Rock avalanche mobility: optimal characterization and the effects of confinement

A Central Asia rock avalanche (rockslide) inventory that includes about 600 case studies with measured parameters is used to present a quantitative characterization of rock avalanche mobility and its dependence on the controlling parameters such as volume and height drop. The mobility can be characterized by runout and angle of reach, as well as by the affected area. The database was analyzed after dividing the rock avalanches into three confinement categories—frontally confined, laterally confined, and unconfined. In addition to the traditionally used slope failure volume and height drop, we correlated mobility parameters with their product that is proportional to the potential energy released during rock avalanche emplacement. It was found that coefficients of determination of the regressions of the affected area with volume and, especially, with its product with maximal height drop are higher than those of volume with runout and much higher than those of volume with angle of reach for all confinement conditions. Thus, these relationships provide an optimal characterization of the rock avalanche mobility. Relative influence of failure volume and height drop on rock avalanche mobility was also analyzed. The regression equations obtained in this study were successfully applied to several case studies from other mountain regions. The proposed regression equations can be used to predict the exposure of elements at risk threatened by anticipated rock avalanches. They can also be used to estimate the parameters of rockslide dams that might originate at the sites with anticipated large-scale rock slope failures, if their volumes and height drops can be assessed. The confinement conditions are statistically proved to influence the rock avalanche mobility and must be taken into consideration during hazard and risk assessment.