Investigation Into Causes of Oso Landslide Underway

An investigation into what caused the March 22 landslide that devastated the community surrounding Oso, Wash., is being conducted with the help of Joseph Wartman, a geotechnical engineer based at University of Washington.

Eleven days after the catastrophic landslide in the foothills of the Cascade Mountains in Washington state, 27 people are dead and another 22 are missing and presumed dead.

The university says the Geotechnical Extreme Events Reconnaissance Association (GEER) is mobilizing a national team which will investigate why the slope above the North Fork of the Stillaguamish River near Oso collapsed in the hopes of preventing a similar disaster in the future.

"The purpose is to collect data before the site is changed or altered in rescue and recovery. There is a lot of valuable information about how that landslide occurred in the landscape itself," Wartman said in a statement. "Ultimately, we want to learn from these disasters so we can prevent reoccurrence of future catastrophes."

According to GEER, the landslide occurred on a valley slope with a history of landslide occurrences dating back to the 1940s.

"The Oso landslide is one of many landslides that have occurred on slopes in the valley of the North Fork of the Stillaguamish River," GEER said in a statement. "The March 22, 2014 Oso landslide became a rapidly moving, unchannelized debris flow that spread out as it travelled about [0.5 miles], damming the North Fork of the Stillaguamish River, destroying and carrying away about 50 homes, and burying about 1 mile of State Highway 530."

According to The Daily Herald of Everett, Wash. the landslide has caused an estimated $32.1 million in damage.

Precipitation leading up the land landslide was recorded at about twice the average amount, GEER reported.

The GEER investigation, which has support from the National Science Foundation, will be quick, with the data being collected, processed and compiled into a report within one month, according to the University of Washington.

Logging is being considered a potential trigger for the Oso landslide, although it will be difficult to prove that it was, according to a report by National Geographic, which cited Josh Roering, a geomorphologist at the University of Oregon, Eugene, who has done extensive studies of logging and landslides.

Roering told National Geographic that there is a widely recognized link between logging and shallow debris flows that send a torrent of mud and soil flowing downhill.

However, the Oso landslide is considered a deep landslide and it is currently inconclusive whether logging plays a role in this rare type of landslide.