Slope instability in historic hilltop towns of Basilicata, southern Italy

The importance of preserving Italian hilltop towns through a general geotechnical strategy is discussed and is followed by a specific review of the hydrogeological conditions responsible for regional mass movements at ancient hilltop towns in Basilicata. A historical survey of reactivations in colluvial deposits at selected sites in the region suggested that increased activity was taking place in response to extreme rainfall events, possibly related to long-term climatic changes. The importance of natural and anthropogenic processes along critical hydrogeological boundary conditions in relation to this activity is then reviewed and one example of urban landsliding from Grassano in the Basento valley is described. Local structure, such as faulting, was shown to be especially important in the location of both groundwater discharge (springs) and the landsliding. The landslide activity in the town was also shown to be related to a period of population expansion and possible domestic water leakages following the provision of a pumped supply. It is suggested that these anthropogenic processes reduce the usefulness of empirical links between landslide frequency, rainfall extremes or other explanations involving climatic change. Finally, a strategy for landslide management based on the use of hydrogeological conceptual models and GIS technology is proposed.