Ask A Scientist General Science Archive

Question:  Here on the coast of B.C. we have a strange form of frost that 
developes on dead, barkless branches.  It looks like fine white hair.
What is it called and how is it formed?
 jessica a scholten

Answer 1:
I have no idea what causes this but I can suggest an experiment to
help you determine the cause.  Ice needs a substrate (a surface) to
precipitate on.  I am guessing that the dead barkless branches
are covered with a fungus or mold that is not easily seen until
covered with frost.  Try spraying an atomizer (from a perfume bottle)
at the branches.  If my idea is correct, the "hairs" will be
revealed.  It is important to use a very fine atomizer.  You may
also see the same effect if you place some hot steamy water under the
branches.  You could also clean some branches and see if they
are able to support the growth of "hair".
Let everyone on NEWTON know what you find!
 michael b lomonaco

Answer 2:
Sounds like you are referring to hoar frost, which forms in
calm, humid air, when water vapor in the air comes in contact with
a frozen surface.  The water vapor sublimates onto the
surface, forming the frost.  Sublimation means that instead of
the vapor becoming liquid (water) and then solid (ice), the
vapor forms a solid directly without ever being a liquid.
One of the definitions of the word "hoar" is gray or white
with age.  Hoar frost was probably given this name because
it looks like an old man's beard.
-Grant