Safety of trees

Let us not forget, trees can weaken the snowpack in many situations.
Think: perforations in a sheet of paper...the paper (layer of snow) usually tears (breaks) at the perforations when stressed enough .

Getting swept through trees can be traumatic to anyone caught in a slide like that. We have all seen slides that propagated into and through tree stands...Always do stability tests on a representative slope and don't count on trees increasing snowpack anchoring.

Two anecdotes, worth what you paid for them (and neither quite addressing the type of terrain in your pictures, Koda)...

Right before the slide broke on the Phantom last year, I remember looking just uphill at the trees I was perched near, thinking that they were a dubious safe spot at best. The slab broke right across the base of the trees, fracturing in a broken line down to the next small cluster. Obviously in the aftermath we were flushed through trees, with the expected results. This was all much more open terrain than you're talking about.

Second one -- a few years back, a friend on a cat skiing trip was skiing a heavily treed slope. It was the second lap on that slope of a full guided cat and she was second to last, or something. Probably skier 16 or 17 on that slope? Anyway, the slope fractured when she skied it and flushed her through the trees, with very serious (thankfully not fatal) injuries. The guides had never seen that slope show any sign of activity in many years, so it was clearly an uncommon release.

Pretty sure that last slope was more "christmas trees" and not more established old growth or second growth like in your photos.

More in line with your pictures, I've definitely cut loose small slabs on steep rolls in terrain show in your pictures -- at Yodelin, specifically, on the north slopes that everyone skis. Didn't travel very far or propagate much, but in the right circumstances I can see it flushing you into the trees or breaking out into a larger section of the forest. Not common, probably, but very high consequence if it did happen.

Two anecdotes, worth what you paid for them ....

There is definetly some good information trickling in, your two ancedotes here are helpful... I'm curious to learn more about the second one, first hand details of that would be helpful to this discussion. I have also kicked off small surface slabs in heavy trees, but they were always in locations of more open spaces... I think "open spaces" here are the weak link. I'm curious if said open space had anything to do with your second anecdote incident?

Your reference to cat skiing recalls a memory of cat skiing at Mt Bailey years ago on a very unstable day, the guides kept us confined to low angle glades, but tested fate on a steeper tree run. The guide ski cut the top and a large slab resulted and destroyed the area below... in a split second. IIRC, this "tree run" was similar to my photo #2... (notice the open fall line in otherwise heavy timber slope + the open space I'm standing taking the photo), the location of ski cut the guide performed was an open space worth a few turns below not unlike my photo #2. I don't recall the propagation spreading farther than the open space....  but this was many years ago.

What I am gathering here is there is a relation between tree spacing, slope angle, and overhead canopy. I can say that tight trees often offer much greater stability in otherwise unstable conditions but this thread is helping my define or measure those elements.

• fall lines that stay well under the canopy contribute the most stability
• burn areas with no canopy only offer marginal stability only in the snags themselves... there is also more likely less ground vegetation
• "open spaces" contribute to instability and offer larger distances of propagation. The larger the open space, the greater the danger

I think at some point it might help to define "tree spacing" with an actual measurement in order to help define "really tight tree skiing" like I am referring to. Right now all I can describe how I define "tight trees" is spacing short enough to constantly disrupt your fall line....

this thread came to mind on a recent tour this week we noticed a very reactive surface layer. Lots of creep and fractures propagating in about the top 2" of snow. It was snowing heavily the latter half of the day, and we concluded a thin layer of surface hoar under the recent 2" layer.

Well our objective was under a heavy canopy of old growth and after a few hours we came back around hooking up with our original skin track through the timber were a natural point release (maybe from a tree bomb) had slid across our skin track. This reactive surface layer was present... even under the heavy canopy of 'tight trees'. Now I am imagining this suspect layer preserved a few days with more loading....