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Glacier Athabasca et des champs de glace Columbia
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As much as anything - its stark beauty, raw power, easy accessibility or hidden menace - the Athabasca Glacier is memorable for its links to the past. Look down. Here, beneath your feet, is ice that is at least 150 years old. A ball of snow will gradually turn to ice if it can be protected from thawing, but a thickness of at least 30 metres (nearly 100 feet) is required before the overlying pressure forces the ice to flow. It takes many years for snow to accumulate to that depth and much longer for it to flow from the heights of the parent icefield to the end of one of the outlet glaciers.
Look up. High on the horizon is the edge of the Columbia Icefield. Covering an area of more than 300 square kilometers (120 square miles), this is the largest glacial remnant in the Rocky Mountains. Fifteen thousand years ago, it was part of an ice sheet that stretched from the foothills of the Rockies to the Pacific Coast, mantling Canada's western edge so thickly that only the tips of the highest mountains poked above the frozen wastes. In the past 12, 000 years, periods of global warming (abetted in the recent past by humankind's increased emissions of carbon dioxide) have greatly reduced the dominion of the ice, but Earth's astronomical cycle is tending toward lower temperatures and another glacial advance seems inevitable.
On your right the effects of the glacier's most recent advance are clearly evident in the high lateral moraines along the valley walls. About 700 years ago, having shrunk to a tiny relic of its former glory, the Athabasca Glacier began once again to expand. Feeding on the long, snowy winters and brief, cool summers of a period climatologists call the Little Ice Age, it surged down the valley, mowing down a forest of spruce and fir that had grown up during an earlier period of relative warmth. You can see a remnant of the forest between the Athabasca and Dome Glaciers. Some of the gnarled Engelmann spruces in the triangular patch are between 680 and 720 years old. By 1840, the Athabasca Glacier stretched far down the Sunwapta River Valley. Had the Icefields Parkway or Icefield Centre existed then in their present locations, they would have been scoured from the landscape, just as the forest was.
In the latter half of the 19th century, the climate began to warm and the ice slowly began to melt, leaving a large terminal or end moraine to mark its farthest extent. Since then, it has receded about 1.5 kilometres (one mile); Parks Canada has placed markers along the road to the upper parking lot to mark its retreat during the past century. Still, even today, the Athabasca Glacier is a sizeable chunk of ice - six kilometers (3.7 miles) long, one kilometer (two-thirds of a mile) wide and up to 365 metres (1,197 feet) thick. Despite its size and thickness, if current warming trends continue, much of the glacier may melt over the next century, and the world could lose about half its glacial ice.
Some experts believe the icefield was born as long as a million years ago, and that it may have weathered many other periods of interglacial warmth. Guarded by 11 of the Rockies' 22 highest peaks and located at an average elevation of 3,000 metres (9,840 feet), it is nourished by about 10 metres (33 feet) of snowfall annually, snow that accumulates in every month of the year. In places the ice is 900 metres (2,952 feet) thick.
Its highest point is called the Snow Dome. This is the hydrographic apex of North America, the only point on the continent from which rivers drain into three oceans - the Arctic, the Atlantic and the Pacific. Ice flowing away from the Snow Dome down the Athabasca Glacier eventually ends up in the Artic Ocean, via the Sunwapta, Athabasca, Slave and Mackenzie Rivers. Ice flowing to the southeast, down the Saskatchewan Glacier, ends up in the Atlantic Ocean, travelling via the North Saskatchewan, Saskatchewan and Nelson Rivers into the Hudson Bay. And ice flowing west and southwest is headed to the Pacific Ocean, via Bryce Creek and the Bush and Columbia Rivers.
Just as the advance of the Athabasca Glacier has left its imprint on the valley, so its retreat is leaving equally explicit signs. Some of the most obvious are the till ridges that can be seen between the toe of the glacier and the highway. Called recessional moraines, they are created by the stones and debris that melt out of the toe of the glacier.
During a period of increasing warmth, like the one Alberta has experienced for more than a century, the ice melts faster than it can be replaced and the front of the glacier retreats. But because it is on a mountain slope, the ice in the glacier is also continuously flowing downhill. But it is important to understand that, because the rate of melt has generally surpassed the rate of flow in the recent past, as a whole the glacier has shrunk substantially. The recessional moraines serve as markers or signposts of this retreat, like a reverse growth chart.
The rate of retreat varies from year to year. In 1976, Parks Canada judged that the middle of the glacier flowed forward at least 35 metres (115 feet), but melted back about 38 metres (125 feet), receding a total of three metres (10 feet). In other years, the total meltback can be as much as 30 metres (98 feet), or as little as none at all. When the rate of advance and retreat are about equal, the ice front stalls for a time, depositing the rock and mud debris that accumulates in a growing moraine. There are several of these distinctive ridges between the toe of the glacier and the highway, each marking a time of hesitation in the overall retreat of the ice.
Over near the V-shaped remnant forest, you can also see lateral moraines, sharp-edged ridges of till and fallen rock that have collected on the sides of the glaciers. The Athabasca Glacier's lateral moraines now stand high above the ice surface, showing how much melting has occurred in recent decades.
The process of colonizing the lifeless glacial till of both recessional and lateral moraines begins almost immediately, but takes years to accomplish. Lichens and mosses are usually first, followed by pioneer plants such as river beauty and yellow dryad, and later by shrubby cinquefoil and mountain avens. Tiny Engelmann spruce seedlings shelter among the boulders. A century or more after the ice departs, the landscape will be carpeted with willows and grasses, and a new forest of Engelmann spruce will complete the takeover.
Where it's snow covered, the Athabasca Glacier is white, but its edges and deep crevasses reveal the real color of the ice. Formed under intense pressure, glacier ice has little air in it and the light that would normally be reflected by air bubbles instead penetrates deep into the ice, where it is largely absorbed. Only the blue-spectrum waves are reflected and scattered, giving the glacier its deep turquoise color. This is particularly obvious in crevasses and in millwells, rounded drain shafts that carry meltwater from the surface of the glacier to its base, where it runs in tunnels under the ice. In these millwells light rebounds upon itself, increasing the intensity of the color.
A good part of the Athabasca Glacier's popularity is due to its remarkable accessibility. This is the only glacier in North America located just a short walk from a parking lot.
Walking and coach tours are available, and can be arranged at the Icefield Centre. These are led by knowledgeable guides. Others should stay off the ice. The surface is often wet and slippery, and there are many deadly crevasses in the glacier, hidden by snow until mid-summer. Several deaths have occurred when unknowing visitors have slipped into crevasses.
GETTING THERE: The Athabasca Glacier is located about midway along the Icefields Parkway, just north of the boundary between Banff and Jasper National Parks, 125 kilometres (78 miles) north of Lake Louise and 106 kilometres (66 miles) south of Jasper. The adjacent Icefield Centre, which opened in the spring of 1996, provides parking, carries information and displays about both the glacier and the Columbian Icefield, and offers food and accommodation.
Reprinted from Barbara Huck and Doug Whiteway's In Search of Ancient Alberta with kind permission from Heartland Associates, Inc.