3 January 2018
Rattlesnake Ridge: a large failure forming in Washington State, USA
Rattlesnake Ridge is a large hillside located above the I-82 highway to the south of the town of Yakima in Washington State, NW USA. The Google Earth image below shows the location of the site (at 46.524, -120.467), taken in May 2017. The image is looking towards the east – note the large active quarry on the south side of the ridge, and other signs of earlier (and smaller scale) excavation on the slope. Note also the proximity of the slope to I-82.
In October 2017 a major fissure started to develop through Rattlesnake Ridge. Over the last three months this apparent tension crack has widened to encompass a volume of about 3 million cubic metres. KXLY has this image providing a perspective of the size of the block that is on the move at Rattlesnake Ridge:-
Whilst the best impression of the feature can be seen in this Youtube video by Steven Mack:
This view of the feature is perhaps the most interesting, showing how the crack extends into the rear face of the quarry.
The latest reports suggest that the crack is widening at a rate of about 30 cm per week at present. Interestingly KIMA TV reports that the expectation is that the slope will self-stabilise:
Senior Emergency Planner Horace Ward said they have not determined a cause yet and said it’s just nature. Ward said the ridge is being monitored and they think the slide will stop itself.
“It could continue to move slowly enough to where it kind of just keeps spilling a little bit of material into the quarry until it creates a toe for itself to stop and stabilize the hillside,” he said.
Combined with the potential for weakening the materials controlling the deformation, this makes forecasting the likely future behaviour of this slope quite challenging, but of course it is the geologists on the ground who are best placed to make a judgement. In the short to medium term high resolution monitoring is the right approach.
Many thanks to the various people who highlighted this one to me, and provided links. Your help is very much appreciated.