SI Vault
John Hildebrand
December 15, 1980
A nameless range of hills runs across the U.S. from central Montana as far east as Long Island. Like a Great Wall whose origins lie in the distant past, this rim of earth outlines the farthest advance of the last great ice sheet of the Ice Age. Retreating north 10,000 years ago, the glaciers left behind a moraine, a belt of hills and hollows with Middle-Earth names like kettles and kames and eskers. Even in New York City one can see the imprint of glaciers on the ice-eroded rock outcroppings of Central Park. But the best place to track down the ice sheet is in Wisconsin, where the 1,000-mile Ice Age Trail follows the moraine across the state. And the best time to do so is in the dead of winter.
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December 15, 1980

In Which A Solitary Skier Traverses The Icy Remains Of A Glacial Epoch

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I awoke at dawn after a fitful sleep and fixed breakfast. The down-filled mummy bag had been warm but too constricting, and I awoke often during the night, not from the cold but from vivid dreams of live burial. Repacking the sled, I was off again, skiing hard to warm up. The trail recrossed the Yellow River on a puncheon bridge and veered northeast through a hardwood forest broken by flat-topped hills. Called perched lake plains, these truncated hills were once the bottoms of ice-walled lakes on the surface of the glacier. As the glacier melted, the lakes filled with sediment until only the lake bottom remained elevated.

Atop one of these hills, the wind chill became appreciable, as if the gusts were coming off the ice pack. I had become aware of a growing numbness in my left index finger where the wool lining of my mitten had worn thin. Removing the mitten, I stuck the finger in my mouth to revive it. It felt disconnected from the rest of my hand, like a lump of wax. Slowly, feeling returned in a wave of prickly pain, a sign that frostbite hadn't occurred.

By noon I'd covered perhaps four more miles of undulating trail. I set a lunch of venison sausage and cheese on a granite boulder, a souvenir of Canada's Laurentian Plateau that was carried along and laid down in this oak forest by a long-vanished glacier. Among the farms bordering the Chequamegon were smaller granite stones stockpiled along fencerows or set into the foundations of tottering barns.

The incongruity of such enormous rocks, called erratics in geologic terminology, existing far from their native bedrock, triggered a heated scientific debate in the last century. The most popular theory held that the boulders had been moved hither and thither by the Great Deluge of Noah. A variation of this idea was that icebergs had rafted the erratics about when the sea level had been much higher. But the most preposterous explanation, the most incredible, came from Louis Agassiz, a young Swiss naturalist, who told the Swiss Society of Natural Sciences in 1837 that all of Europe had been covered by a massive sheet of ice!

Agassiz was familiar with the effects of glaciers in the Swiss Alps and recognized ice-eroded landmarks far from the mountains. His explanation was that in an earlier time, glaciers had wandered far from their modern haunts in mountain redoubts. While not the first to propose glaciation as the mover of erratics, Agassiz gave the world its first look at the Ice Age.

Snow was falling as I made my last camp on an esker ridge overlooking the frozen Mondeaux Flowage. The-light dusting didn't interfere with my fire building. The ice fishermen had all gone home, and I was thinking about how nice it would be to return here in the summer and fish for muskellunge.

How easily we accept the certainty of seasons, and feel assured that winter necessarily gives way to spring when seasonal change is in reality a constant struggle. What if, as occurred during the Pleistocene epoch, winter never left?

Pleistocene wasn't one interminable cold snap but four separate stages when winter won out over milder seasons and glaciers began to march. The most recent stage is called the Wisconsin because the ice sheet left its imprint so visibly in that state. But many scientists believe we are still in the Pleistocene, living in an interglacial lull.

"A surprisingly small reduction in temperature could start glaciers advancing again," Tanner had told me. "We're only talking about a 5° to 10° change in the mean annual temperature, say from 58° to 53°. Once a winter climate is established—if, for example, the snow doesn't melt one year—we're on our way to another ice age."

Even if the glaciers are coming, I'm not very anxious to buy that desert rancho in The Sunbelt. Winter offers its own rewards, and one of these is snow-camping. After the fire is made, dinner boiled and eaten, the woodpile and the last of the brandy loom ahead as the evening's entertainment. In the dark woods a coyote howls. Other coyotes join in until the night rings with their wailing. Heard alone on a winter's evening, the howling seems at once alarming and melancholy, like some primordial country music played on the listener's nerve endings.

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