Rockfalls, rock slides and rock avalanches in high mountains
The terms rockfall, rock avalanche and rockslide are often used interchangeably. Different authors have proposed definitions based on volume thresholds, but the establishment of fixed boundaries can be tricky. Rockfall can be defined as the detachment of a mass of rock from a steep rock-wall, along discontinuities and/or through rock bridge breakage, and its free or bounding downslope movement under the influence of gravity[1,2]. Usually, we use this term when the volume is limited, and there is little dynamic interaction between rock fragments, which interact mainly with the substrate. Rockslides involve a larger volume (up to 100,000 m3) and the blocks often break in smaller fragments as they travel down the slope. In both rockfall and rockslide, the blocks move downslope mainly by falling, bouncing and rolling. On the other hand, rock avalanches involve the disintegration of rock fragments to form a downslope rapidly flowing, granular mass demonstrating exceptionally high mobility. The size of these rock failures can vary from single boulders to several million cubic meters (e.g. the catastrophic failures of Triolet, 1717, and Randa, 1991).