Landslides in Portugal — Extent and economic significance

This paper examines the landslide situation in Portugal including the Atlantic islands of Azores and Madeira. In spite of its small area (89 000 sq.km) Portugal presents considerable contrasts concerning both geology, physiography, rainfall and population, which strongly influence the geography distribution, frequency and severity of landslides. In Portugal landslides rarely reach imposing dimensions and only very few cases can be regarded as purely natural geological hazards. The majority of landslides have been triggered by human activity although always related to periods of continued rainfall. For these reasons landslides are of higher significance in the western mesozoic sedimentary borderland, a region of lower relief energy but where the majority of important construction activities for housing, roads and highways have been developed. Procedures for hazard zonation and prevention of landslides have been developed only for few particular areas of increasing urban growth where the majority of landslides are reactivated and controlled by the residual strenath of quaternary clayey solifluction deposits over Jurassic marls. Although losses due to landslides are very dispersed and difficult to quantify it can be said that annual costs are significant if direct and indirect costs are considered.