- December 8, 2012 at 5:12 am #577780
Hey all. I’m interested in learning about how you all go about choosing a location for snow pits. Specifically, what are some best practices in assessing a slope when coming over a ridge line? For example, you climb the west face and plan to drop in on the east. Lets assume there is no cornice to cut.
Do most people set an anchor and belay down a few yards and dig a pit while on rope? Do many of you carry rope with you?
How do you assess a slope when you come over a ridge and haven’t had any test slopes or any similar aspects to investigate?December 8, 2012 at 6:07 am #662674websherpaParticipant
Even if you belay down and dig a pit it will be unrepresentative of the slope you will ride. Climbing a west slope and dropping in on an east facing slope with prevailing westerly winds will typically result in a deeper snow pack near the ridge than lower in the slope due to wind deposition. This will on the long term provide more stable snow, but in the short term during or shortly after a wind event less stable snow than the rest lower on the slope.December 8, 2012 at 6:37 am #662675
That is why I’m curious what people do. Everything I’ve read indicates that the upper part of the slope, close to the ridge, will be have larger deposits of wind transported snow. So digging right at the top won’t tell you anything about mid-slope. What do you do in this situation websherpa?December 8, 2012 at 4:46 pm #662676
I think before you even step on snow you should have a basic understanding of what the snow is doing from the UAC. Once you have a basic idea of what the issues are you can start planning your tour. Is it going to be trees, meadows, peaks, etc. I’m looking at general snowpack, deep slab, wind slab, new snow, crust sandwiches, etc. New snow if any, how much and what density. Winds especially, danger rose readings, direction, speed. Recent activity, observations from the UAC and here.
Once on snow I’m trying to use my own observations with what I read to form my final decision. Depending on what your looking for I like punching my handle around to get a feel for layers/crusts, density inversions,etc. Little hasty’s for wind slab, or to check how new is bonding to old. Pit’s to see how a persistent weak layer heals over time or with the weight of new snow and for general snow structure. I’m also looking for recent acitivity and taking advantage to jump around on every little small test slope I come across on the way up.
Known: winds hammered higher elevations, possible wind slab.
Recent activity on the same aspect.
Obvious wind slab, clean shears with the hasty. Jumped on some test slopes stubborn.
Obvious cross loading.
Pocket, slight convex/roll feature, rocky area. Changed my exit plans which were a gully exit and took the long way back out.
More to the point of strategies once on top. If theres a cornice I’ll kick it but I think more importantly I think is to have a descent plan. I think you can ride many slopes that have a potential to slide (not including deep slabs of course just wind slabs, soft slabs, etc.) by choosing a smart route. Intentionally avoiding sweet spots, ski cutting, considering your runnouts, and having a general plan, cut here straight there.
I watched Alta bombs pulliing out similar soft slab pockets. I kicked some cornices with no result. My plan was couple turns and then straight it, thinking I might find a pocket in the apron. I did, and was able to use it for the up.
This one speaks directly to what you asked. This is this year, no new snow but winds were in the 70mph range. Slope were getting wind loaded. It was a blessing in a sense because it reset lines that were probably already ridden. You climb W and ride E/NE, so I had no first hand data what conditions were like. When I got to the top the winds were nuking and the slope was obviously cross loaded. However it was isolated and I felt I had a good plan for the descent. Ski cut to perfect safe zone. Stay riders left on a more bench lower angle part of the slope then cut into the chute and straighten out the nose. I chose not to ride a fun line lookers right in the photo because it had a small roll and a sharp turn in the runnout and instead take my same line down for lap two.
Those are my thoughts. Long winded but It’s fun to organize my ideas into writing once and a while, thanks for the great post.December 8, 2012 at 6:51 pm #662677
My point as it relates to the original question is kind of spread out in all my tangents and is confusing so I thought I would summarize what I was trying to say. I think the idea is the same whether it’s a slope you have hands on data for or a slope you have no hands on data for. That is what do you do with the information you already have or observed so far, what is your final decision. Hopefully, you already have some information, wind speeds, wind direction, new snow amounts, etc. You have a general plan based on the current hazards. If it’s deep slabs and persistent weak layers your simply writing certain slopes/aspects/angels etc., out of your plans for the day and sticking to meadows or S. faces etc. If it’s wind slabs or small soft slabs that are not really propogating but pockety etc., your looking to avoid those obvious features that hold pockets and really making a plan for the descent, ski cutting if possible, paying attention to runouts, rolls and other features, etc. so if you do find a pocket you can react. I hope that makes sense. I think roping up and digging a pit is excellent, really just roping up and doing a hard ski cut across the sweet spot would even be better. But like you said spacial variability, slight changes in aspects, features like gullies and roll overs, etc all play a role.
Edit to add one more thing related to my pictures. In the first instance I had multiple red flags plenty of hands on information yet I justified riding the slope which was a bad decision. In the second and third instances I no chance to dig a pit yet felt comfortable with the info I had observed and read and my overall plan, the terrain, etc enough to justify the decision which I feel were good choices.December 12, 2012 at 6:49 am #662678
Utah – I must of read this post like 5 times through over the past few months. I’m sure it won’t be the last time either. Thank you so much for the lengthy response. It’s super helpful to have the pictures with overlaid commentary. I usually keep it pretty mellow but as I learn more I’m looking to get into some more fun and steep terrain.February 13, 2013 at 5:47 pm #662679
Utah – I’m curious about the run with the soft slab. Did you suspect a pocket in the apron solely by your observation of Alta ski patrol during the ascent or were their other clues as well? Why on the apron and not in the chute as well?February 17, 2013 at 6:30 pm #662680
Alta gave me a bit of info on aspect and elevation and the apron provided a nice prone to avy feature. The chutes and rock features in the cirque are steep 40+ so snow doesn’t really stick it flushes itself as snow builds and gravity wins and ends up in the apron which is a 35+ degree wide open bowl perfect for avalanching. Your question prompted me to pull out my “Chuting Gallery” book which talks about an avalanche that happened in that same chute. The picture of that slide is identical to the slide I triggered a bit deeper though. So I knew it could slide which is also why I bombed that stuff, I was afraid of what I would find in the apron. Take care.November 4, 2013 at 5:11 am #662681vtbackcountryParticipant
Sure looks like Roman’s in Wolverine, a definite repeat offender…
I might refer you to some AAI standards for choosing an ideal test pit location, just to help simplify things. Your pit location should be ‘SAFE, REPRESENTATIVE, and POLITE’.
Safe DOES NOT mean out in the chute/bowl where you plan to ride, but instead on a similar and smaller slope, possibly a sub-shoulder or spine just off the main ridge. this might require a little more skinning, but its SAFE(R). that’s rule number one. look and choose a ‘safe’ spot, agree on it as a group, then head there. just remember, it STILL has to be representative…. that comes next.
By ‘representative’ they mean a slope w/ a similar aspect (a directional heading) as the slope you’re planning to ride and the same slope angle (buy a slope meter). if you’re gonna ride a chute that faces east, then don’t dig a pit that faces north, or even NE. make sure it’s also east (compass). again, you’re not out the slope you’re about to drop in on. instead you’re looking for a safe spot with the SAME ASPECT, near to where you’ll be dropping in. If possible, look for it on your approach while you’re also checking out your descent route. ALSO, ‘representative’ means w/ similar exposure to the sun. you don’t want to dig a pit in the trees if you’re gonna ride the chute/bowl, and vice versa. if you’re gonna ride out in the open, your pit has to be out in the open (but safe).
Then there’s ‘polite’. This should be the easy one. Basically, don’t set up to dig your pit right where others might drop in or could come down from above you w/o notice. be out of the way and visible.
Beyond that, when it comes to pits and tests there are just a few other things to keep in mind. First, learn the tests and practice them. Become more familiar with what they each test for (just failure, sheer quality, propogation, etc.) I would recommend learning at least the Compression Test (CT), the Shovel Shear test, and the Extended Column Test (ECT). each of these will give you different data, but a better picture overall of stability hazzards. remember though, you NEVER do just one of each test. you do multiple tests looking for consistencies across each test. if you find failure on the 9th tap from the wrist on your first CT, and then twice more on the 8th tap from the wrist, NOW YOU HAVE SOME DATA (and consistent results). then onto the other tests. fyi, these pit tests can take anywhere from 5-10 min to 20-30 min to complete depending on your experience.
And, make sure you’re completely isolating your columns before your tests. this is vital. investing in a good snow saw and a nice length of cordage to cut out the back wall of the column on the ECT is crucial. my saw actually fits into my shovel handle, then attaches to my BD 3-section poles to allow me to isolate the back of the column easier.
Let us know if you have more questions White Pine, hope this helps manNovember 28, 2013 at 11:25 pm #662682nordicbordnParticipant
One thing i’ve learned with cornices, in regard to the OP- they form similar to a wave in that wind will blow snow from one compass direction to the opposite. you can observe windloading on your slope by the appearance of your cornice.. no cornice means, often, no wind loading.
edit: happy 100th post thanksgiving!November 30, 2013 at 6:10 am #662683MethodParticipant
I’ve only just come across this thread, information is power in the avalanche game so thanks to everyone who has contributed to this thread, keep it coming. :thumbsup:
Regarding site selection for Propagation Saw Tests (tests the propagation propensity of a specific weak layer and slab combination independently of any loading required for fracture initiation – yes I cut and pasted that 😯 ) apparently , and this is from some information on PST’s published by the sensei himself, Bruce Tremper:
Although it is important to select an aspect and snowpack representative of the start zone/ski slopes of concern, the PST has been shown to work successfully on flat and shallow slopes, and since it is independent of surface loading it is capable of indicating propagation propensity in deep layers.February 8, 2017 at 7:48 pm #799799HansGLudwigParticipant
Hey @Utah – I literally just referenced your post while teaching the ‘Terrain’ section in last night’s Avy 2 class. I might just send everyone a link over here.
Thanks for putting your ideas down and giving us some meat to chew on. *thumbsup*
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