Physics Photo of the Week
Physics Photo of the Week
March 20, 2026
Ice Sprouts - Photos by Henry Willis; Discussion by Donald Collins
My friend, Henry Willis, sent me this photo of "ice sprouts" taken during a trek in the Great Smokies National Park earlier this winter. Although fairly common, ice sprouts this large are quite unusual. These sprouts are about 2 inches tall.
Ice sprouts are formed when bare ground, that has been saturated with rain water, freezes. The amazing property of water is that the ice phase is less dense than water. Ice cubes float on top of your drink of iced tea. Most solid objects are more dense than their liquid counterparts. When the muddy soil freezes, the freezing takes place on the top of the mud. The frozen surface confines the remaining water beneath the surface. The remaining water under the top shell freezes and expands; pressure builds up and the expansion force breaks through cracks in the shell; the water is forced out and freezes fairly quickly, allowing the sprouts to grow arbitrarily long. Ice skating is possible because the pressure beneath the skate blade compresses the ice causing a film of liquid water between the skate blade and the ice making excellent lubrication. The water film after the skater has passed freezes again quickly.
The ice sprouts resemble bean sprouts that are sold in stores to place on a leafy salad adding interest and nutrients. However these ice sprouts, having pushed through the mud in their sprouting, have bits of mud and dirt on their tops. Washing the mud flecks off would only melt the sprout "stems"! However, even though these sprouts come from frozen muddy water, they look surprising clear. This clarity of the ice sprouts is a process called zone refining.
When a liquid freezes it forms crystals. Any impurities in the liquid are exuded from the crystals because the molecular bonding within the forming crystal lattice essentially "squeezes" out the impurities - microscopic bits of clay in this case. In the old days when milk was delivered daily to porch steps in the winter, the milk would sometimes freeze in the milk bottles, squeezing off the caps (the caps were pressed on foil - not screw caps) there would be a lump of ice in the neck of the milk jug. The ice was clear - not milky - due to the zone refining in the freezing of the milk.
The image at left shows a larger field of view - showing other familiar objects in the image, which give a sense of scale as to the size of the ice sprouts.
Thank you, Henry, for sharing your interesting photos!
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Physics Photo of the Week is published periodically during the academic year on Fridays by Donald F. Collins, professor emeritus of Warren Wilson College. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photo-provider is forbidden.
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