The Presumpscot River is a 25.8-mile-long waterway that flows through Westbrook, Maine. And it’s now host to the small city’s newest attraction. Though the river has been a transportation corridor for years, people are not crowding the shore to watch a barge float past—they’re there to see the giant ice disk.
This naturally occurring, perfectly round rink of ice looks man-made, but it’s not. Robert Mitchell, owner of a nearby office building, noticed the peculiar disk on the morning of January 14 and promptly notified the city, in hope that they’d be able to get a drone’s-eye-view. “On first look I thought it looked like a cool shape had formed, but after a minute or so I realized it was rotating,” he says.
This rare phenomenon, a frozen Lazy Susan if you will, is not without precedent. In 2017, a family hiking in the Adirondacks discovered a similarly perfectly round (though much, much smaller) ice bog, and were stunned by their good fortune. These ice disks result from a perfect storm of flow and changing water temperatures, but the rotating happens when they begin to melt. A 2016 study published in the journal Physical Review E used a “particle image velocimetry technique” to investigate the water below ice disks. Through their research, they found that the flow of meltwater goes downward and also moves horizontally to form a vortex, and “any vertical flow that generates a vortex will induce the rotation of a floating object.”
According to eyewitness Mitchell, the formation “looks like a perfectly formed disk spinning at a consistent, counterclockwise rotation.” Apparently, it stays firmly centered on its axis, making it look “mechanized,” he says. Another onlooker, web developer Doug Bertlesman, estimated that the disk is roughly 100 yards in diameter, in an interview with the Portland Press Herald. The icy frisbee has also been changing in size and color, depending on the temperature, the time of day, or the sun’s position. “For example, this morning the disk was larger and more opaque,” Mitchell says. “[But] this afternoon it is smaller and more clear in color.”
Ducks have reportedly been seen sitting on the rare, rotating platter, and it’s a pity we can’t ask if they’re getting dizzy.