Permafrost Dynamics

In late July, I had the opportunity to attend a soils conference hosted by the NRCS (National Resource Conservation Service) and University of Alaska Fairbanks. The presentations varied from policy, regulations, and research, but every presentation focused on permafrost. Technically, permafrost is any soil that is frozen solid continuously for 2 or more years, but there’s so much more to it. There’s stable permafrost, which is much deeper and less likely to thaw. On top of it lies an active layer that is more likely to thaw, changing in depth year to year given the range of air temperatures.

This native Alaskan orchid was found in calcareous soils associated with the frost boils of Sukakpak Mountain.

This native Alaskan orchid was found in calcareous soils associated with the frost boils of Sukakpak Mountain.

Within this active layer, a variety of land formations can develop including ice wedges, pingos, and sorted circles. These unique landforms often create a diverse set of microclimates that can support a more diverse plant community. Ice wedges start to grow when rapidly cooling air temperatures crack the ground, allowing snowmelt to enter in the spring and freeze in the winter. Over time, these cycle grows the wedge and pushes soil up and out of the way. At some point, the wedge starts to die. This dying wedge can be the source for a seep, leaving a depression in the ground when it’s completely gone.

Pingos or frost boils result from ice pooling and building underground, pushing the above soil into a dome. Once the soil cracks, all the insulation is gone and the ice melts away. This cracking can be explosive. Local folktales include people building houses or cabins on small hills only to have the house forcefully ejected as the hill implodes. Finally, sorted circles come from the repeated freeze-thaw cycle pushing rocks up to the surface and sorting them by size. However, what all permafrost seems to have in common is a high silt and organic content in a matrix of ice.

Frost Boil at Sukakpak Mountain

A frost boil at Sukakpak Mountain surrounded by wetland in calcareous soils.

As a part of the conference, we were allowed to visit the permafrost tunnel in Fairbanks to see some of these formations in real life. Imagine a dusty tunnel that smells like an old attic at about 31 degrees F with evenly spaced work lights. Hanging from the ceiling is a veil of tangled, fibrous roots of long dead plants. That’s essentially what the permafrost tunnel is like, except in the dusty walls and ceiling you can also see giant blocks and lens of murky black ice. This particular tunnel was built to better understand how to mine in the permafrost. Since it’s construction, it’s now used to study the permafrost itself and the creatures it has encapsulated. For example, one outcropping of plants is an ancient overturned riverbank. The plants were preserved so quickly that they’re still green if you shine a light on them. Steppe bison and woolly mammoth remains are routinely excavated. Towards the deepest end of the shaft is a branch carbon dated to 46,000 years old!

A look down the Permafrost Tunnel in Fairbanks, Alaska. The tunnel is maintained by the Army Corps of Engineers.

A look down the Permafrost Tunnel in Fairbanks, Alaska. The tunnel is maintained by the Army Corps of Engineers.

 

The permafrost is a dynamic soil type, but climate change is accelerating and intensifying that dynamic beyond the norm. As Alaska broke its hottest day of the year record this summer, the permafrost has been receding, the active layer encroaching into areas that have historically been more stable. This has some major implications for life in Alaska. When water melts from permafrost, that silty organic mix is a perfect recipe for quicksand, meaning more buildings and roads being swallowed underground and greater dangers of mudslides like this one in Denali National Park. It means greater deterioration of hunting trails that Native Alaskans rely heavily on for subsistence and traditional practices. It also means a greater acceleration of climate change.

Remember that 46,000-year-old branch? The reason it hasn’t decayed is because it’s surrounded by ice. Remove the ice and it’ll start to decompose, along with all the other organic matter in the permafrost. Because it’s deep underground where there’s no oxygen, that decomposition will create methane, which can and does bubble to the surface and escape to the atmosphere. It’s already happening as demonstrated by these scientists. The tundra will go from a carbon sink to a carbon source. Some predictions even show the tundra shifting to a grassland ecosystem if warming continues. Climate change is real and during a summer of record heat and rainfall, it’s quite noticeable here in Alaska.

Want to learn more about permafrost? There’s a new documentary coming out in 2017 specifically on Alaskan permafrost dynamics. Check out the trailer for Between Earth and Sky here.

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