MOUNT ST. HELENS, ERUPTION OF, the most deadly volcano attack ever to have occurred on U.S. soil. On the morning of March 27, 1980, at 8:32 Pacific Standard Time, Mount St. Helens, then a little-known member of the Cascade mountain range, erupted with the explosive force of nearly seven megatons—comparable to that of a hydrogen bomb’s detonation.
Fifty-seven people perished in the blast and hundreds more were left homeless. A panic ensued over vulnerability to the nation’s roughly 170 officially dormant volcanoes, and President Jimmy Carter’s inability to convince the voting public that his administration was not “soft” on the environment ultimately cost him his re-election that November.
