State officials say they didn't approve clearcutting inside a no-logging zone directly above Saturday's deadly landslide in the town of Oso. But aerial photos show a clearcut extending into the zone where a loss of trees would heighten the risk of landslides.
Removing forest cover can increase the amount of rainwater that finds its way underground. Geologists say the extra groundwater can destabilize the already unstable soils deep beneath landslide zones.
Records obtained by the Seattle Times and by KUOW show that a clearcut in 2005 did take out trees inside that zone for the Oso slide. The question that remains is whether the Department of Natural Resources approved cutting where it shouldn't have, or whether the land owner cut beyond the boundaries approved by DNR.
The owner, Grandy Lake Forest Associates of Mount Vernon, could not be reached for comment. Grandy Lake proposed a 15-acre clearcut at the upper edge of the Oso landslide zone in 2004.
"We rejected that application," said Aaron Everett, a Washington State Forester. "The one that was approved in the end eliminated the part of the harvest that would have been inside the groundwater recharge area."
On Wednesday, Everett told KUOW that the resulting 7-acre harvest, also known as a clearcut, went right up to the edge of the groundwater danger zone.
"It is right outside the area that is essentially prohibited from harvest at the head of the landslide," said Everett.
On Thursday, Everett and his boss, Washington Lands Commissioner Peter Goldmark, declined to be interviewed. But their agency did release aerial photos showing a clearcut, shaped like a seven-acre slice of pizza, crossing over the edge of the official no-cutting zone.
The zone where it's officially unsafe to log might not be the same as where it's actually unsafe.
Without drilling wells deep into the earth, geologists can only make educated guesses how groundwater moves. Geologist Paul Kennard stated that nobody's drilled wells at the Oso site, so they can't say precisely which plots of land would funnel water beneath the landslide zone--and make it more prone to slumping downhill.
"I think since the groundwater recharge to the actual landslide has been changing and getting bigger over time, it's a bad idea to harvest right up to the edge of the current groundwater recharge area, especially if that is based on incomplete knowledge," says Kennard.
Kennard and fellow Seattle geologist Dan Miller have spent years studying the Oso landslide site. Miller says it's unlikely that just a seven-acre clearcut could trigger the 400-acre slide that destroyed a community on Saturday.
Much larger clearcuts were carved out of the forests above the slide in the 1980s. Geologists say it can take decades for the recovering forest to keep as much rain water out of the ground as it did before a clearcut.
Copyright 2014 KUOW