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Satellite altimetry has been traditionally used in the past few decades to measure elevation of land ice, quantify changes in ice topography and infer the mass balance of large and remote areas such as the Greenland and Antarctic ice sheets. Radar altimetry is particularly well suited to this task due to its all-weather year-round capability of observing the ice surface. However, monitoring of ice caps and ice fields - bodies of ice with areas typically smaller than ~ 10,000 km2 - has proven more challenging. The large footprint of a conventional radar altimeter and coarse ground track coverage are less suited to observing comparatively small regions with complex topography. Since 2010, the European Space Agency’s CryoSat-2 satellite has been collecting ice elevation measurements over ice caps and ice fields with its novel radar altimeter. CryoSat-2’s smaller inter-track spacing provides higher density of observations compared to previous satellite altimeters. Additionally, it generates more accurate measurements because (i) the footprint size is reduced in the along-track direction by means of synthetic aperture radar processing and (ii) interferometry allows to precisely locate the the across-track angle of arrival of a reflection from the surface. Furthermore, the interferometric capabilities of CryoSat-2 allow for the processing of the delayed surface reflections after the first echo. When applied over a sloping surface, this procedure generates a swath of elevations a few km wide compared to the conventional approach returning a single elevation. In this thesis, swath processing of CryoSat-2 interferometric data is exploited to generate topographic data over ice caps and ice fields. The dense elevation field is then used to compute maps of elevation change rates at sub-kilometer resolution with the aim of quantifying ice volume change and mass balance. A number of algorithms have been developed in this work, partly or entirely, to form a complete processing chain from generating the elevation field to calculating volume and mass change. These algorithms are discussed in detail before presenting the results obtained in two selected regions: Iceland and Patagonia. Over Icelandic ice caps, the high-resolution mapping reveals complex surface elevation changes, related to climate, ice dynamics and sub-glacial, geothermal and magmatic processes. The mass balance of each of the six largest ice caps (90% of Iceland’s permanent ice cover) is calculated independently for the first time using spaceborne radar altimetry data. Between October 2010 and September 2015 Icelandic ice caps have lost a total of 5.8± 0.7 Gt a ̄1, contributing 0.016± 0.002 mm a ̄1 to eustatic sea level rise. This estimate indicates that over this period the mass balance was 40% less negative than the preceding 15 years, a fact which partly reflects the anomalous positive balance year across the Vatnaj ̈okull ice cap (~ 70% of the glaciated area) in 2014/15. Furthermore, it is demonstrated how swath processing of CryoSat-2 interferometric data allows the monitoring of glaciological processes at the catchment scale. Comparison of the geodetic estimates of mass balance against those based on in situ data shows good agreement. The thesis then investigates surface elevation change on the Northern and Southern Patagonian Ice Fields to quantify their mass balance. This area is characterized by some of the fastest flowing glaciers in the world, displaying complex interactions with the proglacial environments (including marine fjords and freshwater lakes) they often drain into. Field observations are sparse due to the inaccessibility of these ice fields and even remotely sensed data are limited, often tied to comparisons to the topography in 2000 as measured by the Shuttle Radar Topography Mission. Despite gaps in the spatial coverage, in particular due to the complex topography, CryoSat-2 swath radar altimetry provides insight into the patterns of change on the ice fields in the most recent period (2011 to 2017) and allows to independently calculate the mass balance of glaciers or catchments as small as 300 km2. The northern part of the Southern Patagonian ice field displays the strongest losses due to a combination between ice dynamics and warming temperatures. In contrast Pio XI, the largest glacier on this ice field and in South America, is advancing and gaining mass. Between April 2011 and march 2017, the two ice fields combined have lost an average of 21.29± 1.98 Gt a ̄1 (equivalent to 0.059± 0.005 mm a ̄1 eustatic sea level rise), 24% and 42% more negative when compared to the periods 2000-2012/14 and 1975-2000. In particular the Northern Patagonian ice field, responsible for one third of the mass loss, is losing mass 70% faster compared to the first decade of the 21st century. These results confirm the overall strong mass loss of the Patagonian ice fields, second only to glaciers and ice caps in Alaska and the Canadian Arctic, and higher than High Mountain Asia, which all extend over areas ~ 5-8 times larger (excluding glaciers at the periphery of the Greenland and Antarctic ice sheets).

Este estudo apresenta padrões de flutuações das geleiras do Nevado Cololo, Bolívia, no período 1975–2011, determinado partir de dados orbitais, cartográficos e climáticos. As massas de gelo do Nevado Cololo são representativas das geleiras tropicais andinas que estão sujeitas a alternância entre condições atmosféricas úmidas (novembro-abril) e secas (maio-outubro) (outer tropics). Essa sazonalidade é determinada pela oscilação latitudinal da Zona de Convergência Intertropical (ZCIT) e perturbada pelos eventos não sazonais do fenômeno ENOS. A fase positiva, o El Niño, contribui negativamente para o balanço de massa dessas geleiras e foi frequente no intervalo investigado. Esse trabalho usou imagens TM/Landsat-5 para determinar a cobertura de gelo em 1989, 1997, 2008 e 2011. Aplicando o Normalized Difference Snow Index (NDSI), que utiliza as características espectrais opostas das massas de gelo no visível e no infravermelho próximo, este trabalho delimitou as geleiras do Nevado Cololo. Utilizando as informações de carta topográfica foi obtido um Modelo Digital de Elevação (MDE), elaborado pela interpolação de pontos de elevação usando o método geoestatístico krigagem ordinária. As informações obtidas do sensoriamento remoto e da cartografia foram incorporadas a um Sistema de Informação Geográfica (SIG) para se obter parâmetros das geleiras. A análise da séries temporais de precipitação e temperatura usaram dados do Global Precipitation Climatology Centre (GPCC)/NOAA, do Climate Research Unit Time Series (CRUTS)/University of East Anglia e de duas estações meteorológicas. Os dados climáticos não apresentam tendências estatisticamente significativas, mas há uma fraca redução da precipitação durante os meses de novembro, dezembro e abril, condições essa que podem indicar menor nebulosidade durante o verão. Em 2011 só restavam 48 das 122 geleiras identificadas em 1975. Geleiras pequenas (< 0,1 km²) com cotas máximas baixas foram as mais afetadas e atualmente não existem geleiras abaixo de 4.626 m a.n.m. A cobertura de gelo era de 24,77 ±0,00032 km² em 2011, 42,02% menor do que em 1975. A perda superficial ocorreu em todas as vertentes, independente de orientação, mas as geleiras voltadas a leste foram mais afetadas. Mesmo a maior geleira do Nevado Cololo, face SW, perdeu 21,6% de sua área total e sua frente retraiu cerca de 1 km durante o intervalo de 36 anos. Proporcionalmente, houve o aumento do número de geleiras cuja declividade média está entre 30° e 40°. A redução da espessura gelo é atestada pela fragmentação de geleiras e afloramentos do embasamento em suas partes internas. A perda de massa dessas geleiras estudadas foi provavelmente causada pela intensificação dos processos de ablação. / This study presents fluctuations patterns for the Nevado Cololo glaciers, Bolivia, in the period 1975–2011, as determined from orbital, cartographic and climatic data. Nevado Cololo ice masses are representative of Andean tropical glaciers subjected to alternations of humid (November to April) and dry (May to October) (outer tropics) atmospheric conditions. This seasonality is determined by the Inter-tropical Convergence Zone (ITCZ) latitudinal oscillation and disturbed by the no seasonal ENSO phenomena. The positive phase, El Niño, contributes negatively to these glaciers mass balance and was frequent during the investigated time period. This work used TM/ Landsat-5 imagery to determine the ice cover in 1989, 1997, 2008 and 2011. Applying the Normalized Snow Difference Index (NDIS), which uses the opposite spectral characteristics of ice masses in the visible and near infrared region, this work delimited the Nevado Cololo glaciers. Based on information from a topographic chart, we obtained a Digital Elevation Model (DEM) using elevation points interpolated by the ordinary kriging geostatistical method. Information derived from remote sensing and cartographic sources was incorporated into a Geographic Information System (GIS) to obtain glaciers parameters. The analyses of precipitation and temperature time series used data from the Global Precipitation Climatology Centre (GPCC)/NOAA, the Climate Research Unit Time Series (CRUTS)/University of East Anglia and from two meteorological stations. Climatic data show no statistically significant trend, but there was a weak precipitation reduction during November, December and April months, a condition that may indicate low cloudiness during the summer. By 2011, there were only 48 of the 122 glaciers identified in 1975. Small glaciers (<0.1 km²) with low maximum elevations were most affected and currently there are no glaciers below 4,626 m asl. The ice covered 24.77 km² in 2011, 42.02% less than in 1975. Surface loss occurred in all slopes, regardless of orientation, but glaciers facing east were most affected. Even the largest glacier in Nevado Cololo, SW face, lost 21.6% of its total area and its front retreated about 1 km during the 36 years period. Proportionately, there was an increase in the number of glaciers whose average slope is between 30° and 40°. The ice thickness reduction is attested by glaciers break up and bedrock outcrops in its internal parts. These glaciers mass loss was probably caused by the intensification of ablation processes.

Les glaciers rocheux sont l'une des expressions visibles du pergélisol de montagne et sont à ce titre l'objet d'études nombreuses et variées depuis plus de 20 ans. Deux principaux thèmes sont actuellement étudiés par la communauté scientifique : i) mieux appréhender les mouvements qui affectent les glaciers rocheux ainsi que les mécanismes qui les régissent et évaluer l'impact des changements atmosphériques globaux sur ces formes périglaciaires. Dans ces travaux de thèse nous proposons de contribuer au premier de ces deux thèmes de recherche en utilisant un des outils offerts par la télédétection, déjà utilisé dans d'autres pays pour l'étude des glaciers rocheux : l'interférométrie radar différentielle (D-InSAR). L'interférométrie radar différentielle (D-InSAR) est une méthode basée sur la mesure de la différence de phase entre deux images radar qui couvrent la même zone à différents intervalles de temps et depuis des orbites quasi-similaires. Déjà été utilisée dans d'autres domaines, notamment en glaciologie, volcanologie et sismologie, cette technique crée des interférogrammes, cartes de la déformation du sol en deux dimensions dans la ligne de visée du satellite, qui permettent de détecter et de quantifier un déplacement de quelques centimètres survenu au sol entre deux acquisitions radar. Des recherches en Suisse ont également montré que cette technique pouvait être utilisée pour semi-quantifier les mouvements de glaciers rocheux sur de vastes secteurs et parfois les quantifier (sous réserve de respecter certains critères lors de la création et l'analyse des interférogrammes). Dans ce travail de thèse, nous avons acquis des images radar provenant des satellites ERS (datant de 1991 à 1995) et TerraSAR-X (datant de l'été 2012) grâce à l'ESA (agence spatiale européenne) et au DLR (Deutschen Zentrums für Luft und Raumfahrt, agence spatiale Allemande) dans le but de créer et d'analyser des interférogrammes dans le secteur des Alpes françaises. Nous nous intéressons principalement à la détection des glaciers rocheux. Les archives des satellites ERS-1 et 2 nous ont permis de travailler à l'échelle de l'ensemble des Alpes françaises avec une résolution moyenne (25m en géométrie sol). Les données provenant de TerraSAR-X (TSX) ont permis des analyses plus fines grâce à une meilleure résolution en géométrie sol (10m). Cependant le secteur d'études s'est restreint à la Haute Maurienne/Haute Tarentaise à cause du coût des données et du temps nécessaire à la création et à l'analyse des interférogrammes. Pour les données ERS, nous avons pris en compte l'ensemble des images disponibles au-dessus des Alpes françaises et choisi celles adaptées pour notre étude. Finalement 9 interférogrammes ont été créés. Pour analyser ces données deux méthodes ont été employées : i) une analyse visuelle par des géomorphologues dans un SIG (aidée par des ortho-images et des données topographiques) ; ii) une évaluation de la pertinence des résultats par l'intermédiaire d'une comparaison entre les résultats D-InSAR et des inventaires de glaciers rocheux existants. Finalement une carte de l'ensemble des glaciers rocheux détectés dans les Alpes françaises a été produite. Les données TSX ont été analysées sensiblement de la même manière. Enfin, une troisième étude s'est concentrée sur le cas peu commun du glacier rocheux « déstabilisé » de Pierre Brune (mouvements > 2m/an). Une reconstitution historique des déplacements a été réalisée à partir d'images optiques d'archive et des données GPS ont été acquises durant l'été 2012 et comparées aux données obtenues par D-InSAR. En nous basant sur ces études aux résolutions d'image et aux échelles spatiales variées, nous proposons une discussion sur la pertinence de l'utilisation de la méthode D-InSAR pour du « monitoring » à moyen et long termes des glaciers rocheux mais également sur les atouts et inconvénients de la méthode. / Rockglaciers are one the visual expressions of mountain permafrost and have been the focus of numerous and various studies in the last two decades. Two main topics are studied by the scientific community: i) better understanding the movements of active rockglaciers and the phenomena that generate those movements; ii) assessing impact of global atmospheric change on these periglacial shapes. Here we propose to contribute to the first topic by using remote sensing method of displacement measurements already used in other countries for rockglaciers studies: Differential Interferometric Synthetic Aperture Radar (D-InSAR). D-InSAR is a method of measurement based on the phase difference between two radar images, which represent the same area but at different time intervals. The technique generates interferograms, maps of surface deformation in two-dimensions allowing for the detection and quantification (in centimeters) of variations in distance between the target and the radar between two different data acquisitions. Recent research has shown that the InSAR technique can be used to semi-quantify rockglacier deformation (under the assumption that certain conditions are respected with regard to generating and interpreting the interferograms). In the present thesis, ERS radar images (dating from 1991 to 1995) and TerraSAR-X data (dating from summer 2012) were obtained in courtesy of ESA (European Space Agency) and DLR (Deutschen Zentrums für Luft- und Raumfahrt, German Space Agency) with the aim of generating interferograms. We are interested by the detection of rockglacier movements. The ERS archives allowed us to work at French Alps scale with moderate resolution (25m in ground geometry) whereas TerraSAR-X data have better ground resolution (10m) but our analysis are more local (Haute Maurienne/Haute Tarentaise) due to the cost of the data and the time-consuming nature of the analyzes. With ERS, we selected all archives data and chose the more relevant of them. Finally 9 interferograms were generated. To analyse this amount of data two methods were employed: i) a GIS analysis of interferograms by geomorphologists (helped by ortho-images and topographic data), ii) a comparison between interferograms and existing rockglaciers shape inventory to evaluate the quality of the radar detections. At the end of the analysis a map of the French Alps with all detected rockglacier movements was produced. With TerraSAR-X data, the method of analysis was almost the same. Analyzes focused on the Haute Maurienne/Haute Tarentaise massif. A third scale of analysis is focus on Pierre Brune rockglacier which has been detected on ERS interferograms as destabilized rockglaciers (movement > 2 m/year). Further investigations have been carried out on this site (historical movements reconstitution and GPS acquisitions). Based on these studies with different scales and resolutions, we proposed a discussion about suitability of D-InSAR measurements method for long term rockglaciers monitoring as well as drawbacks and benefits of the method.

Este estudo apresenta padrões de flutuações das geleiras do Nevado Cololo, Bolívia, no período 1975–2011, determinado partir de dados orbitais, cartográficos e climáticos. As massas de gelo do Nevado Cololo são representativas das geleiras tropicais andinas que estão sujeitas a alternância entre condições atmosféricas úmidas (novembro-abril) e secas (maio-outubro) (outer tropics). Essa sazonalidade é determinada pela oscilação latitudinal da Zona de Convergência Intertropical (ZCIT) e perturbada pelos eventos não sazonais do fenômeno ENOS. A fase positiva, o El Niño, contribui negativamente para o balanço de massa dessas geleiras e foi frequente no intervalo investigado. Esse trabalho usou imagens TM/Landsat-5 para determinar a cobertura de gelo em 1989, 1997, 2008 e 2011. Aplicando o Normalized Difference Snow Index (NDSI), que utiliza as características espectrais opostas das massas de gelo no visível e no infravermelho próximo, este trabalho delimitou as geleiras do Nevado Cololo. Utilizando as informações de carta topográfica foi obtido um Modelo Digital de Elevação (MDE), elaborado pela interpolação de pontos de elevação usando o método geoestatístico krigagem ordinária. As informações obtidas do sensoriamento remoto e da cartografia foram incorporadas a um Sistema de Informação Geográfica (SIG) para se obter parâmetros das geleiras. A análise da séries temporais de precipitação e temperatura usaram dados do Global Precipitation Climatology Centre (GPCC)/NOAA, do Climate Research Unit Time Series (CRUTS)/University of East Anglia e de duas estações meteorológicas. Os dados climáticos não apresentam tendências estatisticamente significativas, mas há uma fraca redução da precipitação durante os meses de novembro, dezembro e abril, condições essa que podem indicar menor nebulosidade durante o verão. Em 2011 só restavam 48 das 122 geleiras identificadas em 1975. Geleiras pequenas (< 0,1 km²) com cotas máximas baixas foram as mais afetadas e atualmente não existem geleiras abaixo de 4.626 m a.n.m. A cobertura de gelo era de 24,77 ±0,00032 km² em 2011, 42,02% menor do que em 1975. A perda superficial ocorreu em todas as vertentes, independente de orientação, mas as geleiras voltadas a leste foram mais afetadas. Mesmo a maior geleira do Nevado Cololo, face SW, perdeu 21,6% de sua área total e sua frente retraiu cerca de 1 km durante o intervalo de 36 anos. Proporcionalmente, houve o aumento do número de geleiras cuja declividade média está entre 30° e 40°. A redução da espessura gelo é atestada pela fragmentação de geleiras e afloramentos do embasamento em suas partes internas. A perda de massa dessas geleiras estudadas foi provavelmente causada pela intensificação dos processos de ablação. / This study presents fluctuations patterns for the Nevado Cololo glaciers, Bolivia, in the period 1975–2011, as determined from orbital, cartographic and climatic data. Nevado Cololo ice masses are representative of Andean tropical glaciers subjected to alternations of humid (November to April) and dry (May to October) (outer tropics) atmospheric conditions. This seasonality is determined by the Inter-tropical Convergence Zone (ITCZ) latitudinal oscillation and disturbed by the no seasonal ENSO phenomena. The positive phase, El Niño, contributes negatively to these glaciers mass balance and was frequent during the investigated time period. This work used TM/ Landsat-5 imagery to determine the ice cover in 1989, 1997, 2008 and 2011. Applying the Normalized Snow Difference Index (NDIS), which uses the opposite spectral characteristics of ice masses in the visible and near infrared region, this work delimited the Nevado Cololo glaciers. Based on information from a topographic chart, we obtained a Digital Elevation Model (DEM) using elevation points interpolated by the ordinary kriging geostatistical method. Information derived from remote sensing and cartographic sources was incorporated into a Geographic Information System (GIS) to obtain glaciers parameters. The analyses of precipitation and temperature time series used data from the Global Precipitation Climatology Centre (GPCC)/NOAA, the Climate Research Unit Time Series (CRUTS)/University of East Anglia and from two meteorological stations. Climatic data show no statistically significant trend, but there was a weak precipitation reduction during November, December and April months, a condition that may indicate low cloudiness during the summer. By 2011, there were only 48 of the 122 glaciers identified in 1975. Small glaciers (<0.1 km²) with low maximum elevations were most affected and currently there are no glaciers below 4,626 m asl. The ice covered 24.77 km² in 2011, 42.02% less than in 1975. Surface loss occurred in all slopes, regardless of orientation, but glaciers facing east were most affected. Even the largest glacier in Nevado Cololo, SW face, lost 21.6% of its total area and its front retreated about 1 km during the 36 years period. Proportionately, there was an increase in the number of glaciers whose average slope is between 30° and 40°. The ice thickness reduction is attested by glaciers break up and bedrock outcrops in its internal parts. These glaciers mass loss was probably caused by the intensification of ablation processes.

O efeito de alterações climáticas sobre os micro-organismos ainda é incerto, pois pouco se conhece sobre as espécies que habitam regiões extremas como o gelo, solo antártico, e o solo permanentemente congelado (permafrost). O permafrost tem como característica a preservação de material biológico por milhões de anos, servindo como fonte para estudos de evolução e biogeografia de micro-organismos. O objetivo deste trabalho foi estudar a diversidade microbiana em amostras de gelo, solo exposto por recuo de geleira e permafrost polares, e a diversidade funcional do gene alcano monoxigenase (alk). Métodos independentes de cultivo baseados no gene 16S rRNA foram utilizados, como DGGE, clonagem e pirossequenciamento. As geleiras da Ilha Rei George (Península Antártica) e do Pólo Sul Geográfico possuem cerca de 3.104 cél./mL e são compostas por micro-organismos diferentes, com predominância dos Filos Proteobacteria, Actinobacteria, Firmicutes e Cyanobacteria, muitos dos quais já descritos em outros ambientes criogênicos. O solo em frente à geleira Baranowski apresenta uma estrutura de comunidade diferente do gelo. O solo exposto por recuo de geleira apresenta uma sucessão ecológica, com predominância de heterotróficas durante todo o processo. Fixadores de nitrogênio no solo foram compostos por cianobactérias no início, e por Rhodopseudomonas e Rhodobacter no final da sucessão. Estes resultados foram melhor observados com o pirossequenciamento. As mudanças observadas podem estar relacionadas ao aumento de K, Mg+, NH4+, NO3- e/ou CO2 detectados após 15-20 anos de exposição do solo. A comunidade de permafrosts varia com o local e a idade de congelamento (de 5.000 a 8 milhões de anos). O gene alkM foi detectado em permafrosts do Ártico com 3 milhões de anos, e o gene alkB em amostras do Ártico com 15.000 e 120.000 anos, e em solos modernos da Antártica. Alguns clones indicam que podem representar novos genes para alcano monoxigenases. As contribuições deste projeto abrangem os objetivos do Ano Polar Internacional (IPY 2007-2009), sobretudo na avaliação da ecologia microbiana da Antártica. / The effect of climate changes on microorganisms is still unclear, because little is known about the species that inhabit the extreme regions as the glacial ice, antarctic soils and the permanently frozen soil (permafrost). The permafrost is able to preserve the sedimented biological materials by thousands or even millions of years, being an important source for microbiological studies. The objective was to study the microbial diversity in cryogenic samples: glacial ice, soil exposed by glacial retreat and polar permafrosts, as well as to study the functional diversity of alkane monooxygenase genes (alk) in the permafrost. Cultivationindependent methods based on the 16S rRNA gene were used, as DGGE, clone library and 454 Pyrosequencing. Analysis of the King George Island (Antarctic Peninsula) glaciers and the South Pole ice revealed about 3x104 cells/mL each, and different micro-organisms were detected, predominantly members from Proteobacteria, Actinobacteria, Firmicutes and Cyanobacteria, many of which already described in other cryogenic environments. The soil in front of the Baranowski Glacier has a different community structure compared with the ice. Soils exposed by glacier retreat revealed an ecological succession, and heterotrophic bacteria occurred all through the process. Nitrogen-fixing populations were composed by cyanobacteria at the early stages, and shifted to Rhodopseudomonas and Rhodobacter in the older soils. The observed changes may be related to an increase of K, Mg+, NH4 +, NO3- and/or CO2, detected after 15-20 years of soil exposure. The community of permafrosts varies by location and age (5,000 - 8 millions of years). The alkM gene was detected in old Arctic permafrosts (3 millions of years), while alkB genes were found on Arctic samples from 15,000 to 120,000 years, and in Antarctic modern soils. Some of these clones may represent new alk genes. The contributions of this project covers the goals of the International Polar Year (IPY 2007-2009), particularly in assessing the microbial ecology of Antarctica.

Les environnements montagneux sont un lieu privilégié d'échange d'eau et d'énergie. Les rivières de montagne alimentent en eau 40% de la population mondiale et sont sujettes à une pression démographique et climatique important. Dans ce contexte, la compréhension des processus météorologiques, hydrologiques et hydrogéologiques est fondamentale pour la gestion globale de la ressource en eau. L'étude, présentée dans ce manuscrit de thèse, se positionne au sein des environnements montagneux où l'hydrologie est influencée par le couvert neigeux saisonnier et par les glaciers, et propose une approche de modélisation interdisciplinaire afin d'améliorer la compréhension des processus en jeu.Aujourd'hui, si les modèles sont capables de simuler le débit sur les rivières de montagnes jaugées sous influence nivale et glaciaire, un certain nombre d'incertitudes persistent quant à l'utilisation de tels modèles hors de leur conditions de validation (en réponse à un climat différent ou sur un domaine non-jaugé). La principale source d'incertitude est liée au manque de connaissance des précipitations en montagne, dont la mesure est rare et incertaine. C'est pourtant la principale composante du bilan hydrologique. A cet égard, nous proposons d'exploiter l'information fournie par la géométrie du couvert neigeux et des glaciers, en tant que “pluviomètres géants” à l'échelle de ces réservoirs, dans un modèle hydrologique à réservoirs conceptuels reposant sur la notion de bassin versant.L'information, hydrologique, nivale et glaciaire est évaluée dans un cadre de calibration multi-objectifs. Les résultats montrent que, dans cette configuration, la validation conjointe du modèle hydrologique par le débit journalier, le bilan de masse glaciaire annuel et la hauteur de neige locale journalier permet de réduire fortement l'incertitude sur le forçage météorologique journalier et d'améliorer la robustesse du modèle. Ce résultat préliminaire nous a permis de reconstruire, en conséquence, le bilan de masse local annuel à l'échelle des glaciers.Par ailleurs, la représentation des glaciers au sein d'un modèle hydrologique pose un certain nombre de défis, surtout dans la perspective de simuler les processus hydrologiques à l'échelle pluri-annuelle. En particulier, la prise en compte de l'évolution de la géométrie des glaciers au sein d'un modèle hydrologique est balbutiante. A cet égard, nous proposons, dans cette étude, des axes d'amélioration de la représentation des glaciers au sein d'un modèle hydrologique par un angle d'investigation géomorphologique. Cette approche a permis d'élaborer un modèle probabiliste permettant de décrire les surfaces englacées au sein d'un bassin versant selon une courbe de niveau. / Mountainous environments are a privileged place of water and energy exchange. Mountainous rivers feed about 40% of the world population and are subjected to climate change and a growing demography. In this context, the comprehension of meteorological, hydrological and hydrogeological processes is essential for a better overall management of water resource. This PhD study is focused squarely on the mountainous environments where hydrology is influenced by snow cover and glaciers, and introduces a multidisciplinary modeling approach in order to improve our comprehension of the process involved.Today, hydrological models are able to simulate gauged mountainous river streamflows under the influence of snow and glaciers but some uncertainties remain when applying such models out of their calibration phase (for instance in response to a different climate or on a ungauged basin). The main uncertainty source is the lack of knowledge of mountainous precipitations, whose measure is sparse and uncertain. It remains the principal component of the hydrological budget though. In this study, we suggest using the meteorological information provided by snow cover and glaciers as “giant pluviometers” to their reservoir scales, with a conceptual reservoir model associated with the concept of watershed.The information provided by hydrology processes, snow and glaciers is assessed in a multi-objective calibration phase. Results show that, in this configuration, the joint validation of the hydrological model by daily streamflow, annual mass balance and daily local snow depth reduces significantly the uncertainty on the meteorological forcing and improves the model robustness. This preliminary result has motivated, consequently, the local annual mass balance of the glaciers.Also, the representation of glaciers in a hydrological model raises a certain amount of issues, especially in the perspective of simulation long-term hydrological processes. In particular, the consideration of the evolution of the glacier geometry is at an early stage. To this end, we propose, in this study, ways of improvements for the representation of glaciers from a geomorphological perspective. This approach allowed us to build a probabilistic model able to describe the glaciated surfaces within a watershed according to a given topographic contour line.

Numerous moraines front the Coe Glacier on the north side of Mount Hood, Oregon. These moraines were identified and dated using a multiple methodology approach in order to establish a chronology for the advances and stillstands of the Cae Glacier. This chronology was compared to chronologies established for other glaciers on Mount Hood, North Sister, Mount Rainier and Mount Baker as well as glaciers in Scandinavia. The chronology was also compared to a long term temperature record from Longmire, Washington. The maximum identified extent of the pre-Little Ice Age Coe Glacier was indicated by moraines located at an elevation of about 1530 m and about 2 km downvalley of the present terminus. A general period of shrinkage of the pre-Little Ice Age Coe Glacier followed resulting in the deposition of moraines upvalley of the older pre-Little Ice Age moraines. The Little Ice Age Coe Glacier reached its maximum downvalley extent of about 1650 m elevation prior to 1731 AD. An earlier advance (1607 AD) was more extensive laterally than the 1731 AD advance. The Coe Glacier has been in a general state of recession since the mid to late 1700's. The prominent lateral moraines formed prior to 1882 AD. Four low moraines located within the Coe Glacier trough formed before 1901. Historical records indicate that the Coe Glacier has generally continued to recede since then. A comparison of the moraine ages and the historical activity of the Coe Glacier to other glaciers on Mount Hood as well as others in the Pacific Northwest and Scandinavia reveals that fluctuations of the glacier termini are generally synchronous. This similarity, combined with the similarity of the ages of Coe Glacier moraines to cool periods in a long term temperature record, indicates that hemispheric climatic patterns have played a major role in the past fluctuations of the Coe Glacier.

At least four glacial stands occurred since 6.5 ka B.P. based on moraines located on the eastern flanks of the Three Sisters Volcanoes and the northern flanks of Broken Top Mountain in the Central Oregon Cascades. The youngest of these advances was the Little Ice Age (LIA) glaciation, which reached its maximum advance 150-200 yrs. B.P. and is defined by the large sharp crested and unvegetated moraines adjacent to the modern glaciers. In isolated locations less than 100 m downslope from these moraines, a second set of sparsely vegetated lateral moraines marks the Late-Neoglacial stand of the glaciers between 2.1 ± 0.4 and 7.7 ka B.P, A third set of Early-Neoglacial end moraines is 300-700 meters downslope of the modern glacier termini, and postdates 7.7 ka B.P. From SST temperature data (Barron et al., 2003) and a speleothem record (Vacco, 2003), we infer that this advance occurred between 4.5 and 6.5 ka B.P. Finally, the Fountonnor stand is marked by moraines 500-900 meters downslope of the modern glacier termini, and we infer these are latest Pleistocene or early Holocene. Modem equilibrium line altitudes (ELAs) at the Three Sisters and Broken Top are approximately 2500 - 2600 m. During the LIA, the ELAs were 40 - 180 m lower, requiring cooler mean summer temperatures by 0.7 - 1.0°C and winter snowfall to increase by 10 - 60 cm water equivalent. The average Early Neoglacial and Fountonnor ELAs were 130 - 300 m and 290 - 320 m lower than modem glaciers, respectively, requiring air temperatures to be 0.7 - 1.6°C and 1.5 - 1.7°C cooler during the summer and winter snowfall to be 40 - 100 cm water equivalent and 90 - 100 cm water equivalent greater.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia-Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss. / by Laura A. Stevens. / Ph. D.