The slow-moving landslide that sparked home evacuations and shut down state Route 530 near Oso over the past few days has stopped moving — but the land is still unstable and the highway will remain closed until at least Thursday.
Geologists and state and local authorities have been investigating since they discovered 6-inch-wide cracks in a hillside road early last week in a rural part of Snohomish County near Oso. Then on Friday, the Department of Natural Resources discovered the hillside had dropped about 4 feet after heavy rains, while the crack in the road had grown.
Residents of eight homes voluntarily evacuated, while the state shut down a 3½-mile stretch of SR 530 between Oso Loop Road and C-Post Road. The moving hillside is about 300 feet above the highway.
After the hillside stopped moving Saturday, authorities had said they might be able to reopen the highway by the Monday morning commute.
But the Washington Department of Transportation on Sunday said there was still an unstable slope above the southwest side of the highway, and the road would remain closed until at least Thursday.
Officials said they had not detected any additional movement from the landslide on Sunday — the second straight day the land stayed put — but geologists still think the hill could move again.
“If the entire 24-acre slide were to give way, it could completely cover SR 530 and potentially reach Whitman Road” to the north, Dave McCormick, the department’s assistant regional administrator, said in a statement. “We know this is huge disruption to the lives of those who live and work in the Stillaguamish River Valley, but there’s still a heightened risk that this slide could still move.”
The remote area does not have good alternative transportation options. The detour route — using state Route 20 to the north — will add at least one hour to one-way trips between Oso and Darrington, the department of transportation said.
No injuries or property damage have been reported.
The slide is about 1.5 miles southwest of the 2014 slide that killed 43 people in Oso on the opposite side of the highway.