Mt. St. Helens - 1980

  • is a stratovolcano in the Cascades of the Pacific Northwest
  • had not erupted since 1857
  • geologic evidence suggested the volcano had a violent past
  • on March 20, 1980 earthquakes occurred
  • a week later an 80 meter crater burst opened at the summit spewing gas and pyroclastic debris
  • geologists, who had set up monitoring stations to observe the volcano noted that its north side was bulging
  • this suggested the area was filling with magma
  • authorities evacuated local



  • on May 18th at 8:22 am an earthquake triggered a 3 km landslide on the volcano's weakened north side
  • the sudden landslide released pressure on the magma in the volcano
  • a sudden and violent expansion of gasses blasted through the side of the volcano
  • rock, steam and ash screamed north at the speed of sound (767 mph)
  • the forest and everything in it was flattened in a 600 square mile area
  • 60 people died
















May 18, 1980, at 8:32 a.m. Pacific Daylight Time








Lakes nearest to Mount St. Helens have been partly covered
with felled trees for more than thirty years. This photograph was
taken in 2012.




North Fork Toutle River valley
filled with landslide deposits





The ash cloud produced by the eruption, as seen from the village of Toledo, Washington, 35 miles away, northwest from Mount St. Helens. The cloud was roughly 40 miles (64 km) wide and 15 miles (24 km) high.

By Rocky Kolberg - Rocky Kolberg, CC BY-SA 3.0,






By Murraybuckley - Own work, Public Domain,