Badland dynamics in the Central Pyrenees: temporal and spatial patterns of weathering processes

17 páginas, 8 figuras, 5 tablas.

The genesis and development of badlands is controlled by bedrock lithology, topography and climate. The development of badlands in the Central Spanish Pyrenees is favoured by the presence of marls and a climate with a marked seasonality; the combination of these factors results in active hydrosedimentological processes. The aim of the present work was to study the dynamics of badlands in the Central Pyrenees, with a focus on the temporal and spatial patterns of the dominant weathering processes. The study area was a small mountain catchment, and we focussed on the continuous observation of a number of physical parameters that control regolith development and weathering processes. Samples collected from different depths at sites with different aspects enabled temporal comparisons of the factors involved in the development of surface regolith that can be considered as indicators of the weathering of the marls. These indicators were then related to environmental variables (moisture and temperature). Atterberg limits were established and related to moisture content to explain slope dynamics and related processes. Finally, analyses of carbonate content were performed in the laboratory. The results validate the employed methodology, supporting our description of weathering processes, the established chronological sequence and the relation of these processes to climatic and topographic parameters. The results obtained since January 2004 show that the chosen indicators are sensitive to seasonal dynamics, variations in temperature and water supply, and slope aspect. The development and dynamics of regolith on north-facing slopes is more active than that on south-facing slopes. Freeze–thaw is the main weathering process on north-facing slopes, while south-facing slopes are dominated by the development of crusts associated with wetting–drying processes. Washing effects and lower temperatures upon north-facing slopes mean that the dissolution of carbonates is more pronounced in such areas compared with south-facing slopes, especially within the upper layers of the regolith.

This research was financially supported by the following projects: ‘Hydrological processes in Pyrenean catchments in relation to land-use changes and climatic fluctuations’ (PIRIHEROS, REN 2003-08678/HID) and ‘Characterization and modelling of hydrological processes and regimes in gauged basins for prediction in non-gauged basins’ (CANOA, CGL 2004-04919-C02-01), both funded by the CICYT, Spanish Ministry of Education and Science. The monitoring of the badland catchment was also funded by a consortium between the CSIC and the Spanish Ministry of Environment (RESEL Project). The contribution of the first author was made possible thanks to a fellowship of the CSIC, in the framework of Program I3P supported jointly by the Social European Program.

Peer reviewed