A debris avalanche is caused by a sector collapse. The most famous documented debris avalanche was that causing the eruption of Mt St Helens in 1980. A debris avalanche occurs under water unsaturated conditions compared to lahars which are water saturated mass flows.
The worldwide rate of large debris avalanches is four per century.
Examples of debris avalanches
Mt St Helens 1980, Shiveluch 1964, Bezynianny 1956, Bandai 1888, Unzen 1792, Papandayan 1772.
A prehistoric avalanche at Lastarria Volcano has an unusually high velocity of 300 km/hr.