Skier compaction in the backcountry

[palikona]

I’ve been thinking a lot about skier compaction in the backcountry, especially at very popular spots like Berthoud Pass, Loveland Pass and Meadow Mtn Bear Minturn.

For instance, in specific areas of Berthoud Pass (Mainline, Powderline/Bonanza...the 20° slopes right off the parking lot at the top), there appears to be so much traffic starting after the first snowfall, that I wonder if the amount of skier compaction makes these slopes almost as safe as an inbounds resort?

There’s also a ton of skier compaction in other steeper areas like the 80s/90s but the pitch is steep so I figure those are going to be more hazardous no matter what.

Thoughts?

 

[Mike Rogers]

The popular sidecountry at louise and sunshine get hit pretty hard, yet people get caught in slides every year.

Skier compaction can make slopes safer, but it is difficult for non-pros to determine how much safer a popular spot might be....and people seem to overestimate the effects of skier compaction.

I don't know the area that you are referencing. A heavily trafficked 20 degree slope should be treated as backcountry, but assuming there isn't overhead or a nasty terrain trap, it is probably fairly low risk.

 

[Rod9301]

I assume you guys are talking about Continental climate areas. Where it doesn't really matter how many skiers ski it, a weak persistent layer can still kill you.

 

[Analisa]

If it's a 20 degree slope, it's not avalanche terrain. The mellowest start zones tend to be around 25-30 degrees, depending on how dry or sticky the snowpack is in the area. Otherwise, I wouldn't count on compaction for slide protection. Any amount of extra safety you get from compaction is likely offset by the "social proof" heuristic, where you overestimate how safe it is based on other people being in the same area for really popular spots.

My avy forecaster friend always cites an example in his avy awareness classes from CO where a woman triggered a slide at a popular spot that has webcam coverage. They counted the number of skiers who skied the same slope that day something like 80-100 skiers had skied the slope before her.

 

[Near Nyquist]

Anytime you are out of bounds
You are out of bounds
I didn’t think you should treat it any differently
Than any other backcountry situation
It’s your life and that of others that you risk

 

[Ken_R]

I’ve been thinking a lot about skier compaction in the backcountry, especially at very popular spots like Berthoud Pass, Loveland Pass and Meadow Mtn Bear Minturn.

For instance, in specific areas of Berthoud Pass (Mainline, Powderline/Bonanza...the 20° slopes right off the parking lot at the top), there appears to be so much traffic starting after the first snowfall, that I wonder if the amount of skier compaction makes these slopes almost as safe as an inbounds resort?

There’s also a ton of skier compaction in other steeper areas like the 80s/90s but the pitch is steep so I figure those are going to be more hazardous no matter what.

Thoughts?

Generally even at busy spots ski traffic is not even close to being enough compared to a resort. Also, slope angle needs to be at around 30º or above for snow to slide. At Berthoud most of the steep slopes are off the ridge and are exposed to wind so they get loaded up quickly during periods of high winds and are untouched for relatively long periods of time so the slabs remain intact and can slide easily.

Bottom line, you need to treat steep slopes with respect regardless of traffic.

 

[Slim]

I don’t have the link handy, but I recently read an article that tested skier compaction, and the conclusion was that skier compaction is not very effective at reducing the avalanche problem. This was inbounds even.

 

[jmeb]

Skied a couple days on Berthoud recently with a local SAR member who just ticked 400 days at Berthoud. This topic came up on the skin track. Short answer is maybe, but there is no way to tell and it would be foolish to make decisions using it as part of the criteria.

If you at actual avalanche compaction regimes using human power , it is done systematically, early, and typically in boots. Highlands bowl is a good example.

 

[Slim]

The boots vs ski was the critical difference. Skis don’t penetrate the snowpack deeply enough to disturb any (weak)layers.

 

[palikona]

All very interesting comments. I figured as such but am interested in this.

So I am curious why more slopes around 30-35° inbounds that don’t get skied that much don't slide more? For instance, I bet more people ski some of the lines on Loveland Pass that could slide than some remote lines in the Stone Creek Chutes at BC, or every square foot of Breck’s wind-loaded alpine. Patrol obviously bombs certain spots in Peak 7 Bowl, but does that really mitigate the danger and break up the persistent layers underneathe all over? There a lot of acreage up there that seems like it’s not skied a ton and therefore doesn’t get the skier compaction and doesn’t get bombed.

 

[Analisa]

I’m not super familiar with spots around CO, but patrollers either feel they can mitigate most of the risk through bombing (or other techniques), or if they know they can’t keep up with snowfall or wind transfer, they’ll usually shut down the area. Slackcountry gets a lot of people in trouble, since boundaries start to get fuzzy, and they can’t mitigate all the risk, so there are definitely days I ski with a beacon+shovel+probe inbounds.

 

[headybrew]

I’ve been thinking a lot about skier compaction in the backcountry

For instance, in specific areas of Berthoud Pass (Mainline, Powderline/Bonanza...the 20° slopes right off the parking lot at the top), there appears to be so much traffic starting after the first snowfall, that I wonder if the amount of skier compaction makes these slopes almost as safe as an inbounds resort?


Thoughts?

I’ve never skied it but would assume all the low angle stuff directly ABOVE the parking lot at Berthoud is safe. They wouldn’t build a parking lot in an avalanche run out zone would they?

 

[Analisa]

@headybrew I mean, there’s a slide path at Crystal Mountain called “Employee Housing” for a reason.

If people haven’t heard of Caltopo, it’s a great topographic map site where you can flip on slope angle shading and find out easily whether you are or aren’t on slide terrain. Gaia’s also incorporated it into their subscription plan so you can see it in real time.

 

[tball]

So I am curious why more slopes around 30-35° inbounds that don’t get skied that much don't slide more? For instance, I bet more people ski some of the lines on Loveland Pass that could slide than some remote lines in the Stone Creek Chutes at BC, or every square foot of Breck’s wind-loaded alpine. Patrol obviously bombs certain spots in Peak 7 Bowl, but does that really mitigate the danger and break up the persistent layers underneathe all over? There a lot of acreage up there that seems like it’s not skied a ton and therefore doesn’t get the skier compaction and doesn’t get bombed.

Patrol goes to great lengths to break up the persistent layers underneath the entire slope. They won't open the slope until they believe they have, except maybe on Prima Cornice at Vail.

You have to have faith in the ski area to do proper control work.

Some or all of these techniques are used, and probably others I'm missing:

1. Boot pack the entire slope from day one.
2. Use a compaction roller to break up the persistent slabs on the entire slope.
   
3. Bomb the crap out of it until the slope either slides to the ground to start over or it looks like a war zone if it doesn't slide.

The first two are more work, but get terrain open sooner by preserving the snow.

Here's a good story from local Denver TV news about compaction rolling at Copper that also has a good overview of the mitigation process:
https://www.9news.com/article/news/local/the-new-way-copper-is-preventing-avalanches/73-381348032

 

[jmeb]

I’ve never skied it but would assume all the low angle stuff directly ABOVE the parking lot at Berthoud is safe. They wouldn’t build a parking lot in an avalanche run out zone would they?

The stuff immediately above is fine. It's not steep enough to slide.

The problem is, it is very very easy to ski into avalanche terrain from just above the parking lot by simply following some fresh snow or a different fall line. Not to mention surprise cliffs.

 

[headybrew]

The stuff immediately above is fine. It's not steep enough to slide.

The problem is, it is very very easy to ski into avalanche terrain from just above the parking lot by simply following some fresh snow or a different fall line. Not to mention surprise cliffs.

Which is exactly why I have not skied on the pass. It seems that most of the people I talk to who go up there (and who try to get me up there) are all fooling themselves that since everyone else is doing it that it is safe.

 

[jmeb]

Which is exactly why I have not skied on the pass. It seems that most of the people I talk to who go up there (and who try to get me up there) are all fooling themselves that since everyone else is doing it that it is safe.

It can be completely safe. You just need some basic route planning skills and be able to stick to a plan. The most dangerous thing about the pass is other users (in very particular spots that are easily avoided).

I'm not fooling myself to in saying I've skied the pass safely several dozen times. It has nothing to do with what other people are doing. And its certainly not safe if you're skiing something just because other people did which is classic heuristic trap in the backcountry -- the "T" and "S" of FACETS.

 

[SBrown]

Patrol goes to great lengths to break up the persistent layers underneath the entire slope. They won't open the slope until they believe they have, except maybe on Prima Cornice at Vail.

You have to have faith in the ski area to do proper control work.

Some or all of these techniques are used, and probably others I'm missing:

1. Boot pack the entire slope from day one.
2. Use a compaction roller to break up the persistent slabs on the entire slope.
   
3. Bomb the crap out of it until the slope either slides to the ground to start over or it looks like a war zone if it doesn't slide.

The first two are more work, but get terrain open sooner by preserving the snow.

Here's a good story from local Denver TV news about compaction rolling at Copper that also has a good overview of the mitigation process:
https://www.9news.com/article/news/local/the-new-way-copper-is-preventing-avalanches/73-381348032

ABasin has one of these now, too. http://arapahoebasin.blogspot.com/2018/11/disruption-season.html

 

[DanoT]

If there is enough skier compaction to create moguls, then it should be safe.

Having said that, we once had a fissure open up across a in bounds run that was not steep enough to slide. The fissure was IIRC about 4 feet deep and 2-3 feet wide, maybe 20 feet long.

 

[palikona]

I use CalTopo often for slope angle / terrain research. Great resource.

Jmeb: I’d imagine the spots you’re talking about on Berthoud that are easily accessible from the parking lot are: HHA & Fingers, Floral Park, 80s -100s and the Chutes on the west side above the highway? Any others right there?

Has anyone here been caught or seen an avalanche below 25° on skier compacted terrain?