By David Jacobson, Temblor
Since October, a large crack in a hillside near Yakima, Washington has been developing, leading to concerns that 8 million tons of rock could come crashing down into Union Gap. This crack, which is growing at approximately 2.5 inches per day. is along Rattlesnake Ridge 8.5 km south of Yakima, which is home to around 100,000 people. Because it is likely that eventually this side of the hill will fail, 70 people have been evacuated from their homes, and barriers are being placed alongside Interstate-82, which runs through Union Gap.
The video above shows recent drone footage of the crack developing on Rattlesnake Ridge near Yakima, Washington
Unlike most landslides, which are either rain or earthquake-induced, this one appears to be primarily due to geology. In this part of Washington, the bedrock is primarily what is known as basalt, a hard volcanic rock. In between these basalt layers, which in some areas are 17 million years old, there are weaker interbeds. This slide appears to have originated along one of these beds. At its current rate, 1.6 ft/week, up from 1.0 ft/week, scientists estimate that the slide could occur between the end of the month and early March.
While geology is definitely a contributing factor, there is also a rock quarry just to the south of the slide. While officials have not yet said whether the quarry is responsible, Columbia Asphalt and Gravel has launched an investigation and has moved all operations. Because the slide is moving south towards the quarry, experts believe that the most likely scenario is that the mass will fall into the quarry. However, because there is a possibility the slide could block Interstate-82 and the Yakima River, which could result in flooded farmland, precautions are being taken.
In the meantime, the slope continues to be monitored, and large shipping containers are being filled with concrete and places at the southwestern corner of the slide to try and prevent rocks from tumbling onto the highway. Additionally, should the slide continue to pick up speed, the highway will be close and alternative routes have already been set up. Should there be any new developments, we will post a new blog.
Washington Geological Survey