Risk of slide ‘unforeseen’? Warnings go back decades
TIMES WATCHDOG: While a Snohomish County official said the area hit by the mudslide “was considered very safe,” the hillside’s history of slides dates back more than 60 years. One expert says he was shocked when homebuilding was permitted after a big 2006 slide.
Seattle Times staff reporters
Since the 1950s, geological reports on the hill that buckled during the weekend in Snohomish County have included pessimistic analyses and the occasional dire prediction. But no language seems more prescient than what appears in a 1999 report filed with the U.S. Army Corps of Engineers, warning of “the potential for a large catastrophic failure.”
That report was written by Daniel J. Miller and his wife, Lynne Rodgers Miller. When she saw the news of the mudslide Saturday, she knew right away where the land had given way. Her husband knew, too.
“We’ve known it would happen at some point,” he told The Seattle Times on Monday. “We just didn’t know when.”
Daniel Miller, a geomorphologist, also documented the hill’s landslide conditions in a report written in 1997 for the Washington Department of Ecology and the Tulalip Tribes. He knows the hill’s history, having collected reports and memos from the 1950s, 1960s, 1980s and 1990s. He has a half-dozen manila folders stuffed with maps, slides, models and drawings, all telling the story of an unstable hillside that has defied efforts to shore it up.
That’s why he could not believe what he saw in 2006, when he returned to the hill within weeks of a landslide that crashed into and plugged the North Fork of the Stillaguamish River, creating a new channel that threatened homes on a street called Steelhead Drive. Instead of seeing homes being vacated, he saw carpenters building new ones.
“Frankly, I was shocked that the county permitted any building across from the river,” he said.
“We’ve known that it’s been failing,” he said of the hill. “It’s not unknown that this hazard exists.”
Miller has done analyses for the Environmental Protection Agency and U.S. Forest Service, and was hired by King County in the 1990s to map out its geologically hazardous areas.
“Considered very safe”
His perspective stands in contrast to what John Pennington, head of Snohomish County’s Department of Emergency Management, said at a news conference Monday. “It was considered very safe,” Pennington said. “This was a completely unforeseen slide. This came out of nowhere.”
The 2006 slide took place in winter, on Jan. 25. Three days later, as the new channel cut the land, “residents and agency staff reported the eerie sound of trees constantly snapping as the river pushed them over,” wrote the Stillaguamish Tribe’s Natural Resource Department on its website. But the sound of construction competed with the sound of snapping trees.
“They didn’t even stop pounding nails,” said Tracy Drury, an environmental engineer and applied geomorphologist who assessed the area with Miller soon after the landslide. “We were surprised.”
At least five homes were built in 2006 on Steelhead Drive, according to Snohomish County records. The houses were granted “flood hazard permits” that required them to be jacked up 1 to 2 feet above “base flood elevation,” according to county building-permit records. Another home was built in the neighborhood in 2009.
Snohomish County Executive John Lovick and Public Works Director Steve Thomsen said Monday night they were not aware of the 1999 report. “A slide of this magnitude is very difficult to predict,” Thomsen said. “There was no indication, no indication at all.”
Irvin Wood and his wife, Judith, of Bothell, owned the last home permitted in the slide zone, a double-wide mobile home they bought and moved onto a forested lot last year.
The Woods used the property as a weekend getaway, sometimes bringing their grandkids. But they were not there on Saturday when the mudslide wiped out the mobile home and swept away neighbors who are now missing and presumed dead.
Wood, who has owned other property in the area for decades, said “nobody was warning anybody” about the probability of a massive landslide. But he said it was “an unrealistic expectation” for people to think the government could prevent such disasters.
“That’s like saying the river is going to flood,” Wood said. “If the hillsides were going to slough away, they were going to slough away. That’s kind of what happens around here.”
Named for landslides
The hill that collapsed last weekend is referred to by geologists with different names, including Hazel Landslide and Steelhead Haven Landslide, a reference to the hillside’s constant movement. Some residents, according to a 1967 Seattle Times story, referred to it simply as “Slide Hill.”
After two landslides on the hill — one in 1949, another in 1951 — two state agencies, the Department of Game and the Department of Fisheries, commissioned a report from Seattle engineering firm William D. Shannon and Associates.
The 1949 slide was nearly 1,000 feet long and took out about 2,600 feet of the river bank, according to the Shannon report. The scarp — the face of the cliff where the slide broke away — was 70 feet tall in places. There were no injuries and no reports of structural damage.
In 1951, debris from the denuded slide area formed a mudflow that partially dammed the river. Shannon noted that the two creeks in the area are known as “Slide Creek” and “Mud Flow Creek.”
The Shannon report was not commissioned out of safety concerns but over complaints that sediment from the slide was clogging the river and degrading the salmon fishery.
Shannon concluded that a main cause of the slides is the river eroding the “toe” of a previous slide, which supports the millions of tons of dirt behind it, like someone with their back against a bulging door. Eventually, the toe would fail and gravity would pull the mountain down again.
Asked if there was a way to control the slides, Shannon wrote that one possibility would be permanently diverting the river.
He also suggested building berms and reinforcing the slide area. However, he noted that a professor he had hired to look at the issue from a geological standpoint, Howard Coombs of the University of Washington, concluded that any fix would likely be temporary and that the slide area could be expected to expand.
“It is almost impossible from a practical standpoint to stabilize this slide in its present position. The slope will continue to slide and the area will increase,” Coombs concluded in an addendum to the Shannon report. “Drainage ditches, dikes, walls, etc., would give at best only temporary relief. The structures would need constant repair and replacement.”
State records show that “no actual embankment control measures were done until the fall of 1960. At that time more than a thousand feet of berm was constructed at the upstream end of the slide,” using rocks and other material.
The berm was “largely destroyed” by high water in the Stillaguamish the following year, state records show.
In 1962, the state installed a “revetment” — a sort of rock barrier — to try to protect and support the riverbank. But oozing mud “overtopped” the barrier two years later. In 1967 the barrier was buried when a massive slide hit, damaging dozens of homes.
In 1969, a geologist with the state Department of Natural Resources, Gerald Thorsen, submitted a memorandum after visiting the site of the slide. He explained that “aerial photographs taken as far back as 1932 show the river has cut at this clay bank for many years.”
Thorsen noted that a 150-foot section of the scarp wall had caved, resulting in a dangerous, several-hundred-foot mudflow of the same sort — albeit small in comparison — that rescuers are facing today.
“Travel across the slide surface is extremely treacherous,” Thorsen wrote, “because of hidden ‘pockets’ of saturated material that will not support a man’s weight.”
An investigation done in the 1980s said the landslide activity had expanded from 10 acres in 1942 to 35 acres in 1970.
Saturday’s monster slide left a scarp of nearly 600 feet, about nine times taller than the 1949 slide and four times taller than the one in 1967.
The 2006 slide disrupted risk-mitigation projects already in the works. Officials planned to move the river’s flow 430 feet to the south, providing more buffer at the base of the hillside. The landslide, however, moved the river 730 feet.
In the summer of 2006, crews went on to install a 1,300-foot “crib wall” of boom logs — some more than 3 feet in diameter — anchored with 9,000-pound concrete blocks every 50 feet. The wall was designed to protect fish by preventing sediment from washing into the river.
It was no match for this week’s mudslide.
“We always thought there was a possibility that a catastrophic event could come,” said Pat Stevenson, environmental manager of the Stillaguamish Tribe. “We were hoping that wouldn’t happen.”
Drury, the environmental engineer, and Stevenson said there were discussions over the years about whether to buy out the property owners in the area, but those talks never developed into serious proposals.
“I think we did the best that we could under the constraints that nobody wanted to sell their property and move,” Drury said.
Stevenson said county officials who approved development seemed more focused on whether the homes were in flood areas than on the risk of a landslide.
Lucky to be alive
Ron and Gail Thompson moved into a one-bedroom cabin on five acres on Steelhead Drive in 2003, said their daughter, Jennifer Johnson, of Arlington.
When the 2006 mudslide hit the area, the Thompsons made soup and tater tots for Army Corps of Engineers officials and a TV news crew, Johnson said.
“I had conversations with the Army Corps of Engineers the last time this happened. They showed me a map and said Mom and Dad’s house would be safe,” she said Monday.
“When we moved them in there, I never in a million years, never in a billion years, thought about (a mudslide) ... Dad was like, ‘We’re going to be fine,’ and I just believed him.”
Johnson’s parents and 85-year-old grandmother left their house eight minutes before the slide hit on Saturday morning for a trip to Costco, Johnson said. The couple lost everything, including Ron’s new John Deere tractor and Gail’s Volkswagen.
“I don’t regret them living there. ... I hurt for my parents, but that’s where they wanted to be,” Johnson said.
Johnson said she won’t let her parents live on the water again.
“They are in mourning; they’re in shock,” she said. “They’re heartbroken for their neighbors.”
Reporters Sara Jean Green, Jim Brunner and Brian M. Rosenthal contributed. Ken Armstrong: email@example.com or 206-464-3730; Mike Carter: firstname.lastname@example.org or 206-464-3706.