First crop circles, now this? Video of an enormous ice circle spinning in a river in North Dakota is making its way around the Internet after a hunter filmed the strange phenomenon last Saturday. The footage shows the ice circle, shaped like a giant flapjack, revolving like a frozen merry-go-round in the middle of the dark river. The icy disk was estimated to be nearly 55 feet in diameter.

The Associated Press reported that George Loegering, a 73-year-old retired engineer, was hunting with relatives when he spotted the ice circle in the Sheyenne River. He pulled out his camera to film what he told the Associated Press was a “surreal” encounter.

“It’s an amazing wonder,” Loegering said while filming the ice circle. “Don’t have a clue how it did it, but that thing is rotating, as you can see.” He even described how concentric rings of ice near the ice circles’ edge made him think the ice circle was growing.

So what caused the amazing ice circle in North Dakota? Although strange, ice circles aren’t as rare as you might think. According to NBC News, spinning frozen disks turn up every now and then in cold climates, especially in the Arctic, Scandinavia and Canada. And there’s actually a perfectly logical explanation for why they occur -- and it doesn’t involve extraterrestrial spaceships making splash landings on Earth.

According to Allen Schlag, a National Weather Service hydrologist in Bismarck, N.D., floating bits of ice in the river were caught in an eddy, a circular movement of water like a whirlpool that doesn’t move with the rest of the current. He told the Associated Press the ice circle is pretty much a “collection of ice cubes” swirling about in the eddy.

The National Post explained the ice circle phenomenon slightly differently, noting that as water cools, it releases heat that turns into frazil ice -- loose, needle-shaped particles of ice that can cluster together. If the current of the river allows this frazil ice to accumulate, it can form an ice circle, “a dense, heavy piece of ice with high ridges and a low center.”

Another theory is that ice circles form at bends in the river where the rushing water creates a force called “rotational shear.” This force can break off a piece of ice that rotates. As it spins, its edges become smooth as they grind against surrounding ice.

To see Loegering’s video of the ice circle in North Dakota, click here. Below, check out a similar ice circle video uploaded to YouTube by YouTube user ‪Jérôme Joncas.

Canada Water Sea ice