Global Volcanism Program | Image GVP-02867
The material in the lateral blast from Mount St. Helens on 18 May 1980 had a velocity of at least 100 m/s (224 miles per hour), perhaps much higher. It completely removed large trees standing near the volcano, and reached a distance of 30 km, blowing down mature trees like matchsticks. The blast devastated 600 km2 over a broad area north of the volcano.
Photo by John Dvorak, 1980 (U.S. Geological Survey).
This image is made available as a Public Domain Work, but proper attribution is appreciated.