[MCR] Rockies: Bow Summit

Spent Day two of an ACC Calgary AST2 course at Bow Summit today. Saw some relatively recent avalanche activity in the major slide paths on Observation Peak, including the skier triggered avalanche reported previously. I have the feeling that despite the fact that the snow pack is not as reactive as it was a week ago there are still some big surprises lurking out there. Certainly a few folks have a higher risk tolerance than I do based on the location of some of the tracks on and beneath major features.

Made for interesting group discussions regarding risk tolerance and where to place your up track when avalanche hazard is Considerable. The fact that I find interesting is that the definition of the rating Considerable begins with the statement “Dangerous avalanche conditions...”

Be that as it may, we had time to do some quick compression tests below treeline and found the January 5 Surface Hoar down 25cm and the December Surface Hoar down 50cm in a snowpack that was around 100 to 120cm deep. We had failures in the moderate range in compression tests on these layers with some tests producing sudden results (pops and drops). Our extended column test did produce a failure in the moderate range but no propagation.

We postulated that this was due to the fact that where we were below treeline the snowpack was not stiff or cohesive enough to propagate. For example, the upper 25cm in our location was low density or soft snow that you could easily push your fist into (ie. fist resistance). Another 25cm beneath this and above the December surface hoar the snow allowed you to relatively easily push four fingers into it (4F resistance). We felt that if the snow above either of these two buried surface hoar layers was a bit stiffer, as you might find on an open or lee loaded slope, that it may be conceivable that the weak layer would fail and the fracture would propagate in a slab avalanche.

Looking around and doing a bit of digging didn’t inspire all that much confidence in me to ride the bigger features yet. I am probably going to still be fairly conservative, especially in light of the weekend forecast for more snow together with some wind. Things that make you go “Hmmmmm.”

Going touring again tomorrow. Ride safe!

Cyril Shokoples MG
ACC Calgary AST2 Group




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