Mass-movement, geologic structure and morphologic evolution of the Pizzotto-Greci slope (Calabria, Italy)

Deep-seated mass-movements of different types affect the Pizzotto-Greci slo pe in northwest Calabria, Italy. The slope is carved out of phyllitic rocks capped by gneissic layers. Its geological structure is extremely complicat ed by tectonic structures that pervasively cross the slope transversely and downslope. A large-scale gravitational deformation of sackung type affects the slope. On the upslope side a debris-flow source area feeds a large fan constructed by recurrent debris-flow deposits. Aggradation is consequently occurring along the stream at the base of the slope. In order to define the internal structure of the slope for a stability slop e model, geological, geostructural, geomorphological, historical and dendro geomorphologic studies, as well as direct geotechnical logs and indirect ge ophysical investigations have been carried out over a two-year project fina nced by the EC Environment Programme. The main aspects of the geological and geomorphological studies and some pr eliminary geotechnical data are presented here, along with a conceptual mod el aimed at describing the relationships between the mass-movements on the slope and the construction/destruction stages of the fan at the base of the slope. The model is based on the assumption that aggradation has a stabili sing effect on the slope, thus debris-flow activity is reduced and, consequ ently, destruction of the fan occurs, bringing the slope again towards unst able conditions. The reactivation of mass-movement, however, leads to the r econstruction of the fan and the buttressing effect at the base of the slop e is restored. Thus, the process is cyclic and self-regulating. (C) 1999 El sevier Science B.V. All rights reserved.