Icicle Arrays

These periodic arrays of icicles formed on a clothesline during a freezing rain storm in St. John's, Newfoundland. Similar icicle arrays decorated every available surface. The spacing of the icicles is 2.30.2 cm. The icicles develop from a layer of water which coats the clothesline. A layer of heavy fluid (water) lying on top of a layer of light fluid (air) is unstable the more-dense water wants to be underneath the less-dense air. As a result of this instability (which is known as the Rayleigh-Taylor instability) the bottom of the layer of water on the clothesline develops ripples of a particular wavelength. If the rippled water layer then freezes, the ripples will become the roots of icicles which grow as more freezing rain falls. A calculation of the wavelength of these ripples for water at 00C gives 2.47 cm, in agreement with the measured icicle spacing.

John de Bruyn
Memorial University of Newfoundland
Category 2 (Open) 3rd prize

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