Huge ice disc makes rare appearance on South Thompson River

A strange, swirlingcircle of ice that appeared at a bend in the South Thompson River has attractedplenty of attention in the Kamloops, B.C., area.

The 40-metre ice discis an example of an uncommon and fascinating naturalphenomenon, saidLaval University chemistry professorNormand Voyer.

"The one you're seeing right now in Kamloops is really cool but it's not unique," Voyertold Daybreak Kamloopshost Shelley Joyce. "It has been observed last year in Gasp,and two years ago there [was]one observed in Maine, which was twice as big as this one, almost 100 metres in diameter."

"These ice discs have mesmerized people for years and there have been a lot of claims, especially about alien stuff," he said. They've also been compared to crop circles.

"But scientists have been studying the phenomena for years and you know what?They came up with a very simple explanation."

'Magnificent chemical'explains oddity

The simple explanation involves "a magnificent chemical called H2O:water," Voyer said.

Water is one of the few chemicals with a lower density in its crystallized form, he said. Meanwhile warm water is less dense than cold water, so it rises to the surface.

Watch the ice disc slowly revolve in the South Thompson River:

Huge ice disc makes rare and fleeting appearance on the South Thompson River

5 years ago

Duration 0:23

A strange, swirling 40-metre wide circle of ice that appeared at a bend in the South Thompson River in mid January has attracted the attention of area residents, and explanation from a Laval University chemistry professor

Nature's recipe for a rotating ice disc is "a littleopen water, a little water current and an ice patch," Voyer said.

When the temperature warms a bit, water molecules begin to warm up and migrate to the top. If the water surface is covered with an ice patch, those warm water molecules begin to move laterally with the current, creating a vortexlike water down a bathtub drain.

Perfect conditions needed

"So the warm water vortex will push up the ice cover," Voyer said. "Eventually the ice cover will crack along the edge of the vortex. And the reason for that is because the forces are stronger along the edge and the water is warmer."

The result is a very rough ice disc, which then grinds itself into a perfect circle as it rotates, he said.

Ice discs rarely form, because conditions must be perfect: warming temperatures, not too much current andnot too much wind.

The phenomenon is often fleeting, lasting a couple of days or a couple of weeksbefore wind or strong current causes the fragile disc to break apart.

"Also, there is the possibility that during the night there's aliens that will come and throw rocks at it or something like that," Voyer joked.

With files from Daybreak Kamloops