Mount St. Helen eruption 1980
In May 18, 1980 St. Helens erupted violently, blowing off the entire north side of the peak into the air. The explosive eruption removed more than a cubic mile of material from the mountain, and reduced it's elevation from 9,677 to 8,365 ft.
Not just the mountain itself, but the landscape of western Washington state was completely transformed as pyroclastic flows roared down the flanks of St. Helens, filling in lakes and river, destroying forests, and sending torrents of debris flows down the drainages.
Ash clouds turned day into night in cities east of the Cascade mountains, as far away as Montana. Scientists said the ash from St. Helens' eruption entered the jet stream and completely circled the globe.
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Mt. St. Helen Eruption