Thirty-six years ago today Washington’s natural landscape reminded us how volatile and hazardous it can be when Mount St. Helens erupted.
The eruption sent ash east, covering much of the state and traveling on trade winds into Montana. Pyroclastic flows and lahars traveled swiftly across the Pumice Plain and down the North Fork Toutle and Cowlitz Rivers, destroying houses and bridges along the way.
As home to the Washington Geological Survey, DNR has mapped the hazard zones and written volumes of reports about Mount St. Helens, it’s historic eruptions and its future. Check out our geologists’ profile of our spectacular neighbor on the Washington State Geology Blog. The blog includes information about Mount St. Helens and the other geologic hazards surrounding Washingtonians. For regular updates, subscribe to the blog and check out DNR’s other regularly updated natural resource newsletters by clicking here: http://dnr.us8.list-manage.com/subscribe?u=686976a400749d61e09522350&id=c8cf71d34a
Location: Skamania County, WA
Elevation: 2,549 m (8,363 ft)
Nearby towns: Castle Rock, Olympia, Vancouver, Portland (OR)
Mount St. Helens produces dacitic to andesitic lava flows, pumice, and lahars. Like Glacier Peak, the composition of its magma makes it erupt more explosively than other Cascade volcanoes that erupt andesitic lava.
The areas prone to lahars are determined in part by figuring out where lahars traveled in the past. The map shows the distribution of lava flows and lahars mapped at the surface compared to hazard zones (gray shaded areas). Evidence of repeated eruptions can be found in many of the valleys that drain Mount St. Helens.
ERUPTION AND LAHAR HISTORY
Mount St. Helens was formed from four eruptive stages starting ~275,000 years ago, and intermittent eruptions occur to this day. During one such eruption around 2,000 years ago, lava flowed down the side of the volcano in streams, one…
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