Jackson Hole News and Guide, Angus M. Thuermer Jr
Saturday, April 19, 2014 | 12:26 a.m.
CHEYENNE, Wyo. — A slow-moving landslide in the Wyoming resort town of Jackson sped up significantly Friday, splitting a house in two, causing a huge uplift in a road and a Walgreens parking lot, and threatening to destroy several other unoccupied homes and businesses.
The 100-foot-high hillside is unlikely to liquefy and collapse suddenly like the March 22 landslide in Oso, Wash., that killed 39 people, a geologist said at a town meeting Friday. But large blocks of earth could tumble down one piece at a time, presenting a drawn-out threat to four homes on the hill and to two apartment buildings and four businesses below, said George Machan, a landslide specialist consulting for the town.
"Is it weeks, is it longer? I really don't know," Machan said. "I think it's really unpredictable how long it might take. I don't expect it to end in a day."
Geologists were still trying to fully understand the mechanics of the slide, he said.
On Friday morning, a crack that ran beneath one house vacant for the past year shifted downward several feet and split the structure in two, the Jackson Hole News & Guide reported. Inside the home, floor planks have been coming apart and cabinets have been falling off the walls for the past two weeks. Three nearby homes also are in the high-risk zone.
A sewer line ruptured and electric power had to be rerouted because the slide is moving a utility pole, officials said. The slide breached a retaining wall, and gravel was spilling into a parking lot.
Town officials first noticed significant hill movement April 4. They evacuated 42 homes and apartment units April 9, when the slide was moving at about an inch a day.
By Friday, the rate had surged to a foot a day. Overnight, the shifting earth had bulged a road and a parking lot at the foot of the hill by as much as 10 feet. The groundswell pushed a small town water pump building 15 feet toward West Broadway, the town's main drag.
A large crack continued to widen near the four homes at highest risk partway up East Gros Ventre Butte, a small mountain on the west side of town. Meanwhile, a steady stream of rock and dirt tumbled off the hill gouged with fresh gullies.
Efforts to slow the slide — such as pouring rock and dirt fill behind large, L-shaped concrete barriers arranged in a line at the base of the slide — were on hold to keep workers out of the danger zone.
"It's really not safe to put people out there. You try to do what you can, but at some point you're really restricted from entering the area," Machan said.
On a town webcam, pedestrians could be seen pausing in the rain now and then to gawk at the slide zone that's as big as three or four football fields. Cars and trucks on West Broadway also slowed occasionally, the cause of at least one fender-bender Friday and a police warning for lollygaggers.
"Everybody's looking over there instead of looking where they're driving," Lt. Cole Nethercott said.
On Monday, town officials lifted the evacuation for residents of about 30 homes outside the high-risk zone but said they couldn't drive on the neighborhood street. They have had to walk to and from home by cutting across private property.
On Friday, not even work crews could drive on Budge Drive, which was buckled several feet.
Town officials said they didn't know what was causing the slide, but they have noted the area has seen considerable road-grading over the past few decades. The latest work was last year's construction of the Walgreens drug store, which opened in January.