An ice disc, ice circle, or ice pan is a natural phenomenon that occurs in slow moving water in cold climates.
Ice circles are thin and circular slabs of ice that rotate slowly in the water. It is believed that they form in eddy currents. Ice discs have most frequently been observed in Scandinavia and North America, but they are occasionally recorded as far south as England and Wales. An ice disc was observed in Wales in December 2008 and another was reported in England in January 2009. An ice disc was observed on the Sheyenne River in North Dakota in December 2013. An ice circle of approximately 50 ft. in diameter was observed and photographed in Lake Katrine, New York on the Esopus Creek around January 23, 2014. In Idaho, extreme weather led to a rare sighting of an Ice disk on the Snake River on January 22, 2014.
Ice discs form on the outer bends in a river where the accelerating water creates a force called 'rotational shear', which breaks off a chunk of ice and twists it around. As the disc rotates, it grinds against surrounding ice — smoothing into a circle. A relatively uncommon phenomenon, one of the earliest recordings is of a slowly revolving disc spotted on the Mianus River and reported in an 1895 edition of Scientific American.
River specialist and geography professor Joe Desloges states that ice pans are "surface slabs of ice that form in the center of a lake or creek, instead of along the water’s edge. As water cools, it releases heat that turns into 'frazil ice' that can cluster together into a pan-shaped formation. If an ice pan accumulates enough frazil ice and the current remains slow, the pan may transform into a 'hanging dam', a heavy block of ice with high ridges low centre.
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- David Derbyshire (13 January 2009). "Ice one! Walker discovers 10ft-wide, spinning frozen circle in British waters for the first time". Mail Online (Daily Mail). Retrieved 2009-01-13.
- "Spinning ice disc phenomenon seen in British river for first time". Telegraph.co.uk (Telegraph Media Group Limited). 13 January 2009. Retrieved 22 April 2010.
- Daniel Ostler news.yahoo.com, recordonline.com
- Blake Nicholson, Unusual ice circle forms in North Dakota river, November 26, 2013, Associated Press
- Pete Thomas, Giant spinning ice circle discovered in North Dakota’s Sheyenne River, November 26, 2013, GrindTV
- Patrick Garrity (February 7, 2010). "VIDEO: Moscow Ice Disk a rarity of nature". Burlington FreePress.com. Retrieved 19 February 2010.
- Bates, J. M. (9 February 1895). "A revolving ice cake". Scientific American 72 (6): 86. Retrieved 30 November 2013.
- Rickard, B et al: Unexplained Phenomena, page 190. Rough Guides, 2000.
- Joe Desloges. "Perfect "Ice Circle" Forms near Toronto, Canada". Retrieved 14 January 2009. cited in: Scroggins, Kate; Roberts, Rob (18 December 2008). "Man stumbles on round, spinning ‘creek circle’". Posted Toronto (National Post).
- Joe Desloges. "Perfect "Ice Circle" Forms near Toronto, Canada". Retrieved 14 January 2009.
- Theories abound on how the river got those patterns - MIT News
- Video of ice disc in Germany: "Eisscheibe beim Kunsthof Pösling (Ice disc in Kunsthof, Pösling)" (in German). YouTube. 18 January 2009. Retrieved 27 April 2010.
- Video of ice circle in Ontario, Canada: Rattray Marsh Creek Circle |date=13 December 2008