Slow motion landslide on Wash.’s Rattlesnake Ridge threatens I-82

Updated Feb 3, 2018
Photo courtesy of WSDOT.Photo courtesy of WSDOT.

A crack in Rattlesnake Ridge above the small town of Union Gap, Wash., discovered in October 2017, has turned into a crevasse, widening at a rate of 1.7 feet per week, Courthouse News reports. Geologists expect the entire section of bedrock to break off completely by May and slide down the side of the mountain, possibly burying a portion of Interstate 82.

Sixty-seven people were evacuated from their homes directly below Rattlesnake Ridge were advised that the move would most likely be permanent. “We told them they should not plan to go back to their homes,” Jeff Emmons, director of the Yakima Valley Office of Emergency Management, told the news agency.

If the worst-case scenario plays out, I-82 could be covered by the rockslide, and the Yakima River and an irrigation canal that feeds the region’s vineyards and orchards could become dammed, causing flooding upstream.

However, there is the possibility that the rock could settle into Anderson Quarry, which is located just below the ridge and is owned by LSL Properties and leased to Columbia Asphalt and Gravel. But even if the quarry absorbs most of the landslide, oil and chemicals stored there could flow into the Yakima River, causing environmental problems.

The Washington State Department of Transportation (WSDOT) is using a laser monitoring system to track the landslide’s movement. Emergency managers created a barrier from concrete-filled shipping containers between the base of the ridge and I-82.

According to the news agency, Washington Gov. Jay Inslee issued a statement saying that he is ready to mobilize additional state and federal resources “the moment” they are needed. And Union Gap Mayor Roger Wentz said the town is getting plenty of help from dozens of government agencies, but worries about flooding.

State geologists say they won’t know what caused the slide until after it concludes. “We’re really focused on safety at this point,” Stephen Slaughter, landslide hazards mapping program coordinator with the Washington Department of Natural Resources, told the news agency. “Right now, we’re just collecting data to help emergency managers.”

Scott Burns, a landslide expert at Portland State University, points to the quarry as a possible cause, but Anderson Quarry disputes that claim.

“There’s no correlation whatsoever between our activities and the movement of that hill,” K.C. Klosterman, the quarry company’s communications director, said by phone, according to the news agency. But the company did step up and pay for the evacuation of the town below the quarry and has hired consultants to help WSDOT monitor and analyze the slide.

Klosterman told the news agency that the company is motivated by simple goodwill, not by any sense of responsibility for the impending landslide. “We took it on our own accord to step in and help,” he said. “We realize that our industry is a heavy industry, and we want to be a good neighbor.”