Christophe Lambiel - Academia.edu (original) (raw)

Uploads

Papers by Christophe Lambiel

Verbier constitue l'une des plus grandes stations de sports d'hiver des Alpes suisses. Son domain... more Verbier constitue l'une des plus grandes stations de sports d'hiver des Alpes suisses. Son domaine skiable de premier ordre est cependant situé sur des pentes fortement encombrées de débris rocheux gneissiques amenés par la combinaison des processus gravitaires, glaciaires et périglaciaires. De tels terrains posent de gros problèmes pour la pratique du ski. D'importants travaux ont donc été effectués afin d'aplanir les pistes de ski. Dans cet article sont étudiées les modifications apportées à la morphologie de deux vallons situés dans le domaine skiable de Verbier : Médran et La Chaux. Dans le premier cas, les glaciers rocheux et la couverture morainique ont été presque entièrement nivelés. Dans le deuxième cas, la marge proglaciaire d'un petit glacier qui a subi un fort recul depuis la fin du Petit Age Glaciaire a été plus légèrement modifiée. Les impacts de ces travaux sur la modification du régime thermique du sous-sol par l'amincissement du niveau actif des terrains gelés et la suppression des gros blocs de surface sont également étudiés, de même que le refroidissement du sol provoqué par le damage des pistes. Enfin, le cas de la fonte d'une moraine gelée provoquée par la construction d'une station de départ d'un téléphérique est également abordé.

Resume Le versant d’eboulis au nord-est de la Pointe du Tsate constitue un exemple typique d’ebou... more Resume Le versant d’eboulis au nord-est de la Pointe du Tsate constitue un exemple typique d’eboulis «a galets». Les materiaux de surface constitues par des cailloux et graviers dans une matrice tres fine permettent de stocker d’importantes quantites d’eau. Les tomographies des resistivites electriques (ERT) realisees et les temperatures de la surface du sol mesurees ont permis de determiner la repartition du pergelisol dans le versant et de proposer des considerations sur le role de l’eau liquide dans la formation et la preservation de la glace du pergelisol. Ces donnees montrent que, en raison de la lithologie particuliere du site, les valeurs de resistivite normalement utilisees pour definir la repartition du pergelisol dans les eboulis «a blocs» ne sont pas valables ici. Cet eboulis «a galets», en raison de sa granulometrie, est donc soumis a des conditions rheologiques et de formation, saturation et deformation de la glace du pergelisol tres particulieres qui sont typiques des ...

Stochastic Environmental Research and Risk Assessment, 2021

In this paper, we compare the performance of two data-driven algorithms to deal with an automatic... more In this paper, we compare the performance of two data-driven algorithms to deal with an automatic classification problem in geomorphology: Direct Sampling (DS) and Random Forest (RF). The main goal is to provide a semi-automated procedure for the geomorphological mapping of alpine environments, using a manually mapped zone as training dataset and predictor variables to infer the classification of a target zone. The applicability of DS to geomorphological classification was never investigated before. Instead, RF based classification has already been applied in few studies, but only with a limited number of geomorphological classes. The outcomes of both approaches are validated by comparing the eight detected classes with a geomorphological map elaborated on the field and considered as ground truth. Both DS and RF give satisfactory results and provide similar performances in term of accuracy and Cohen’s Kappa values. The map obtained with RF presents a noisier spatial distribution of ...

Physio-Géo, 2019

Le 16 juin 1818, la debâcle d'un lac de barrage glaciaire au Gietro provoquait une vague deva... more Le 16 juin 1818, la debâcle d'un lac de barrage glaciaire au Gietro provoquait une vague devastant la vallee de Bagnes, dans le canton du Valais (Suisse), faisant 34 morts et de tres nombreux degâts materiels aux infrastructures (ponts, voies de communication), aux habitations et aux constructions agricoles et hydrauliques, ainsi qu'aux cultures et prairies. La cartographie de l'extension geographique de l'inondation a ete realisee en croisant differentes sources environnementales, historiques et sociologiques : 1/une liste des degâts aux terrains et bâtiments prives a ete etablie sur la base des archives repertoriant les dommages declares par les sinistres ; 2/ cette base de donnees a ete combinee avec une base de donnees genealogiques regionales afin de reconstituer les pertes a l'echelle de certains individus ; 3/ elle a egalement ete croisee avec une base de donnees toponymiques afin de localiser les degâts ; 4/ un releve systematique des traces geomorphologiques de la vague (rebords d'erosion, epandages de blocs) a ete etabli sur le terrain et au moyen d'un modele numerique de terrain (MNT) ; 5/ finalement, des entretiens ont ete realises dans un village particulierement sinistre, afin d'apprehender la memoire orale de l'evenement. Cet article discute l'interet d'un tel croisement pluridisciplinaire en presentant les caracteristiques des differentes sources, les apports a la reconstruction de l'extension geographique de l'inondation et des degâts a deux echelles differentes, ainsi que les difficultes (lacunes, incertitudes) relatives a ces sources. Ce travail permet de discuter les enjeux lies a la reconstitution de catastrophes naturelles anciennes au moyen de differentes sources, environnementales, historiques et sociologiques.

In many high mountain regions, warming of perennially frozen ground in both coarse debris and roc... more In many high mountain regions, warming of perennially frozen ground in both coarse debris and rock walls has a major influence on slope stability. In this context, indications of destabilizing active rock glaciers, such as high horizontal velocities (up to 4 ma-1), front advance rates of up to 4 ma-1, and development of crevasse-like cracks (up to 14 m deep), have been documented and monitored in the Alps for a few years. Beside the limited knowledge of rock glacier dynamics, our principle hypothesis is that the primary factors controlling the development of cracks and the destabilization of rock glacier tongues are the rheological properties of warming ice. In addition, we postulate that hydrological effects of unfrozen water within the active layer, the permafrost body, or at its base may contribute to the initiation of the slide-like mass wasting.

Ground Surface Temperatures (GST) are mainly controlled by atmospheric factors and topographical ... more Ground Surface Temperatures (GST) are mainly controlled by atmospheric factors and topographical effects and represent an important standard element within the operational permafrost monitoring network PERMOS in Switzerland. Due to its shape, position and extent the Alpine arc is influenced by prevailing winds from several directions provoking a complex and highly variable pattern of precipitation in different regions of Switzerland with a general trend to a more continental climate in some inner-alpine valleys. The lower boundary for the occurrence of mountain permafrost in the Swiss Alps is located at about 2500 m asl., close to the free atmosphere where air temperatures are almost homogenous in all regions, but precipitation usually shows large regional differences regarding timing and quantity depending on the meteorological conditions. At the elevation range of mountain permafrost the ground surface remains snow-free only for about 4-5 months (between June and November) with a ...

Géomorphologie : relief, processus, environnement, 2008

The anomaly has first been attributed to redistribution of snow by avalanches (Haeberli, 1975). R... more The anomaly has first been attributed to redistribution of snow by avalanches (Haeberli, 1975). Recent studies (Lerjen et al., 2003 and Luetschg et al., 2003) stress the importance of granulometry and graded bedding, which facilitate the overcooling of the lower part of the talus slopes. At low altitude, several authors have demonstrated that the overcooling of foot Géomorphologie : relief, processus, environnement, 2008, n°2, p. 87 La répartition du pergélisol dans trois éboulis alpins du massif de la Dent de Morcles (Valais, Alpes suisses)

2012 IEEE International Geoscience and Remote Sensing Symposium, 2012

ABSTRACT This paper describes a new method to monitor active rock glaciers using DInSAR technique... more ABSTRACT This paper describes a new method to monitor active rock glaciers using DInSAR technique with Terrasar-X data acquired with mode facing slope and 11 days time interval during late summers 2009 to 2011. Where the spatial distribution of the rock glacier surface deformation derived from the DInSAR data using conventional unwrapping processes fails due to the relative small size and the complex movement of some rock glaciers, a specific profile is here defined through the rock glacier and is used to analyze the DInSAR products along it. Firstly, the prerequisites to perform such analysis at local scale are given. Then a quantification and discussion of results are achieved through different examples of active rock glaciers encountered in Western Swiss Alps.

Permafrost and Periglacial Processes, 2004

The use of real-time kinematic (RTK) GPS for studying the dynamics of creeping mountain permafros... more The use of real-time kinematic (RTK) GPS for studying the dynamics of creeping mountain permafrost is evaluated on the basis of measurements carried out on three test sites in the Western Swiss Alps. The high precision of the method and its ease of use make the RTK GPS appropriate for this kind of study. A wide range of information can be obtained by comparing the position of a set of surveyed points after two campaigns of measurement: determination of both horizontal and vertical components of surface movements, identification of compression and extension zones, estimation of thickness variation and, finally, determination of three-dimensional (3D) rotational movements of individual boulders. Temporal variations of all these parameters can then be identified after more than two repetitions of the measurement series. The results obtained on the test sites are presented and discussed from a geomorphological point of view. They were sometimes surprising, for instance the strong difference in surface velocities of two morphologically similar rock glaciers situated in the same area or the small 3D rotation of blocks located on the front of a rapidly moving rock glacier.

Permafrost and Periglacial Processes, 2004

Norsk Geografisk Tidsskrift - Norwegian Journal of Geography, 2001

Lambiel, C. & Reynard, E. 2001. Regional modelling of present, past and future potential dist... more Lambiel, C. & Reynard, E. 2001. Regional modelling of present, past and future potential distribution of discontinuous permafrost based on a rock glacier inventory in the Bagnes–Hérémence area (Western Swiss Alps). Norsk Geogra sk Tidsskrift–Norwegian Journal of Geography Vol. ...

Proceedings, 8th …, 2003

Since the end of the Little Ice Age (LIA), glaciated surfaces in the Alps have considerably decre... more Since the end of the Little Ice Age (LIA), glaciated surfaces in the Alps have considerably decreased, exposing large areas of unconsolidated sediments. The LIA proglacial forefields of most of the small glaciers (Ͻ1 km 2) are situated within the belt of discontinuous permafrost (Ͼ2200 m a.s.l.). Few attempts have been made to map the ground ice distribution in such recently deglaciated terrains (e.g.

Verbier constitue l'une des plus grandes stations de sports d'hiver des Alpes suisses. Son domain... more Verbier constitue l'une des plus grandes stations de sports d'hiver des Alpes suisses. Son domaine skiable de premier ordre est cependant situé sur des pentes fortement encombrées de débris rocheux gneissiques amenés par la combinaison des processus gravitaires, glaciaires et périglaciaires. De tels terrains posent de gros problèmes pour la pratique du ski. D'importants travaux ont donc été effectués afin d'aplanir les pistes de ski. Dans cet article sont étudiées les modifications apportées à la morphologie de deux vallons situés dans le domaine skiable de Verbier : Médran et La Chaux. Dans le premier cas, les glaciers rocheux et la couverture morainique ont été presque entièrement nivelés. Dans le deuxième cas, la marge proglaciaire d'un petit glacier qui a subi un fort recul depuis la fin du Petit Age Glaciaire a été plus légèrement modifiée. Les impacts de ces travaux sur la modification du régime thermique du sous-sol par l'amincissement du niveau actif des terrains gelés et la suppression des gros blocs de surface sont également étudiés, de même que le refroidissement du sol provoqué par le damage des pistes. Enfin, le cas de la fonte d'une moraine gelée provoquée par la construction d'une station de départ d'un téléphérique est également abordé.

Resume Le versant d’eboulis au nord-est de la Pointe du Tsate constitue un exemple typique d’ebou... more Resume Le versant d’eboulis au nord-est de la Pointe du Tsate constitue un exemple typique d’eboulis «a galets». Les materiaux de surface constitues par des cailloux et graviers dans une matrice tres fine permettent de stocker d’importantes quantites d’eau. Les tomographies des resistivites electriques (ERT) realisees et les temperatures de la surface du sol mesurees ont permis de determiner la repartition du pergelisol dans le versant et de proposer des considerations sur le role de l’eau liquide dans la formation et la preservation de la glace du pergelisol. Ces donnees montrent que, en raison de la lithologie particuliere du site, les valeurs de resistivite normalement utilisees pour definir la repartition du pergelisol dans les eboulis «a blocs» ne sont pas valables ici. Cet eboulis «a galets», en raison de sa granulometrie, est donc soumis a des conditions rheologiques et de formation, saturation et deformation de la glace du pergelisol tres particulieres qui sont typiques des ...

Stochastic Environmental Research and Risk Assessment, 2021

In this paper, we compare the performance of two data-driven algorithms to deal with an automatic... more In this paper, we compare the performance of two data-driven algorithms to deal with an automatic classification problem in geomorphology: Direct Sampling (DS) and Random Forest (RF). The main goal is to provide a semi-automated procedure for the geomorphological mapping of alpine environments, using a manually mapped zone as training dataset and predictor variables to infer the classification of a target zone. The applicability of DS to geomorphological classification was never investigated before. Instead, RF based classification has already been applied in few studies, but only with a limited number of geomorphological classes. The outcomes of both approaches are validated by comparing the eight detected classes with a geomorphological map elaborated on the field and considered as ground truth. Both DS and RF give satisfactory results and provide similar performances in term of accuracy and Cohen’s Kappa values. The map obtained with RF presents a noisier spatial distribution of ...

Physio-Géo, 2019

Le 16 juin 1818, la debâcle d'un lac de barrage glaciaire au Gietro provoquait une vague deva... more Le 16 juin 1818, la debâcle d'un lac de barrage glaciaire au Gietro provoquait une vague devastant la vallee de Bagnes, dans le canton du Valais (Suisse), faisant 34 morts et de tres nombreux degâts materiels aux infrastructures (ponts, voies de communication), aux habitations et aux constructions agricoles et hydrauliques, ainsi qu'aux cultures et prairies. La cartographie de l'extension geographique de l'inondation a ete realisee en croisant differentes sources environnementales, historiques et sociologiques : 1/une liste des degâts aux terrains et bâtiments prives a ete etablie sur la base des archives repertoriant les dommages declares par les sinistres ; 2/ cette base de donnees a ete combinee avec une base de donnees genealogiques regionales afin de reconstituer les pertes a l'echelle de certains individus ; 3/ elle a egalement ete croisee avec une base de donnees toponymiques afin de localiser les degâts ; 4/ un releve systematique des traces geomorphologiques de la vague (rebords d'erosion, epandages de blocs) a ete etabli sur le terrain et au moyen d'un modele numerique de terrain (MNT) ; 5/ finalement, des entretiens ont ete realises dans un village particulierement sinistre, afin d'apprehender la memoire orale de l'evenement. Cet article discute l'interet d'un tel croisement pluridisciplinaire en presentant les caracteristiques des differentes sources, les apports a la reconstruction de l'extension geographique de l'inondation et des degâts a deux echelles differentes, ainsi que les difficultes (lacunes, incertitudes) relatives a ces sources. Ce travail permet de discuter les enjeux lies a la reconstitution de catastrophes naturelles anciennes au moyen de differentes sources, environnementales, historiques et sociologiques.

In many high mountain regions, warming of perennially frozen ground in both coarse debris and roc... more In many high mountain regions, warming of perennially frozen ground in both coarse debris and rock walls has a major influence on slope stability. In this context, indications of destabilizing active rock glaciers, such as high horizontal velocities (up to 4 ma-1), front advance rates of up to 4 ma-1, and development of crevasse-like cracks (up to 14 m deep), have been documented and monitored in the Alps for a few years. Beside the limited knowledge of rock glacier dynamics, our principle hypothesis is that the primary factors controlling the development of cracks and the destabilization of rock glacier tongues are the rheological properties of warming ice. In addition, we postulate that hydrological effects of unfrozen water within the active layer, the permafrost body, or at its base may contribute to the initiation of the slide-like mass wasting.

Ground Surface Temperatures (GST) are mainly controlled by atmospheric factors and topographical ... more Ground Surface Temperatures (GST) are mainly controlled by atmospheric factors and topographical effects and represent an important standard element within the operational permafrost monitoring network PERMOS in Switzerland. Due to its shape, position and extent the Alpine arc is influenced by prevailing winds from several directions provoking a complex and highly variable pattern of precipitation in different regions of Switzerland with a general trend to a more continental climate in some inner-alpine valleys. The lower boundary for the occurrence of mountain permafrost in the Swiss Alps is located at about 2500 m asl., close to the free atmosphere where air temperatures are almost homogenous in all regions, but precipitation usually shows large regional differences regarding timing and quantity depending on the meteorological conditions. At the elevation range of mountain permafrost the ground surface remains snow-free only for about 4-5 months (between June and November) with a ...

Géomorphologie : relief, processus, environnement, 2008

The anomaly has first been attributed to redistribution of snow by avalanches (Haeberli, 1975). R... more The anomaly has first been attributed to redistribution of snow by avalanches (Haeberli, 1975). Recent studies (Lerjen et al., 2003 and Luetschg et al., 2003) stress the importance of granulometry and graded bedding, which facilitate the overcooling of the lower part of the talus slopes. At low altitude, several authors have demonstrated that the overcooling of foot Géomorphologie : relief, processus, environnement, 2008, n°2, p. 87 La répartition du pergélisol dans trois éboulis alpins du massif de la Dent de Morcles (Valais, Alpes suisses)

2012 IEEE International Geoscience and Remote Sensing Symposium, 2012

ABSTRACT This paper describes a new method to monitor active rock glaciers using DInSAR technique... more ABSTRACT This paper describes a new method to monitor active rock glaciers using DInSAR technique with Terrasar-X data acquired with mode facing slope and 11 days time interval during late summers 2009 to 2011. Where the spatial distribution of the rock glacier surface deformation derived from the DInSAR data using conventional unwrapping processes fails due to the relative small size and the complex movement of some rock glaciers, a specific profile is here defined through the rock glacier and is used to analyze the DInSAR products along it. Firstly, the prerequisites to perform such analysis at local scale are given. Then a quantification and discussion of results are achieved through different examples of active rock glaciers encountered in Western Swiss Alps.

Permafrost and Periglacial Processes, 2004

The use of real-time kinematic (RTK) GPS for studying the dynamics of creeping mountain permafros... more The use of real-time kinematic (RTK) GPS for studying the dynamics of creeping mountain permafrost is evaluated on the basis of measurements carried out on three test sites in the Western Swiss Alps. The high precision of the method and its ease of use make the RTK GPS appropriate for this kind of study. A wide range of information can be obtained by comparing the position of a set of surveyed points after two campaigns of measurement: determination of both horizontal and vertical components of surface movements, identification of compression and extension zones, estimation of thickness variation and, finally, determination of three-dimensional (3D) rotational movements of individual boulders. Temporal variations of all these parameters can then be identified after more than two repetitions of the measurement series. The results obtained on the test sites are presented and discussed from a geomorphological point of view. They were sometimes surprising, for instance the strong difference in surface velocities of two morphologically similar rock glaciers situated in the same area or the small 3D rotation of blocks located on the front of a rapidly moving rock glacier.

Permafrost and Periglacial Processes, 2004

Norsk Geografisk Tidsskrift - Norwegian Journal of Geography, 2001

Lambiel, C. & Reynard, E. 2001. Regional modelling of present, past and future potential dist... more Lambiel, C. & Reynard, E. 2001. Regional modelling of present, past and future potential distribution of discontinuous permafrost based on a rock glacier inventory in the Bagnes–Hérémence area (Western Swiss Alps). Norsk Geogra sk Tidsskrift–Norwegian Journal of Geography Vol. ...

Proceedings, 8th …, 2003

Since the end of the Little Ice Age (LIA), glaciated surfaces in the Alps have considerably decre... more Since the end of the Little Ice Age (LIA), glaciated surfaces in the Alps have considerably decreased, exposing large areas of unconsolidated sediments. The LIA proglacial forefields of most of the small glaciers (Ͻ1 km 2) are situated within the belt of discontinuous permafrost (Ͼ2200 m a.s.l.). Few attempts have been made to map the ground ice distribution in such recently deglaciated terrains (e.g.