On Saturday, an acquaintance of mine
was caught in (triggered) a size 2.5 slab avalanche in the SelkirkMountains. Luckily, she was not killed, but, unluckily, did suffer
relatively severe injuries. I know the area reasonably well, having
hiked, climbed and skied there many times, and things could certainly
have been worse. The terrain is typical Kootenay skiing – steep
sided treed valleys with little gullies and terrain features all of
which worsen the consequences of getting caught in an avalanche.
The party did many things well,
apparently after the avalanche, the injured skier was rapidly reached
and a rescue quickly activated (she was not completely buried), they
exposed only one person at a time to the slope thus reducing the
potential number of victims and leaving more people to render
assistance if needed, the party had obviously made a number of
snowpack observations, and were all carrying standard safety
equipment. But, of course, any time we trigger an avalanche, unless
it is small and intentional, we've also clearly made some mistakes.
I've triggered a number of avalanches
over the course of my skiing career, so many, in fact, that I am not
sure I could recall all of them if pressed. I have been, of course,
terrifically lucky, in that I never triggered anything big, most were
small and intentionally triggered (or at least half expected) or were
triggered remotely from a safe location. Many times, I triggered
smallish slabs that were unexpected, but was saved from further harm
because I routinely practised safe ski practices, such as exposing
only one person at a time, getting out of the way at the bottom,
avoiding high consequence slopes in times of uncertain stability
avoiding convex rolls, starting out on smaller terrain and all of the
other fairly standard tactics that can improve ones safety margin in
the mountains.
In the first year after I took my CAA
Level 1 Avalanche Operations Course, I did, however, do what many new
graduates of that course do, and got caught (in my case almost
caught) in a big dangerous avalanche, the result of being too cocky.
The episode scared the shit out of me as it had the potential to kill
or at least seriously injure everyone in the party. There was one
clear sign that I chose to ignore (and I take full responsibility for
ignoring this sign as I was the most highly trained and experienced
person in the group) and that was a moderate sudden planar failure on
a compression test 40 cm down on a suncrust. I ignored this obvious
red flag because we were on a ski traverse that I had wanted to do
for ages and I had finally managed to get the weather and the
companions to do the trip, and, we were at the base of the final
avalanche slope - beyond this one slope, we had no further danger to
contend with. All those things, irrelevant as they are, somehow
blinded me to the danger into which we skied. We were lucky, we were
in similar terrain to my friend - steep, lightly treed so that the
trees could not anchor the slope but only increase the consequences
of getting caught – and, while the entire slope from one side to
the other cracked and shifted, some magic of gravity held the slope
in place and we were able to safely “get the hell outta there.”
My friend and her party made similar
mistakes but just weren't so lucky. They too had dug snow-pits, and,
somewhat chillingly, found a buried surface hoar – moderate to hard
sudden planar failure (but down a whopping 115 cm) on compression
tests. The avalanche bulletin for the day rated treeline as moderate
and alpine as considerable and noted that remotely triggered
avalanches (always a scary sign) were still being triggered on the
buried surface hoar (buried almost one month before). The bulletin
also noted that, and I quote verbatim: “February 12th [surface
hoar] is now down about 100-150 cms and continues to be triggered by
light additional loads on Southerly aspects where it is
sitting on an old sun crust.”
Hindsight is always 20/20. In
retrospect it is clear that while the group may have thought they
were in treeline terrain (moderate hazard), the snowpack
characteristics (and terrain) were clearly alpine (considerable
hazard), sudden planar failures should always make us think twice
about the stability of a slope (even with hard test scores), a skier
is a light additional load and, despite it being statistically less
likely, a weak layer down 115 cm can be triggered by a skier, solar
radiation and heat can rapidly destabilize the snowpack, widespread
surface hoar layers can propagate large distances and release above a
skier, and, finally, but most importantly, deep persistent weak
layers require conservative terrain choices – skiing a 38 degree
slope (even one at a time) is not an appropriate terrain choice for
this classic low probability/high consequence deep persistent weak
layer situation.
I have no idea how decisions were made
in the group, always the most informative aspect of any accident
analysis. Perhaps the party thought that they were in treeline
terrain because of scattered trees and considered the hazard
moderate. Perhaps they thought that a layer buried over a metre
could not be triggered by a skier (statistically unlikely, but
practically irrelevant), perhaps they under-estimated the effect of
the sun and heat on the snowpack (it was a warm sunny day), or
perhaps like me, they were too motivated by ambition and too little
by prudence.
After my serious near miss, I
consciously became much more conservative in my terrain choices
whenever stability was uncertain. The big lines only got skied on
very select days when stability was bomber and I was with a solid
party. I became, quickly, abruptly, and with some chagrin, aware
that, despite some education and experience, what I didn't know far
exceeded what I did know, and I needed to allow some margin around my
terrain choices in case my analysis of stability was wrong. I can
only hope my young friends have the same epiphany.
Hi Sandy, glad you posted a link to your blog on pebbleshoo. I like your writing style. I'm learning to ski backcountry with people who've taken their AST-1. I like your statement "too motivated by ambition and too little by prudence". Ambition definitely causes personality conflicts when in the backcountry.
ReplyDeleteSadly, I've always been too motivated by ambition myself. I think that people who are really goal directed (me) tend to be that way. One of my friends always says "your greatest strength can be your greatest weakness."
ReplyDelete