Surface Hoar

Last weekend I did a quick trip to Arches National Park. The park is pretty in the winter with the snow covered red rocks, but I was surprised how many people were out hiking in the cold weather. Anyways, when we arrived at Delicate Arch, while everyone was gazing at the amazing arch, I was looking at the incredible surface hoar!

Surface hoar is found on the surface of snow after a cold night. It looks like this...

Photo by NGB

 It forms by vapor deposition, which is when water vapor (water in its gas phase) freezes, or deposits, to a snow surface. It makes these feathery like structures on the snow surface. It is most common after a cold, clear night in areas when the air is humid. It is especially common in areas with a water source like a river or stream. Light winds are also favorable to surface hoar formation because the light wind will re-supply the air right above the snow with more water vapor to condense on the surface.

http://www.fsavalanche.org/encyclopedia/surface_hoar.htm

Surface hoar can become an avalanche hazard when it is buried by a layer of new snow. It makes a slick, unstable layer which the new snow can slip easily on.