Gordon Farquharson / UW An aerial view of the slide site at Oso, Washington, from March 31, 2014.
University of Washington - The disastrous March 22 landslide that killed 43 people in the rural Washington state community of Oso involved the "remobilization” of a 2006 landslide on the same hillside, a new federally sponsored geological study concludes. The research indicates the landslide, the deadliest in U.S. history, happened in two major stages. The first stage remobilized the 2006 slide, including part of an adjacent forested slope from an ancient slide, and was made up largely or entirely of deposits from previous landslides. The first stage ultimately moved more than six-tenths of a mile across the north fork of the Stillaguamish River and caused nearly all the destruction in the Steelhead Haven neighborhood. The second stage started several minutes later and consisted of ancient landslide and glacial deposits. That material moved into the space vacated by the first stage and moved rapidly until it reached the trailing edge of the first stage, the study found. The report, released Tuesday on the four-month anniversary of the slide, details an investigation by a team from the Geotechnical Extreme Events Reconnaissance Association , or GEER.
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