Carl writes, “Icicles form when melt water from sunlit areas or stream water flowing over rock ledges freezes. Icicles can be pencil-sized and a few inches long or hundreds of feet in height below a waterfall and weigh thousands of pounds. Icicles attached at the top would be called stalactites, while those forming from the ground up are stalagmites, like those that form in caves from mineral rich water. Unlike those which normally form in the quiet air of a cave over hundreds of years, wind may cause a deflection in the shape of an icicle that forms on a sunny afternoon.”
Icicles on houses are often a sign of poor insulation. Heat rises to the eaves, the snow on the roof melts, and it drips over the edge, into the gutter, and into the air, where it freezes. New England, fortunately, also has a lot of sunshine in winter, between the snowstorms. Even when the temperature stays below freezing, sun on a dark roof melts its snow blanket very gradually, and this too creates big icicles. My house, and others around, are crowned right now with beautiful ice.