Massive landslide buries Highway 410 and Naches River

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By Melissa Sanchez and David Lester
Yakima Herald-Republic

NACHES, Yakima County — A "heaving, moving mass" of mud oozed across a section of Highway 410 Sunday, destroying at least two homes and changing the course of the Naches River, and the slide could continue to advance for several more days, officials said.

Transportation officials closed a 47-mile stretch of the highway from Mount Rainier National Park's Lake Tipsoo to its junction with Highway 12 west of Naches.

Emergency personnel said the landslide pushed chunks of earth and pavement into the Naches River, damming its width.

"The slumping of the hillside and the uplifting of the valley floor continues," state Department of Transportation regional administrator Don Whitehouse said in a news release Sunday. "It will take several weeks before we can have a new roadway constructed and ready for traffic."

Fear of flooding prompted the evacuation of dozens of nearby residents as the Naches River found its way around the slide and back into the river channel, said Robert Cunningham, a U.S. Bureau of Reclamation foreman who surveyed the area Sunday morning.

"The water is not backing up. It has rediverted over the Nile River Road and is taking its own course around the slide," he said.

Officials say it could be weeks before Highway 410 is reopened, and it is unclear when power will be restored to hundreds of residents along the route.

The slide, about 10 miles west of Naches just west of the Woodshed Restaurant, was estimated at a quarter mile wide and up to 30 feet deep.

Sliding south toward the Naches River at about 6 a.m. Sunday, it buckled the roadway, breaking it into huge slabs and pushing the asphalt into the Naches River.

Initial signs that something was happening on the hillside began around 2 p.m. Saturday, said DOT spokesman Meagan McFadden.

Nile Fire Assistant Chief Steve Smith noticed heaving in the driveway that leads to his home near the slide, officials said. Concerned about the movement, Smith left his home Saturday.

The home was engulfed in the slide Sunday morning.

With its normal channel blocked by the slide, the river flooded the south end of Nile Loop Road and the nearby area.

No injuries were reported, said Jim Hall of the Yakima County Department of Emergency Management.

While geologists assess the hill's stability, hundreds of people in the Nile area will likely remain without power for a few days. Pacific Power officials said they don't want to restore power until the ground stops shifting.

Authorities advised evacuation for all homes within a four-mile radius of Nile — including a boarding school for troubled youth — although a handful of residents chose to stay.

It is unknown when the 60 or so evacuated residents will be able to return home.

What caused the slide isn't known. There's been no discernible rainfall.

Calling it a "rotational landslide," State Patrol Sgt. Tom Foster said the blockage appears to be a result of earth shifting under the surface of the hillside, and not a classic landslide.

Soil from the slide area continued to slough off Sunday afternoon, according to Nile Fire Department Lt. Ty Brown.

"Our main concern is the river is changing its own channel, trying to find its own way around the slide. We are dealing with flooding in that area," Brown said. "Our next problem is to try to take care of the folks who live up the valley. They aren't going to have power for some time."

Pacific Power cut off power to about 800 residents as the slide knocked down power poles in the area, said Art Sasse, a utility spokesman in Portland. The move was an attempt to isolate the outage and prevent it from spreading as temperatures dipped below freezing at night, he said.

Emergency shelters were set up on both sides of the slide — at the Nile Valley Community Church and Naches High School.

Among those evacuated were 12 boys who live at the Flying H Ranch, a Christian residential program for troubled boys south of the Nile Loop Road off Highway 410.

Chris Rodriguez, a counselor at the ranch, described the slide: "It was like a knife had cut through the hill and moved everything to the side."

Some ranch employees who stayed behind after the evacuation reported some ranch buildings being threatened by water from the Naches River.

As the boys unloaded from a van at Naches High School, a dazed-looking family wandered into the parking lot.

"Our house got hit," said a woman in the family, before making her way into the school to speak with American Red Cross volunteers. "We knew we were going to get hit — we're right up against the hill."

Jesse Lanier, of Bremerton, was visiting family who live in the area of the Woodshed Restaurant. She said residents were told to evacuate shortly before 11 a.m. Sunday. "We saw some rocks coming down."

Emergency personnel and residents attempting to leave the area are using Bethel Ridge Road, a gravel road that connects the Nile area to U.S. Highway 12 to the south.

from: http://seattletimes.nwsource.com/html/localnews/2010044629_webmudslide11m.html

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By Sandi Doughton
Seattle Times science reporter

The landslide that smothered a stretch of Highway 410 Sunday could be among the largest ever to hit a state roadway, but its cause remains a mystery.

"I've been around for 25 years, and this is definitely one of the biggest," said Tom Badger, geotechnical engineer for the Washington State Department of Transportation (DOT).

Unlike the slides that pop up across Western Washington during rainstorms, the slide on the east side of the Cascades occurred on a clear morning. There was no earthquake in the vicinity, and DOT officials say they don't believe a local rock quarry destabilized the slope.

"To be honest, right now we're just trying to get our arms around this," Badger said.

A DOT map identifies Highway 410 east of Chinook Pass as a region prone to rockfalls. But the agency hadn't singled out the section that slid as a particularly risky slope.

"We haven't had any problems with this area until now," DOT spokeswoman Meagan McFadden said.

The highway west of the town of Naches probably will remain closed throughout the winter, McFadden said. The road will have to be rerouted around the massive pile of dirt and rock, which is up to 40 feet deep in places and covers more than one-quarter mile of pavement.

"Right now, it doesn't look like 410 will be where 410 originally was," McFadden said.

Engineers and geologists flew over the slide Monday and poked around its edges. They found that the slide has continued to move slowly downhill in some places.

"It's kind of creaking and groaning at this point," said Dave Norman, state geologist for the Department of Natural Resources (DNR). "Nobody would want to go up and stand on it."

By later in the afternoon, the main slide appeared to have stabilized.

But officials were keeping watch on an adjacent section of slope where cracks and stress fractures had appeared.

Construction will start today on a temporary dirt road to provide access for approximately 1,500 people who live along the Naches River and adjacent valleys.

The slide slammed into the river, and the riverbed itself was uplifted dozens of feet. Jason Smith, DOT's regional environment manager, found a chinook salmon and a rainbow trout high up in the pile of dirt.

Displaced from its banks, the river flooded over the Nile Loop Road, a main route for many local residents.

The director of the Yakima Valley Office of Emergency Management told the Yakima Herald-Republic that damage could run as high as $20 million.

The slide probably was a "rotational slump," University of Washington geologist David Montgomery said. A big hunk of the valley wall basically slid along a scoop-shaped fracture line. As the top of the slope slumped, the bottom was thrust upward.

Rotational slides can be triggered by rain — but it could be rain that fell a year ago or more. The water percolates deep into the ground, creating hidden weakness, Montgomery said.

"There can be months to years of delay," he said.

Gravel mining also can trigger major landslides if operations undermine the toe of an unstable slope, Montgomery said. "That is one of the textbook examples used as a general factor that contributes to slope instability," he said.

DNR inspectors saw evidence in the past of slope movement at the gravel pit in the slide area, Norman said. At the agency's request, the owners conducted an engineering survey and made regular measurements to detect slipping.

"The report concluded this was an area with some soil creep, but it didn't anticipate any kind of catastrophic failure," Norman said.

The operation, Simmons & Son Hauling and Rock Crushing, covered about 10 to 15 acres.

The quarry was on the western margin of the slide area. DOT officials say they believe the operation was too small to have undermined the slope.

Owner Robin Simmons was at the site a few hours before the hillside let loose.

"It was rumbling," she said. "Kind of like when kids drive by with these boom boxes in their cars." She and her staff worked frantically to move equipment, but soon were warned to evacuate.

The slide buried much of the pit and swallowed up a rock crusher, a crane and a loader.

"That was our livelihood, and it's gone," Simmons said.

Two nearby homes owned by family members were destroyed or damaged.

Simmons is convinced the pit was not at fault.

"Mother Nature did what she planned on doing."

from: http://seattletimes.nwsource.com/html/localnews/2010051939_landslide13m.html

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By Seattle Times staff

An emergency Nile Loop Road route around the landslide closure on Highway 410 near Naches, Yakima County, is open to all traffic, and a "residents only" restriction has been lifted.

Meanwhile, the state transportation department is working on a new route through the Nile Valley and around the massive landslide that covered the highway near Yakima on Oct. 11.

The emergency route, which detours around a four-mile section between mileposts 104 and 108, is a rough, gravel-surfaced road. State officials said the road could be closed at any time for safety if landslide activity or an increase in river flows is detected.

WSDOT says the most reliable access to restaurants, cabins and stores along the Highway 410 corridor is from the west over Chinook Pass, which will remain open until heavy snow creates avalanche danger.

Motorists using the emergency route could experience long delays due to construction work. No stopping or parking will be permitted on the emergency route.

from: http://seattletimes.nwsource.com/html/traffic/2010102817_webroute21m.html