On icicle ripples

Natural icicles have an overall conical shape modulated by surface ripples. It has been noted from many observations of icicles formed in nature and in the laboratory that the wavelength of the ripples has a very narrow spectrum between about 8 and 12 mm and that, as time evolves, the phase of the ripples migrates upwards. Developing from a very simple, intuitive model, I review previous mathematical studies of this phenomenon and provide new physical insight into the physical mechanisms involved.