@snowheid, Thanks for boosting the discussion on this. I too would like a better understanding of the PWL and suspect we're quite similar in wanting some type of understanding we can get our heads around and finding that any contradictions or unclarity we have is an itch that must be scratched. That may irritate some people but it's just the way it is. Earlier in this thread I queried if and how a failure propagates within the PWL. I was having trouble because I was thinking of the way cracks propagate in the overlying slab and couldn't believe that the crystaline, crunchy stuff had enough structural integrity to crack in that way. It now sounds more like the vertical structure of the crystals is much more like that diagram of upturned wine glasses (in Tremper I think), relatively strong in compression but, if tilted as on a slope, once some glasses are knocked over or break many others follow. That suggests a different type of propagation within this layer that you'd think would extend mainly down the slope rather than across. It'd be interesting to know how far a failing PWL actually goes if the slab doesn't move (a whoomph maybe?). For an avalanche to happen you wouldn't think it'd need to go that far as long as the failure was extensive enough to result in an unsupported slab above that starts to crack. Once part of the slab cracks I imagine the cracks can spread and multiply to other parts of the slab even if the PWL is still intact underneath those parts. The slab is not much bonded to the PWL so any lateral force can easily result in the slab moving over the PWL. As somebody said earlier, once enough stuff is moving anything can happen. Voila, I will be very grateful for any helpful criticism or correction of my rather homemade theory.
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?
@DB @davidof Thanks both. I just looked at the second of DBs vids and that clearly shows that propagation within the weak layer most definitely does happen and what's more it can go laterally. So two of my previous hypotheses abandoned already. Now I'll look at your links @davidof Excellent progress, thanks!
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
@Ed_sec, The propagation can also go up the slope - heard a story from a guide a couple of years ago of a tourer crossing a frozen lake triggering the weak layer and resulting in a propagation that avalanched a skier 1 km away and 200 meters up a slope! The key learning point for me there was that when touring or traversing under a slope remember you can trigger it from below.
The discussion is really useful as I find it is a good way to imprint information and distill a better understanding.
@davidof The duclos one is very useful. It distinguishes between propagation within the basal layer and cracking of the crown. Often when I've heard people and guides explaining these things it's not clear what part of the snowpack they're talking about. I was in Aussois today as it happens. On or near the gently sloping piste areas in light of all this worrying discussion!
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
Ed_sec wrote:
@davidof The duclos one is very useful. It distinguishes between propagation within the basal layer and cracking of the crown. Often when I've heard people and guides explaining these things it's not clear what part of the snowpack they're talking about. I was in Aussois today as it happens. On or near the gently sloping piste areas in light of all this worrying discussion!
and a fatality in the same Combe de Balme in Aussois this afternoon. SW slope, skier on the (closed) Balmes black run. Avalanche triggered at around 2250m. There was a lot of snow transport from N->S on Sunday so this is maybe the cause.
Lots of incidents in ski resorts at the moment. They are far from safe options if you are passing below big steep slopes on cold aspects or skiing > 30 degrees. There will be a lot of natural activity over the next few days with high altitude rain and significant snow above 2000 meters.
Alain Duclos lives in Aussois btw.
After all it is free
After all it is free
Copied from Verbier thread. The slides usually come from the cliffs above, not on this convex slope, which gets heavily skied. That is a huge slab down to a buried weak layer. Can only think the weight of the last snow took it past a tipping point where it triggered. No one caught but very scary...
A big slab skiers right of Mont Fort this morning...
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There was also an avalanche on the north face of the croix de cassini yesterday killing one ski tourer. Overlooking the Sarenne and Alpe d'huez I assume they started from the Col de Sarenne. I've hiked up there in the summer. It's been picked up on pistehors.
There was blasting here yesterday afternoon to protect lifts, etc. A communication was sent out by pisteurs warning people to keep out of the way.
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snowHeads are a friendly bunch.
Mont Gelé South face after it was bombed. Look at those 2 (even 3) distinct slab layers down to the rocks
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.
BobinCH wrote:
Mont Gelé South face after it was bombed. Look at those 2 (even 3) distinct slab layers down to the rocks
Impressive photo.
What is the assessment for the remaining snow mass? It is a bit difficult to see from the photo but I presume that a slight easing of the angle and possibly a bit of concavity is holding the large slab with the fracture lines in it. Will it be bombed again or be presumed to be stable enough?
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
I don’t think they will bomb it again. If someone skis onto that they deserve a Darwin Award and will have a fast and bumpy ride down the rocks!
You know it makes sense.
You know it makes sense.
davidof wrote:
Ed_sec wrote:
@davidof The duclos one is very useful. It distinguishes between propagation within the basal layer and cracking of the crown. Often when I've heard people and guides explaining these things it's not clear what part of the snowpack they're talking about. I was in Aussois today as it happens. On or near the gently sloping piste areas in light of all this worrying discussion!
and a fatality in the same Combe de Balme in Aussois this afternoon. SW slope, skier on the (closed) Balmes black run. Avalanche triggered at around 2250m. There was a lot of snow transport from N->S on Sunday so this is maybe the cause.
Lots of incidents in ski resorts at the moment. They are far from safe options if you are passing below big steep slopes on cold aspects or skiing > 30 degrees. There will be a lot of natural activity over the next few days with high altitude rain and significant snow above 2000 meters.
Alain Duclos lives in Aussois btw.
Les Balmes is notorious for avalanche danger and in fact I have never seen the piste open (though I don't go to Aussois many times a season normally). I too went to the top of the lifts as they apparently did. If they headed down toward Les Balmes form the top they were the only ones mad enough. The East side of the ridge above is almost totally stripped by wind and the West must be loaded and wind-slabbed to the max. I came back more or less as I'd gone up as did anyone else. No steep slopes above and gentle gradients. It's not clear if they skiied over that slab on the upper section but at 2250 they were just dropping into a steeper lower section the goes through a narrow valley and gives a good impression of a classic and nasty terrain trap.
The other place I thought about going yesterday was La Norma but having seen the pics of the slide Alain Duclos himself seems to have triggered there the day before am glad I didn't
http://www.data-avalanche.org/avalanche/1611682812579
It happened in the logical place to skin and a place we often ski OP when the lifts are open as not too steep, nice bits of varied terrain, some trees etc.
It's certainly very tricky out there at present.
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
BobinCH wrote:
Mont Gelé South face after it was bombed. Look at those 2 (even 3) distinct slab layers down to the rocks
Wow, there a couple of massive snowfalls / accumulations in there. We all get excited when it's falling but remembering a picture like that should give us pause before jumping onto any new snow. Good pic.
Poster: A snowHead
Poster: A snowHead
@BobinCH,
Great pic.
People often talk about the layers and crystal formations etc as if it's all uniform and you can calculate something from it or see something on the surface.
IME, in reality by the time you can see something you are most likely in the wrong place already (or getting swept down the mountain).
That pic clearly shows nothing is uniform (varying layer thickness, No of layers, No of weak layers, layer density & depth etc).
Depending on the snowfall, wind, sun, temps etc. the snowpack at that point next season could be very different.
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
Yesterday I was not too far from here, and as you can see when the lift is open that face near to or under the chair gets skied a lot, and when lifts are running it is controlled!
It's a very humbling reminder along with Bob's picture that when ski-touring in resort when the station is closed that you must not take any chances on slopes that you'd often ski.
I'm quite happy with my meadows and am a proud member of the 2021 <25% Club
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?
Weathercam wrote:
I'm quite happy with my meadows and am a proud member of the 2021 <25% Club
Yes I find that drinking anything stronger means my skiing goes to pot.
That's 14 Deg I take it you mean 25 Deg which is probably a sensible solution for this season in these risky areas.
Aaaah yes <25° that's a hiccup from road biking where we talk about gradients in % terms
Anyway glad you knew what I meant
If we get the snow-fall that is forecast will be interesting to hear if they do any control given the number of people ski-touring in resort, but I've not heard any since New Years and now that the resort will not open is PIDA also not happening?
Like @Claude B, says they might to protect susceptible lifts, but there's a touch of irony to that in Serre Che given what happened at the beginning of last season
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Weathercam wrote:
If we get the snow-fall that is forecast will be interesting to hear if they do any control given the number of people ski-touring in resort, but I've not heard any since New Years and now that the resort will not open is PIDA also not happening?
are you sure there's been no control? l'Alpe d'Huez were bombing stuff yesterday. Les 7 Laux did a huge blast last week. They need to protect the infrastructure if not the pistes so I would suggest the PIDA is still in place for that.
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
Lots of Cham bombing and some very big slides resulting visible from town
Per this AM, Chamonix security council:
- col des Montets closed
- rando itineraries closed
- rte des Gaillands closed (which is actually sort of in town )
- generally, don’t go walking in the mountains or at the bottom of them
After all it is free
After all it is free
Not heard anything and I do hear them from where I am.
Plus up where we were yesterday I can see a long way across into the usual suspects that get controlled and no signs of any fresh activity.
Like I say wait till tomorrow. They might be doing Monetier maybe as more suspect terrain there?
And here we did not get the snow-fall accumulations that North of the Lautaret had, but we did get the wind and lot of that snow has gone somewhere!
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Warning for Backcountry Travellers
Quote:
The situation at the start of winter is difficult and it does not seem likely to get better, at least at altitude.
I know that this kind of message will lead to complaints, but 2 Swiss guides and a French instructor died in avalanches over the weekend. It would not be serious not to learn from this.
So the current bad news:
- the snowpack is generally thin and fragile, even if the thicknesses are sometimes higher than average at modest altitudes in the Chartreuse, Bauges, Aravis, etc.
- The fragility concerns all the exposures, and is not limited to just shaded slopes
- Remote triggering are particularly numerous, because of the buried fragile layers (thin snowpack + often very cold surface temperatures).
- The departures of slabs are often vast because of the buried fragile layers.
- The wind, which has been blowing in almost all directions for the past ten days, has formed accumulations that are difficult to anticipate
- The slides often develop aerosols, but remain relatively small because the snowpack is generally thin (valley bottoms rarely reached by dense avalanches).
- The warmth of last weekend did not really help matters, above around 1500 m: the humidification then the return of the cold formed crusts, up to about 2000 m, but have not induced stabilization in depth (variable depending on the beds and exposures of course).
Coming bad "news":
- warmth and heavy precipitation announced especially in Savoie and Haute Savoie from Wednesday evening.
- Episode of purges with warm weather and rain.
- It will be necessary to worry about large departures at altitude (still because of the buried fragile layers), which this time will mobilize large layers ... and therefore generate large flows, which risk going far.
In short: these situations, current and future, are not usual (from a snow-weather point of view too!).
Conclusion: maintaining greater prudence than our usual standards and wax your skis to glide better on slopes less than 30 °
Ski the Net with snowHeads
Ski the Net with snowHeads
The closer to the vertical axis the lower the bonding. You
can see the 2 weak layers that are collapsing to the ground and at 35cm. And the big layer of fresh on top that is adding the weight
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.
BobinCH wrote:
The closer to the vertical axis the lower the bonding. You
can see the 2 weak layers that are collapsing to the ground and at 35cm. And the big layer of fresh on top that is adding the weight
With the greatest respect, you have posted an image of a snow profile and passed comment about 2 weak layers collapsing to the ground at 35cm, This profile doesn't say anything about any layers collapsing to the ground. It does clearly show the temperature gradient....
Last edited by And love to help out and answer questions and of course, read each other's snow reports. on Thu 28-01-21 10:29; edited 1 time in total
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
Markhandford wrote:
BobinCH wrote:
The closer to the vertical axis the lower the bonding. You
can see the 2 weak layers that are collapsing to the ground and at 35cm. And the big layer of fresh on top that is adding the weight
With the greatest respect, you have posted an image of a snow profile and passed comment about 2 weak layers collapsing to the ground, This profile doesn't say anything about any layers collapsing to the ground.
I wouldn't leap on Bob too much, I think the profile he posts gives the general picture.
Just off the top of my head looking at that chart I see a strong TG, 20C over 1 meter. There is depth hoar at ground level but that is normal then a crust at 30cm with facetts on top then more facets at 45cm and I guess this what we can see in the photo although the snowpit may be in a different location. The vertical that bob mentions is the hardness - finger test, how the crystals at that point are bonded to each other if you like.
You know it makes sense.
You know it makes sense.
I looked at that profile and thought, bollox did nigh on a week course of logging snow-profiles after digging pits etc and could not remember what the key nuances/parameters were to draw up a profile like that
But as @davidof, says the finger test is the driver behind the profile, in much the same way as you push your pole through the snow-pack and you'll get some resistance and then all of a sudden you'll feel the pole go through really quickly.
Yes the Wolfhound device was new to me as well. Your pistehors report on the development trials was from 10 years ago, so possibly it took some years for it to be adopted by the French S&R teams, or perhaps it has been in use for a number of years now?
@jbob, yes, in my 7 full season, I think it's only been 5 a couple of times. As the freezing level is high another danger will be heavy slabs sliding off the roofs. I think it was Jan 2 or 3rd 2019 when we were confined to the building by text from the Mayor in Tignes.
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
We were told to stay indoors in St Anton the week of the galtur avalanche. Don’t remember many 5/5 at all. When I got the train out of St Anton after 2m of snow they apologised profusely for being 10 mins late. A friend spent over 4 hours digging out his car.
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They're blasting everywhere here tomorrow. Including Vallée Blanche which is my gentle goto area. I didn't know they ever needed to blast there at all The main gentle snowshoeing and hiking areas are there too.
Ski the Net with snowHeads
Ski the Net with snowHeads
Alastair Pink wrote:
Yes the Wolfhound device was new to me as well. Your pistehors report on the development trials was from 10 years ago, so possibly it took some years for it to be adopted by the French S&R teams, or perhaps it has been in use for a number of years now?
I had some trouble when I wrote the original article as it was still a 'secret défense' in France and the article had to be checked over by the authorities to make sure I wasn't leaking any sensitive information. Diginext, who were manufacturing one of these devices at the time were pretty pissed I knew about it.
In my job I've worked on some other secret squirrel stuff since then including a system used by the gendarmerie a bit like in the TV series "Person of Interest"
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