fuckyeahfluiddynamics:

Winter weather in northern latitudes sometimes brings with it unusual phenomena like this ice disk spinning in the

Middle Fork Snoqualmie River in Washington state. Photographer Kaylyn Messer ventured out to capture photos and videos of the event over the weekend. There are a couple theories as to how such disks form, but swirling river eddies are a key ingredient. One theory posits that chunks of ice forming on the river get caught up by the spinning eddy and slowly freeze together to form the disk. Another theory proposes that the disks occur when an existing chunk of ice breaks away, gets caught in the spinning eddy and slowly has its edges ground down into a circle. Personally, I lean toward the former explanation, though there is likely grinding at the edges either way. See more about this ice circle over at Messer’s blog.  (Image credit: K. Messer; GIF by @itscolossal; via Colossal)

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