where to dig a snowpit?

[RambleOn]

the few avy classes ive attended havnt touched on this question. Do you guys have any tips/links that could help me out. I dont get how you CAN dig a snowpit on a similar slope to what your planning on skiing without being in the same danger? And if you chose to build on a different slope, wouldnt the readings be very different? I guess im asking how do you get an accurate assessment of the slope you want to ski without putting yourself in danger? Thanks for any input.

~RambleOn

[Missing Link]

I agree, finding a representative slope similar to one you intend to ride thats low enough angle you won't trigger it (like 2 guys in Canada that died digging a pit a couple years ago http://www.clubtread.com/sforum/topi...TOPIC_ID=24657 is difficult.

The reason why it may not have been emphasized in courses you've taken is that instructors are afraid to place much emphasis on telling students they can gather pertinent information from profiles. Instructors fear that student will leave with the idea that they can "dig a pit, then decide" to ride a slope. Its fairly common for those who believe that 'science' has all the answers to believe they can dig a pit and "then decide."

There is too much variability in how the mountain snow lays over terrain and really, a bulletin and simple "red flag' observations can give you much more relevant information then attempting to extrapolate a life and death decision on a meter wide profile.

Certainly, dig, but understand it takes years of digging these things to understand whats going on and most experienced BC travellers never spend time digging on ride day - the clues are typically obvious as to whether or not its a steep day or not so steep day. The bulletin will give an enormous amount of background info and theres a good chance that you won't get a representative slope and certainly the layering will likely be different - its just not as homogeneous as we'd like to think it is out there.

There is more than one case study out there where the fracture cut right through the pit wall after the call was made that its "good to go" that either killed or injured the diggers. Dig to understand snow and layering and try to find the weak layer identified in bulletins, but never make a "go" decision based on what you see, or think you see.

ML

[LeeLau]

Ramble.

What ML said.

But sometimes I dig pits because I'm in a new area or an area I haven't been to in a while. I might just want some profile data.

If I'm a bit nervous about where I'm digging I'll find a representative aspect with a steepish slope (say 30 degs plus) above a bench. If the slope slides, it slides onto the bench. Having said that I'm rarely that nervous about the pit because I've gathered a bunch of data beforehand. Frankly if I think conditions are so poor stability-wise that a pit might trigger a slide I'd usually opt for some quality couch time

[Shadam]

From my experiance (limited perhaps) most slides I've been involved with are triggered between turn 2 and three ... soooo should get my shovel, probe and snow study kit and hike 50 meters down hill to the slight roller to get the perfect profile pit where its more wind loaded because the top 50meters is "wind farked".
If I'm on new terrain, I'll dig about 3 "quick pits" on the up track in "places of interest" on various aspects, and try to get a good one on a similar aspect to the desired line.
However ... in recent years there seems to be less confidence in pit profiles in professional circles ( Canadain Avalanche Association bulletins) and I can see their point of view as there is so many other resourses available to the backcountry traveller that didn't exist 15 years ago, such as wot your looking at right now. Each morning we check several web sites and formulate our plans from there.
If a pit profile gives you confidence to go bigger, try smoking dope in the car on the way home after a successful day touring, not on the skin track up!!!

[wra]

If an avalanche instructor is teaching how to dig a snow pit and they fail to include where to dig they should not be teaching how.
Snow pits should not be used as a method for decisions on whether to ski or not. They are used for learning the history of the snow pack and what layering could produce avalanches.
I pick location in the same manner as where to put the up track. Use the terrain to your advantage. If a total novice, use the same suggestions as for "test slopes". Small hills lacking consequences, road cuts, etc.
If there's layers capable of producing avalanche, they will be found on most representative slopes, not just the one that slides.
Spatial variability means: don't dig in locations scoured or loaded by wind. If interested in ne facing, don't dig on south facing. Don't dig at the ridgeline or the bottom of the hill.
I'd suggest digging one or two pits every time you go out. Think about the where and when. Draw profiles and keep a history. If you see a slide and feel good about having a look at the crown, by all means, have a look. Dig a pit above or off the side to see why the adjacent slope didn't slide.
Learn by doing. A bulletin gives no information on specifics but will provide general information you can use to help in deciding where and when to dig pits.

[RambleOn]

so basically if theres no red flags a snow pit is just another small test and dont rely on it heavily?

[Sirshredalot]

Not at all.

A pit is another way to gather information. Try to dig several quick pits on your way up. Some may not be on the exact same slope angle, some may not be at the same elevation or aspect, but they will supplement the information you already have. You want to try to build a complete picture of what is going on with the pack, because on the slope where you drop in, there may not be a safe place to drop in and dig.

[snowfish]

What do people think about digging pits on slopes 20 degrees or less? Worthwhile? Not worthwhile? Obviously would not get relevant data from pit tests (CT, ECT, PCT, etc), but perhaps a safe way to evaluate and identify potential layers. Any thoughts?

[BFD]

I'm an amateur. I dig pits and make decisions based on what I find in a pit. I'll even go bigger if I like what I see. Shadam had some good points about getting a represenative area. I don't see a problem of digging on low angle slopes if they are similiar aspect to what you want to ski. You can identify a layer and maybe conclude you don't want to go steeper or maybe things look good so you find something steeper to look at. I dig in almost every line I ski. I like to know what to expect. Even if I have already decided to ski the line I like to have an idea how firm and for how far to soft snow I'm looking at. Also like to get a good idea on sluff potential. Hate when my dog gets taken out. Get out and dig if your scared bring a rope. My opinion the best way to know is to get out there with a shovel and check.

[CookieMonster]

RE ( "so basically if theres no red flags a snow pit is just another small test and dont rely on it heavily?" ) and RE (other subsequent posts ).

It really depends on your goal.

A. If you're looking for instability, then the results of instability tests are not valuable unless the test reveals the presence of instability.

B. If you're just taking a look at the snowpack, then the results of a test profile may or may not reveal any useful information.

C. If A, sometimes you won't find answers and you may remain highly uncertain. It's wise to make conservative decisions when this happens.

From a forecasting perspective, the collective purpose of your observations, including snowpack tests, is to help you determine for the slopes over which you wish to travel, 1.] the amount of weaknesses ( rare to widespread ) 2.] the propagation potential ( low to high ), and 3.] the triggering energy required to release an avalanche ( low to high ).

Data sampling has a very strong effect on your perception of instability. If you're not careful, it is easy for your perception of instability to shift from "unstable" to "stable" or "unaware" without any real basis except a few disjointed "facts".

[Shadam]

dig as many pits as you can. on days of poor snow, go and hike just to dig. learn if the hoar frost is on all aspects or just north, north east. where does wind crust end down slopes. dig into a cornice to learn its streghts and weaknesses. and to learn how to create an entry to a potential chute.
Its similar to beacon practise, some people will laugh at you for wasting all that time and energy, and we know wot they really do at a saftey meeting.
There will come a day when you will tell your crew to turn around and go home. will they listen, will they do as told? will you tour with them again? reading snow is one thing, dealing with personalites is another.

[F.D.V.]

On belay....

Lower you ass onto the slope you are about to ski with a good solid rope (9mm or larger) and get down onto that bad boy and dig the pit. Your cord should be tied off at the end, so in the event of a slide if it slips through your belay device the know will catch you at the end of your line. I prefer to look at the exact slope I am about to drop onto, rather than relying on a similar slope. I live in a continental snowpack around though, so I am paranoid and anal retentive.

[scuplacap]

I accept with informationata sampling has a very strong effect on your perception of instability. If you're not careful, it is easy for your perception of instability to shift from "unstable" to "stable" or "unaware" without any real basis except a few disjointed "facts".

[smitchell333]

Spatial Variability is a significant challenge.

See this study here on the newer extended column compression test (which looks like a good pit testing tool) that shows the realities of variability of pit results even when performed by the experts.

http://www.avalanche.org/~nac/NAC/te..._Simenhois.pdf

The picture below shows the varying results within a grid on the same slope that the study authors found.

P is propagated or a less stable result (ECTPV – fracture propagates across the entire column during isolation)

N is not propagated or a more stable result (ECTN – fracture doe not propagate across the entire column, or there are 2 or more taps between the initiation and propagation of the fracture)

[Nick_C_123]

To each their own, but I'm not too into the digging pits on belay idea. If you're deep inside that pit and the snow rips out big time, something will have to give. The weak point in the system is not the rope, the harness, the biner, or (probably) not the anchor, its your body, which will break badly, starting with your pelvis. Long story short you'll likely die in a slide you might have otherwise had a chance of surviving. Lots of factors and possibilites here, like snow depth, height above you, strength, etc., but it doesn't take too much heavy, hard snow to break bones and shred joints - I unfortunately learned the hard way once upon a time.

Not saying it doesn't have its time and place, but certainly not a technique I'd recommend for a novice. I can only think of few, very specific situations where I might consider the technique.

[Missing Link]

Good story - short excerpt:

"After completing our tests we realized the snowpack was very weak and that, as we'd guessed, skiing the face was not an option. I took my skis off to climb back up to the ridge and John moved skier’s left where the snow was only about two feet deep. We were less than fifteen meters apart when suddenly the entire face settled, creating an eerie hollow sounding "whoomph" that makes your heart leap to your throat. We'd hardly registered the sound when the snow fractured above us. John began to scrabble, jump and hop to avoid the sliding snow, but two huge blocks of snow rolled over him."

"The avalanche was a climax side so all the snow on the entire face moved at one time, trapping me in a huge 60 mph cloud of snow and air."

Experience is probably the best teacher.

It gets a lot better or should I say a lot worse - read about it below

Link:
http://www.wildsnow.com/articles/hay...nt-hayden.html

ML

[idopyigeobids]

I tested in a city landfill once. And there was a site, beneath 18 ft of landfill.
Another time in the floor of a disused laundromat. Lots of lint.

I think the worst "You want me to dig where?" was a STP transect across a slope down which the farmer tossed his dead livestock. Thank god it was cold.

No photos of these though

[montanaskier]

I never dig looking for a reason to ski a slope. I dig to confirm my thoughts of not skiing a slope. I normally have a general idea when I leave the house about what is going on in the pack based on reports. I have some guidelines that I use based on the rose that day. In addition, my wife and partners keep things pretty mellow in the winter due to our shitty pack. I normally dig several quick pits on the way up, lots of pole probing and looking around at what clues are in the area. If I think a slope is a no go, then I sometimes I will find a safe area that is representative of the slope and dig just to see.

Also a good idea to get out without the idea of great skiing and to just poke around, that kind of learning is great and the pressure to get great turns is taken out from the get go.

Finally the spacial variability issue scares me more than anything else. Totally fine, totally fine, totally fine....not fine and no way to really know. YIKES.

[Ivan Oder]

Along the lines of what others have said, the information from a snowpit analysis shouldn't be the only factor in your go/no-go decision making process. Avalanche reports and predictions, the five 'red-flags', your ability and your group's abilities are all just as important.

Just always remember that a pit only shows you what the snow pack looks like where you dig and that the weak layer could be 6 inches below where you decided to stop digging.

[Core Shot]

Good story - short excerpt:

"After completing our tests we realized the snowpack was very weak and that, as we'd guessed, skiing the face was not an option. I took my skis off to climb back up to the ridge and John moved skier’s left where the snow was only about two feet deep.
http://www.wildsnow.com/articles/hay...nt-hayden.html

ML

that is so wrong. If you reallly "guessed skiing was not an option" then what where you both doing on the slope.

If its that sketch, you have to rope up to dig, or not ski it at all.

-------
As for spatial variability, that always comes to mind with a buried surface hoar.
Did I dig a pit where it was blown away by the wind?
Does this slope still have hidden pockets of hoar?
hard to say sometimes.

That is where the modern luxury of an avy center and internet shared data is so awesome.
I say the internet bulletin is more important than the pit.
If I could choose only one, I would take the pro forecast (particularly including the detailed season summary and pit pages, not just the one day forecast) over a pit I dig.

[Missing Link]

10-4 on the bulletin CS - staying up to speed with those on a regular basis gives you a good idea of regional weak layer and skier triggering trends.

While the bulletin does represent a large area typically it still provides a good overview that you can then verify through your own weather, avalanche and snowpack obs.

I've got an old story regarding Ron Perla, published in the 1976 Winter issue of Mariah magazine recalling how the pressure on his body and consequently the 5/16 belay rope snapped and he took a big ride down Baldy at Alta.

ML

[inthemtns]

All this talk about quick pits and ects, when do you use rouche blocks? I've always felt like they have the most information about potential skier weighted triggering. This thread makes me think I'm wrong though... any thoughts?

[1000-oaks]

Slackcountry analysis is another can of worms and can be spooky, since you don't get a look at things on the way up. I've dug pits just below the top of slackcountry ridges before dropping, realizing that if it goes it'll take me with it but hopefully at the tail end of the slide and be somewhat less dangerous. (yeah I know...not the best logic)

Of course, I only go slackcounty in the first place if the conditions appear okay (and safe to dig), but I've been VERY wrong on at least one occassion...and survived by sheer dumb (and I mean dumb) luck. Now I'm f-ing paranoid about slides, even in-bounds.

[Missing Link]

inthemtns, the Rutchblock is a viable snowpack test, just takes long to dig and isolate correctly so its pretty rare to see them outside of an avalanche course.

I know of a study this guy did, and saw this pic he took - he had something like 30 or so RB's he dug on a on a 30 degree +slope. They basically were dug in long lines across and down the slope next to one another.

The results varied widely - some came out on a step onto the block - RB2 - and others didn't budge - RB7 - all on a pretty uniform slope.

So - we've got wicked variability across slopes and the "tests" that we're inclined to put faith in (for whatever reasons - science will save us?) often will give us false positive results.

I only dig a RB if I'm being paid by the hour - otherwise I'm checking the bulletin, looking for red flags, probing for layers and doing hand shears - the bulletin is going to give me a ton of info and if I'm sketched - I'm stickin to lower angle, less consequential terrain. That a science that I know works.

ML

[wra]

All this talk about quick pits and ects, when do you use rouche blocks? I've always felt like they have the most information about potential skier weighted triggering. This thread makes me think I'm wrong though... any thoughts?

To get the most from your digging:
Dig deep enough and wide enough to do shovel shears(identify weak layering), compression(sensitivity) and ect(propagation). Finally, do a rutchblock, both for data collection and as a simple easy method of filling in the hole.
Should take about 10 minutes with proper tools.
My preference is to gather my own objective data first hand, not going by secondary subjective data obtained from what may or not be a reliable source.