davidof - 05 March 2008 03:18 PM
The crust itself may actually bridge over a weak layer. Of course a thick wind crust is effectively a large slab of snow (windslab) which is sufficiently loaded, normally by a group, can break and slide on the surface below. But I assume what you saw was a thinnish crust formed overnight by the freeze/thaw cycle.
Very good point that a thick wind crust is effectively a thin wind slab. Or maybe not so thin. Once the crust is not thin enough to be breakable, you really don’t know how thick it is.
I almost got into trouble a couple of months ago when there was a transition from a thin breakable wind crust over most of the slope I was climbing to a hard surface near a terrain feature. I was trying to pound my ski edge into the surface so I wouldn’t slip, and all of a sudden the snow broke loose and took me 10m down the hill. Fortunately it wasn’t over a cliff. I was real surprised when I got up looked around and saw that I was surrounded by some blocks of hard snow over one foot high. Turned out to be a wind slab 3m x 4m in area—and over 30cm thick.
My analysis:
Wind crust is a sign of lots of wind. Where there is lots of wind, there can be wind slabs. Then it becomes a question of how well bonded the slab is to what’s underneath it. My lesson: If the breakable wind crust unexpectedly becomes non-breakable, and I don’t know how thick and heavy it is, and don’t have good reason to think it’s well-bonded to the underlying snowpack—then I should carefully gently step backwards down my track - (and surely not start aggressively pounding on the snow).
Ken