The deadliest and most destructive volcanic eruption in the history of the United States began in southwestern Washington state on 18 May 1980 at 8:32 am.
Mount St. Helens experienced a magnitude 5.0 earthquake which enabled a lateral hydrothermal blast that triggered a landslide a half mile wide and a mile in length from top to bottom.
That explosion removed the upper portion of the volcano as a plume of ash rose 12 miles.
In an inner zone extending nearly 10 km (6 mi) from the summit, virtually no trees remained of what was once dense forest. Just beyond this area, all standing trees were blown to the ground, and at the blast’s outer limit, the remaining trees were thoroughly seared.
Although state and federal officials had urged residents to evacuate, 57 people died. U.S. Geological Survey volcanologist David Johnston died while at an observation post about five miles from the peak. Harry Truman, owner of the Spirit Lake Resort, died as well.
Within two weeks, volcanic ash circled the globe.
Prior to the 1980 blast, the most recent “significant eruption” probably occurred in 1857.
Mount St. Helens as seen 42 years ago today — one day before its devastating eruption.
— Washington State Dept. of Natural Resources (@waDNR) May 17, 2022
Located about 100 miles south of Seattle, Washington (55 miles northeast of Portland, Oregon), Mount St. Helens was — and still is — a popular destination for backpackers, fisherman, hikers, mountain climbers and photographers.
A fixture in the Cascade Mountain range, the 9,677-foot forested peak was the fifth tallest mountain in Washington on 17 May 1980. After 18 May, the mountain had dropped rank to 30th.
Scientists had begun monitoring the mountain after a series of earthquakes began two months earlier, on 16 March 1980.The mountain has been in a continuous state of recovery ever since that day.
In September 2004, Mount St. Helens had renewed earthquake activity as a new volcanic dome began form in the crater left behind in 1980.