Odds are low landslide will 'lurch'
Posted: Friday, April 11, 2014
By Ben Graham Jackson Hole Daily |
The odds are low that the East Gros Ventre Butte landslide could "lurch" and fall into the Walgreens below, but instability on the hillside could become a long-term problem.
A landslide specialist said Thursday there is less than a 5 percent chance that the open slope above the pharmacy will catastrophically fail.
Spring rains could cause movement to accelerate, but the slide is still a slow-moving one, said George Machan, who works for Landslide Technology in Portland, Ore. Machan flew into Jackson Hole on Thursday morning. He met with the Town Council and spoke to the public during a community meeting Thursday night at Davey Jackson Elementary School.
"I can't rule out that there will be a big lurch, but it's not likely," Machan said.
The news came after geologists and engineers spent the day monitoring the hillside. Firefighters kept an eye on the surveyors from a platform extended from a fire truck high above the Jackson Whole Grocer parking lot.
But with Machan's projections, authorities have decided to allow businesses to the west of Sidewinders in the Hillside Complex to reopen today. Evacuated residents will still have to wait.
The news should be somewhat reassuring for those who feared the worst. The town issued an evacuation order Wednesday evening because the slide was found to be larger than previously thought. Subterranean movement has accelerated in recent days, resulting in visible cracks in the hillside, stretched power lines and buckled pavement on Budge Drive and the Walgreens parking lot.
A map drawn up by authorities divides the areas of the butte side into low-, medium- and high-risk regions. The east parking lot of Sidewinders Tavern, Walgreens and the house on the cliff directly above the pharmacy are the structures included in the high-risk zone.
The slide itself measures about 100 feet deep by the house at the top of Budge Drive, Machan said. Below the Walgreens parking lot the surface of the slide is as shallow as 5 to 10 feet.
Town and Wyoming Department of Transportation officials said there isn't concern yet about the slide impacting West Broadway.
Despite the good news, the prospects of the slide becoming a long-term issue could make life difficult for the dozens of residents who have had to evacuate their homes on Budge Drive.
Police Lt. Cole Nethercott told the crowd of about 130 people at the community meeting that the evacuation order would be in effect for at least another five to seven days. Late Thursday night, the order was downgraded to an advisory.
Authorities have explored alternative ways to access the houses on the butte, but any action would require easements from private landowners.
The Town Council held a last-minute meeting Thursday evening to officially declare a state of emergency and to grant authority to two incident commanders to oversee the potential disaster. The commanders are Lt. Nethercott and Jackson Hole Fire/EMS Chief Willy Watsabaugh.
The council also authorized $50,000 to be spent on the efforts.
At the council meeting, Machan said human activity likely contributed to the slide.
"It's not just nature by itself causing it," Machan said.
The geologist spoke of a number of actions that could have had impacts, including the grading of the Walgreens site by 8 feet, the construction of the Hillside Complex and a water leak at the house above the cliff.
Despite the new information on the slide, a lot of surveying and measuring still must be done to figure out its exact size and speed, Town Manager Bob McLaurin said.
"We've got to map the limits of this slide, understand what we're dealing with," McLaurin said.
More about Landslide
- ARTICLE: Crews continue to monitor, prepare for landslide
- ARTICLE: Small slide in Snake Canyon leaves road unscathed
- ARTICLE: Forecasted rain won't help with landslide
- ARTICLE: Emergency meetings scheduled for landslide threat
More about East Gros Ventre Butte
- ARTICLE: Forecasted rain won't help with landslide
- ARTICLE: Refugees shocked by sudden evacuation
- ARTICLE: Emergency meetings scheduled for landslide threat
- ARTICLE: Slide fear prompts evacuation
More about Walgreens
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