Ninth International Conference on Permafrost ... - IARC Research

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Collapse of the Bérard Rock Glacier (Southern French Alps)Jean-Michel KrysieckiInstitute of Alpine Geography, University of Grenoble, FranceXavier BodinUniversity Paris-Diderot (Paris 7), Institute of Alpine Geography, University of Grenoble, FrancePhilippe SchoeneichInstitute of Alpine Geography, University of Grenoble, FranceIntroductionIn the Mediterranean French Alps, the summer 2006 hasbeen marked by the sudden collapse of the Bérard rockglacier (Parpaillon Range, Alpes de Haute Provence, France),a very rare event and exceptional by the amount of disturbedmaterial estimated to be about 2 millions m 3 (Fig.1).Located near the southern limits of the EuropeanAlpine permafrost, the Bérard rock glacier case is perhapsrepresentative of the potential consequences of mountainpermafrost degradation under present global warming, andraises questions about the evolution of ice-debris mixtureson steep slopes; for example, rock glacier under permafrostconditions. An atmospheric warming of 0.5 to 1°C between1900 and 2000 is indeed currently observed in the Alps(Casty et al. 2005). In the same way, recent observations onthermal evolution of the ground in high mountains (Harris etal. 2003), as well as the occurrence of new and unexpectedphenomena, for example, acceleration of rock glacier flow(Ikeda & Matsuoka 2002, Roer et al. 2005, Delaloye et al.2006, Kääb et al. 2006, Delaloye et al. 2008) or rock glaciercollapse (Evin et al. 2007), seem to indicate that mountainpermafrost could respond much faster to global warming thanexpected, and that areas at its lower limits could experiencea morphogenetic crisis.Crucial questions in terms of natural hazards and associateddangers are being raised (Harris et al. 2000): the speed-up ofcreeping landforms (Kääb et al. 2006), the destabilisationof the frontal part of rock glaciers (Arenson 2002), and an2500m2650mFigure 1. An upward-looking view of the collapsed Bérard rockglacier (July 2007).increase of the rockfall activity (Haeberli et al. 1997, Noetzliet al. 2003) and of the frequency of debris flow have alreadybeen observed in mountain permafrost areas.In this context, the main objective of our study is tounderstand the mechanisms that triggered the Bérard rockglacier collapse, which could subsequently gain new insightsinto the destabilisation of ice-rich deposits on mountaincatchments.The Bérard Rock Glacier SituationThe Bérard rock glacier is located in the Parpaillon Range,one of the southernmost ranges of the European Alps,including the summits of Grand Bérard (3046 m) and LaChalanche (2984 m). Topoclimatic and geomorphologicalconditions are favorable to permafrost occurrence in thisvalley.MethodsWithin a larger research project intending to study theconsequences of permafrost degradation in the French Alps,a complete monitoring of the site has hence been set up. Thisincludes:• the geodetic survey (Differential and Permanent GPS)of marked blocks during the summer, in order to quantify thevelocity and the characteristics of the movement;• the use of radar interferometry to reconstruct thehistory of the event during the previous years and to map themain destabilised areas;• the interpretation of electrical resistivity and refractionseismic tomographies to assess the physical properties of theinternal structure of the rock glacier;• the analysis of the ice to determine its origin and itsmain physical properties;• the survey of the climatic parameters (air temperature,solar radiation, wind speed and direction, snow height) withan automatic weather station; and• the survey of the thermal state of the ground (withminiature temperature dataloggers) to allow the monitoringof pertinent indicators; for example, mean annual groundsurface temperature (MAGST) or mean annual active layertemperature.First ResultsAmong the above-mentioned methods, geomorphologicalstudy, DGPS results, and ice analyses have given firstresults.153
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 2. 3-D displacement of marked blocks on the Bérard rockglacier between June and September 2007.The geomorphological study of the site has alreadyrevealed that the breaking of the rock glacier is probablypartly related to an underlying rockslide in the schist series,which may have been activated by storms during summer2006.First results are DGPS measurements of more than 40marked blocks on the Bérard rock glacier and the slidedmass, in June and September 2007. The 3-D vectors mapshows that the slided mass has not experienced importantmovements during the three surveyed months. Z valuessuggest a general settling (about 5–15 cm), certainly due tothe ice melt in debris. Remains of the rock glacier, especiallynear the collapse area, are affected by large movements (morethan 5 m in three months) and the destabilisation is effectiveas far as the saddle point (displacements are around 1 m inthree months). Permanent GPS, located above the scar on aflat area, indicates a mean displacement of 6.4 mm.day -1 inthe north direction, corresponding to an annual displacementof more than 2 m, which fits with the surrounding DGPSmeasurements.Stratigraphic observations on near-surface ice outcropsreveal that Bérard rock glacier has been affected byperiglacial and glacial mechanisms. Preliminary analyses ofice structure have revealed the sample to be similar to glacierice (Vallon, pers. com.). Little Ice Age period is suspected inthis mechanism change, but other analyses have to confirmthat.Our study, thanks to the various monitoring devices, hasalready clarified the respective roles of the meteorologicalconditions, the recent climatic warming, and the geologicalsettings in the collapse of the Bérard rock glacier. Most ofthe results are coming during the summer 2008 and willbring new precision on the Bérard rock glacier event.ReferencesArenson, L.U. 2002. Unstable Alpine permafrost: A potentialimportant natural hazard – Variations of geotechnicalbehaviour with time and temperature. PhD Thesis,ETH Zurich.Casty, C. et al. 2005. Temperature and precipitation variabilityin the European Alps since 1500. <strong>International</strong>Journal of Climatology 25: 1855-1880.Delaloye, R. et al. 2006. ERS InSAR for detecting slopemovement in a periglacial mountain environment(western Valais Alps, Switzerland). <strong>Ninth</strong><strong>International</strong> Symposium on High Mountain RemoteSensing Cartography (HMRSC-IX), Graz, Austria.Delaloye, R. et al. 2008. Recent interannual variations ofrock glacier creep in the European Alps. Proceedingsof the <strong>Ninth</strong> <strong>International</strong> <strong>Conference</strong> on Permafrost,Fairbanks, Alaska, 29 June–3 July 2008.Evin, M. et al. 2007. Rupture et glissement en masse d’unglacier rocheux dans le vallon du Bérard (Massifdu Parpaillon, Alpes du Sud, France) au cours del’été 2006, Grenoble, SHF - Section Glaciologie/Nivologie.Gruber, S. et al. 2004. Interpretation of geothermal profilesperturbed by topography: the Alpine permafrostboreholes at Stockhorn Plateau, Switzerland.Permafrost and Periglacial Processes 15(4).Haeberli, W. et al. 1997. Slope stability problems related toglacier shrinkage and permafrost degradation in theAlps. Eclogae Geol. Helv. 90: 407-414.Ikeda, A. & Matsuoka, N. 2002. Degradation of talusderivedrock glacier in the Upper Engadin, SwissAlps. Permafrost and Periglacial Processes 13: 145-161.Kääb A. et al. 2006. On the response of rockglaciercreep to surface temperature increase. Global andPlanetary Change 56(1–2): 172-187, doi:10.1016/j.gloplacha.2006.07.005.Noetzli, J. et al. 2003. Mountain permafrost and recentAlpine rock-fall events: A GIS-based approach todetermine critical factors. Proceedings of the Eighth<strong>International</strong> <strong>Conference</strong> on Permafrost, Zürich.Swets & Zeitlinger, Lisse.Roer, I. et al. 2005. Rockglacier “speed-up” throughoutEuropean Alps: A climatic signal? Second European<strong>Conference</strong> on Permafrost, Potsdam, Alfred-Wegener-Stiftung.154
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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