- Who
- Mount St. Helens eruption
- What
- 402.3 kilometre(s) per hour
- Where
- United States (Mt. St. Helens)
- When
The volcanic explosion of Mt. St. Helens on May 18, 1980, triggered the fastest recorded avalanche in history on the mountains north slope. The velocity reached was 402.3km/h 250mph.
