The International Information Center for Geotechnical Engineers

Tuesday, 26 March 2019 00:00

5 years from the tremendous Oso landslide

The Oso landslide in Washington The Oso landslide in Washington.

The families of the unfortunate victims that lost their lives due to the catastrophic Oso landslide held a 5-year memorial ceremony.

The slide, known as the SR 530 landslide, occurred on March 22, 2014 and destroyed a riverside in Oso. According to the U.S. Geological Survey (USGS), it was triggered by heavy rainfall that saturated the soil. Logging may also have contributed to the failure.

The mudslide which was the deadliest in the history of the United States, was propagating for years. "That landslide mass prior to March 22 was really in some sense poised to fail. It was really unstable," Joseph Wartman, an engineer at University of Washington, stated.

Under these circumstances, continuous rainfall that saturated the soil was enough to trigger the landslide which affected the towns of Oso and Darrington and covered an area of about 2.60km2. 40 houses and other structures were buried near State Route 30. Unfortunately, 43 people lost their lives in the Steelhead Haven community.

On March 22, 2019, people related to the victims gathered together to honor their memory. They held a moment of silence at 10:37 a.m., the actual time of the landslide. A bronze sculpture of mailboxes was dedicated to the victims and survivors. Still, the community insists on building a permanent structure that will survive much longer. "We need something that lets that legacy that each one of them lived to live on," said Dayn Brunner, a local who lost a sister in the tragic incident. A committee is trying to raise a $6 million fund for the design and construction of such a structure.

USGS is monitoring the landslide since 2014. Right after the incident, USGS provided instruments including 3 portable packages called "spiders" which contain high-accuracy GPS to alert people if soil movement is detected. Moreover, USGS has been conducting field survey and laboratory testing to determine the causes of the landslide's high mobility. Scientists believe that those findings will help in the development of models that would better predict the behavior of such landslides.

Regarding the mechanism of the slide's failure, USGS suggests that the slope collapsed in two stages over a one-minute period. During the 2nd stage, the liquefaction of a saturated sand layer caused high acceleration of the moving mass that quickly covered the river valley.


For more information about Oso landslide, click the video below.

Read 182 times Last modified on Tuesday, 26 March 2019 15:39


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