Mid-term geomorphological evolution of the Covatta Valley, Biferno river Basins, Molise, Italy

Abstract

On April 12, 1996, a complex system of landslides involved the left side of the Biferno River (Campobasso, Molise), in the Covatta area, interrupting the State Highway 647 and damming the Biferno River, forming a lake. Previous studies consisted of a geological survey and production of a geological map, as well as geomorphological analysis of the landslide of April 12, 1996,. In the Covatta area, several mass movements (translational-rotational slides and lateral spreading), which become rapid earthdebris flows in their terminal regions, have been generated. Progressive sliding of secondary earthflows has divided the landslide of April 12, 1996, into many different subsystems, each of which is characterized by various lithological associations and different morphologies. Fig. 1 is a synthesis of this and shows both the geological situation and the typology of the landslide subsystems. A new substantial movement of the landslide occurred in the Spring of 1997, making the slopes smoother in the upper part and the soils more fluid in the central and lower parts. This work is a report on the study that has been developed on the morphoevolutive phases of the slope analyzed during the years before its final collapse and their relationship with the rainfall patterns. Examination of the slope’s morphological stages in the period 1954-1997 and the analysis of the hydrological parameters has shown that the morphological features were mainly governed by a sequence of extraordinary climatic conditions. The heavy rainfalls and snowfalls in the Winter of 1986, for example, produced an acceleration of the slope’s evolutive phenomena, whereas their deceleration in 1992 should be considered a consequence of the very low rainfalls of the previous three years. Actually, in the case of deep phenomena like that of April 12, 1996, it is very difficult to predict the time necessary to prepare the slope collapse; it is in any case considerable (at least several decades). On the other hand, most of the single, small phenomena are assumed to occur in a period of a few years, because of slight increases in the water surplus.