Often asked: When Did Mount Saint Helens Erupt?

How long was the eruption of Mount St Helens in 1980? Summary of Events A wave of decreasing pressure down the volcanic conduit to the subsurface magma reservoir, which then began to rise, form bubbles (degas), and erupt explosively, driving a 9-hour long Plinian eruption. Steam-blast eruption from summit crater of Mount St. Helens. When … “Often asked: When Did Mount Saint Helens Erupt?”

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