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Nine dominantly nonexplosive episodes of dome growth at Mount St. Helens during 1981-83 added about 40 million cubic meters of dacite lava to the active composite dome in the volcano's 1980 crater. Endogenous and exogenous growth, the latter mostly in the form of stubby lava flows that accumulated on the dome, combined to build an edifice 880 meters long, 830 meters wide, and 224 meters high by December 1983; the total volume (1980-1983) was about 44 million cubic meters. Every 1-5 months during 1981-82, periods of increasing seismicity and ground deformation lasting 1-3 weeks culminated in extrusions lasting a few days. Endogenous growth became increasingly important during this interval, and in February 1983, the style of activity changed from episodic to essentially continuous endogenous and exogenous growth.
-- Swanson, et.al., 1987
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[Schematic,22K,GIF]
[Schematic,14K,GIF]
