Alaska scientists study accelerating land subsidence affecting North Slope coastal communities

When a house on Qigalik Avenue in Point Lay was first built, a staircase led from an upstairs door to the ground. Thirty years later, an 8 foot ladder is now required to access the top step of the staircase.

“Every year we have to add a step or two to these stairs because of the sagging,” said 50-year-old Point Lay resident Bill Tracey, who lives near the house. He said the problem is common among local landlords. “We started noticing the ground subsiding and ponds forming, the roads developing sinkholes. … We are doing what we can, but the doors won’t close, the windows are cracking, the walls are cracking. separate – things you would expect when a house moves.

Permafrost thaw and coastal erosion affect Point Lay and other northern slopes and Communities in northwest Alaska, as well as most places on the Panarctic coasts. With land subsidence, the rate of coastal erosion and the danger of flooding could increase, and all of these processes are expected to continue to cause loss of land, damage to infrastructure and habitat, and destruction of important cultural sites.

Tracey said a new study can help residents decide if they can adapt to the changes or if they should move.

Louise Farquharson, assistant research professor at the University of Alaska’s Fairbanks Geophysical Institute, is working on long-term projections of how coastal erosion and land subsidence at Point Lay, Wainwright and Kaktovik could cause significant seawater flooding.

“When permafrost thaws, the ground ice on it melts,” Farquharson explained. “This leads to the lowering of the ground surface.”

The amount of ice in the permafrost varies between communities and even within a village, making up between 40% and 90% of the ground in the Arctic, explained UAF geophysicist Vladimir Romanovsky. In coastal villages like Point Lay, the ice content tends to be higher. If 10 meters of permafrost thaws in such a place, 9 meters of ice may melt and flow away, leaving only one meter of soil in its place. Such dramatic land subsidence can bring coastal land below sea level, allowing ocean waves to rush in.

Predict permafrost thaw

Researchers have developed preliminary estimates of how permafrost will change in coming years, based on a combination of ground temperature measurements across the North Slope and numerical modeling of heat flux across the ground, Farquharson said.

Several climate change models were used to construct the estimates. In a scenario where the climate warms significantly, Farquharson concluded that by the year 2100, ground temperatures in the tundra could increase by 6 to 8 degrees Celsius, or about 11 to 14 degrees Fahrenheit. Gravel-covered roads and tracks absorb heat even faster than untouched tundra, and the temperature can soar 7 to 9 degrees Celsius, or about 13 to 16 degrees Fahrenheit.

“Any type of gravel on the surface will increase the temperature of the entire surface because it absorbs much more solar radiation during the summer,” Romanovsky said. “The tricky part is that for different landscapes, the changes in permafrost will be a bit different.”

The researchers plan to refine the study during fieldwork over the next two years by obtaining ground temperature measurements and permafrost ice cores to quantify ground ice content. They plan to incorporate data from temperature sensors from a range of structures with different foundation types and a range of vegetation and soil types across the three communities involved in the study.

Scientists are currently in the process of applying for permits to install temperature sensors at Point Lay and Wainwright and expect fieldwork to take place this summer, Farquharson said.

“When we have this projection and some knowledge of the ice content, we will be able to produce surface subsidence maps,” Romanovsky added. “Then the idea is to compare with sea level and see if an invasion will occur.”

In addition to analyzing permafrost change, UAF scientists are sharing their data with experts from the Cold Climate Housing Research Center and engineers from Penn State and Missouri University of Science and Technology, who produce technical estimates and develop mitigation efforts based on this data.

Penn State civil engineering professor Ming Xiao and his team examined the performance of infrastructure in Alaska in the face of climate change and developed computer models of how infrastructure will be affected. He said predicting future ground conditions will help engineers design better foundations and infrastructure solutions.

“Before implementing solutions, I think the first step is to better understand and even predict the performance of civil infrastructure over the next few decades,” Xiao said. “Ultimately, we want to develop a so-called infrastructure risk map.

Dealing with loss of land

Meanwhile, the Arctic landscape has already changed. Shorelines are eroding, and shrubs and other plants with deep root systems now compete with shallow-rooted tundra plants and berries.

“The tundra used to be hard, now it’s spongy, just like the carpet inside your house.” Rossman Peetok of Wainwright said in an Alaska Native Tribal Health Consortium report.

A continued rise in ground temperature leads to above-freezing conditions and melting ice, Farquharson explained. Ice thaw and widespread land subsidence cause the development of thermokarst – irregular surfaces of marshy hollows – both in and around communities.

To address problems caused by thawing permafrost and repair damaged infrastructure, the North Slope Borough is working to implement new construction and maintenance methods, according to the ANTHC.

Six years ago, the community of Point Lay lost its source of fresh water when the lake eroded and dried up, Tracey said. Now the inhabitants draw water from the river and desalinate it.

The Taġiuġmiullu Nunamiullu Housing Authority is using different foundation styles on the north slope to mitigate permafrost degradation, said the authority’s executive director, Griffin Hagle. For example, they previously used a foam “raft” foundation – a continuous slab made of an insulating material that distributes its weight over the entire surface of the building – which can prevent the heat of the house from penetrating deep into the building. frozen ground, thawing permafrost. and destabilize the structure.

The authority has also experimented with adjustable foundations using either adjustable telescoping footings or a “sled” steel frame that allows for adjustment, as well as moving the whole house if necessary.

“We haven’t had to…yet,” Hagle said.

Hagle added that while the authority doesn’t “build homes with hot tubs, saunas, or other lavish amenities,” designing portable, adjustable foundations adds tens of thousands of dollars to the cost. The addition is necessary to protect federally funded housing projects from undue risk.

“Such engineering solutions are justified as a hedge against the far more catastrophic expense of moving (or abandoning and replacing) conventional structures as the Arctic continues to experience disparate climate impacts,” Hagle said. “In a nutshell, it’s an insurance policy.”

In addition to adjusting infrastructure, the changes occurring with the land and sea also require residents to develop new knowledge to continue traditional subsistence practices, for example by expanding water-based hunting and decreasing ice-based hunting.

“You can’t use old traditional knowledge,” Tracey said. “In winter, when the rivers don’t freeze like they used to, you have to wait and a caribou doesn’t wait. So if you miss a caribou season, because things aren’t frozen and you can’t travel, you’re out of luck.

Because of the subsidence, residents of Point Lay lost all of their coolers used to store harvest, whether caribou, whale, walrus or seal, Tracey said. Some of them have been inundated with salt water or flooded by the thaw, and some have been destroyed by squirrels who can dig into the now softer ground.

“The last working cellar was about 10 years ago,” Tracey said. “Every ice cellar has disappeared. No one has room in your home for more than one freezer, so food safety has become an issue because of these changes.

Residents are increasingly relying on products they can buy at their store — the fastest growing store on the North Slope, according to Tracey. But the main help comes from sharing: other coastal villages share the harvest of whales after a successful catch, and hunters get seals for the elders.

“The whole North Rim fits into the old traditional split,” Tracey said.

The question remains whether these adjustments will be sufficient for Point Lay to maintain its way of life, and how quickly these changes will catch up with the northernmost communities.

“Our new normal is not to expect what happened yesterday because it’s different today,” Tracey said. “If we can learn from science, maybe we could help ourselves and understand that.”

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