Skier Compaction: How much is enough?

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Originally Posted by glademaster

It really shoots your argument to shit when you give an example of a guided group getting buried in a massive slide on your home turf, then state "our avalanche forecasting is a lot more advanced, precise and accurate than what you have over there in North America."

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Uh, no. Avalanche forecasting in many part of Europe IS " a lot more advanced, precise and accurate than what you have over there in North America."

Europe also has many MANY more off piste users and much easier access and consequently more bad accidents.

@ SP, I am not that familiar with the Munter method but in my opinion, any system that gets you to dispassionately apply a set of risk factors is far preferable to, "well the hazard went down to Moderate and I had an airbag so WTF we skied it, oops".

Attachment 359452
Who needs boot packer when you have a disruption roller and a winch cat

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Originally Posted by glademaster

It really shoots your argument to shit when you give an example of a guided group getting buried in a massive slide on your home turf, then state "our avalanche forecasting is a lot more advanced, precise and accurate than what you have over there in North America."

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ahm no, not according to logic? ;)

It was very unlikely that they trigger a slide on that day on that aspect and steepness, so the guide gave it a go. (they stopped in the slope to regroup so it became a catastrophe instead of one person buried, but thats also an entirely different story). They triggered one and it ended in a catastrophe. It doesn't matter how big the slide is considering the risk. guided groups get hit "all the time" (each year) in the alps. But there are like a gazillion guided days every year so the probability is still low. (actually i don't have data concerning guided vs. unguided accidents divided by ski days, but it should be. otherwise guides would be a liability ;) )

we had a big discussion over here about some of the guided accidents because the guides seem to push it quite a bit to deliver the goods to their clients, but that is a completly different animal than a low risk high consequence scenario.

@ bunion well it also has it's downsides. for example i always "ski in small groups, one by one" and tend to finde other favourable things to factor in if the snow is good (no of course i do not actively try to, but psychology is an important part so that you do not try to get the risk below 1 and get a "go" from the system. but i guess the human factor in groups is ALWAYS super tricky. ;) )
And yeah i felt totally helpless in AK when I knew that the bulletin guys i met the day before do not know THAT mauch more than me and don't have that much info as the guys in the slf who have dozends of observers measuring stations in every mountain range and so on.... so I had to look at the actual snowpack and it told me.. yeah well nothing. Of course i came to my own conclusions, but i really like a well prepared bulletin and math as a basis for my decision making.

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Originally Posted by subtle plague

I always wonder how you get to a stop or or decision in North America. :D
For example I've never dug a pit because it's basically useless since it only says something about the 10m of the slope you're in and findings are so random compared to a well researched avie bulletin and reduction. But having seen how you guys get your info in the bulletin from some semi volunteers at turnagain pass I can understand you want your own assessment. ;)

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I actually read up on münter again last night after writing that post and realized I, as usual, had very little idea what I was talking about. And, from what i could find, it's really no different than any other checklist ultimately and is to serve kind of as a "double-check" to one's decision. I.e. you are with a group, getting ready to drop in, and you run through the list and potentially the reduction method catches something you missed? In this case i get it, and i'm actually going to print a card and bring it with me out of curiosity just to get some experience using it. Is this in general how you see it used?

The reason I've been skeptical about it in the past is working with people using the reduction method as an excuse to send groups in an avalanche class (academic / university level, not a practical course) into avi terrain with a DPWL. As with any tool, i guess it's how you use it.

Point taken with regards to the avi forecasting too. Forecasting in the alps is on another level.

As I said it wasn't about bragging it's just a methodical way to plan your tours and to judge a situation with more than just a pit and a hunch.

To be fair: the original deep layer persistent problem can not be tackled with that method either because of the high consequences. We've discussed that over here and came to no other conclusion than terrain management. Even if it is moderate and statistically you could go, we chose not to. I'd rather take my chances on some nice fresh snow in a level 3. (not some windloaded obviously stupid stuff. Just a " new snow considerable" meaning you crossed a certain amount of fresh and that's an automatic level 3) , than ski a big line in moderate conditions, but deep instabilities.

Skiers (and sledder) activity is definitely good for some things, like disturbing a surface hoar layer on a slope or getting weak layers within storm snow to bond. But if you know there's a deep persistent weak layer like depth hoar lurking in the snowpack, don't expect skier compaction to do anything. Skier traffic can lead to slab formation above a DPWL, and it can wake up and avalanche with the right trigger, like intense, rapid warming.

Edit: The last picture in this article provides a good example of a skier-compacted deep persistent slab avalanche at a ski resort.

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Originally Posted by whipski

Attachment 359452
Who needs boot packer when you have a disruption roller and a winch cat

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That thing is really cool. Seems like an effective tool as well if you can just drag it up a slope. Why isn’t that used more often?

I believe that is a T-Ride home built device. You need to be able to get a winch cat to/above the starting zone.

Not possible in many cases but you are right, it is pretty cool.

Early iteration:

https://arc.lib.montana.edu/snow-sci...98-348-351.pdf

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Originally Posted by Bunion 2020

I believe that is a T-Ride home built device. You need to be able to get a winch cat to/above the starting zone.

Not possible in many cases but you are right, it is pretty cool.

Early iteration:

https://arc.lib.montana.edu/snow-sci...98-348-351.pdf

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A-Basin also uses one for the starting zone on Pali

IIRC, Winter Park uses a roller in the Cirque. Have heard of it a few other places too, but forget where else.

I'm not sure where that roller is in use but it isn't T-ride.

Edit: Refering to the photo.

That would Monarch if memory serves

Sent from my SM-G988U using TGR Forums mobile app

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Originally Posted by rocca

That would Monarch if memory serves

Sent from my SM-G988U using TGR Forums mobile app

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whipski's photo is most definitely Monarch (top of Mirkwood)

Invented at Telluride

https://www.powder.com/stories/this-...lize-snowpack/

The definitive answer is that it all depends.

You can think of skier compaction in terms of location, distribution, density, depth, and duration. Not so simple.

Scariest example I have seen was in Lake Louise. A steep bump run, huge waist hight moguls. We had 2 weeks of high pressure and -40 temps. Patrol had dug some test pits and got scared. The bommed the slope and nothing happened, increased the charge and nothing - Put a stupid huge amount of explosive on the slope and the whole thing slid. But slid like a carpet, looked so strange a crumpled carpet at the bottom of the hill, with all the moguls still intact. Slope went to ground in most places.

Was this Rocket?

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Originally Posted by skiracer88_00

A-Basin also uses one for the starting zone on Pali

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They use that and "Team Summit". We always laugh at the fact that they are using a bunch of 50 lb rich kids to pack down areas around Pali.

Skier compaction isn't a myth. Take La Grave for example. There, there is almost no avalanche control, yet people are constantly skiing the slopes. The terrain is perfect for avalanches, but you don't hear about many people triggering slabs on persistent weak layers. Now imagine if each person that got off at the top of the telepherique were treated to an untouched backcountry snowpack. Way more people would be dying in avalanches.

The OP asked about skier compaction and its net effect in a backcountry setting.

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Originally Posted by plugboots

Thats what I thought. There's some ski movie/video that shows people stomping up and down a bowl at Aspen? or somewhere, and they get to ski there for free if they do this, (if I remember correctly). I wonder if that's still going on?

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Yes, I think that was in an 80's Warren Miller movie, and Aspen sounds right to me. That compaction is a lot different than what that photo shows (I would think of that as minimal, at most), and presumably at Aspen the patrol was overseeing it so little/no danger to those people.

Highlands Bowl boot packing crew

Paging TeleFreeWasatch to the white courtesy phone...
"Moguls from the dirt up"
Also worth listening to the Avalanche Hour podcast with Dave Richards. He's the avalanche office lead for Alta Ski Area and says he doesn't believe in skier compaction.

Didn't Big Sky or Bridger have a mogul run rip out to the dirt in the past decade, too?

Disclosure: avalanche amateur stating how I think about this. Feel free to critique, someone might save my life.....

I think it's been mentioned, but the effect of skier compaction must be seen in relation to the avalanche problem. For some problems (soft slabs building up in layers over few days with intermittent snow fall and wind) I can't understand how skier compaction wouldn't work. If there are weakt layers forming during or after the skier compaction (facets close to the ground) the effect must be close to nothing. But might reduce the potential of the upper layers to propagate - due to less cohesion?

Snow crystals constantly change, either getting smaller or bigger, often with temperature gradient as the main driver. This means that most avalanche problems come and go over time, and that what was a positive effect from skier compaction on a soft slab might be irrelevant if there over time is a thick layer of facets forming near the ground or under a ice layer that the skier compaction hasn't affected. This sounds what might be the cause of the mogul slide in Lake Louise mentioned above. Would be interesting to see results from a pit on that one.

Now, tell me if I'm wrong.