Mother Nature gave hikers an impromptu treat with a strange spinning ice circle out on an icy river.

The strange phenomenon was seen earlier this week in Middle Fork Snoqualmie River near North Bend, Washington. Although it might look like the work of lost extraterrestrials, it’s actually a well documented natural phenomenon. They’re found on fresh water in cold climates, often in North America and Europe, and can be as small as a few inches or as large as 17 meters (55 feet) wide.

Physicists published a study on these ice circles in the journal Physical Review E just last year. Their study found that the spinning was not only caused by currents in the water, but also the increasing temperatures in the water, which are causing the disks to melt. You can learn more about that right here.

But first up, take a few minutes to enjoy these stunning videos of the Washington ice disc by photographer Kaylyn Messer.