Regolith behaviour 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 that 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 different aspect, depth and lithology, and periodical determination of regolith moisture and bulk density were carried out. Changes in surface regolith have also been monitored by means of photographic techniques, using an especially designed tripod. Finally, the hydrological and erosive response of the regolith trough the seasons were studied using rainfall simulations. The results obtained support and confirm previous knowledge on the role of frost action in mudrock weathering and the role of subsequent regolith development and wetness status on infiltration and runoff generation. These seasonal changes of behaviour are so important that they raise serious questions about the validity of observations or experiments carried out in only one season.This work confirms that erosion processes are controlled by regolith formation during winter and regolith depletion by storm rainfall erosion during summer, spring and early autumn. It also raises important points about annual trends of infiltration and erodibility, that should be used as guidelines for modelling runoff and sediment production.