Preparedness

Washington State Workers to Install Equipment to Monitor Slow-Moving Landslide

Geologists say the 20-acre, 200-foot-deep mass could continue sliding for years, if not decades, and will likely fall bit by bit into the quarry pit owned by Columbia Asphalt. It will not become a fast-moving, catastrophically damaging landslide, they say.

by Alec Regimbal, Yakima Herald-Republic, Wash. / December 6, 2018
In this Monday, Jan. 8, 2018, photo, James Gleeson, a surveyor with the Washington State Department of Transportation, takes measurements from the shoulder of Interstate 82 to monitor a slow-moving landslide on Rattlesnake Ridge beyond Union Gap, Wash. Large containers line a road below the ridge, an effort to help block rocks and debris from reaching the highway. AP/Elaine Thompson

(TNS) - If you see construction crews drilling into the western slope of Rattlesnake Ridge, where 8 million tons of rock and dirt are inching down the hillside, the Yakima Valley Office of Emergency Management says not to be alarmed.

On Wednesday, the agency said a contractor will be installing new monitoring equipment into the hillside near the site of the slow-moving landslide. The purpose of informing the public early was so passersby didn’t become concerned when they saw workers on the ridge just east of Union Gap.

“The reason for this update is to provide advanced notification to the public in order to reduce the presumptions that may arise if left without explanation,” the agency said in a news release.

The contractor was hired by Columbia Asphalt, which operates a quarry at the base of the ridge. Crews will be on the ridge starting next week and are expected to finish during the first week of January.

Columbia Asphalt is in charge of installing the new equipment as part of a deal with the state Department of Natural Resources, said Horace Ward, senior emergency planner with the Yakima Valley Office of Emergency Management.

The landslide was detected in October 2017. At that time, it was thought to be an impending landslide. As geologists studied the slide and tried to predict its impact, emergency officials prepared a response, which included evacuating 60 people living at the base of the ridge.

Geologists say the 20-acre, 200-foot-deep mass could continue sliding for years, if not decades, and will likely fall bit by bit into the quarry pit owned by Columbia Asphalt. It will not become a fast-moving, catastrophically damaging landslide, they say.

Dozens of GPS units and seismometers remain on the hillside as geologists continue to monitor the slide. The latest reports from geologists say the slide continues to move, but slowly.

The cause of the landslide is unknown.

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