Factors Explaining the Spatial Distribution of Hillslope Debris Flows

The spatial distribution of 961 debris flows in the Upper Aragón and Gállego valleys (Central Spanish Pyrenees) was analyzed. Most were located in the Flysch Sector (with a colluvium mantle derived from strongly tectonically modified materials), between 1000 and 1400 m above sea level, on 25–35° gradients with sunny exposure. These gradients were either hillslopes covered by frequently burned scrubland, abandoned fields, or reforested land, confirming the influence of land use and disturbed landscapes on the occurrence of debris flows.