It’s Maine’s version of Miracle on Ice — a spectacular icy disc spinning in the Presumpscot River. Is it (as some onlookers and tabloid writers suggest) an aquatic version of a crop circle? Icy cover for a lurking alien spaceship?
Uh, no. The truth is more down to earth, says Paul Barrette, an ice specialist and research officer with Canada’s National Research Council. “None of the events that produced this disc are unusual on its own. What is unusual is that all of these events occurred together,” Barrette says.
In ice-science terms, it’s a case of “the planets lining up, figuratively speaking,” producing a 90-metre wide platter of ice that spins like an oversized vinyl LP. First, “you need a river with bends and eddies, where the water makes a circular motion,” Barrette says.
Second, ice is required, and it could be supplied in a range of ways. Upstream floes might drift into the river bend and get caught in the whirling current. Or shoreline ice could break off and spin into the vortex. The water could also be cold and turbulent enough to spawn “frazil” ice — small, needle-like ice crystals that eventually clump together in buoyant, slushy masses.
Add chilly temperatures, and this jostling, rotating mass of ice begins to grow, expanding until it grinds against shoreline ice or the shore itself. “As soon as the ice reaches the point where it grinds against the shore, it starts breaking off at the rim,” Barrette says, giving the disc its circular shape.
The Maine disc’s celebrity springs both from its size and urban location, but there could be more modest examples out there, quietly spinning about their business in cottage country rivers and creeks. “It’s hard to say if (the disc) is rare and unusual,” Barrette says. “There may be ice discs forming in Canada, but they’re in places where nobody’s there to observe them.”
If you’re scouting of ice discs around the cottage, Barrette recommends admiring your discoveries from a safe distance. Even if you’re not worried about aliens, be wary of open water, weak ice, and potentially dangerous currents.