What are ice disks?

To many, the massive and mysterious disk of ice seen floating and spinning atop the Presumpscot River in Westbrook, Maine, in January 2018 might have looked like winter's version of a crop circle.

The fascinating ice disk, which is reportedly 300 feet wide, garnered a "ton of interest" from around the world, said City of Westbrook marketing and communications manager Tina Radel, who told AccuWeather that she had heard of sightings of smaller ice disks in the past in other parts of Maine.

The unusual yet mesmerizing frozen formation is a natural phenomenon that is fairly common in the colder climates of North America.

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Ice disk forms on Presumpscot River in Westbrook, Maine
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Ice disk forms on Presumpscot River in Westbrook, Maine
A large, circular ice floe sits in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
An onlooker watches a large, circular ice floe in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe sits in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder TPX IMAGES OF THE DAY
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
Birds sit on a large, circular ice floe spinning slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
Onlookers photograph a large, circular ice floe spinning slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A woman looks at a large, circular ice floe spinning slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
Onlookers watch a large, circular ice floe spinning slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A woman photographs a large, circular ice floe spinning slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
A large, circular ice floe spins slowly in the Presumpscot River in Westbrook, Maine, U.S., January 16, 2019. REUTERS/Brian Snyder
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"Ice disks/circles tend to form on the outer bends of rivers where the accelerating water creates eddy currents," said Jason Nicholls, senior meteorologist and manager of international forecasting for AccuWeather.

These formations were also observed in Wales and England in the winter of 2008-09, according to Nicholls.

The ice disk in Westbrook formed from the churning water current created by Saccarappa Falls, located 100 feet away from the huge formation, which caused it to slowly spin counterclockwise, according to city officials.

"These currents cause chunks of ice to break off and rotate," Nicholls explained, adding that as the ice chunks rotate, they continue to do so against the surrounding ice.

This process then smooths out the edges to create circles or disks.

"The ice associated with the ice disks is usually thin, [thus] easier to rotate," Nicholls said.

The sizes of ice disks/circles vary in size, with some disks spanning more than 65 feet, or 20 meters, according to Nicholls.

"They are fairly common in the northern United States and Canada as well as Scandinavia, but usually tend to be much smaller, so [the ice disk that formed in Maine] is certainly unusual due to its immense size."

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