Guy Dore/Laval University
NOT SO PERMANENT A pool of permafrost meltwater has formed along the Alaska Highway near Beaver Creek, Yukon.
WHITEHORSE, Yukon Territory ? In February 1942, President Franklin D. Roosevelt gave the Army Corps of Engineers an assignment: Build a road from British Columbia across the Yukon to Alaska ? in eight months, before winter sets in.
Japan had just destroyed much of the Pacific fleet at Pearl Harbor. Alaska was vulnerable to invasion (in fact, the Japanese occupied two Aleutian Islands that June). If Americans did not build a supply road linking Alaska to the heart of North America, the thinking went, invading Japanese would do it for them.
But prospects for success were poor. The road would traverse 1,500 miles of mountainous subarctic terrain, most of it unsettled, heavily forested and unmapped. Engineers would face fierce cold, fierce heat, vicious insects, and vast stretches of permafrost and boggy terrain called muskeg that swallowed bulldozers whole.
Nevertheless, the Alaska Canada Military Highway was declared open the following October. Nicknamed the Alcan, this so-called pioneer road was little more than a gravel lane passable only by military trucks. Still, people called it the 20th century?s greatest engineering feat, after only the Panama Canal.
Today, as the road now known as the Alaska Highway celebrates its 70th birthday, cars and trucks flash along what Wally Hidinger calls ?a very good standard two-lane highway? from Dawson Creek, British Columbia, to Fairbanks, Alaska. ?Our mantra is bare, dry pavement 365 days a year,? said Mr. Hidinger, who directs transportation engineering for the Yukon territorial government. It is a vow he and his staff can keep.
They rely on remote sensing technology to anticipate bad weather and keep the pavement clear. They work to unkink twists and turns left over from the original construction, when the builders dealt with muskeg and other obstacles by curving the road around them.
But today the Alcan faces challenges that could not have been predicted when it was built. By far the biggest is permafrost, the permanently frozen ground that underlies much of the road.
As the climate warms, stretches of permafrost are no longer permanent. They are melting ? leaving pavement with cracks, turning asphalt into washboard and otherwise threatening the stability of the road.
Not all of the melting is due to climate change. Road improvements like heat-absorbing dark pavement alter conditions in the ground beneath, particularly if a lens of ice lies close to the surface. Merely removing roadside vegetation to uncover dark soil can have a melting effect.
Another problem is fire. ?Even a natural forest fire will change the surface of the road,? leading to melting, said Bronwyn Benkert, who studies cold-climate issues at the Yukon Research Center, and who is researching highway conditions north of here, near the Alaska border.
But climate change is most worrisome of all. Not only is the world warming: it is warming fastest in high northern latitudes. And the problem is getting worse, with no easy solutions.
If the permafrost is patchy ? ?discontinuous,? in geological parlance ? even identifying areas of melt risk is tricky. Highway engineers have been drilling core samples along the roadway for 50 years, but ?if you don?t drill in the right place you won?t find it,? Mr. Hidinger said. ?We don?t even have a precise picture of the soil conditions under the road.?
So engineers are using ground-penetrating radar and instruments to measure gravity variations, among other techniques, to try to identify permafrost areas.
In a test section near Beaver Creek, at the Alaska border, researchers and engineers are also experimenting with ways to limit permafrost melting along the highway, including rock embankments that insulate the ground in summer, keeping it relatively cool, and help carry cold air below ground in winter. Elsewhere, the engineers have replaced asphalt with light-colored pavement to reduce the amount of heat the road absorbs. Unfortunately, it costs up to 10 times as much as ordinary pavement.
Source: http://feeds.nytimes.com/click.phdo?i=13af46738ed3fbf4e3cce331ff5cb128
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