Felssturz

Felssturz is a geologic term used in the German-speaking world to describe rapid downslope movement of rock material caused by gravity. It refers to events in which rock or rock fragments detach from a cliff or slope and descend rapidly, often accumulating at the base as talus. The term covers processes ranging from single-block rockfalls to extensive fragmentation and cascading blocks.

Causes and triggering factors include natural weathering and fracturing of rock, freeze-thaw cycles, heavy rainfall or rapid snowmelt, undercutting by erosion, thermal expansion, and seismic shaking. Human activities such as blasting, quarrying, or road construction can also contribute to rock detachment and instability.

Motion in a felssturz is typically rapid, with velocities that can reach tens of meters per second. Debris may strike infrastructure, roads, or people below, causing property damage, injuries, or fatalities. The event can also obstruct valleys and watercourses.

Risk assessment involves mapping unstable rock masses, monitoring for new cracks or rockfalls, and modeling potential runout areas. Early warning systems using sensors and cameras may help reduce risk in high-hazard zones.

Mitigation measures focus on preventing detachment and containing debris. Common approaches include rock bolting, scaling to remove loose blocks, improving drainage, installing protective nets or fences, and constructing debris basins. In some cases, slope stabilization or pre-emptive rock removal is employed to reduce the likelihood of a felssturz.