Evolution of a landslide creating a temporary lake: successful prediction

The Anzola landslide is a complex landslide that failed on the left side of the Ceno Valley (Northern Apennines, Italy). It was studied using a multidisciplinary approach, in which geomorphology, geology and engineering geology were combined to understand the kinematics, evolution, the main rock mass characteristics, the behavior of the landslide, and its morphologic evolution. The Anzola landslide in 1996 was probably a neo-activation. It was affected by at least three re-activations recently, always in connection with heavy rainfall, which twice caused the blockage of the valley and formed a small lake. The possibility of river blockage as a consequence of the re-activation of the landslide was investigated using a GRASS GIS-based shell script that simulates the landslide material descent and computes the dam and lake sizes. The simulations allowed assessment of the amount of the depleted material coupled with the morphological situation, characterized by a very narrow riverbed that can lead easily to the formation of consistent damming and lakes. This situation, of course, can represent a serious risk in case of a dam break, and the ensuing flooding could affect downstream infrastructures and small villages.