The Weather Notebook: Getting Frazzled by Ice

Getting Frazzled by Ice
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A surprising fact is that ice can form in moving water. This ice is called frazil ice. Hi, I'm Dave Thurlow for The Weather Notebook. I caught up with hydraulic engineer Steve Daly at the Cold Regions Research & Engineering Lab, in Hanover, NH. He described the formation of frazil ice in fast flowing streams.

Fine, small, needle-like structures or thin, flat, circular plates of ice suspended in water. In rivers and lakes it is formed in supercooled, turbulent water. CRREL
SD: "Most water in streams and rivers is turbulent. If the air is cold, the river's losing heat to the atmosphere. It cools down to 32, but then it just keeps on cooling and it will actually become supercooled. And it's very difficult for ice to form initially in the water. And generally, you don't start seeing ice until about...it won't form spontaneously until you get at least 1 degree Centigrade of supercooling."

And even at that point, it takes some tiny nucleus to act as a surface on which an ice crystal can grow.

SD: "That's right. What happens is ice crystals from the air fall in the water and when its just a little bit supercooled, then these ice crystals that fall in from the air are entrained into the turbulent flow and they can start growing. And they break up very quickly, a few crystals introduced from the air and you end up with thousands and thousands of ice crystals.

DT: Are they visible?

SD: "They start out they are about 1 millimeter in size and they are quite difficult to see, but if you shine a bright light into the water it looks like snowstorm of crystals going by the light.

Steve Daly is research hydraulic engineer at a lab in Hanover, NH called CRREL, Cold Regions Research and Engineering Laboratory. It's part of the Army Corps of Engineers, they study cold regions throughout the globe by looking at scientific and engineering research, and then they put that knowledge to work in the field. For more information on CRREL, please check out our website at weathernotebook.org.