This week’s spate of mudslides blocking roads and railroad tracks might end soon, as drier conditions give soggy soil a chance to drain.

Share story

This week’s spate of mudslides blocking roads and railroad tracks might end soon, as drier conditions give soggy soil a chance to drain.

The National Weather Service predicted a chance of showers varying between 20 percent and 50 percent the next two days, followed by rain on Sunday, then intermittent or light showers early next week.

“We’re not really forecasting anything too heavy for the next couple days,” said meteorologist Johnny Burg. The rainfall could total only a half-inch he said.

Most Read Stories

Unlimited Digital Access. $1 for 4 weeks.

A few hours of sunbreaks reduced landslide risks across the Seattle-Everett region by Thursday afternoon, according to U.S. Geological Survey rainfall data. But the soil remained saturated enough to cause slide risk, a USGS chart said.

Fallen dirt and trees closed three Seattle-area transportation routes Thursday:

• Westbound Interstate 90 approaching Issaquah, which fully reopened at 2:45 p.m. Thursday, after a slide covered the freeway with up to 2 feet of debris about 5 a.m. For most of the day, only one left lane operated, while commuters detoured through two-lane suburban roads.

On Friday the right lane will close at 9 a.m., so crews can add additional crushed rock on the hillside, said spokesman Travis Phelps.

• Sounder North commuter trains between Everett and Seattle, where a late Wednesday slide caused service to be suspended Thursday and Friday, with a likely reopening Monday. Substitute buses will serve the stations.

• Maple Valley Highway approaching Renton and the Interstate 405 junction. Eastbound lanes reopened at 1:30 p.m. and one westbound lane reopened by 3:30 p.m.

All three mudslides were shallow and not located in notoriously unstable areas — unlike past railway disruptions along Mukilteo cliffs, or the giant Oso mudslide that claimed 43 lives in 2014.

In West Seattle, Highland Park Way Southwest remains closed between Southwest Holden Street and West Marginal Way Southwest after a slide on Wednesday. It is expected to reopen by late Friday afternoon, according to the Seattle Department of Transportation.

Another slide closed Pioneer Road in Puyallup all day Thursday, and possibly into Friday, the city said. The blockage is one mile south of the Highway 167/410 junction, the most recent of several slides in that area.

In Southwest Washington, a slide closed northbound Interstate 5 near Woodland, Cowlitz County, about 4 p.m. Thursday. Two lanes were reopened after 9 p.m.

A slide closed northbound Interstate 5 near Woodland, Cowlitz County, for several hours Thursday afternoon. (Photo courtesy of Washington State Patrol)
A slide closed northbound Interstate 5 near Woodland, Cowlitz County, for several hours Thursday afternoon. (Photo courtesy of Washington State Patrol)

Travis Phelps, spokesman for the Washington State Department of Transportation, compared the Issaquah incident to frosting that falls off a cupcake.

The most unstable place was 50 feet above I-90, where WSDOT crews unclogged a culvert and dumped rock to replace waterlogged soil, Phelps said. Creeks and ditches overflowed onto a park trail, where rushing water broke through the hillside, he said.

University of Washington geomorphology professor David Montgomery, author of Dirt: The Erosion of Civilizations, said severe downpours can trigger “shallow soil slides.” Such slides often result from late-season rainfall, as soil moisture accumulates, he said.

“There’s lots of places that are vulnerable, but in any given winter, some will go,” he said.

Sounder service was first disrupted by a small debris flow near Carkeek Park that prompted transit operators to reverse a northbound train around 6 p.m. and send it back to King Street Station, after three evening trains had already passed.

Sound Transit learned later that was a “nonblocking” slide, said Sounder operations manager Martin Young.

Nonetheless, he said officials were discussing a pre-emptive safety shutdown ­— until a larger slide around 11 p.m. made that decision inevitable.

Sound Transit announced a safety protocol in December 2014 — after sliding mud knocked a freight train off-track near Everett — to consider canceling Sounder North service on days that U.S. Geological Survey data show slide hazards, in two of three criteria.

It did suspend north-line Seahawks gameday service one Sunday that month and considered it two other times.

But even Wednesday night, the USGS measurements for 15-day cumulative precipitation, and the intensity of the downpour, were still below hazard levels, though soil wetness exceeded the safe levels, Young said.

Young said trackside monitoring stations, and reports from railway workers, also inform the decisions, and Wednesday’s slide wasn’t in a typical slide zone.

So far this season, only 41 train trips will be canceled by week’s end. That compares with 207 cancellations in the worst season for trackside slides, Oct. 1, 2012, to March 31, 2013, he said.

That season, the agency’s citizen oversight panel flagged mudslides as a drag on ridership. Longtime critic John Niles has urged a rainy-season shutdown.

Since then BNSF Railway has reinforced four frequent-slide areas around Mukilteo, aided by a $16 million state grant.

“What would have been on the tracks is held back,” Young said. “In those locations that were historically problematic, in fact we’ve had no slides.”