Surface Hoar: Beautiful, Fun and Spooky
During clear, sunny weather the layer of air above the snowpack warms during the day and holds moisture in the form of vapour. As temperatures drop (late in the day and overnight) the vapour sublimates
(Goes from a vapour to a solid directly - no liquid stage) and forms a point on the snowpack. As this process continues more points attach to the start of the surface hoar and eventually build the feather like flakes we are familiar with. While surface hoar resists change (no tendency to round out and bond) it is easily effected by wind. If undisturbed surface hoar becomes buried by subsequent snowfall it becomes a layer of weakness within the snowpack.
On the surface this crystal is a delight. It sparkles and skiing through deep layers of large crystals produces a tinkly/swishing noise.
With new snow in the forecast keep a heads up for pockets of buried surface hoar. All conditions provide us with great opportunities to learn. Travel safe and enjoy this next weather cycle.
-text by Brian Hall
Note from Admin: As stated above, check your facts. Here are a couple of references to get you started (but seriously, don't take our word for it, look into it yourself!):
- The Avalanche Handbook By David McClung, Peter A. Schaerer (pg 49)
- (US) Forest Service National Avalance Center
-The Canadian Avalanche Centres Report Glossary:
Crystals, often shaped like feathers, spikes or wedges, that grow upward from the snow surface when air just above the snow surface is cooled to the dew point. The winter equivalent of dew. Surface hoar grows most often when the wind is calm or light on cold relatively clear nights. These crystals can also grow during the day on shady slopes. Once buried, layers of surface hoar are slow to gain strength, sometimes persisting for a month or more as potential failure planes for slab avalanches.
If you agree or disagree, let us know in the comments below!