Major landslide occurred 4 miles (6.4 km) east of Oso, Washington, United States, on March 22, 2014, at 10:37 local time. Some of the unstable hills collapsed, sending mud and debris south across the North Fork of the Stillaguamish River, engulfing the countryside, and covering an area of ​​about 1 square mile (2.6 km 2 ). Forty-three people were killed and 49 homes and other buildings destroyed.
Video 2014 Oso mudslide
Overview
Landslides March 2014 swallowed 49 homes and other buildings in an unidentified neighborhood known as "Steelhead Haven" 4Ã, mi (6.4 km) on the southern side of the North Fork of the Stillaguamish River, east of Oso, Washington. It also stems the river, causing massive flooding upstream as well as blocking State Route 530, the main route to the town of Darrington (population 1.347), about 15 miles (24 km) east of Oso.
Natural rock formations and minerals (referred to by geologists as "geological features") with recent activity in the Oso region known as Hazel Avalanche; Recent landslide events are referred to in the media as "Oso landslide." Excluding landslides caused by volcanic eruptions, earthquakes or collapsed dams, the Oso slide is the single most deadly single landslide event in US history.
Hazel Landslide has a history of instability that occurred in 1937. Before the March 2014 mudslide, the Oso region had experienced heavy rains for 45 days earlier, up to 200 percent normal. The slides, described by witnesses as "fast moving mud walls," contain trees and other debris; it cuts through the house right at the bottom of a hill on the south side of the Stillaguamish River. A firefighter at the site stated, "When landslides hit the river, it's like a tsunami". A Washington state geologist declared that the landslide was one of the largest landslides he had ever seen. The mud, soil and rock debris left over from the mudslide cover an area of ​​1,500 feet (460 m), 4,400 ft (1,300 m) wide and loose debris 30 to 70 ft (9.1-21.3 m). A national geologist stated that extreme landslide flows due to the mud and debris are remarkable. While landslides are well documented, the Geotechnical Extreme Events Reconnaissance (GEER) team of researchers announced in April 2014 that they will investigate the factors contributing to the slide.
Maps 2014 Oso mudslide
Victims and damage
More than 100 first responders from Snohomish County and other neighboring countries were dispatched to aid emergency and search-and-rescue medical efforts, including a Navy search and rescue unit stationed near Naval Air Station Whidbey Island. More than 600 personnel, including more than 160 volunteers, are working in a landslide recovery operation.
On the afternoon of March 22, 2014, Washington Lt. Brad Owen's Governor declared a state of emergency in Snohomish County. Washington state governor Jay Inslee toured the area the next day before joining local officials at a press conference.
On March 22, launch day, eight people were rescued and taken to a local hospital. Four survivors of the landslide were still at a medical facility in Seattle on April 7, with two out of four patients being treated in intensive care, another in stable condition at Harborview Medical Center, and another dismissed from Harborview to a rehabilitation facility. While the official search for casualties ends in April 2014, workers and volunteers continue to screen debris and search for a victim still unaccounted for. On July 22, the Snohomish County Sheriff's Office confirmed 43 deaths after the last remains of victims had been found and identified.
Slide blocking the North Fork of the Stillaguamish River, causing it to head back east. Due to concerns that mud dams and debris could fail and cause downstream flooding, the National Weather Service (NWS) issued a flashflood watch. On April 2, with a stream flowing in a new channel at the north end of a garbage dump, the service raised a flashflood watch. Flooding due to the partially obstructed river continues to occur in the upper reaches of the dam. As a result, NWS continues to issue flood warnings for Stillaguamish one month after the March 2014 slide.
State Route 530 closed indefinitely after being slipped by the Washington State Department of Transportation (WSDOT), with a local alternative route opened the following week after the snow was cleared of an unpaved part of South Loop Mountain Road south of Darrington. The highway was pretty cleaned on May 31 to open a single escorted lane of traffic. Because the highway was badly damaged, and since the topography of the area had been altered by landslides, WSDOT decided to raise the section of the highway when it was rebuilt. On July 27, the first of four stages in rebuilding the highway has been completed. The new road opens Sept. 22, ahead of schedule of the project completion date of early October 2014.
Federal help
On April 3, the mudslide was declared a major disaster by President Barack Obama. The declaration was requested on April 1 by Governor Inslee, stating that about 30 families needed help with housing and other necessities. Inslee said that the estimated financial loss has reached $ 10 million. Director of Emergency Management of Snohomish County John Pennington advised residents to apply to FEMA. Four days later, during the part of the Green Heritage Lookout Heritage Protection Act, Senator Patty Murray (D-WA) mentioned the landslide, saying the bill would "give a glimmer of hope for the long-term recovery of the region."
On April 22, President Obama visited the west side of the slide area. Upon arriving at Air Force One at Paine Field in Everett, he meets with officials and rises to Marine One. There, he joined the Governor of Inslee and Senators Patty Murray and Maria Cantwell and Rep. Suzan DelBene to build flyovers and debris. After viewing the site, the president met personally with survivors, the victim's family, and some of the first respondents and rescuers at the scene in the chapel and fire hall at Oso.
Controversy
"Completely unexpected"
On March 24, two days after launch, John Pennington, Director of the Snohomish County Department of Emergency Management, told a press conference: "This is a really unexpected drop. It comes from nowhere." On the same day The Seattle Times publishes articles about previous slides in the same location, as well as possible slides in the future. The article contains comments from geologists, engineers, and locals, and states that the area is known among the locals as "Slide Hill". The next day, The Times follow up with a full-page article, "'Unexpected' risk slide? A few decades back warning". Snohomish County Public Works Director Steve Thomsen was quoted as saying: "The shear of this magnitude is very unpredictable, no indication, no indication at all."
On March 27, 2014, The Seattle Times reported that a 2010 study, commissioned by the area, warned the hillside on Steelhead Drive is one of the most dangerous in the county. According to Rob Flaner, one of the authors of the 2010 report, "For someone to say that this plan does not warn that this is a risk is falsehood." In the days following the slide, critics of Snohomish County officials received national attention in the editorial of the New York Times . The Seattle Times further reported that in 2004, local officials became concerned about the possibility of dangerous landslides in the Steelhead Haven area, and considered buying the residents of the area. The idea was rejected with the county building a new wall in an attempt to stabilize the slope. Some disaster experts have criticized this decision as a serious mistake. According to environmental engineer and applied georophologist Tracy Drury, "[after slide 2006] they did not even stop hitting the nails." For any purchase program, Drury further stated, "I think we are doing the best we can under the limit that no one wants to sell their property and move elsewhere."
The improvement of the slides area extends decades before the March 2014 slides. A rock revetment installed in 1962 to protect the bottom of the slide area from the erosion of the river was overrun by a slide two years later. Efforts in 2006 to move the river 430 feet (130 m) south of the erosion area failed when another landslide moved the river a total of 730 feet (220 m).
Logging
In the days after the slide, scientists questioned whether logging in the area could be a contributing factor to the collapse of the hillside. Grandy Lake Forest Associates of Mount Vernon, Washington proposed a 15-hectare (13 ha) clearance at the upper edge of the Oso avalanche zone in 2004. Washington state official Aaron Everett stated in an interview with KUOW that the application was denied and "The one that agreed to ultimately eliminate any portion of the harvest that will be in the groundwater catchment area. "Everett further declared a 7 hectare (2.8 ha) clearance operation reaching the edge of the groundwater hazard zone. An investigation is under way to determine whether Grandy Lake crossed into a forbidden area that could theoretically feed groundwater into an avalanche zone, affecting for 16 to 27 years.
Aftermath
Two years after the mudslide, about 11,000 tons of debris had been moved from the slide area. 34 plots of land have been purchased by Snohomish county from property owners who are too dangerous for a place to live. Properties in areas adjacent to State Route 530 and across the slide area remain salable.
In October 2016, the victims and their families reached a settlement with the State of Washington and a timber company, Grandy Lake Forest Associates, each costing $ 50 million and $ 10 million.
Public warnings
Next to State Route 530, the entrance to Steelhead Drive is closed by a gate decorated with monuments. In addition, there is a three-row road of 43 cedar trees, one for each victim. Each tree is decorated with special memories for everyone.
Basic activity around slides
The vibrations of land generated by Oso landslides are recorded in several regional stations and then analyzed by the Pacific Northwest Seismic Network (PNSN). The initial collapse begins at 10:37:22 am local time (PDT; 17:37:22 UTC), which lasts about 2.5 minutes. The debris that was loosened by the initial collapse is believed to contain material previously disturbed and undermined by the 2006 slide. After the initial event was another big slide that took place at 10:41:53 PDT.
Additional incidents, the possibility of smaller landslides breaking head shells, continued for several hours. The last important signal comes at 14:10:15. Examination of records from nearby seismic stations 7 mi (11 km) to the southwest showed a small seismic event beginning at around 8am launch day and stopped in the afternoon. However, they are not detected at the nearest seismic station. They are also seen in the days before and after the slide, but only during the day. They are believed to be related to some kind of human activity. There are no other indications of precursors that may be found.
In the days after the slide, Snohomish County's Emergency Management Director John Pennington speculated a magnitude 1.1 earthquake on March 10 may have triggered a landslide. The data collected by the PNSN shows a magnitude 1.1 earthquake on that date around the Oso landslide (about 2 Ã, Â ± 0.8 km to the northeast), at a depth of 3.9 Ã, Â ± 1.9 km. Regardless, the US Geological Survey (USGS) determined that the slide was not caused by seismic activity.
Geological context
The landslide occurs at the southeastern end of Whitman Bench, a ground terrace of about 800Ã, ft (240 m) above the valley floor and consists of gravel and sand stored during the most recent glacial. When Lobe Puget from the Cordilleran Ice Sheet moved south from British Columbia, Canada filled the lowlands of Puget, various mountain valleys were dammed and lakes formed. Sediments stranded from the higher mountains settled at the bottom of the lake, forming a clay layer.
As glacial ice presses higher against the western tip of the Frailey Mountain, the water that flows around the edge of the ice from the north is forced around the mountain, eventually flowing through the long valley that stretches to the northwest and is now occupied by Lake Cavanaugh. Sand and gravel carried by the stream and enter the glacial lake out to form a delta, the remains now known as the Whitman Bench.
After the glacier retreats and allow the lake to be released, the river carves most of the clay deposits and silt deposits, leaving the former delta "hanging" about 650Ã, ft (200 m) above the valley floor today When the sand part of the sediment has very little clay or "fine" to unite it, structurally weak, make the area around it vulnerable. Such areas are also sensitive to water accumulation, increasing internal "pore" pressure and then contributing to ground failure. Water that creeps from the surface will flow through the surface, saving contact with less permeable clays, allowing water to accumulate and form a zone of stability weakness.
Variations such as pore pressures and water flux are one of the major factors leading to slope failure. In the case of the area of ​​the Stillaguamish River where the March 2014 landslide occurred, erosion at the bottom of the slope of the river stream further contributed to the instability of the slope. Such conditions have created a series of landslide complexes on both sides of the Stillaguamish valley. The additional bench at the Whitman Bench margin is due to the decline of the large block, which also creates a weakness of the plane for future ditches and channels for water infiltration.
History of slide activity
According to a 1999 report submitted to the Army Engineering Corps by geologist Daniel J. Miller, PhD:
Hazel's landslides have been active for more than half a century. Thorsen (1996) noted a strict river bend struck the northern bank with an active landslide seen in 1937 aerial photographs. The next 60 years involve two periods of relatively low landslide activity, and two relatively high periods of activity, the latter extending to the present day [1999].
Known activities on this particular site include the following:
- 1937: aerial photograph shows an active mudslide.
- 1951: mudflow from the side channel briefly blocks the river.
- 1952: large movement, whole block, leaving the head of scarps 70Ã, ft (21 m) high. Then photographs show continuous activity over the next decade.
- January 1967: the decline of large blocks and the accompanying mud flow drove a river channel of about 700 ft (210 m) to the south. It protects the toes from erosion, its activity is small for about two decades.
- 1988 November: erosion of the toes leads to another slide, and the river moves south again, but not so far in 1967.
- 2006 January 25: Large culverts block the river, new channels cut to reduce flooding.
See also
- Debris stream
- Mud Smud
- Avalanche
- Bulk waste
- Slides rotation
Note
References
External links
- Official Snohomish County 530 Slide Updates (including the latest list of victims and missing persons)
- The Seattle Times : Oso mud casualties (photos and short bios of people killed or missing)
- Victims of avalanche mudslides (interactive aerial view of the victim's address)
- The USGS simulation shows how quickly Washington landslides melt
- Landslide in Washington: before and after (landslide area aerial view)
- Thorsen, 1967: Avalanche January 1967
- Tetra Tech Report, 2010, Ch. 14: Landslide
- Update on Natural Disaster Mitigation Plan for Snohomish District (presentation)
- Air History and LIDAR from the Stilliguamish Blocking Block
- Professor Cliff Mass, Cliff Mass Weather Blog: Meteorological Background for Stillaguamish Avalanche
- Dr. Dave Petley, Landslide Blog
- Department of Natural Resources, Question & Answer A About Landslide and Geology
Source of the article : Wikipedia
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