Icicle waves go with the flow

Many icicles develop wavy surfaces that look as wrinkled as pushed-up shirtsleeves. That’s strange, but what really has captured some scientists’ attention

RIPPLY RODS. Competing heat-loss patterns can cause these icicle waves. Ogawa

is that the distance between surface bulges always averages around 1 centimeter, no matter how thick the icicle is.

A trickle-down effect could generate that surprisingly regular waviness, propose Naohisa Ogawa and Yoshinori Furukawa of Hokkaido University in Sapporo, Japan.

During an icicle’s growth, a thin film of water from melting snow and ice above an icicle flows along the hanging shaft and refreezes onto the icicle’s surface. Because any slight, random bulges in an icicle’s girth pack extra surface area, heat more readily escapes from them and so meltwater more readily refreezes onto them than onto smoother areas.

As a result, the bulges thicken, encouraging the formation of a rippling surface. On the other hand, water that’s slightly churned by passing over the bulges doesn’t carry heat away from them efficiently. This tendency counteracts the enhanced freezing at the bulges.

Using a mathematical model for the competition between those trends, the Japanese researchers calculate that the average between-bulge spacing for any icicle should indeed always be around a centimeter. They report their findings in the October Physical Review E.


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