Mother Nature often does not provide warning of environmental disasters, which makes the events unfolding near Yakima a bit unusual.
Rattlesnake Ridge is preparing to evolve into a landslide that could threaten stretches of Interstate 82 and the Yakima River. A crack atop the ridge is growing by about 1 1/2 feet per week, and authorities say it inevitably will send about 4 million cubic yards of rocks and dirt onto whatever is in its way. The timetable is fluid, with the break expected anytime between now and late February.
The events call to mind the tragic 2014 landslide near Oso in Snohomish County that killed 43 people and destroyed 49 structures. They also reinforce the need for diligence in mapping and analyzing potential landslide areas.
While Washington is blessed with an undulating topography that provides countless scenic vantage points, that blessing sometimes becomes a curse. Many states, particularly throughout the Midwest, subscribe the moniker of “mountain” to landscape features we consider to be small hills.
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While we enjoy the advantages of real mountains and many hills, some of those hills are prone to breaking apart and sending debris sliding onto communities or roads that lie below.
Because of that, Washington has undertaken an intense examination of potential landslides. The Department of Natural Resources posts intricate topographical maps being created with lidar — Light Detection and Ranging, which is the latest in technology for assessing the stability of hillsides.
As state geologist Dave Norman said last year, “The most important thing about lidar is it really provides a very accurate elevation model and image of the earth that you can’t get (otherwise) because it’s obscured by vegetation or other things.”
In the case of Rattlesnake Ridge, the fissure is easily observable from the air. Gov. Jay Inslee, who visited the site last weekend, said: “This is a significant risk that we have significant concerns about. We are continuing to determine whether there should be additional monitoring or additional analysis.”
The advance warning has led to the evacuation of more than 60 people who could be in harm’s way when the hillside collapses; the difficulty is the uncertainty about how long they will be displaced.
It also has led to contingency plans should a slide close Interstate 82 or alter the course of the Yakima River. “There is an evaluation of potential flooding risk,” Inslee said. “It is not predicted for this to happen, but if there was a flooding event in Union Gap, there are already emergency preparations.”
The specter of Oso lingers over any potential landslide in Washington.
While that calamity arrived without warning, the unfolding events at Rattlesnake Ridge serve as a test for how effectively state officials have learned the lessons from 2014. They also serve as a reminder for the importance of continued monitoring and the use of lidar mapping.
Identifying trouble spots is crucial to limiting the human and economic toll of potential slides. As one recent evacuee told The Seattle Times: “Oso. We don’t want to feel what they feel.”
Indeed, no residents throughout the state want to go through what Oso went through in 2014. With ample warning provided this time around, we trust that the toll will be limited through diligence and foresight.
But we remind that Mother Nature often does not provide such a warning.