A number of new projects related to morphodynamics in periglacial environments were investigated at the CNRS UMR 6143, Caen, France (D. Amorese, J. P. Coutard, A. Dubois, M. Font, G. Guillemet, J.L. Lagarde, J.C. Ozouf). Laboratory simulation of scarp degradation under periglacial environments was carried out in a cold laboratory where temperature (freeze–thaw cycles), precipitation, and lithology (heterogeneous cryoclasts) were controlled. This experiment was funded by the French “Programme National Risques Naturels”.
The main periglacial slope processes that have been recognised involve cryoreptation, debris flows and gravitydriven mass slips. Landform evolution was characterised by development of concave scarp profiles, scarp ablation as a consequence of debris flows and final slope softening. Quantification of the displaced material volume, along the experimental scarp, leads to values about 1 cm3/cm2 for 41 freeze–thaw cycles. These results have been compared to field data relative to scarp erosion under moist periglacial conditions along the La Hague-Jobourg Fault Zone (North Cotentin, Normandy).
Collaborations exist also with the University of Sussex (Julian Murton) on a research programme on “Bedrock fracture by ice segregation’, funded by the Natural Environmental Research Council. A new project will start in 2004 on physical modelling of mass-movement processes on permafrost slopes, in collaboration with the Cardiff group (Charles Harris). It is proposed that both full-scale (Caen refrigerated tanks) and small-scale physical modelling (Cardiff geotechnical centrifuge) be developed to investigate mass movement processes in clay-rich soils, and at steeper gradients.
Members of the polar team of the laboratory of physical geography of Clermont-Ferrand (GEOLAB, UMR 6042- CNRS) are carrying out a research programme supported by the French Polar Institute in Northwest Spitsbergen. The main objective is to investigate time-space relations among periglacial, paraglacial and glacial dynamics. Particular attention is drawn to the increasing role played by meltwaters in the contemporary paraglacial context, with severe dissection of till deposits and progradation of the coastline. In Iceland and Antarctica, the interplay and succession of weathering processes are being examined by combining detailed geomorphological mapping, micro/ nanoclimate monitoring, SEM observations and XRD analyses (in collaboration with UNBC and BAS in Antarctica). The role of biological, thermal and chemical weathering processes is being emphasized due to the lack of moisture and/or to the low susceptibility of bedrock to frost-derived mechanisms.
A diachronous fluvial forms analysis of the Lena River (satellite images and Navigation Survey maps) has been conducted by E. Gautier and D. Brunstein (Laboratoire de Géographie Physique, UMR 8591, Meudon). This mesospatial- scale approach allows evaluation of the effects of thermal erosion on fluvial units’ mobility. On the basis of sedimentary structure observation, the specificity of the depositional processes is underlined and deposits associated with logjams and ice-jams are identified. High recession rates are observed along some Siberian river banks. A laboratory simulation experiment and physical approach were continued by F. Costard, L. Dupeyrat, R. Randriamazaoro and E. Gailhardis (OrsayTerre, CNRS-UPS FRE2566), and have demonstrated that exceptional erosion rates can be best explained in conjunction with high water temperatures, and that mechanical erosion is associated with some particular geometry of the channel.
On Mars, polygons formed by networks of cracks from 50 to 300 m large and undifferentiated patterned ground at smaller scale are usual. They occur on about 500 high resolution images and are distributed especially in high latitude regions. The interstitial ice is stable in the first meters only at high latitudes because of the low content of water vapor in the atmosphere. This has been recently confirmed by Neutron Spectrometer data on board the Mars Odyssey spacecraft. Maps proposed by Nicolas Mangold (Orsayterre, CNRS-Université d’Orsay) show a very good correlation between the ice-rich ground detected by the probe and the polygons, regardless of their size, thus indicating that they most likely formed by periglacial processes such as thermal contraction. François Forget (Laboratoire de Météorologie Dynamique, Jussieus) currently investigates the climatic control of these features including past periods of seasonal freeze–thaw cycles that could have formed features such as sorted circles, stripes or pingos. The understanding of these landforms will improve our knowledge of the recent climate on Mars.
François Costard (Fcostard@geol.u-psud.fr)