Of Icicles and Ice Sheets

As a geologist, I study ice. Not the kind of ice that you make in your freezer, and not the ice in the snow that rapidly melted this spring, leaving vast swaths of mud behind. I study continental ice sheets, whose thicknesses are measured in kilometers and whose geographic boundaries included whole nations.

This past February, though, I found myself observing a more intimate form of ice – one much closer to home than the ice I study (at least, closer in time). One morning, a blinding gleam caught my eye from my office window, and the icicle refracting the light suddenly seemed a bit more interesting than my email.

Here in Madison, near where those continental ice sheets once tapered out (at least, near in space), we’d had a few weeks of heavy snows – several storms that brought at least 6 inches each. Then, a false spring with warm weather, and falling snow was replaced by the steady drip of snowmelt from the eaves. Then, the cold hit. Endless days when even if the temperature deemed to rise above zero Fahrenheit, the wind conspired to keep the chill negative.

All of this weather, taken consecutively, accumulated to incredible icicles. Long, dangerous daggers menacing the ground below and broad, sturdy cascades suggesting motion and gravity despite clinging stubbornly and still to the straining gutters. When they caught the sun at low angles, in the early morning or late evening, they became more than icicles – they filled with fire.

In my work I study ancient ice – what’s the deep time history of the glaciers that periodically grow across northern North America? It was too tempting to shift to thinking about ice still frozen, far more tangible than searching for the ghosts of ice long since melted.

So, for a week and a half, I bundled up against subzero temperatures, tromped through the surprisingly shin-deep snow, and measured the length of that opaline ice dagger. I figured I was in for a straightforward story of steady growth. After all, when it’s cold, ice should grow. That’s how it works on my glaciers. 

But, there wasn’t a single day that I saw the icicle grow. Instead, each evening I measured a slightly shorter, thinner icicle – becoming more and more a dagger and less a fencing sword. What I thought would be progression was instead retrogression, until it shrank so small that one warm day was enough to do it in.

I realized that the ice, as it slowly wasted away, was sublimating. When it’s cold enough, ice can turn directly to water vapor, skipping the burdensome processes of melting and boiling altogether. This process of sublimation evokes the Romantic use of its root, sublime, which would have been commonly understood in the 19th century to mean “ascending close to god.” That which was sublime transcended its physical bounds and rose to a heavenly source of awe. Much like solid ice dissipating to join the gaseous atmosphere.

Dissipating, that is, until its collapse. By the time temperatures climbed above freezing, in late February, the fire-cicle had only the most tenuous grasp on my eaves. Its last evening, I found only a shattered segment of ice melting into a basement window well.

It was one of the first icicles to give into Spring, but it was a harbinger for its more robust cousins in the neighborhood. Within a few days, the ice cascades that had clung to the rooflines were all gone, contributing to the growing pools of mud that my dogs can never seem to avoid.

I’ve been reminded in the weeks since that thaw of something I was told years ago, after my first Midwestern winter. Up here, apparently spring is “mud season.” In a manner of speaking, all of modern human existence has taken place during the “mud season” of the most recent iteration of the 100,000-year glacial cycle. The perceptible annual cycles of freezing and thawing are superimposed upon a similar cycle that’s orders of magnitudes longer. Over the last ~15 thousand years, we’ve been on the thawing arm of that long cycle. In Wisconsin, we walk across a landscape defined by the melting of glaciers. From the point of view of a kilometer-thick glacier, the rubble-like sediment that defines much of Wisconsin’s soil and surface geology is much like the mud from spring snowmelt from the perspective of a single winter’s snowpack. The hill my house sits on is just a piece of ground that happened to not get scraped away when ice covered Madison.

Much of our current climate depends on the Greenland Ice sheet, currently clinging ever more tenuously to its “roofline” in the north Atlantic Ocean. Our annual spring mud season ends in the warmth of summer. So, too, is the longer mud season coming ever closer to an end defined by the summer of climate change. As a result, our familiar mud season comes earlier and earlier each year after a shorter winter, and a lot less ice gets to sublimate.

When I moved to the upper Midwest as an 18-year-old southerner, I suppose I expected sublimation in the sense of temperature – at least, I knew it would be too darn cold! But I didn’t expect the sublime in the sense of awe-inspiring nature. Now, as I walk through the rocky remains of a post-glacial landscape, or see the incandescence of icicles on my eaves, or even tromp through the mud on that first glorious day of spring each year, I’m grateful that I’ve come to a place that’s so sublime. A place where the boundaries, between ice and vapor, between glacial moraines and muddy paths in the woods, between icicles and ice sheets, between the past, the present, and the future, are all boundaries that can sublimate away – leaving behind only awe, and hope, and spring.

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