Two off piste skiers have been killed today around midday by an avalanche in Tignes. The avalanche occurred in the Bois de la Laye couloir at 2100 meters altitude above the Lac du Chevril. The victims, a local guide and his client were equipped with both avalanche beacons and airbags, both of which had been activated. The avalanche was 80 meters wide and the debris measured 8 meters deep in places. One of the victims had been pushed into the Bois de la Laye river bed by the slide before being buried.

https://maps.google.fr/maps?client=ubuntu&channel=fs&oe=utf-8&q=Bois+de+la+Laye+tignes

The avalanche risk was Considerable (3/5) at the time following strong easterly and southerly winds on Monday and Tuesday which had formed localized small hard slabs likely to be triggered by a single skier.

France 3
http://alpes.france3.fr/2013/03/06/tignes-deux-personnes-decedees-apres-une-avalanche-211479.html

Dauphine Libere
http://www.ledauphine.com/savoie/2013/03/06/tignes-deux-morts-dans-une-avalanche

Radio Val d’Isere
http://www.radiovaldisere.com/article.php?id=4105

Poor souls!
Who knows what kind of ABS system is involved in this accident?
I mean is the original ABS twin system (Germany) or the new one from Mammut (RAS), former Snowpulse (Switzerland)?
At 8 meters depth is a huge avalanche!

Sorry no idea what kind of airbag they were wearing. ABS are popular amongst the Val d’Isere pros. The guide was Olivier Bianchi who was formerly with the PGHM in Chamonix.

I’ve posted a round up of some other incidents here

http://pistehors.com/news/forums/viewthread/1442/

The PGHM (High Mountain Police Rescue Unit) have this to say

The PGHM have warned that there is a risk of slab avalanches due to the wind and also from full depth avalanches due to the quantity of snow and the recent thaw. These avalanches can occur in unexpected locations.

Just looking a bit more at the conditions prior to this avalanche. The wind was largely from the SE, gaining strength from midday of the 4th March and dropping on the 6th March. There was only some very light snow, a few cms at best, but a considerable amount of snow transport from the SE to W. There was a thaw today in Tignes with the zero isotherm around 2600m during the day but conditions were fairly cold still on the day of the slide.

The searchers found two airbags but the victims were buried deep? This is beyond strange, perhaps the victims did not use the strap that goes between the legs?

Some reports said that they had taken their backpacks off to fit climbing skins when the avalanche struck but they why would the airbags have been activated (if they were)? I think we’ll have to wait for more information. The PGHM investigated the slide zone but were unable to determine if it was skier triggered or not as the area had been covered by fresh windblown snow.

As this thread shows, the first reports of this tragic accident seemed contradictory. Henry Schniewind has a view about what happened which I think is probably as well-informed as anything in the public domain: see http://www.henrysavalanchetalk.com/clues-spot-dangerous-windslabs. The part of this video that relates directly to this accident starts 12 minutes 30 seconds into the discussion and lasts about 6 minutes. (You can fast forward to this bit using the slider below the video).

Henry made some points that improved my understanding of this accident in particular, and, more importantly, the risks of tree-skiing in general. Here are some slightly shortened quotes that summarise them.

It is a myth that trees are a safe place.

The only time that trees will hold the snow so that it won’t avalanche is when the trees are so dense that you can’t ski in them. Once you can ski in them, there is a chance of an avalanche. It is true that avalanches are less probable where there are trees, because they do act as anchors to some extent, but they are less effective where they are thinly spaced.

If there is an avalanche, trees are deadly terrain traps. It’s like revving up a motorcycle at full speed and going straight into a tree, except that here the people that were taken probably went into multiple trees. It’s a gruesome thought.

I’ve not watched the video and I wasn’t particularly going to bother but I’m not sure about that. I never thought trees were unequivocally safe anymore than I’m about to accept they’re unequivocally not.

We know that when people start to take avalanche training there’s a statistical blip where they become involved in more incidents (The Role of Training in Recreational Avalanche Accidents in the United States, Ian McCammon, ISSW 2000 etc) and there’s a variety of reasons offered for that but one of the main ones, in my opinion, is related to making these sort of unequivocal statements. At these earlier stages of experience there’s a tendency, hardwired by evolution, to try and formulate heuristics or rules of thumb. I think this occurs because people are naturally struggling to to assimilate large amounts of new information and trying to understand how to apply that new knowledge. So, they establish these heuristics which are sometimes wrong, but more normally incomplete, and then later entirely discard them. When they’re discarded it’s no safer, if the heuristic was incomplete it probably did reflect something of value which is now also discarded.

Sorry, that’s longwinded of saying that trees, their placement and density on a slope is just one piece of information, it’s a characteristic of that slope and one that needs throwing in a mix of other data. The comparative weight you might give that one piece of information is going to vary on the day. It’s also an integral part of several decision support frameworks in the form of avalanche paths of course with the obvious paths stripped of trees. Again analysis of incidents says that at the early-acquired skill level missing obvious clues like avalanche paths is quite common.

Which is still a long winded way of saying that we ought to avoid things like “XXXX is a myth” if it’s really a case that “XXX isn’t always true and has these limitations”