I am a longtime backcountry skier and lately I have been thinking about the math of skiing in avalanche terrain. On some basic level are we ultimately just playing a game of chance/probabilities if we ski in avalanche terrain? Of course those of us who have made a practice of backcountry travel do our best to minimize exposure through terrain management, snow analysis/knowledge, travel protocol, rescue equipment and skills, but if you travel in avalanche terrain ultimately it seems to me that your risk gets down to a game of probabilities that the above practices can mitigate but perhaps not as much as we'd like to think. The odds really start to stack the longer that you are in the game. The recent rash of high profile pro deaths who supposedly knew their stuff have made me think more about this.
I dusted off my rarely used math probabilities knowledge and played with some numbers to illustrate.
See here for the math theory applied to dice: http://hyperphysics.phy-astr.gsu.edu...math/dice.html Feel free to correct me where I'm wrong as I don't claim to be a probabilities expert.
To start lets say that you're ignorant and/or crazy. You ski on high danger days in known repeat offender slide paths. You're odds of triggering a slide are say 30%. It doesn't take a rocket scientist to figure out that you're probably going to trigger an avalanche, if not on the 1st run, then probably on the 2nd, 3rd, 4th, 5th or the 10th. You'll probably learn one way or another pretty fast.
But lets compare with a different situation and say that you're a seasoned traveller in the backcountry. You have taken classes, read books, practiced in the BC for years, etc. You're even so good that you can make the call to a 99.5% good accuracy rate. 995 times out of a thousand, when you chose to ski avalanche terrain, you will not trigger a slide because of your decisions. But lets say that you do that over the course of 20 years, 25 times a year, so 500 times.
Then you're chances of never in those 500 times of avalanche terrain travel of triggering a slide are:
(995/1000)^500 = 0.0816 or 8% or conversely you have a 92% chance of at some point triggering a slide. Basically the math of repeatedly probabilities means that you are highly likely to trigger a slide and at those kind of probabilities, you're most likely going to trigger more than one or two.
Once you've triggered slides then the math of survival comes into play. The math will of course vary, where if you're skiing mellow bowls with several skilled partners you're odds are better versus if you are skiing solo or skiing big couloirs over glaciers, trees, cliffs, or terrain traps. But the math still works against you if you are getting into slides. Lets say that the survivability is 70% and you are in 5 slides in your life. We run the same math as above and you have a 83% chance of dying in an avalanche. Survival odds = (7/10)^5 = 17% or 83% chance of dying.
So what? Well I guess maybe it might make you quit BC(or at least Avy terrain) skiing, as some friends of mine have. Or maybe you shrug it off and accept the odds as the price for the joy of glisse in steep terrain. But for me the lesson is that the math is always at work and that my imperative is to minimize my exposure whenever possible in both when/where/if I choose to ski in avalanche terrain. 99.5% isn't good enough over many years of repeated exposure. You've got to basically be perfect.
What do you think?
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