Nice demonstration of buried surface hoar
Sunday, 9 December 2012 | Evan
Here's another video from "Avalanche Guys", this time giving a very nice demonstration of the problems of a buried surface hoar layer. This is definitely one of your unstable enemies off-piste, and it can be tricky to spot as it is often patchy, so that some lines down a slope will trigger a slide, whereas others won't. This is one of the reasons that it is helpful to regularly moniter the snowpack over the season, as "today's surface hoar is tomorrow's weak layer". In other words, if you're aware of it when it's on the surface and easy to spot, you'll know it's lurking after the snow has fallen. If you can't moniter the snowpack regularly yourself, speak to someone local who has watched it develop over the season or consider taking an expert guide who'll have been carefully analysing the developing snowpack.
The video also shows a demonstration of a column compression test- note how he starts by tapping the blade with his fingers only, then moves on to whole forearm taps, during which the weak layer breaks. If it hadn't broken, he would have gone on to full arm taps.
Remember: one sign of weakness outweighs any signs of stability. If in doubt, choose low angle terrain <25 degrees. Don't take a ticket for this lottery!
The sound quality is a bit wind-affected, but worth sticking with the commentary for some good educational information. Click here for our snow assessment tools. They'll help you in analysing snowpack safety.