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New images show intimidating landslide moving down Rattlesnake Ridge

By Ashli Blow, KIRO 7 News Digital Producer
By Ashli Blow, KIRO 7 News Digital Producer

Drone aerial photography paired with laser scanning shows a new view into the cracks widening in Rattlesnake Ridge’s slow-moving landslide.

The hillside’s 20-acre landslide has gradually inched downward on Rattlesnake Ridge near Yakima for months. Since October, geologists and engineers have monitored it and conceived several scenarios – some including threats to the nearby Interstate 82.

In addition to 24-hour livestreams and site patrols, landslide consultants have used an advanced drone that can calculate the volume and slope of surfaces. With this technology, they were able to scan underneath the hill’s outer layers so that scientists and crews could evaluate the slide through cleaner images.

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The landslide is moving south at the rate 1.6 feet a week. Since the slide is moving each day, it’s gaining momentum, and at one point there will be a large movement of the mass, according to emergency planners.

No one knows for sure when a so-called "failure event" will happen. Based on monitoring data, Washington state geologists and engineers estimate an event will occur sometime in February or March.

As for where the slide will go, there are many possibilities.

The most likely scenario:

The landslide will continue to slowly move to the south, where the landslide mass will fall into a quarry pit and accumulate. Most of the slide will stay in the pit, but some rocks are expected to fall around it -- possibly reaching Thorp Road. In this scenario the landslide likely doesn't hit I-82 or the Yakima River.

Unlikely scenario:

The landslide may move beyond the pit and reach I-883.

Very unlikely scenario:

The slide will run out beyond I-82 and reach the Yakima River.

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Extremely unlikely scenario:

The landslide moves west and blocks I-82 and the Yakima River.

The best that crews can do is monitor and prepare, because blasting the slide isn’t an option.

The best that crews can do is monitor and prepare, because blasting the slide isn’t an option due to safety concerns.

But Washington state leaders are confident that the Rattlesnake Ridge landslide is very different from the deadly Oso landslide that took 43 lives nearly three years ago.

Geologists explained to KIRO 7 that Oso was mud while Rattlesnake Ridge is consolidated rock on the move. Water does not appear to be a factor in the Rattlesnake Ridge landslide.

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Rocks – around the size of baseballs and basketballs – are already falling onto the road below.
Nearly 50 people at the base of the hill, which is right in the landslide's path, were urged to leave immediately in early January.

As monitoring continues, lawmakers and community members are urging Governor Jay Inslee to declare a state of emergency in the event help is needed when the landslide gives way.

More on the Rattlesnake Ridge Landslide

DOWNLOAD THE KIRO 7 NEWS HERE

Cox Media Group

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