Skier Compaction: How much is enough?

There’s a zone in the San Juan’s where I ski. And so do a lot of other folks.

35-38 degrees. N/NE facing glades. Rolling terrain, some small avy paths and gully-features.

It gets skied quickly after a storm, it’s no secret.

Hard to quantify, I suppose...

how much do you trust skier compaction? Has anyone heard reports of slab avalanches releasing on seriously gang-banged slopes?

Discuss?

Attachment 359195 Its a myth.....

Whoa. Sobering.

Where is that picture taken?

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Originally Posted by Hacksaw

Attachment 359195 Its a myth.....

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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?

Read this study:
https://www.researchgate.net/publica...PACK_STABILITY

Duplicate post blues

It looks like in that picture that the upper layers of the snowpack were heavily skied before it’s eventual release...

But was it skied regularly as the depth of the snowpack increased? Or was it undisturbed, then skied a lot all at once? (Like newly opened terrain or sidecountry at a ski area?)

I only ask as it looks like the bed surface is so uniform.

I understand that skier-compaction doesn’t make a slope completely safe...but saying it’s a myth isn’t altogether true either, is it?

I thought (could be wrong!) that i heard that Edelweiss Bowl of Teton Pass hasn’t slid in ___ years. Same with Oh Boy off Red Mountain Pass in CO. Both of those are very-much any terrain, but get skied as soon as the first layers get laid down, and continue to get tracked up as the snowpack increases it’s depth.




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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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I don’t know of a video, but Ski Silverton used to have folks come up and side-step the starting-zones in exchange for ticket vouchers.


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Originally Posted by Hacksaw

Attachment 359195 Its a myth.....

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^ This. A Persistent Weak Layer can hold...until it doesn’t. Skier compaction can only work as mitigation if it is started very early in the snowpack history and maintained regularly throughout the season.

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Originally Posted by Tech Tonics

I don’t know of a video, but Ski Silverton used to have folks come up and side-step the starting-zones in exchange for ticket vouchers.


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There was a recent Avalanche Hour podcast with a snow safety dude from Alta. Way he put it is that he believes that skiing a slope can help break up weak layers if it gets skied early and often. But that it doesn't provide compaction.

Made sense to me.

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Originally Posted by doebedoe

There was a recent Avalanche Hour podcast with a snow safety dude from Alta. Way he put it is that he believes that skiing a slope can help break up weak layers if it gets skied early and often. But that it doesn't provide compaction.

Made sense to me.

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Right, I guess “cutting it up” is more accurate than “compaction.”

Avalanche paths come in many shapes and sizes and that serves to complicate things a great deal.

At my last area the main avalanche problem was associated with narrow and very steep paths with relatively small starting zones, because of the size skier traffic and compaction played a large role in helping to stabilize those paths. We were traveling vertically down those paths long before they are skiable.

The other factor is the aspect is (north) and the snow pack is usually very thin so if you can get on it early and regularly you are doing more than just breaking things up and snow pits confirmed that.

On the same mountain are very wide open and large paths and starting zones that are served by a lift that when running at full speed only puts 250 skiers per hour onto several hundred acres.

In that scenario skier traffic does only serve to break up and mix new snow. Very little effort is made at boot compaction and the area generally experiences at least 1 major avalanche cycle per season.

So, it depends on a lot of factors but in a purely BC setting I would be very leery of counting on skier compaction for much of anything other than some mixing and breaking up of layers.

JMHO.

When someone argues skier compaction,
I always remember the poor soul that died inbounds, in toilet bowl, in JH, wearing a beacon.

Shit happens.
Compaction helps.
But it doesn’t make anything bulletproof.

I, myself, however, do fall into the heuristic trap.
Been there. Skied that. Feeling more confident on a heavily skied slope.

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Originally Posted by Hacksaw

Attachment 359195 Its a myth.....

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Can anyone find a pic of the in-bounds slide at A-Basin from ~15 years ago where there are clearly moguls visible on the bed surface? That one is a real eye-opener.

I believe that was a wet slide due to warm spring temps

^^^ Correct. Different animal entirely.

[QUOTE=Hacksaw;6209291]Attachment 359195

As I remember this photo was taken in France.

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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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Lots of places do that, including Crested Butte and Irwin catskiing. It was always volunteer for a free pass at CB, but now with Vail they also get paid, which is weird. I'm sure some lawyer said they were more protected if something happened to an employee rather than a volunteer, since Vail seems to be run by lawyers. On a year like this with shit snow, the areas they packed before this storm cycle will hold (or if they do go, it will only be the new snow) and the areas they didn't pack will slide to the ground.

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Originally Posted by Hacksaw

Attachment 359195 Its a myth.....

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uhm no. In the reduction method a heavily skied (means constantly after every snow fall, which is very tricky early season or in this picture because we dont know when the lift serving thatb slope opened) slope can be calculated one level below the level of the avie bulletin because you have the reduction factor 2. So it makes it safer, but not safe. (you can't deduct the avie level, but the outcome is the same risk as one avie level below in rarely skied touring terrain).

even avie level 1 and a heavily skied slope are not safe per definition, they are just a lot below the accepted risk of 1:100.000 which is the base for the reduction method.

^coming from N America, the reduction method just strikes me as so odd.

For example "the slope can be calculated one level below the level of the Avi bulletin"? Public advisories don't even operate at the slope scale in terms of danger levels?

It's been forever since I've looked into the method, but i don't really remember it incorporating avalanche problems really at all. Skier compaction, esp in a BC setting, may not help with the (deep) persistent problems to which you are trying avoid exposure. And a moderate rating (AR 2) makes it super easy to get a safety rating or whatever it's called on the reduction method of 1. But moderate days with a nasty DPWL are rarely a go for me in anything over 30 deg. I can't put a number of my risk tolerance though, so maybe a no-go for me is 1:10,000 or whatever.

Not to derail the worthwhile convo otherwise, just came to mind because I still struggle to wrap my head around using münter for decision making. Guess it makes way more sense if you've used it your whole career though.

That slide that killed two guys in Taos a couple years ago was in a chute that had moguls or that's what I was told.

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Originally Posted by NWFlow

^coming from N America, the reduction method just strikes me as so odd.

For example "the slope can be calculated one level below the level of the Avi bulletin"? Public advisories don't even operate at the slope scale in terms of danger levels?

It's been forever since I've looked into the method, but i don't really remember it incorporating avalanche problems really at all. Skier compaction, esp in a BC setting, may not help with the (deep) persistent problems to which you are trying avoid exposure. And a moderate rating (AR 2) makes it super easy to get a safety rating or whatever it's called on the reduction method of 1. But moderate days with a nasty DPWL are rarely a go for me in anything over 30 deg. I can't put a number of my risk tolerance though, so maybe a no-go for me is 1:10,000 or whatever.

Not to derail the worthwhile convo otherwise, just came to mind because I still struggle to wrap my head around using münter for decision making. Guess it makes way more sense if you've used it your whole career though.

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That is the problem with deep instabilities. Low risk high consequences. The reduction method only calculates your risk of setting of a slide at a certain risk level in a certain aspect.(you get better reduction factors if you don't ski the aspects mentioned in the bulletin or leave out sector north and so on). The rest is avie bulletin text advice (e. g. Deep instabilities) , terrain management etc.

And I said you can't deduct a level.. It's just that the outcome is the same because of the added reduction factor. Technicalities. I know.

And here millions of people use it. And fatalities have been constant or decreasing despite the increased traffic in the back country. So it works. And skier compaction works (I see it as one of the reasons that there aren't as many accidents as expected with the freeride trend because people ski crazy shit these days at level 3 and even 4!) remember we don't have inbounds.

You have to factor terrain in if you have low risk high consequence. And in 16/17 we had that and I didn't tour because the bulletin warned that despite the risk moderate it can be dangerous because of size. in that winter guided groups have been buried up to 12m deep. I didn't tour that year. It got super warm after each dump when we finally has a base so wasn't that tempted. I know that klar didn't ski many of her usual haunts that year because the slopes were too big for that constellation. (e.g. The slope the guys were buried 12m)


Edit: and of course you look for local signs in the advanced method: amount of fresh snow, wind, snowpack, but also group size and so on. The reduction or 3x3 filter method is pretty nuanced, really.

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. ;)

When I took a FUAC course in ‘05, the instructors discussed an avi that season at snowbird that slid on a skied-out mogul field. The bed surface was a skied-out mogul field. Apparently, it happened on a full moon.

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Originally Posted by subtle plague

That is the problem with deep instabilities. Low risk high consequences. The reduction method only calculates your risk of setting of a slide at a certain risk level in a certain aspect.(you get better reduction factors if you don't ski the aspects mentioned in the bulletin or leave out sector north and so on). The rest is avie bulletin text advice (e. g. Deep instabilities) , terrain management etc.

And I said you can't deduct a level.. It's just that the outcome is the same because of the added reduction factor. Technicalities. I know.

And here millions of people use it. And fatalities have been constant or decreasing despite the increased traffic in the back country. So it works. And skier compaction works (I see it as one of the reasons that there aren't as many accidents as expected with the freeride trend because people ski crazy shit these days at level 3 and even 4!) remember we don't have inbounds.

You have to factor terrain in if you have low risk high consequence. And in 16/17 we had that and I didn't tour because the bulletin warned that despite the risk moderate it can be dangerous because of size. in that winter guided groups have been buried up to 12m deep. I didn't tour that year. It got super warm after each dump when we finally has a base so wasn't that tempted. I know that klar didn't ski many of her usual haunts that year because the slopes were too big for that constellation. (e.g. The slope the guys were buried 12m)


Edit: and of course you look for local signs in the advanced method: amount of fresh snow, wind, snowpack, but also group size and so on. The reduction or 3x3 filter method is pretty nuanced, really.

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'm in France and the avie bulletin is pretty uninformative.

I always worry about weak buried layers that could propagate and i dig out very often.

Many times the danger level is 3, but due to wind slabs, which are manageable in couloirs, which is what i mostly ski.

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Quote:

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Originally Posted by subtle plague

That is the problem with deep instabilities. Low risk high consequences. The reduction method only calculates your risk of setting of a slide at a certain risk level in a certain aspect.(you get better reduction factors if you don't ski the aspects mentioned in the bulletin or leave out sector north and so on). The rest is avie bulletin text advice (e. g. Deep instabilities) , terrain management etc.

And I said you can't deduct a level.. It's just that the outcome is the same because of the added reduction factor. Technicalities. I know.

And here millions of people use it. And fatalities have been constant or decreasing despite the increased traffic in the back country. So it works. And skier compaction works (I see it as one of the reasons that there aren't as many accidents as expected with the freeride trend because people ski crazy shit these days at level 3 and even 4!) remember we don't have inbounds.

You have to factor terrain in if you have low risk high consequence. And in 16/17 we had that and I didn't tour because the bulletin warned that despite the risk moderate it can be dangerous because of size. in that winter guided groups have been buried up to 12m deep. I didn't tour that year. It got super warm after each dump when we finally has a base so wasn't that tempted. I know that klar didn't ski many of her usual haunts that year because the slopes were too big for that constellation. (e.g. The slope the guys were buried 12m)


Edit: and of course you look for local signs in the advanced method: amount of fresh snow, wind, snowpack, but also group size and so on. The reduction or 3x3 filter method is pretty nuanced, really.

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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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."