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*Repost from @USGSVolcanoes* #MountStHelens - May 18, 1980 USGS’ Coldwater II observation post on South Coldwater Ridge is 5.5 mi N-NW of Mount St. Helens. Scientist David Johnston had taken over from Harry Glicken on the evening of May 17. Before 7 AM, Johnston collects 3 laser measurements of the bulge and radios data to the Vancouver (WA) office. Nothing significant to report. After 8:32 AM, a ham operator records the transmission by Johnston, “Vancouver! Vancouver! This is it!” The fractured bulge on the north flank releases. The sliding, pulverizing rock and ice flows off the volcano, toward Spirit Lake, and 17 miles down the North Fork Toutle River valley. Freed from the weight of north flank, gassy magma and hot fluids explode. It speeds down the flanks to more than three hundred miles an hour. The scorching current surges north, east, and west as a hot hurricane, hugging the landscape. It rides up a near ridge, boils over its top, flows down into the next valley. It rides up and over another ridge, spreading outward. Within 6 minutes, 230 square miles are a barren, scorched waste. In three minutes, the rising ash column punches through 35,000 ft. carrying with it millions of tons of the surge’s sand, silt and tree litter. Residents of Portland (OR) are bestowed with a resplendent view while winds spread a gigantic ash anvil east. Ash falls hundreds of miles away. Street lights blink on in Yakima and Moses Lake as day sinks into darkness. High on the volcano’s flanks, the hot, turbulent current melts snow and ice. Slush-flows converge as muddy floods that pour off the volcano into the heads of South Fork Toutle, Smith Creek and Muddy River. A muddy flood rages down Toutle and lower Cowlitz valleys to the Columbia, smashing bridges, logging camps and houses. In afternoon, the column widens, goes turbulent, and feeds fiery ash flows onto the Pumice Plain. A single-day eruption and everything has changed. #USGS #science #CVO #CascadesVolcanoObservatory #MSH1980 #VolcanoAwarenessMonth #naturalhazards View rarely seen archival footage of the rising ash column ➡️http://ow.ly/e6zJ50JbjEc (link in story)