No description available.

Thesis advisor: Ernesto Livon-Grosman / This dissertation takes a literary and cultural studies model to explain the textual representation of these unique islands since their discovery until present day. The main argument suggests that the depiction of this crucial space for modernity in Western thought, given the rhetoric of travel and fiction writers, deploys the insular area with the intention of conceiving new forms of political displacement and identity endeavors in addition to those of the nation building project that took place in the mainland. As a result of colonial enterprises, scientific excursions, exile, tourism, journalistic pieces, expeditions, etc., travel writings of the Galápagos record the experience of reshaping this space à propos of a theory of travel and travel writing mediated by narratives that complement the formation of the state and its national imagery. The insular space functions as a vacant signifier where travelers are able to communicate their own signified upon narrating the experiences of their journeys. This phenomenon creates a profound conceptual and political division between the identity of the isles and the nation of Ecuador, and the findings of this study can be extrapolated to a historical specificity of explorations and representations that deal with narrative constructions of highly condensed spaces throughout Latin America as a whole, if one can claim they are a case study of an "unfinished" modernity. This separation created a rupture leading to fundamental variations in the manner in which local inhabitants and foreign entities interpret the insular province nowadays. The literature of the Galápagos reflects the scale of friction, migratory tendencies into the islands, and how global interests prevail in the appropriation of the space, reshaping the subjective individuality of the host culture. The first chapter examines texts of discovery written during the colonial enterprise of Spain. Given the anthropological void in the Galápagos, these initial pieces of writing emphasize the monstrosity of the landscape and the biota, but also portray a possibility to find riches. This description ignites a dichotomist infernal-paradisiacal appraisal of the archipelago, and recreates it as a warped textual space which, in turn, develops an imagery that demonstrates the flexibility of the deserted island: writers set forth almost any form of representation that favors imperial interests. The second chapter analyzes travel literature written in English during the nineteenth century. These texts define the islands as a world within itself rather than as a province of Ecuador, and have a major impact on its imagery given the authority of its writers. In the midst of Latin-American independence, the nation-building project, and the quest for a cosmopolitan state, foreign texts are detached from the social and political reality of the entourage, and transmit a fallacious notion of desertedness, which allows for future occupations of transcontinental scope. These books also create a bilingual literature that preludes the migratory movement and touristic commerce that currently defines this province. The final chapter focuses on three books written by local authors and how they combat or appropriate previous insular narratives providing a native perspective. A historiographical novel, defined as a "foundational fiction" that portrays the Galápagos as a prison and pirate hideout, exhibits the violent environment of the newborn Ecuadorian Republic. This piece generates a fissure in the international community that regards the islands as paradise and still is, therefore, largely ignored. A second narrative shows how the Galápagos occupation of the United States during World War II is crucial for interpreting and understanding the archipelago during the twentieth century. It preludes current international interests that dominate policy-undertakings, particularly the ones concerning tourism, environmental, and geopolitical endeavors. Finally, a quarto book exemplifies how texts have enticed and caused not only a critical political and national divorce between the nation and the insular region, but also a market-oriented global milieu triggering migration towards this zone. The discussed works include Tomás de Berlanga's "Carta a su majestad describiendo su viaje" (1535), Sarmiento de Gamboa's Historia de los incas (1572), Darwin's Voyage of the Beagle (1839), Melville's The Encantadas, or Enchanted Isles (1854), Manuel Bilbao's El pirata del Guayas (1855), Bolívar Naveda's Galápagos a la vista (1952), and Hugo Idrovo's Galápagos: huellas en el paraíso (2005). I use critical theory from Adorno, Bartkowski, Bloom, De Certeau, Deleuze, Edmond, Mignolo, Molloy, Musgrove, O'Gorman, Pratt, Sommer, Todorov, Van den Abbeele, and others to show the impact of the construction of an imaginary space that morphs incessantly and responds more to writers' interests than to the inherent qualities of the isles. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Romance Languages and Literatures.

La présente thèse a pour ambition d’interroger les fondements de la protection de la nature à l’ère de l’anthropocène. Le postulat de départ est que l’incapacité à répondre aux enjeux écologiques reflète les contradictions de l’ontologie naturaliste, laquelle s’est imposée comme la conception hégémonique des rapports entre humains et non humains (Descola 2005). L’argumentaire repose sur une analyse critique des politiquesdéveloppées dans un territoire emblématique du naturalisme : l’archipel des Galapagos (Équateur). Lieu fondateur des sciences naturelles, il représente l’archétype le plus abouti des figures, elles-mêmes archétypales, de l’île-laboratoire et de l’île-conservatoire. Il abrite depuis 1959 un parc national couvrant 97% des terres émergées et depuis 1998 une réserve marine parmi les plus vastes au monde. Archipel tropical le mieux conservé du monde, c’est aussi celui qui connaît la dégradation écologique la plus rapide (Snell et al. 2002). Les territoires protégés ont servi de support au développement d’un tourisme de naturequi a enclenché une intégration croissante des îles à l’économie-monde et au reste de l’espace équatorien, rompant ainsi brutalement l’isolement géographique qui garantissait leur intégrité écologique (Grenier 2000). Le tourisme a surtout été le moteur d’une croissance économique et démographique ayant engendré une rapide anthropisation des enclaves peuplées et une profonde transformation de l’espace archipélagique. Bref, les Galapagos représentent un condensé, dans le temps et l’espace, des logiques ayant conduit à entrer dans anthropocène.La thèse propose d’aborder, à travers l’exemple des Galapagos, les enjeux environnementaux de notre époque par une approche renouvelée de la géographie. Fondée comme la science des relations entre les sociétés et leur environnement, cette discipline a été une victime tardive du grand partage entre Nature et Culture se matérialisant actuellement, à propos des questions environnementales, par un tiraillement entre une géographie naturaliste et une géographie du naturalisme. Le présent travail esquisse une voie alternative à ce dualisme en posant les bases d’une géo-graphie de l’anthropocène, c’est-à-dire une étude conjointe des empreintes humaines sur terre et des récits que les acteurs et les sociétés construisent autour de celles-ci. La première partie traite successivement du rôle des territoires insulaires dans l’émergence et l’évolution des politiques de conservation, de la progressive naturalisation des Galapagos et du cadre théorique et méthodologique qui a guidé l’analyse. La deuxième partie montre comment l’ouverture géographique impulsée par l’essor du tourisme de nature a propulsé l’archipel dans l’anthropocène, mettant ainsi à l’épreuve le modèle conservationniste. La dernière partie s’intéresse à la manière dont la nature et le fait insulaire participent à l’affirmation d’un sentiment identitaire (Ospina Peralta 2001) et à des logiques multiformes et multiscalaires l’insularisation entraînant une archipellisation des Galapagos. / The emergence of the conservation movement in the late XIXth century in North America turned natural protected areas into a privileged tool for preserving the living. Designed in the first place as islands of nature shielded from human hold,they were progressively integrated in the 1970s to global environmental policies aiming at reconciling conservation and development. Such a dynamics both led to the increase and diversification of protected areas. However, until now, the development of those structures did not prevent from stopping the reduction of biodiversity, a paradoxical situation that isapplying to all the ecological issues. In spite of a strong global environmental consciousness and an increase of actions, measures and environment-oriented policies, we would have entered into a new epoch characterized by the general and irreversible mark of human activities on the earth : the Anthropocene (Crutzen et Stoermer 2000).This thesis aims at questioning the foundations of nature protection in the Anthropocene era. The starting postulate is that the incapacity to meet environmental issues reflects the contradictions of the naturalist ontology which stood out as thehegemonic conception of the relationships between humans and non-humans (Descola 2005). The argumentation is based on a critical analysis of the policies developed in a territory which is quite emblematic of naturalism, i.e. the Galapagos Archipelago in Ecuador. Being a founding place of natural sciences, it represents the most accomplished archetype of the figures (themselves very archetypical) of the laboratory-island or theconservatory-island. Since 1959, the Galapagos have been sheltering national park covering 97% of the land areas and since 1998 a marine reserve, which is among the largest in the world. As the best-preserved tropical archipelago on earth, it also is the place where the environment deteriorates most rapidly (Snell et al. 2002). The protected areas were used to develop a nature-based tourism leading to an increasing integration of the islands to the world-economy and the rest of the Ecuadorian territory, thus breaking up brutally the geographical isolation that was securing their ecological integrity (ibid.). Above all, tourism was the driving force of the demographic and economic growth, which led to a quick anthropization of populated enclaves and a deep change of the archipelago’s space. In other words, the Galapagos can be seen as a concentrate, in time and space, of the logics leading to the Anthropocene.Through the example of the Galapagos, the thesis deals with the environmental issues of our epoch in order to propose a renewed approach of geography. This discipline, originally founded as the science of the relationships between societies and their environment, was later victim of the great share between Nature and Culture, whichpresently expresses itself by conflicts between a naturalist geography and a geography about naturalism. The present research suggest an alternative way to such a dualism and sets down the bases of a geography of the Anthropocene, i.e. a joint study of the human marks on the earth and the narratives that stakeholders and societies produce about them. The first part successively tackles the role played by insular territories in building conservation policies, the progressive naturalization of the Galapagos and the theoretical and methodological framework conducting our analysis. The second part deals with the way the geographical opening threw the archipelago into the Anthropocene, thus challenging conservation policies. The third part shows how nature and the insular issues pertain to multiform and multiscalar logics, leading to the archipelization of the Galapagos.

Analysis of the satellite altimetry based predicted bathymetry, magnetic anomalies, and earthquake seismic data relating to the geophysical structure on the Nazca plate indicates that the Galapagos Rise system served as the transitional spreading system between Pacific-Farallon spreading and the current East Pacific Rise (EPR) system. First order age/depth relationships for this area indicate that the Galapagos Rise, the most prominent extinct spreading system within the Nazca plate, accommodated most of the Pacific-Nazca plate separation from ~23 million years ago (Ma) to ~8 Ma. After this time, spreading was dominantly along the EPR, with probable ultra slow spreading along the Galapagos Rise continuing until very recent times (0-5 Ma). Magnetic lineations and depth trends across the Bauer Basin suggest that it was captured between the failing Galapagos Rise and the currently active EPR. Anomalously shallow ridge crests along the Galapagos Rise indicate that magmatic activity may have occurred until very recent time (0-5 Ma). Tightly curved (concave southward) fracture zones offsetting Galapagos Rise ridge segments indicate a pole of rotation at the present day position of ~22.5 S and ~99.5 W. The curvature of the fracture zones and the fan-shaped spreading pattern of seafloor structures produced at the Galapagos Rise indicate that the Galapagos Rise initiated parallel to the Mendaña fracture zone. Consistent with the rotation of the Nazca plate after the fragmentation of the Farallon plate, the Galapagos Rise rotated counterclockwise during its active phase. The Galapagos Rise initiated in the vicinity of Gallego fracture zones and propagated southward. Failure of the Galapagos Rise occurred as spreading jumped westward in stages to the East Pacific Rise.

Tuna-dolphin-bird feeding assemblages are unique to the Eastern Tropical Pacific Ocean (ETP). These multiple species groups are believed to forage together in response to the physical properties of the near surface ocean as these constrain the distribution of prey. In the Galapagos Marine Reserve (GMR), intra-annual and interannual changes affect the properties of the water column, inducing mesoscale and fine scale temporal variability. Four three-week oceanographic surveys took place, in September 2008, April 2009, October 2009, and September 2010, between the coast of Ecuador and the Galapagos Islands and one small boat survey took place in June 2010 within the GMR. Marine mammal surveys were conducted during daylight hours and Conductivity, Temperature, Depth (CTD) sensor casts were taken throughout the survey. Data were analyzed to determine the types of water masses present and the strength and depth of the thermocline layer. These data were compared with the sightings of marine mammals, bird feeding groups, and tuna-dolphin-bird assemblages. Additionally, these data were used to predict where tuna would be likely to associate with dolphin groups. Results show Equatorial Surface Water was the dominant water mass throughout the archipelago, regardless of season or ENSO index. High salinity, cold water west of Isla Isabela indicated topographic upwelling of the Equatorial Undercurrent. Tropical Surface Waters from the Panama Current were detected north of the Equatorial Front to the east of the islands. Obvious changes in the water column properties were observed between El Niño and La Niña events in the GMR. Most mixed groups were sighted west and south of Isla Isabela during the four oceanographic surveys, as well as north and west of Isla San Cristobal in June 2010. Most sightings were in cool, high salinity waters, and high chlorophyll concentrations. There were a greater number of sightings during the April 2009 survey (ENSO-neutral conditions) than during any of the three fall surveys. Additionally, tuna-dolphin-bird groups were more likely to be seen near Isla Isabela, with the majority of them sighted during the April 2009 survey and a few sighted in each of the September 2008 and October 2009 surveys. No tuna-dolphin-bird groups were sighted during the September 2010 surveys. Results show that the presence and location of these multi-species groups may be controlled by the inter-annual cycles, the intra-annual cycles, or a combination of both types of changes seen within the Galapagos.

Many insights into ecological and evolutionary processes have come from studies of island systems. Diversity, abundance, and movement of species are restricted on smaller islands, but these dynamics can become increasingly complex as island size increases. In recent decades urbanization and the human population on the Galápagos islands has increased rapidly, affecting wildlife in unknown ways. During 2005 and 2006, we sampled birds along a 4-km transect extending northeast of the city of Puerto Ayora, Santa Cruz Island. This allowed us to collect data on the potential impacts of rapidly growing urban center on passerine bird diversity and abundance. We also documented movement patterns of the medium ground finch (Geospiza fortis), the most abundant species on the transect, with a mark/recapture protocol. Although Darwin's finches have been an influencial model for the last 150 years, little is known about their movements on larger islands. Avian species diversity did not vary significantly along a transect from a periurban area into more remote habitat. Avian abundance, however, was inversely correlated with distance from the urban center. This latter finding is consistent with a well-documented trend in urban ecology, in which periurban areas show higher abundance as compared to adjacent, less developed regions. We also found recapture/re-sight rates for G. fortis within years were 7% and 11% in 2005 and 2006, respectively. The mean distance traveled by individual birds between recaptures or re-sightings was 430.4 m. The majority of movements were less than 500 m from the location of previous sighting. There was no relationship between the distance moved and the time between captures or re-sightings; birds were equally likely to move large distances over short intervals (days) as over longer intervals (years). There was no significant difference in movement distances between males and females. These data document the movement of G. fortis on a larger island. Further studies of gene flow among populations may provide further insight into the genetic and evolutionary consequences of movement patterns documented here.

xv, 151 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / To explain the origin of several distinct aspects of the Galápagos volcanic hotspot, such as the broad geographical extent of recent volcanism and the unusual pattern of geochemical anomalies, we conducted seismic tomography studies of the upper mantle and crust beneath the Galápagos Archipelago. The studies combine measurements of group and phase velocities of surface waves and delay times of body waves. We find that upper mantle seismic velocities are lower than those beneath other regions of comparable age in the Pacific and consistent with an excess temperature of 30 to 150°C and ∼0.5% melt. We attribute the excess temperature and presence of melt to an upwelling thermal mantle plume. Crustal seismic velocity is up to 25% lower than that of very young crust at the East Pacific Rise (EPR) and is comparable to that of Hawaii, which we attribute to heating by increased intrusive activity above the Galápagos plume and the construction of a highly porous volcanic platform. In addition, we find that the Galápagos hotspot is underlain by a high-velocity region whose thickness varies from 40 to 100 km. The tomographic images reveal that the upwelling mantle plume tilts northward (towards the nearby Galápagos Spreading Center) as it rises and then spreads laterally when it reaches the bottom the lid. The lid, which we attribute to residuum from melting, is thickest where it is farthest from the spreading center, suggesting that ridge processes may affect the generation and amount of thinning of the residuum layer. In addition, the thickness of the lid correlates well with the geographical pattern of geochemical anomalies of erupted lavas, suggesting that the lid may control the final depth of decompression melting. We conclude that many of the distinct characteristics of the Galápagos can be attributed to the interaction of the upwelling plume with the lid and the nearby ridge. We further suggest that the ridge affects the geometry of plume upwelling in the upper mantle and also the pattern of lateral spreading of the plume due to its effect on the thickness of the residuum layer. This dissertation includes previously published co-authored material. / Committee in charge: Dr. Douglas R. Toomey, Chairperson; Dr. Eugene Humphreys, Member; Dr. Emilie Hooft Toomey, Member; Dr. Paul Wallace, Member; Dr. John Conery, Outside Member

Invasive species represent a major challenge through their consequences on<p>biodiversity, human health and economy. Their effects are especially important on fragile and<p>unique insular biotas such as the Galápagos Islands. Ants in particular are keystone species<p>implicated in ecosystem functioning and biodiversity and they can be dramatic invaders. In<p>the Galápagos Islands, the tropical fire ant Solenopsis geminata is considered a high-impact<p>invasive species, though it remains surprisingly poorly studied. The objectives of this work<p>are to document the invasion of S. geminata in the Galápagos Islands by 1) updating its<p>distribution; 2) determining its reproduction and dispersal strategies and reconstruct its<p>invasion history throughout the archipelago and 3) evaluating its impact on the native fauna<p>(focusing on ants and arthropods communities and endemic land tortoises).<p>First, we added 66 new records of S. geminata in the Galápagos since 2008. It has<p>now been recorded on seven islands and 11 islets in a wide range of habitats, including<p>nesting sites of 24 endemic and/or endangered vertebrate species, for which it constitutes a<p>potential threat.<p>Secondly, by combining Bayesian clustering methods, coalescent-based scenario<p>testing using microsatellite data and historical records, we determined that genetic diversity<p>of populations of S. geminata collected in Galápagos Islands is significantly lower than the<p>genetic diversity of populations from native areas (Costa Rica). The Galápagos populations<p>form three clusters corresponding to an island or groups of islands. They appear to be the<p>result of a single introduction in the first half of the 19th century, probably from mainland<p>Ecuador, which acted as a bridgehead population to two subsequent introductions within the<p>archipelago, corresponding human colonization fluxes in the archipelago.<p>We sampled ants in all main habitats of Santa Cruz Island. Introduced ant species<p>were largely prevalent, and S. geminata was the dominant species and was associated with<p>low evenness of ant communties and lower abundance of native ants. We found that<p>Galápagos’ ant communities are determined by the vegetation type and altitude, but found<p>only little evidence for competitively structured assemblages, except in disturbed areas.<p>The arthropod diversity was investigated in two agricultural sites of Santa Cruz Island<p>by combining three complementary sampling techniques. More than half of the species were<p>either endemic or native, but introduced species constituted the majority of the catches.<p>Solenopsis geminata was by far the most abundant and common species.<p>Finally, we investigated the mortality of Cheloidis land tortoise’s eggs and hatchlings<p>in an area infested by S. geminata on Santa Cruz Island with regard to the abundance of fire<p>ants and the duration of incubation. Egg survival was negatively associated with longer incubation times but we found no direct relation between ant density and tortoise mortality<p>despite a high abundances of fire ants in the vicinity of the majority of the tortoise burrows.<p>Our work allows addressing ecological and genetical aspects of the invasion of S.<p>geminata in the Galápagos Islands. We analyzed our results in the light of an ecoevolutionary<p>framework presenting different invasion scenarios and discussed S. geminata<p>as an invasive ant. This provided us with information useful for the study and management of<p>this invasive species in the Galápagos Islands.<p>/<p>Les espèces invasives constituent un défi majeur à cause de leur impact sur la<p>biodiversité, la santé humaine et l’économie. Leurs effets sont particulièrement importants<p>sur les environnements insulaires fragiles et uniques comme les île Galápagos. Les fourmis<p>en particulièr sont des espèces clé de voûte du fonctionnement des écosystèmes et de la<p>biodiversité. Elles peuvent de ce fait devenir des envahisseurs spectaculaires. Dans les îles<p>Galápagos, la fourmi de feu tropicale Solenopsis geminata fait partie des espèces invasives<p>à haut impact et cependant elle a été étonnamment peu étudiée. Les objectifs de ce travail<p>consistent à documenter l’invasion de S. geminata dans l’archipel des Galápagos: 1) en<p>mettant à jour sa distribution; 2) en déterminant ses stratégies de reproduction et de<p>dispersion et en reconstruisant l’histoire de son invasion dans l’archipel et 3) en évaluant son<p>impact sur la faune native (particulièrement sur les communautés de fourmis et<p>d’arthropodes et sur les tortues terrestres endémiques).<p>Tout d’abord, nous avons ajouté 66 nouveaux relevés de S.geminata aux Galápagos<p>depuis 2008. À ce jour, la fourmi a été observée sur 7 îles et 11 îlots, et ce dans une grande<p>variété d’habitats. On la trouve également sur les sites de ponte de 24 espèces de vertébrés<p>endémiques ou en voie de disparition, qu’elle menace ainsi potentiellement.<p>Ensuite, en combinant des méthodes bayésiennes de regroupement et des<p>comparaisons de scénarios en se basant sur des séquences microsatellites et des données<p>historiques, nous avons montré que la diversité génétique des populations de S. geminata<p>des Galápagos est significativement inférieure à celle des populations des zones d’indigénat<p>(Costa Rica). Les populations des Galápagos - réparties en 3 groupes correspondant à une<p>île ou un groupe d’îles – sont le résultat d’une introduction unique ayant eu lieu dans la<p>première moitié du 19ème siècle. Elles proviennent vraisemblablement de l’Equateur<p>continental et constituent une population “tête de pont” pour deux introductions ultérieures au<p>sein de l’archipel. Ces mouvements correspondent aux flux de populations humaines.<p>Nous avons échantillonné les fourmis dans tous les principaux habitats de l’île de<p>Santa Cruz. Les fourmis introduites sont largement prévalentes. Solenopsis geminata<p>constitue l’espèce dominante et se trouve associée avec une faible équitabilité des<p>communautés de fourmis ainsi qu’avec une diminution de l’abondance des fourmis natives.<p>Nos résultats indiquent que les communautés de fourmis des Galápagos sont structurées<p>par le type de végétation et l’altitude, alors que les assemblages de fourmis ne sont pas<p>structurés compétitivement, à l’exception des zones perturbées.<p>Nous avons investigué la diversité arthropodienne de deux sites agricoles de l’île de<p>Santa Cruz en combinant trois méthodes d’échantillonnage complémentaires. Plus de la moitié des espèces collectées étaient soit endémiques, soit natives. Les espèces introduites<p>ont toutefois constitué la majorité des individus collectés. Solenopsis geminata était de loin la<p>plus abondante et la plus commune des espèces récoltées.<p>Enfin, dans une zones infestées par S. geminata sur l’île de Santa Cruz, nous avons<p>mis en relation la mortalité des oeufs et juvéniles de tortues terrestres Chelonoidis avec<p>l’abondance des fourmis de feu et la durée d’incubation des oeufs. Le taux de survie des<p>oeufs est négativement corrélé à leur durée d’incubation. Cependant, malgré de très hautes<p>abondances de fourmis de feu à proximité des nids de tortues, nous n’avons pas trouvé de<p>relation directe avec leur mortalité.<p>Pour conclure, ce travail aborde les aspects génétiques et écologiques de l’invasion<p>de la fourmi de feu tropicale dans les îles Galápagos. Nos résultats sont analysés au sein<p>d’un cadre éco-évolutif présentant différents scénarios d’invasion. Nous discutons également<p>de S. geminata en tant qu’espèce invasive. Nous espérons apporter des informations utiles<p>dans le cadre de l’étude et du contrôle de cette espèce invasive aux Galápagos. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

La compréhension du cycle de l'eau d'une région où les ressources en eau sont limitées est fondamentale pour assurer une gestion durable de celles-ci, c'est le cas de Galápagos. Cette thèse présente la première étude intégrée du fonctionnement hydrogéologique des aquifères perché de l'île San Cristóbal. Pour ce faire, une approche pluridisciplinaire, fondée sur la mise en place d'un site expérimental sur le bassin versant de Cerro Gato (CG), a été conduite. Pour quantifier les entrées d'eau dans le système hydrologique une approche canopée-transfert hydrique du sol a été utilise. La recharge est principalement affectée par l'altitude en raison de l'effet orographique sur les gradients de pluie et d'évapotranspiration. Néanmoins, à haute altitude, la différence est principalement associée à la couverture végétale en raison de l'apport additionnel fourni par l'interception du brouillard sous la forêt. Une analyse hydrologique montre que les pertes des bassins versants situés à haute-altitude deviennent les entrées d'eau souterraine des bassins versants situés à moyenne altitude (comme CG). Les données du méthode électromagnétique héliportée SkyTEM permettent définir l'extension du bassin hydrogéologique de CG qui est plus grande que le bassin hydrologique. Des approches précédemment décrites, découlent un modèle conceptuel des sources de CG. Ainsi, les eaux souterraines de ces sources sont issues d'un aquifère perché qui s'est formé à la faveur d'une fine couche peu perméable. Ce modèle est testé par simulations numériques qui montrent cette plausibilité. Cette thèse fournit les fondements scientifiques d'une gestion durable des ressources en eau. / The understanding of the hydrogeological functioning in regions such as San Cristobal Island (Galapagos), where water is limited, is fundamental for a suitable management of its resources. This work is the first study of this type on high-level aquifers in San Cristobal using a multi-disciplinary approach, based in the implementation of an experimental site and modeling strategies. For this purpose, a hydrological network was installed in Cerro Gato (CG) and surrounding watersheds. Inputs to the watershed are estimated using the joint modeling of a canopy and soil water transfer. Recharge rates are mainly affected by altitude in mid-elevation watersheds, whereas land cover is the main controlling factor at high-elevation watersheds because of the additional input of fog interception in forests. A hydrological analysis shows that losses from the high-elevation basins become groundwater inputs in the mid-elevation basins, while others have inputs from watersheds at the same altitude, such as CG. The detailed geometry of its hydrogeological watershed is obtained from the dataset of a high resolution AEM SkyTEM survey, which confirms the assumption that its hydrogeological watershed is bigger than its hydrological one. Results from these approaches allow proposing a hydrogeological conceptual model for the springs of CG, where the groundwater flow of springs is fed by a perched aquifer suspended by a low permeability thin layer. This model is tested with numerical simulations, which confirm the plausibility of the existence of a perched aquifer. This thesis provides scientific basis for an effective water management strategy.

Avec une population croissante et des ressources en eau de surface limitées, l'hydrogéologie des îles Galápagos reste pour une grande part inconnue. Les précipitations sont relativement faibles et inégalement réparties dans le temps et l'espace. Le centre économique de l'archipel, l'île de Santa Cruz, ne dispose que de quelques cours d'eau intermittents tandis que l'île de San Cristóbal présente plusieurs rivières pérennes. Dans le cadre de ce travail, une approche pluridisciplinaire est utilisée afin de caractériser l'hydrogéologie de l'Archipel. Une nouvelle technique d'interprétation des sondages életro\-magné\-tiques héliportés a été développée. Grâce à des méthodes géostat\-istiques, elle permet la construction d'une grille 3D de la résistivité électrique. Les données issues de la mission SkyTEM réalisée sur les îles de Santa Cruz et San Cristóbal en 2006 sont mises en perspectives. Confrontée aux observations de surface collectées par télédétection et sur le terrain, la géophysique permet de proposer un modèle conceptuel pour l'île de San Cristóbal. Les conditions climatiques ont été suivies avec la mise en place de stations météorologiques le long du versant au vent de l'île de Santa Cruz. La présence de brouillard pendant 6 mois de l'année représente un apport supplémentaire pour la recharge des aquifères. Cet apport a été quantifié avec une méthode basée sur un modèle d'interception à base physique. L'aquifère de base de l'île de Santa Cruz a été étudié avec la propagation du signal de marée, des essais de pompage, et la cartographie de la fracturation. Ces travaux montrent que les basaltes ''jeunes'' fracturés ont une forte perméabilité. En revanche, les failles n'ont qu'un effet limité sur l'hydrogéologie régionale, car elles sont peu connectées. Les configurations hydrologiques contrastées au sein de l'archipel sont expliquées par un schéma d'évolution. Dans les îles relativement jeunes, telles que Santa Cruz, les basaltes fracturés sont perméables. Ils offrent peu de résistance à l'intrusion saline et l'eau douce est rapidement drainée jusqu'à la mer. Les conditions sont plus favorables dans les îles plus âgées. Les perméabilités plus faibles et l'incision des vallées permettent l'émergence de sources.