Quantifiable Shear Tests

Cowboy · Joined: 10 Dec 2004 Posts: 132

I would like to hear some discussion on quantifiable shear tests. We are gearing up for an avalanche course this weekend and this topic always comes up. Also, this topic seems to make certain avalanche workers need to loosen their neck gaiters a bit when talking about it.

I have my opinion but I’d like to hear others on which tests are quantifiable and which aren’t.
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Brett Kobernik
UAC

staph infection · Joined: 13 Dec 2004 Posts: 255 Location: land-o-morons

Brett I have always had this question.
There is so much variation in even how the pit is dug and the block is created that its a very gray area.
Is a block that is cut with a pole vs a saw of any vlaue?
Good luck with the class.

powderdave · Joined: 26 Sep 2005 Posts: 269

My thoughts on real-world backcountry stability testing:

CT, RB, SS, even SB tests, are subjective to individual testers. Of course, this is why we are talking about quantifiable and, therefore more objective, test results.

In a quick pit (not full data pits) I don't think we can be truly objective with our results. However, when Cowboy tells me he got an RB2 Q1, I'm scared and ski something else. Over time and with experience our interpretations may become more representative and less subjective, but we will always have to consider who is doing the test to stratify the reliability of the reported data.

Dave

cesare · Posted: Fri Jan 13, 2006 9:29 pm Post subject:

You can perform quantifiable shear tests with a shear frame. However, it is more of a research tool that I have not seen in level 1 courses.
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that sounds like a sure-fire way to get bitch-slapped by devil's club -- dschane

carl · Joined: 07 Dec 2004 Posts: 4074 Location: 1608 folio

skibum · Joined: 06 Dec 2004 Posts: 2377 Location: Colorado

As someone who is out a fair amount but not even close to daily, I always struggle between Q1 and Q2. The roughness of Q3 is fairly obvious. However, I tend to be too conservative and call something a clean shear that my more experienced friends call Q2. I guess being too conservative is a better way to error, but the distinction of just how smooth the shear has to be and a better feal for the interpretation of stored energy is something that could be addressed.

DaWiz · Joined: 12 Dec 2004 Posts: 213 Location: Valdez, Alaska

You will know Q1 when the column jumps out and hits you in the chest. You will notice the energy present in the snowpack.

junkshow · Joined: 12 Oct 2005 Posts: 13

Seems teh stuffblock test is as consistent as it gets.

snowdynamics · Joined: 12 Dec 2004 Posts: 618 Location: Wasilla, Alaska

The two shear tests that I believe are quite quantifiable are the shear frame test and the tilt board test. Neither are used in standard recreational backcountry forecasting. In fact, the only avalanche professionals I have seen use them are in Rogers Pass and Kicking Horse in Golden, B.C.
As far as stability tests in the field, I prefer compression tests and rutschblocks (simply a large sample compression test). Results from these blocks may seem less quantitative than, say the stuffblock test; however, the 20 year Swiss Experience and Canadian studies show these tests to provide reliable information for overall stability evaluation.
The drawback to all tests is that they are a small sample in a big picture game. When evaluating the avalanche hazard and evaluating overall snow stability, these tests are just a piece of the information gathering process.
Good discussion.
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telemike · Posted: Sat Jan 14, 2006 2:31 am Post subject:

au contraire mon frere

Peter Carter was doing a lot of shear frame work at Eaglecrest the last few years before he left to go work for a heli op (I forget which one - I think H2O). Also tilt board.

If you look around, you'll find a paper he and Kent Scheler presented to ISSW - I think it was last year.
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Ad astra per alia porci

fropa · Joined: 07 Dec 2004 Posts: 8

From Merriam-Webster Online Dictionary

quantity ... 2a : the aspect in which a thing is measurable in terms of greater, less, or equal or of increasing or decreasing magnitude b : the subject of a mathematical operation ...

quantitative ... 2 : of, relating to, or involving the measurement of quantity or amount ...

Cowboy · Joined: 10 Dec 2004 Posts: 132

Well, here’s my opinion for what it’s worth. Quantifiable does mean “capable of expressing as a number, measure, or quantity” which means by definition any shear test could be considered quantifiable. It’s my opinion that most of these tests are VERY LOOSELY quantifiable for many reasons Powderdave touched on. I believe Bruce Tremper is going to re-word the next publication of his book to read semi-quantifiable or something like that for many of the tests.

SnowD- I’d forgotten about the shear frame (how could I over look such a tool that is so popular with backcountry skiers?). The shear frame and stuff block are as close to being TRULY quantifiable as possible as you have real measurements with both that don’t vary from person to person. I don’t use either of these tests. (I think there is also one more device that exerts a given force on the top of a column to initiate a shear) I would argue that the tilt board is not truly quantifiable since tapping on the bottom is subjective just like the rest. I don’t use this test either but I really like its cousin the shovel tilt test which is loosely quantifiable at best like the rest.

Cesare- of course we don’t include this topic in the level one, it usually gets discussed between instructors and a few of the more scientific thinking students.

Where I notice the biggest discretion among avalanche workers is with the compression test. I think that every one performs very similar with taps from the wrist and taps from the shoulder but I see a wide margin in taps from the elbow which will give a wide range of results, therefore loosely quantifiable.

One more side note and then I’m done with my babble. Staph I.- I regularly cut columns with my ski pole, nothing wrong there. It’s actually quite easy and effective in snow density of up to 4 fingers or slightly more. Just make sure you completely isolate the column and the weak layer you’re looking for. Another informal test that I’m becoming fond of is what is becoming known around the Wasatch as the “Pole Column” (I have to give credit to Maynard on this, although others may have figured it out as well). This test is very good for new snow instabilities. The procedure is you punch your pole basket into the snow repeatedly in a circle or square to isolate a column of snow then tap on the back of the column with your pole or hand to see if it shears. It’s arguably the laziest shear test I know of. Quantifiable?......by definition I’d say you could place a number or measurement on it. Loose interpretation?........definitely.
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Brett Kobernik
UAC

cesare · Posted: Sat Jan 14, 2006 3:45 am Post subject:

Thanks for taking the time to put that in words, cowboy. I wish I could say anything that well. Wink

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that sounds like a sure-fire way to get bitch-slapped by devil's club -- dschane

wow · Posted: Sat Jan 14, 2006 3:50 am Post subject:

Yeah, I'd call it a babble.
The most common "quantifiable" test I use is a hand pit with a little burp the baby on the back after the digging. Cesare has another name for it that the japanese use.
Anyhow I quantify it for myself as easy moderate and hard with the quality of sheer the only meaningful data retrieved.
Course I'm no scientific student or an instructor, but a dedicated and determined powdah skier and I usually don't care to communicate that info with anyone else, cuz they may poach my line. Wink

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snowdynamics · Joined: 12 Dec 2004 Posts: 618 Location: Wasilla, Alaska

Great insight on things being observed and done elsewhere.