Engineers are designing a bridge that will span the Pretty Rocks landslide at Polychrome Pass on the Denali Park Road.
After years of monitoring and repairing the road at that site, park officials were forced to close the road two weeks ahead of schedule this season for safety reasons.
Pretty Rocks is located at Mile 45 of the park road. It is a rock glacier that began sliding inches per year in 2014. By August 2021, it was sliding more than half-an-inch per hour. More than 100 dump truck loads of gravel were needed every week to keep the road open.
“That’s when we realized we couldn’t keep up with it,” said Dave Schirokauer, science and resources team leader for Denali.
Experts in arctic soil from all over the world convened, studied and determined the road should remain in place rather than be re-routed, according to Brooke Merrell, Denali’s deputy superintendent. A bridge will be designed and installed to span the landslide area. The update occurred during a Zoom meeting Tuesday between Denali National Park officials and the Denali Citizens Council (DCC). DCC is a nonprofit organization that provides citizens a conservation voice in management of Denali National Park. The park also plans to address eight other problem areas along that stretch of park road.
“We’re going to move quickly, especially given what happened this summer,” Merrell said. She takes over as acting superintendent in November. “We’ve got to get this rock slide spanned if we are going to continue to have traffic flow.”
To make sure that process moves quickly, virtual public meetings are planned for Oct. 13 and 14.
“Same meeting, same format, same informations, just offering it two different days,” Miriam Valentine of the National Park Service said.
An updated website that will focus on planning for the Polychrome area improvements project will go live Sept. 29. It will link to the Pretty Rocks Landslide web page.
“We’re on a really accelerated timeline,” Valentine said. A second public comment period will open in January.
According to Valentine, the Federal Highway Administration estimates it will take two to three seasons to get the road back to “what we would consider normal, unrestricted traffic all the time.”
With that in mind, the park service has already begun conversations with tourism groups to provide updates and is considering how to revise its message to visitors for upcoming seasons.
“The hard thing is, everyone is asking us to speculate what is the likely start time? How long of a season do you think you can get?” Superintendent Don Striker said. “The science just isn’t there yet. I think it’s fair to say, if things operate over the winter like they have in the past, we’ll probably be able to fill in the hole.”
If that happens, the park road could open on time. But if slumping continues at an accelerated rate and soils become saturated again in August, the road may be forced to close. It is still too early to predict, Striker said.
“I’m not saying Denali is closed, but there is a point we’re likely to get to due to climate change where the experiences we can offer are going to be different,” he said.
The park estimates that if buses turn around at Mile 43 before climbing up Polychrome Pass, fewer buses per day would be allowed, per the road management plan.
“How do we offer the most people a really quality visitor experience within the vehicle management plan framework? “ Valentine asked. “That’s what we’re working on.”
Park officials will spend the winter figuring out what that Denali experience could look like.
The price tag for the Pretty Rocks project is estimated to be $55 million. That amount is included in the budget currently before Congress. The cost of that and the additional eight projects along that stretch of park road comes to a total of $118 million.
Engineers have been boring holes at Pretty Rocks to make sure the surrounding terrain is strong enough to support bridge pilings.
“It seems a pretty amazing feat of engineering,” according Schirokauer. “Climate change is hitting us really quickly here in Alaska and the alpine environments of Denali,” he added. “We can’t rely on past experience to inform the future. We don’t know what the next thing will be. We don’t know what to anticipate.”