April 18th: “The acceleration has been doubling every 24 hours since April 1, with significant movement in the last 24 hours.”
We humans may pretend we are in control, but Nature, always, in the long run, bats last.
For the backstory:
Photos from helicopter, April 17-18th:
George Machan of Landslide Technologies noticed a formation in the landslide called a ‘graben’ and this formation is dropping down and pushing out the lower portion of the landslide. This is occurring on the western edge of the high risk area. Aerial photos provided by Tributary Environmental allowed this particular feature to be identified. The acceleration in the slide has been doubling since approximately April 1st with significant movement in the last 24 hours. Significant movement has occurred on the hillside with increased depth and width to all cracks delineating the slide. The eastern crack has dropped 10-15 feet down the mountain and is quite visible from the street. Additional continuous gravel slides are expected as well as calving of larger chunks in the high risk area. The retaining wall behind Walgreens has been breached with gravel spilling over into that parking area.
April 18, 2014
Significant movement of the East Gros Ventre Butte landslide Thursday caused crews to stop working on an emergency buttress that is supposed to stop the slow-moving slide.
A nearly constant stream of rock and gravel sloughed off the cliff above Walgreens throughout the day, much of it sliding down the slope and over a barrier into the pharmacy’s parking lot.
About two dozen law enforcement officials, Jackson Hole Fire/EMS personnel, contractors and town workers stopped their work and stood away from the cliff near West Broadway in the early afternoon.
By early evening, more than a hundred people had gathered on the opposite side of Broadway to watch the spectacle.
Existing cracks appeared to be growing. Some witnesses said they had noticed new cracks since earlier in the morning. Consistent rockfall caused chutes in the slope to visibly deepen throughout the day.
The eastern portion of the scarp face that arches through the butte side above the pharmacy dropped 3 feet in 24 hours, said Roxanne Robinson, Unified Incident Command public information officer.
On Thursday night, authorities said there were no public safety concerns for Broadway or the people watching the slide across the street.
A landslide expert hired by the town said last week that the chance of the slope catastrophically failing is less than 5 percent. Wyoming Department of Transportation officials are still not concerned the ground movement will affect Broadway, Robinson said.
Some spectators were wary nonetheless.
Steven P. French sat outside Rocky Mountain Bank, several yards back from the sidewalk along Broadway, where other residents were watching the slope. French had walked to the edge of highway and was “uncomfortable,” he said.
“You gotta assume that whole thing is going to come down,” he said. “All you have to do is go to YouTube or the Nature channel and see these things. It’s not just going to stop neatly at the sidewalks.”
In the morning, crews started building a buttress to slow the “toe” of the slide. They added backfill to a wall of concrete barriers before rockfall forced them to stop.
It is unclear when work will be able to resume. The safety of workers is a concern, Town Manager Bob McLaurin said.
McLaurin has met with Walgreens developer Bencor Inc. to get permission to extend the buttress to the pharmacy’s parking lot.
Permission may be granted soon, but “it may be a moot point,” McLaurin said. “It’s moving too much.”
Town public works crews plan to install valves and hydrants near the site that will allow the town to reroute the 12-inch water main that is under the street. The town’s greatest fear at this point, engineers say, is that the slide will break the pipe — which supplies about a third of Jackson with water — and flood the street with 2 million gallons of water in 30 minutes.
To make way for the work, water will be shut off April 22 for all businesses on the north side of West Broadway, as well as Cutty’s Bar and Grill, Old West Storage and a portion of the Teton Gables Motel.
Jackson Police Lt. Cole Nethercott, co-commander of the unified incident command, is cautioning those who may be working on the site “to know your escape route at all times should it decide to let go all at once.”
A live feed of the slope has been capturing the activity on the butte. It can be found on the town’s website, located at TownOfJackson.com.
A press conference with geotechnical engineer George Machan will be held at 10 a.m. today in Town Hall. Afterward, Geologists of Jackson Hole will give a presentation about the geological history of the site and human activity there.
The slide first raised alarms with the town April 4, when ground movement broke water pipes near Walgreens. Residents of Budge Drive were caught off guard the evening of April 9, when the town issued an evacuation order because of the landslide threat.
The town has gained access from the property owners at the top of the cliff to dig 150-foot test holes to try to determine the depth of the slide and to analyze soil types. The homeowners have been “extremely cooperative,” McLaurin said.
Earlier this week, the Jackson Town Council authorized $750,000 to be spent on efforts to stop the slide. Half the money was supposed to be put toward the buttress.
Authorities have described the ground movement as a “block” slide that is slowly rotating, sagging at the top of the slope and pushing up at the base.
Machan and others have said development on the butte has contributed to the slide.