Slide: The Avalanche Podcast

I've tried to listen while doing something other than driving, and I can't quite absorb the info - too much of a good thing? Humans can't really multi-task anyway I guess...Got em loaded up for the next road trip.

If you're shooting from the hip - I'd love to hear your use-cases & experiences with the PST, specific to your mechanized experience if you've been incorporating it....Slab/bed surface properties, depths, weak layers, correlations to ECT results, awkwardness of changing your system to accommodate excavating down-slope (or maybe its just me..)?

Not being able to listen when I'm trying to work is my only complaint. Luckily skis need waxing and other tasks let me listen.

I've never done a PST, but I've seen them on youtube. Shhh, it's a secret.

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Originally Posted by covert

I've never done a PST, but I've seen them on youtube. Shhh, it's a secret.

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It must be because you don't have Canadian citizenship ;)

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Originally Posted by covert

I've never done a PST, but I've seen them on youtube. Shhh, it's a secret.

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Sounds like a when/what/where/why/how on pits and tests might be a good episode or two.

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Originally Posted by Summit

It must be because you don't have Canadian citizenship ;)

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I'm not a citizen, I just live here. Maybe that's why I can't decide if I like the test or not.

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Originally Posted by Z

I'm not a citizen, I just live here. Maybe that's why I can't decide if I like the test or not.

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The incredibly knowledgable person who is responsible for our local avalanche forecast has explained it to me like this: The PST is nice as a demonstration if you want to show people a block of releasing snow. The ECT will show you weak layers and give you and idea of what they may do, the PST will give you an idea what the layer may do but you have to know exactly where the layer is beforehand. From a purely "huh that's interesting" point of view the PST is very cool and apparently some significant success has been achieved regarding understanding the mechanics of fracture propagation with the help of systematic PST experiments and high speed cameras. From a "do I want to ski this" point of view I have yet to hear an argument how the PST could be superior to the ECT.

I also enjoy the podcast a lot. However, I just tried to listen while also following along with an online yoga video and I fell over attempting firefly pose, so I'm blaming covert for that.

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Originally Posted by klar

From a "do I want to ski this" point of view I have yet to hear an argument how the PST could be superior to the ECT.

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The ECT only produces reliable results on weak layers buried less than about 100-130cm below the surface. The PST is effective on weak layers at deeper depths. To me, that seems like the main advantage. If I'm curious about a layer in the upper 100cm-ish of the snowpack (which is most of the time) I'm definitely going to default to an ECT. About the only time I'd do a PST is when the layer is deeper than that, or a layer won't propagate in ECTs and I want more data.

Not that pit results should really be answering "do I want to ski this" to begin with, of course.

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Originally Posted by adrenalated

The ECT only produces reliable results on weak layers buried less than about 100-130cm below the surface. The PST is effective on weak layers at deeper depths. To me, that seems like the main advantage. If I'm curious about a layer in the upper 100cm-ish of the snowpack (which is most of the time) I'm definitely going to default to an ECT. About the only time I'd do a PST is when the layer is deeper than that, or a layer won't propagate in ECTs and I want more data.

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Yeah fair point. Anything deeper than a meter or so hasn't been very relevant with the crap winters we've been having... I have heard of people doing deep tap tests for this but never seen one done/tried myself.

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Originally Posted by adrenalated

Not that pit results should really be answering "do I want to ski this" to begin with, of course.

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yes poor phrasing on my part. I guess I was trying to say that I find the PST gives more abstract information. What exactly is the data you gain from doing a PST when you want more information? Can you give an example where you learned something from a PST that you didn't know before?

the only quantifiable value is the cut length, no? On an intuitive level I find it a lot more difficult to relate that to skiing than how hard/often I hit an ECT block.

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Originally Posted by klar

the only quantifiable value is the cut length, no? On an intuitive level I find it a lot more difficult to relate that to skiing than how hard/often I hit an ECT block.

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Also the fracture character, ie does the fracture shoot to the end of the column, stop before reaching the end, or shoot up through the slab? See page two here: http://www.alaskasnow.org/wp-content...p-Saw-Test.pdf
Definitely worth noting that PST shows more false-stable results than other tests.

So as a hypothetical, let's say I want to investigate a layer of facets buried 110cm deep. I do an ECT an get moderate results, but no propagation, something like ECTN14. I might consider doing a PST to see if I can get a fracture to propagate that way. If I get PST-SF or PST-arr it would give me greater confidence in the ECTN result.

All that said I learned the PST two years ago and I think I've actually used it only once since then.

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Originally Posted by adrenalated

So as a hypothetical, let's say I want to investigate a layer of facets buried 110cm deep. I do an ECT an get moderate results, but no propagation, something like ECTN14. I might consider doing a PST to see if I can get a fracture to propagate that way. If I get PST-SF or PST-arr it would give me greater confidence in the ECTN result.

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Okay, makes sense.

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Originally Posted by adrenalated

All that said I learned the PST two years ago and I think I've actually used it only once since then.

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Similar time line for me. I can see the value of added information in specific situations as you detailed but it doesn't seem practical as a go to everyday thing.

Side note re fracture character: This year our avalanche center redid the little booklets they hand out to write down pit data and test results so that the only differentiation for fracture character in the ECT is N or P, while previously there were several options in between. The argument was that the in between options only confuse the observers and don't help the forecasters enough that dealing with potentially inconsistent info is worth it. There obviously is value in the more nuanced data on fracture character but apparently when collecting data from an observer network for operational forecasting it is preferable to keep things as simple as possible. I found that interesting.

SWAG was changed to discourage the rating of fx character for ECTs. The reason is that fx character ratings were developed to give an idea of propagation potential. The ECT was developed for the same reason, and the developers feel that adding a fx character rating to it is redundant.

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Originally Posted by covert

SWAG was changed to discourage the rating of fx character for ECTs. The reason is that fx character ratings were developed to give an idea of propagation potential. The ECT was developed for the same reason, and the developers feel that adding a fx character rating to it is redundant.

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This was pretty legible; consider removing more vowels.

I feel like a lot of Avy 1 students come out of the class all gung-ho to dig pits wherever they go, when it seems like in most circumstances, as adrenalated mentioned, pit tests usually aren't there to answer the question of "should I ski this or not." I'd be interested in hearing more about matching avy forecasts to big-picture terrain choices, particularly if you don't have a long history with a particular zone. As well as how those plans might be altered by localized observations.

The deep/hard-slab thought process is generally the response I get when asking professionals about the PST. I suppose it could also be useful for a shallow soft slab where your ECT just compressively (did i just make up a word?) breaks through the slab. Realistically you'd probably feel this underfoot and not necessarily need to dig, but I've been surprised before. Could also help to identify a storm snow interface like preserved stellars or just a tough to detect storm intensity change.

I think I'm looking for some sort of reason to use the test in a real world situation, and I'm not necessarily finding it....As a forecasting tool - maybe, from a daily guiding perspective - not so much?

The avi center covering the Tahoe area has been using pst on some of the early season deeper layer problems that we've had the past few seasons. It's been used to check on changes in the bonding strength of known problem layer(s). They've focused on distance of the saw before failure. Results have influenced their public forecast and their prediction when there's a bunch of water heading into the area.

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Originally Posted by bodywhomper

They've focused on distance of the saw before failure.

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The "critical cut length" is being used as a kind of proxy for stability and is a main variable in a new-ish theoretical approach to crack propagation by Gaume et al (2015) combining some aspects of Heierli's anticrack idea and more traditional approaches. Unlike the anticrack theory, the new idea shows a dependency between slope angle and propagation (i.e. critical cut length). Apparently PST results can be modeled very well using a FEM.

Not terribly useful for skiing but my inner nerd enjoys this and I bet anyone who has tried to get a finite element model to do something would be appreciative.

https://www.youtube.com/watch?v=Tqok...ature=youtu.be

listened to most of these on our journey to and along the bc powder hwy
long time ago mr tremper autographed his book for me somethin to the effect of sharing a journey of becoming avalaunche experts
somewhere along that journey lots of learnins some formal ,most in ,mistakes, lost friends and a bunch of good shit too
i realized i just wanted to be an addict with a strong dose of self preservation and a solid partner
thanks for producing strong content that fits my goals
its damn good

muchas gracias, sorry i've been slack on keeping up with it lately. i'm returning to the san juans next week and should have the time to finish the season strong.

Fill your quota of turns and podcast as time allows...we get paid by the hour out here

Doug-san,

May we anticipate a new episode soon?

Arigatou gozaimasu

Do itashimashite. You may.

It's back.

Special snacks for anybody that can identify at least three of the technical details I should have explained differently.

Stoke.

In case anyone isn't aware: easy to support this every month with a small subscription via Patreon: https://www.patreon.com/avalanchepodcast

It’s great to hear another episode. I think the recurring cadence is a good way to rehash and reinforce information.

Thanks. I used to be wary of repeating myself, then I realized it's often necessary to beat the shit out of that mule.