Rescue workers at one of the number of homes that were wrecked by the mudslide. Credit:AP 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 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." Dr Miller has done analyses for the Environmental Protection Agency and US Forest Service, and was hired by King County in the 1990s to map out its geologically hazardous areas. 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," Mr Pennington said. "This was a completely unforeseen slide. This came out of nowhere."

Brenda Neal, right, looks at aerial photos of the landslide for her missing husband's car. Credit:Reuters The 2006 slide took place in winter, on January 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 Dr Miller soon after the landslide. "We were surprised." Search and rescue personnel continue working the area that was hit. Credit:AP 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 30 to 60 centimetres above "base flood elevation" according to county building-permit records. Another home was built in the neighbourhood in 2009.

Snohomish County Executive John Lovick and Public Works Director Steve Thomsen said on Monday night they were not aware of the 1999 report. "A slide of this magnitude is very difficult to predict," Mr Thomsen said. "There was no indication, no indication at all." An aerial view of the massive mudslide. Credit:AP 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 grandchildren. But they were not there on Saturday when the mudslide wiped out the mobile home and swept away neighbours who are now missing and presumed dead. Mr 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. Darrington High School students make posters following the deadly mudslide. Credit:AP

"That's like saying the river is going to flood," Mr Wood said. "If the hillsides were going to slough away, they were going to slough away. That's kind of what happens around here." 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 300 metres long and took out about 790 metres of the river bank, according to the Shannon report. The scarp - the face of the cliff where the slide broke away - was 21 metres 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. The Shannon report 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. The report 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, Mr 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. 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." He noted that a 45-metre section of the scarp wall had caved, resulting in a dangerous mudflow of the same sort - albeit small in comparison - that rescuers are facing today. "Travel across the slide surface is extremely treacherous," he wrote, "because of hidden 'pockets' of saturated material that will not support a man's weight." Saturday's monster slide left a scarp of nearly , 183 metres 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 130 metres to the south, providing more buffer at the base of the hillside. The landslide, however, moved the river 222 metres. In the northern summer of 2006, crews installed a 396-metre "crib wall" of boom logs - some more than 90 centimetres in diameter - anchored with 4000 kilogram concrete blocks every 15 metres. 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." Mr Drury, the environmental engineer, and Mr 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," Mr Drury said. Loading Mr 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. MCT