Thaw-triggered landslides are a growing hazard in the warming North
The warming climate in Alaska and across the circumpolar North is creating new health and safety risks for people, animals and ecosystems. This piece is the first in a series that explores zoonotic diseases and other hazards emerging in a warming and thawing Alaska.
On a route traveled by hundreds of thousands of Alaska tourists each year, danger looms.
Midway along the 92-mile road that winds through Denali National Park, at a spot with an elevation of 3,500 feet and spectacular views of the Alaska Range and the braided rivers that flow out of it, an unstable wall of rock, ice, soil and clay rises precariously. The slope into which the road was cut eight decades ago is already collapsing gradually — and there are fears that it could collapse much more suddenly in the future.
The site, called Pretty Rocks, near Polychrome Overlook and along an ever-narrowing section of road perched on a steep cliff 1,000 feet above the river valley, can be nerve-wracking for travelers, most of them ferried into the park by shuttle bus. For Denny Capps, the park’s geologist, it’s a persistent source of worry.
The slope had been creeping slightly for several years, but its movement began to speed up in 2014, and it increased five-fold in the last year, Capps said. In the first seven months of the year, movement averaged about 2 inches a day for the first eight months of the year, he said. In August and early September, according to park measurements, it sped to about 3.5 inches a day.
Capps comes to Pretty Rocks every few days in the tourist season to check on the rubble that routinely tumbles from the slope into a culvert dug on the inner edge of the road, the cracks that appear on the crumbling outer edge of the road and the equipment stationed to photograph and record precise movements of the slope.
“If you think in terms of maintaining a road that has buses going across it, well, that’s not easy,” he said.
Pretty Rocks, though considered the most dangerous, is just one of approximately 150 thaw-related landslides identified so far in the park. In several other places in the park, entire slopes have collapsed, leaving bare dirt exposed and sending patches of alpine tundra askew.
All this makes Denali a case study for thaw-triggered landslides that are becoming an increasing hazard across the Far North.
There have already been major slides that have snarled park road traffic. One was at Igloo Creek, at mile 38. In October of 2013, part of the slope collapsed with what the Park Service has described as house-sized chunks of dislodged permafrost blocking the road.
Luckily, Capps said, that slide was after the end of the summer tourist season. “It was like a warning shot across the bow,” he said. “It could have knocked a bus off the road.”
Much of the frozen terrain in the park is doomed, scientists have warned.
A 2014 study on Denali’s permafrost estimated that about half of the park’s terrain was underlain by it but that almost all will be gone by the end of the century. The study, by University of Alaska Fairbanks scientists, predicted that in 2100, only 1 percent of Denali will still have permafrost, with remnant traces at high elevations and north-facing spots.
If anything, those predictions now appear optimistic. The warming trend that has been documented since the 1920s took a dramatic turn after 2013, Capps said. “It was like a switch,” he said. Average temperatures at two key park sites rose 4 degrees Fahrenheit from 2014 to 2019, reaching levels not expected until about 2040, he said.
Warming does more than increase air temperatures. Rainfall has increased in Alaska, too.
In non-permafrost areas, rain is a well-known trigger for landslides, like those that ravaged southeast Alaska during a record-breaking early December storm, causing two presumed deaths in the coastal town of Haines. Winter rains also triggered the devastating Dec. 30 mudslide in the Norwegian village of Gjerdrum that killed 10 people and temporarily displaced about 1,000.