Avalanche danger

Avoid being surprised
Reduce risk level, on a well
Totally avoid danger, if this is what you look for...
...and above all
Be aware of unpredictability

Avalanche danger : 4 vigilance modes

Relaxed mode

no sign of danger
NORMAL VIGILANCE
No avalanches possible in the area
Relaxed mode

Suspicious mode

sign(s) of danger identified
AVOID THE DANGER
possible avalanche (over there)
Suspicious mode

Alert mode

sign(s) of danger identified
REDUCE RISK
possible avalanche here
Alert mode

Risky mode

sign(s) of danger identified
IMPOSSIBLE TO REDUCE RISK
possible avalanche here
Risky mode

Avalanche danger : 6 criteria to take into account

According on your level, from beginner...
Temperature increase, snow thawing
Temperature increase, snow thawing
New overloading: accumulation due to the wind, fresh snow or rain
New overloading: accumulation due to the wind, fresh snow or rain
A possible buried weak layer?
A possible buried weak layer?
...to the most experienced

The Mechanisms of Slab Release
What we can see, playing “stability games”

Buried weak layer

Video Basic identification by probing with your ski pole, confirmed (or not) by the compression test.

Crack initiation

Video Compression test (having isolated a column of the snow pack the shovel blade is placed over the column and tapped with the hand).
Video

Weak layer collapse

Weak layer behavior before and after the compression test.

Crack propagation

VideoVideo Crack initiation using a snow saw to cut the weak layer located below a long isolated slab block, then...

The breaking-off of the slab and its transportation

The « slab » must break off before it slides sliding, if the block has not been pre-cut.

« Bridging index »

Video Multiply the total thickness (cm) of snow layers above the weak layer by their average hardness (1 to 5). If you get less than the critical (empirical) threshold of 130, you may initiate a crack.

Snow overloading

Observe crack initiation and propagation during increased loadings on the long isolated slab block.
Réalisé dans le cadre du projet ProGuides.
Le projet ProGuides est cofinancé par l'Union Européenne dans le cadre du programme Interreg V-A France-Italie ALCOTRA 2014-2020.