A giant circle of ice on the Presumpscot River in Westbrook, Maine, on Jan. 14, 2019.
Photo: Tina Radel (City of Westbrook)

This week in the city of Westbrook, Maine, a huge, rotating circle of ice formed on the Presumpscot River. While it seems like it could be an omen of the impending apocalypse or a particularly low-effort attempt at a crop circle by extraterrestrials, in reality it appears to be another example of a natural yet rare phenomenon resulting from some simple physics.

Photo: Tina Radel (City of Westbrook)

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Photo: Tina Radel (City of Westbrook)

Photos taken by and the city of Westbrook’s marketing & communications manager, Tina Radel, show the gigantic disk of ice appearing to have a surface area larger than a nearby, multi-story parking garage. True to municipal form, the city also published a video of the ice disk with a dramatic soundtrack:

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“It does not appear to be going up or down stream at this time,” Radel told Earther late Monday night. “It continues to spin in a counter clockwise direction. My guess is it could get bigger as more ice forms. We have snow coming in at the end of the week.​”

Curiosity about giant, rotating ice disks dates to at least the late 1800s. Research on prior instances of the phenomenon, published in Physical Review E in 2016, found that as melting ice sinks off disks it “goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk.” Speaking with the the Press Herald, Bowdoin College in Brunswick associate physics professor Mark Battle suggested the Westbrook ice disk’s rotation could also be the result of thick ice moving with the river current, getting trapped, and grinding against the shoreline.

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According to the Press Herald, Ethos Marketing web developer Doug Bertlesman estimated the size of the disk to be at least 100 yards (91 meters). If true, that would make it larger than examples of similar ice discs observed in Sweden in 1987 and 1994 and described in a 1997 study as particularly large (another in 1941 received a rough size estimate that places it at slightly larger than Westbrook’s). Rob Mitchell, owner of the Ash Street office building where Bertlesman’s company is based, told the paper he had notified the city of the disk at approximately 10:00 a.m. ET on Monday. He added, “There were ducks sitting on it. The ducks were rotating on this big Lazy Susan. It was a big duck-go-round.”

Like Radel, Mitchell’s best guess is that the disk will only continue to grow in size.

“It’s stuck right there,” Mitchell told the Press Herald. “It’s not going anywhere... I think it will continue to gain in thickness as long as it keeps spinning.”

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In any case, if you lost this thing, the city of Westbrook has it. Just be sure to get there before it melts, and also bring help, because it almost assuredly weighs several hundred tons.