The slide is blocking westbound lanes of Interstate 90 traffic in Issaquah. No injuries were reported.
UPDATE 4:28 p.m.:
All lanes of westbound Interstate 90 reopened at 2:45 p.m. just east of Issaquah, where an early-morning soil slide covered the roadway with up to 2 feet of debris.
For most of Thursday, only one far-left lane stayed open, as morning commuters detoured through clogged, two-lane suburban roads.
Crews for the Washington State Department of Transportation (WSDOT) unclogged a culvert and dumped crushed rock to replace waterlogged soil, said WSDOT spokesman Travis Phelps. The worst spot was about 50 feet above the freeway, where creeks and ditches overflowed into a park trail, he said.
The right lane of westbound I-90 will close again at 9 a.m. Friday, he said, so workers can drop more crushed rock on the hillside, Phelps said.
A mudslide has closed all but one westbound lane of Interstate 90 in Issaquah after 13 vehicles got stuck in the mud, with one vehicle high-centered on a rock, said Rick Johnson, a State Patrol trooper.
There were no injuries, Johnson said Thursday morning.
Traffic is being diverted to Highway 202, according to the Washington State Department of Transportation (WSDOT).
The slide happened east of Sunset Way just before 5 a.m. and snarled the morning commute, with traffic backing up for more than a mile before 6 a.m. Crews scraped the mud to open one lane of traffic by 7 a.m, but it was closed again about 7:45 a.m., only to reopen about an hour later.
There is no estimated time for all westbound lanes to reopen.
Electrician Austin Taylor was commuting to Kirkland in his BMW when he hit the slide at highway speeds.
Bending his rims, denting his fenders and undercarriage, he spun around and ended up in the median. He was happy not to be injured.
“I saw some taillights blink but that was it — too late to slow down,” he said.
Geotechnical inspectors have arrived near I-90 to examine that slide and determine whether more are likely to occur, said spokesman Travis Phelps of WSDOT, at 9:45 a.m.
“We need to make sure this hillside is safe and stable before we open it to traffic,” Phelps said.
WSDOT currently thinks the slide was a relatively shallow “debris flow,” which Phelps compared to the frosting falling off a cupcake. The top layer of soil became supersaturated from rain along with flowing water atop a slope, he said.
It’s not a known slide area where an entire hillside has broken apart, Phelps said, and added that there are no plans for a temporary slide barrier.
One to 2 feet of mud, rocks, and woody debris was in the roadway Thursday morning. The area was not known to be a historic slide area, Phelps said.
The cause of the slide was heavy rainfall.
“This is more of a water issue, and there seems to have been some water diverted there, too,” Phelps said.
Heavy rain — and other slides
The National Weather Service issued a landslide warning for Western Washington as rainfall totals for the month inch toward a record high.
After a slide, authorities canceled the north-line Sounder trains between Everett and Seattle Thursday morning and do not expect to run trains again until Monday morning.
Another mudslide blocked Maple Valley Highway, a busy traffic route approaching downtown Renton, on Thursday morning. Eastbound lanes reopened about 1:30 p.m.
In Puyallup, a tree and small mudflow blocked East Pioneer Way, a mile south of the Highway 167/410 interchange. The city anticipates a possible early afternoon reopening.
A mudslide in Seattle’s Delridge neighborhood closed Highland Park Way Southwest on Wednesday. The roadway, which connects southern West Seattle to the Duwamish area and Highway 599, will remain closed all day Thursday, according to the Seattle Department of Transportation.
Seattle Times photographer Steve Ringman contributed to this report.