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St. Helens

Pryroclastic surges originating from secondary phreatic explosions at Mount St. Helens in 1980 produced these cross-bedded layers. They were deposited from successive, rapidly moving horizontal clouds of gas, ash, and rock fragments that resulted from the interaction of still-hot pyroclastic-flow deposits from the May 18 eruption with groundwater and fragments of Mount St. Helens glaciers carried down by the collapse of the summit.

Type/Process: Pyroclastic Flow
Volcanic Status: Historical
Image Number: 029-008
Photographer: Norm Banks, 1980 (U.S. Geological Survey)
Summit Elevation: 2549 meters
Latitude/Longitude: 46.20 N / 122.18 W
Timeframe: Last known eruption 1964 or later
Region: Canada and Western USA


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