A collection of small ice pans (the largest about 12" (30 cm) in diameter) observed on the River Llugwy at Betws-y-coed, North Wales in December 2008. A fortnight of no rain had resulted in low water levels, and there had been sub-zero temperatures for a week.
An ice disc/disk or ice circle is a rare natural phenomenon that occurs in slow moving water in cold climates. They are thin and perfectly 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.
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 perfect circle.A relatively uncommon phenomenon, one of the earliest recordings is of a slowly revolving disc was spotted on the Mianus River and reported in a 1895 edition of Scientific American.
A collection of small ice pans (the largest about 12" (30 cm) in diameter) observed on the River Llugwy at Betws-y-coed, North Wales in December 2008. A fortnight of no rain had resulted in low water levels, and there had been sub-zero temperatures for a week.
An ice pan is a surface slab of ice that forms in the centre of a lake or creek instead of along the water's edge. They are formed by quick shifts in temperature. As water cools it releases heat that turns the water into frazil ice – a collection of loose, needle-shaped ice particles that can cluster together into an pan-shaped form. If a lake accumulates enough frazil ice and the current is slow, over time, the pan can become a 'hanging dam' – a dense piece of ice with high ridges and a low centre
