Influence of the behaviour of soft rocks on cliff evolution

Two cases, of evolution of mor phostructure of cliffs in soft rocks like tuff and calcarenite, respectively outcropping in the Cape of Posillipo in Campania and in the Agrigento town and Valley of Tem- ples in Sicily, are analyzed on the basis of mor phologic characteristics of the sites, mesostructural survey and mechanical characterisation of the lithotypes. The cultural and environmental heritage of these sites is heavily hastened by instability processes, due to the super position of different lithotypes, the presence of dis- continuities and differential erosion and deformation of bedrock. Both the rock masses are characterized by variability of the cohesion and the cementation, and well developed oriented structure. The theoretical analysis car ried out with the FLAC code, evidences that some sets of subvertical discontinuities are consistent with the strained surfaces of the model and that they would be pertaining to mor phological processes rather than tectonic events.