Rockfall

Primary reference(s)

Highland, L.M. and P. Bobrowsky, 2008. The Landslide Handbook – A guide to understanding landslides. U.S. Geological Survey Circular 1325.

Additional scientific description

Falls are abrupt, downward movements of rock or earth, or both, that detach from steep slopes or cliffs. The falling material usually strikes the lower slope at angles less than the angle of fall, causing bouncing. The falling mass may break on impact, may begin rolling on steeper slopes, and may continue until the terrain flattens (Sassa et al., 2018).

Metrics and numeric limits

Very rapid to extremely rapid, free-fall; bouncing and rolling of detached soil, rock, and boulders. The rolling velocity depends on slope steepness (Hungr et al., 2014).

Examples of drivers, outcomes and risk management

Drivers for rockfall include undercutting of slopes by natural processes such as streams and rivers or differential weathering (such as the freeze/thaw cycles), human activities such as excavation during road building and (or) maintenance. Volcanic activities and earthquake shaking or other intense vibration are also drivers for rockfall (Hungr et al., 2014).

Falling material can be life-threatening. Falls can damage property beneath the fall-line of large rocks. Boulders can bounce or roll great distances and damage structures or kill people. Damage to roads and railroads is particularly high: rockfalls can cause deaths in vehicles hit by rocks and can block highways and railroads (Highland and Bobrowsky, 2008).

Mitigation measures for rockfall include rock curtains or other slope covers, protective covers over roadways, retaining walls to prevent rolling or bouncing, explosive blasting of hazardous target areas to remove the source (scaling), removal of rocks or other materials from highways and railroads can be used to minimise risk (Sassa et al., 2018).

Rock bolts or other similar types of anchoring used to stabilise cliffs, as well as scaling, can lessen the hazard. Warning signs are recommended in hazardous areas for awareness. Stopping or parking under hazardous cliffs should be warned against (Highland and Bobrowsky, 2008).