By Jonathan Kaminsky
DARRINGTON, Wash., March 27 (Reuters) - Ken Root used to live just five minutes west of Steelhead Drive, an idyllic spot on the North Fork Stillaguamish River in Washington state that was washed away in a deadly landslide last Saturday.
"I got the hell out. I'm really glad I don't live there any more," said Root, 60, who moved eight years ago and took his insulation business 15 miles down the road to Arlington, partly because he feared landslides and floods in the valley.
"I've lived right on the riverbank and I did have some nightmares about my house falling into the river," he said of his old home, which was not affected by the weekend landslide.
Root was just one of as many as 30,000 inhabitants of hilly Snohomish County - equal to 5 percent of the total county population - who are exposed to some kind of landslide risk, according to a report commissioned by the county in 2010. But unlike Root, many others have chosen to stay put despite the risks.
Because of glacial sediment and sand, vast tracts of Washington state are susceptible to landslides, said Daniel Miller, a geomorphologist who wrote a study of the Oso area in 1999 and warned of potential catastrophe.
"Here in Washington, right around Seattle, there are areas that are built on sand. The potential for very large landslides exists in many areas of the United States," said Miller.
Far from Oso, a slow-moving landslide hit the Washington state town of Kelso in 1998-1999, damaging 138 homes and causing more than $30 million in damage, with no casualties.
Killer landslides have hit elsewhere in the country as well. In 1969 slides and flooding in Virginia killed 150 people, and a California landslide killed 10 in 2005.
Beyond the immediate area around Oso, the U.S. Geological Survey has estimated that about 30 percent of the land area in the lower 48 U.S. states has some exposure to impact from landslides, though not necessarily in populated areas.
In Washington state, a map included in the 2010 Snohomish County report shows the area around Oso as one of hundreds highlighted in red as high-risk 'landslide hazard' zones. Nearly all of the lightly populated valley linking the towns of Arlington and Darrington is shaded yellow, representing 'landslide potential'.
LITTLE SLICE OF PARADISE
Many residents know the risks, but are willing to trade uncertainty for a slice of paradise, even after Saturday's slide that has so far claimed at least 25 lives and left 90 people missing.
The combined effects of rivers eroding the bases of soft, unstable glacial sediment and years of rainfall mean that attractive spots, such as hilltops or riverbeds in steep valleys, may also be the most vulnerable.
"The mountain up there, you can't do better," said Gerald Howard, 72, a retired sawmill plant manager living in a section of eastern Darrington, on the cusp of the yellow and red zones. "The water's clean, the air is clean."
Robin Youngblood, 63, who survived when her house was ripped from its foundations and carried a quarter mile by a wall of mud, said she was not aware of the heightened risk or that a report documenting the hazards had been circulated to authorities in 1999.
"Nobody told any of us," she told CNN. "Those houses on Steelhead Drive were built after they got that geology report. This is criminal as far as I'm concerned."
Some residents are more sanguine.
"A lot of us moved out there for the solitude," said Pete Carlson, 56, a machinist who chose a house less than a half mile from the slide area seven years ago and has no plans to leave. "No matter where you move, there's something. Earthquakes, volcanoes ... you just don't know."
Nels Rasmussen, a chiropractor who lives a few miles east of Oso, said mudslides were a fact of life, but a big one was always considered unlikely.
"I've had that fear ever since I've been in this area," he said. "I tried to deliberately get a place not too close to the river and not backed right up against the mountain."
A number of smaller slides near Oso, most recently in 2006, and a catalog of geological reports from the 1950s make clear the steep hill above Steelhead Drive was vulnerable to a catastrophic collapse. But most residents did not seem overly concerned, and were not asked to move by local authorities.
"It's just that one area that's prone to it, not the whole valley," said one woman who works at Hesby & Daughters Mill Co, which makes wooden garden structures a few miles east of Oso.
Local governments cannot effectively tell people where they can and cannot live, said Tracy Drury, a geomorphologist who wrote a report presented to the Army Corps of Engineers in 2000 warning of a potential "catastrophic failure" of the hill.
Drury, who helped construct a barrier of logs and concrete blocks between the 'toe' of the slope and the river to prevent further erosion after the 2006 slide, said he was surprised development had continued.
"The fact that the 2006 slide came down really slowly may have given them a sense of security," Drury said of the residents. "This one didn't come slow, it came like a wall."
Snohomish County's emergency management director, John Pennington, has said the Oso community understood the risks, yet he also described Saturday's slide as unforeseen. Miller, who wrote the 1999 report, said the truth may lie somewhere in the middle.
"It depends what timeframe you are looking at. If you are a geologist who thinks in terms of thousands of years, it is inevitable," he said. "If you are a county planner who's thinking in terms of less than a human lifespan, it's very improbable." (Writing by Bill Rigby in Seattle; Editing by Cynthia Johnston and Gunna Dickson)