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00000179-65ef-d8e2-a9ff-f5ef8dd70000In early October 2017, large cracks were spotted on the ground at Rattlesnake Ridge, a hillside about three miles south of Yakima, Washington. By January, the cracks had widened and emergency officials became concerned that a major landslide could imminent.Around 50 residents who lived on a small tract of land at the bottom of the hillside were evacuated and officials prepared for the worst.By the end of the month, geologists and engineers concluded that the landslide was a slow moving one and the risk of a major, catastrophic slide was low. Warning signs were taken down and residents were allowed to return to their homes.

Landslide Experts Walk Back Time Estimate For Rattlesnake Ridge Slide

Washington DNR
These large cracks on Rattlesnake Ridge photographed earlier this month have since widened and offset.

Geology experts with Washington's Department of Natural Resource have quit making predictions for when a slow-moving landslide might break loose. About 20 acres of the hillside are in motion near the community of Union Gap, Washington. 

DNR Hazards Geologist Stephen Slaughter briefed a state Senate committee about the Rattlesnake Ridge slide Monday. He walked back a previous estimate of early March for when the hillside most likely would collapse into a quarry pit at its base. 

"It could potentially run out a little farther. It could just stop,” Slaughter said. "Landslides are really poorly understood, this one especially because we can’t get in the subsurface.”

Slaughter said there is no sign that groundwater is lubricating the underside of the sliding layer of basalt rock. Water is normally a factor in landslides. 

"It could self-arrest potentially," he said. 

Slaughter said the thing that made the monitoring team uncertain is that the slide stopped accelerating. It's now grinding downslope at 1.6 feet per week. 

Dozens of people living at the base of the ridge have heeded government warnings and evacuated to hotels or other temporary housing.

Now semi-retired, Tom Banse covered national news, business, science, public policy, Olympic sports and human interest stories from across the Northwest. He reported from well known and out–of–the–way places in the region where important, amusing, touching, or outrageous events unfolded. Tom's stories can be found online and were heard on-air during "Morning Edition" and "All Things Considered" on NPR stations in Washington, Oregon, and Idaho.