Landslide inventory and main geomorphological features affecting slope stability in the Picentino river basin (Campania, southern Italy).

The landslide inventory of the Picentino basin was realized at 1:25,000, with focus on main geomorphological features affecting slope stability. It is based on different sets of air-photos (scales 1:33,000-1:18:000, dated up to 1998, i.e. the age of the last major geo-hydrological event in the study area), and on field surveys. Among shallow landslides, channelized debris flows strongly prevail: they originated as debris slides on moderately-steep slopes and propagated downslope, building detrital fans at the outlet of secondary basins along the valleys. Most sources can be found on 0.5-2 m thickness of regolith, and on 20-40° slopes in forests. Further sectors are affected by deeper slope movements of greater extent. These latter are, mainly, old complex earth slide-earth flows, followed by earth slides, and earth flows. Few rock falls can also be found in the mountainous sector of the basin. Items related to tectonics, erosion processes on slopes and along the valleys, and anthropized sectors are also mapped. Relevant predisposing factors to slope instability (lithotype, thickness of regolith, slope, and land use) are shown in 1:100,000 thematic maps. In addition, shallow landslides of the 1998 inventory were compared to those derived from two event-based inventories (PSAI 2002, PSAI 2011), realized by the regional Basin Authorities employing further flights (dated 1998-2005 at 1:13,000-1:10,000). Except for landslides triggered after 1998, discrepancies are mainly ascribable to types of employed air-photos, age of surveys, scale of mapping, and freshness of forms. Results remarked the relevance of suitable shallow-landslide inventories for susceptibility evaluations.