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.