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Surface Process Hazards Unit 4 Oso , Washington, Landslide

Surface Process Hazards Unit 4 Oso , Washington, Landslide. Sarah Hall (College of the Atlantic) Becca Walker ( Mt. San Antonio C ollege). Version: June 19, 2017. Oso Landslide Event. S aturday March 22, 2014 , 10:37 a.m . 43 people killed (most in U.S. landslide event )

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Surface Process Hazards Unit 4 Oso , Washington, Landslide

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  1. Surface Process Hazards Unit 4Oso, Washington, Landslide Sarah Hall (College of the Atlantic) Becca Walker (Mt. San Antonio College) Version: June 19, 2017

  2. Oso Landslide Event • Saturday March 22, 2014,10:37 a.m. • 43 people killed (most in U.S.landslide event) • Nearly 50 buildings destroyed • 6 km east of Oso, WA, in Snohomish County, which is about 80 km north of Seattle.

  3. Perfect Storm • Steelhead Haven community on the floodplain across the river from the base of the unstable slope was immediately buried by about 8 million m3 of debris that encompassed an area exceeding 1 km2. • The landslide dam created a lake, hampering search efforts and resulting in the urgent need to drain it to prevent establishment of a new channel along the south margin of the valley, which was the focus of the search efforts • 1.5 km of Highway 530(including access to 35 homes)was blocked for two months by landslide material that locally exceeded 25 m of depth • Damages - $150 million

  4. Perfect Storm • Weak glacio-lacustrine silt & clay • Logging is common in the area • 7.5 acres intruded into a restricted zone;caused excess water infiltration • Wettest March in Seattle History,” recieving more than200% of the normal rain in justfew weeks

  5. Shaded-relief image calculated from the 2013 lidar survey. Colored areas show older landslide deposits, distinguished by their relative age: A, youngest, to D, oldest. The red cross-hatched area marks the approximate extent of deposits from the March 22, 2014, landslide.

  6. Rotational Slump

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