The Brazil Nut Effect — How To Survive an Avalanche


Post by WildSnow.com blogger | November 24, 2006      

The amount of knowledge we have about snow avalanches has increased immensely over the past several decades. Using this information, experts are constantly reformulating survival techniques and devising improved safety gear. The Avalung came out of knowledge that avalanche victims are frequently poisoned to death by their own exhalations. Beacon improvements come from knowing how important things like reliability and ease-of-use are to a quick search. Knowing how violent being ‘lanched is, experts now recommend keeping your backpack tightly strapped when in avalanche terrain so it’ll protect your spine if you take a ride.

More, experts are re-thinking what you need to do while you’re caught in a snow slide. The recommended plan used to be fight and swim — do anything to stay on top or escape to the side. This appears to be changing. Dale Atkins, who investigated avalanche accidents for years while working with the Colorado Avalanche Information Center, is promulgating a new way of looking at survival. In an excellent presentation, he recommends one thing when you’re caught: Don’t bother with attempts to swim or fight. Instead, get your hands in front of your face, keep them there, and if you’re buried do anything to make an air pocket when the slide stops. (Or if you have an Avalung, concentrate on getting it in your mouth and keeping it there.)

Beyond the importance of a breathing space, the key concept Atkins covers is that while a snow avalanche behaves somewhat like a river or waterfall, it is actually a “granular flow,” meaning a snow avalanche is a bunch of solid particles falling down a mountain. Such behavior is similar to dumping sand out of a wheelbarrow down a hillside. In a granular flow, larger or less dense objects tend to rise to the surface. For example, snowmobiles are twice as likely to stay on the surface of an avalanche than a human. And humans tend to rise to the top as well, hence the large percentage of people avalanched who end up unburied. He calls this the “Brazil nut effect,” as when you shake a can of mixed nuts and all the larger nuts rise to the top. As for swimming versus concentrating on an air pocket, the point of this concept is that swimming and struggling have less to do with ending up unburied than simple physics. Thus, working to create an air pocket may be more important than things (like swimming) that keep your hands away from your face.

As for gear, the reality of the Brazil nut effect means that avalanche airbags are quite possibly as effective as their makers claim they are, and truly worth developing as a viable avalanche safety device. I’m certain we’ll see this happen — it’ll be interesting.



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Comments

7 Responses to “The Brazil Nut Effect — How To Survive an Avalanche”

  1. Matt Kinney November 24th, 2006 12:55 pm

    Thanks for the link Lou. Very good interview with D. Atkins. Would not have found it without Wildsnow.

  2. Bob Berwyn November 24th, 2006 2:31 pm

    Hey Lou, I saw Dale’s Brazil Nut presentation at the Colorado Snow and Avalanche Workshop back in October. Interesting stuff. There was a lot of discussion afterward among the snow-pros present — ski patrollers, avy forecasters, etc — about swim v. no-swim. Not everyone agreed with Dale and there were a few avalanche survivors there who attributed their presence to the fact that they swam when they were caught. Dale’s idea is really interesting and the physics seem to jibe, but there are still a lot of people out there who say “Swim like crazy,” then go for the airpocket if burial seems inevitable. Also, the way I heard it, one his big points was just to get people thinking about what they would do if caught. I wrote a blurb in the Summit Daily News about Dale’s talk, and Steve Lipsher also reported on it in the Denver Post.
    Summit Daily story http://www.summitdaily.com/article/20061025/NEWS/110250049&SearchID=73263952159929

    Denver Post story: http://www.denverpost.com/search/ci_4550539

  3. Lou November 24th, 2006 3:02 pm

    I think it all has to do with the size and density of the avalanche, and the discussion is moot without categorizing what kind of slide for a given behavior. In a big one you have no body control, in a small one you could swim for a few seconds then, if you could see you were near the end, get your hands by your face. And perhaps it’s all kind of ludicrous, as the things are incredibly likely to take your life no matter what. Sort of like talking about what to do if you see you’re heading into a headon crash with a loaded cement truck.

  4. Nick Thomas November 25th, 2006 6:40 am

    I always thought that the very old advice to dump your sack when caught was wrong. Unless you are carrying bricks your sack will be less dense than you are and should therefore help float you to the surface. Any protection for the spine is a bonus.

  5. Dan November 25th, 2006 9:20 am

    One time on Snodgrass mountain in Crested Butte I was hit from behind by a powder slide and knocked down head first. After that the whole thing grew exponentially. I was sling head first downhill on my belly and getting deeeper. I arched my back as much as I could and this action caused me to rise up in the snowpack to the top. This seemed to work real well in this situation and I believe it saved me that day. My body poition was like a boat, or big ski and the snow was pushed underneath me and my head stayed out of the depths.Hope I never have to do that again but in the head down/face down position this seemed to be the instinct and it worked.

  6. avy jong November 27th, 2006 7:39 am

    total avy jong here, but interested and reading… as a possible thought starter: the last reply (Ie “boat like body shape”) instantly made me think of body surfing. Granted, an avy is more like a wave that has broken than a curl but still…

  7. david beck November 27th, 2006 10:16 am

    what does one do when hit by a Mac Truck? At times in a more gentile, non-turbulant avalanche one can swim, and when stopping make an air space with one hand and stick the other hand up as a marker.
    I wuould guess that if there is a lot of force on your body a rounded ball would have an easier ride then having arms and legs sticking out and getting turned any which way.
    Dales presentations are some of the most thought out. I think air bags work; your body will be a punching bag near the surface rather than down deep.

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