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St. Helens

The hill in the background is one of many hummocks forming the surface of the massive debris-avalanche deposit produced by collapse of the summit of Mount St. Helens on May 18, 1980. The different-colored rocks represent portions of the former volcano that were transported relatively intact far from the volcano. The avalanche traveled 25 km, filling the upper North Fork Toutle River to a maximum depth of nearly 200 m. The lighter-colored rocks in the foreground are pyroclastic-flow deposits.

Type/Process: Volcanic Landslide
Volcanic Status: Historical
Image Number: 029-001
Photographer: Lee Siebert, 1982 (Smithsonian Institution)
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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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits