‘Ottawa’ Science of Winter: The Man Who Grows icicles For a Living
This winter, the Citizen’s Tom Spears looks at snow and ice and wildlife to find out what makes our coldest season tick. It’s a series we call The Science of Winter, and today we chat with a man who’s still wrestling with why the tiniest pinch of salt changes the shape of an icicle.
There’s a lab at the University of Toronto where people grow icicles and try — so far without success — to figure out why they grow in the shape that they do.
Stephen Morris is a physicist, the J. Tuzo Wilson Professor of Geophysics, and he has been wrestling with this problem for years. But so far his long, complicated theory isn’t enough to explain the shape, and specifically what he calls ripples on the side of the icicle.
“The reality is, we know more about the mass of the Higgs boson than about the ripples on your garden-variety icicle,” he says.
He studies icicles “for the same reason as people climb Mount Everest, because it’s there. … What gets me out of bed in the morning is that these are beautiful things that we can spend time puzzling ourselves about. It’s an appreciation of nature.
“I’ve always been interested in the physics of everyday natural objects you see beside the road. I’ve worked on things like washboard roads. I’ve worked on lava that cracks into columns. … If you have your eyes open for unexplained patterns in nature, the bumps or ripples on an icicle are something that jump out at you.”
A few years ago, Morris built himself an icicle-growing machine: A box covered in pink insulation, with controls for variables including temperature, wind and how fast the water flows inside it.
He grows icicles as water drips down a wooden dowel that’s on a homemade rotisserie, and a camera takes photographs every 30 seconds that meld into a time-lapse video. (The slow rotisserie makes sure that the icicle gets equal exposure to cold and wind all the way around.)
An icicle made from distilled water will have a classic smooth cone shape, he found.
But when he uses tap water, he gets a different shape. There are ripples on the icicle — a regular series of bulging rings “sort of like the Michelin man.”
These form on natural icicles, too. And Morris concluded that impurities that dissolve in the water (such as salt) are the cause, changing the freezing point of the water slightly.
“The weird thing was that ripples were not observed in distilled water but they were observed even with the tiny levels of impurities in tap water,” he said.
An oddity: The ripples are always about one centimetre wide, no matter how big the icicle is or where it forms.
Morris doesn’t know why. “We’ve tried everything,” he said. “We’ve changed the flow rate of the water, we’ve changed the air motion … we’ve turned basically every knob we’ve got,” with no change.
Another puzzle: When he adds just a tiny amount of salt, the ripples form and then slowly shift higher and higher as the icicle grows. The original ice itself isn’t moving anywhere, but new ice forming on top of it is making the ripple effect rise up the outside. Yet when there’s more salt, the ripples slowly descend as the icicle grows.
He doesn’t know why one needs impurities to get ripples. Or why ripples shift up and down as the salt concentration changes.
Morris ended up with 230,000 photos of icicles and put them all into an online Icicle Atlas — free data to all, inviting the world to wrestle with the problem.
If you like the icicle videos, you won’t want to miss his x-ray tomography of columnar joints in cornstarch.