The flowing mud carries rocks, bushes, and other debris as it pours down the slope. A debris avalanche is a fast moving debris flow that travels faster than about 10 mph or approximately 25 yards in about 5 seconds. Speeds in excess of 20 mph are not uncommon and speeds in excess of 100 mph, although rare, do occur locally.
Debris avalanches pose hazards that are often overlooked.
Houses in the path of debris avalanches can be severely damaged or totally demolished. Persons in these structures can be killed or severely injured. Most rainstorms are of such low intensity that they do not trigger debris avalanches. However, when the ground is already saturated from previous rain, even relatively short high-intensity rainstorms may trigger debris avalanches. The most common cause of debris avalanches and debris flows is the combination of heavy rainfall, steep slopes and loose soil.