OSO — The state’s top forestry official on Friday said a 2005 timber harvest is not the cause of the fatal Oso mudslide.
A clear-cut area on the hill above the Steelhead Haven neighborhood has led to finger-pointing about the role it may have played in the March 22 disaster, in which at least 30 people died.
“This is speculative and ignores the factors that expert geologists generally recognize as the primary causes of deep-seated landslides,” state Forester Aaron Everett said. “In this instance, these include the inherently unstable geology of the Stillaguamish River Valley, the ongoing erosion of the toe of the hill slope by the river, and near-record rainfall in March.”
Water fuels landslides around here. Clear-cutting trees lets water soak into the ground, which can build up over years.
The area north of the slide was heavily harvested by the land’s previous owner, Summit Timber in the late 1980s.
In 2004, the current owner, Grandy Lake Forest Associates clear-cut a 7.5-acre site. Starting in 2009, it thinned some of the areas that were clear-cut more than 20 years earlier, said Ken Osborn, whose company, Arbor-Pacific Forestry Services, of Mount Vernon, manages Grandy Lake Forest Associates’ land.
“I’m 100 percent convinced that geologists are correct in that it was a perfect storm of heavy rains, weak soils and washing out the toe of the slope,” Osborn said Thursday.
In 2004 he followed state rules and brought in two experts — geologist Dan Miller and Pat Stevenson, environmental manager for the Stillaguamish Tribe — to make sure timber wasn’t taken that would increase the chances for a landslide on the hill overlooking the neighborhood.
“I was out there with those two, and I know that was our focus,” Osborn said.
About half the proposed harvest area was inside the state’s boundary for restricted logging because it could affect how much water went into the ground. Wetter soils are more likely to slide.
Miller proposed monitoring to see what the effects could be.
Instead, it was more efficient to eliminate those areas from the timber permit application, which the state later approved, Osborn said.
“Ken must have really been trying to do the right thing if he brought Pat and me out there,” Miller said, recalling their walk.
A 1997 analysis he conducted for the Department of Natural Resources, Miller said, told him a bigger chunk of the hill needed to have tighter logging restrictions, to keep more water from soaking into the ground.
Miller said he believed the state had changed its map based on his analysis. That wasn’t the case.
It is not at all clear, though, that timber harvests increased the likelihood of a landslide, he said.
Randall Jibson, a research geologist with the U.S. Geological Survey, said this week that logging did not factor into the landslide.
“This has nothing to do with logging — this landslide was a couple of hundred feet deep,” Jibson told the Wall Street Journal.
Still, there is plenty more studying ahead to determine causes and effects. “Since we haven’t done the work, we can’t rule out any factors,” said Jonathan Godt, one of the USGS geologists on site.
Dan Catchpole: 425-339-3454; firstname.lastname@example.org; Twitter: @dcatchpole.