UFO-enthusiasts claim that, like crop circles, the perfect discs are created by visiting aliens, but scientists believe the extreme cold weather combined with an unusual current is the more likely reason.
David Ricks, an ocean engineering graduate, helped systematically rule out effluent from submerged pipes, down draughts from helicopters, alien activity, bubbles from decomposition and underwater springs.
He concluded that eddies from the Harvard bridge caused parts of the sheet ice to break away and the movement of the ice created circular holes which were filled by further ice formation. Other theories suggest that slow moving rivers can create eddies which spin the ice until it takes on a circular shape.
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."
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