Saturday, December 22, 2012

Surprising Snowpack Changes at MCS - 12.22.2012

John and I toured North East of Top of the World and skied into the headwaters of Whoop Em Up creek headwaters. It was evident that a pod of skiers toured that same general area either Thursday or Friday, leaving behind their tracks.

It has been now a full month where skiing at Mores Creek Summit (MCS) is accessed via the Pilot Peak road due to low snow below 7000 feet. The great news is that skiing continues to be quite good at all aspects above 7200 feet. Although tracks are present in most of the popular ski runs. For those willing to explore, there are plenty of untracked nooks and fun lines waiting for you to track them.

Lunch at the bottom of Whoop Em Up Steeps; John, Chago, Cal, Mark - Left to Right.
Lunch at the bottom of Whoop Em Up Steeps; Cal, Mark, Chris, John- Left to Right.
I was REALLY surprised when early in the day, as we reached the 7800 feet level we experienced a pretty significant whumphf. That is a sign of fracture propagation. We ran into another party of friends that experienced whumphfs as well.

To be honest, I felt like discounting the observation, particularly when last Wednesday there was no evidence of propagation propensity. Stability testing at a North aspect as well as South East aspect, both at 7800, confirmed that the snowpack has changed from last Wednesday due to facet metamorphosis above the buried crust layer. Steep gradients were identified at both snow pits above a buried crust.

The SE aspect weak layer above the crust is buried 60 cm from the snow surface. This same weak layer was found buried at 45 cm at a protected location with North aspect. It is worth noting that SE aspect slope we evaluated is in a slope susceptible to wind loading.

Below a short clip for a PST (propagation saw test) in a slope with SE aspect, at 7800 feet, and a steepness of 26 degrees. The weak layer was buried 60 cm.

ECT results were conflictive, but PST testing clearly suggested a propensity for fracture propagation after cutting 20-30 cm on a 1 meter column. I tend to never put all my eggs in a single basket, and I have been playing with an ECT column where the saw is use to initiate a fracture (similar to PST). Check the next video for the ECT without compression taps, where a saw cut is used to nucleate a fracture at the weak layer buried 45 cm in a slope with North aspect, 7800 feet of elevation, and a steepness of 36 degrees.

Compression test results resulted in CTMQ1 (SP -Suden Planar)  scores at the North Aspect 45 cm layer, and CTMQ1(SC - Sudden Collapse) at the SE aspect 60 cm layer.
Stability Wheels: Integration of Avalanche Mechanism Likelihoods and Structural Weaknesses
Stability Wheels (see above) are great visual tools to visualize instability leading to avalanches. Notice that slip and propagation likelihoods are HIGH, and that structural weaknesses (Lemons) are concerning. The trigger likelihood are moderate, which basically means that all it takes is to find areas in the snowpack where a fracture nucleation can be easily triggered due to shallower snowpack, facet garden, stress concentration, loading, or other possible factor. Since several whumphfs were experienced today,  that is clear INDICATION that triggering is possible at the right spots.

In the meantime, we have a storm heading our way that can possibly increase instability and make the buried weak layer above the crust (45-60 cm) more reactive.
John getting blasted by Snow at Pilot Peak
About 6 cm of new snow fell today. The probabilistic models are calling for a 70-80% probability of more than 10cm for December 24th and 25th. depending on the rate and totals, the buried weak layer might become reactive. Please - Please - Please manage your angles during the next few days and carefully evaluate slopes you intend to ski.