Shifts in landslide frequency-area distribution after forest conversion in the tropical Andes

Guns, M. Vanacker, Veerle [UCL]

The impact of anthropogenic disturbance on landslide occurrence has been clearly demonstrated for several case-studies worldwide. Deforestation has been identified as the main trigger for landslide activity. These studies are mainly based on landslide inventories from aerial photographs or remote sensing data, and often focus solely on the total number of landslides. Looking at the total number of landslides alone does not allow us to get a comprehensive insight into the overall anthropogenic impact on landslide denudation. In this study, we analysed the anthropogenic impact on landslide frequency-area distributions. Three small catchments of about 11-30 km2 were selected within the Ecuadorian Andes. They have a similar topographic setting but differ in their land cover dynamic. Our data show that human disturbances significantly alter the landslide frequency-area distributions. Human-induced land cover change is associated with an increase of the total number of landslides and a shift of the frequency-area distribution towards smaller landslides. However, the frequency of large landslides is not affected by anthropogenic disturbances. When analysing the geomorphic work realised by landslides in different environments, it becomes clear that the majority of landslide-induced sediment is coming from anthropogenic environments. The strong increase in the frequency of small landslides in anthropogenic environments thus plays an important role in enhancing the overall landslide denudation rate in tropical mountain regions.