Road-grading projects over a number of years may have contributed to a slow-moving landslide that has displaced residents of four homes and two small apartment buildings and cut off road access to dozens of other homes, according to a consultant for the town.
Meanwhile, Jackson officials got to work Wednesday on a project to put a massive amount of weight at the foot of the slide to try to halt the movement.
The ground has cracked and is slipping at a rate of about an inch a day partway up East Gros Ventre Butte. At the foot of the slide, the earth is bulging upward and buckling the pavement in a Walgreens parking lot.
Officials hope putting weight on top of the bulge will counteract the movement.
Town officials might also remove earth from the partly evacuated neighborhood located 100 feet or more uphill from the foot of the butte. The butte looms several hundred feet over Jackson but is puny compared to the awe-inspiring Teton Range a dozen miles northwest of town.
Landslide Technology engineer George Machan recently told town officials the slide at the foot of the butte has not been a strictly natural phenomenon, the Jackson Hole News & Guide reports (http://tinyurl.com/ocrouv8 ).
The area around the slide has been the site of grading and construction over decades, including construction of a residential road and grading of the town's main drag, West Broadway.
Town officials said exactly what happened that is to blame remains difficult to determine.
"The fact of the matter is, in an event like this, we're going to spend the next months and years, and there's going to be insurance adjusters, judges, juries and lawyers involved. We all know that," Town Manager Bob McLaurin said at a meeting this week.
The most recent earth-moving activity was last year's construction of the Walgreens. The pharmacy opened in January. Town officials approved grading for the site multiple times based on geotechnical analyses of the butte.
In 2011, a 200,000-gallon water leak occurred at the house above the lot now occupied by the Walgreens. Geological activity probably caused the leak, officials said.
Also, West Broadway crosses land graded down by as much as 20 feet over the years.
"It appears that there were some activities out there in the last few years that probably contributed to its moving," Machan told the Town Council. "It's not just nature by itself causing it."
Town officials say they've known the hillside has been moving for at least a year. They became more alarmed when the pace picked up around April 4, when a water line broke and a large crack appeared in the ground. They ordered an evacuation for 42 homes and apartment units April 9.
To date, the landslide has damaged only one home that already was vacant, pulling apart floorboards and causing cabinets to fall. On Monday, town officials said residents of all but four homes atop the slide zone, and two apartment buildings with a total of nine units beneath the hillside, could return.
However, the only street into the neighborhood has remained closed, forcing residents up the hill to walk to and from their homes across neighboring private property. They also needed to sign waivers releasing the town from legal responsibility in case of an emergency.
Town officials said they couldn't provide police, fire or ambulance service to the neighborhood.
Information from: Jackson Hole (Wyo.) News And Guide, http://www.jhnewsandguide.com