Historic Earthquakes

Mount St. Helens, Washington
1980 05 18 15:32 UTC
Magnitude 5.0
Intensity IV
Earthquake and Volcanic Eruption

An earthquake occurred at 15:32 UTC, only seconds before the explosion that began the eruption of Mount St. Helens volcano. This eruption and blast blew off the top of the volcano, reducing is elevation by 393 meters, killed 31 people, and caused an estimated property damage of between $0.5 billion and $2 billion. About 53 earthquakes having magnitudes larger than 4.5 were located near Mount St. Helens before the main event and eruption. No earthquake having magnitudes higher than 4.5 were located following the eruption. The sound from the explosion and the vibratory effects from the earthquake were inseparable, resulting in a felt area that was based on both.

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.


USGS Photographic Library: Mount St. Helens May 18, 1980