Sun Jan 25, 2009 3:30 am Reply with quote
Think of it this way, the top of the lake or river is frozen, but underneath the ice is unfrozen water, flowing in a current. At some point, a hole was made by the melting surface, allowing the flowing water from underneath to be exposed. The hole begins to get bigger as the water underneath erodes/melts the surface ice. There's no place for this water to flow, left is blocked, right is blocked, north, south, east, west, and 360 degrees in every direction is blocked by the surface ice. So the current of the water underneath forces water up through this hole, causing the surface water to spin in a circle, because the water has no place to flow to, because the surface ice is blocking the flowing water inward. The spinning circle will keep getting bigger because it's melting the walls of the surface ice. I'm curious to how big these circles can get, at some point the current underneath would be too weak to propel a circle.
.....not so much. 
