Abstract
The Central Spanish Pyrenees show a great diversity of geomorphic processes in relation with topographic and climatic heterogeneity and according to the strong altitudinal gradient. Human activity in the last millenniums has contributed to disturb the original landscape and its hydromorphological dynamics: the upper forest belt was eliminated by means of Jire during the Middle Age, in order to enlarge the extent of summer pastures; and the hillslopes located under 1600 m were cultivated in heavy topographic conditions, being frequently burnt in order to improve the quality of pastures. At present, evidences of this human activity are visible everywhere; in the subalpine belt mass movements and dense rill networks caused the loss of many soils and the expansion of gelifluxion terracettes; in middle mountain, overland flow has much increased the soil surface stoniness, and debris flows of different size have developed on the hillslopes and on the river channels. Rivers show a strong torrentiality, prevailing unstable channels and coarse sediment transport. The authors apport information on some historical geomorphic processes, related with human activity.
Highlights
1600 m were cultivated in heavy topographic conditions, being frequently burnt in order to improve the quality of pastures
Ne belt mass movements and dense rill networks caused the loss of many soils and the expansion of gelifluxion terracettes; in middle mountain, overland flow has much increased the soil surface stoniness, and debris flows of different size have developed on the hillslopes and on the river channels
In Acción humana y desertificación en ambientes mediterráneos O.M. García Ruiz and P
Summary
El Pirineo Central español se organiza en una sucesión de bandas paralelas alargadas de oeste a este, que la red fluvial atraviesa formando valles orientados de norte a sur (Fig.l). 1) La banda más septentrional está formada por materia-. El Pirineo Central español se organiza en una sucesión de bandas paralelas alargadas de oeste a este, que la red fluvial atraviesa formando valles orientados de norte a sur (Fig.l). Inmediatamente al sur se localizan las Sierras Interiores, un gran anticlinal cabalgante, compuesto por calizas cretácicas y eocenas, con areniscas y calizas margosas intercaladas. 3) El flysch eoceno está muy plegado pero su homogeneidad litológica produce un relieve más uniforme, con divisorias suaves que descienden progresivamente hacia el sur. 4) La Depresión Interior se desarrolla en margas del Eoceno y forma un amplio valle dominado por depósitos cuaternarios (terrazas y glacis). 5) El Prepirineo está formado por una sucesión de cuestas de areniscas y arcillas oligocenas de origen fluvial y deltaico (molasas) y, más al sur, por las Sierras Exteriores, un anticlinal cabalgante que separa a los Pirineos de la Depresión del Ebro. Entre 1750 y 2400 m se desarrolla el piso de pastos subalpinos y alpinos, utilizados en verano por el ganado
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