Extended Column Test - How to interpret?

From the NSAS Thread as posted by Lowell:

Okay, since Oyvind convinced me that I need to carry my iPhone in the mountains, and since Karl Birkland explained the Extended Column Test (ECT) more clearly than I've heard before, I combined the two and loaded a quickie checklist into my iPhone task manager (Toodledo) to remind myself how the ECT is supposed to be done:

_Dig pit with exposed face at least 90cm wide
_Use probes to define corners of a 90cm by 30cm column
_Isolate column by cutting around probes using knotted string
_Place shovel flat atop one end of the column
_Angle shovel so downward force will be parallel to force of gravity
_Tap shovel (10 from wrist, 10 from elbow, 10 from shoulder)
_Does the column fail? Does failure propagate across column?
_Failure across entire column indicates instability
_Lack of failure doesn't necessary indicate stability
_Slope angle doesn't matter much
_Number of taps doesn't matter much
_Test is only usable to about 1 meter depth

Did I get it right? Feel free to copy and use ...

Geek alert! Here's a back-link to the NSAS thread where this got started:

www.turns-all-year.com/skiing_snowboardi...61.msg95312#msg95312

www.turns-all-year.com/skiing_snowboardi...61.msg95316#msg95316

Here's the post that caused this thread fork:

After thinking about it a little more, I remembered that Karl Birkland stressed how you mustn't use the test to verify stability. It can only tell you instability. So I added the following item to the checklist:

_Lack of failure doesn't necessarily indicate stability

I think somebody could do a whole presentation on the psychological challenge of trying to hold in your mind the notion that you should not use tests like ECT to confirm stability. As Karl Birkland was describing that, I was thinking, "OK, I understand that conceptually. But how many of us can actually do it? How many us aren't strongly reassured by a negative instability test."

More food for thought...

While I appreciated Karl's statement that the ECT should be used as evidence of instability, not stability, I disagree with the some of the underlying assumptions. What I think Karl was saying, is that you should be looking for potential problems, you should not be seeking affirmation that everything is fine and you can go skiing.

This makes a lot of sense when in a familiar area. For example, the frequent trip to Table Mountain, you should be on the lookout for signs of danger. You should not go out there on a high avy day and look for justification that it "really isn't that bad".

However, when confronted by new terrain and little information, such as being dropped off by helicopter at a hut in the Canadian Rockies, it is best to assume that the danger is high. When in this situation, I assume the worst and go looking for evidence of stability rather than assuming everything is safe and go looking for trouble. I dig a pit and do tests with an open mind, but seeking evidence that suggests that I can go skiing safely.

There is a certain subtly in the different approaches. I think it is hard to draw much of a rule of thumb beyond "keep an open mind, and look at your stability test data".

Here's something I think about.

1. You have a high fever and can't keep down food or water.
2. Your doctor performs a complete blood count.
3. The test reveals normal cell counts.

What are your expectations? How do you interpret the results? How does your doctor interpret the results?

A key thing to keep in mind is that Karl said that the ECT (like all instability tests) is known to give "false negatives" a certain percentage of the time. In other words, the test doesn't always reveal instability when the slope can be shown to be unstable (by bombing it, for example).

My brain is already fuzzy on the false-negative rate for the ECT but I believe it was below 10% and better than the other tests that Karl mentioned.  The propagation saw test has a false negative rate around 30%. (Yikes--but you can use the PST in situations where you can't use ECT, such as deep instabilities.) Karl made the case that if you regularly use the ECT to make go/no-go decisions, and your chance of being wrong is 10%, you won't live very long. That's a powerful notion to keep in mind.

Here's something I think about.

1. You have a high fever and can't keep down food or water.
2. Your doctor performs a complete blood count.
3. The test reveals normal cell counts.

What are your expectations? How do you interpret the results? How does your doctor interpret the results?

It probably means you have the flu and you need an IV if dehydrated. It could be early symptoms of appendicitis, but that usually means elevated white count. I don't  know what this has to do with an ECT.

jk Mike. Negative result don't mean your not sick.

Nice breakdown of potential scenarios that may effect a stability vs. an instability approach jd.  I was thinking it was just semantics, but your description brings it home.

Thanks for the list Lowell. It may also be helpful to mention for those who weren't there that the knotted string can be tied to the ends of two avalanche probes for saw-like use to create the test block.

Did a quick google; didn't find any of the vids Karl used, but there's a couple others. Here's one: Extended Column Test

www.turns-all-year.com/skiing_snowboardi...61.msg95316#msg95316

After thinking about it a little more, I remembered that Karl Birkland stressed how you mustn't use the test to verify stability. It can only tell you instability. So I added the following item to the checklist:

_Lack of failure doesn't necessarily indicate stability

I like the way you put that Lowell - "...doesn't necessarily indicate stability" (italics are mine)

While no single test can be used to determine stability, test like the ECT can be helpful in the process of confirming your theories about stability.  If all signs point to stability and the ECT also points to stability I would factor that result into my evaluations.  The key is to not give that test too much weight.  There are too many factors that could give you a false stable result (spatial variability, poor site selection, etc...)

Now if all signs point to instability and the ECT points to stability I'd probably just throw that result out.  I believe that is what Karl was getting at. 

What I use the ECT most often for is to track the trends in a layer of concern.  I've found it too be a good test to see if a layer is gaining or losing strength.  We often get surface hoar layers here on the east side of the cascades that can last for months.  These things can go dormant for a long time until there's finally enough weight to tip the scales.  The ECT is one more tool to help you keep an eye on these layers.

As far as physical tools go, I've found the long saw to be indispensable for the ECT.  The probe - cord combo works but doesn't give you as clean of a cut.  A 70 cm folding saw is cleaner and I believe faster than the cord.  Personally I prefer something stiff like the Brooks Rang Igloo 70 so the cuts stay straight.  Some of the long saws out there are a little too flimsy in my opinion.   

As far as physical tools go, I've found the long saw to be indispensable for the ECT.  The probe - cord combo works but doesn't give you as clean of a cut.  A 70 cm folding saw is cleaner and I believe faster than the cord.  Personally I prefer something stiff like the Brooks Rang Igloo 70 so the cuts stay straight.  Some of the long saws out there are a little too flimsy in my opinion.   

One point that Karl emphasized and even joked about was not filling our packs with more things. This of course is from the perspective of ski touring - I imagine if you're heli skiing or on a sled that this would be different. Seems he did most of his research using the probe/knotted cord combo. The beauty is that the only addition to your pack is a piece of cheap nylon (or whatever) string with a couple of knots in it.

A friend of mine was telling me that there was a new test for slab fracture propagation. Any one know if its true or what it is?

www.alaskasnow.org/wp-content/uploads/2011/01/Prop-Saw-Test.pdf

I think this is what you mean and related to the ECT.

One point that Karl emphasized and even joked about was not filling our packs with more things. This of course is from the perspective of ski touring - I imagine if you're heli skiing or on a sled that this would be different. Seems he did most of his research using the probe/knotted cord combo. The beauty is that the only addition to your pack is a piece of cheap nylon (or whatever) string with a couple of knots in it.

I agree that keeping your pack light is very important.  A heavy pack slows you down and wears you out, increasing your likelihood of needing all of that rescue gear, but the long saws are only a few ounces heavier than your standard saw.  Now if you are suggesting not using a saw at all, I think trying to do stability tests without a saw is like trying to carve a turkey with a spoon (gets the job done but its often a little sloppy).   I've tried the probe-cord method for everything from Rutschblocks to Compression Tests and it doesn't provide consistently clean cuts, which adds to the potential for inaccurate results.  Possibly the probe cord combo works better in shallower, lower density snowpacks but my results with it have been less than ideal. 

I'm always carrying a saw in the backcountry, whether I'm being dropped off by a helicopter or earning my turns (I spend approximately %95 of my time touring as opposed to heli skiing).  I actually find the saw more useful when I'm earning my turns because I have more time to do stability tests.  For me the extra 9 ounces are worth it. 

Ski touring is inherently slower paced when compared to heli skiing.  When ski touring I usually have extra time at the transitions, extra time at rest breaks, and the ability to stop on the way up to give my guests an extra rest (rest breaks on the way up in the helicopter are less common  ), and with me being a bit of a snow geek I end up digging more pits. 

The reason I don't dig more pits when I'm heli skiing is because I'm working with a team of guides.  There are definitely more pits dug by the heli ski guides, especially when you factor in they're out there almost every day, but I personally don't get to dig them all.

If I could ask one more question. Do you think that it is proper etiquette to drop a load of heli- skiers above a group of touring ski mountaineers? I mean, isn't the first thing you guys do is perform ski cuts to midigate any unstable snow?

I think your question is a reasonable one but a bit off topic. I will send you a personal message.

I think the question of looking for instability relates to last year's NSAS topic on "when to dig". If there are already visual and/or audio signs of instability, there is no point in digging; turn around! On the other hand, if there are no obvious signs, then dig a pit. The idea is to keep looking for instability and stop when you find it as opposed to using further testing to overrule the instability signs already in hand.

What happened to the PMs that were shared and the narrative of the avalanche that mixed a recreational group with a guided group? It was interesting info to read and learn from.

There was some miscommunication between the two parties as to what was going to be shared, so I removed it. If they work out the details, the info may be posted again, but they both have to be pretty comfortable with that, which wasn't the case with today's post.

Not sure the "only useful for 1 meter depth" is correct.

See this video.
vimeo.com/35967109

Some scary layers in UT at the present as shown in this ECT.

Not sure the "only useful for 1 meter depth" is correct.

See this video.
vimeo.com/35967109

Some scary layers in UT at the present as shown in this ECT.

Nice video Scotsman.

I believe the reason the ECT does not do a good job of testing layers deeper than 1 meter is because it is hard for the energy of the "taps" to reach deeper than 1 meter (much like the weight of a skier).

I'm sure we'll see a "Deep ECT" similar to a "Deep Tap Test" at some point in the near future. avalancheinfo.net/ASARC/DeepTapTest.pdf

Nice video Scotsman.

I believe the reason the ECT does not do a good job of testing layers deeper than 1 meter is because it is hard for the energy of the "taps" to reach deeper than 1 meter (much like the weight of a skier). 

I'm sure we'll see a "Deep ECT" similar to a "Deep Tap Test" at some point in the near future.  avalancheinfo.net/ASARC/DeepTapTest.pdf

Hi Jeff,
Well that's the conventional wisdom but look at the video again. The problem it UT at the moment is a deep PWL that many have assumed( to their detriment) was deep enough to be "bridged". The ECT in the video is 1.65 M deep and the taps produce a shear at my guess about 1.15 to 1.2 M down..... exactly the result the testers where looking for and worried about.
If they had just dug a 1 M ECT, the Q1 at 1.2M would not have been evident???
Maybe for these type of instabilities a deeper ECT can be revealing.

Maybe for these type of instabilities a deeper ECT can be revealing.

True enough, but that's a lot different from the assertion that the ECT is a good way to test layers below 1 m.... I bet the 1 m was chosen as a 'conservative' estimate -- along the lines "if you're interested in deep instabilities, ECT may not be the way to go".

I'm sure in very unstable snowpacks, like the one in the Wasatch right now, the ECT could produce results below 1 meter, as shown in this video. I'm guessing that the forecasters in the Wasatch are describing the problem well and people are aware of this deeper instability, which would warrant deeper snowpack tests. The one concern I would have is if someone dug that same test pit, did an ECT and did not get a result, and then thought they were dealing with a stable snowpack.

In my experience, many tests on layers that deep can be unreliable (deep tap tests and propagation saw tests seem to fair better at depth). Hopefully people are looking at the bigger picture and not basing their decisions solely on snowpack tests.

True enough, but that's a lot different from the assertion that the ECT is a good way to test layers below 1 m.... I bet the 1 m was chosen as a 'conservative' estimate -- along the lines "if you're interested in deep instabilities, ECT may not be the way to go".

I never made the assertion that the ECT was a "good way" but as this video shows, it can be revealing and " useful "for these sort of conditions. I was surprised by how well it worked in the video and that was my point and question.

What test, other than a deep tap test would be a "good way" to test for deep instabilities?
If you remember last year and our MLK layer that got very deep, and then revealed itself in some huge( ANFO assisted ) slides last year at Crystal......one of the  hot topics for discussion last season between my BC buddies was how well that layer was bridged and how to test for it so deep down. Some never trusted it and stayed off the big stuff all year...others continued to test the top 4ft with CT's and hand shears and "hoped" the MLK was sufficiently bridged and skied the bigger stuff if this relatively "shallow" layer showed a good result in line with observed stability( no naturals, good temps  etc,)

Even though forecasters can spell out a deep PWL in their forecasts....the question of "is it deep enough to be bridged" seems to be causing a lot of the troubles in UT at the moment amongst the avid. The concept of deep enough to be bridged seems a fallacy in UT at the moment as the video and their "tall" ECT shows.

If the snowpack is producing avalanches then bridging isn't happening. It's just another rationalisation.

Desire is the root of all suffering.

My partner & I were present on the day of the avalanche referenced above.  It was a high hazard day as noted in the avalanche report.  We were at the hairpin skiing a low angle treed run.  We crossed the avalanche terrain in question one at a time to access the run.  There were several recreational parties as well as Jeff Ward's guided party who was clearly behind us.  Everyone was concentrated in the same area. Breaking trail was very difficult & this was all done by recreational skiers.  Mr. Ward's party followed our skin track.  As he was skinning up our trail for his first run, we skied by him on our first run down. 

On our second run, one of the recreational skiers, drunk on powder, was skinning up on his own, he got ahead of everyone, we didn't know his plan.  He made a bad choice & entered the trigger point at the head of the avalanche zone.  He triggered an avalanche that swept to the bottom & partially buried Mr. Ward's 2 clients.   One of his clients lost their ski which was not retrieved.  The skier who triggered the avalanche hurt his ankle & also lost a ski, which was not retrieved.  The recreational skiers helped him get to his sled.  Fortunately no one was hurt or died that day.  There is a definite danger placing yourself under parties skiing above.  I hope we can all learn from this.

Here's another "tall" ECT performed by an avy pro.
Looks like an ECT 30 Q1 at 1.55 m to me.
These guys seem to be using it deeper than the recommended 1M!!!

vimeo.com/35999040

Would you ski after getting that result with no naturals or any other observed instability and strengthening upper snowpack???

Would you ski after getting that result with no naturals or any other observed instability and strengthening upper snowpack???

That's a good question, I'm still learning the ECT test so help me out here but isn't the ECT for determining propagation not failure? In this case, I'd say that one propagated easily which would be an indicator of instability so I would not ski that slope. A more difficult question for me would be if that ECT test propagated only half way on the 30th blow...

Another "tall" ECT and this time by a beautiful young lady avy pro.
Deep Slab Tutorial.

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Schwiiiiing!

Out of town for a week. I removed a few posts here that weren't on topic for the ECT. Freeski, you and Jeff need to have a more clearly defined agreement than you appear to have had if you're going to post your PMs to each other. If you want to talk about that, PM me, but please don't use this thread for it.

Another ECT video this one with a nice Saw Propagation Test from avy pros in UT.

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Love these videos.

UT=screwed this winter.