During the winter, if conditions are just right, something strange can happen in lakes, rivers and creeks. Something that when witnessed -- even in this day and age -- still makes people question if something supernatural is going on. We're talking about ice circles.
Ice circles, also called ice discs or ice pans, form in water when ice gathers in the center of the body of water in the midst of an eddy. Here's how handy dandy Wikipedia puts it:
Ice discs form on the outer bends in a river where the accelerating water creates a force called 'rotational shear', which breaks off a chunk of ice and twists it around. As the disc rotates, it grinds against surrounding ice — smoothing into a circle. A relatively uncommon phenomenon, one of the earliest recordings is of a slowly revolving disc was spotted on the Mianus River and reported in a 1895 edition of Scientific American.
They are quite a strange sight when they pop up, after all how often do you see a round bit of ice freely spinning in a river instead of the usual jagged and oddly shaped chunks of ice?
This "Supernatural ice circle" isn't technically supernatural, but it is natural and it is super, so close enough:
And here is a thin ice circle spinning in the current of a creek near Sheridan Creek in Rattray Marsh Conservation area in Mississauga, which stirred up the Internets in 2008:
While some might be quick to call it paranormal activity or a sign that UFOs are real and visiting us, there's a more earthly explanation.
National Post reports:
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.
It's uncommon to have an ice circle as perfectly round as the one found in Mississauga -- not impossible, but unusual -- or ice pans as lovely as those in the photo above. So if you're keeping an eye out for these rare formations this winter, look for something a little less than perfect but be excited if you find them at all.