A major landslide
occurred 4 miles (6.4 km) east of Oso, Washington
, United States, on March 22, 2014, at 10:37 a.m. local time. A portion of an unstable hill collapsed, sending mud and debris to the south across the North Fork of the Stillaguamish River
, engulfing a rural neighborhood, and covering an area of approximately 1 square mile (2.6 km2). Forty-three people were killed and 49 homes and other structures destroyed. Overview
The March 2014 landslide engulfed 49 homes and other structures in an unincorporated neighborhood known as "Steelhead Haven" on the south side of the North Fork of the Stillaguamish River, approximately 4 miles (6.4 km) east of Oso, Washington
. It also dammed the river, causing extensive flooding upstream as well as blocking State Route 530
, the main route to the town of Darrington
(population 1,347), 16 miles (26 km) east of Oso.
The natural rock and mineral formation (referred to by geologists as a "geological feature
") with the most recent activity in the area of Oso is known as the Hazel Landslide; the most recent landslide event was referred to in the media as "the Oso mudslide."
Excluding landslides caused by volcanic eruptions
, earthquakes or dam collapses
, the Oso slide is the deadliest single landslide event in United States history.
The Hazel Landslide has a history of instability dating to 1937. Prior to the March 2014 mudslide, the Oso area had had heavy rainfall during the previous 45 days, up to 200 percent of normal. The slide, described by witnesses as a "fast-moving wall of mud," contained trees and other debris; it cut through homes directly beneath the hill on the south side of the Stillaguamish River. A firefighter at the scene stated, "When the slide hit the river, it was like a tsunami
". A Washington state geologist stated the slide was one of the largest landslides he had personally seen. The mud, soil and rock debris left from the mudslide covered an area 1,500 ft (460 m) long, 4,400 ft (1,300 m) wide and deposited debris 30 to 70 ft (9.1 to 21.3 m) deep. A national geologist stated the flow of the landslide was extreme because of the extraordinary run-out of mud and debris. While the landslide was well documented, a research team from the Geotechnical Extreme Events Reconnaissance (GEER) announced in April 2014 that it would investigate the factors contributing to the slideCasualties and damage
More than 100 first responders
from Snohomish County
and other surrounding counties were dispatched to assist with emergency medical and search-and-rescue efforts, including the Navy's search and rescue unit stationed at nearby Naval Air Station Whidbey Island
. Over 600 personnel, including more than 160 volunteers, worked on landslide recovery operations.
Late in the evening of March 22, 2014, Washington's Lieutenant Governor Brad Owen
declared a state of emergency
in Snohomish County. Washington state Governor Jay Inslee
toured the area by air the following day before joining county officials at a news conference.
On the day of the slide, eight people were rescued and taken to regional hospitals While the official search for victims ended in April 2014, workers and volunteers continued to screen debris and look for one victim still unaccounted for. On July 22, 2014 the Snohomish County Sheriff's Office confirmed 43 fatalities after remains of the final victim had been located and identified.
The slide blocked the North Fork of the Stillaguamish River, causing it to back up eastward. Because of concerns that the mud and debris dam
could fail and cause downstream flooding, the National Weather Service
(NWS) issued a flash flood watch
. On April 2, 2014, with the river flowing in a new channel at the north end of the debris dam, the service lifted the flash flood watch. Flooding due to the partially obstructed river continued to occur upstream of the debris dam. As a result, the NWS continued to issue flood warnings for the Stillaguamish one month after the March 2014 slide.
State Route 530 was indefinitely closed after the slide by the Washington State Department of Transportation
(WSDOT), with an alternative local route opened the following week after snow was cleared from the unpaved portion of Mountain Loop Highway
south of Darrington. The highway was cleared enough by May 31 to open one lane of escorted traffic. Because the highway was badly damaged, and because the topography of the area had been altered by the landslide, WSDOT decided to elevate that section of the highway when it was rebuilt. As of July 27, the first of four stages in rebuilding the highway had been completed. The new roadway was opened September 22, ahead of schedule of the projected completion date of early October 2014.Federal aid
On April 3, the mudslide was declared a major disaster by President Barack Obama
. The declaration was requested on April 1 by Governor Inslee, who stated that approximately 30 families needed help with housing and other needs. Inslee said that financial loss estimates had reached $10 million. Snohomish County Emergency Management Director John Pennington advised residents to register with FEMA
. Four days later, during passage of the Green Mountain Lookout Heritage Protection Act
, Senator Patty Murray
(D-WA) mentioned the landslide, saying the bill would "provide a glimmer of hope for the long-term recovery of this area."
On April 22, President Obama visited the west side of the slide area. After arriving in Air Force One
at Paine Field
, he met with officials and boarded Marine One
. There, he was joined by Governor Inslee and Senators Patty Murray and Maria Cantwell
as well as Rep. Suzan DelBene
for a flyover of the slide and debris field. After viewing the site, the president met privately with survivors, families of the victims, and some of the scene's first responders and rescuers at the Oso fire hall.Site memorials
Alongside State Route 530, the entrance to what was Steelhead Drive is closed by a gate that was decorated by impromptu memorials. Alongside, three rows of 43 cedar trees were planted, one for each of the victims. At the time of the planting, each tree was decorated with mementos specific to each person.
In September 2017, one of the few trees in the path of the slide that remained standing near Highway 530 and was seen by locals as a memorial, was cut down as a danger tree
. County officials decided to cut the Sitka spruce
tree down after it was determined its roots had sustained enough damage that it could no longer be considered stable and not a hazard to both the Whitehorse Trail parallel to the highway as well as the highway itself. Following the slide, a memorial sign carved out of cedar and reading, "Oso. 10:45 a.m. 3/22/14", was placed on the spruce and remained until the tree was removed. The Snohomish County Department of Parks, Recreation & Tourism announced on March 22, 2018 that plans had begun for a permanent memorial commemorating the victims. The tribute is set to be built at the location of the slide and fundraising efforts are underway with wood from the formerly standing memorial tree to be re-purposed and use