Known to the Klickitat as Louwala-Clough, or "smoking mountain," Mount St. Helens erupted on this day in 1980 and became the deadliest and most destructive volcanic eruption in U.S. history.
On March 27, 1980, the volcano produced its first eruption in over 100 years. Steam explosions created a 250-foot wide crater. 
This photograph shows the ash-darkened east slopes of Mount St. Helens on March 30, 1980. Ninety-three explosions took place that day.
The mountain erupted at 8:32 a.m. on May 18, 1980.
Following the landslide, a massive vertical ash column that stretched 12 miles above the crater formed. The swirling ash particles in the atmosphere generated lightning, which, in turn, started several forest fires.
Following the landslide, a massive vertical ash column that stretched 12 miles above the crater formed. The swirling ash particles in the atmosphere generated lightning, which, in turn, started several forest fires.
Smaller eruptions occurred throughout the summer and fall. The magma at Mount St. Helens is very sticky, and by October 1980, the episodic eruptions built a new lava dome that reached 1,000 feet above the crater floor.
Lidar imagery shows us lava dome growth at Mount St. Helens between 2002 and 2009. The Crater Glacier is highlighted in the last frame.
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