Saturday, January 28, 2012

Avoiding Avalanches in a known to be Dangerous Snowpack

It was a matter of time before backcountry conditions became vastly unstable here in Utah. Weak snow formed over a several week period and then the snow came in on top leaving a slab; a perfect recipe for an avalanche.

So when conditions are dangerous, as the last several days have proven to be with dozens of large avalanches and a fatality today in Big Cottonwood, how do we avoid getting caught?

At a certain point snow analysis goes out the window. When it is known that it is lethal in the backcountry it is more valuable to spend time with a slope meter and a map in your hands than it is spending that time digging pits. When we know that slopes are dangerous the only things that you are going to find by digging pits is what you already know or conflicting information, which may lead you to believe that slopes perhaps are safer than they actually are.

When it is as dangerous as it is out there at the moment you need to be certain that you are in terrain that is mellow or you will likely die! Stay in terrain that you know is mellow,  you need to be certain it is. Stay out of complex terrain where small navigational errors or other mis-judgements will bite you in the ass!

When everything is telling you that it is very dangerous out, think and don't be an idiot alpha. On that note, be careful what other group members influence you to do. Use your own brain!

Lets look at the avalanche off of west Kessler today:
UAC Kessler preliminary report here

I normally try to avoid passing judgement related to avalanche accidents but this is so far out there I feel somewhat obligated to break down the massive red flags that were evident here. It was a big, steep slope, one that funnels debris when it slides. It was slope above a cliff band, with lethal avalanche hazard present and dozens of other recent avalanches reported in the area. This accident happened in complex terrain... all of Kessler is complex in fact. Hello!?
With the known avalanche hazard this is was no place for a ski tour unless everything affecting the slopes route you would be on had already slid and slid recently.

Things the group did well: one person died, not everyone in the group.

The bottom line:
With deeply buried instabilities; just because avalanches are less frequent after a storm cycle ends it does not mean that you cannot trigger them. The difference is often only whether the slope will avalanche naturally or whether it will wait for you to trigger it (difference between High and Considerable Hazard). Think about that a bit.

With a deeply buried persistent weakness in the snowpack as there is at the moment, slopes usually get a bit more stubborn to slide over time but this isn't to say that they aren't going to still slide though. During a storm avalanches may be easily triggered or are even releasing naturally. In the days just after, slides may not be going naturally anymore but are still easily triggered; maybe even by just being near slopes, walking on ridge tops, etc. you may cause slope to slide. As days turn to weeks, slopes commonly hang on a bit more, even when the structure of the snow is still compromised beneath, often resulting in a mixed bag of user feedback (this is when most accidents happen). These are the sort of conditions where a slope test may not lead you to believe there is still a dramatic instability. Ten tracks may be on a slope and then all wash away in a slide as the eleventh skier gets smoked. If the snow structure is prime for it, all that is necessary is to find the right spot on the slope for it to fail. With a deep instability this often translates to finding a thinner portion of the slab above, where the weaknesses beneath can more easily be affected (this is the same reason why these sort of avalanches commonly break down slope, away from ridge-lines a little ways where thicker wind deposited pillows may allowing a skier a few misleading turns before breaking away).

For more information about common early season snowpack weakness and avoiding slides relating to such see my prior post: Avoiding Early Season Avalanches

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