A landslide along the road leading into Denali National Park and Preserve has significantly accelerated, demonstrating why closing off the road to vehicles just before the slide is essential this summer, park officials say.
A week and a half ago, a crew arrived at the site of the Pretty Rocks Landslide, near the Denali Park Road’s halfway point, and found that the road had dropped some 20 to 45 feet since August.
In one area, the landslide had dropped around 40 feet and more than doubled how much it had dropped the previous year, said Brooke Merrell, current acting superintendent at Denali National Park.
That didn’t surprise park officials, Merrell said. It was consistent with how the slide has been moving since 2016, though the sight of the steep dropoff — basically a cliff — on the east side was still a jolt.
“It was really shocking,” Merrell said.
Of the park and preserve’s more than 6-million-acre expanse, which contains the continent’s tallest peak, only 92 miles are drivable via the Denali Park Road. The road starts at the entrance to the park and cuts west. Only official buses and bike travelers are typically allowed past Mile 15 of the road.
In a usual summer, those buses would be seen cruising toward the farthest reaches of the road.
But this upcoming summer, vehicles will turn around at Mile 43, given the significance of the landslide. Park officials announced the change in October.
“Walking up to the edge of the cliff just made us quite sure we made the right decision last fall,” Merrell said.
While the Pretty Rocks Landslide has probably been active since before the road was built there in the 1930s, according to the park service, its pace sped up in recent years.
“The rate of road movement within the landslide evolved from inches per year prior to 2014, to inches per month in 2017, inches per week in 2018, inches per day in 2019, and up to 0.65 inches per hour in 2021,” the park service says on its website.
Lots of work went into getting the road open last summer: Crews brought dump trucks full of material to make the surface drivable each day, Merrell said.
But the road eventually began subsiding so fast that the park could not move in enough material to keep it safe for driving, prompting the midseason closure of the road last August at Mile 43, Merrell said.
Photos of the road from last week show a section of the road had entirely sloughed off the side of the slope. Crews stood at the edge of a steep dropoff where buses had driven until last August.
Work to address multiple issues between miles 44 and 46 of the road is set to begin this summer, according to the park service. During the first phase of the work, which will take around two years, the park is planning to construct a 400-foot bridge across the Pretty Rocks Landslide. The bridge will span the slide area and connect to the more solid areas on either side of it, Merrell said.
While problems caused by the Pretty Rocks Landslide could have been solved by small repairs in the past, climate change has exacerbated the issue, according to park officials. Increasing temperatures and rainfall are thought to cause permafrost thaw, which is speeding up several landslides in the park.
Even with the closure, the number of buses driving into Denali will match what the park experienced in 2019, a year that broke visitation records, Merrell said.
Visitors can still get into the park for day hiking and backpacking, but if they’re accessing areas west of the landslide, “they’re really in for a backcountry experience without National Park Service infrastructure or personnel in place,” Merrell said.
She encouraged those seeking that type of experience to come prepared and have done their research.