The road crew at Denali National Park is filling in the park road’s most well-known landslide so that buses can drive past and into the park for the 2021 season.
“The biggest challenge facing this team will be filling in the slump at the Pretty Rocks landslide, at mile 45.4, just east of Polychrome Pass,” according to a post on the park’s Facebook page.
This winter, the road slumped a total of 29 feet below its original height, creating an 18-foot escarpment on its eastern flank. An escarpment is a steep slope or long cliff caused by erosion that separates two level areas at different elevations.
The road crew reached Pretty Rocks on March 20 and was able to assess the extent of the road damage throughout the winter. Pretty Rocks has been a safety concern for the past couple years. The rate of movement as it slumps continues to increase dramatically. Although it is one of more than 140 mapped unstable slopes along the entire park road, it has been in the spotlight because of its precarious location at Polychrome Pass and its potential to disrupt transportation and to affect public safety.
The park road is a one-lane gravel road that winds through Denali National Park. When it snakes over Polychrome Pass, there are mountain walls on one side of the road and steep drops to the valley floor below on the other side.
Measurements indicate the landslide movement at Pretty Rocks has increased somewhat since last year and necessary repairs will be more extensive than last spring, according to the park service. It is estimated that repair will require 6,700 cubic yards of gravel — about 550 truck loads — to fill the slump this year, according to Paul Ollig, acting public affairs officer.
“This is a not insignificant increase over last year,” he said.
In addition to filling the slump, road crews will grade the road for daily traffic.
The park plans to open the road to Toklat at Mile 53 for public bus access by May 20 and to Eielson Visitor Center at Mile 66 by June 1, as usual.
“There is potential for some unplanned traffic interruptions and/or road restrictions this summer due to the challenges of maintaining the road in the face of increased geohazard activity,” according to the park service.
The park road is currently open to Mountain Vista at Mile 13 and will remain open, depending on weather.
As road crews work to make the road passable at Pretty Rocks in 2021, the park service continues seeking a longterm solution. Options include building a bridge to span the landslide area, removing material from above the road, re-aligning the road to the north of Polychrome Pass, or re-aligning the road to the Plains of Murie in the valley floor below. The park must also address five other areas nearby that are slumping, including an ongoing slump at Bear Cave at Mile 44.8.
So far, building the bridge over the Pretty Rocks landslide area and finding engineering solutions to other nearby slumps appears to be the preferred solution.
Reach columnist/community editor Kris Capps at 459-7576 or follow her at twitter.com/FDNMKris.