Geodynamics of the alpine permafrost: functioning, spatial distribution and recent evolution. The example of the Combeynot Massif (French Alps)

• Main Author: Bodin, Xavier
• Other Authors: Pôle de recherche pour l'organisation et la diffusion de l'information géographique (PRODIG), Université Paris 1 Panthéon-Sorbonne (UP1)-Institut de Recherche pour le Développement (IRD)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris-Sorbonne (UP4)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Diderot - Paris VII, Monique Fort([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: Permafrost; mountain; Alps; geomorphology; climatology; rockglacier; global change; Alpes; géomorphologie; glacier rocheux; climatologie; Pergélisol; montagne; changement climatique; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; permafrost; pergélisol
• Online Access: https://tel.archives-ouvertes.fr/tel-00203233; https://tel.archives-ouvertes.fr/tel-00203233/document; https://tel.archives-ouvertes.fr/tel-00203233/file/Bodin_these_2007.pdf

This study intends to understand the state and the functioning of the mountain permafrost in a crystalline and poorly glacierised massif (Combeynot Massif, Hautes Alpes, France) on one hand, and on the other hand to express its distribution and evolution at variable spatial and temporal scales. First, the monitoring devices, helped by three very different years in nivo-meteorological terms, have revealed some of the main features of the thermal processes at the Laurichard rockglacier surface. The spatialisation of the winter surface temperatures clearly shows the influence of the very warm 2003 summer followed by the snowy 2003-2004 winter, that both contributed to prevent the cooling of the ground. This relation with the seasonal snow history, especially in early winter, is also demonstrated by the analysis of the annual velocity of the rockglacier and of the climatic data during the last two decades. At the scale of the whole massif, the relation climate/permafrost has been modelled by a statistico-empirical relationship which reproduces the influence of the topoclimatic conditions on the permafrost. Four case studies have nevertheless revealed that the geodynamical context and its evolution during the Quaternary are essential in understanding the state and the distribution of the permafrost at slope and watershed scales. Finally, the recent climate warming seems to have induced a temporary speed-up of the creeping velocity of the permafrost, which subsequently arises the question of the stability of degrading slopes. La présente étude vise d'une part à comprendre l'état et le fonctionnement du pergélisol de montagne dans le contexte d'un massif cristallin très peu englacé (massif du Combeynot, Hautes Alpes), et d'autre part à en restituer la répartition et l'évolution à des échelles de temps et d'espace variables. Tout d'abord, les dispositifs de suivi du pergélisol, aidés par la succession de trois années contrastées en termes nivo-météorologiques, ont révélé les particularités du fonctionnement thermique ...