 Poster: A snowHead
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I'm aware that pits aren't the best way to assess snowpack stability when boarding/skiing but they are a useful indicator especially if the slope is likely to slide. I've been taught two methods:
Firstly dig a pit then excavate round a cube marking the layers and testing finger penetration then attempting to slide each layer off the block. Indicators being adjacent layers of massively different softness or any layer being easy to move.
Secondly dig around a block ~1m^2, observe the layers as before and assess the block stability on the following scale (1) collapses under it's own weight, (2) collapses under light pressure, (3) collapses under body weight, (4) collapses with small jumps, (5) collapses with large jumps (6) survives large jumps. 1-4 being unstable and 5/6 being OK.
However, in the excellent quiz on the Glenmore lodge site (Download at http://www.glenmorelodge.org.uk/avalanche.asp ) in the snowpack stability section (question 2) they place the shovel blade over a smaller cube of snow ~ the size I'd dig in the first example then hitting it with progressively stronger taps until a fracture line appears or preferably doesn't appear. Are there any particular advantages to this method over the other two and what is the exact methodology? I assume it's similar to the second example above but would like to know for sure as it's always a good idea to know more techniques.
Thanks.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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can't remember whether there is a name for what you are describing but it is based on a similar idea to the rutschblock test (the one with the skier jumping you have described). you isolate a column of snow with about the surface area of the shovel blade. then you place the shovel blade flat on the top of the column and hit it progressively harder to see when and where the snow pack fails. you try to be relatively consistent in how hard you tap it so you start just moving your hand from the wrist, then just your forearm from the elbow and so on. you can do all these tests from one snow pit.
as to the value of pits, well that is a whole other question!
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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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Arno, thanks I'd been meaning to ask that for a while.
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| as to the value of pits, well that is a whole other question! |
Quite, although I do a fair bit of winter climbing when you're spending significantly more time on a similar area of snow and I would say they're definitely useful then and it's always useful to have a few different ways to reach a conclusion.
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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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Is it also useful to watch the snowpack reports that can warn for the various signs such as visible weak layers?
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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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plectrum, i tend to think of digging a pit as often being a poor substitute for visiting the relevant area every day and watching the snowpack build up so keeping an eye on reports over the season is definitely useful. but my feeling is that it is only going to alert you to very big trends. eg. from following the reports, I know that there is a troublesome layer of depth hoare in the Whistler area which was deposited in December. that's probably going to be there all season so it would probably make me a bit more wary than normal. but that's a very big picture thing - doesn't provide much detail
the other issue with pits is that while they provide a whole lot of info, how do you decide whether you go or not? sure, there will be times when the results are either rock solid or scary as hell but what do you do with the majority which fall somewhere in between?
i'd recommend buying the book published by these people: www.powderguide.com
it concentrates much more on the "go or no go" question than on the theory of how the snowpack works and i have found it really useful. it's a good idea to read a book on the theory too - Bruce Tremper's "Staying Alive in Avalanche Terrain" is my choice but I know there are others which are very good
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You'll need to Register first of course.
You'll need to Register first of course.
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| how do you decide whether you go or not? |
The million dollar question which of course comes down to experience, but then you need to get that experience and no matter how many times you have a guide one day it'll be your call. I've just ordered that book from amazon for £10, I've got lots of books on snowpack theory but as you say they don't really give any guidelines beyond almost certainly safe or death on a stick.
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Have skied many questionable days but we head for the trees, stay off the open slopes and sometimes just turn around and go have a beer. With the rutschblock no skiing under a 3.
Skiing the local hill I'll dig fewer pits than unknown areas, and I watch what the explosives and ski cuts are releasing from the patrol work.
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| Arno wrote: |
| can't remember whether there is a name for what you are describing but it is based on a similar idea to the rutschblock test (the one with the skier jumping you have described). |
it's called a compression test and the scores are denoted as "CTx" where "x" is the number of taps taken to fracture bounded by CTV - very easy, fractures during cut or insertion and CTN for no failure, the range goes CT1 through CT30.
you can see detailed tests here : http://www.slf.ch/avalanche/spmap-de.html using rutschblock and ram penetrometer testing, each icon can be clicked on for a local analysis like this http://www.slf.ch/avalanche/sdsmap/20080116/17670.jpg
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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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Thanks to all the contributors of this thread. Really interesting.
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Arno, I got the powderguide book last night and spent a few hours reading through it. It seems to bring together a lot of different things I'd been taught on various courses and as you say gives you much more information on wether to say yes or no. I'll be reading it again a couple of times to make sure it's pretty well embedded. Thanks for the recommendation.
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