Danny Zimmermann avalanche accident summary 3-5-11

Thanks Mike and Chris. I had a similar reaction to Jason as to the trigger point. Not what I had envisioned. But it seems to fit a pattern of slab releases in trees I've noticed this year. That's scary because it runs contrary to the safety we often associate with trees.

What's become apparent to me is that trees offer only a small fraction of anchorage relative to the totality of the slope and the condition it's in - - and that my sense of tree security is additionally confounded by their potential to increase terrain hazard, should the slope release.

I don't know, I'm just thinking out loud here.

Mostly I just want to extend my deepest condolences to the family and friends of Daniel. It's tough to lose someone with so much life ahead of him, even if he was doing what he loved.

After reading the report I'll never look at trees quite the same way again. Forget about potential anchor points--they're weapons aimed right at you.

I have had a couple avalanches take me down in the trees and by no means is it a time to lose ones evaluation process. Last week in Snowbird I was traversing to some side country and as we came around several aspects there was a buried layer of 4inches of groupel in a reasonably dense tree area. It reminded me that even in the trees, there is a reason to be aware of PWL's.

My condolences to Danny's family. This was violent was to go out. May he enjoy eternal powder turns.

Sure is sobering.  I have been looking at the photos to try to get a sense of how I would feel on that slope and I still am having a hard time thinking that I would decided not to be there.

To me the one photo that scares me is the one that is looking right down the slide path.  That one photo makes it look like a trap. Almost like a drain that steepens dramatically.  I think I am a bit of a chicken when it comes to traveling in the BC, so while I may normally be comfortable on a slope with that benign slope angle, when I pass above dangerous terrain the fear factor rises.  To me most of the photos show an untreed area, albeit not very large, that let loose and then ran into the steeper treed section. I am not sure what people's expectations are with respect to trees being able to anchor a slope, especially the large number of standing dead trees.  I think we all need to re-evaluate that one.

On the other hand the photos looking up from the bottom to me look just like a regular treed slope.

To me the scary thing was the combination of what looked like a rather benign terrain (considering the trees) and the fact that the snow pack was thin there and rather wind scoured.  Would I feel unsafe there?  I can't say, but from the report, I think not.  Such a shallow fracture to start would almost seem like a sluff that one could arrest from.  I wonder if the stepping down to deeper layers below was too rapid for the skier to arrest, or if the hard base layer either made that impossible or allowed for a more rapid than usual acceleration?

Alan

My take and understanding on trees is this -- if they're thick enough to truly anchor the slope, they're probably close to unskiable. Anything less than that is a series of potential weak points and terrain traps. Scary, scary stuff.

Marcus,

I think that is a conservative view that is also a healthy attitude for personal safety.

I am not sure it is fully accurate though. I am not the expert, but I think that trees offer an environment that can support the snowpack. If dense enough they impact the amount of accumulation and certainly the type of deposition, such as wind deposition and slab generation. In addition, snow that accumulates on branches and then falls will potentially create additional micro anchoring in the snowpack. I would also guess that trees greatly impact radiative loss and also reduce hoar frost development under clear night conditions. On the other hand trees might have some negative impacts as well.

In the avalanche we are discussing, it does not appear that the starting zone really propagated into the trees. Certainly the slide ran through trees.

Anecdotally, does one see much if any avalanche control at local ski areas within treed areas? Certainly in starting zones above or within, but actually within? And if so, as frequent as open areas? Maybe patrollers who use this site can chime in.

There are some pretty dense trees between Double Diamond and Wildkatz at Stevens that are certainly steep enough to slide, but the only control that I have seen is on Double itself. For the type of snow that we get here in the PNW, it is hard for me to believe that those trees do not anchor.

I think any slope can slide under a wide range of stability/instability. I think what is important for the backcountry traveler is not IF it can slide (then there would almost never be travel in avalanche terrain) but what are the odds of this slope sliding NOW. So I then extend the question: Do trees generally reduce the odds of a slope sliding? Is that any less valid a question than is this concave slope less prone to sliding than that convexity?

I think that answer for the user is maybe, maybe not. I know that I will never assume that a treed slope is plain safe just because it is treed.

Alan