Rockslide, rockfall and rock-avalanches

Rock slides, rock falls and rock avalanches can represent a sequence of linked phenomena sharing some mechanisms or involving the evolution of the same mechanisms under different conditions. Sliding can be at the origin of a fall or avalanche; a fall can originate an avalanche. Rock breakage, comminution and fragmentation can occur along the shear zone of a rock slide, at the impact point of a small (single block) or large (multiple blocks) rock fall, or of extremely energetic rock falls, or within the mass of a rock-debris avalanche. In general, these mechanisms can participate in controlling the evolution of the phenomenon. This even more important in complex and compound landslides where they mix during the motion from the initial stages up to the final deposition. It is suggested that these mechanisms, acting under different boundary conditions, can be relevant to understand the landslide motion even if they can only explain some of the observed behaviors and of the features typical of the deposits. This set of mechanisms seems to occur in different ways in the three different classes of phenomena here considered, and in many other processes involved in geological and geomechanical problems. Sliding implies continuous shearing and damage which can become localized in very different conditions; falling implies instantaneous and repeated impacts; avalanching allows for a dynamic and almost continuous action of the fragmentation s.l. On the other side, the experimental tests usually adopted to quantify the effects of these processes at the laboratory scale do not always represent the natural conditions under which the rock fragmentation can occur within the moving mass. Grain size distributions are the simplest tool used to describe fragmentation and to check for possible controls. In this contribution some examples of these processes are reported for the different landslide types, or evolutionary stages, presenting data for some real case studies, together with the main features, the possible mechanic and hydraulic consequences, as well as the possible adoption of simplified models for their description. The local environmental conditions are considered and their role on the final results is suggested.