Prediction of the dimensions of rock avalanches’ affected areas based on the empirical relationships derived from the Central Asian database

Mobility of long-runout catastrophic landslides (debris flows, debris and rock avalanches) can be characterized by several parameters. Those, allowing predicting exposure of elements at risk that might be threatened by such hazardous natural phenomena if they will occur—the affected area and runout, are most important for risk assessment. They can be estimated using two general approaches—one based on the numerical modeling and another one based on the empirical relationships between runout and affected area on the one hand and parameters characterizing the potential source zone on the other hand. The latter are volume of the anticipated rock slope failure and height of the unstable slope. Both can be assessed prior to failure with certain accuracy by contrast with the height drop defined as the elevation difference between headscarp crown and the deposit tip. The optimal input parameter is the product of the unstable slope height and possible failure volume that is, in general, proportional to the potential energy of the unstable rock massif. According to the analysis of the Central Asian rockslides/rock avalanches database that includes quantitative parameters of 515 case studies with defined confinement, the relationships of such product with runout and affected area have high correlation coefficients regardless of the confinement conditions and, therefore, allow prediction of the parameters in question with sufficient reliability. It is pointed out that requirements to the accuracy of slope height and failure volume assessment depend on a large extent on the variability range of these parameters within the inventories used to derive the empirical relationships.