Mount St. Helens Eruptive Activity, 1980-1984

Dome-building Eruptions

Eleven eruptions after October 1980 were dominantly nonexplosive events that built a composite lava dome about 800 feet high and 2500 feet in diameter in the crater. Each eruption extruded near the top of the dome and crept three to 15 feet per hour down one side over a period of several days; between 100 and 150 million cubic feet of new lava was added to the dome during each of these episodes.

Dome-building eruptions in 1981-82 were episodic, occurring every one to five months. Between February 1983 and February 1984, the dome grew continuously both by the intrusion of magma into it and by the extrusion of lava onto its surface. As of May 1984, it appeared that Mount St. Helens had returned to the episodic style of dome growth. At the then current rate of dome growth, which averaged about 35 million cubic feet per month, it was estimated that some 150 to 200 years would be needed to build Mount St. Helens to its former height. However it was considered unlikely that such a simple scenario would prevail.

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