I remember, as a child, discovering that the best place to find huge icicles—the kind that were three or more feet in length and several inches in diameter—was a section of roof in the back of our church. I don’t know if those icicles grew so big because the conditions were just right, or because it was an out-of-the-way place and nobody bothered them. Whatever the reason, I always wished we could grow such impressive icicles at our house. Alas, we never did.
What is an icicle?
Ice, obviously. But where does it come from, and how does it grow?
An icicle can form whenever the air temperature is below freezing, but water is present in liquid form, such as:
• Melted snow on a roof caused by either the sun or interior heat
• groundwater seeping through cracks in rocks
• water spray from a waterfall
A typical roof icicle begins when melted snow runs down the roof under the insulating snow layer. When it hits the cold air at the edge of the roof, it refreezes. An icicle starts when enough frozen drops coalesce so that the next drop flows over and drips from the bottom of the structure. Then water will begin to sheet down the outside of the drip, forming a thin film of ice on the way down, creating a long, pointy icicle. This process is akin to making a hand-dipped candle. Airborne water from freezing rain or waterfall mist can also solidify on an existing icicle or sub-freezing surface.
The icicles growing on rocks along the roadway form in a similar manner. When the groundwater seeps from the rock and hits the freezing air, an icicle begins to form. These icicles can grow quite large because, unlike roof icicles which only grow when the snowpack melts, the groundwater doesn’t stop seeping.
Are you bored enough to watch icicles grow?
Go on, take a look, it’s really short. (Email viewers click here to go the website.)
Notice those ripples along the sides of the icicles? Nobody is sure why they develop, although various theories have been proposed. Experiments show that impurities in the water tend to cause rippled icicles, but do not explain why they form. [But don’t worry, someday some intrepid scientist will figure it out.] If the science behind icicles fascinates you, watch this video on icicle ripple formation.
Or read this Inside Science article on icicle ripple formation.
Before you click over to Inside Science, don’t miss the info at the bottom about the complex physics and mathematical modeling behind the realistic snow in Disney’s Frozen. Yay, science!