Surface Hoar

A type of crystal that forms on the surface of snow by direct deposition of water vapour out of the surrounding atmosphere. The crystal can be needles, plates, or other forms, and the crystal diversity can be as complex as dendritic stellars.

Indeed, as vapour diffusion has a tough time growing stellars in the atmosphere beyond 5 mm in size (because the vapour droplets become so relatively small in relation to the complexity of the surface they must add to), it is quite a wonder of Nature that we can get 20 mm of surface hoar growth on a single night.

Considered by some to be the snow crystal with the most personality. It has a distinct propensity, once buried, to propagate layer failure and create avalanches. It often has a 'sweet spot' of burial depth where skier-sized triggers will set off such propagation.

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