Lahars are mudflows that occur on the slopes of erupting volcanoes , and are caused by the rapid melting of snow and ice, as well as the mobilization of soil water found on the slopes of the volcano. They often start as slumps or slides, but become debris flows as the material mixes with more water and even air. A debris avalanche is an extremely rapid downward movement of rock debris, regolith, and soil, more common in areas with steep slopes. The term avalanche is generally applied to any type of fast-moving downward movement of any type of material, but is associated with much steeper slopes than debris flows. Such debris avalanches move downslope through avalanche chutes .
Few people survive if caught in the path of a debris avalanche.
In 1970, an earthquake in Peru triggered a debris flow from the Andes Mountains that killed 30,000 people. The front of this debris flow was 260 feet high, and was preceding by a roaring wind. The debris flow was probably traveling at least 100 miles an hour, and perhaps even faster. Mass Wasting caused by Humans Many human activities also cause mass wasting, which are then referred to as induced mass wasting . However, such terraces are often unstable and can give way under heavy rains.