Mount St. Helens eruption photograph and ephemera collection, 1980

On March 16 1980, a series of small earthquakes were the first signs of activity on Mount St. Helens. On March 27, after hundreds of additional earthquakes, Mount St. Helens erupted for the first time in over 100 years. The blast created a 200 to 250 ft wide crater through the volcano’s ice cap and covered the snow in the southeast sector with dark ash. Within a week, the crater had grown to about 1,300 ft. On average, eruptions occurred about one per hour during March and then decreasing to about one per day by April 22, when the first period of activity stopped. Small eruptions resumed from May 7 to May 17. By that time, more than 10,000 earthquakes had shaken the volcano. The north flank had now grown outward by about 450 ft to form a prominent bulge. This bulge grew about 6.5 feet a day. This type of growth was strong evidence that molten rock (magma) had risen high into the volcano. Also, a cryptodome was developing beneath the bulge that had yet to erupt onto the surface.