The Ice Finger of Death

Last year, BBC cameramen  H. Miller and D. Anderson filmed the formation of an underwater icicle:

Credits: cameramen Hugh Miller and Doug Anderson for the BBC One series Frozen Planet Because it is formed by freezing brine sinking into sea water, this phenomenon has been named "brinicle".It was first described in the sixties but, because it is very difficult to know when and where it will occur, it's the first time someone has actually managed to film it.  The cameramen also have to work under extreme conditions: freezing water under a thick layer of ice. "I do remember it being a struggle... All the kit is very heavy because it has to sit on the sea bed and not move for long periods of time" says Mr. Miller How does the brinicle form? When cold water freezes, it excretes impurities (such as salt) in the crystallization process. This leads to the formation of little pockets filled with very dense salty water which does not freeze at 0°C (the salt lowers the freezing point). The brine then travels through a tiny network of channels until it reaches the sea surface. Being denser and colder than sea water, it sinks and, as it freezes the relatively warm sea water it comes in contact with, forms a thin and fragile tunnel of ice which grows into a brinicle. Brinicles don't last very long; it has to be relatively calm for them to grow. Eventually, sea currents will destroy them, often before they reach the ground. Learn more on the BBC website

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