Educating Backcountry Skiers - Deep Instabilities

[TahoeJ]

Re: Sheep Creek - they did travel one at a time, just not far enough apart. Of course their line choice was the bigger problem.

I had never heard of Project Zero before I read about it in Backcountry today... my first thought was, good luck with that.

[MagnificentUnicorn]

Re: Sheep Creek - they did travel one at a time, just not far enough apart. Of course their line choice was the bigger problem.

I had never heard of Project Zero before I read about it in Backcountry today... my first thought was, good luck with that.

They didn't travel one at a time. They just increased their interval. Not the same at all. One at a time means only one person exposed to the hazard and everyone else is waiting and watching.

[TahoeJ]

They didn't travel one at a time. They just increased their interval. Not the same at all. One at a time means only one person exposed to the hazard and everyone else is waiting and watching.

Yes, I understand that. I mis-remembered because three of them were waiting on their "island of safety" for the others to arrive, but you're right that they just spread out by 50 feet and kept going. Everything about that incident is just strange - I'm not sure it really makes for a great case study to be honest. http://www.americanavalancheassociat...3_Feb_2014.pdf

[SkyIsland]

They didn't travel one at a time. They just increased their interval. Not the same at all. One at a time means only one person exposed to the hazard and everyone else is waiting and watching.

Yes, they also had even read about DPS as the primary avalanche problem that morning so the more experienced members of the group even had consciousness of the risk. There was a lot in common between that accident and several others over a few year period, including lacking travel protocol and treating trees as islands of safety. Because of the time cost of one at a time, it can be hard to manage a larger group, among other things, but it is a good case study on multiple levels.

[MagnificentUnicorn]

Yes, they also had even read about DPS as the primary avalanche problem that morning so the more experienced members of the group even had consciousness of the risk. There was a lot in common between that accident and several others over a few year period, including lacking travel protocol and treating trees as islands of safety. Because of the time cost of one at a time, it can be hard to manage a larger group, among other things, but it is a good case study on multiple levels.

Another curious thing is why they would choose and "island of safety" on the same slope they were concerned about with no real prominence. I could understand if it was a sub ridge on the slope with significant prominence from the general slope and travel to it one at a time, if that was the only option. This isn't meant to imply they should have been there in the first place.

[Telemarketeer]

Yes, I understand that. I mis-remembered because three of them were waiting on their "island of safety" for the others to arrive, but you're right that they just spread out by 50 feet and kept going. Everything about that incident is just strange - I'm not sure it really makes for a great case study to be honest. http://www.americanavalancheassociat...3_Feb_2014.pdf

Makes for a great case study for decision making, route selection, and human errors. They had the forecast, understood it as much as they possibly could, having it explained to them by Scott Tepfer, a CAIC forecaster the night before and reviewed it that morning as well. Where things broke down was their travel protocols and decisions making. They were trying to access a different slope, and didn't give enough thought to the slope they were crossing even though it was the exact thing they were trying to avoid completely. Almost every other party that day was across the highway skiing Trelease, a S facing, low angle slope with very little avalanche hazard.

[TahoeJ]

I guess I just mean that the incident lacks any nuance and it's more of a big "what were they thinking?"

[Telemarketeer]

I guess I just mean that the incident lacks any nuance and it's more of a big "what were they thinking?"

So one of the deadliest avalanches in CO history doesn't have enough "Nuance" for you? In a thread about PWLs and DPSs, I'd say it fits right in. A lot to be learned from mistakes made and why they were.

[kootenayskier]

IMO the CAA does a great job with its special bulletins. http://www.avalanche.ca/blogs/danger...itions-brewing
If anyone cares, the appropriate information is in circulation.

[SkyIsland]

Another curious thing is why they would choose and "island of safety" on the same slope they were concerned about with no real prominence. I could understand if it was a sub ridge on the slope with significant prominence from the general slope and travel to it one at a time, if that was the only option. This isn't meant to imply they should have been there in the first place.

This is a great example of one of the bits of "nuance" to be gained from looking at the incident.

While we don't have a record of their specific conversations, there was and is this idea floating around that trees = safety. The last 20+ years may have seen efforts to change that notion, but it's still out there. While it's possible that they chose the grove of trees simply as a visual marker, I think it is much more likely that they just plugged in "trees=safe" and headed there.

[TahoeJ]

So one of the deadliest avalanches in CO history doesn't have enough "Nuance" for you? In a thread about PWLs and DPSs, I'd say it fits right in. A lot to be learned from mistakes made and why they were.

A tragic result doesn't necessarily make an incident nuanced. Blatant disregard for the specific hazards emphasized in the avy bulletin (which said specifically to avoid travel beneath or adjacent to steeper slopes due to many observations of remote triggering) and some very poor decision making, isn't nuanced IMO. There are plenty of other incidents where as you read along you're saying, okay, I can understand where they were coming from. This was not one of them. But whatever, that's just my opinion and you don't have to agree with it.

[covert]

I think almost every accident or near-miss has nuance that is frequently downplayed or overlooked. By definition, nuance is less than obvious, you have to look for it.

[whipski]

"how do you do that voodoo that you do do"?

[rod9301]

I always thought that couloirs were safer than big faces, from an avie standpoint.

But I never came up with a reasonable reason, except perhaps better anchored.

Now, I think it's because the snow is deeper in a couloir than on an adjacent face, because snow sloughs off the walls into the couloir.

And with deeper snow, you have a lower temperature gradient, so a buried weak layer has a better chance of healing.

Maybe.

[sf]

And with deeper snow, you have a lower temperature gradient, so a buried weak layer has a better chance of healing.

I'm no expert, so bear with me here........ My understanding is that (and of course this is a simplification):

A lower temperature gradient will reduce the chance of some kinds of weak layers forming within the snowpack (at the bottom primarily, or beneath ice layers), but it will not affect the rate of bonding within the snowpack. A buried weak layer will primarily heal because it in some way or another turns into a melt form and refreezes.

Ok, fire away....

[rod9301]

Is it possible then that the faceted layer will never form?

[sf]

Is it possible then that the faceted layer will never form?

Again, I'm no expert, but yes; given the same temperature in an area, a locally deeper snow pack should produce less depth hoar. If your theory about snow falling from the rock walls leads to a deeper snowpack is right, then there should be less depth hoar. But a little bit is still dangerous. And as you know, any number of other factors affect the snow pack. For example; sunlight/heat, or the lack of it, will be one factor affecting stabilization. Or; If a couloir is sheltered from wind, maybe surface hoar might survive and produce a weak layer just as dangerous as the depth hoar, etc

In another words; I feel this is a bit hypothetical.
If a person said to me "I'm not going to ski that powder field today, but in that couloir I should be fine", based on only this.........no bueno.

[Ted26]

As has already been mentioned to some extent, I think there's a tendency to associate danger rating with the severity of the slide. People see "high" and think the avalanches will be really dangerous that day, but the rating really only conveys probability. People see "moderate" and assume the avalanches themselves won't be that dangerous that day, but again the rating is for probability, not severity. I feel this nuance is too often ignored and the rating becomes associated with severity rather than probability, which is a result of human psychology to some extent. Given that, I don't really know how deep slab problems can be better conveyed in a way that will lead people to make better decisions.

[SkyIsland]

I always thought that couloirs were safer than big faces, from an avie standpoint.

But I never came up with a reasonable reason, except perhaps better anchored.

Now, I think it's because the snow is deeper in a couloir than on an adjacent face, because snow sloughs off the walls into the couloir.

And with deeper snow, you have a lower temperature gradient, so a buried weak layer has a better chance of healing.

Maybe.

This is sort of a variation on the trees adding to risk theme. How much gets added to consequence is going to be very couloir-dependent. On average I think it's fair to say your probabiity assessment needs to take into several factors, and may or may not be lower versus higher. But, your consequence is normally going to be far higher. Possibly not as clear a case as steep trees in terms of piling on risk, though.

[TahoeJ]

Right. I'd much rather go for a ride down an open bowl than get flushed through the choke of a rock walled couloir. Cornice hazard is also much greater since there's not much of a chance of dodging it compared to an open face (assuming you are booting up the couloir).

[Bunion 2020]

I'm no expert, so bear with me here........ My understanding is that (and of course this is a simplification):

A lower temperature gradient will reduce the chance of some kinds of weak layers forming within the snowpack (at the bottom primarily, or beneath ice layers), but it will not affect the rate of bonding within the snowpack. A buried weak layer will primarily heal because it in some way or another turns into a melt form and refreezes.

Ok, fire away....

You have it sort of close. Snow Metamorphism is interesting as a subject but is probably way over emphasized, especially for the recreational skier.

A lower temperature gradient will reduce the chance of some kinds of weak layers forming within the snowpack (at the bottom primarily, or beneath ice layers), but it will not affect the rate of bonding within the snowpack. A buried weak layer will primarily heal because it in some way or another turns into a melt form and refreezes.

To clarify that statement.

A lower or smaller Temp. Gradient will encourage the formation of smaller and more rounded grains. Due to shape and size those grains will tend to form bonds between the grains and overall the snow layer should gain strength.

A higher or stronger Temp. Gradient will encourage the growth of larger and more squarish/faceted grains. Because of the larger size and shape there is less contact area between the grains so the bonds are weaker and there are less of them and generally speaking this is a weaker structure.

Unless the grains temperature rises above 0 Deg C there isn't any melting, just water vapor transport which is always happening within the snow pack but is driven by temperature gradients or the lack of them.

A strong Temp Gradient (> 1 Deg C/10 CM) will generally tend to form faceted grains.

A weak Temp Gradient (< 1 Deg C/10 CM) will generally form rounded grains.

Does that make sense?

As for facets, they will usually always be present during the early part of the winter, the exception being in a Maritime regime but that is a maybe yes, maybe no.

As the snow pack depth increases, the Temp. Gradient should become smaller or less and the facets may tend toward rounding and gaining strength.

Note all the qualifier words used in the explanation.

[rod9301]

Right. I'd much rather go for a ride down an open bowl than get flushed through the choke of a rock walled couloir. Cornice hazard is also much greater since there's not much of a chance of dodging it compared to an open face (assuming you are booting up the couloir).

Since I like skiing couloirs, I thought about consequences a lot.

Assuming the couloir is straight, without a dog leg, once the avie reaches the apron, the snow will spread over a much larger area, so you have less of a chance to get buried.

I think hitting a tree in an avie is a lot more likely than hitting the walls of the couloir.

Cornices, no doubt, as are upper walls that take sunlight.

I was only talking about the much deeper snow in a couloir as producing a lower temp gradient than in an adjacent face.

And not all couloirs will have deeper snow, some are gullies without high walls, or the walls are too vertical.

To get deeper snow, the walls must open up, so the couloir is much wider at the top of the walls than at the bottom.
In other words, the walls must have an angle, not vertical, say 60 degrees, then all the snow that falls on the walls will slough off into the couloir, adding to the snow depth.

[rod9301]

And by the way, I was thinking of a maritime climate. Even though, I could see that if you have a depth of 3meters in a couloir (vs half m on an adjacent face) in a continental climate, the snow could act more like a maritime, or in between, because of the lower temperature gradient.

Similar to high elevations close to the coast where the snow pack will have more continental features.

[klar]

To get deeper snow, the walls must open up, so the couloir is much wider at the top of the walls than at the bottom.
In other words, the walls must have an angle, not vertical, say 60 degrees, then all the snow that falls on the walls will slough off into the couloir, adding to the snow depth.

My take on this super hypothetical discussion: If the snowpack in a couloir is significantly different than on an adjacent, open slope, I suspect it has more to do with differences in the compaction/settling process due to snow falling in from the walls (mechanical, destructive) and the assumed much larger snow depth (weight/overburden) than with facets that may or may not form due to different temperature gradients.

Not sure if this fits your definition of a couloir but for me this was one of the more educational examples of persistent weak layer avalanches I've seen. Several people had skied it before someone else triggered it. A lot of similar terrain got skied that day without issue.

[covert]

I like couloirs because I find them less complex than open terrain.

The North American Public Avalanche Danger Scale actually addresses Likelihood, Size, and Distribution.
http://www.avalanche.org/danger_card.php

The danger rating can never be more than the broadest of brush strokes though. The useful information is always in the problem descriptions and the discussion.