Geologists: Slow-moving landslide could take years to fall

Photo: Steven Mack

UNION GAP, Wash. - Multiple geologists are now saying the steadily-moving landslide on Rattlesnake Ridge may not fall for decades.

About two weeks ago, Governor Jay Inslee called for another geologist to take a look at the landslide. Norman Norrish is that geologist and he has spent the last few weeks going through the data to try to predict what the slide is going to do and who's at risk.

He said the slide is a serious threat to public safety, but that it's both predictable and manageable.

Washington Department of Transportation Chief Engineering Geologist James Struthers said Norrish confirmed the slide probably won't suddenly fall at all and that the four million cubic yard massive slab of rock will probably continue to move about three inches a day.

With the slow movement Struthers said the slide could take years or even decades.

"As you may have heard the time frame for this movement could drag out over a period of quite some time," Struthers said. "Up to years."

In case activity on the ridge does speed up, Norrish recommended the county add to their monitoring systems, in areas that are poorly covered.

Struthers said they also discussed potential risks with Norrish.

"He did however find that it was fairly improbable to have large scale failures that would impact residences, interstate 82 or the Yakima river," Struthers said.

Washington Department of Natural Resources said they've already seen rocks fall towards Thorp Road but none have hit the road yet.

The new report said a big slide could still happen but it will speed up first, giving people time to evacuate.

"We're ready at a moments notice so if something were to change or the situation warranted, we can ramp back up and meet the needs of public safety," said Director of Yakima Valley Office of Emergency Management Jeff Emmons.

Geologists said a landslide taking years or even decades to fall is not that uncommon and they have monitored similar ones throughout Washington for that long before.

Emergency Management is changing the evacuation level for Thorp Road near the landslide from a Level 3 “Go” to a Level 1 “Be Ready”.

Starting February 1, officials are no longer recommending an evacuation for the homes on Thorp Road, meaning any person that is living in those homes can return, but should be prepared to evacuate again if conditions change.

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