Geomorphological evolution of “Ripe Rosse”, a coastal cliff in Cilento Geopark (Italy)

This paper illustrates the mid-term geomorphological evolution of the "Ripe Rosse", one of the most important rocky coast geosite in the Cilento, Vallo di Diano and Alburni UNESCO Global Geopark. During the last decades, such area was affected by frequent and high-intensity landslide events that induced a significant increase in the landslide risk along the unique state road connecting all the touristic villages of the southern Cilento Coastland. This high risk level was related to the anthropogenic factors (slope cuts and wild fires) on the upslope and to an accelerated downslope cliff retreat, similar to other coastal stretches of Cilento described in the specific literature. Therefore, in order to better identify integrated strategies to both preserve the geosite and prevent the road damages, a geomorphological study was performed, based on detailed field surveys, multi-temporal aero-photogrammetric analysis, digital geomorphological mapping, qualitative geomorphic modelling, supported by orientated numerical engineering modelling. The “Ripe Rosse” coastal slope has referred to a typical "slope-over-wall" model, composed by a convex, colluvial, debris upper slope, laying on remnants of buried, uplifted marine platform, covered by rounded, gravelly marine deposits, hanging on the cliffed bedrock toe slope. The original, more long convex-concave profile was connected to a lower sea level during the last glacial age. The cliffed toe slope was progressively modelled by pure slope retreat mechanism due to the post-glacial sea level rising until present time. A threshold behaviour of the entire coastal slope profile, with a general gravitational collapse, was recognized after the complete disruption of the buried marine platform. The application of a numerical model has given promising results on how the coast will retreat in the next 500 years and therefore on how to mitigate the risk according to exceptional value of the site.