SEATTLE — Searchers on Tuesday pulled what they believe was the last missing body from debris left by a landslide in Washington state that researchers said was likely triggered by heavy rainfall.
The intensive search for the 43 people killed in the March 22 disaster in Oso ended in April, but workers have been screening debris and watching for the body of 44-year-old Kris Regelbrugge.
Her husband, Navy Cmdr. John Regelbrugge III, also was killed when the slide crossed the North Fork of the Stillaguamish River and decimated their home in the community about 55 miles northeast of Seattle.
“I’m humbled and honored that we are able (to) return Kris to her family,” Snohomish County Sheriff Ty Trenary said in a statement.
Researchers said precipitation in the area in March that might have exceeded 30 inches was one of multiple factors that contributed to making the slope unstable. Others included groundwater seeping into the slide mass as well as changes in slope stress and soil that was weakened by previous landslides.
The landslide, the deadliest in U.S. history, occurred in two major stages minutes apart, according to the team of seven independent researchers with the Geotechnical Extreme Events Reconnaissance Association.
A fast-moving mudflow remobilized a previous 2006 slide, bringing down old slide deposits across the valley that moved hundreds of meters beyond the river. That first stage caused all or most of the destruction.
The upper section of the slope collapsed a few minutes later, with the main mass of that slide dropping about 350 feet and traveling as far as 2,000 feet in less than two minutes.
The scientists said there have been 15 large mapped landslides in the river valley over about 6,000 years. The slides are estimated to happen every 400 to 1,500 years.
The team wrote that its investigation wasn’t intended to be “a final, conclusive study of the landslide.”
Joseph Wartman, an associate professor of civil and engineering with the University of Washington and a team leader for the study, said there could be any number of factors that triggered it.
The group said examining practices such as timber harvesting was beyond the scope of its investigation, so it couldn’t say to what degree that practices contributed to the slide.
The team collected data during a four-day trip to Oso for the investigation funded by the National Science Foundation.
The report noted that the slide’s run-out was long but not particularly exceptional for a slide of its size.
“When you look at the site, you can’t imagine that it would run out that far. It’s really mind-boggling,” said Jean Benoit of the University of New Hampshire.
The report makes several broad recommendations including urging that landslide risks be examined and that the public should be consistently told of those risks.
