The angle of repose for granular (not slab) snow is 28 degrees
Does that mean any slope less than 28 degrees won't avalanche? I take it it's probably not that simple.
I'm embarassingly naive about this kind of thing.
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The angle of the slope is only one of the many factors that determine whether or not the slope is likely to slide.
Measuring the angle of the slope so accurately is I believe an academic exercise which will give one a false sense of security. I have rarely come across a slope that is of uniform slope angle from top to bottom and therefore what is the angel of the slope?. If you're going to measure the angle of the slope shouldn't you also dig a snow hole every 50 metres in order to study the different levels of the snow pack and measure the temperature gradient between the top and bottom of the snow pack?
If you are really interested in the subject of "Avalanches" there are courses and talks like Henry's Avalanche Talks (HAT), which will give you a more balanced view on the risks of avalanches.
There was a thread about 6 weeks ago on this subject, can't remember exactly when.
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...
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welshflyer wrote:
........Measuring the angle of the slope so accurately is I believe an academic exercise which will give one a false sense of security. .....
Quite apart from the avalanche risk, I am interested in the steepness of slopes I ski on. For example, I had thought the start angle for The Tunnel at ADH ( a benchmark of a tough slope for me) was 45°, but have been told by skiers I respect that it is 38°. Equally, I have leapt into slopes I would not normally have skied on because they were so steep simply because I was with an instructor who knew my abilities. I would have liked to know the angle, as a measure of what I can do given the right conditions.
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i have an inclinometer. every time i have been on a slope where, in retrospect, i would like to have used it (purely for boasting in the bar afterwards) it has been steep enough that i haven't wanted to be messing around getting it out of my pocket, measuring etc
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Arno, I can see that happening to me, too. Even so, might do it for the odd slope, just to start getting a feel for angles.
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.
quick question, how steep (generalisation I know) is a typical black (30 degrees?) and a typical red (25 degrees?), just as a broad point of reference, because it might be useful to have an idea if off piste and the slope looks 'redish' or 'blueish' or 'blackish'
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I would say that your typical black will have an average angle of no more than 20 degrees, with it reaching 30 degrees perhaps in one or two short sections.
A typical red is about 15 degrees average, with short sections of 20 degrees.
You know it makes sense.
You know it makes sense.
achilles, there are very good cheapo apps for your ipod touch which will acts as an inclinometer.
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
philingle wrote:
I would say that your typical black will have an average angle of no more than 20 degrees, with it reaching 30 degrees perhaps in one or two short sections.
A typical red is about 15 degrees average, with short sections of 20 degrees.
Probably not true. I would think a black is probably mid 20s even though I've never skied in Europe BUT supposedly a harder black in NA Rockies is similar to Alps Black which is about 25 degrees with sections of 30-40 degrees.
Poster: A snowHead
Poster: A snowHead
skiking4, agreed.
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
skiking4 and stoatsbrother - I'd have to disagree. I know a thing or two about slope angles having skied over 40 degrees a few times myself. I really dont think I have ever skied a black run that was as steep as 40 degrees.
So to prove my point I have just gone and measured all the black runs at our local resort, which is a very typical French resort and the average slope angle of all the black runs works out as 18.4 degrees. Notably the slope angle of the Flying K run where they are holding this years world champs is only 24.1 degrees.
As well as a google earth file that you can download to check the measurments for yourself.
If anyone else can muster up the effort to do the black runs in their local resort it would be interesting.
Cheers
Phil
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?
i read something recently that said the average slope angle of the Grand Couloir at Courchevel was about 22.5 degrees, which i thought was quite instructive. that starts out quite steep but there is a relatively flat bit at the end
talking about something maxing out at 30-40 degrees isn't very helpful because if feels very different standing at the top of slopes which are 30 degrees or 40 degrees!
i do think that there is some inbounds terrain at north american resorts which equals or exceeds 40degrees - haven't skied a huge amount of different resorts there but i can think of some lines off Spanky's Ladder at Whistler which must be about that steep for a pitch or so
skiking4 and stoatsbrother - I'd have to disagree. I know a thing or two about slope angles having skied over 40 degrees a few times myself. I really dont think I have ever skied a black run that was as steep as 40 degrees.
I'm not sure you guys are disagreeing. I think the other posters are looking at the steeper sections of the black. If you take something like the Sarenne in l'Alpe d'Huez what you remember are the steeper 20-25 degree bits, not the average 12 degree gradient (unless you are a boarder of course )
Many people would consider la Face de Bellevarde as very steep - I posted some measurements I made with a clinometer on sH a while back, I think the steepest it gets is 28 degrees. The exit left from the tunnel is in the 35 degree mark for the first few meters as Achilles says above.
Personally if a slope has ice on it (not just hard snow but verglas) I won't ski it if it is 10 degrees let alone 45 degrees.
Regarding slope angles, dry slabs are common in the 25-55 degree range with the peak angle around 38-39 degrees (which is why Munter uses this angle in is reduction method). However they can occur outside that range. Wet snow avalanches can occur on slopes of 10 degrees but are common in the 25-30 degree range. In short, slopes that you may be skiing are liable to avalanche.
How do you tell the slope angle?
Ask you buddy how steep the slope looks and subtract 10 degrees.
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Scotland's own Fly Paper has a fall line angle of only 39 degrees (measure it yourself from this picture I took half way down). It just feels steeper than that when you're looking down over the concave headwall at the rocky outcrops below. It is also avalanche prone and you can see the results of one slide in this thread ... http://www.winterhighland.info/forum/read.php?2,60934
Notably the slope angle of the Flying K run where they are holding this years world champs is only 24.1 degrees.
Phil
I think we were talking the steepest long pitches rather than the whole run.
What you say about the speed track may be true of the place where they take the measurement but it starts at about 40º (the public are never allowed to ski from the top) and gets progressively less steep to almost flat at the bottom.
moffatross, the only place you get a reasonably accurate measure is level with yourself on the slope. Is that where you measured? I'd have said by eye it was at least 40º but I'm probably wrong.
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The 24.1 degrees for the flying k run at Vars is the average over the whole length. the steepest part of the run is 28.4 degrees. It is a marked black run open to the public right from the top.
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Oh sorry, didn't read carefully - I was talking about Les Arcs, none of which is a piste.
On another thread spyderman said "The very top is 54 degrees, then 45 degrees shallowing out to about 35 degrees for most of the kilometre."
I think the last statement must be wrong - the part after the measuring point gets progressively much less.
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Les Arcs might not be a piste but
http://www.speedski.com/lesArcsFranceTrack.htm
there are moguls all the way down the side of the track.
It really doesnt look over 30 degrees in those pictures.
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snowball wrote:
moffatross, the only place you get a reasonably accurate measure is level with yourself on the slope. Is that where you measured? I'd have said by eye it was at least 40º but I'm probably wrong.
I was measuring the angle of the snow against the sky near where the kids were skiing and that is just a fraction under 40 degrees. The point where I was standing is a little steeper but not much, maybe a couple more degrees at most so let's say 41 degrees. Statements I've read elsewhere talking of 45 degrees for the Fly Paper are therefore likely to be pitch spin but it's possible I suppose under the right snow conditions and at the right spot. What you do get on the Fly Paper is absolutely no mogulling but small (and sometimes not so small) vertical linear separations (someone told me the name for these once) big enough for a ski and most of a leg to drop into !! At the nearby Spring Run which is often underskied and like the Fly Paper, never groomed, although only 30 degrees or so at the steepest points is prone to sluffing which can be quite alarming when you're the only one around. I've never heard of a full blown avalanche on that run though.
Last edited by Ski the Net with snowHeads on Sun 4-01-09 22:52; edited 2 times in total
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philingle, It is just possible that some of us might have also skied 40-45 degree slopes. Your assertion that a typical black has short sections reaching as much as 20 degrees but an average of 15 degrees would not hold much water in Jackson Hole where I was skiing last week, where even the middle line of Rendezvous bowl has an average of 35 (mush shallower at the far edge). More stats here which doesn't include details of many of the steeper bits - but gives a flavour.
Not sure choosing Vars is a great comparator? A bit like me suggesting the most gnarly steeps in Sussex? And having skied down the side of the flying K at Les Arcs (plenty of turns mind you) I would say much of that upper bowl area is steeper than 30 degrees.
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.
stoatsbrother wrote:
Your assertion that a typical black has short sections reaching as much as 20 degrees but an average of 15 degrees
he didn't make this assertion.
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
Arno, you are right - that was his claim for Reds
But I still think that his assertion of an average slope of no more than 20 degrees with a few bits of up to 30 degrees is wrong for most black runs I have skied in the last few years.
You know it makes sense.
You know it makes sense.
Clearly someone has to go out and measure but, like Arno, I know from experience that on the bits needing measurement I am enjoying myself too much to stop.
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
my biggest ever tumble was on the off piste bit well above the flying K. several hundred metres of terror while i slid down so i remember it well , defo more than 35 at the top entry well above the actual speed track and prob close to 40...
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Poster: A snowHead
Stoatsbrother - I wasnt doubting that you had skied 40 or 45 degree slopes. I was just responding to rayscoops question which was
Quote:
how steep (generalisation I know) is a typical black
. There are expections like some of the slopes at Jackson Hole obviously, but a typical black in Europe is around 20 degrees. The site that you linked to is pretty useful as it points out that at Whistler for example the steepest two runs are both 23 degrees and at Telluride the steepest two are 25 degrees. Vail 21 degrees, Fernie 24 degrees
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
When avalanche risk is high (3 or above) the advice of sticking to low angle slopes is often quoted and seems very sensible, given the sweet spot for slab avalanches is around 39 degrees. I'd always assumed that low angle slopes would be the equivalent of red pistes or less, but if a European black is typically 20º (with some steeper pitches) would sticking to slope angles that are roughly equivalent to black pistes be considered "low angle"?
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?
rob@rar, i don't there's any substitute for getting out there and measuring some angles yourself. philingle's technique for judging 30degrees is pretty handy
don't know about you but when i think of a black run, i think of the steep bits rather than the cruisy bits between. the steep bits will often be in the "steep enough to slide" range
I've skied in Japan a couple of times, and one of the things I loved was that they printed the piste angles on the map. I've wished ever since that Europe would do the same.
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
And if Vars is not typical enough, then at Serre Che the famous Luc Alphand is only 16 degrees, the casse boeuf is 16.4 degrees, the steepest line off the top of the eychauda is 24 degrees, the steepest line off the clot gauther is 20 degrees and the black run from the Bachas chair down to Monetier is 12.7 degrees.
At La Grave the steepest section of the Glacier du Vallon is 21 degrees, and the average angle down to the lake is 21 degrees.
At Mont Genevre Les Rhodos - 14.1, the steepest bit of la crete - 22.7, Tremplin - 16.6, rocher rouge 18.5, trois fourneous - 20
don't know about you but when i think of a black run, i think of the steep bits rather than the cruisy bits between. the steep bits will often be in the "steep enough to slide" range
Yes, I appreciate that. I'm just trying to get a feel for what people think is "low angle terrain". If the steepest pitch of the Face du Bellevarde is 28º it's only beginning to get into the steepness where slab avalanches normally can occur. Or am I mis-understanding things?
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
Arno and snowball are right....if you think it is steep enough to measure it..it isn't the place you want to measure it. I have this issue with a vid cam... is it too much faff..??
Most things are not as steep as we might think..or want to think, but who really cares...!! A slope isn't likely uniform anyway... I'd be more concerned about the terrain and its dangers than a few degress.
You should be looking at the fall-line and the run-outs and the traps, how much snow can slide, how far, convex..etc etc If you are only thinking in terms of degrees..then...????????
philingle, post some more stoke...
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After all it is free
No you are correct, black runs at their steepest sections are about the angle that avalanches start to occur at, i.e. 30 degrees. There is only one reported incident in France of a fatal avalanche occuring on a slope that was under 30 degrees, and that was at 29 degrees and in very specific conditions. The first snow came before the Larch trees had finished shedding their needles, then there was a long cold spell with no snow, when the next snow fell it was on top of a bed of larch needles which provided an uncharacteristically weak shear layer.
Staying on slopes lower than 30 degrees is not enough though, you need to stay out of the range of slopes over 30 degrees.
If you can read french then this article on the Quermoz avalanche is a worthy read
http://www.data-avalanche.org/alea_avalanches/view_item/Avalanche/50000007
Alain Duclos is THE expert on avalanches in Europe and this is a very detailed report of a slide that ended in 2 deaths. The slide was triggered by the people caught in it - as is the case in 90 or 95 percent of slides. Of note in this case is that they had stayed a good 70m distance from the base of the slope. They triggered the slide by collapsing the weak layer of snow under their feet, this caused a domino effect that travelled all the way up the slope and caused the slab to fracture 135m above them. The effect is called 'remote triggering'
Belle Plinier is another good read
http://www.data-avalanche.org/alea_avalanches/view_item/Avalanche/50000005
Here there are two factors worth noting. firstly it was the fourth person to cross that set off the slide, i.e. just because there are tracks there does not mean it is safe. The second thing is that the depth of the slab varied between 0.5m and 2m thick. they triggered the slide when passing over the thinner section because this allowed their force to have an impact on the weak shear layer. where the slab was 2m thick their force was well enough distributed to have no effect. A very common misconception is that if there is less snow there is less danger, this is simply not the case. Less snow means higher temperature gradient - hence greater likelyhood of depth hoar creation - hence a weak layer, and it means it is easier to have an effect on that weak layer.
Punta Alta
http://www.data-avalanche.org/alea_avalanches/view_item/Avalanche/50000147
Thanks to all having the correct equipment and acting quickly and professionally there were no fatalities in this incidence. Again this is an example of remote triggering which is the domino effect of them breaking the weak layer under their feet and the wave travelling up the slope till there is enough force to create an avalanche. In this case another interesting fact is that the rocks were the weak point. It is often a misconception that they act as 'pins' to stabalise the snow. This is wrong, the air gap that forms around the rock allows cold air to get closer to the ground, so increasing the temperature gradient and the creating depth hoar, so they are weak points. If you look at this picture you can see how the snow has fractured from rock to rock.
Another falsehood is that trees 'pin' the snow down and make it more stable, for the same reason as the rocks above they make it less stable. The fact that there are trees does not mean the slope is safe. Evergreens that hold snow and then drop it 'pack' the snow somewhat and make it more stable. Larch (Meleze in French) loose their needles and the snow passes through them as if they were not there and is just as unstable as on a neighbouring treeless slope.
Some eye candy http://youtube.com/v/k9-i7VxFRe4 again this is an example of remote triggering. look carefully after the second bomb drop, the first fracture is not in the location of the bomb at all but some 200m down the slope.
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philingle, thanks for that helpful post.
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another goodie, here the bomb triggered a sluff slide, then the weight of this sluff on the lower slopes triggered the fracture.
FAQ
Poster: A snowHead
you are right - that was his claim for Reds
, defo more than 35 at the top entry well above the actual speed track and prob close to 40...
