The deadly mudslide in Washington that buried the rural community of Oso March 22 may have been caused by logging above the slope that collapsed.

The Seattle Times reports that a nearby plateau has undergone logging for nearly a hundred years, and that the slope had reportedly become unstable in recent years, possibly a result of too much water entering the soil because of tree removal. And yet, logging was still authorized by the state as recently as 2004.

There have been landslides in the area since at least the 1940s. In 1988, private landowner Summit Timber sought approval from the state Department of Natural Resources (DNR) to log above the slope. But experts warned the plan could be dangerous.

Paul Kennard, a geologist for the Tulalip Tribes, told the state that harvesting could lead to “the potential for a massive and catastrophic failure of the entire hillslope.” Concerns expressed by Kennard and other scientists forced DNR to halt Summit Timber’s logging in August 1988.

Sixteen years went by before another property owner, Grandy Lake, applied for a permit to clear a 15-acre tract near the plateau’s edge. The proposal was rejected at first, but then DNR approved it after Grandy Lake agreed to harvest half as many trees as it originally intended.

But the cutting, which concluded in 2005, wound up bordering the slope that collapsed, and even ventured into a “restricted” zone where no trees were to be removed because of the risk of groundwater eroding the slope.

The following year, a large landslide occurred next to the area that gave way on March 22. The 2006 slide released so much mud that it diverted the Stillaguamish River.

The death toll from the recent slide stood at 28 as of March 30, with another 30 people still reported missing.

-Noel Brinkerhoff

To Learn More:

State Allowed Logging on Plateau Above Slope (by Mike Baker, Ken Armstrong and Hal Bernton, Seattle Times)

Logging OK’d in 2004 May Have Exceeded Approved Boundary (by Mike Baker and Justin Mayo, Seattle Times)

Concern Over Landslide-Logging Connection Near Oso Is Decades Old (by John Ryan, KUOW)

Risk of Slide ‘Unforeseen’? Warnings Go Back Decades (by Ken Armstrong, Mike Carter and Mike Baker, Seattle Times)