TORONTO – Have you ever wondered what causes the ripples in icicles?
Some scientists at the University of Toronto have, and they finally have an answer: salt.
Sure, it’s barely fall, and icicles are likely far from your mind. But these researchers wanted to understand why the Michelin-Man-like ripples form in icicles.
“Nobody has systematically investigated what causes the ripples so we began growing them in the lab,” said Antony Szu-Han Chen, lead author of a paper published online this week in New Journal of Physics.
So Chen and experimental physicist Stephen Morris decided to grow icicles in their lab.
This wasn’t merely to satisfy their curiosity, however.
“Our motivation is pure curiosity about natural patterns, but the study of ice growth has serious applications, including ice accumulation on airplanes, ships and power lines,” said Morris. “This result is totally unexpected, not just by us before we did this, but by theorists and experimentalists in our field who study ice dynamics and pattern formation.”
This movie shows icicles grown under identical conditions of ambient temperature, water supply rate, and nozzle temperature. The icicle grows from a rotating support over a period of about 10 hours. The support looks like it’s rotating fast, but actually takes about four minutes per rotation.
Using pure distilled water, distilled water with small quantities of sodium chloride (salt) as well as Toronto tap water, which contains sodium chloride and other impurities, they grew icicles under a range of conditions.
Distilled water didn’t provide ripples; icicles with a small amount of salt did, about 20 mg of salt per litre.
“No theory accounts for the effect of salt, so the shape of icicles and the reason for their ripples are still mysteries,” said Chen. “Except we now know that a little salt is required in the recipe.”
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