PisteHors.com has published its annual in-depth review of the season's avalanche avtivity in France. It reports that, with 55 deaths in 49 accidents, avalanches claimed more lives in France than in any year since records beagan in 1971, And indeed, twice the long term average...
This is very valuable reading if you are trying better to understand what conditions lead to avalanche conditions.
rob@rar, I find it really worrying that there's such a deficit of knowledge in avalanche awareness for so many skier/boarders. IMNSHO anyone with the intention of heading off-piste, including between runs in resort should have the ability to assess snow conditions beforehand; yet I would make a generous guess that the number with this ability lies between 10-20%.
I would ask how much information there is avaliable in this country for skier/boarders wishing to learn more about avalanche awareness. I know the BMC run seminars around the country at this time of year for climbers on winter safety and the theory behind avalanche cause and assesment but I don't think there's anything similar for other winter sports enhusiasts.
Remember it takes less than 5 minutes to dig a pit and the number one cause of a slip is people.
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Having been caught in a slide last year, I'm even more aware of the dangers and somewhat apprehensive about my forthcomming trip in January. I've continued to read as much as I can to educate myself. The article is very good, and does highlight that anyone can be caught, even the experts who live in the mountains and supposedly have easy access to all relevant information.
I'm particularly interested in the stability of the snow pack, and how it becomes stable. The conditions last year were such that a weak layer was produced early in the season and that the snowpack had not been able to stablise through a freeze / thaw cycle for some time. I guess my question is how long does it take to make the snowpack stable? and what conditions are required to make it so.? If I understand this then at least I can question my guide / instructor, as to how he knows it is safe before putting my safety partly in his hands. After all I only go for one week, so my knowledge will be limited to what I can find for the area before I go, which at that level is not widely available on the Net.
BOD, my understanding is that once you get a layer of faceted snow crystals like the one described in the article, they can take a very long time to disappear. i expect that the best thing for stabilising that layer is a proper thaw followed by a full re-freeze - ie melt water actually has to penetrate the weak layer then refreeze.
aside from thawing and refreezing, snow stabilises by a process called sintering whereby the "arms" of a snowflake gradually bond to the arms of neighbouring flakes to form a relatively well bonded layer. the problem with faceted crystals is that, as the name suggests, they become exactly that - ie they have flat surfaces rather than arms. these don't bond and just slide off eachother - if you try to make a snowball out of this sort of snow, you'll have a very hard time.
this is just a brief and not very scientific explanation. well worth buying one of the avalanche science texts (staying alive in avalanche terrain by bruce tremper is the one i have read) for more of a description
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
Swirly: Very generous ! I think 1 to 2 % !!
After all it is free
After all it is free
BOD wrote:
I'm particularly interested in the stability of the snow pack, and how it becomes stable. The conditions last year were such that a weak layer was produced early in the season and that the snowpack had not been able to stablise through a freeze / thaw cycle for some time. I guess my question is how long does it take to make the snowpack stable? and what conditions are required to make it so.?
Arno has covered this in some depth. Once the snow has metamorphised beyond a certain point (depth hoar) it remains in that form until it melts or gets saturated with meltwater. This means there is always a weak layer adjacent to the ground during the winter months.
Depth hoar isn't in itself a problem. If all the snowpack is depth hoar it is effectively like skiing in powder, this was the case in the Tarentaise in January last year where all of the 80cm of snow depth was facetted snow. Great because even though it hadn't snowed for 2-3 weeks you are still skiing in powder snow off-piste. Okay if there is enough depth of this stuff it could powder avalanche, but it only exists because the snow depths are not too great.
The problem is when it snows on top and this layer is more (hard slab) or less (soft slab) cohesive. The top layer can weigh thousands of tonnes. If a passing skier breaks the weak bonds between this slab, the underlying weak layer and the surrounding snow the whole slab can move and bury the skier. 90% of fatal avalanches are slab avalanches and 90% of them are triggered by the victim or a member of his party. Here is a bit more info:-
Of course depth hoar, surface hoar (same crystals formed by a temperature difference between the snow surface and air) are not the only weak layers. Ice due to freezing rain and graupel (ball bearing shaped snow pellets) are also a problem.
What can stabilize all this? Well soft snow will settle and form stronger bonds with the surrounding snow, if it is subjected to a freeze thaw cycle these bonds will be quite strong. Hard slabs (formed by wind transported snow) will also grow deeper over time. In both cases they end up bridging the weak layer, as a rule of thumb once a weak layer is buried by more than a meter of snow it is no longer a problem due to the bridging effect. Of course as spring comes and these layers start to melt the weak layer can cause problems again as it has never really gone away.
Key points from last year.
1.) Very thin snow cover over the Northern and Southern Alps until the end of January in most places above 2000m which meant that much if not all of the snowpack was depth hoar.
2.) Fresh snow covering this weak layer.
3.) Avalanches!
However there was a cycle of avalanches around the end of January, if you look at figure 5 you will see no fresh snow but strong, southerly winds. These piled snow onto north sector slopes, exactly the slope aspects where you would not get much of a freeze/thaw cycle in winter and where depth hoar is most common.
If you want a couple of rules of thumb to keep you reasonably safe without knowing anything at all:
Don't ski off piste without a guide or experienced (in avalanches not skiing/boarding) friend when the avalanche headline risk is 3,4,5 in France or 2,3,4,5 in Switzerland. Don't ski within 2 days of fresh snowfall off piste without a guide or experienced friend
You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
Last edited by You'll get to see more forums and be part of the best ski club on the net. on Fri 27-10-06 20:43; edited 1 time in total
Ski the Net with snowHeads
Ski the Net with snowHeads
davidof,
Many thanks for a very clear explanation. I only every ski Off piste with a guide / instructor and realised last year that I cannot completely delegate responsibility for my safety. I'm certainly wiser from my experience and one lesson I learnt was to try and understand more so I can take part in risk assesments, and not just accept what someone else says.
I have to admit that for years I have been a follower and probably like a lot of recreational skiers couldn't tell you which way north or south when in the mountains.
admin,
I've seen this video a number of times. What surprises me is that once it goes the skier doesn't seem to have been swept down with the snow. Any idea how this was possible?
snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
rob@rar, excellent link - thanks Rob.
And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
BOD wrote:
I've seen this video a number of times. What surprises me is that once it goes the skier doesn't seem to have been swept down with the snow. Any idea how this was possible?
I think you are seeing an optical illusion a bit like when you are at a railway station and the train next to you pulls out but you think your's is the one that is moving. In this case the skier, Jerome Buc, decided to get a few turns on the slopes of Piau in the Pyrenees before the resort opened. He was skiing a north facing convex rollover. There had been fresh snow and southerly winds the previous days. This is a soft slab avalanche, an area of powder snow that is just slightly cohesive so it can move as a whole. They are pretty much invisible. Jerome got taken some distance down the slope but because a lot of the snow was moving faster it gives the appearance that he was not moving much. When he looks up you can see he was taken maybe 100-150 meters.
It was a small avalanche and he was lucky not to have been buried, even 20-30cm below the surface could have been fatal as he was alone. As it was he finished with lacerations, his butt was strained over the underlying rocks and ripped the seat off his new salopettes and his underwear. On returning to his car someone asked if it was "gay pride week". It is a great piece of footage that he managed to capture with his helmetcam.
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
BOD, next time you go with a guide, ask him to talk you through his safety decisions. most will be happy to, especially British ones - I find them generally a bit more into educating their clients
You know it makes sense.
You know it makes sense.
davidof wrote:
It was a small avalanche and he was lucky not to have been buried, even 20-30cm below the surface could have been fatal as he was alone.It is a great piece of footage that he managed to capture with his helmetcam.
I thought this as well, he kept his head up which was good going. If you notice at the bottom of the slope the snow builds up as it was a short slope. It would have been a lot worst if it was a longer slope.
What also amazed me about the man was the lack of swearing or general "oh *&^%$%^&*" just one quitely said word.
I will spend my slack time at work on monday reading the report.
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
Does anyone know of a source for forecasts in English ? I'm looking for one to cover the Spanish Pyrnees (Baqueira area) but so far can only find it in Catalan.
FAQ
Poster: A snowHead
And the graph in figure 7 shows the increase in a really striking fashion.
