Joined: 14 Jan 2009 Posts: 72 Location: north vancouver, BC
Posted: Tue Jan 22, 2013 6:31 pm Post subject: what do small cracks mean?
Skinning up around Paul Ridge I noticed some small (maybe 30-50cm long) cracks in the snow on near the downward side of the skin track. I remember on my AST1 course this happened as well and the instructor said it wasn't a problem, but I can't remember the reason why.
Any ideas? The cracks didn't appear as I went up, they were already present in the snow.
Joined: 03 Nov 2008 Posts: 358 Location: neither here nor there...
Posted: Wed Jan 30, 2013 6:11 pm Post subject:
Generally speaking, short, shallow cracks are benign, but you are doing the right thing by observing the snow surface and wondering what it tells you about snow stability. Cracks that propagate can be a red flag of instability.
How do you tell the benign cracks from the ones that have a story to tell?
I'll throw out a few ideas and maybe some of the shrewd, longtime practitioners that hang out in these parts will add to the list or correct/clarify my ideas:
The first question I'd ask is: What type of snow cracked? Loose, freshly fallen snow? Soft slab? Hard slab? A wind "skin" or a breakable melt crust? In general it will serve you very well to constantly make note of what type of snow is under your skis and how it changes as you change elevation, aspect, slope angle, etc.
Small, shallow cracks in a surface skin or crust are pretty benign. Loose, new snow seems prone to allowing cracks that are shorter than a ski length or so. Hopefully it isn't too much of a generalization to say that if these don't propagate, the cracks themselves are usually benign, but you will still need to consider how all that new snow is affecting snow stability in the bigger picture. The deeper cracks you will see in soft or hard slab surfaces are note worthy even if they don't propagate because you will need to consider if cracks will propagate through these slabs on different slope angles, aspects, thicker or harder slabs, as the weather changes (warming, additional wind loading, etc).
The next question I'd ask is: What caused the cracking? Are you on an existing skin track and do you suspect that earlier skiers caused the cracking, or do you think they are natural cracks?
Deep natural glide cracks on convex slopes with a smooth ground surface should generally be avoided, but particularly so when the snowpack is warming.
Constantly wondering about the snow and how it is changing, is the first step towards developing a more intuitive understanding of snow and avalanches. Furthermore, it is fun stuff to think about! It is important, however, to not get too bogged down in the details, particularly when you are a novice. As you learned in your AST, read the bulletin before heading out, consider the terrain carefully, and constantly be on the look out for red flags on instability.
Thanks for posting the question and enjoy your ski touring and avalanche learning!
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