January 31st, 2022
I was struck by the ribbing on this icicle:
Why do these ribs form? Why are they of this size and spacing? Here’s my hypothesis:
I visualize the formation process as caused by a thin sheet of water slowly creeping down the icicle, partly freezing as it continues. Now, when the water freezes, it releases a tiny amount of heat, which warms the water that doesn’t freeze; that slightly warmer water is able to move a bit further down the icicle before it again partly freezes, renewing the cycle. Thus, the “wavelength” of the ribbing is based on the air temperature and motion. At lower temperatures, the water freezes more quickly and the ribs will be closer together.