Published: 2013-03-19 08:58:24
Updated: 2013-03-19 08:58:24
Posted March 19, 2013
By Mike Moss
A viewer named Harrell sent us a question about a 5-gallon bucket that had collected rain water for a week or so in advance of a rather cold morning that occurred on Monday, March 4th. When he peeked in the bucket that day, he was not surprised to see that the water had frozen, but was surprised to see a very well-formed triangle, about one inch on each side, sticking up out of the remaining ice an inch or so above its surface. He sent us a few pictures of the bucket and its interesting phenomenon, which I've posted here.
His description made me suspect he had observed an example of something called an "ice spike," and the photos confirmed this was the case. An ice spike can form when a layer of ice forming rapidly across the top of a container seals in water below that hasn't yet frozen. As the trapped water begins to freeze and expand, it can extrude upward through a crack or hole in the top layer to form a spike or vase-like structure. These form most readily with pure water and temperatures around 15-25 degrees (the low at RDU on that date was 26, but it certainly may have been colder in some locations).
These spikes may take on a variety of shapes, depending on the conditions under which they form, but it has been observed in the pas that there is a tendency for sheet of ice initially extending downward beneath the surface of the water have a tendency to join at 60-degree angles, and in some cases this can influence the shape of the spike to be an equilateral triangle, this one being a very nice example. They can also form as elongated round tubes or in some cases, very complex and beautiful shapes that defy easy explanation but relate to changing temperatures and rates of cooling, different shapes and depths of the container and perhaps varying winds during the time of formation. There are some very nice photographic examples of a wide variety of ice spikes that you can see at the link I included here (be sure to click the "ice spikes" and "other people's ice spikes" link). So, next time we dip well into the 20s (which may or may not happen again this season), have a look in your birdbath or other container of water outdoors. You could find a neat little icy sculpture there...