How Fast Is Debris Flow?

Debris flows surge downhill at 72 km/h — mud, rock and water in a single torrent. The Mount St. Helens debris flow of 1980 reached 240 km/h, a wall of pulverised rock and ice obliterating everything in its path.

Mount St. Helens' 1980 eruption stripped 600 km² of forest in seconds — every standing tree in the blast zone was knocked down, all aligned in the same direction.

• Faster than ostriches sprint
• Mount St. Helens debris hit 240 km/h