During Mount St. Helens’ eruption on May 18th, 1980 a vigorous plume of ash erupted and remained for more than nine hours, eventually reaching 12 to 15 miles (20–25 kilometers) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 kilometers/hour), with ash reaching Idaho by noon. By early May 19, the devastating eruption was over. Shown here is a close-up view of the May 18 ash plume.
Donald A. Swanson
1980-05-18
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