Ice Polygons and Other Follygons

April 01, 2005

Apice copy

Provided by: John A. Adam, Old Dominion University
Summary author: John A. Adam

The above photo was taken near Norfolk, Virginia on a cold, clear morning (-10 degrees C or 14 F) in early February 2005. These ice polygons had formed in a quiet little tidal backwater, with concrete boundaries between the water and the road. My first instinct was that they had formed as a result of slow convection in the water below the ice, but upon further investigation, it appears that the polygonal boundaries may have occurred as a result of the wave-ice interaction. So-called flexural-gravity waves can break up ice sheets into floes, though usually on larger length scales than are present here. This is entirely possible since the boundary was in the approximate shape of a rectangular enclosure, and wave reflections might account for the sometimes hexagonal-looking patterns. There's also a phenomenon known as pancake ice, but the patterns associated with these ice floes are more circular than the ones pictured above (see link below).

Unlike the irregular polygons above, a related pattern is more difficult to explain. Notice the amazingly consistent array of regular, almost square cells in this disk, and the small protuberance near the top of the picture, and the irregularities to the left. What could have caused such a fascinating pattern? In view of the lack of recognizable features in the background, it's difficult to estimate the size of the object. Further speculation is pointless, although it is tempting to waffle that pancake ice may be involved, but in the spirit of scientific discovery, this puzzle of nature is left to others to decipher.

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