by Patricia Robertson
Fabrice Calmels is spending a lot of time these days getting to know the Alaska Highway - or more accurately, the permafrost underneath it.
A research associate with the Northern Climate ExChange (NCE) at the Yukon Research Centre in Whitehorse, Calmels is carrying out a three-year survey of the Alaska Highway in order to map the distribution and characteristics of permafrost.
“Some parts of the highway are settling because of thawing permafrost,” says Calmels. “We need to know exactly where the problems are and where we have to intervene.”
Working in collaboration with the Department of Highways and Public Works, he’s focusing on the 200 kilometres between Kluane Lake and the Canada/U.S. border because “it’s the most problematic section of the highway,” built almost 90 to 95 per cent on permafrost.
Calmels’ job of locating and characterizing sensitive permafrost areas along the highway is part of addressing one of the most important issues facing northern Canada during the upcoming decade.
“Parts of southern and central Yukon are in a discontinuous permafrost zone, where some areas have permafrost and some don’t,” explains Calmels. “In the High Arctic, the temperature of the permafrost might be 10 degrees below zero. But when you have discontinuous permafrost, as in the southern Yukon, the temperature of the permafrost is close to zero degrees already.”
And that means that it doesn’t take much of a rise in temperature for the permafrost to begin thawing, with serious consequences for infrastructure like highways.
This year, the first year of the project, the team is mapping the distribution of permafrost as well as drilling close to the highway to see what kind of permafrost exists below some of the most critical sections.
Which begs the question: Is there more than one kind of permafrost?
It turns out that permafrost, or cryotic soil, is any kind of ground - soil, rock, organic matter, even ice - that remains at or below the freezing point of water (0°C) for two or more years. “The definition of permafrost is about this temperature,” says Calmels.
If you’re at an altitude where the air temperature is cold enough, you can have permafrost - even in Hawaii. “Climate is the main factor. But surface conditions are important, too. If you’re in a wetland, the surface water will keep the ground warm and you won’t have permafrost. You need a mean annual air temperature at the ground surface equal to or below 0 degrees C.”
Even non-porous bedrock can be permafrost, in which case there may be no ice at all. “If you have frozen bedrock, you don’t have a problem because there’s no ice in it,” Calmels notes. “Bedrock can freeze, and it freezes even deeper than sediment. It’s very conductive. The cold can penetrate more easily in bedrock than in other material.”
But permafrost often does contain ice, and that leads to problems with highways or buildings built on permafrost, especially in an era of climate change.
“The problem with permafrost is where the volume of ice exceeds the natural porosity of the soil or rock,” says Calmels. “If you have a lot of excess ice, as in the photo, obviously when it melts it leaves a void, and then you have settlement and ponds forming. That affects transportation infrastructure like the Alaska Highway.”
Permafrost is a moving target because it has a layer at the surface, called the active layer, which thaws and then refreezes each year. “You can see it in the landscape - you see small frost mounds with tilted spruce trees growing on them,” says Calmels. “The spruces are tilted because of the thawing and refreezing of the active layer. The trees have to adjust to these movements.”
Those frost mounds, called palsas, are islands of permafrost in the landscape or along the highway. “You can see these mounds easily from the air or by visiting the site, so we use this kind of indicator to map permafrost,” says Calmels.
Calmels also uses a permafrost probe, which he inserts in the ground along the highway to find the top of the permafrost. “You go through the soft material (the active layer) and touch the top of the permafrost, which is hard like concrete. Then we take the drill and extract sample cores that we can examine in the lab to find the volume of ice in the permafrost, what kind of sediment it contains, and how much.”
The drill they’re using this year can’t go below about six or seven metres, “so if there’s ice buried beneath that, we won’t find it. In some areas we suspect that there is ice at deeper levels. Next year, we’ll go back to those areas and use a different kind of drill.
“Sometimes sites look similar on the surface, but when you drill you find different kinds of soil, different kinds of permafrost. We’re learning more about the laws that govern discontinuous permafrost.”
In the project’s third year, with the distribution of permafrost mapped, the team will work with a climate model to see how the permafrost will degrade and at what rate. “That will mostly depend on the nature of the ground, the quantity of ice, the ground temperature, and the air temperature used for modeling,” says Calmels. “It takes more heat to thaw solid ice than frozen sediment, so ice may take longer to melt.”
Calmels has also turned to archival records to determine where sections of the original highway were realigned to make them straighter, sections that are now often experiencing degradation. “For example, if you block a stream with an embankment, the water will start to accumulate and melt the permafrost. The wind blowing snow will start to accumulate on one side of the road and will insulate the embankment and cause degradation. These problems are not related to climate warming, but they do not help.
“When they built the highway, 70 years ago, they scraped the organic layer off, which is bad because you’re removing the protective layer and that automatically starts the degradation of the soil. You have to use good engineering practices to keep your permafrost happy. But now the climate is warming, and even if we build properly and use devices to maintain the permafrost, in time it’s still going to degrade.”
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.