Ice circles

[JohnD]

Cousin to APOD is EPOD, Earth Picture Of the Day, a site that suffers in comparison by not having a discussion page like Asterisk attched to it.
So if I may use this site to draw your attention to today's pic of an Ice Circle:
http://epod.usra.edu/blog/ (4th March '12)

Theories?
In moving water, attrition and abrasion of existoig slabs seems reasonable, as in those seen on the Llugwy at Betws-y-Coed:
http://en.wikipedia.org/wiki/Ice_circle

Such a perfect circle has to be due to movement in an eddy, so how is that possible in still, pond water? Such ponds will have small springs in their bottoms, or regular release of bubbles of gas from decaying vegetation. Bottom water will be warmer than at the surface so it would rise in a column and would account for the less icy middle, seen in this pic? http://www.environmentalgraffiti.com/fe ... ed-uk/5963
But would such a column rotate, to provide the driving power for the abrasion effect?

Lastly, the excellent video at the bottom of this page shows that the disc does not rotate in one peice. The radial velocity of the rim is faster than the centre.
http://forgetomori.com/2009/science/ice ... d-kind-of/
This would indicate that the circle is driven by an edge effect, like a cogwheel, that could only occur in moving water. In still water, a rising, rotating column would drive the circle more quickly at the centre, until the circle was solid.

John

[Beyond]

Really neat!! I've never seen that before.

[neufer]

So if I may use this site to draw your attention to today's pic of an Ice Circle:
http://epod.usra.edu/blog/ (4th March '12)

Theories?

Click to play embedded YouTube video.

[JohnD]

neufer,
you get everywhere.
Unfortunately, embedded youtube videos don't and this is excluded.
What were you saying?
John

[neufer]

neufer,
you get everywhere.
Unfortunately, embedded youtube videos don't and this is excluded.
What were you saying?

You simply have to tap on the Watch on YouTube link, John.