Why are death percentages of death from trauma in an avalanche so different between USA, Europe, and Canada?
I am reading this highly-rated book about avalanches and I was impressed by this sentence, in its beginning.
Over 25 percent of avalanche victims in the U.S. die from trauma from hitting trees and rocks on the way down (about 6 percent of avalanche victims in Europe and as many as 50 percent in Canada)
How can there be such a massive difference? 6 percent of people dying from trauma from hitting trees and rocks in Europe and 50 percent in Canada... with the US being about in the middle of that statistic.
The very first - quite rough - idea that comes to my mind is, there may be much more trees and rocks in the average Canadian ski route compared to European ones.
But, it sounds quite superficial. Still, those numbers differs too much; there must be some reason behind this spread. Does anyone knows what this reason is (or are)?
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I wouldn't read too much into any avalanche statistic. While there may be plausible reasons behind the difference, the data sizes are just too small to make any reliable comparisons.
Avalanches are exceptional events and avalanches that involve injuries that get reported are even more exceptional events. When you look at statistics based on infrequent events the "law of small numbers" applies. This means that you will see wide variation in any statistic simply because the sample size is so small. This in no way means that avalanches are not a serious risk in Canada, but since Canada only accounts for 10% or less of reported fatalities world wide, in a statistical sense you expect to see wide variations in a small sample.
Our brains are built to make coherent stories based on minimal data, and when we see such a striking difference, we want to build a story around it to explain it.
For example: Imagine that I flipped a coin 4 times in Canada and they all came up heads, I then flew to Europe and flipped a coin 4 times and they call came up tails. It would be very tempting to then create some theory around why coins behave differently in different continents, but in reality it's just random chance at work.
Learning to recognize and compensate for the inherent heuristic traps in your thinking is likely the most important skill for long term survival in avalanche terrain. Given the highly random nature of avalanches it's very easy to fall into the trap of confusing luck with skill.
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I don't have my copy of How to Survive in Avalanche Terrain in front of me, but one of the things that stood out to me relating to this is the wide variety of avalanche climates that exists not just from country to country but from mountain to mountain.
You've got intermountain, continental, and maritime avalanche climates all with their own habits and characteristics. There are so many variables at play here that Bruce was able to write an entire book about it. Avalanches tend to occur at a specific slope angle in each climate, and that angle can be very different from each other climate, but trees and rocks probably tend to exist in the same type of terrain.
Taking all of that into consideration, what seems to be going on here is that the avalanche terrain in Canada that lures back-country snow-goers must contain slopes that allow for more rocks and trees. There are several types of avalanches in that book that aren't necessarily powerful enough to easily bury you, but still powerful enough to sweep you into a tree. Combine those types of avalanches with slopes rich in trees, and you've got the recipe for the blunt force trauma.
Europe, on the other hand, could very well have mostly terrain that either doesn't promote as many trees and rocks, or does promote larger avalanches that are more likely to bury the victims.
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While it does not account for the difference between Canada and the USA, I'm pretty sure that one reason for the low numbers in Europe is that the latter has a lot of seasonal mountain pastures in active use, so livestock grazing keeps many slopes completely free of trees:
In fact, the word "Alps" for Europe's main mountain range is related to the words for such pastures in German (alm/alpe) and French (alpage).
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