Cool Creek Circle!

Source: blog TO
Hat Tip: Chicago Boyz

[These creek circles] ...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.”

Source: Posted Toronto

Is that not a cool sight?

I think the easiest way to explain it is to tell people that it is a frozen eddy in the current.