The Pretty Rocks landslide, spurred by greater warmth and rainfall, will force Denali National Park’s main access road to close at the halfway point in 2023 for the second full summer.
To help park managers plan for and mitigate such events, Alaska CASC scientists assessed future landslide risks along road corridors in Denali and other Alaska parks.
“Park managers were interested in looking at park climate data to figure out how much warming has occurred and what the future might bring,” explained Pam Sousanes, a physical scientist with the agency in Fairbanks.
Sousanes turned to Rick Lader and his team.
“In Denali we had data from sites that were relatively close to the landslide area and we were able to determine that the average annual temperatures were approaching, and in some cases, exceeding the thawing threshold of zero degrees Celsius [32 Fahrenheit],” said Sousanes. “We wanted some way to incorporate those into really good downscaled climate projections, and we didn’t have the skills to do that. So we reached out.”
Lader and his team used the data from park weather stations to fine-tune projections from global climate models. The Alaska CASC and other staff and faculty at the International Arctic Research Center provide this dynamical downscaling service to Alaska’s decision-makers so they can incorporate climate data into local planning.
To identify the local landslide risk, Lader focused on mean annual air temperature and summer precipitation. Permafrost starts thawing and the ground slumps when mean annual air temperature rises above freezing. Heavy precipitation then can reduce the soil integrity and exacerbate or cause additional slumping.
For Denali, Wrangell-St. Elias and Gates of the Arctic national parks, Lader and his team created a set of maps and datasets predicting where and when these critical thresholds will occur. Though historically all three parks had a mean annual air temperature below freezing and a relatively stable precipitation trend, that’s changing.
Gates of the Arctic will likely see the biggest change in temperature and the second greatest increase in summer precipitation. That said, the park is considerably colder than the others, so the permafrost is more stable. Along the still undeveloped Ambler Road corridor, landslide risk likely won’t become a concern until after 2060.
“They will actually have the information before they try to build something, which is potentially more valuable than saying it’s already sliding,” said Lader.
The risk is more immediate in both Denali and Wrangell-St. Elias. Both parks are already seeing occasional years with above freezing mean annual air temperature. By 2060, that threshold will be consistently met. Precipitation is also increasing, especially in Denali. By 2060, Denali may become 5.8 degrees Fahrenheit warmer and see almost 6 inches more summer precipitation. As evidenced by the Pretty Rocks landslide, some areas along the Denali Park Road are already at risk, while others will remain stable for a few more years.
The Pretty Rocks landslide, which the Denali road has traversed since its completion in the 1930s, has increased in speed recently as warmer temperatures and heavy rain thawed frozen soil. Construction of a bridge at the crossing site, costing up to $102 million, will begin this summer.
“We’re right on the cusp in Denali and Wrangell-St. Elias. These changes are happening now, and they’re happening fast,” said Sousanes. “And even though they’re out in the future for Gates of the Arctic, we’re still moving in that direction.”
Sousanes said the landslide risk assessment will pay off years down the road as Alaska park managers plan for new and existing infrastructure to stand up in a changing climate.