WOODSON - The major landslide that damaged several homes and blocked traffic on U.S. Highway 30 near Clatskanie Dec. 11 was caused by heavy rain, as well as water and debris buildup behind an old railroad grade, according to the Oregon Department of Forestry.
The possible effect of nearby timber clear-cuts is still unclear, said Kevin Weeks, an ODF public information officer.
Bill Burns, engineering geologist at the Oregon Department of Geology and Mineral Industries, said that landslides are affected by multiple factors, including vegetation, geology, slope and precipitation.
"To say clear-cuts caused the whole thing is not giving someone the entire picture," he said. "It's not something you can simply point your finger at and say, 'That's the cause of the problem.'"
Burns said the timber harvests and other factors likely contributed to the slide, but it's unclear whether the event would have occurred even if the trees were not removed, he said.
"We don't know the answer to that question," said Burns.
That conclusion is quite different than one printed on the front page of Tuesday's edition of The Oregonian, which referred to the two clear-cuts on Oregon State University land as the "initial trigger" that "set into motion last week's torrent of mud and debris..."
Burns said The Oregonian never asked him whether the landslides were the direct cause of the landslide. That conclusion was made without attribution in the article.
As for the Oregon Department of Forestry, the agency cannot confirm what effect the clear-cuts had on the landslide, said Weeks.
"We're still evaluating what role having a timber harvest had," said Weeks. "It's too early to draw any conclusions whether that led to the debris flow occurring."
The Oregonian made that conclusion on its own, he said.
Weeks said that two significant harvests occurred in the vicinity of the railroad grade. One area was logged in 1992, and the other in 2004; both were subsequently replanted per Forest Practices Act regulations, he said.
Research conducted by the ODF after the massive flooding and landslides in 1996 indicated that tree stands younger than 10 years and older than 100 years had a higher potential of experiencing landslides, Weeks said.
The Oregon Department of Forestry was first notified of the danger a day before the actual slide occurred by Eric Evenson, who owns the property where the railroad grade was located, said Dan Postrel, ODF's agency affairs director.
A culvert beneath the railroad grade had clogged, causing water and debris to collect behind it and eventually burst through the soil, he said. Luckily, the agency was able to evacuate the area before the slide occurred, and nobody was hurt, Postrel said.
"A real key message is that many areas in the Coast Range have steep slopes, and landslides are part of that landscape," he said.
The situation was also aggravated by the foot of rain that the region received in the 48 hours prior to the actual collapse, said Weeks. "It really can't be overlooked."
While the jury is still out in regard to the Clatskanie landslide, ODF expects to have a final analysis complete by the end of December, he said.