Oso Landslide, Washington March 22, Compiled by Scott Burns Portland State

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1 Oso Landslide, Washington March 22, 2014 Compiled by Scott Burns Portland State Monday, March 31, 2014

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3 Snohomish County Oso is highlighted

4 DETAILS 29 Dead; 13 missing 49 houses destroyed (25 full time occupants) 55 miles NE of Seattle Losses: $7 million houses $3 million house contents 32 million rescue/emergency response $22 million to remove debris

5 Geology of the Landslide Glacial-Fluvial Deposits of the Hazel Formation Plateau Whitman Bench Previous Landslides at the site: 1951, 1967, 1988, 2006 Landslide 300 acres debris field Volume: 15 million cubic yards Classification: Debris Avalanche/Debris Flow (Dick Iverson) Toxic debris and gas tanks

6 Factors Affecting the Landslide Steep Slope Weak soils Near record rainfall March was twice normal amount River undercutting the base of the slope at the meander bend while it was flooding Small change is slope hydrology from clear cutting of trees at top of slope

7 Most Deadly American Landslides a) 1928: St. Francis Dam, California: 500 b) 1985: Mameyes, Puerto Rico (Hurricane Isabel): 129 c) 1980: Mt. St. Helens (not all from landslide) 57 d) 2014: Oso Washington (24 dead + 22missing) 46 e) 1959: Madison Canyon, Montana 29 f) 2005: La Conchita, California 10 g) 1974: Canyonville, Oregon 9 One event over many valleys killed 150 in 1969 from Hurricane Camille in Nelson County, Virginia from debris flows. Source: Lynn Highland

8 Chronology of events on the Oso landslide 1949: A large landslide (1000 feet long and 2600 feet wide) affected the river bank 1951: Another large failure of the slope; the river was partially blocked 1967: Seattle Times published an article that referred to this site as Slide Hill 1997: report, by Daniel Miller, for the Washington Department of Ecology and the Tualialip Tribes 1999: US Army Corps of Engineers report by Daniel and Lynne Rodgers Miller that warned of the potential for a large catastrophic failure 2006: January 25: large movement of the Steelhead landslide blocked the river Source: The Yakima Herald

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10 On the hillside overlooking what was Oso Source: Jim Wilson/ The New York Times

11 March 24, landslide blocks river

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16 Stillaguamish River (North Fork), site of the March 22, 2014, Oso mudslide; the unstable area is covered with red alder, bigleaf maple and black cottonwood (light green) forest (right of center and below river). An eroding slope on the far side of the unstable area was left by a smaller slide that briefly dammed the river on January 25, 2006, and by similar previous events. The mudslide flowed to the upper left, across the river into the Steelhead Drive area. Most, if not all, of the houses visible in the image were destroyed. Source: Wikipedia

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18 B e f o r e s l i d e

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20 Source: Dr. Jeff Master s Wunder Blog

21 Source: CNN

22 Jan.,

23 Oso landslide Source: Wikipedia

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25 Readings from the Pacific Northwest Seismic Network reveal that the hillside collapsed in two stages: The lower part of the slope gave way at 10:37 a.m. PT, triggering seismic activity that lasted two and a half minutes. That material could have been disturbed and weakened by a landslide that occurred in 2006

26 The landslide cut off the small town of Darrington and prompted an evacuation notice for fear of a potentially catastrophic flood event

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28 Washington State Patrol trooper arrives on the scene on March 22, 2014

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30 March 30, 2014

31 Search and rescue on March 26, 2014

32 March 25, 2014

33 King County Sheriff s Office helicopter lowers a rescue worker on March 24, 2014

34 Downed power lines in debris on March 23, 2014

35 March 29, 2014

36 Near Darrington, March 29, 2014

37 Air National Guard, Staff Sgt. Jonathon Hermas, almost waist deep in debris still searching March 29, 2014

38 March 25, 2014

39 March 25, 2014

40 Emergency vehicles fill State Route 530 on March 26, 2014

41 March 27, 2014

42 March 27, 2014

43 Searchers pause for moment of silence for victims on March 29, 2014

44 March 29, 2014

45 Moment of Silence March 29, 2014

46 March 29, 2014

47 Volunteers help with search, March 24, 2014

48 March 22, 2014

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51 Clear Cutting on the Whitman Bench 2005: a pizza pie shape of 7.5 acres cut with the tip touching the slope Boundaries based on the 1988 report, not the 2006 report (5 acres would have been protected using the 2006 Miller report)

52 GEER: Geotechnical Extreme Events Reconnaissance Joseph Wartman, Geotech Professor, Univ. of Washington Jeff Keaton, AMEC David Mongomery, Geology Professor, Univ. of Washington John de LaChapelle, Golder Associates Scott Anderson, Federal Highways This banner committee will be researching the causes and put together a report

53 Future Counties: communications needed between maps and planners Counties: need landslide susceptibility maps Insurance: need landslide insurance or all hazard insurance like New Zealand

54 Post-landslide LiDAR (courtesy of Dr. Scott Anderson) An intact house sits at the edge of the landslide on March 24, 2014