Modelling of permafrost thickness during the late glacial stage in France: preliminary results

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Abstract
Research on permafrost in France has concentrated on field evidence of fossil permafrost and the mapping of its possible distribution. Few attempts have been made to estimate permafrost thickness. Studies devoted to this subject in North America and Siberia have shown that permafrost may be very thick (several hundred metres), may be rapidly laid down (in < 2000 years in northwest Canada) and causes complex water flow patterns between the base of the permafrost and the soil surface. Using the "Gelsol" code developed by the Laboratoire central des ponts et chaussées (Central Laboratory of the French Department of Public Works) for geotechnical purposes, this paper presents the first results of modeling permafrost development at depth. These preliminary tests show the influence of parameters such as mean annual ground temperature, heat flow, thermal conductivity related to lithology, and water content of the rocks involved on permafrost depth during the last glacial cycle (Weichselian). The results from simple cases indicate that the permafrost was from ten of metres to over 300 m thick. Although these are only calculated values, they are much higher than the few figures found in the literature, and must betaken into consideration when searching for fossilized traces of deep permafrost.

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