The May 18, 1980 eruption of Mount St. Helens was the deadliest and most destructive volcanic event in modern U.S. history, killing 57 people and causing over $1 billion in damage.
Key Facts
- Death toll
- 57 people killed
- Eruption column height
- 80,000 feet (24 km)
- Thermal energy released
- 26 megatons of TNT equivalent
- Damage cost
- Over $1 billion (≈$3.5 billion in 2024)
- Volcanic Explosivity Index
- 5
- Ash dispersal
- 11 U.S. states and Canadian provinces
By the Numbers
Location
Cause → Event → Consequence
An injection of magma at shallow depth beneath Mount St. Helens created a large bulge and fracture system on the volcano's north slope. A series of earthquakes and steam-venting episodes preceded the main eruption beginning in March 1980, progressively weakening the north face of the mountain until a magnitude earthquake at 8:32 a.m. on May 18 triggered a massive sector collapse.
The collapse of the north face—the largest subaerial landslide in recorded history—depressurized the magma chamber, causing a catastrophic lateral explosion. An eruption column rose 24 km into the atmosphere, pyroclastic flows and lahars swept across hundreds of square miles, glaciers melted, and volcanic ash fell across 11 U.S. states and parts of Canada.
Fifty-seven people died, hundreds of square miles were reduced to wasteland, and over $1 billion in damage was recorded. Thousands of animals perished, and the volcano's summit was reshaped with a large north-facing crater. The site was subsequently preserved as the Mount St. Helens National Volcanic Monument, and Washington State designated May as 'Volcano Awareness Month.'
Human Cost
Each dot represents approximately 10,000 deaths. Total estimated: 57 (eruption)