A landslide that been moving slowly for two weeks on a hillside in Jackson, Wyo., has picked up speed and force, splitting apart a house and threatening others.
"The amount of movement is stunning," said Jason Rolfe, a local geologist advising the city. "In a geologic sense, it’s happening very quickly. To people displaced from their homes, it’s happening very slowly."
Jackson officials have warned residents living on top of the hill to stay away and businesses at the bottom to shut down. The house sheared apart had already been evacuated when the landslide cut it in half.
Photographs taken by a geologist flying a camera on a drone early Friday show the house partly tilted with a collapsed roof, surrounded by cracking earth. At least three other homes are close by.
The landslide has become an object of fascination as well as worry in the city of 10,000, and officials set up a live online video stream using a camera placed across the street.
If the landslide maintains its force, a critical water pipe, electric poles and town favorites like Sidewinders Tavern are likely to be no match.
The city is already planning to shut off water in the area during the day Tuesday to install contingency measures in case the water main does rupture.
Walgreens lost electricity Thursday, and Lower Valley Energy said it was readying backup plans should power poles become a casualty of the slide.
With gravel trickling toward them, construction crews have backed off an effort to finish a concrete wall to protect the businesses at the foot of the 100-foot hill.
A scarp several feet long had formed by Thursday night at the top of the hill, showing how far the collapsing hillside had traveled. By midday Friday, the gap had spread to nearly 15 feet in some spots, Rolfe said.
"As a geologist, it’s very exciting," Rolfe said. "We get landslides in Wyoming, but having one directly in town is unique."
The landslide encompasses a space about 500 feet wide and 400 feet long, Rolfe estimated.
"The biggest question we all have is the depth," he said. Geologists haven't found a safe opportunity to drill into the hillside, which has loose rock and silt on the top and a greasy clay sandstone farther down. That deep marine shale layer is prone to sliding when saturated with water, Rolfe said, and is "more than likely the culprit" for the latest slide.
He said a leak at one of the houses spilled an estimated 200,000 gallons of water into the area during the last couple of years. Combined with the melting snow from a hard winter, the clays had enough lubrication to go for a ride. The construction of the Walgreens on the site of an old road-rock quarry might have also further weakened the toe of the hill.
"It’s easy to see in hindsight now to see the comedy of errors that occurred, but I think the standards of industry were followed," Rolfe said. "But the paint hasn’t even started to dry on the store, and here it’s closed down."
The landslide comes about a month after a much wetter and larger landslide in Washington state ravaged the town of Oso and killed 39 people.
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