29 April 2013
"Ice needles" emerge from a Minnesota lake
Filmed at Medicine Lake in Minnesota by Nadalie, via KARE 11 News.
This is occurring during the (delayed this year) spring ice-out phase, so the ice moving ashore is different from the ice heaves that occur in midwinter when a solidly frozen ice surface expands on a warmer-than-usual winter day. Here the ice is being driven ashore presumably by prevailing winds.
The wondrous aspect of this particular event is the needle-like shape of the ice crystals. One type of needle-shaped ice is frazil ice, but I think that's different - at least in the video I bloggged some years ago of frazil ice moving at Yosemite - because frazil ice forms in supercooled water. I think what is seen here is the result of fracturing of the ice sheet.
But the video is cool. Wish I had been there to see it happen.
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What a delicious slithery icy sound it makes!ReplyDelete
Seriously cool video! Thank you!!ReplyDelete
As for what's going on.. definitely not frazil ice. Frazil ice forms in supercooled water when small particles of ice are mixed through the entire depth of the water.
What I think is going on here is that the warm weather and the wind conditions are blowing the ice cover on the lake up onto the shore. What you're seeing in the picture looks like fracture planes in the ice cover of the lake. The water in the lake is still very cold, but outside it looks pretty warm (the current weather is up to like 79F I think, but the lake is still frozen over).
So the wind blows the ice up onto these sharp fracture planes, and it quickly goes from very cold to very warm, with the pressure on one side of the ice blocks from the pressure of the wind forcing the ice blocks up -- and the edges fracture and shatter like glass. The long sharp crystals are from how the ice blocks froze, and as they shatter they break along the planes of how the ice crystals formed -- so the ice essentially just falls apart like broken pieces of glass, back into the long crystals the ice was formed out of, then pressed together by the expansion of the ice as it froze.
Really cool phenomena...