An icicle is a spike of ice formed when water falling from an object freezing.
Icicles form on surfaces which might have a smooth and straight, or irregular shape, which in turn influences the shape of an icicle. Another influence is melting water, which might flow toward the icicle in a straight line or which might flow from several directions. Impurities in the water can lead to ripples on the surface of the icicles.
Icicles elongate by the growth of ice as a tube into the pendant drop. The wall of this ice tube is about and the width . As a result of this growth process, the interior of a growing icicle is liquid water. The growth of an icicle both in length and in width can be calculated and is a complicated function of air temperature, wind speed, and the water flux into the icicle. The growth rate in length typically varies with time, and can in ideal conditions be more than per minute.
Given the right conditions, icicles may also form in caves (in which case they are also known as ice stalactites). They can also form within salty water (brine) sinking from sea ice. These so-called can kill and starfish, which was observed by BBC film crews near Mount Erebus, Antarctica.Ella Davies: 'Brinicle' ice finger of death filmed in Antarctic filmed by Hugh Miller and Doug Anderson, Frozen Planet, BBC Nature, BBC One, broadcast 23 November 2011.
The story of an English youth killed by a falling icicle in 1776 has often been recounted.
Large icicles that form on cliffs near highways have been known to fall and damage motor vehicles.
In 2010, five people were killed and 150 injured by icicles in Saint Petersburg, Russia after heavy snow that also caused apartment block roofs to collapse, as well as creating water damage to private homes and to the National Library of Russia.
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