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 Post subject: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 9:32 am 
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this should be in the avy discussion forum but i wanted people to see this so i posted it here.

after reading the backing away and staying safe report i want to get everyone's protocol and views on their pits.

here is what i do.

1) on a slope that is the same aspect and angle as my run i dig a nice uniform shaped pit with a front wall that is 6 feet wide or so. i like to dig down till i find a nice bonded base layer, deeper than 4 feet or so.

2) I isolate one column, do a shovel shear test and observe where the layers break off, and how clean the the shear is.

3) then i poke at the snow on the identified layers to see if its finger hard or fist hard snow, and see how well bonded it is.

4) i do the ct test to identify how much energy it takes to release the layers.

5) i do an ect test and compare it to my first ct test. with a pit 6 feet wide or so it gives you enough columns do this a few times, and i make sure i get consistent results.

6) Then i clean up the front wall and do a rutschblock test. i find this gives the most real world assessment of the snow pack.

7) Identify danger spots and safe spots on your run, pay attention to windloading and wind direction, warming and rollerwheels.

anyone have any different protocol or anything to add to this? feel free to post your own thoughts and process when doing your stability tests. and feel free to ask questions about the shovel shear, ct test, ect test and rutschblock.

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 11:58 am 
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Your approach seems solid! That said, that is a lot of time to spend in one pit. Remember that "representative" is problematic, and even a pit dug at the base of a couloir you're planning on riding isn't necessarily going to reflect what's really going on. In that vein, I think with the amount of time you spend running your CT/ECT/RB series, you could easily be digging two or three pits in different "representative" locations and just doing ECTs in each of them.

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 12:19 pm 
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these usually take me 20-30 minutes to do. i like to do this sequence at the beginning of the day to get a good feel for the snowpack. later on through the tours i'll do more quick impromptu tests.

how much time do you spend digging yours? how deep and wide do you go? do you do multiple ect's in each pit? its hard for me to get the ect to be consistent, maybe its just the way PNW snow is?

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 12:23 pm 
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That's a solid approach if you are digging a pit, but I wouldn't ever get that involved unless I am riding in a completely new area for the first time. All a pit does is give you some info for that exact spot, so unless you dig several and incorporate all the data, it's pretty limited for basing a decision, as well as time consuming. Granted, I live in Tahoe (and general stability is one of the factors involved with me deciding to move here), but I find following the snowpack throughout the season yields better info. I might occasionally dig a quick pit just to see how the new storm layers are bonding, but most of my "tests" involve cutting the slope, both on small rollovers I find on the way up and using safe zones on what I want to ride (if I were real nervous, I would be on a rope, or not ride it at all).

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 12:27 pm 
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ect IS inconsitent - also has little bearing on actual strength of snowpack, as that type of action is different from how you would stress the snowpack skiing or boarding. Just another piece of info, but almost useless on its own.

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Fri Apr 06, 2012 12:33 pm 
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fustercluck wrote:
I wouldn't ever get that involved unless I am riding in a completely new area for the first time.


I want to be self sufficient in my travels, (not that i dont pay attention to local avy forecasts, but sometimes you cant get them) and a life goal of mine is to ride and mountaineer in new areas as much as possible. really the ones i dig i just see as practice for the future...

anyone have anything to add about snow cards and snow thermometers?

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 Post subject: Re: snow stability tests and digging pits
PostPosted: Sun Apr 08, 2012 7:37 am 
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The Rutshblock test has fallen out of favor a bit. The general feeling seems to be that more useful information can be obtained from spending that time doing more ECTs and hasty handpits. The ECT is pretty much the gold standard right now. While for sure there are a lot of factors involved in an assessment, I disagree that it is useless on its own.

The importance of slope angle on representative pit results is debatable. There is a lot of data showing angle to not be an important issue, although it sure seems intuitive that sun exposure and wind exposure at least would be a factor. Here is a short videoshowing some good tips on choosing a good pit location

For a field assessment, I don't see a lot of value in a temp profile, especially since recent studies have shown temperature gradients tend to "bubble up" and are inconsistent spatially. I think looking at crystals is worthwhile, providing some insight to the nature of a threat, how consistent it is, and how long it might last.

What is your access to local avalanche reports like? If you have access to good local information, I think that standard test procedure is a bit redundant - you shouldn't see anything surprising. If I were venturing into a region where I didn't have any history or a credible forecast, I'd say that sound like a pretty good assessment tool, along with the basics of observing avalanche activity and collapsing.

Overall I think that sounds like a really good approach and is far more than 95% of backcountry users do. The next step is a discussion about how you use that information. Are you looking for signs of stability? If you get favorable pit data, are you good to go? Sometimes, in some places, that can be deadly. This year has been characterized around the west and certainly in Utah by inconsistent results. Good results can be found in one spot and not the next. The only really effective way to ride safely in those conditions is to manage slope angle and exposure to consequences down.

Lots more good videos of assessment tools here.

Yesterday was ( I think) the first Low danger powder day in Utah this season. Felt good to be back on some big lines at least once this season.


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 Post subject: Re: snow stability tests and digging pits
PostPosted: Sun Apr 08, 2012 9:36 am 
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Location: reiter hills
All good stuff.



I prefer doing a ct, then a propagation test. But really, it takes only a minute per test... if you are going through the trouble to dig, you might as well do them all. Including measuring the temp gradients.

Ruestch blocks are helpful if you intend on riding unsupported cliff lines. I prefer using pillows since I don't dig many pits.

You should have good idea what you are digging for. You should already know the weather and avi forecast... test your mental! Tell me what you are going to find.

I have a daily routine to test myself;
1. Look at the history, usually the previous night unless it's a new area.
2. Look at the weather forecast.
3. Put 1 & 2 together and make my own avi forecast.
4. Check the avi forecast. (The answer key)


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 Post subject: Re: snow stability tests and digging pits
PostPosted: Sun Nov 03, 2013 11:00 pm 
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Location: N. VT & Central Wasatch
ale_capone wrote:
I prefer doing a ct, then a propagation test.


I couldn't agree more.

Still, I start by examining the pit wall first for obvious weak layers and obvious snowpack density changes (both visually and manually w/ fingers/brushes, looking for 'gray lines' in the pack), then I move onto my CT tests. Yeah, I said tests plural. Consistency in results on the same test mean MUCH MUCH more than only one piece of data from each type of test. I do the CT at least three times in each pit to check for consistencies in my 'results' (failures or no-failures). and with the right slope angle, it should also give you indications on sheer quality and whether the slab shoots out like a cash register drawer (Q1) or just simply collapses (Q2), but still 'planer' after pulling out the slab and flipping it over.

The other thing to keep in mind is that the ECT is really only meant to identify 'propensity for propagation'. I CERTAINLY wouldn't be using the ECT as my only type of test in the field. But again, I wouldn't pass up a few ECT tests on top of some CT tests. That's when the data begins to stack up.


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 Post subject: Re: snow stability tests and digging pits
PostPosted: Sun Dec 22, 2013 10:59 am 
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Location: N. VT & Central Wasatch
christoph benells wrote:
fustercluck wrote:
anyone have anything to add about snow cards and snow thermometers?


I might recommend the dark lexan crystal cards (BCA) mostly for contrast against grains, but also because the metal ones tend to melt the crystals quicker while viewing. For thermometers, def go with a digital one.


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 Post subject: Re: snow stability tests and digging pits
PostPosted: Sun Dec 22, 2013 6:36 pm 
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Location: Altadena SoCal
vtbackcountry wrote:
ale_capone wrote:
I prefer doing a ct, then a propagation test.


I couldn't agree more.

[...]Yeah, I said tests plural. [...] I do the CT at least three times in each pit to check for consistencies in my 'results' [...] it should also give you indications on sheer quality [...]
the ECT is really only meant to identify 'propensity for propagation'.
I CERTAINLY wouldn't be using the ECT as my only type of test in the field. [ECT + CT 3x] is] when the data begins to stack up.


For clarification, you do four tests in a pit (CTx3 & ECTx1) with multiple pits a day, looking for consistency while 'flagging' Q1 shears.
:thumpsup: Sounds right to me.
FWIW, you've done most of the work for an Rutschbock (a la Benells)

Or was that . . .
ale_capone wrote:
I prefer doing a ct, *sp: than* a propagation test.

i.e. You prefer multiple CTs over any propagation test (e.g. ECT or Propagation Saw Test)

Which sounds sketchy to me.

RE: Cards - I used the grid etched into my saw (G3 Bonesaw) to look for differences in grain size greater than 1mm between adjacent layers. When I lay it on the snow, especially in the shade, melting is not an issue. :twocents:
(In full disclosure, I've only done this once. It just takes too much time.)
I would only do it if I had inconclusive results and 'yellow light' conditions. I just find it easier to stick to mellow terrain when the snowpack is in question.


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