THE BUZZ: Sliding into the Future

By on April 11, 2017

As temperatures rise, is the valley destined for more landslides?

(Photo: WYDOT)

JACKSON HOLE, WY – The landslide that bulged and cracked Highway 191 at milepost 133.8 was nearly impossible to predict. But a likely prediction into the future is that the valley could be seeing more landslides as the Earth’s temperature continues to rise.

Water world

An unusually high amount of precipitation and moisture in the ground caused the landslide. The snowpack this winter was 168 percent higher than normal, explained Stephanie Harsha, communications director for Wyoming Department of Transportation.

Climate experts are quick to observe that no one incident can be attributed to climate change, but they can look at patterns and deviations.

Jeff Lukas, a climate specialist at the University of Colorado, said that this year has indeed been unusually wet. Compared to any other year in history with complete precipitation records, this year’s winter since the beginning of October has the highest precipitation on record.

What does that mean for landslides? The simple answer is the more moisture on the ground, the less stable the slope. More moisture begets more landslides.

Scientists cannot yet say definitively whether this year’s precipitation and subsequent landslide activity are directly caused by climate change. But climate change and landslides are indeed closely related, and there is research to illustrate this.

“That climate changes affect the stability of natural and engineered slopes and have consequences on landslides is … undisputable,” reads a study by Stefano Luigi Gariano and Fausto Guzzett of the University of Perugia in Italy.

Their research explains how climate change directly impacts rates of precipitation, which in turn impacts slope stability. “Direct climate impacts influence parameters that directly control landslide occurrence, like a change in rainfall regime,” the study reads.

High-altitude mountainous regions are even more susceptible to the shifting climate. Biologist Corinna Riginos from the Teton Research Institute says that the rapid snowmelt this spring is  “consistent with a warming climate.” Such hasty snowmelt and permafrost thawing in high elevations result in “a reduction in the shear strength of soil and rock masses … increasing the frequency of rock slope failures.”

Scientific jargon aside, the takeaway is this: climate change affects precipitation rates and moisture affects slope stability. If this winter is the new normal, it follows that each spring will see more landslides, and bigger landslides.

“This time of year is always busy,” said Mark Falk, chief geologist for Wyoming Department of Transportation. But he also admitted that there isn’t much WYDOT can do to anticipate such events, except monitor the slides they already know exist. “We just pretty much have to take things as they come … as far as new [landslides], we can’t predict that. We just have to react.”

Falk says that WYDOT has never seen slide activity in that area before. His team can’t monitor slide activity until they know where to look.

The winter of our discontent

Landslides are common natural phenomena in Wyoming. According to the Wyoming State Geological Survey, parts of Wyoming—Teton and Sublette Counties among them—have the highest landslide densities in the United States. A single incident, then, is neither surprising nor particularly concerning.

Three years ago almost to the day, the Budge Drive landslide devastated a Jackson home and a newly constructed Walgreens. The slide also blocked access to a neighborhood of around 60 people. Reparations are still underway—Walgreens just handed over its land and $1 million to the Town of Jackson to finish demolition and land stabilization.

The 191 slide, though comparatively benign, is one in a series of natural phenomena that made this winter particularly eventful. Recall: February’s “snowpocalypse” that downed power lines and closed all three of Jackson’s main arteries. That same storm, or series of storms, contributed to the snowpack that is now causing landslides in places they have never occurred before.

These destructive incidents are hard to predict on their own, Riginos said. But, she noted, “there are some things that are easier to anticipate.” What is certain is that weather will be more variable, less predictable, and more extreme.

“We can predict with higher confidence that spring is happening earlier, warmer temps are happening earlier,” she said. So peak snowmelt will also happen earlier. While the exact outcomes of such weather are unpredictable, Riginos says that having “good infrastructure” and open communication are key to adapting to a shifting climate.

Mitigation and policy

Harsha says that after this winter, crews were on high alert throughout the state. While they could not have seen this slide coming, she says she is not surprised. Landslide movement is often triggered by “saturated slope conditions,” Falk explained, which result from excessive moisture on the ground. This winter’s excessively high snowpack combined with spring’s early onset and rapid snowmelt created the perfect landslide cocktail.

“We got well above-average snowpack in that whole area,” Falk explained. “Once it started to melt and the water had a chance to go into the ground, we ended up with saturated slope conditions. That’s how most landslides are triggered, this year was just kind of extreme given the snowpack.”

Damage from this particular slide is nothing too serious, Harsha said, but she is certain it won’t be the last one. “Lots of snow means a lot of water … Once the snow really starts to melt, we’re going to see even more of this.”

Gariano and Guzzett offer some general mitigation efforts and adaptation solutions in their report. They conclude that such effort must include a combination of “structural” or “hard” measures—physical barriers, walls, drainages, etc.—and “non-structural” measures, which include education and policy change.

WYDOT is quick to respond with structural measures, but non-structural measures are beyond its scope. Policy change happens slowly, and as Teton County Commissioner Mark Newcomb told PJH back in February, is tied up in resources the county simply doesn’t have.

WYDOT also acts alone in its mitigation efforts. The Wyoming Geological Survey monitors landslides across the state, but WYDOT is the first and often only agency to respond when slides affect travel, Falk said. “As a department, we’re trying to be vigilant, checking on every report of something new,” he said. Falk runs a department of 21 geologists monitoring and responding to activity across the state. “We’re prepared to do whatever we need to do.”

Highway 191 is still open—there are no landslide closures anywhere in the state right now, Falk said. For now, the area is patched and passable. Geologists have installed a pipe in the ground to monitor activity, and haven’t noticed any new movement since last week, but will continue to monitor the area as they investigate possible mitigation. Falk and Harsha both hope for a milder, cooler spring ahead, but they are prepared for anything. PJH

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