Ice is known by a wide range of identities in nature, from tiny snowflakes to Chicago-sized icebergs and canyon-covering glaciers. Still, a neatly shaped circle of frozen, rotating river water is strange to see, even in a wintry place like North Dakota.

The video above shows such a circle spinning serenely atop the Sheyenne River, where retired engineer George Loegering was out hunting with relatives on Nov. 23. "At first I thought, 'No way!' It was surreal," Loegering tells the Associated Press, which published the video this week. "You looked at it and you thought, 'How did it do that?'"

Was this a Thanksgiving miracle? A heavenly reminder to place unwieldy serving dishes on a lazy Susan? Maybe, but the AP got a more down-to-Earth answer from experts at the U.S. National Weather Service. NWS meteorologist Greg Gust says a mix of cold, dense air last weekend started turning the river's surface to ice, but remaining warmth didn't let the water freeze evenly. And when floating ice chunks drifted into an eddy, or small whirlpool, they began spinning in a circle and created the illusion of a solid disk.

"It's not a continuous sheet of ice," NWS hydrologist Allen Schlag tells the AP. "If you were to throw a grapefruit-size rock on it, it would go through. It's not a solid piece of ice — it's a collection of ice cubes." Although such disks aren't unheard of, they are rare — especially at this size, which Loegering estimates was about 55 feet in diameter.

"That might be one of the better examples I've seen," Schlag says. "It's a pretty cool one."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.