On Monday, January 10, 2011 ATI staff came in to work to discover that the view out of their windows has changed dramatically. One of the perks of working at Applied Technology Institute is the expansive views of the Beards Creek and South River. However, what we saw that morning was entirely different. The surface of the water was covered in large ice circles 4-6 ft. in diameter.
As it turns out, an ice disc, ice circle, or ice pan is a natural phenomenon that occurs in slow moving water in cold climates. Ice circles vary in size but have been reported to be more than 4 metres (13 ft) in diameter.
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 was spotted on the Mianus River and reported in a 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.