OSO — Authorities have closed Highway 530 until at least Monday while they keep watch for further movement on a soggy, sloughing hillside.
Both directions of the highway are shut down between Oso Loop Road and C-Post Road near Darrington.
State geologists recommended the shutdown after watching the ground shift on a hillside an estimated 4 feet during the past week. Authorities are concerned about potential dangers for passing motorists and about 10 nearby homes.
The cracking ground is on the south side of the highway, southwest of where a massive mudslide came down three years ago, killing 43 people and injuring others.
Geologists along with representatives from the county and other agencies returned to the area Saturday, but detected no major changes.
“If no further movement happens on the slope, we’ll be able to open on Monday morning,” said Dave McCormick, an assistant regional administrator of maintenance and operations for the state Department of Transportation.
The precautionary closure started around 8 p.m. Friday in the area of Montague Creek.
Several families left for the night after Oso firefighters warned of the danger. Most of the potentially threatened houses are along Whitman Road, on the opposite side of Highway 530 and across the Stillaguamish River from the unstable slope.
For now, Darrington is only accessible from the west by Highway 20 in Skagit County. That’s likely to add up to 90 minutes to some commutes. The Mountain Loop Highway isn’t likely to reopen until later this spring.
“I hope it doesn’t go beyond Monday, but there’s not much we can do about it if it does,” Darrington Town Councilman Kevin Ashe said. “It’s a concern, but we’re just going to have to wait and see what happens.”
The detour echoed the isolation the community faced in 2014, following the deadly mudslide. Highway 530 remained buried under mud and debris, and blocked to traffic. It took a month for an emergency bypass road, which was built to help disaster crews, opened up for limited public use. A one-lane stretch of the highway reopened at the end of May of that year. Highway 530 did not return to full function until six months after the disaster.
The new slide problem involves about 25 acres on private land, said Dave Norman, the state geologist with the Department of Natural Resources. DNR has an easement through the area along an unpaved road that leads to nearby forest lands.
The site is about a mile and a half west of where the hillside collapsed in 2014, burying a portion of the North Fork Stillaguamish River, the Steelhead Haven neighborhood and Highway 530.
“This is a smaller landslide,” Norman said. “It doesn’t have quite as much of the elevation.”
The deadly 2014 mudslide involved a 600-foot-tall slope. This one is approximately 345 feet tall, he said. The soil characteristics are similar, with layers of glacial deposits on top of clay. The ground is saturated from recent heavy rains.
A geologist from the state first observed cracks in the area on Tuesday and made measurements, Norman said. DNR geologists spotted more cracks on Friday. Locals also noticed fallen trees.
Those are all signs that the ground is shifting. The questions is what comes next.
“We don’t know whether it’s moving gradually or moving in lurches and episodic,” Norman said.
The slope is one of many geologists are watching throughout the state. Concerns are heightened because of the valley’s history. The hillsides are scarred from numerous slides in modern times and also bear marks from prehistoric events that make what happened in 2014 appear small.
Assistant Oso Fire Chief Toby Hyde helped lead his community’s response to the 2014 disaster. As in the past, the community will be resilient, ready to work together and pull through.
“Now that we have this local knowledge, we have to be on the other side of caution,” Hyde said. “We have a great, supportive community. When we come knocking on their door, they listen to us.”