Mount Saint Helens
erupted on May 18, 1980 after 123 years
of dormancy. Although this volcano
was carefully monitored,
the actual eruption caught geologists by
surprise and caused
at least 62 deaths (including one geologist).
1. MARCH 1980
Seismic activity began in the middle of March.
2. APRIL 1980
A bulge in the northern slope became noticeable.
3. MAY 1980
A large earthquake triggered a landslide that led first to
a
lateral eruption and then a vertical eruption (diagram).
Debris flows filled in the North Fork Toutle River Valley
