La compétition entre les processus internes et externes contrôle l'évolution des surfaces continentales à l'échelle des temps géologiques. La topographie et le réseau de drainage actuels des Cordillères Bétiques apparaissent comme transitoires (surfaces aplanies sommitales, knickpoints) impliquant que la réponse érosive du système géomorphologique n'a pas encore contrebalancé les dernières étapes de surrection. L'exhumation des zones internes montre un épisode d'aplanissement majeur de la topographie à une altitude proche du niveau marin entre ~ 17 et 8 Ma. Certaines de ces surfaces sont préservées de l'érosion en altitude. Les rivières montrent une incision relativement mature dans les sierras orientales initiée lors de l'inversion tardi-miocène, et une surrection régionale plus récente reliée à de la topographie dynamique. Le raccourcissement post-tortonien dans les zones internes est faible (~ 5 km) tandis que la déchirure E-W de la lithosphère ibérique depuis la fin du Miocène entraîne un soutien mantellique permettant d'expliquer les hautes topographies orientales. A l'ouest, la lithosphère ibérique subit la traction du panneau plongeant impliquant une topographique moyenne plus basse. L'implication de ces processus engendre une forte composante non-isostatique de la topographie. La géométrie de la déchirure de la lithosphère ibérique permet d'expliquer l'instabilité de la ligne de partage des eaux séparant les versants atlantique et méditerranéen. Le rajeunissement du relief bétique et la réorganisation dynamique du réseau de drainage suggère une surrection brève et récente (quelques Ma) rattachée à un fonctionnement discontinu de la déchirure de la lithosphère. / Competing between internal and external processes controls the evolution of continental surfaces at geological time scale. The topography and associated drainage network of the Betics are transient (summit surfaces, knickpoints) implying that the erosional response of the geomorphic system hasn’t counterbalanced the last stages of uplift yet. Exhumation history of the internal zones shows a major planation event near sea level between ~ 18 and 7 Ma. Some of these surfaces are preserved from erosion at the summit of several sierras. Rivers in the eastern sierras show relatively mature incision pattern initiated since the Late Miocene inversion. At the regional scale the drainage network shows a more recent uplift related to dynamic topography. Post-Tortonian shortening in the Internal Zones is low (~5 km) whereas E-W tearing of the Iberian lithosphere since the Late Miocene has led to an important mantle support of the eastern topography. To the west, Iberian lithosphere is pulled by the slab and the mean topography above is deflected. These deep processes are responsible for an important non-isostatic component of the Betics topography. The tear geometry of the lithosphere beneath the Betics can explain the instability of the main divide (Atlantic/Mediterranean). Rejuvenation of the relief and the dynamic reorganization of the rivers suggest a brief and recent uplift (few Ma) related to a discontinuous tearing of the lithosphere.

abstract: Land surface fluxes of energy and mass developed over heterogeneous mountain landscapes are fundamental to atmospheric processes. However, due to their high complexity and the lack of spatial observations, land surface processes and land-atmosphere interactions are not fully understood in mountain regions. This thesis investigates land surface processes and their impact on convective precipitation by conducting numerical modeling experiments at multiple scales over the North American Monsoon (NAM) region. Specifically, the following scientific questions are addressed: (1) how do land surface conditions evolve during the monsoon season, and what are their main controls?, (2) how do the diurnal cycles of surface energy fluxes vary during the monsoon season for the major ecosystems?, and (3) what are the impacts of surface soil moisture and vegetation condition on convective precipitation? Hydrologic simulation using the TIN-based Real-time Integrated Basin Simulator (tRIBS) is firstly carried out to examine the seasonal evolution of land surface conditions. Results reveal that the spatial heterogeneity of land surface temperature and soil moisture increases dramatically with the onset of monsoon, which is related to seasonal changes in topographic and vegetation controls. Similar results are found at regional basin scale using the uncoupled WRF-Hydro model. Meanwhile, the diurnal cycles of surface energy fluxes show large variation between the major ecosystems. Differences in both the peak magnitude and peak timing of plant transpiration induce mesoscale heterogeneity in land surface conditions. Lastly, this dissertation examines the upscale effect of land surface heterogeneity on atmospheric condition through fully-coupled WRF-Hydro simulations. A series of process-based experiments were conducted to identify the pathways of soil moisture-rainfall feedback mechanism over the NAM region. While modeling experiments confirm the existence of positive soil moisture/vegetation-rainfall feedback, their exact pathways are slightly different. Interactions between soil moisture, vegetation cover, and rainfall through a series of land surface and atmospheric boundary layer processes highlight the strong land-atmosphere coupling in the NAM region, and have important implications on convective rainfall prediction. Overall, this dissertation advances the study of complex land surface processes over the NAM region, and made important contributions in linking complex hydrologic, ecologic and atmospheric processes through numerical modeling. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

<p>The boreal forests represent 8 % of all forested areas on the earth and have a significant role in the control of greenhouse gases and an impact on global climate change. The main objective of this thesis is to increase the understanding of how evaporation and heat-flux processes in the boreal forest zone are affecting the regional and global climate.</p><p>A meteorological mesoscale model with an advanced land-surface parameterization has been utilized to study aggregation of fluxes of water vapour and heat. The model has been compared against four other methods for flux estimation in a southern boreal landscape. The results show that the mesoscale model is successfully reproducing 24-hour averages of fractionally weighted mast measurements of sensible and latent heat flux.</p><p>The model was also evaluated against in-situ observations of surface fluxes and other meteorological variables. The results reveal that a correct initialization of soil moisture is crucial to simulate a realistic partitioning of the sensible and latent heat fluxes. Significant differences in surface fluxes and friction velocities between two apparently similar forest sites indicate the need for careful assessment of areal representativity when comparing mesoscale model results with in-situ observations.</p><p>A parameterization for the absorption of solar radiation of high-latitude sparse forests was implemented and tested in the model that significantly improved the simulation of high wintertime midday sensible heat fluxes. A scheme for heat storage in vegetation was also implemented which improved the results, but the scheme needs further evaluation for high latitude forests.</p><p>Two commonly used strategies for the description of land-surface heterogeneity, the effective parameter approach and the mosaic approach, were tested in the mesoscale model against airborne observations of sensible and latent heat fluxes. The results show that the mosaic approach produces better results especially when small lakes are present in model grid-squares.</p> / <p>Norra halvklotets barrskogsbälte representerar 8 % av all skogsbeklädd mark på jorden och har stor betydelse för kontrollen av växthusgaser och påverkan på globala klimatförändringar. Syftet med denna avhandling är att öka förståelsen av hur avdunstning och värmeflöden i den boreala skogszonen påverkar klimatet regionalt och globalt.</p><p>En meteorologisk mesoskalemodell med en avancerad landyteparameterisering har använts för att studera aggregering av avdunstning och värmeflöden. Modellen jämfördes med fyra andra metoder för uppskattning av värmeflöden i den boreala skogszonens södra delar. Resultaten visade att mesoskalemodellen reproducerar 24-timmarsmedelvärden av sensibelt och latent värmeflöde från areellt viktade mastmätningar med bra resultat.</p><p>Modellen utvärderades även mot markbaserade mätningar av sensibelt och latent värme och andra meteorologiska variabler. Resultaten visar att en korrekt initialisering av markvatteninnehållet är avgörande för att simulera en realistisk uppdelning av de sensibla och latenta värmeflödena. Markanta skillnader i markyteflöden och friktionshastigheter mellan två liknande skogsmätstationer påvisar nödvändigheten av en noggrann bedömning av den areella representativiteten när man jämför resultat från mesoskalemodellen med markbaserade mätningar.</p><p>En parameterisering för absorption av solstrålning i glesa skogsbestånd på höga breddgrader infördes och testades i modellen vilket markant förbättrade simuleringen av de höga sensibla värmeflöden som observerats vid middagstid på vintern. Ett uttryck för att beskriva värmelagring i vegetationen infördes också vilket förbättrade resultaten, men uttrycket behöver vidare utvärdering för skogsbestånd på höga breddgrader.</p><p>Två ofta använda strategier för att beskriva markytans heterogenitet, effektiva parametermetoden och mosaikmetoden, testades i mesoskalemodellen mot flygburna observationer av sensibla och latenta värmeflöden. Resultaten visar att mosaikmetoden ger bättre resultat särskilt när mindre sjöar förekommer i modellrutorna.</p>

The boreal forests represent 8 % of all forested areas on the earth and have a significant role in the control of greenhouse gases and an impact on global climate change. The main objective of this thesis is to increase the understanding of how evaporation and heat-flux processes in the boreal forest zone are affecting the regional and global climate. A meteorological mesoscale model with an advanced land-surface parameterization has been utilized to study aggregation of fluxes of water vapour and heat. The model has been compared against four other methods for flux estimation in a southern boreal landscape. The results show that the mesoscale model is successfully reproducing 24-hour averages of fractionally weighted mast measurements of sensible and latent heat flux. The model was also evaluated against in-situ observations of surface fluxes and other meteorological variables. The results reveal that a correct initialization of soil moisture is crucial to simulate a realistic partitioning of the sensible and latent heat fluxes. Significant differences in surface fluxes and friction velocities between two apparently similar forest sites indicate the need for careful assessment of areal representativity when comparing mesoscale model results with in-situ observations. A parameterization for the absorption of solar radiation of high-latitude sparse forests was implemented and tested in the model that significantly improved the simulation of high wintertime midday sensible heat fluxes. A scheme for heat storage in vegetation was also implemented which improved the results, but the scheme needs further evaluation for high latitude forests. Two commonly used strategies for the description of land-surface heterogeneity, the effective parameter approach and the mosaic approach, were tested in the mesoscale model against airborne observations of sensible and latent heat fluxes. The results show that the mosaic approach produces better results especially when small lakes are present in model grid-squares. / Norra halvklotets barrskogsbälte representerar 8 % av all skogsbeklädd mark på jorden och har stor betydelse för kontrollen av växthusgaser och påverkan på globala klimatförändringar. Syftet med denna avhandling är att öka förståelsen av hur avdunstning och värmeflöden i den boreala skogszonen påverkar klimatet regionalt och globalt. En meteorologisk mesoskalemodell med en avancerad landyteparameterisering har använts för att studera aggregering av avdunstning och värmeflöden. Modellen jämfördes med fyra andra metoder för uppskattning av värmeflöden i den boreala skogszonens södra delar. Resultaten visade att mesoskalemodellen reproducerar 24-timmarsmedelvärden av sensibelt och latent värmeflöde från areellt viktade mastmätningar med bra resultat. Modellen utvärderades även mot markbaserade mätningar av sensibelt och latent värme och andra meteorologiska variabler. Resultaten visar att en korrekt initialisering av markvatteninnehållet är avgörande för att simulera en realistisk uppdelning av de sensibla och latenta värmeflödena. Markanta skillnader i markyteflöden och friktionshastigheter mellan två liknande skogsmätstationer påvisar nödvändigheten av en noggrann bedömning av den areella representativiteten när man jämför resultat från mesoskalemodellen med markbaserade mätningar. En parameterisering för absorption av solstrålning i glesa skogsbestånd på höga breddgrader infördes och testades i modellen vilket markant förbättrade simuleringen av de höga sensibla värmeflöden som observerats vid middagstid på vintern. Ett uttryck för att beskriva värmelagring i vegetationen infördes också vilket förbättrade resultaten, men uttrycket behöver vidare utvärdering för skogsbestånd på höga breddgrader. Två ofta använda strategier för att beskriva markytans heterogenitet, effektiva parametermetoden och mosaikmetoden, testades i mesoskalemodellen mot flygburna observationer av sensibla och latenta värmeflöden. Resultaten visar att mosaikmetoden ger bättre resultat särskilt när mindre sjöar förekommer i modellrutorna.

The representation of high-latitude surface processes and quantifying surface-climate feedbacks are some of the most serious shortcomings of present day Arctic land surface modelling. The energy balance of seasonally snow-covered sparse deciduous forests at high latitudes is poorly understood and inaccurately represented within hydrological and climate models. Snow cover plays an important role in wintertime fluxes of energy, water and carbon, controlling the length of the active growing season and hence the overall carbon balance of Arctic ecosystems. Snow cover is non-uniform and spatially variable, as wind redistributes snow from areas of exposed open tundra to sheltered areas within the forest, where a deeper snowpack develops. Low solar zenith angles, coupled with sparse deciduous leafless trees, cast shadows across the snow surface. The spatial distribution of canopy gaps determines the timing of direct radiation which penetrates down through the canopy to the snow surface. The forest canopy also excludes incoming longwave radiation and yet also emits longwave radiation to the snow surface. Consequently the forest canopy plays a key role in the radiation balance of sparse forests. To improve our knowledge of these complex processes, meteorological and field observations were taken in an area of highly heterogeneous birch Betula pubescens ssp. czerepanovii forest in Abisko, Sweden during the spring of 2008 and 2009. Detailed measurements of short and longwave radiation above and below the canopy, hemispherical photographs, tree temperatures and snow surveys were conducted to quantify the radiation balance of the sparse deciduous forest. An array of below canopy pyranometers found the mean canopy transmissivity to be 74 % in 2008 and 76 % in 2009. Hemispherical photographs taken at the pyranometer locations analysed with Gap Light Analyzer (GLA) showed reasonable agreement with a mean canopy transmissivity of 75 % in 2008 and 74 % in 2009. The canopy transmissivity was found to be independent of the diffuse fraction of radiation as the canopy is very sparse. A series of survey grids and transects were established to scale up from the below canopy pyranometers to the landscape scale. Hemispherical photographs analysed with GLA showed the sparse forest canopy had a mean transmissivity of 78 % and a mean LAI of 0.25, whereas the open tundra had a mean transmissivity of 97 % and a mean LAI of < 0.01. Snow surveys showed the sparse forest snow depth to vary between 0.34 and 0.55 m, whereas the snow depth in the open tundra varied between 0.12 and 0.18 m. Observations of canopy temperatures showed a strong influence of incident shortwave radiation warming the tree branches to temperatures up to 15 °C warmer than ambient air temperature on the south facing sides of the trees, and up to 6 °C on the north facing sides of the trees. To reproduce the observed radiation balance, two canopy models (Homogenous and Clumped) were developed. The Homogeneous canopy model assumes a single tree tile with a uniform sparse canopy. The Clumped canopy model assumes a tree and a grass tile, where the tree tile is permanently in shade from the canopy and the grass tile receives all the incoming radiation. These canopy models identified the need for a parameter that accounts for the spatial and temporal variation of the shaded gaps within the sparse forest. JULES (Joint UK Land Environment Simulator) is the community land surface model used in the UK Hadley Centre GCM suite. Modifications of the land-surface interactions were included in JULES to represent the shaded gaps within the sparse deciduous forest. New parameterisations were developed for the time-varying sunlit fractions of the gap (flit), the sky-view fraction (fv), and the longwave radiation emitted from the canopy (LWtree). These model developments were informed by field observations of the forest canopy and evaluated against the below canopy short and longwave radiation observed data sets. The JULES Shaded gap model output showed a strong positive relationship with the observations of below canopy shortwave and longwave radiation. The JULES Shaded gap model improves the ratio of observed to modelled short and longwave radiation on sunny days compared to the JULES model. The JULES Shaded gap model reduces the time to snow melt by 2 to 4 days compared to the JULES model, making the model output more aligned with in-situ observational data. This shortening of the modelled snow-season directly impacts on the simulated carbon and water balance regionally and has wider relevance at the pan-Arctic scale. When JULES Shaded Gap was evaluated on the global scale, it improved the modelled snowmass across large areas of sparse forest in northern Canada, Scandinavia and Northern Russia with respect to GlobSnow. The performance of the land surface-snow-vegetation interactions of JULES was improved by using the Shaded gap to model the radiation balance of sparse forests in climate-sensitive Arctic regions. Furthermore these observational data can be used to develop and evaluate high latitude land-surface processes and biogeochemical feedbacks in other earth system models.

Dans un contexte où des millions de personnes dépendent de la ressource en eau exposée au caprice de la mousson en Afrique de l'Ouest, ce travail de thèse vise à mieux appréhender les processus hydrologiques en zone de socle, et notamment à évaluer le rôle de la redistribution latérale de l'eau dans le sol par les interactions entre les réservoirs souterrains, la végétation et l'atmosphère, par la caractérisation et la modélisation à l'échelle de la parcelle et du versant. Ce travail s'appuie sur le dispositif expérimental déployé dans le petit bassin versant de l'Ara dans le cadre de l'observatoire AMMA-CATCH. La mise en oeuvre du modèle ParFlow-CLM permet de simuler les transferts dans la zone saturée et la zone non saturée par la résolution de l'équation de Richards en 3D, en étant conditionné par un forçage atmosphérique en surface. Après avoir identifié les paramètres influents pour les transferts verticaux, une caractérisation spatiale de ces paramètres a été menée. La configuration du modèle a ensuite été évaluée en 1D. Il est montré que le modèle reproduit de manière pertinente les séries temporelles du bilan d'énergie et la distribution de l'eau dans le sol. L'effet de la variabilité spatiale des paramètres hydrodynamiques est ensuite étudié à l'échelle de la parcelle. Enfin, en incluant les géométries de socle connues et une distribution de végétation, les transferts horizontaux souterrains sont mis en évidence avec la formation de zones sèches ou humides en relation avec des distributions spatiales d'évapotranspiration. / In West Africa, millions of people rely on water resources exposed to the monsoon variability. In this context, the aim of this thesis is to better understand hydrological processes in bedrock areas, and more particularly to estimate the role of lateral redistribution of soil water by the interactions between underground reservoirs, vegetation and atmosphere, using hydrogeological prospection and modeling at field and catena scale. This work is supported by the experimental device implemented in the small Ara catchment in the framework of the AMMA-CATCH observatory. The use of the ParFlow-CLM model allows the simulation of transfers in the saturated and the vadose zone by solving the Richards equation in 3D. The model was forced using observed atmospheric forcing at the surface. We first identify influential parameters for vertical water transfers. Then a spatial characterization of these parameters is carried out. The 1D version of the Parflow-CLM model is assessed using observed data. We show that the model provides relevant times series of the surface energy balance and of soil water distribution as compared to the observations. The impact of the spatial variability of the hydraulic parameters at the field scale (<1 ha) is studied. Finally, the bedrock geometry and the spatial distribution of vegetation are taken into account in the modelling. This allows the identification of horizontal subsurface lateral fluxes, which generate wet and dry patterns, which are related to the spatial distribution of evapotranspiration.

The post-orogenic history of the Appalachian Mountains, particularly the persistence of rough topography and the degree of river incision throughout the region, has been a longstanding focus of geomorphology studies. Numerous models have been developed to explain the evolution of this landscape, variously invoking episodic or continuous processes of uplift and erosion to drive the generation or reduction of topographic relief. Recently, late Cenozoic uplift has found favor as a mechanism for rejuvenating the topography of the southern and central Appalachians. This hypothesis has drawn on longitudinal river profiles, seismic tomography, and offshore sediment records as evidence of Neogene uplift.<div><br></div><div>Radiometric dating of surficial deposits provides a means to directly test models of episodic and continuous landscape evolution, as well as the Neogene uplift hypothesis. The research described in this thesis dates surficial sediments (river terraces, alluvial fans, and a filled sinkhole) and supergene manganese oxides using 26Al/10Be burial dating and 40Ar/39Ar geochronology, respectively. Our cosmogenic 26Al/10Be dating provides detailed histories of aggradation and incision along the Shenandoah and Tennessee Rivers since the early Pliocene. 40Ar/39Ar dating of manganese oxides permits estimates of surface preservation and denudation in the Shenandoah Valley and nearby watersheds throughout the Cenozoic.<br></div><div><br></div><div>The results of our work in the Shenandoah Valley, Tennessee River basin, and intervening areas indicate that the Appalachians experienced no significant pulse of uplift during the Cenozoic. Long-term preservation of supergene manganese oxides dates as far back as the Eocene, demonstrating minimal denudation and discontinuous formation that lend evidence to episodic landscape evolution models. Cosmogenic26Al/10Be burial ages along the Shenandoah and Tennessee Rivers reveal Pliocene aggradation, with enhanced deposition in the Shenandoah Valley during the mid-Piacenzian Warm Period. Both rivers likely experienced incision during the Pleistocene, likely due to climatic fluctuations. These results demonstrate that while the Appalachian landscape has remained largely unchanged for tens of millions of years, rapid Pleistocene changes in base level recently triggered significant incision of major drainages.<br></div>

This thesis deals with the role of precipitation on erosion and landscape formation in the Nepal Himalayas. I investigate all successive steps involved in the erosion process: 1) Starting from the evaluation of precipitation datasets, 2) the transfer of precipitation to river discharge, 3) the mobilization and transport of material out of the mountain range, 4) and finally, erosion constrains over longer time-scales. I show that the dataset derived from the interpolation of rain gauge data performs best in the Himalayas. I demonstrate the importance of an until now unconsidered, major compartment of the Himalayan discharge cycle, which I identify as a fractured basement aquifer, and estimate the snow and ice melt contribution to the Himalayan rivers. Erosion rates calculated from suspended sediment fluxes and cosmogenic nuclide analysis range between 0.1 and 4 mm/yr. The rivers in the Nepal Himalayas are supply limited and the hillslopes as contributing source are transport limited. Last I show that over several thousand years erosion is not related with precipitation, but with relief. / Cette thèse porte sur le rôle des précipitations sur l’érosion et la formation des reliefs dans l’Himalaya Népalais. J’étudie chaque étape du processus d’érosion : 1) Evaluation des bases de données de précipitations, 2) Transfert des précipitations au débit fluvial, 3) Mobilisation et transport du matériel dans le bassin versant, et enfin 4) Mécanismes d’érosion sur de longues échelles de temps. Je montre que la base de données de précipitations obtenue par interpolation de données pluviométriques est la plus performante pour la région de l\'Himalaya. Je démontre l’importance d’une composante majeure, jusqu’alors ignorée, du cycle de débit de l’Himalaya que j’identifie comme étant les aquifères de sous-sol fracturé, et j’évalue la contribution de la fonte des neiges et glaces aux rivières Himalayennes. Les taux d’érosion calculés à partir des flux de sédiments en suspension et des analyses de nucléides cosmogéniques varient de 0.1 à 4 mm/a. Les rivières au Népal sont limitées par l’apport sédimentaire alors que les versants, en tant que source de sédiments, sont limités par le transport. Enfin, je montre que l’érosion sur des milliers d’années ne dépend des précipitations mais du relief. / Die vorliegende Arbeit beschäftigt sich mit der Rolle des Niederschlag bei Erosions- und Oberflächenprozessen im nepalesischen Himalaja. Ich untersuche die Abfolge der Erosionspsozesse im Himalaja: 1) Ausgehend von der Bewertung von Niederschlagsdatensätzen, 2) die Prozesse der Abflussbildung in Flüssen, 3) die Mobilisierung und Transport von Material, 4) und Erosionsraten über längere Zeiträume. Ich zeige, dass interpolierte Niederschlagsdaten die beste Qualität im Himalaya haben. Ich zeige auf, wie wichtig der bislang unberücksichtigt Grundwasserzwischenspeicher für die Abflussbildung im Himalaya ist und schätze den Anteil der Schnee-und Eisschmelze an dem Gesamtabfluss der Flüssen im Himalaja. Erosionsraten die mittels Schwebestofffracht und der Analyse kosmogener Nukluide berechnet wurden, liegen zwischen 0,1 und 4 mm pro Jahr. Der Sedimenttransport in den Flüssen in Nepal ist limitiert durch die Verfügbarkeit von transportierbarem Material, während der Transport und die Mobilisierung auf den Hängen durch die Verfügbarkeit von Wasser limitiert ist. Zudem sind die Erosionsraten über mehrere Jahrhundert nicht von der Niederschlagsverteilung abhängig sondern vom Relief.

Orogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion models. / Orogenic belts are fundamental features of plate tectonics. The crustal structure of orogens around the world shows a wide range of deformation styles from narrow, asymmetric wedges like the Pyrenees to wide, plateau-like orogens such as the Zagros or the Himalaya. The primary controlling factor on the size and structure of an orogen is the amount of convergence between the colliding plates. However, there are important additional factors providing major controls on the structural development of orogens. Among the potential parameters that can affect the style of deformation are the crustal strength, inherited weaknesses, and the surface processes. These parameters have been studied extensively in the past but their relative importance remains unclear. The aim of this thesis is to improve our understanding of: (1) How surface processes affect mountain building, with a special focus on the relationship between thin-skinned foreland and thick-skinned internal deformation of orogens. (2) How inherited extensional structures affect mountain building. The study was carried out using the Pyrenees as a special reference case. To answer our research questions we have used a wide range of state-of-the-art numerical modelling tools. In paper 1 we present a new method where we couple a structural-kinematic model and a thermo-kinematic model to evaluate the consistency of existing balanced section reconstructions with independent thermochronology data. In papers 2 and 3 we use 2D lithospheric scale thermo-mechanical models with surface process algorithms. Using the above toolset, we demonstrate that syntectonic sedimentation results in longer basement thrust sheets as well as longer thin-skinned thrust sheets and a generally wider orogen. Conversely erosion tends to narrow the wedge and reduce the orogenic loading of the colliding plates, limiting the space available for deposition in the flexural foreland deeps. We also demonstrate that inherited extensional structures play a crucial role in mountain building as they facilitate the migration of deformation into the undeformed basement of the overriding plate. Moreover, a significant amount of lower-crustal/mantle-lithospheric material is preserved at shallow depths only in the presence of extensional inheritance, but significant erosion is needed in order to bring this material to the surface. Our models also show that thin-skinned thrust sheets are generally rooted in the footwall of basement thrusts as they form outward-propagating sequences. As soon as a new basement thrust forms, the thin-skinned sequence situated on top of the new basement thrust-sheet is abandoned in favour of starting a new sequence in the footwall of the new thrust. Regarding our case study, it was possible to reproduce the section restoration using a structural-kinematic model with high accuracy up to the 36-Ma time slice and with limited accuracy up to the 50-Ma time slice. The thermochronometric ages predicted by the thermo-kinematic modelling are generally in good agreement with both the high- and low-temperature thermochronology data available in the Central Pyrenees; hence we conclude that the restoration is to a first order consistent with these datasets. The predicted thermochronological ages approximate the available low-temperature thermochronology data better by taking into account the late-stage burial and re-excavation scenario affecting the southern flank of the Pyrenean wedge presented by Coney et al. (1996), and quantified by Fillon and van der Beek (2012). In conclusion, our model experiments suggest, that extensional inheritance played a prime role in the structural evolution of the Pyrenees, with the major characteristics of the North Pyrenean Unit, including the presence of steep, inverted normal faults, the relative tectonic quiescence of the area after the early inversion and the presence of a lower-crustal body at shallow depth below the unit, best recaptured by our accordion models.

<p>Alpine glaciers around the world are in retreat and are unlikely to reverse course. This dissertation focuses on improving our understanding of the impact of glacial melt on mountainous alpine groundwater systems. Studies on glacial melt-groundwater interactions have become more prevalent, particularly in the past 5 years, because we are recognizing that the contribution of glacial melt to the hydrologic cycle is not limited to melt-season surficial streamflow. The importance of glacial melt to mountain groundwater systems has the potential to not only influence spring and streamflow generation, but also the longevity of alpine specific, and frequently endangered species, dependent on this source of recharge. This recharge may be vital for human water needs such as potable water, agriculture, and hydrothermal power.</p>The impact that a transition from glacial melt to snow- or rain-dominated streamflow and recharge will have on alpine ecosystems in a continually warming climate is far reaching. This dissertation: 1) tests whether glacial melt is an important source of recharge for mountain springs and their microbial communities, 2) investigates the spatial impact of glacial-melt recharge on residence times and flowpaths that support alpine springs, and 3) explores the impact of post-peak water on alpine baseflow using a statistical, timeseries approach. My results show that the groundwater systems in glaciated mountainous, alpine regions are particularly vulnerable to climate change. Springs in Mount Hood National Forest and Glacier National Park were sampled over a 4-year period, and in addition, publicly available long-term streamflow datasets were are also utilized. The chapters composing this work build upon each other, and compare and contrast the factors most important in glacial melt recharging the mountain-block. Information that is vital to the management of alpine water resources by landowners, watershed groups, scientists, and others interested in mountain groundwater systems in glaciated alpine regions is presented in the following pages.