Ice, Ice Baby

Reported February 2007

ORLANDO, Fla. (Ivanhoe Broadcast News) -- Icicles can be dangerous and deadly, yet they can create some of the most amazing winter scenes. And for scientists, those winter scenes are playgrounds for discovery.

It's on those playgrounds that experts in physics and mathematics are building their theories on what it takes to create an icicle.

We all know icicles form when melting snow begins dripping down a surface. But what scientists didn't know is how their shape is formed. What makes each icicle different?

University of Arizona Physicist Martin Short, Ph.D., turned to mathematics to find out.

"Icicles have a certain mathematical shape, and this mathematical shape is universal among icicles," Dr. Short tells Ivanhoe.

So what is the math behind an icicle?

"Here I've drawn the profile of an icicle. Here is the height, and here's the radius ... Here's the profile here, and I've written the formula here. The height is proportional to the radius to the four-thirds," he says.

What does the formula have to do with an icicle's shape? "It kind of looks like a carrot," says Dr. Short. "It starts out flat and then sort of up as you go."

As water drips onto an icicle and freezes, it releases heat. The warm air rises up the sides of the icicle. Dr. Short says that warm air layer acts like a blanket that's an insulator, and so the blanket is very thin near the tip and thick at the top. That allows the top to grow very slowly and the tip to grow rapidly -- creating a long, thin icicle.

It's the same equation scientists use to study stalactites in caves, but instead of water, stalactites are formed by the buildup of calcium left after the water evaporates.

"If we know the mechanisms by which stalactites form, well, we could better preserve our natural caves that we have here, and try to stop them from eroding," Dr. Short says.

And now that scientists know how icicles are made, it could lead to breakthroughs to prevent them from forming on power lines and trees.

The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.

Click here to Go Inside This Science or contact:

Martin Short, Ph.D.
Physicist
University of Arizona
(520) 621-6786
mshort@physics.arizona.edu

American Meteorological Society
45 Beacon Street
Boston, MA 02108-3693
(617) 227-2425

American Geophysical Union
Washington, DC 20009-1277
(800) 966-2481

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