How To Perform A Compression Test

Backcountry Skiing Canada along with Summit Mountain Guide explain how to perform a Compression Test.
For more gear snow stability tests and everything else backcountry skiing visit www.backcountryskiingcanada.com

[@MartynasShnaresys]

That part about shears was very confusing. If someone is confused too, then this may help: Researchers at the University of Calgary have been systematically classifying fractures in compression and rutschblock tests since the winter of 1996-97. The classification system was refined in December 2002 and presently comprises five categories: Progressive Compression (PC) - Fracture usually crosses column with one loading step, followed by gradual compression of the layer with subsequent loading steps. Resistant Planar (RP) - Planar or mostly planar fracture that requires more than one loading step to cross column and/ or block does not slide easily* on weak layer. Sudden Planar (SP) - Planar fracture suddenly crosses column with one loading step and the block slides easily* on the weak layer. Sudden Collapse (SC) - Fracture suddenly crosses column with one loading step and causes noticeable slope normal displacement. Non-planar Break (B) - Irregular fracture surface.

[@Backcountryskiingcanada]

So great that shears are now classified Martynas, but you may have confused people even more with those classifications and no explanation on how they differ. Can you provide more info on each to help further explain?

[@MartynasShnaresys]

@@Backcountryskiingcanada Yep, my mistake, copy pasted wrong text, now it's fixed, just refresh page.

[@Backcountryskiingcanada]

Much better, thank you! @@MartynasShnaresys

[@MartynasShnaresys]

@@Backcountryskiingcanada Thanks for very informative videos!

[@Backcountryskiingcanada]

@@MartynasShnaresys You bet, keep watching!

[@christucher6324]

These videos are great. Can you recommend one of your videos or a webpage that explains how to apply all this good information to actual skiing decisions? When is it appropriate to dig a pit and test for compression and propogation? Once I know where there's surface hoar or depth hoar, what decisions do I make? Have you published video or articles on that?

[@Backcountryskiingcanada]

Hey Chris, that is a pretty loaded question but a really good one. The ability to know when and where to dig a pit comes with experience and basically anytime you feel the need to. It doesn't take long and is always a good idea to get a better understanding of the snowpack prior to skiing any slope. I'd suggest a AST 1 and 2 course for sure and then skilled and experienced ski partners. Always trust your gut, get the right gear and know how to use it.

[@sunnywyrzykowski6922]

Could you explain how many taps until a sheer is concerning. For instance I took 21 taps for this test to fail. Is that a cause for concern? If it took 5 taps that would obviously be concerning. 10? How concerning is that. 15? 20? Thanks for the vids. Very informative

[@Backcountryskiingcanada]

Glad you enjoyed the video and thanks for your question. As I mentioned in the answer to your other question there is no hard and fast rule as to how many taps are related to safety as we all have different thresholds for what we consider to be safe. Because of this you really just have to gain some experience digging pits and performing this and other tests, just like you need to gain experience in other aspects of backcountry travel. This test is just one of many indicators you would use to make a 'go' or 'no go' verdict. All of these things will be taught in an avalanche course, which I highly recommend everyone take! Obviously, if you get a fail on tap 1 you would not consider things to be safe. but, as you mention where do you draw the line then? Is a fail on tap 10 ok or perhaps tap 15? This all depends upon how the column fails, is clean, does it crumble or does it 'cash register' off the block with enough force to fall to the ground? Also, the results are relative to the terrain you are performing the test on and where you plan to ski. Remember that the test you perform only provides results for that exact location, it has no bearing on the snowpack down the slope, to the left or right. This means that the results are not only subjective to your risk and tolerance levels but also only tell you what is happening in that exact location. Sorry for such a vague answer but there are so many parameters that affect the decision process and ultimate outcome. If you can take a course please do so and if you already have then find a mentor or hire a guide so that you can gain the valuable experience needed to safely travel in avalanche terrain.

[@markymarkpowpow]

did you ski it? thanks for the information!

[@Backcountryskiingcanada]

That was a while back so I can't remember, but I think that day was all about filming videos for the site.

[@egmikola]

Can you share how you can confirm the surface hoar was the event and not a near surface facet event that got burried? I want to know how to tell the Difference better thank you

[@summitmountainguides]

Hi Miko, the answer to your question revolves around snow science. It is a more advanced topic than simply performing or interpreting a snowpack test. You would be able to tell the difference if you were to isolate the actual snow crystals at the interface and analyzed them with a loop and crystal screen. Knowing the history of the weak layer would also help, this is something the avalanche bulletin will speak to. Surface hoar form a thin film of feathery crystals, often visible and in the 7-15mm range some times, on the surface of the snowpack before getting buried by subsequent snowfall. Faceted grain for inside the snowpack layering due to cold temperatures or strong temperature gradient. Faceted grains ar usually smaller 0.5-1mm and squared shaped, a faceted layer is thicker usually (2-15cm thick or more). The crystals at the interface are important however, not as important as the kind of shear result you get. If you are interested in snow science, I would recommend picking up a copy of the "avalanche handbook" or "staying alive in avalanche terrain" for more in depth description. All the best and happy safe/skiing! David Lussier acmg mountain guide

[@Benjibobsiering]

So at what point or CT number do you decide not to ski?

[@Backcountryskiingcanada]

well, that is where experience comes in along with a lot of other variables like other signs of instability. Obviously, a higher number is better but there are no hard and fast rules for "go, no go". Best to take an avalanche course to you can get some experience with how to know what the results mean as this is just one of many test and factors to determine if a slope is safe to ski.

[@Benjibobsiering]

@@Backcountryskiingcanada Thanks for the reply! So far I have been keeping off 30°+ slopes and doing this test before riding, checking the avi bulletin, stopping if the snow starts melting, keeping away from land traps. But I wish to get into steeper terrain. I'll be getting myself an avi course as online I can find loads of tips and tests but no solid conclusions to wether it's skiable or not.

[@Backcountryskiingcanada]

@@Benjibobsiering Good idea! The AST1 course is a great introduction and teaches you how to recognize and avoid avalanche terrain whereas the AST2 shows you how to navigate avalanche terrain. Both are a must. Good luck. Be safe out there.

[@vitaminb4869]

I've never seen anyone say what is a reasonably safe test result to ski a slope (as if it's some big secret). But it would be helpful to know what is the typical result people accept as safe in the real world and practice. And what results are an absolute no-go. At least provide some real world scenarios from few recent touring trips. Otherwise these snow pit test educational videos are of very little use.

[@travisprovin1336]

@@vitaminb4869 His test produced a full propagating sudden crack 50 cm deep at 22 taps. That is a definite no go for me. He even stated this is a low probability high consequence scenario. No one on Youtuve will give you a "this is safe" determination due to liability. It's not up to anyone except for you. To me, out on the slopes, if I conducted this test it would be a very useful and clear piece of information. Take an avalanche safety course (if you haven't already) and learn how to conduct your own snow pit tests.

[@nikcezar2445]

very well explained tnx i am just geting into the backcountry and i wanna make sure i don t end up in an avalanche like a dumbfuck i will keep researching

[@Backcountryskiingcanada]

Glad it provided some insight for you. Be sure to register for an AST course and find yourself a good mentor to ski with. Experience is key as is knowledge!

[@Honzula88]

Can you make these videos with a bit better quality? Now it is hard to see the details of what you are talking about.

[@Backcountryskiingcanada]

It is hard, especially in low light to snow the person and the snow detail w/o washing one or the other out. We try and zoom in on close up shots but this one is not so much about the results but the process to complete the test. We'll keep on trying though.

[@Honzula88]

I fully undestand that bad light condition ruin good result. I would just consider pushing resolution a bit higher. I do not know if it my computer/connection (Europe), but I can see your videos only in 480p. Maybe this is the problem of details...?

[@Backcountryskiingcanada]

We publish them at 540p and sometimes 720p but it depends upon file size and upload times. KZbin seems to compress them quite a bit and hence the quality loss.

[@TheCybertomate]

You dont need to repeat everything 5 times. Just tell how to do it

[@Backcountryskiingcanada]

That is actually what he is doing, and was nice enough to volunteer his time to make this video with us so maybe phrase your comments in a more positive way next time as negativity never gets you anywhere.

[@brozenthesnow]

Consider not typing things that you wouldn't be bold enough to say face to face. This team provides very educational and FREE instruction for those that want to learn. These aren't concepts most would hear once and retain in any useful real-world application (like when stress is high post avy while performing search & rescue, for example).

[@TheCybertomate]

@@Backcountryskiingcanada just make sure to argue most of your time with internet strangers :D

[@Backcountryskiingcanada]

@@TheCybertomate Answers and explanations are not really arguing.