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St. Helens

The twisted girders of a highway bridge lie entombed in mudflow deposits from Mount St. Helens. This May 18, 1980 mudflow was produced by dewatering of the debris-avalanche deposit in the North Fork of the Toutle River and traveled as far as the Columbia River, decreasing the depth of the navigational channel from 11 meters to 4 meters.

Type/Process: Lahar (Mudflow)
Volcanic Status: Historical
Image Number: 028-095
Photographer: Dan Miller, 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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