Work planned for Yellowknife airport to deal with thawing permafrost

The Yellowknife airport is planning for some work in the coming years on its runways, to deal with thawing permafrost.

Yellowknife Regional Airport manager Randy Straker says geotechnical engineers were contracted last year to look at ground settling found on the runways.

"They basically said climate change resulting in permafrost loss was the contributor to the settling that we're seeing at the airport. Settling is never a good thing when you're talking runways," said Straker.

Permafrost is present in ground that has been at 0 C or lower for at least two years in row. When permafrost thaws, it can cause ground movement including settling or subsidences and those can be more severe in areas where there was more ice in the permafrost.  

After the N.W.T. government sought proposals from contractors in February 2023 to complete the geotechnical study at the airport, Tetra Tech was contracted for $232,066. Engineers took observations and drilled for core samples in areas where the ground was settling.

Straker says Tetra Tech presented its findings in March of this year after studying ice and moisture content as well as surveying areas for permafrost or bedrock. He says they found that the permafrost beneath the airport had changed significantly over the last decades. 

"In 2005, all bore-holes that they drilled at the time encountered permafrost except for two. During the study done last year, only five of 14 bore-holes encountered permafrost," he said.

Straker said in locations where there was still permafrost, it had "degraded significantly."

He says currently there are no immediate threats to the runway but getting the scientific data helps determine the sort of work that may be needed in the next five to ten years. 

Permafrost thaw across the North has put some infrastructure at risk, including buildings and homes, as well as roads. 

Steve Kokelji, a senior permafrost scientist at the Northwest Territories Geological Survey, says climate change is one factor causing ground settling but disturbing the natural state on the ground is an important part to consider as well.

He noted how vegetation, soil and snow on the ground can affect how energy is exchanged from the atmosphere to the ground. That changes when areas are developed and built on. 

"Regardless of whether the climate is stable or the climate is cooling, or you're in the high Arctic where it's cold or in the subarctic where it's warmer — when you actually take those natural conditions away and replace them with infrastructure, that changes," said Kokelji.

On places like a runway or a road, Kokelji said clearing snow can help cool the ground beneath because snow acts an insulator. But when snow is removed and collects on the edges, it can accelerate the warming of the soil beneath there, he said.