Are rocks ready to roll on the Pass?
A section of hillside above the last steep stretch of Independence Pass is “an accident waiting to happen,” said longtime Aspenite Bob Lewis this week.
Lewis, who has spent decades of his life trying to repair the scars left behind when Highway 82 was built over Independence Pass, is worried that a section of steep bedrock looming above the road at the so-called “top cut” may give way and tumble down.
And the reason he thinks this particular stretch might come crashing down is because it has already happened once this summer in that same general area.
On June 22, a segment of the rock face broke loose and smashed down on the highway, reducing it to one lane of drivable surface and forcing the Colorado Department of Transportation to close the road for several days while the mess was cleaned up.
No one was injured by that rockslide, but it deposited 330 dump-truck loads of material onto the road, Lewis said. He maintained that is enough dirt and rock to fill up Aspen’s City Hall to the third floor.
With between 3,000 and 4,000 cars passing over Independence Pass on a busy day this summer, the chance that the rest of the rock face along that particular stretch of road may also slide is what’s worrying Lewis and Mark Fuller, director of the Independence Pass Foundation.
“There’s a potential for the same kind of thing to happen along this face,” said Fuller, gesturing toward the remaining section of rock outcropping.
The situation has been studied by geologist Jon White of the Colorado Geological Survey, and White has suggested the state “should consider either taking it down or stabilizing it.”
White, after looking over the rockfall site, said the June 22 rockslide was caused by a “fault line” that had allowed water to seep between two layers of rock. As the water froze in the winter and thawed each spring, the rock face loosened and became unstable.
He said it is likely that rainfall on June 22 lubricated the fault line, and the sudden deluge of water may have triggered the slide.
And after further investigation, White said that the same fault line extends farther up the hill toward the Pass, behind what’s left of the broad outcropping of rock.
But White stressed that, although he believes the “remnant” of the outcropping will give way some day, it is not that unusual a situation.
“As a hazard, there’s worse all over the state,” he said. “Rockfall hazard on state highways is a risk everybody takes. I don’t think it [Independence Pass] is unsafe for the traveling public, per se.”
He said other, similarly sized rockfalls have occurred along the top cut in recent years, “but usually they happen when the road is closed.”
Lewis pointed out that all of the stabilization work on the Pass to date has been directed toward eroded areas where loose rock and dirt pose a hazard when they fall on the roadway, not toward what were believed to be relatively stable rock outcroppings.
It was, he said, a stroke of luck no one was hurt in the June 22 slide, which “alerted us to a safety hazard we didn’t know existed.”
CDOT Regional Director Owen Leonard, reached at his office in Grand Junction, had not yet seen White’s report and could not say what will be done about the outcropping.
Meanwhile, Leonard said, his engineers have given him no indication that there is an “imminent event” that should be dealt with on Independence Pass.
“We are concerned, and we want to make sure we don’t have a problem up there,” Leonard continued. “We do have slides like this periodically around the state.”
He said there are some possible remedies, such as the placement of monitoring devices to detect movement, or using explosives to trigger a rockslide deliberately after closing the road.
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