This is the time of year when the small mysteries of winter can occupy us for literally minutes at a time.
We give you the amazing ice disk of the Nokasippi River in Brainerd, Minn., courtesy of Forum News Service.
“So you get ice forming and it gets bigger as it gets colder and then the water that is moving faster is not freezing up, so what you get in the end is this big pancake of ice that is moving slowly around in a circle,” Minnesota Department of Natural Resources climatologist Peter Boulay says. “You see pancake ice on water that’s moving. When the lakes are trying to freeze up this past weekend, I saw a lot of that kind of ice forming in circles.”
An ice circle was a big deal on the Salmon River in Idaho a few years ago.
Gary Lane, who documented it, provided his version of the physics involved.
Everything in the world is round. Even photos of ice circles (rosettes) go round and round. Here’s my long version of how ice rosettes form: It takes the round and round of an eddy to form an ice circle. As water swirls around in a circle, gravity eventually brings everything to the center.
As chunks of ice begin floating downriver and getting trapped in an eddy, they eventually collide, hook together, and spin around continuously adding size. If the freeze continues long enough, the ice circle will be as large as the eddy itself, and will eventually attach with shore and/or create ice bridges which in turn capture more ice and soon the entire river may freeze up.
The ice circles then form again, when warming begins to melt things, and the process is reversed. Detaching from shore and area where the main current melts faster, the circle is again formed. It either then melts, and/or gets pushed out far enough to engage with large bergs of ice free floating downstream that collides and begins to chunk away at the island of round ice.
In a nutshell – it is all about physics. Bottomline. When 23 yr old Newton observed an apple falling from a tree, he wondered if the moon also fell. It led him to the most important discovery of the universe and the calculus of motion: gravity. Indeed, the moon is constantly falling towards earth due to the force of gravity. So the same force that is at work as the moon orbits earth and planets go around the sun, helps explain the basics of origin for ice circles.”