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Officials: Central Washington landslide continues to slow

October 12, 2021 GMT

YAKIMA, Wash. (AP) — The pace of the 20-acre (8-hectare) Rattlesnake Ridge landslide in central Washington near Union Gap is continuing to slow, officials said.

Yakima County emergency services director Tony Miller said measurements taken in August show the slab is moving less than 2 inches (5 centimeters) each week, The Yakima Herald-Republic reported.

In 2020, the slab was sliding 2 to 3 inches (5 to more than 7 centimeters each week). The slab is expected to continue sliding south, with debris depositing in a nearby quarry.

“It’s moving a little bit, crumbling and falling right into the pit,” Miller said.

State and county officials, as well as scientists, have been monitoring the slide since a crack was spotted on the ridge in 2017.

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Initially, officials said the slide could pose an immediate danger and 60 people living nearby were evacuated. Some residents returned after an assessment firm hired by the state confirmed the landslide was not likely to rapidly slip.

Stephen Reidel, a research faculty member at Washington State University, said the slab is sliding on a sedimentary layer between basalt flows. As the basalt slides into the quarry, it will stack up and eventually build up enough to act as a barrier, stopping the landslide.

“It’ll just stabilize itself and then stop moving,” he said.