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Epilogue To The Ice Age

Epilogue To The Ice Age

Massive landslides and shifting rivers may mean the Laurentide Ice Sheet is only now disappearing from Canada’s North
By Tim Edwards
May 30
2017
From the April 2017 Issue

A moose sniffs the air on the Peel Plateau. While the sedges and willows around him are fine, a richer smell hangs in the air, and that scent brings him to a strange place. Here, the land has split open. 

A hill has been crumbling for a decade, as its underlying permafrost melts away. In its place are rivers of mud, as slow as lava, flowing into a little stream—but in the middle of the swirl, bright greenery grows in the virgin soil this landslide has uncovered. The moose makes a break for it. Later, researchers find his bones among the muddy debris.

Wounds like this are opening up throughout the northwest of the Northwest Territories. Two years ago, news agencies across Canada reported on a landslide that was gradually approaching a small lake in the Mackenzie Valley. Since then, the lake has been reached and its wall has been breached. All around the edges of the landslide, trees and grass drip down like foam over the rim of a pint glass.

The scale and method of change is unlike anything North America has seen since the Laurentide Ice Sheet retreated to its few holdouts in the High Arctic, thousands of years ago—and in fact, it seems to be exactly like that. The thawing ground is behaving as if the Laurentide Ice Sheet had just retreated.

The border between the Laurentide Ice Sheet and the underlying ground was not always well defined, because it wasn't cold, hard ice all the way down. Imagine a cross section of the Northern earth and overlying, with a line running through it, deep down at the lower limit of the permafrost. This signifies where the chill of the atmosphere meets the geothermal warmth of the planet. In some places, where the ice sheet was kilometres thick, the geothermal warmth of the planet caused the base of the ice sheet to melt, allowing the ice to slide and deform. In other places the ice sheet was frozen to the earth. These factors combined and made the base of the glacier a slurry of water, sediment and rock, mixed ground and ice. 

When the ice sheet retreated, this debris was left in unstable places—pushed up against a mountainside, left in steep hills held together by underground ice and preserved by permafrost—and warming temperatures, rainfall and the flow of nearby rivers all worked to dismantle this landscape until it settled into a new equilibrium. You can see the end result in the gently rolling hills, called "moraines," of northern Ontario. But according to a group of researchers, you can see that earlier picture, of the unstable hills of sediment and ice, today in Canada’s North. ˚

The entire phenomenon is wrapped up in the complexities of climate and environment. As the Earth's climate warmed, the ice sheet retreated. The North was warm enough that there were forests where Tuktoyaktuk now sits. The intense period of warmth was short-lived enough that much of the now-ancient permafrost and ground ice remained, but strong enough that this landscape is more stable because it already had some chance to stabilize. Areas like Banks Island, an icy polar desert to the north, has big moraines that, as acclaimed Arctic researcher John England says, looks as if the glacier had just retreated. The cold of the North has largely preserved a glacial landscape.

But now, as the planet’s climate warms due to atmospheric changes—and with related phenomena like increased rain in places like the Peel Plateau—the last stages of deglaciation, which took place across much of the continent thousands of years ago, is finally taking place here.

“We have learned that the glacial inheritance of permafrost landscapes has a very strong influence on landscape sensitivity and how it's likely to change in the future,” says Steve Kokelj, a permafrost scientist with the Government of the Northwest Territories. Kokelj has been a leading researcher on the phenomenon, and just co-authored a paper on the climate-driven thaw of preserved post-glacial landscapes in northwestern Canada, published in the journal Geology.

Kokelj and his team built on previous research, that of England and others, to link the pattern of these massive landscape changes across the North to a map detailed with the positions of the Laurentide Ice Sheet as it retreated. The result is striking. In a place like the Beaufort Delta, which was never completely covered by the ice sheet, you can see the stability of the land that was never covered contrasted with the extreme instability once you hit the previously glaciated terrain. “These landscapes have been hung up in time,” says Kokelj.

This ground ice is not melting from the surface down. Often, it begins on the side of a hill, worn away by rainfall that is more frequent these days than it has been before, revealing a portion of permafrost. Exposed to the warm (and gradually growing warmer) seasonal air, that permafrost melts away in a slurry of saturated sediment. This wound eats its way through the hill like one would eat a candybar, until it reaches stable ground, creating new ridges and depressions. It also happens in river systems, where the banks are eroded away to reveal their permafrost banks, which are then eaten away, changing the flow of the rivers (not to mention turning them muddy and inhospitable in the process, which they will remain until all the sediment is flushed out of them downriver, way in the future).

The research means different things for different people. For the communities nearby—like Fort McPherson in the Mackenzie Delta and Sachs Harbour on Banks Island—this research can be used to predict the extent of change to the surrounding landscape that they can expect. For geomorphology nerds, it’s a window into the past. (And what’s more, though the paper didn’t delve into it, Kokelj believes much of the permafrost in this northwestern region of the NWT may actually contain buried glacial ice—actual ancient remnants of that dirty, deformed bottom of the Laurentide Ice Sheet.) For zooarchaeologists, these landslides are uncovering items like the jawbone of a miniature horse, whose species roamed these lands in the Pleistocene Age.

In general, this is showing an immediate effect of climate change. While the permafrost is not all thawing, it is more unstable than it has been in colder times. And this sensitive ground is the perfect theatre to view how different the climate is now than it has been for most of the last 10,000 years. The Northern landscape is changing as it finds its new equilibrium in a warmer, wetter climate. “We just need to be prepared to see things that we haven’t seen before,” says Kokelj.