brazilian electrical system considering four subsystems is presented. The results have shown that this subsystems separation technique reduces significantly the computation time when compared with the traditional techniques, demonstrating the effectiveness of the proposed methodology. Thus, the proposed methodology can be used for a fast and initial analysis of the case study, serving as a basis for further studies.

Kawah Ijen (2386 m) is a stratovolcano located within Ijen Caldera, at the easternmost<p>part of Java island in Indonesia. Since 2010, the volcano has been equipped with seismometers<p>and several sensors (temperature and level) have been immersed in its acidic lake waters and in the acidic river seeping on the volcano flanks. While finding instruments capable of resisting to such extreme conditions (pH~0) has been challenging, the coupling of lake monitoring techniques with seismic data improves the knowledge of the volcanic-hydrothermal dynamics. Moreover, the monitoring capabilities have been considerably<p>enhanced supporting the decision-making of the authorities in case of emergency.<p><p>Several methods and processing techniques were used to analyze the seismic data. Much effort has been given to implement the seismic velocities (Moving Window Cross Spectral Analysis (MWCSA)) calculations. At Kawah Ijen, the frequency band that is less affected by the volcanic tremor and the seasonal fluctuations at the source ranges between 0.5-1.0 Hz. Moreover, a stack of 5 days for the current CCF gives reliable results with low errors and allows to detect fluctuations which are missed using a 10-day stack.<p><p>The background seismic activity mostly consists in low frequency events and a continuous tremor of low amplitude. Fluctuations of the lake temperature and level result from the recharge of the hydrothermal system during the rainy season. Kawah Ijen lake waters are not perfectly mixed and a shallow stratification occurs during the rainy season, because meteoric waters are less dense than the lake fluids.<p><p>Different unrest occurred during our study. Some of them strongly affected the volcanic lake, while others did only weakly. In the first category, a strong unrest commenced in October 2011 with heightened VT (Volcano Tectonic) earthquakes and low frequency events activity, which culminated mid-December 2011. This unrest was correlated with an enhanced heat and hydrothermal fluids discharge to the crater and significant variations of the relative velocities (~1%). This suggests an important build-up of stress into the system. VT earthquakes opened pathways for the fluids to ascend, by increasing the permeability of the system, which latter allowed the initiation of monochromatic tremor (MT) when the steam/gases interacted with the shallow portions of the aquifer. Our calculations evidence a higher contribution of steam in March 2012 that might explain the increase of the MT frequency when bubbles were observed at the lake surface. This period was also characterized by short-lived but strong velocity variations, related to water level<p>rises containing important amount of bubbles, and important heat and mass discharges<p>into the lake. On the contrary, the second category of unrest did only slightly affect the<p>lake system. This could be explained by a dryer hydrothermal system and/or locations of<p>the seismic sources, which were not directly linked to the lake.<p><p>While a magmatic eruption will likely be preceded by a strong seismic activity, the major challenges remain to understand why the unrest we studied did not lead to an eruption and to identify precursory signs of a phreatic eruption. Even a small phreatic eruption would be devastating for the people working everyday in the crater and the ones<p>who live nearby the voluminous acidic lake. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Orientador: Prof. Dr. Thales Souza / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, Santo André, 2018. / Atualmente, no Brasil, a matriz elétrica é composta predominantemente por fonte hidráulica e térmica, na proporção de 70% e 30%, respectivamente. Nesse sentido, para a segurança do Sistema Interligado Nacional, o mesmo é considerado um sistema hidrotérmico, onde a disponibilidade de armazenamento das bacias hidráulicas e de combustíveis representa a quantidade de energia elétrica disponível para atendimento a demanda. Assim, os critérios para cálculo de Energia Assegurada representam as Garantias Físicas das Usinas Hidrelétricas e Usinas Térmicas, que são calculadas através das médias de gerações dos empreendimentos disponíveis no Sistema Interligado Nacional com a previsão de 15 anos. Contudo, a expansão dos aproveitamentos de usinas com reservatório encontra-se no limite de exploração no sul e sudeste/centro-oeste, havendo apenas na região Norte potenciais a serem avaliados. Entretanto, devido às restrições ambientais, não há previsão de construção de novas Usinas Hidrelétricas com reservatório na região Norte, o que indica a necessidade de viabilização de outras fontes de energia elétrica. Nesse sentido, a Garantia Física é utilizada para balizar qual o risco de déficit futuro considerando o balanço de demanda e oferta no sistema. Dessa forma, o presente trabalho propôs a análise dos parâmetros de risco da Garantia Física do sistema imputados no modelo de projeção elétrico NEWAVE. Por fim, com objetivo de validar a análise proposta, as projeções de Garantias Físicas das Usinas Hidrelétricas e Usinas Térmicas que fazem parte do Sistema Interligado Nacional foram avaliadas, a partir do método de escolha do risco de déficit. / Currently, in Brazil, the electrical matrix is mainly composed of hydraulic and thermal sources, in the proportion of 70% and 30%, respectively. In this sense, for the safety of the National Interconnected System, it is considered a hydrothermal system, in which the storage capability of the hydraulic basins and fuel availability represent the amount of electrical energy available to meet demand. Thus, the criteria for calculation of Assured Energy represent the Physical Guarantees of the Hydroelectrical Power Plant and Thermal Power Plants, which are calculated through the average of generations of the enterprises available in the National Interconnected System with a forecast of 15 years. However, the expansion of uses of power plants with reservoirs is at the exploration limit in the South, Southeast/Center-West, with only the North region with potential to be evaluated. Still, due to environmental restrictions, there is no prevision of construction of new Hydroelectrical Power Plant with reservoir in the North region. Being so, the Physical Guarantee is used to identify the future deficit risk by making a balance of supply and demand in the system. In this way, the present work proposed an analyze of Physical Guarantee system risk parameters imputed in the electrical projection model NEWAVE. So, to validate the methodology proposed the Physical Guarantee projection of the Hydroelectrical Power Plant and Thermal Power Plants that are part of the National Interconnected System were evaluated consdering the method of choosing the risk of deficit.

Surface manifestations of hydrothermal fluids such as fumaroles and hot springs provide valuable information about the level of activity of a volcano during quiescent period. Geochemical study of gas and spring waters is useful to elaborate geochemical model for magmatic-hydrothermal system. Furthermore, temporal geochemical monitoring of these fluids with time provides a better understanding in processes occurring inside the volcano and can be useful to detect any changes in the activity of the magmatic-hydrothermal system. This thesis investigates two hydrothermal systems at Kelud and Papandayan volcanoes that are located at Java Island in Indonesia. Kelud is considered as one of the most dangerous volcanoes of Java because of its frequent eruptions. After the last eruption that occurred in 1990, a new lake rapidly filled the crater of Kelud volcano. Water samples collected since 1993 are near neutral Na-K chloride fluids and are typical of aged hydrothermal system where the acidity has been completely neutralized by fluid-rock interaction and where the emission of acid magmatic gases has stopped. Two sudden increases in lake temperature in 1996 and 2001 were accompanied by rapid changes in lake water compositions and suggest the existence of two hydrothermal systems feeding the lake: a shallow hydrothermal system dominated by Ca-Mg sulfate waters and a deepest aquifer with neutral alkali chloride waters. From 2001 to 2005, measurements of CO2 emitted by the surface of the lake were performed by using the accumulation chamber method modified in order to work at the surface of a crater lake. Two statistical methods were used to process data: the graphical statistical and stochastic simulation methods. The results of graphical statistical approach showed that two different degassing processes are acting at the lake surface: one corresponding to CO2 fluxes resulting from rising bubbles and the other corresponding to equilibrium diffusion of dissolved CO2 at the water-air surface. Total CO2 emission rate estimated by stochastic simulation ranges from 105 t/day for 2001 to 32 t/day for 2005. Thermal energy released by the lake was also estimated by using an energy balance model with a new constraint using the CO2 flux. The thermal flux decreased from 200 MW (2001) to 100 MW (2002) and then remained stable. Correlation between the chemical data of waters, the fluxes of CO2 and energy show that a constant decrease in the level of activity of the volcano since 1993 occurred although the lake temperature has been stable since 2003. Since the last magmatic eruption that occurred in 1772, phreatic eruptions occur on Papandayan volcano with the last one in 2002. The volcanic material ejected during this eruption is essentially made of altered rocks from within the hydrothermal system. The interaction of acid waters with the host rocks corresponds to an advanced argilic alteration. The chemical compositions of waters from Papandayan volcano and Kelud lake waters are contrasting. Indeed, the spring waters sampled since 1994 are acid sulfate-chloride waters and acid sulfate waters. The chemical and isotopic analyses of gases and waters suggest a significant magmatic contribution in SO2, HCl and HF to the hydrothermal system. The chemical composition of waters sampled after the 2002 eruption have provided information about origin of this eruption. Decrease in chloride concentration and in delta 34S of dissolved sulfates showed that the magmatic contribution in these fluids are less important and that the waters are likely to be formed by the condensation of steam (H2O, H2S) rising from a boiling aquifer.

Surface manifestations of hydrothermal fluids such as fumaroles and hot springs provide valuable information about the level of activity of a volcano during quiescent period. Geochemical study of gas and spring waters is useful to elaborate geochemical model for magmatic-hydrothermal system. Furthermore, temporal geochemical monitoring of these fluids with time provides a better understanding in processes occurring inside the volcano and can be useful to detect any changes in the activity of the magmatic-hydrothermal system. This thesis investigates two hydrothermal systems at Kelud and Papandayan volcanoes that are located at Java Island in Indonesia. Kelud is considered as one of the most dangerous volcanoes of Java because of its frequent eruptions. After the last eruption that occurred in 1990, a new lake rapidly filled the crater of Kelud volcano. Water samples collected since 1993 are near neutral Na-K chloride fluids and are typical of aged hydrothermal system where the acidity has been completely neutralized by fluid-rock interaction and where the emission of acid magmatic gases has stopped. Two sudden increases in lake temperature in 1996 and 2001 were accompanied by rapid changes in lake water compositions and suggest the existence of two hydrothermal systems feeding the lake: a shallow hydrothermal system dominated by Ca-Mg sulfate waters and a deepest aquifer with neutral alkali chloride waters. From 2001 to 2005, measurements of CO2 emitted by the surface of the lake were performed by using the accumulation chamber method modified in order to work at the surface of a crater lake. Two statistical methods were used to process data: the graphical statistical and stochastic simulation methods. The results of graphical statistical approach showed that two different degassing processes are acting at the lake surface: one corresponding to CO2 fluxes resulting from rising bubbles and the other corresponding to equilibrium diffusion of dissolved CO2 at the water-air surface. Total CO2 emission rate estimated by stochastic simulation ranges from 105 t/day for 2001 to 32 t/day for 2005. Thermal energy released by the lake was also estimated by using an energy balance model with a new constraint using the CO2 flux. The thermal flux decreased from 200 MW (2001) to 100 MW (2002) and then remained stable. Correlation between the chemical data of waters, the fluxes of CO2 and energy show that a constant decrease in the level of activity of the volcano since 1993 occurred although the lake temperature has been stable since 2003. Since the last magmatic eruption that occurred in 1772, phreatic eruptions occur on Papandayan volcano with the last one in 2002. The volcanic material ejected during this eruption is essentially made of altered rocks from within the hydrothermal system. The interaction of acid waters with the host rocks corresponds to an advanced argilic alteration. The chemical compositions of waters from Papandayan volcano and Kelud lake waters are contrasting. Indeed, the spring waters sampled since 1994 are acid sulfate-chloride waters and acid sulfate waters. The chemical and isotopic analyses of gases and waters suggest a significant magmatic contribution in SO2, HCl and HF to the hydrothermal system. The chemical composition of waters sampled after the 2002 eruption have provided information about origin of this eruption. Decrease in chloride concentration and in delta 34S of dissolved sulfates showed that the magmatic contribution in these fluids are less important and that the waters are likely to be formed by the condensation of steam (H2O, H2S) rising from a boiling aquifer.<p><p> / Doctorat en sciences, Spécialisation géologie / info:eu-repo/semantics/nonPublished