A huge ridge cracks near Yakima prompts evacuation warning. The huge crack on Rattlesnake Ridge is active since October 2017. It is 20 acres in size, is moving at a rate of about 1.3 feet per week and is accelerating each week. The concern is that the landslide would keep moving, even closer to I-82. The below drone video shows the landslide in striking clarity, with giant fissures in a hillside, widening, as the earth shifts:
The area of concern is east of Union Gap, east of Thorp Road – an area also known as Anderson Quarry. A section of Thorp Road has been closed as a precaution and Yakima County Emergency Management has urged some homeowners to evacuate.
So what caused this?
One possibility is a quarry at the base of the hill. Geologists and emergency managers are trying to learn more about its impacts. A classic way to destabilize a slope is to undermine the toe of that slope, and sometimes a little bit of undermining can cause a cascade that causes a much larger failure. And what about rain or an erthquake?
Meanwhile, the state is monitoring the hillside’s movement with GPS and a laser and large shipping containers have been placed at the base of the hill to block boulders and other debris from reaching I-82.
One possible outcome is that all this earth just slumps onto itself and stops, but emergency managers are taking this very seriously, making sure they can quickly close roads and get more people away if they see this movement accelerating.
The question is how much of the slope will go and how fast will it go. There’s a high probability that the slide will keep moving. This is a big slide. It’s started to move. It’s been accelerating since October, but there’s a very low probability in all likelihood that it would move so far as to reach the highway.