A landslide is a slope failure characterised by the downward sliding movement of rock and/or loose stone. Old, dormant landslides can be re-activated gradually or suddenly. Shallow landslides on slopes are a particular type. They are mostly triggered by intensive rainfall. The resulting slurry of loose stone and copious water flows fast and freely without forming channels. Shallow landslides can therefore be especially dangerous on steep slopes.
Unlike landslides, debris flows occur in usually steep channels, such as the stream channels carved by torrents. Muddy debris flows consisting of a slurry of water, rock and sometimes tree trunks can reach very high velocities. These avalanche-like flows deposit the debris in the runout zone where the terrain flattens.
A rockfall occurs when individual rocks or blocks of stone fall. The rocks and boulders usually come to a standstill when the slope gradient is less than 30 degrees. Trees and forests can absorb a significant portion of the energy generated by falling blocks of stone.