Rockfall Causes and Transport Mechanisms - A Review

Abstract

Rockfalls are distinguished from rock mass falls and rock avalanches by their physical transport mechanisms. A common term used for this differentiation is “fragmental” rockfall, where individual blocks mainly interact by impacts with the substrate along the downslope motion, which can be described by rigid body ballistics. Rockfall is very frequent in steep rock slopes, and one of the most frequent hazards to alpine traffic lines and settlements, an important process of geological mass movements along slopes, and a key mechanism for coastal cliff erosion. Most rockfall blocks or rock masses are released from steep cliffs with a high fracture density. The temporal frequency of rockfall is strongly correlated with daily rainfall magnitude, diurnal freeze-thaw cycles, the occurrence of earthquakes with magnitude greater than 4, and local rock slope stability. During a fragmental rockfall event the movement of blocks occurs in the release, transit and deposition zone. The zone boundaries are diffuse and the four types of movement – fall, bounce, roll and glide – occur everywhere. During ground impacts the blocks loose part of their translational energy and each deceleration history is unique and not comparable to the others. This energy loss depends most on the flight path, the inclination and the properties of the ground.