Most icicles have the same carrot shape. But differences in temperature, wind conditions and water composition affect their final form
One morning in January of 1998, residents of eastern Ontario and southern Quebec awoke to find their world covered in ice. Icicles hung from everything – homes, trees, electrical wires – and more than a million people were left without power. Physics professor Stephen Morris is not interested in the atmospheric conditions that caused the ice storm, but is intrigued by the spectacular results – the icicles themselves. Are there physical laws that cause them to take the shape they do? And are all icicles the same?
Morris is attempting to answer these questions in a chilly, closet-sized laboratory in McLennan Physical Labs. His interest in the subject is not purely whimsical. He points out that it’s important to know how ice forms on surfaces such as airplane wings, and says the physics behind icicle formation can be applied to other phenomena, such as how roads get ripples and how stalactites form in caves.
In his lab, Morris and PhD student Antony Chen tested a mathematical model for the ideal or Platonic icicle (as theorists call it), an elegant set of formulas that predicts a universal shape for all icicles. Using a machine with a central rotating dowel, they created icicles and photographed them as they formed over 10-hour stretches.
While most icicles are carrot-shaped and some are very close to the Platonic ideal, Morris and Chen found that differences in temperature, wind conditions and water composition affect their final form. Curiously, icicles grown in perfectly still air split at their tips, and water impurities can cause asymmetrical lumps.
While the wide variety of icicle shapes they created was surprising, the physicists took greater interest in the mathematical aspects of the problem and the motion of ripples that form on the icicles’ surface. Morris added that theories about the patterns that emerged can be applied in fields as diverse as economics and, yes, weather.