Avalanche Situation

[jmeb]

"Buried" being the operative word here. Basically, the only way for the problem to go away is for the snow/layer to melt.

Not true. Snowpack metamorphizes happen. Bridging is a real thing. Avalanches flush layers.

 

[HardDaysNight]

But all that said, this is clearly an area with significant terrain over the "rule of thumb" 30 degrees, which is just a rule of thumb anyway as has been discussed above regarding the Mill Creek slide

This is really important. It’s obviously true that slopes of 30° or less aren’t as prone to sliding as steeper ones but it’s absolutely no guarantee. Much depends on the crack-face friction characteristics of the snow in the area in question. Slopes as shallow as 20° can slide! You can bet that this would be a year when that might happen.

 

[jmeb]

Slopes as shallow as 20° can slide! You can bet that this would be a year when that might happen.

Serious question: any documented instances of slopes <27 or 28 degrees sliding in a hard or soft slab incident? My understanding is that those truly low-gradient avalanches are glide, (or at least wet-snow) avalanches. Which present at entirely different times of the year and temperatures.

 

[HardDaysNight]

Mechanisms of slab avalanche release and impact in the Dyatlov Pass incident in 1959
An unsolved fatal accident of 9 Russian mountaineers in the northern Urals in 1959 can be explained by a slab avalanche released due to a slope cut to install the tent and wind-blown snow accumulation affected by an irregular topography, according to analytical and numerical models.

www.nature.com

To quote:

“While a 28° slope may still be perceived as being too mild to cause an avalanche—based on the often-quoted and implicit rule of thumb that a minimum of 30° is required10—in reality, the critical slope angle can be as low11 as 20° (Fig. 2b), provided the dynamic friction angle (sometimes called crack-face friction11) of the snow is sufficiently low. In fact, field measurements have shown that the dynamic friction angle of snow can be as low as 15°, especially for very low temperatures12.”

The references in the Nature article speak to your question. Certainly mid-winter slides happen at slope angles well below 30° although I’d think 20° must be exceptional.

 

[dbostedo]

FWIW, the AIARE page has these two statements on the Slope Angle page...

"Slab avalanches generally occur at slope angles between 25 and 60 degrees."

"Most slab avalanches occur with start zones that have slope angles between 30 and 45 degrees."

 

[James]

Mechanisms of slab avalanche release and impact in the Dyatlov Pass incident in 1959
An unsolved fatal accident of 9 Russian mountaineers in the northern Urals in 1959 can be explained by a slab avalanche released due to a slope cut to install the tent and wind-blown snow accumulation affected by an irregular topography, according to analytical and numerical models.

www.nature.com

To quote:

“While a 28° slope may still be perceived as being too mild to cause an avalanche—based on the often-quoted and implicit rule of thumb that a minimum of 30° is required10—in reality, the critical slope angle can be as low11 as 20° (Fig. 2b), provided the dynamic friction angle (sometimes called crack-face friction11) of the snow is sufficiently low. In fact, field measurements have shown that the dynamic friction angle of snow can be as low as 15°, especially for very low temperatures12.”

The references in the Nature article speak to your question. Certainly mid-winter slides happen at slope angles well below 30° although I’d think 20° must be exceptional.

Interesting. What a bizarre event. Still doesn’t explain a bunch of the injuries and other weird things, but the avalanche theory itself seems plausible.
Essentially they dug a snow pit and pitched their tent in it, the slab became more loaded from wind, and eventually broke due to very unusual topogrophy.
Note to self, dig a snow cave instead.

 

[Ken_R]

I think that's the right area... FATMAP does have slightly different shading. It's probably right around 35 degrees and/or may depend on what topo maps and data underlie the shading. Caltopo shows something similar, with pockets above and below 35 degrees.

FATMAP view:
View attachment 124721


But all that said, this is clearly an area with significant terrain over the "rule of thumb" 30 degrees, which is just a rule of thumb anyway as has been discussed above regarding the Mill Creek slide.

The only point in talking about 35 degrees, was that a lot of the area is below that, so it may not be viewed as "extreme" terrain, or what folks in resorts would think is beyond any normal steepness. I was responding to a comment that it looks "relatively tame and not very steep at all". But certainly still clear avy terrain.

The final report is in. Per the report: The alpha angle of the avalanche was 23 degrees. The victim was traveling alone, he was wearing an airbag backpack which he activated, he had the backpack sternum strap on but not the leg loops (the strap can be a choking hazard without the leg loops, it might have contributed to his death), the victim had suffered significant trauma even with the airbag deployed.

That is key to know. That is pretty low number but not the lowest. IIRC I have measured 20º alpha angles in some avalanches I have come across in Colorado. The lowest possible I think is in the 18~19º range (dry snow avalanches). If you know you will skiing near steep slopes and you want to be safe you can use an app to measure the alpha angle pretty accurately.

Conditions right now are such that you not only need to worry about the steepness of the slopes you are on but also the distance you are from avalanche prone slopes. Most of the recent deadly avalanches have been triggered from below and some from a distance. Find the right spot and boom, it all comes crashing down.

 

[locknload]

Mechanisms of slab avalanche release and impact in the Dyatlov Pass incident in 1959
An unsolved fatal accident of 9 Russian mountaineers in the northern Urals in 1959 can be explained by a slab avalanche released due to a slope cut to install the tent and wind-blown snow accumulation affected by an irregular topography, according to analytical and numerical models.

www.nature.com

To quote:

“While a 28° slope may still be perceived as being too mild to cause an avalanche—based on the often-quoted and implicit rule of thumb that a minimum of 30° is required10—in reality, the critical slope angle can be as low11 as 20° (Fig. 2b), provided the dynamic friction angle (sometimes called crack-face friction11) of the snow is sufficiently low. In fact, field measurements have shown that the dynamic friction angle of snow can be as low as 15°, especially for very low temperatures12.”

The references in the Nature article speak to your question. Certainly mid-winter slides happen at slope angles well below 30° although I’d think 20° must be exceptional.

Well now...some heavy math in that article...but definitely an interesting unsolved mystery or maybe partially solved. 20 degrees seems incredibly low to slide but it probably could happen under the right circumstances. I always like the magazine on the glass table analogy. The magazine is the slab and keep gently tipping the table to see when it actually slides off...not a perfect away but a good way to picture the way a slab releases as a massive piece of snow and god help you if you are below it.

 

[tball]

The comments in the final Mt Trelease report nicely emphasize five educational points broken into paragraphs:

Traveling alone in avalanche terrain increases the consequences if you are caught in an avalanche. Although this was a very large avalanche, Rider 2’s head was buried only a foot beneath the snow surface. A partner that was not in the avalanche may have quickly rescued Rider 2. Rider 2 did have traumatic injuries, so we don’t know if a speedy recovery would have produced a different outcome. ​

​

The avalanche ran over a well-used skin track. During certain conditions it might be reasonable to put a skin track in this location. On the day of the accident the avalanche danger was Considerable (Level 3), and there had been reports of remotely triggered and wide-breaking avalanches for over two months. During unusual snowpack conditions, “normal” routes and what are considered safe spots must be re-evaluated.​

​

The victim was wearing an avalanche airbag but no avalanche rescue transceiver. Although we do not know the exact time the avalanche released, it is safe to assume Rider 1 would have recovered Rider 2 much faster if he was wearing a transceiver. We recommend you always wear a transceiver when you are traveling in avalanche terrain, even if you are traveling by yourself. There is always a chance another group could rescue you if you are in an area with other people. It will also help search and rescue groups find you and return your remains to your family if you are killed in the mountains. Traveling in the mountains alone is a personal choice, but if you get into an accident people will come looking for you. If you are in an avalanche and not wearing a transceiver it could take them a long time to find you. An extended search and rescue effort will put members of your social circle and search and rescue volunteers in harm’s way in the days and weeks after the accident. Extended searches put volunteers at much greater risk and use resources needed to help other people. Your family members may have to wait until the snow melts to find you, and this will exacerbate an already devastating situation.​

​

Rider 2 deployed his avalanche airbag.The deployed bag may have kept him from being buried deeper, but it did not keep his head from being buried under the snow. When rescuers found Rider 2, he was wearing the sternum strap on his airbag pack but not the leg loop. The sternum strap was pushed up against his neck. As with any safety device, it is important to follow the manufacturer's instructions. Most airbags come with a leg loop to prevent the pack’s sternum strap from sliding up and posing a choking hazard. It also keeps your upper body closer to the bag. Problems with not using the leg loop on an avalanche airbag pack have been documented in other accident reports (Leahy 2013).​

​

Other backcountry tourers traveling in the area on this Sunday morning made a valiant effort to help search and rescue efforts and any potential victims. Skiers 1 and 2 and Rider 1 alerted 911 immediately and also coordinated their own rescue effort before organized rescue arrived. Without the efforts of these three tourers, it would be hard for authorities to know how many people were buried. The actions of the three tourers led to the relatively quick recovery of the transceiver-less victim and an efficient clearing of the accident site.​

Lessons learned, even if just tragic reminders, are why I read these reports. The point about wearing transceivers also applies to inbounds skiers. I need to wear mine inbounds more often than just on big days.

Edit to add that the point about not skiing alone also applies to inbounds skiing. It's amazing how your brain can block what you don't want to hear. I had to read it a second time before realizing it applies to me big time.

 

[dusty]

^^^ There's a trailhead at the Loveland Pass exit plus a gate near the bottom of 8. I've only hiked from the I-70 trailhead in the summer. Not sure which access most skiers use.

I put a red circle at the approximate location of the backcountry gate. I don't think there's another gate up higher, but someone please correct me if I'm wrong.

View attachment 124616

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There used to be a gate up high skier's left of rock chutes. I think they keep moving it higher and I'm not sure if its there anymore. It was more used for golden bear and hanger/citadel laps I thought.

 

[Lauren]

Went to CAIC to read the Trelease report...saw this:

Hope this one ends well

 

[jmeb]

There used to be a gate up high skier's left of rock chutes. I think they keep moving it higher and I'm not sure if its there anymore. It was more used for golden bear and hanger/citadel laps I thought.

Not there anymore. Only gate is down below Hook'em'Horns along the runout of Awesome.

This photo is haunting. The skin track that you see coming out of the debris is traveled by many people, often.

 

[charlier]

I finally had a chance to listen to this whole thing. Really interesting conversation, with a lot of good information. I few points that stood out to me in the discussion:

- Discussion on float packs and if they give you a false sense of security, or are they actually safer. I feel like both of these things are true. My instructor for an AIARE course discussed the impacts float packs had on his decision making. For a period of time he always wore one, and slowly realized he made less conservative decisions when he had it. Now he leaves it home more and that takes the decision away from him when he's in those questionable areas.
- Discussion on the emphasis on snow pits in AIARE courses, and how there should be more emphasis on terrain management and "feeling" the snow, rather than full blown snow science. Not saying they should take pits out of the equation, just that they may not be the most important thing for people to learn that are starting off in the backcountry. They did discuss the importance of feeling the snow, testing with your poles, and hasty pits.

Based on my experience, many AIARE instructors use float packs. My feeling is that education, and not leaving your airbag pack at home, is the solution. AIARE Level 1 courses emphasize using the avy forecast to choice safe terrain options. The L1 class much more focused learning on safe travel through avalanche terrain, group dynamics, team communication and reinforces decision-making by consensus. There is not a lot of emphasis on snow science.

 

[Lauren]

Based on my experience, many AIARE instructors use float packs. My feeling is that education, and not leaving your airbag pack at home, is the solution.

I think there's a time and a place for airbags. But if you're making a decision to stay out of avalanche terrain based on the current conditions, I think it's fine to leave that pack at home. When you make that decision, you're committing to staying off of that terrain regardless of your feeling when you get to the trailhead...it's essentially putting all avalanche terrain (and below it) into your "red zone" for the day.

AIARE Level 1 courses emphasize using the avy forecast to choice safe terrain options. The L1 class much more focused learning on safe travel through avalanche terrain, group dynamics, team communication and reinforces decision-making by consensus. There is not a lot of emphasis on snow science.

This was also my experience when taking an L1 class as well. Maybe this is the norm? I made the point based on what was discussed in the interview.

 

[charlier]

I think there's a time and a place for airbags. But if you're making a decision to stay out of avalanche terrain based on the current conditions, I think it's fine to leave that pack at home. When you make that decision, you're committing to staying off of that terrain regardless of your feeling when you get to the trailhead...it's essentially putting all avalanche terrain (and below it) into your "red zone" for the day.

This was also my experience when taking an L1 class as well. Maybe this is the norm? I made the point based on what was discussed in the interview.

Whoops, I mis-read your post. In the IFMGA guiding and avy education community, many professionals use airbags, and I always discuss the proper use of float bags while teaching L1 classes. There have been a few studies regarding airbags and increased risk acceptance and a link to Pascal’s recent study -https://www.sciencedirect.com/science/article/pii/S2213078019300817

 

[DanoT]

there have been a few studies regarding airbags and increased risk acceptance

This argument of higher risk acceptance for airbags was also applied to helmets when they first became popular. But once helmets became ubiquitous and just normal safety gear, imo they no longer elicited above normal risky behaviour. I suggest that wider acceptance and use of airbags could also result in no increase in risk acceptance going forward.

 

[dbostedo]

But once helmets became ubiquitous and just normal safety gear, imo they no longer elicited above normal risky behaviour.

I don't know that that's actually true.

 

[Lauren]

This argument of higher risk acceptance for airbags was also applied to helmets when they first became popular. But once helmets became ubiquitous and just normal safety gear, imo they no longer elicited above normal risky behaviour. I suggest that wider acceptance and use of airbags could also result in no increase in risk acceptance going forward.

Do you think what is considered "normal risky behavior" has changed due to the use of helmets?

 

[crgildart]

Do you think what is considered "normal risky behavior" has changed due to the use of helmets?

I'm way more likely to quickly pull the bar down without asking anyone when everyone on the chair is wearing a helmet.

 

[DanoT]

I don't know that that's actually true.

Yeah, that is why I wrote "imo" because there is no real way of knowing for sure, but it is interesting to consider the impact of safety devices on risk behaviour.