The climactic eruption in full fury in the
late morning of May 18, 1980 (Photograph by Joseph Rosenbaum).
May 18, a Sunday, dawned bright and clear. At 7 a.m. Pacific Daylight
Time (PDT), USGS volcanologist David A. Johnston, who had Saturday-night
duty at an observation post about 6 miles north of the volcano, radioed
in the results of some laser-beam measurements he had made moments earlier
that morning. Even considering these measurements, the status of Mount St.
Helens' activity that day showed no change from the pattern of the preceding
month. Volcano-monitoring data--seismic, rate of bulge movement, sulfur-dioxide
gas emission, and ground temperature--revealed no unusual changes that could
be taken as warning signals for the catastrophe that would strike about
an hour and a half later. About 20 seconds after 8:32 a.m. PDT, apparently
in response to a magnitude 5.1 earthquake about 1 mile beneath the volcano,
the bulged, unstable north flank of Mount St. Helens suddenly began to collapse,
triggering a rapid and tragic train of events that resulted in widespread
devastation and the loss of 57 people, including volcanologist Johnston.
Reawakening
and Initial Activity
URL: <https://pubs.usgs.gov/gip/msh/climactic.html>
Contact: John Watson
Last updated: 06.25.97
