REGOLITH BEHAVIOR AND PHYSICAL-WEATHERING OF CLAYEY MUDROCK AS DEPENDENT ON SEASONAL WEATHER CONDITIONS IN A BADLAND AREA AT VALLCEBRE, EASTERN PYRENEES

Studies on badland areas in the Vallcebre basin (Pyrenees) suggest tha t erosion rates are controlled by the weathering rate of mudrocks. To obtain the temporal pattern of physical weathering and its control on the erosive processes, monitoring of regolith temperatures at differen t aspect, depth and lithology, and periodical determination of regolit h moisture and bulk density were carried out. Changes in surface regol ith have also been monitored by means of photographic techniques, usin g an especially designed tripod. Finally, the hydrological and erosive response of the regolith trough the seasons were studied using rainfa ll simulations. The results obtained support and confirm previous know ledge on the role of frost action in mudrock weathering and the role o f subsequent regolith development and wetness status on infiltration a nd runoff generation. These seasonal changes of behaviour are so impor tant that they raise serious questions about the validity of observati ons or experiments carried out in only one season. This work confirms that erosion processes are controlled by regolith formation during win ter and regolith depletion by storm rainfall erosion during summer, sp ring and early autumn. It also raises important points about annual tr ends of infiltration and erodibility, that should be used as guideline s for modelling runoff and sediment production.