FROM THE WEATHER CENTER by John Simon
We have all seen icicles…they can form during bright, sunny, but sub-freezing weather, when ice or snow melted by the sunlight or some other heat source (such as a poorly insulated building) re-freezes as it drips off under exposed conditions. Over time, continued water runoff will cause the icicle to grow.
The growth rate of an icicle can exceed 1 centimeter (0.39 inches) per minute!
Also, in the right conditions, icicles may form in caves (in which case they are known as ice stalactites). Large icicles that form on cliffs near highways have been known to fall and damage passing motor vehicles. In 2010, for example, five people were killed and 150 injured by icicles in St. Petersburg, Russia after a heavy snow that also caused apartment building roofs to collapse, as well as water damage to private homes and to the National Library of Russia.