 Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Just to correct a misconception. A slab doesn't slide under the "weight" of a skier as such. A slab is hundreds, maybe thousands of tonnes of snow. The weight of a skier is of no consequence. For a slab to be a slab it has to sit on a weak layer. This could be depth hoar, surface hoar or even fresh snow. In the latter case the fresh snow will only be a transient weak layer, maybe a day. The other layers are much more persistent.
So this tells us a number of useful things:
1. The old saw about not skiing fresh powder for a couple of days holds true for transient weak layers. A persistent weak layer is there until the thaw. Skiers have triggered slabs in June on weak layers formed in November! However it does remain a fact that the majority of avalanche fatalities occur within 48 hours of fresh snowfall or snow transport by wind. With fresh snow being the major factor. However this is due in part to the fact that slopes are getting skied out in the first couple of days.
2. What causes slab release, as far as our understanding goes, is a skier putting pressure on the weak layer causing it to collapse locally. This collapse then propagates out like dominoes falling. It is then the weight of the slab locally that triggers the rest of the slope. From this we can also see that it is more likely for a skier to cause a collapse where the snow pack is thinner. 1 meter of fresh snow will tend to soften the pressure exerted on the weak layer. But snow rarely falls evenly, you'll have roll overs with less snow due to wind erosion, rocks etc and it is here where the skier is most likely to cause the weak layer to collapse. You'll also see that you can have 100 people ski a slope and it could be the 101st who hits the trigger point, either by skiing in just the wrong area or by the skiers slowly punching down through the snow to the weak spot (see Ste Foy avalanche video from Jan 2015). It also means that tracks are no guide to security.
3. This also explains remote triggering. There is no weight on the slab but someone passing below a slab causes the weak layer under their feet to collapse which then propagates up slope. It also means that notions of who triggered the slab - the person upslope or downslope are somewhat moot. French law tends to blame up slope skiers (its gravity innit) but anyone who is on the slab could be to blame.
4. Where you have widespread weak layers, like last season in the Savoie and Hautes-Alpes, you get remote triggering and very big slides. I'm not sure if we have the same situation this year, experience would suggest that with anticyclonic conditions in December that weak layers are widespread over a given slope. However the high level rain and heavy snowfall since 1st January will also be a factor. As in the Verbier photo there will probably be some very big slides this season but maybe not so easy to trigger. Group spacing will be a big factor in survival. Don't expect your ABS to do much for you in a very big slide.
Skier compaction does help break up weak layers. This season we've not had much of that as the snow cover was thin so popular off piste routes were not getting skied. We can expect some of these routes to be more dangerous than usual.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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@davidof, fantastic informative educational post
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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I was skiing in the Aosta valley today and set off a small Avalanche. I'm posting the details as it may be of interest. It was a 3/5 day, aspect south, altitude Aprox 2200 m. There was a stiff wind and a wind slab of around 80 MM. present in places.
We were skiing off piste and sticking to low angles. I was traversing some untracked snow less than 30deg with a steeper slope above. I was just at or below where the slope steepened. As I traversed, the slope released about 20 feet above Aprox 30 feet wide. It slide and stopped as it run into the flatter slope. It didn't affect me as I was moving reasonably quickly. It didn't affect my friend as we were skiing a little apart.
There was little danger as the slab was thin and the runout open however I was surprised how far above me my presence had impacted. Also I'll be way more aware in future of not only selecting appropriate angles to ski but also the steepness of adjecent slopes.
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You'll need to Register first of course.
You'll need to Register first of course.
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I am going to La Clusaz this weekend, I see the Freeride World Tour event has been cancelled. Not sure is it the high avalanche risk or the base not being enough to cover all the rocks, on Facebook event page just says "the necessary conditions were not fulfilled"?
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Very big slide in a popular ski touring area near to here in the Izoard sector.
More here
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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.
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@Weathercam, that crown wall looks big, and a km wide!
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| peanuthead wrote: |
| @davidof, fantastic informative educational post |
Following up on what I said, the two recent Valais victims were both wearing airbags. One killed colliding with trees, one lost his airbag - not properly strapped on. The St Columbans victim in France earlier in January was in a big slide, probably with thin early season snowpack and probably died in collision with obstacles. It is something I've been saying for a long time now, an ABS is good in risk 2, normal risk 3 conditions in open terrain. Not so good on high risk 3, risk 4 days and in trees, rocky terrain. A lot of people are using airbags to take on too much risk and are outweighing the device's capabilities.
Again to echo what I said, we do now seem to be seeing a number of very big slides, be very careful about safe travel procedure in these conditions. The bulletin's risk 3 may lull some people into a feeling that sides will be small and limited but this isn't the case on the terrain.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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I'm nipping down to my local CAF tonight to see if anything is planned for their mid week tour, but I think they've postponed organised sorties.
That slide is so feckin scary as it looks like they were not on the steep part of the route.
We did a tour up that way last year when conditions were very sketchy but we did not go out much above the trees.
And this is the headline on my CAF's FaceBook Attention, lors du choix de vos itinéraiires...restez dans les bois
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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.
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| Weathercam wrote: |
I'm nipping down to my local CAF tonight to see if anything is planned for their mid week tour, but I think they've postponed organised sorties.
That slide is so feckin scary as it looks like they were not on the steep part of the route.
We did a tour up that way last year when conditions were very sketchy but we did not go out much above the trees.
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Remember that 30 degrees, give or take a degree, is the critical slope angle and that there have already been a number of remote triggered slides this season (as last year in your area - such as the galibier fatality) so that you have to give suspect slopes a wide berth. The stuff you've been doing - low angle, low altitude or up through the villages of the Nevache is the kind of tours that seem sensible this year. I've noticed a lot of the locals have wound their necks in for the moment and routes that would typically be getting skied out have not been touched.
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You know it makes sense.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| Woosh wrote: |
| http://www.thelocal.fr/20160114/how-to-avoid-dangers-of-alps-avalnches |
Pretty lame article, daily mail level information,
I read it earlier today as I do keep half an eye on 'the local' for general tit bits of news.
Try the SLF.ch for proper information,
I'm not sure where it is on their website, but on their app you can view recently dug snow-pit profiles. What a superb bit of information. Of course, be aware, that 10 metres up the slope to the right the snow pit profile could be completely different, but it gives you clues as to what is happening. Collecting clue's is the best we can do.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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You need to Login to know who's really who.
You need to Login to know who's really who.
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| Quote: |
I am going to La Clusaz this weekend, I see the Freeride World Tour event has been cancelled. Not sure is it the high avalanche risk or the base not being enough to cover all the rocks
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@Peter Ross, heading to La Clusaz later this weekend (also from Dublin) and interested to see conditions there especially as it's due to warm up next week.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Conditions getting a little better with iso going above 3000m this weekend down here in the Southern Alps (and further across the Alps) which hopefully will help stabilise snow pack a little more.
However there is still a major concern that the strong winds of last week have created substantial wind slabs and that along with the rising Iso could trigger more slides.
The real concern is that these slides can occur when the skier is sometimes far from the peaks so whilst you might be skinning up a nice mellow 20% the snow from up top could come down on you Some thick breaks are even feared, sometimes carrying all the snowpack up (weak layer near the base of the snowpack). and see photos above.
I'm actually looking forward to some spring like conditions next week as we have some nice safe mellow terrain that is not surrounded by large steep ridges that might come tumbling down.
That said tomorrow doing a big tour (1,300) with my local CAF on wooded North facing slopes (they are still playing it safe) and I think it's going to be a sh!te descent, but the token Brit can't really suggest an alternative route!
This is the latest bulletin for our area run through Google Translate
MASSIF THABOR ( Rédigé le 21 janvier 2016 à 15h )
Snowpack stability
The conditions are starting to improve with the snow that settles slowly. However, especially above 2200/2400 m, the snowpack is still not stabilized (snow layers stack windy and not windy, the presence of snow pellets and grains without cohesion, the link between these layers is bad). The strong winds last weekend has trained many accumulations and wind slabs.
The main risk is that of triggering a wind slab, they are often sensitive to the passage of a single hiker, sometimes far from the peaks. Many slopes are concerned but particularly to the northern slopes southeast to above 2200 m, as shown by the recent accidents. Some thick breaks are even feared, sometimes carrying all the snowpack up (weak layer near the base of the snowpack).
The risk of spontaneous departures, with the current warm spell, cast or small natural avalanches are possible in the sunny steep slopes and many corridors, the sweetest hours.
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You'll need to Register first of course.
You'll need to Register first of course.
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@Weathercam, nice one, 1200m in 2:40 is good going.
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@jbob, Naah that's a little wrong - must be the feckin autopause we were going at around 425-450m an hour. Mind you the guy leading did not exactly stop for many rests!
Whilst we were just below the top where I and one other decided to leave our skis and bootpack the final 15m as I thought no way could I kick turn up there these guys well into their 60's came flying up and had no issues whatsoever, just goes to show 
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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.
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| jbob wrote: |
| @Weathercam, nice one, 1200m in 2:40 is good going. |
Is 450m /hr. Which is a fair old pace.
The track I use at Les Houches is used by loads of skimo racers, it feels like you're going backwards when they come past.
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@jbob, dooooh worked that out when I was going down to the bar to rehydrate 
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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@Weathercam,
nice but still pretty thin?
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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.
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I've xposted this from the Weather thread as it may be of long term interested.
I've put this article together about the snow conditions surrounding the fatal avalanche near la Clusaz in France on Saturday.
http://pistehors.com/risk-levels-and-the-aravis-avalanche-24238748.htm
The ski tourer was very unlucky but things could have been much worse given the 50 or so skiers in the bowl at the time. A reminder that if slopes are steep enough to slide there is no zero risk and you do need to have an idea of what is going on under your feet; through the bulletins and local observations.
The scale of the avalanche surprised me. I'd been in the Beaufortain on the Thursday where I observed the same as the guide, Francois, in my article. On our tour we'd crossed a couple of slopes with avalanche potential and I did consider it at the time but thought the stabilization over the previous days would be sufficient.
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Just read that there was an avalanche earlier this week where six people were killed last year in the Queyras.
Hautes-Alpes: An avalanche took place on Tuesday in the town of Ceillac not far from the site or another avalanche had killed 6 people in January 2015. 3 hikers off piste were swept away by a wind slab in a group of 20 hikers who had left in the morning ski tours. Two skiers were shocked and evacuated on Briançon hospital by firefighters SDIS 05. The third person died within hours of his injuries. She was airlifted to the hospital Briançon in a desperate state. This is a woman of 59 years, residing near Albertville, member of the French Alpine Club Albertville.
Hikers all belong to CAF Albertville. They were staying for the week in the municipality of Ceillac. 3 buried victims were identified by their hiking colleagues. They were between Lake and Mirror Lake St. Anne, the Heuvières sector.
According to the evidence we have gathered, the trackers of Ceillac resort, had strongly advised the group to get into ski tour on Tuesday. see below. This is what explains Muriel Berard, director of the ESF Ceillac and Fabrice Fournier, ski instructor. It was he, who witnessed the avalanche, which gave the first alert.
A preliminary investigation was opened by the prosecutor of GAP (HIGH-ALPS) the charge of manslaughter, in accordance with the usual practice.
Raphael Balland, the prosecutor Gap indicates that skiers were fully equipped with the appropriate equipment.
Bulletin of avalanche risk was 3 of 5 over 2200m altitude. The Briancon PGHM boss recalls that the risk of wind slabs is marked on the northern and eastern areas above 2200 m. It just explains the risks of the moment, and that have complicated action of his men realize.
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You know it makes sense.
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Bit of a close one today here in Serre see Serre thread http://snowheads.com/ski-forum/viewtopic.php?t=120004&start=760
Had the adrenaline going as I skied very quickly down thinking it might have just happened as I saw two guys at the bottom of the slide looking up so skied down searching and praying that I would not pick a signal up.
They skied off and became clear all was thankfully ok, twas the group before that one.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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Scary moment for me yesterday dropping into one of the last lines yesterday. Snow pack at top of the line didn't seem any worse than other runs we'd previously done. Dropping in I cut a line and just seen a 3-4m fracture line from the corner of my eye from my drop in. Had enough speed to make it to the safety zone on our far right. Not a big slide by any means but scary none the less. Powder was amazing for the rest of the run
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Poster: A snowHead
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FAQ
