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Barack Obama last week became the first sitting U.S. president to visit the nation's Arctic territory, using a sojourn in this vast state to highlight the risks posed by climate change. They include, Obama said, the accelerated thawing of the frozen permafrost that sits beneath “the earth on which 100,000 Alaskans live, threatening homes [and] damaging transportation and energy infrastructure.”
It was a familiar warning to geological engineer Margaret Darrow of the University of Alaska, Fairbanks. Just before Obama arrived, she had spent a week in the field with a research team seeking to better understand one emerging hazard caused by thawing perma frost: a massive, slow-motion landslide that threatens the Dalton Highway, the only land route into Alaska's lucrative North Slope oil fields and arguably the state's most important road. Researchers have so far identified 43 of these frozen debris lobes (FDLs) along the highway's route through the rugged Brooks Range—including a 20-meter-high slide that has bulldozed its way to within 40 meters of the northbound lane. If the slide, dubbed FDL-A, reaches the road, it would dump some 45 metric tons of debris daily—more than enough to fill a dump truck.
The slides create what looks “like a war zone,” Darrow says: cracked earth, toppled trees, and layers of moss and debris wrapped into jelly rolls. When it's quiet, she adds, you can hear trees straining as the mass creeps along at an average of 1.4 centimeters a day. As Alaska's warming softens their icy underpinnings, FDLs are now “a serious impending geohazard,” Darrow says, noting that FDL-A's speed has increased by 40% in the past 7 years.
FDL's didn't get much attention in 1974, when engineers built the gravel, 666-kilometer-long Dalton Highway from outside Fairbanks to Deadhorse, near the Arctic Ocean, in order to service the Trans-Alaska Pipeline System, which parallels the road. Geologists knew the FDLs existed on adjacent slopes, but they were barely moving. Then, in 2008, satellite photos revealed that a mass of frozen earth about 260 meters wide and 1200 meters long had inched to within 150 meters of the road at milepost 219, near the town of Coldfoot. Soon, state and federal officials were asking researchers to take a closer look at FDL-A, and others like it—and to consider ways of stopping them in their tracks.
Since then, scientists have used airborne radar and other sensors to create 3D maps of the slides and estimate how fast they are moving. On the ground, they're drilling cores through the FDLs to see inside. In a bid to understand why some lobes are moving faster than others, they have measured slope angles and identified soil types.
There have been plenty of surprises. One was the liquid water that gurgled up from under FDL-A in 2012, as scientists probed the critical “shear zone” in the permafrost beneath the slide. “You see water coming out and you're like: ‘What the heck?’” recalls Darrow, who says the liquid likely seeps in from the surrounding soil and remains supercooled in the frozen ground. Its high pressure—155,000 kilograms per square meter—enables it to lubricate the FDL's downhill slide, in the same way a thin layer of water enables a hockey player's skate blade to slide across the ice, says state geohydrologist Ronald Daanen in Fairbanks. As Arctic soil temperatures rise, basic physics holds that the pressure—and the lubrication—will increase, he adds. “Just a little more [water] pressure and [the lobes] will be floating,” allowing them to slide faster, Daanen says.
That worrying scenario could also hold true for other perma frost formations found in Alaska on steep slopes. Daanen says vegetation often holds in place these piles, which are slower moving, but “I'm afraid with warming temperatures there's a tipping point after which gravity takes over.”
In the meantime, researchers are mulling ways to defend the Dalton Highway from FDL-A. (The pipeline, some 800 meters away, is not at risk in the near-term.) Digging a trench to funnel water away from the lubricating shear zone is one idea. But researchers aren't sure how to best configure the ditch, because they have data only from the 2012 borehole. Engineers have also envisioned a buttress wall to block the slide, but Darrow fears it might be little more than “a speed bump” for the massive lobe. A more radical idea is to install underground cooling pipes to freeze the slide in place. But the immense forces could rip apart the pipes, and they may not work as intended, Daanen says. For starters, the state plans to simply reroute the road “to buy some time,” says Michael Coffey of Alaska's Transportation Department in Juneau.
Coffey estimates that, at current movement rates, it could take 10 years for FDL-A to reach the highway. But researchers say it could speed up given the unpredictable behavior of other FDLs, which have moved as much as 10 times as fast.