Ice Circle - Extremely rare cold-weather phenomenon
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Stumble ThisA rare phenomenon usually only seen in extremely cold countries, scientists generally accept that Ice Circles are formed when surface ice gathers in the center of a body of water rather than the edges. A slow moving river current can create a slow turning eddy, which rotates, forming an ice disc. Very slowly the edges are ground down until a gap is formed between the eddy and the surrounding ice. These ice circles have been seen with diameters of over 500 feet and can also at times be found in clusters and groups at different sizes.
http://www.environmentalgraffiti.com/featured/massive-10ft-spinning-ice-circle-discovered-uk/5963
Sorry, bit of a Les Mis reference there for ya!
edit: Undrunk version: Awesome.
Attach a turbine to it and away you go
But, seriously:
These close encounters can be explained by quick shifts in temperature, said Joe Desloges, a river specialist and geography professor at the University of Toronto.
Mr. Desloges explained that the frozen circles are actually ice pans, or surface slabs of ice that form in the center of a lake or creek, instead of along the water’s edge.
As water cools, it releases heat that turns into frazil ice – a collection of loose, needle shaped ice particles that can cluster together in an ice pan. If it accumulates enough frazil ice and the current is slow, over time, the pan can become a hanging dam – a dense, heavy piece of ice with high ridges and a low centre.
But he admits that the near-perfect circular shape of the Mississauga ice pan is very strange.
“Normally, you do not get edges of the ice pan so clean and even. It may occur when a pan forms quickly, then melts a bit before starting to refreeze,” he said. “There is the chance that these can form so perfectly, but not common at all.”
http://network.nationalpost.com/np/blogs/toronto/archive/2008/12/18/man-stumbles-on-round-spinning-creek-circle.aspx