# Any theories what causes these circles? **URL:** \ **Category:** Factual Questions\ **Created:** [February 8, 2009, 4:22pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927 "2009-02-08T16:22:30Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [February 8, 2009, 4:22pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/1 "2009-02-08T16:22:30Z")
The first YouTube link is to a video I made a couple winters ago. I found the other two links recently. All seem to involve circles of ice or slush on the surface of slowly moving water. They appear to be some sort of natural phenomena. Maybe the last two are more closely related because of the rotation. Maybe the rotating circles are formed by underwater currents. What about the first one? How and why do those circles form in the waves? Is anyone familiar with these or similar phenomena? [![](https://img.youtube.com/vi/xsDq_8_19PA/hqdefault.jpg "strange circles") ](https://www.youtube.com/watch?v=xsDq_8_19PA) [![](https://img.youtube.com/vi/7JoGXbP0bVg/hqdefault.jpg "Rattray Marsh "Creek Circle"") ](https://www.youtube.com/watch?v=7JoGXbP0bVg) [![]( " - YouTube") ](https://www.youtube.com/watch?v=2NvB9H1yEr0) ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [February 8, 2009, 4:55pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/2 "2009-02-08T16:55:51Z")
It’s [pancake ice](http://en.wikipedia.org/wiki/Pancake_ice). It’s formed by the pieces of ice constantly bumping in to one another. It’s very common in areas with plenty of wave action. on edit: Didn’t see the second & third videos. Pretty cool, although I don’t know about those. Seems to me it’s just an eddy with ice on top. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [February 8, 2009, 6:04pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/3 "2009-02-08T18:04:22Z")
Pancake ice, huh? Thanks. That seems to be the closest identification I have found. The circles in my video don’t seem to have a disc, just the rim, which makes them a bit more curious. Wiki indicates that the rims may be precursers to the discs, but that’s a bit hard to imagine. What would cause circles of ice to form in the first place? On the other hand, it may be that there had been discs and they melted, leaving just the remnants of rims. Still, I think I happened upon a relatively rare phenomenon and I’m glad to have any explanation. ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [February 8, 2009, 6:26pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/4 "2009-02-08T18:26:12Z")
In your first video, you’re definitely looking at pancake ice. Pancake ice forms when large slabs of ice are broken up due to melting and/or wave motion. The smaller chunks are rounded off because they are constantly smashing into other chunks of ice. In addition to the rounding of the edges, the edges get pushed up from the same forces. Many time, the rims around the edges can re-freeze and become solid; otherwise the edges are just piled ice shavings. However, the middle of the circle is still ice. In some cases, the middle part will fill with water, giving the appearance of an ice circle with no ice in the middle. This is just appearance, however, as the circle would collapse without a hard ice center. Your first video shows pancake ice, and many of those ice pieces have water inside the rimmed edges from the waves. However, the water inside those rimmed edges is sitting on top of ice. I’ve spent a lot of time working in the ice, and I assure you that’s what you’re seeing here. Your second videos are something completely different. I’ve never seen anything like them, but I’m guessing it’s simply an eddy in the river. A river will still run under a layer of ice. If the ice is thin, and an eddy is strong enough, I can see where a large section of ice could start to rotate with the eddy. The slow, steady grinding along the outer edge of the ice over a prolonged period of time will certainly give it the perfect circle you see in the videos. This is just my theory, and will happily stand corrected. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [February 8, 2009, 8:26pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/5 "2009-02-08T20:26:50Z")
[Here’s](http://www.telegraph.co.uk/earth/4227030/Spinning-ice-disc-phenomenon-seen-in-British-river-for-first-time.html) an article about an ice disc (same as 2nd link?). The Wikipedia article on ice discs is so short that it’s not worth linking to. ---
**Author:** ![Khadaji](https://avatars.discourse-cdn.com/v4/letter/k/9e8a1a/32.png) [@Khadaji](https://boards.straightdope.com/u/Khadaji)\ **Post date:** [February 8, 2009, 8:30pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/6 "2009-02-08T20:30:50Z")
Aliens. Just like crop circles, Aliens are trying to tell us something. ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [February 8, 2009, 8:44pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/7 "2009-02-08T20:44:55Z")
> [@Khadaji](#): > > Aliens. Just like crop circles, Aliens are trying to tell us something. They’re trying to give us the answer. That’s why it’s always a circle. A circle’s circumference to diameter ratio is Pi, or 3.14. 3.14, or 3-1 (+) 4 gives us 24. 24 backwards is 42. 42 is the answer. But what’s the question? WE NEED THE FRIGGIN’ QUESTION! ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [February 8, 2009, 9:47pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/8 "2009-02-08T21:47:09Z")
> [@Scruloose](#): > > on edit: Didn’t see the second & third videos. Pretty cool, although I don’t know about those. Seems to me it’s just an eddy with ice on top. I agree - and the solidity of the ice means that in order to rotate, it must be almost perfectly circular - so it must either happen to form that way, or maybe it’s a case of some initial motion causing a non-circular thing to carve itself round. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [February 8, 2009, 9:50pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/9 "2009-02-08T21:50:37Z")
> [@Scruloose](#): > > They’re trying to give us the answer. That’s why it’s always a circle. A circle’s circumference to diameter ratio is Pi, or 3.14. 3.14, or 3-1 (+) 4 gives us 24. 24 backwards is 42. 42 is the answer. But what’s the question? WE NEED THE FRIGGIN’ QUESTION! Q: What is the frequency, Kenneth? ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [February 8, 2009, 10:14pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/10 "2009-02-08T22:14:33Z")
> [@Mangetout](#): > > I agree - and the solidity of the ice means that in order to rotate, it must be almost perfectly circular - so it must either happen to form that way, or maybe it’s a case of some initial motion causing a non-circular thing to carve itself round. I’m guessing the ice that forms on the relatively still center of the eddy will gradually freeze outwards towards the edge of the circular current. Ice obviously forms on still water more easily than on moving water, and the water towards the edge of the eddy will be moving faster than anywhere else. Then, as the disk ice contacts the firm, unmoving ice outside the eddy which had already formed because it’s still, the disk grinds itself into a perfect circle, shaping it as if it were on a lathe. I could see where you would get some impressive ice-disks with a quick deep freeze and strong eddy. All in all, pretty cool looking. **ftg** ’s article says this phenomenon is normally found in Scandinavia. I wonder if it’s common elsewhere. **CC** : A. 42 kHz. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 8, 2009, 10:59pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/11 "2009-02-08T22:59:01Z")
> [@](#): > > CC: A. 42 kHz. Actually, 42 kHz would be a slightly flat E, not an A. 6 ovtaves above the E above middle C. ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [February 8, 2009, 11:03pm UTC](https://boards.straightdope.com/t/any-theories-what-causes-these-circles/484927/12 "2009-02-08T23:03:14Z")
> [@Chronos](#): > > Actually, 42 kHz would be a slightly flat E, not an A. 6 ovtaves above the E above middle C. Or so you would have us believe, \*\*Chronos \*\*- if that is in fact your real name… :dubious: