Whenever we experience a long really cold spell, flat crystals of ice grow on top of the snow and pond ice. This is called Hoar Frost. I noticed some examples of hoar frost yesterday on the pond ice.
A layer of hoar frost can be very dangerous when it forms up on the mountain slopes, once more snow covers it. The hoar frost layer is very unstable and when the heavier snow blankets it, the hoar frost layer can slide which causes an avalanche.
Ski technicians constantly test the stability of the mountain slopes by digging down through the snow to see if there is any weak layers that might cause instability and avalanches.