Slope instability in historic hilltop towns of Basilicata, southern Italy

Abstract

The importance of preserving Italian hilltop towns through a general geotechnical strategy is discussed and is followed by a specificreview of the hydrogeologicalconditions responsible for regional mass movements at ancient hilltop towns in Basilicata. A historical survey of reactivations in colluvial deposits at selected sitesin 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.

Hindcasting extreme events: the occurrence and expression of damaging floods and landslides in Southern Italy

“…These changes are attributed to the substantial influx of fine sediments into the channel from the adjacent slopes during the 1959 event. In terms of mass movements, the main road links in eastern Basilicata were affected by at least 12 landslides (Caloiero and Mercuri, 1982), and landslides were also reported from the towns of Pisticci, Ferrandina, Salandra and Grassano (Table I) and Craco (Gostelow et al, 1997). The antecedent rainfall conditions at Pisticci prior to this storm event were exceptional, with a 2-day (P 2 ) total of 375Á6 mm and a 30-day (P 30 ) total of 570Á9 mm.…”

“…Motorway and rail links between Potenza and Grassano Scalo were severed by large landslides (La Gazzetta del Mezzogiorno, 3/4/1973), and a rockfall failure involving 350 000 m 3 of material occurred at Massa Abate, near Grottole (Clarke and Rendell, 2006). The newspaper headlines seem dramatic: 'Basilicata: An entire region destroyed' (La Gazzetta del Mezzogiorno, 31/3/1973, p. 1); but they focus on the impact of renewed landsliding at Craco, which prompted the Regional Government to force the permanent evacuation of 1800 inhabitants (Gostelow et al, 1997) to a purpose-built new town, Craco Peschiera, in the Salandrella-Cavone valley (see Figure 1). …”

“…Basilicata is one of the most vulnerable regions in Italy (Gostelow et al, 1997), in which 58 per cent of the 114 comuni are classified at high risk and a further 13 per cent at very high risk of landsliding or flooding (Ministero dell'Ambiente, 2000). Parts of Basilicata are tectonically active, with a long history of earthquakes affecting the western part of the region caused by movements on the Apennine fault systems (Del Prete et al, 1992).…”

“…All the hilltop towns in Basilicata are prone to periodic landsliding (Boenzi and Guira Longo, 1994) caused by rotational-translational movements with slide planes typically 20-30 m deep (Del Prete et al, 1992). In the eastern part of Basilicata, slide planes are often associated with contacts between unconfined aquifers in layers of sands and conglomerates and underlying impermeable clay and shales (Gostelow et al, 1997). Topographic slopes are steep and the formation and enlargement of fissures are often precursors to landslide activity (Guerrichio and Melidoro, 1979).…”

“…Topographic slopes are steep and the formation and enlargement of fissures are often precursors to landslide activity (Guerrichio and Melidoro, 1979). Large landslides, which have caused structural damage at Pisticci, Ferrandina and Grassano (Figure 1) and the abandonment of the town of Craco, have been linked to extreme rainfall triggers (Beneo, 1967;Guerrichio and Melidoro, 1979;Del Prete and Petley, 1982;Del Prete et al, 1992;Gostelow et al, 1997).…”