The eruption of Mount St. Helens, March–September 1980

The violent eruptions of Mount St. Helens in 1980 have dramatically brought volcanism to public attention. Scientists of many disciplines have been provided an unparalleled opportunity to study explosive volcanism and its effects. A brief summary of the eruptions and of the varied research on its processes and products follows.After a week of local seismicity, Mount St. Helens began to eject steam and ash on March 27, breaking 123 years of quiet. The eruption was the first in the contiguous United States since the 1914–1917 activity of Mt. Lassen, California. Pulses of steam and ash rose as much as 3 km above the summit of Mount St. Helens during the first 10 days, producing slight ashfalls as far away as Spokane, 500 km to the east‐northeast. By April 8, two initially separate active vents had coalesced into a single crater at least 500 m long by 350 m wide. Explosions decreased in both size and ash content through April, and by late month, episodic explosions had been replaced by continuous steaming. No fresh magma was identified in any of the March‐April ejecta.