Entretien avec Yvette Dewolf

L’entretien porte sur l’ouvrage d’Yvette Dewolf et Guilhem Bourrié, Les formations superficielles, Genèse, Typologie, Classification, Paysages et environnements, Ressources et risques. Paris, Ellipses, 2008, 798 p

Iceberg jam floods in Icelandic proglacial rivers: testing the self-organized criticality hypothesis

In this paper, we describe a fluvial marginal process associated with the formation of iceberg jams in Icelandic proglacial lakes. The floods triggered by the release of these iceberg jams have implications for the geomorphic evolution of the proglacial fluvial system. The process of iceberg jam floods share some conceptual characteristics with Self-Organized Criticality (SOC) approach of complex systems. Using a simple numerical model and field observations, we test the hypothesis that iceberg jam floods exhibit SOC. Field observations and aerial photo-interpretations in southeastern Iceland demonstrate the occurrence of icebergs jam in ice-contact lakes. The mapping of the south Vatnajökull margins between 2003 and 2012 reveals an increase of the calving potentiality and a rise in the likelihood of iceberg jam flood occurrence. Based on the results of the numerical model and field observations, we suggest that iceberg jam floods should be recognized as a SOC phenomenon. Analysis of the simulated time-series show that the iceberg jam floods become less frequent and more similar in magnitude over time. This global trend is related to the gradual enlargement of the lake outlet channel

Les variations glaciaires en Haute Durance (Briançonnais, Hautes-Alpes) depuis la fin du XIXe siècle : mise au point d'après les documents d'archives et la lichénométrie

Les travaux reconstituant les variations glaciaires récentes se sont longtemps fondés sur des séries de mesures directes établies sur quelques glaciers sélectionnés. Nous proposons de compléter ces séries en étudiant les fluctuations, depuis la fin du XIXe siècle, du front d’une trentaine de glaciers, situés sur la retombée orientale du Massif des Ecrins. Des relevés géomorphologiques, la lichénométrie, et les documents anciens ont été utilisés conjointement, ce qui a permis d’identifier trois générations de moraines, délaissées respectivement entre 1915-1930, autour de 1950 et lors de la décennie 1970. Ces formations suggèrent l’existence de trois stades d’avancée et/ou de stationnement des glaces dans un contexte général de retrait glaciaire depuis le Petit Âge de Glace. Au cours du XXe siècle, la surface englacée a diminué dans ce secteur de 30% environ (35 à 25 km2). Cette évolution s’explique par un bilan de masse déficitaire de l’ordre de -0,2 à -0,4 mee.an-1, valeurs qui sont de même ordre de grandeur que celles établies ailleurs dans les Alpes Occidentales.Until recently, studies on glacial fluctuations were mostly relying on direct measurements of a few, selected glaciers. In order to complete these former datasets, we studied thirty glaciers located in the eastern part of the Massif des Ecrins. By using geomorphology surveys, lichenometry dating method, coupled with archives investigations, we identified three main stages of moraines deposition: between 1915-1930, around 1950, and in the 1970’s. These moraines suggest the occurrence of three stages of glacial advances and/or stationnary equilibrium in a general context of glacier recession subsequent to the Little Ice Age. The glaciated surface has decreased from 35 to 25 km2 during the 20th century, thus representing a mass-balance ranging from -0,2 to -0,4 mwe.yr-1, in agreement with what is known from other parts of western Alps

Modulation of host cell processes by T3SS effectors

Two of the enteric Escherichia coli pathotypes-enteropathogenic E. coli (EPEC) and enterohaemorrhagic E. coli (EHEC)-have a conserved type 3 secretion system which is essential for virulence. The T3SS is used to translocate between 25 and 50 bacterial proteins directly into the host cytosol where they manipulate a variety of host cell processes to establish a successful infection. In this chapter, we discuss effectors from EPEC/EHEC in the context of the host proteins and processes that they target-the actin cytoskeleton, small guanosine triphosphatases and innate immune signalling pathways that regulate inflammation and cell death. Many of these translocated proteins have been extensively characterised, which has helped obtain insights into the mechanisms of pathogenesis of these bacteria and also understand the host pathways they target in more detail. With increasing knowledge of the positive and negative regulation of host signalling pathways by different effectors, a future challenge is to investigate how the specific effector repertoire of each strain cooperates over the course of an infection

L'activité torrentielle dans un haut bassin versant alpin en cours de déglaciation durant le XXe siècle : le vallon de Celse-Nière (Massif des Écrins, France)

International audienceDans les hauts bassins versants alpins, les changements climatiques survenus depuis la fin du Petit Âge de Glace engendrent la fusion des glaciers et exacerbent l'activité des torrents proglaciaires. Les modèles établis tendent à mettre en parallèle l'évolution de l'activité torrentielle avec le rythme de la fonte des glaciers. Or, à la suite du recul glaciaire, la mise en place des relais de processus fluvio-glaciaires nécessaires à l'exportation des sédiments depuis les hauts bassins versants vers leur exutoire peut nécessiter plusieurs décennies. Aussi le recul glaciaire maximal ne coïncide-t-il pas toujours avec la période d'exportation maximale des sédiments par les torrents proglaciaires. Ce décalage est dû aux phénomènes de barrage, exercés notamment par les édifices morainiques

« Le Morvan est-il maudit ? », analyse géographique d’un territoire hyper-rural

International audienc

L’(in)efficacité géomorphologique des cascades sédimentaires en question : les apports d’une analyse réseau

The formalization of sediments cascades within a catchment is one of the main field research in geomorphology. Since the pioneering studies on geomorphic open systems, inefficient sediment exportation at catchment sinks has been widely observed. The complexity of sediment fluxes patterns is also enhanced. Well defined in concepts such as the sediment delivery problem or sedimentological anarchy, these observations are however only partially understood. After a brief synthesis of previous works led on sediment cascades, we propose in this paper to consider sediment cascades as a network. Such networks are described through graph theory and simulation tools. These methods are applied to explore how sedimentary cascades work, especially by evaluating a net contribution of the network to the volume flow. Applied to an alpine watershed, these methods show that the connectivity properties of sediments cascades can explain their structural inefficiency to export sediments

Do deglaciated mountainslopes contribute significantly to paraglacial sediment fluxes

International audienceSediment generation and pathways, as influenced by post-glacial collapse of mountain slopes in particular, arestudied in three steps. First, the processes involved in rock failure are identified and their possible influence onmass-movement locations at different spatial scales in various places is discussed. This comparison reveals avariable pattern of paraglacial landslide distribution, and allows the local/regional controlling parameters to beidentified. Second, the rate of triggering of mass-movement over time is roughly assessed in various settingsbased on a review of recently published data. This comparison aims to identify typical temporal-models forslope evolution through the time elapsed since deglaciation. Third, an attempt is made to assess the contributionof landsliding to the whole paraglacial cascading system by evaluating the somewhat contradictory findingsand assertions from previous authors: Some authors have argued for a high sediment yield at catchment sinksin relation to paraglacial landsliding (Church & Ryder, 1972; Ritter & Ten Brink, 1986), whereas others haveidentified that some long-lived sediment dams can occur after the deposition of a landslide mass, so that no or littlesediment exportation occurs (Korup, 2009; Cossart & Fort, 2008). We add to this debate by developing a typologyof geomorphic couples, between paraglacial landslides and other geomorphic processes, and present simulationsof sediment yield evolution since glacier disappearanc