What's going on? This closeup photo of a metal handrail support on an outdoor stairway in northern Virginia was sent to the Monitor by a reader. We were struck by the beauty of the ice forms, but we were also curious. How had this happened?
Here are the circumstances of the photo, taken late last winter by Ernie Greene, a transportation systems coordinator for the Fairfax County, Va., Public Schools: After a brief rain, a strong cold front had moved in overnight with high winds and plummeting temperatures. At the time the photo was taken, 6:30 a.m., it was 12 degrees F. - even colder if the wind-chill factor is taken into account. Two beautiful spirals of ice had formed, with a trace of a third.
Before you read further, you might want to try to come up with your own idea for how the spirals formed. (No, the railing did not move as the ice formed.)
George Dewey, a longtime teacher of physics in Fairfax County's public schools, offers this explanation:
Rainwater had found its way into this 14-inch section of the railing support, filling it with water. As the water began to freeze, it expanded (as water does) when its temperature fell below about 39 degrees F. As the chilly water turned from liquid to solid, the ice was forced upward through the small holes at the top of the pipe.
Yes, ice can flow. Glaciers flow. Even solid rock can bend and flow under pressure and over time. (Did you ever notice graceful curves of rock layers in a road cut along the highway?)
As the ice moved upward inside the vertical pipe, it hit the lower portion of the handrail. It was then forced along the outside curve of the pipe and, perhaps because of that geometry, emerged as a pair of semicircles from the holes in the pipe. This, plus the pull of gravity, accounts for the downward-spiral shape of the ice (what scientists call a helix). The striations (scratches) on the ice are further evidence that the ice flowed as it was squeezed through the holes.