Deep Seated Gravitational Slope Deformations in a Ligurian Apennines catchment (Italy): evidences, characterizations and consequences

The Upper Scrivia Valley in the Ligurian Apennines is characterized by a large-scale landslides area wider than regional and national averages. A number of deep-seated gravitational slope deformations (DSGSDs) were detected and mapped on the basis of geomorphological constraints such as closed depressions, trenches, double ridges, counterscarps and para-karst formations. The DSGSDs make up about 10% of the area studied. The majority of large, paleo-and active landslides spread out within these DSGSDs and processes due to gravity are the main geomorphological issue. DSGSDs were distinguished according to geological and geo-mechanical features of rock masses into six case studies. Each case study represents different slope dynamic and exhibits its own geomorphological features. These case studies can be a valuable model for the study of DSGSDs within the Apennines. The authors hypothesize as a factor of main trigger a phase of gravitational instability related to the evolution of the Ligurian-Adriatic watershed and a deepening of the erosional base levels set up at the end of the Pleistocene. The reasons are: i) the distribution and the geological and tectonic characteristics of the case studies, ii) the geomorphological conditions of this sector of Apennines, iii) the absence of a glacial withdrawal phase and iv) the low seismicity. The massive presence of DSGSDs raises important implications for geological cartography, land planning and monitoring because of the extent and kinematics of these phenomena.