Ice circle
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 Creekaround January
23, 2014.
Snow and freezing temperatures have battered many parts of
the U.S in January, with temperatures as low as -10 °C/14 °F recorded in many
States. In Idaho, the extreme weather led to a rare sighting of an Ice disk on
the Snake River on January 22, 2014.
An unusual natural phenomenon, ice disks occur in slow moving
water in cold climates and can vary in size, with circles more than 15 metres
(49 ft) in diameter observed.
Ice discs
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..
Ice pans
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.
Source: Wikipedia.