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St. Helens

The horseshoe-shaped crater at Mount St. Helens is typical of scarps formed by massive landslides. On May 18, 1980 the upper 400 m of the summit was removed, leaving a 2 x 3.5 km horseshoe-shaped crater open to the north. Explosions played only an incidental role in formation of the crater, which resulted primarily from a massive landslide, the world's largest during historical time. The volume of the missing portion of the volcano closely matches the volume of the debris-avalanche deposit filling the North Fork Toutle River below the volcano.

Type/Process: Volcanic Landslide
Volcanic Status: Historical
Image Number: 029-017
Photographer: Terry Leighley, 1981 (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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