Gathered over a period of two to three months, the images are like short videos that show cracks widening and parts of the slope slumping.
A new series of laser images shot from a drone offers a dramatic, dynamic look at the unfolding landslide on Rattlesnake Ridge south of Yakima that threatens Interstate 82.
Gathered over a period of two to three months, the images are like short videos that show cracks widening and parts of the slope slumping. The laser scanning method used by the drone can “see” through vegetation, providing zoomable, bare-earth images that reveal every topographical wrinkle on the 1,800-foot high ridge at Union Gap. The scans also show the slide from multiple angles.
The images are part of ongoing monitoring of the hillside by Cornforth Consultants, a geotechnical engineering firm hired by the operators of a quarry at the base of the hill where some of the first cracks were spotted in October.
Portions of the slope have moved as much as 10-12 feet since then, according to Cornforth’s monitoring reports. The fissures probably started forming as early as May, says one analysis.
The slope is currently sliding about 1.6 feet per week. At that rate, the consultants predict the hillside is likely to collapse in early March – but they warn that it could also happen sooner.
The approximately 70 people living in homes and trailers below the hill have all evacuated. Based on the current motion, geologists and engineers say the unstable slope — which covers about 20 acres and comprises 4 million cubic yards of rock and soil — is most likely to slump into the evacuated quarry pit, sparing the freeway.
But in the worst-case scenario, the slope could fail rapidly and send debris across the freeway and potentially into the nearby Yakima River, according to the Washington Department of Natural Resources web page on the slide.
I-82 remains open, but the Washington State Department of Transportation is poised to close it when necessary, said agency spokesman Randy Giles.