Erosion assessment in the middle Kali Gandaki (Nepal ) : A sediment budget approach

International audienceActive mountains supply the largest sediment fl uxes experienced on earth. At mountain range scale, remote sensingapproaches, sediments provenance or stream power law analyses, collectively provide rough long-term estimatesof total erosion. Erosion is indeed controlled by rock uplift and climate, hence by a wide range of processes(detachment, transport and deposition), all operating within drainage basin units, yet with time and spatial patternsthat are quite complex at local scale. We focus on the Kali Gandaki valley, along the gorge section across theHigher Himalaya (e.g. from Kagbeni down to Tatopani). Along this reach, we identify sediment sources, storesand sinks, and consider hillslope interactions with valley floor, in particular valley damming at short and longertime scales, and their impact on sediment budgets and fluxes. A detailed sediment budget is presented, constrainedby available dates and/or relative chronology, ranging from several 10 kyr to a few decades. Obtained resultsspan over two orders of magnitude that can best be explained by the type and magnitude of erosional processesinvolved. We show that if large landslides contribute signifi cantly to the denudation history of active mountainrange, more frequent, medium to small scales landslides are in fact of primary concern for Himalayan population

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

Spatial heterogeneity in the paraglacial response to post-Little Ice Age deglaciation of four headwater cirques in the Western Alps

International audienceThis paper aims to understand how the paraglacial response to recent glacier retreat varies between four cirques in the Western Alps. Post‐Little Ice Age glacier retreat has created extensive forelands where a variety of gravitational and fluvial process operate on both till‐floored and rock‐floored cirques. These processes may affect transitions from subglacial to proglacial landsystems, by reworking sediment and reorganising drainage. Landsystems achieve a state of preservation once no more adjustment is possible due to buffering by channel network evolution, channel armouring, and sediment exhaustion. We find no consistent trajectory of change across all studied sites: paraglacial responses differ from the classical valley–glacier model, involving variable slope‐channel coupling. Proglacial drainage networks on till surfaces have become more integrated by reducing their low‐order bifurcation ratios, unlike streams locked into rock channels. Reasons for diverse and site‐specific behaviour include cirque floor width, gradient, and surface materials (bedrock, fine till, and/or blocky till). At some cirques, these restrict the downstream diffusion of a paraglacial “signal” of fluvial‐transported sediment. At others, increased sediment flux originated from the erosion of terminal moraines. A high proportion of glacial material generally remains within the glacier foreland, due to proglacial basin sediment traps, inefficiency of fluvial networks, armouring of floors by coarse tills, and rock‐controlled channels. The millennial‐timescale preservation potential of most recent primary glacial deposits and within‐cirque paraglacial landforms appears to be hig

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

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