Avalanche Initiation & Snow Mechanics – Continued Professional Development IFMGA

This week we have had the first winter snowfalls here in the Alps and I got the chance to meet up with Alain Duclos once again to discuss his favourite topics of snow mechanics and in particular crack initiation, weak layer collapse and crack propagation. It’s kinda comparable to my work as an engineer and fracture mechanics in weld and acceptable flaw size that wouldn’t result in weld failure for the design load.

Alain is an avalanche expert, responsible for road safety in the Haute Maurienne which is home to the Frejus Tunnel – a major freight and transportation link between France and Italy that is over looked by some impressive alpine terrain. Sadly, Alain is often called as an expert witness for avalanche accidents in the Alps.

survivors are generally surprised that the slope avalanched and often underestimate the slope angle.

This highlights 2 things. The ability to accurately gauge a slope angle, remembering anything above 30 degrees puts you in avalanche terrain while also considering overhead terrain & the fact that they were surprised means they were operating in a relaxed mode, perhaps due to failing to recognise they were in avalanche terrain or failure to assess the risk. Alain’s website data-avalanche is a ‘go to’ teaching, training, and reference resource for everyone to use.

There are 6 main criteria to review and assess for avalanche danger; the avalanche bulletin, slope angles >30º, recent avalanche observations, rising temperature & thawing, overloading due to wind accumulation / new snow / rain, and the possibility of a buried weak layer which a bulletin should highlight for well frequented areas.

There are 4 vigilance modes, relaxed, suspicious/cautious, alert & risk or gambling mode. It is clear that if you are relaxed and get caught in an avalanche, then there has been a failure in the observations made.

Play long enough in gambling mode and the statistics will catch up with you. However to complicate the matter further, Humans fall into 4 different categories for decision making traits, and at best only 2 of these types of people are likely to make conservative stand alone decisions (ref Powder magazine’s – The Human Factor 2.0).

Extract from Powder mag’s The Human Factor 2.0

To set the scene we were on the mountain after the first 30 cm snowfall of winter. The Alps has another hot summer and then a cold snap at the end of September brought around 1.5 m of snow and was followed by nearly 2 months of Indian Summer. Meteo France had not started avalanche forecasting and so digging a number of snow pits would provide valuable current information on snowpack stability. 

Usually I would have been skiing since September but with the new norms this was my first day on snow. We did a number of investigative snow tests between 2750 m and 2350 m on northerly aspects on 30-35 degree slopes. At each site 2 Compression Tests (CT) and a Propagation Saw Test (PST) were performed. For the first time all the tests yielded similar results – a weak layer lying just below the crust of the old snow surface yielding crack initiation, propagation and failure. Skinning around on the flat yielded a number of whoomps indicating collapse/failure of the weak layer. Its early days yet and no avalanche control has been done yet but it was definitely interesting to see whats going on right now.

Preparing the extended site for 2 Compressions Tests and Propagation Saw Test – circa 2.5 m long worksite
Compression Test 30 x 30 cm isolated column
Failure with Propagation Saw Test

I run 1 day avalanche awareness courses throughout the winter so don’t hesitate to contact me at rosshewittguiding@yahoo.com or phone/WhatsApp +33781287608 If you want to expand your knowledge and safety margins this winter.