http://time.com/5504483/ice-circle-maine/

Nature loves to make things round: planets, soap bubbles, oranges, eyeballs, the circular swirl of a spinning hurricane. A lot of forces are at play in favoring natural circles and spheres—the equalizing force of air pressure pushing out or gravity pulling in; the rotation of the Earth, creating vortices in air; the evolutionary imperative of efficient packaging.

The power of the round is in the news again, with the appearance of a massive, rotating ice disk in the Presumpscot River in Westbrook, Maine. The disk was first noticed on January 14, spinning in a lazy, counterclockwise direction. On social media, the ice circle was an instant sensation, alternately said to resemble a British crop circle or the mottled face of the moon—both fair descriptions. Either way, the Presumpscot ducks loved it, settling down for a slow-motion ride as the sights of Westbrook passed before them.