Since the last French report, a number of new projects related to permafrost have emerged with three main subjects: geomorphological studies, modelling permafrost and periglacial processes and extraterrestrial permafrost studies.
Current geomorphological studies carried out by the GEOLAB team in Clermont-Ferrand by M.-F. André, S. Etienne, D. Mercier and D. Sellier deal mainly with past and present dynamics of periglacial areas. Special attention is paid at Spitsbergen to paraglacial runoff processes reshaping or destroying landforms and deposits generated by frost-related processes, which slowed down since the Little Ice Age. Bioweathering, chemical processes, salt weathering and frost shattering in combination with rock weathering processes is tentatively evaluated in Iceland, Spitsbergen, Antarctica, Scotland and continental Norway, based on high resolution microclimate monitoring, SEM examinations, in vitro experiments and XRD analyses. The Spitsbergen programme is supported by the French Polar Institute and the Antarctic programme by the British Antarctic Survey through a collaboration with Kevin Hall, University of British Columbia, Canada.
A. Decaulne, University B. Pascal, Clermont Ferrand completed a fi eld study on snow avalanches and debris-fl ows in northwestern Iceland. Snow avalanches only impact slopes in a few areas, where avalanches boulder tongues accumulate by mobilizing rock fall material, and cause accumulation of debris cones. On the contrary, debris-fl ows always have a high geomorphologic impact on slopes, by transporting from 500 to 3500 m3 of debris from moraines or from periglacial material located in numerous chutes at the mountain tops.
The last years V. Jomelli, Laboratoire de Géographie Physique, Meudon, observed permafrost (rock glaciers) and periglacial processes (snow avalanches, rock fall, sorted stripes and debris fl ows) in the Andes of Bolivia, Peru, and Equator and in the French Alps, to study the response of these landforms to recent and Little Ice Age climatic change. In the Bolivian Andes measurements on the Caquella rock glacier show symptoms of degradation. Debris fl ow frequency in the Massif des Ecrins, France shows decreasing recurrence time since the 1980s and a shift of the triggering to higher altitudes.
T. Brossard and D Joly, University of French-Comté, continued their studies at the Kongsfjord area at Svalbard on vegetation responses to global change. They focus on a description of the modern distribution of plants and temperature, on a validation of vegetation and temperature models and on studying the potential infl uences of land cover changes on climate change.
The extent of permafrost at the Last Glacial Maximum (LGM) in Hungary were studied by B. Van Vliet Lanoe, University of Lille, in cooperation with the Geology Department of the Ëötvös University in Hungary. Periglacial features can be differentiated from neotectonism and seismic deformation. The study shows that permafrost existed in the main Pannonian basin at the LGM. The relationship between ice cap dynamics, geothermal gradient and permafrost during the Last Glaciation in Northern Iceland was studied in the programme IPEV in collaboration with A. Gudmunsson, Icelandic Geological Survey.
Investigations of fl uvial thermal erosional processes along the Lena River was continued by F. Costard and L. Dupeyrat, Orsay University, in collaboration with E. Gautier, Laboratoire de Géographie Physique, Meudon. Various laboratory simulations within a cold chamber demonstrate the validity of the previous mathematical model for the range of laboratory conditions. A hierarchy of parameters (Reynolds number, water and ground ice temperature) is proposed to explain the present effi ciency of thermal erosion along the Siberian rivers.
Since 1998 the camera of the Mars Global Surveyor space probe has provided thousands of high-resolution images (2-5 m/pixel) showing close-up over striking geomorphic features like recent gullies. These unexpected landforms are interpreted by the camera team as debris fl ows due to subsurface seepage. F. Costard, N. Mangold and J.P. Peulvast, Orsay University, together with F. Forget, Laboratoire de Météorologie Dynamique, Jussieu proposed that these debris fl ows areproduced by the seasonal thaw of near-surface ground ice like in cold regions on Earth (Costard et al., Science, 2002). This is possible especially in periods of higher obliquity of 40° predicted by astronomers compared to the current 25°. The gullies are distributed poleward of 30° latitude and over poleward-facing slopes preferentially in agreement with a process triggered by obliquity. On the other hand, the surface of Mars is also covered by patterned ground, like polygons and striated soils, at various scales from several tens to hundreds of meters. The fi nal goal is thus the understanding of the climatic evolution and the water cycle of Mars.
Costard, F., Forget, F., Mongold, N. And Peulvast, J.P. 2002. Formation of Recent Martian Debris Flows by Melting of Near-Surface Ground Ice at High Obliquity. Science, 295, 110-113.
François Costard (email@example.com)