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Last winter, I received the following question from Ann Alpern of Buffalo, New York, a listener of The Weather Notebook radio show to which I am a frequent contributor.
Question: We were able to stay late at our summer-only house on the Canadian shore of Lake Erie. We saw many things...the strangest didn't fly it rolled.
Initially, I thought they were fieldstones exposed by the breaking waves. I'm always looking for fieldstones for my rock garden so I hurried down to the water's edge to harvest some stone. I was trying to figure how I was going get them all back into the yard cause those suckers are heavy. The first one I picked up was the size of a basketball but it weighed next to nothing. I dropped it and it shattered. It was composed of ice crystals, seaweed and small shells. Thank goodness they stayed around for about a week rolling around the waters edge.
Any explanations or name for this phenomenon?
Answer: What you most likely saw are called, appropriately enough, ice balls and are likely common on the Great Lakes during the winter. They form early in the cold season arises because Lake Erie is the shallowest of the Great Lakes. It normally freezes beginning in late November or early December.
When the water temperature drops to near freezing, slabs of ice usually form first along a shoreline exposed to strong wind and waves. But rather than form as large uniform sheets, lake ice begins as irregular, flat chunks of ice scattered along the water's edge. Much of this ice is broken up over time by wind and wave action along the shore, and smaller chunks can float back out into the lake.
If wind and wave are high, these chunks are quickly pushed back onshore forming an "ice foot" from the beach into the water. But, if the waves are small and wind light, some chunks move out into the lake. These floating chunks then become rounded into balls through their jostling in the waves. The iceballs then can migrate along the longshore until they melt or are again tossed back onshore.
After time, grounded ice balls lose their rounded character and combine with other ice pieces to form the shore ice seen each winter. The observed ice balls likely picked up bits of weed and shells when they first froze on the shoreline.
You can hear my answer to this at: The Weather Notebook
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