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With 24 people confirmed dead and 90 still missing four days after a massive mudslide buried homes near the rural Washington hamlet of Oso, residents, state officials and experts are beginning to look for answers as to what caused the disaster, and what, if anything, could have been done to prevent it.
Since Saturday, local government leaders have said repeatedly that there were few ways of knowing a slide this size — capable of risking the lives of hundreds — was a possibility.
But to those familiar with the mountains in the Oso area, as well as geomorphologists who’ve studied the causes of landslides, the event was far from surprising.
They say there were several warning signs that should have at least made local officials think twice about allowing people to live at the base of the mountain.
“I don’t think the fact that the slide happened surprised anyone who has looked at this area before,” said Doug Heiken, the conservation and restoration coordinator with Oregon Wild, a local nonprofit organization. “It wasn’t really a matter of if, but when.”
Heiken and others said that while it’s nearly impossible to know when and exactly where a landslide will happen, it was still very clear that the area of mountain across the Stillaguamish River from Steelhead Drive was at tremendous risk of breaking away.
The area where the mudslide occurred was known for the instability of its land.
A landslide in 2006 was large enough to send debris down the mountain and into the river. That mudslide didn’t damage any property, but new development has been permitted in the area since then, leading some to question whether local housing officials paid enough attention to the information that could have been gleaned from the past.
Some say, given the number of red flags raised over the years, the site should not have been considered safe by state and local governments, and perhaps left undeveloped.
A 2010 report commissioned by Snohomish County warned that the neighborhoods along Steelhead Drive were at great risk for being affected by a mudslide.
“For someone to say that this plan did not warn that this was a risk is a falsity,” Rob Flaner, one of the report’s authors, told the Seattle Times.
There were other reports of the area’s potential for disaster as far back as the 1950s.
More recently, in 1999, a report filed to the Army Corps of Engineers warned of “the potential for a large catastrophic failure.”
“Frankly, I was shocked that the county permitted any building across from the river,” one of the authors of that report told the Seattle Times.
Others had also warned that years of logging could weaken the root system of the hill and lower the ability of trees to absorb water, increasing the likelihood that the land could move if it was heavily saturated.
“In 1988, when they were logging, I wrote a letter to the [Washington State] Department of Natural Resources that said it could fail catastrophically,” said Paul Kennard, a geomorphologist with the National Parks Service who had previously worked for the fisheries department of the Tulalip Indian Tribes, which has citizens located in Snohomish County.
The hill where the landslide occurred, part of the larger mountain, was even known as “Slide Hill” by some local residents, and geologists called the area different names, including “Hazel Landslide,” and “Steelhead Haven Landslide.”
The widespread knowledge of the hill’s vulnerability has led many to question why local authorities permitted housing in the area.
However, Snohomish County Department of Emergency Management leader John Pennington defended the county’s actions earlier this week, saying that residents were well aware of the potential for a landslide, that the area was “considered very safe” and that this slide “came out of nowhere.”
The county's Department of Emergency Management and the Snohomish County Department of Planning and Development Services would not comment for this story.
But others say the warnings were clear enough that more could have been done.
“We need better communication between experts looking at risks like this and the people issuing building permits,” Heiken said. “The people who issued permits to the people living in this area were essentially issuing death sentences.”
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