Physics Photo of the Week

December's Ice Storm

On December 15, 2005 it rained all day when the temperature was freezing or about a degree below freezing.  The rain freezes on any surface on which it lands - often the rain is supercooled and freezes very quickly upon contact with solid surfaces.  As can be seen from the spokes of my  garden windmill taken in the late afternoon, the ice had accumulated about 1/4 inch all the way around the spokes.  The ice storm had started about midnight the previous night.  By morning the windmill bearing had frozen and ceased to spin, even though the wind continued all day.  Because the windmill was not spinning, the icicles that formed around the perimeter were affected by gravity and dripped straight down.  Compare with the centrifugal icicles from previous years.  Luckily this ice storm did minimal damage in the Warren Wilson Area.  However, neighboring Henderson County in North Carolina suffered major damage to power lines where many costumers were without power for about 5 days.

I'm inspired to publish this photo primarily by the question posed by Dr. Vicki Garlock.  She asks "With the wind coming from one direction, why does the ice build up evenly on all sides of small twigs and wires?".  Click here for the answer as best I can describe it.




Early in the morning, soon after the windmill's bearings froze, remnants of centrifugal icicles could be seen in the photo at right.  Much better centrifugal icicles may be seen in previous years' ice storms.

Donald F. Collins

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