Swinging between the Northern and Southern Hemisphere winters, I’ve found a pattern over the past four years. Testy Utah seasons have begun on the heels of relaxing NZ seasons. An example: A fairly straight-forward 2011 Austral winter with infrequent snow and enough rain to reset any lingering layers was followed in Utah by a series of small storms occurring through November. Interspersed with cold, clear high-pressure systems, a weak basal layer formed in the Wasatch, which then persisted for much of the winter.
When snow did finally arrive (as it always does) the resultant powder frenzy resulted in avalanche incidents like that of November 12 2011– when famous free-skier Jamie Pierre died in a slide on the yet unopened or controlled slopes of Snowbird.
In Utah, these tiresome winters of infrequent top-ups and tiptoeing on the eggshells of 20 cm basal facets have begun to feel like the norm. The cold dry powder we know and love eventually arrives but with it, a price. We await a massive storm to bury the facets far below the stress bulb (spatial variability notwithstanding). In 2011-12, it never really came. In 2013-14 it came in February.
Waiting for snow, as the existing 2 feet rots to the ground, becomes an exercise in reflection. During the past three leaner seasons I’ve been lucky enough to work avalanche classes with some experienced avalanche practitioners (Bruce Tremper, Don Sharaf, Kelly Elder and many others). While the skiing has often felt restricted, these are great seasons to take avalanche courses.
Trickiest periods in these low snow seasons with persistent weak layers are always the few days post-storm, as the snow pack “tightens” and the likelihood of triggering a slide is reduced. The classic situation of low probability-high consequence. Test results can be hazy (I mostly use CT and ECT and I oscillate between the American system of rating the failure quality and the Canadian system of fracture character). The Sharaf-McCammon stability wheel is useful. Discussion with friends and colleagues revolve around the fact that the mere existence of the weak layer meant that strength tests (alone) were insufficient for making firm decisions. 30 taps on a column is often not enough to cause failure. Add a boot stomp (or continue tapping beyond 30: Canadian Deep Tap Test) and a fast, clean (SC) shear may result. It’s dodgy stuff when unorthodox test methods produce high-energy results. The arbitrary number 30. Accidental avalanches do occur relatively frequently when tests do not produce results.
False stable results. During avalanche classes I’d bleat about enduring weak layers. I emphasized the weak snow pack structure, and on field days, easily demonstrated the incongruity of strength during tests. My own words would echo in my mind as I planned backcountry trips. Frequently using a probe to establish snow depth, I thus applied some of McCammon and Sharaf’s “Five Lemons”: Persistent weak layer crystal type, down 100cm or less, weak layer <10cm thick, grain size (=/>1mm) and one step or more hand-hardness between layers. Not every category applied – but enough boxes checked out to keep me on my toes. Given the sometimes wide publicity of avalanche issues in Utah in this type of season, my clients would watch with interest as I probed, impressed with the sudden dive as the stick hit basal facets. Structure demonstrated with minimal fuss!
So enter the human factor. You get bored with a dangerous snow pack. You even get used to it. You begin to imagine, hope, assume, that it’s bridged (hence the probe – it doesn’t lie about snow depth). As the season progresses with additional snow accumulation, crux times where the weak layers re-activated become harder to call and attention to crucial areas pre-storm are essential. I use more discipline to manage travel – ensuring that clients practice beacon searches, more spacing, digging regularly and using my probe to establish the depth of weak layers. I frequent familiar places. My clinometer is kept handy in my leg pocket – it won’t lie about slope angle. Another season of tree skiing!
The past three years, I’ve been keen to have it over with by April and will happily ski corn the following season in New Zealand with ice axe and crampons kept handy! Interestingly back in 2011, control work on the Little Cottonwood Canyon road brought down big slides in the last week of April – the weak layer being wet basal facets. As the forecasters predicted – such a weak layer will only be history once we drink it. With basal facets already set up in the Wasatch will the 2014-15 season be a repeat?
Anna Keeling is an IFMGA mountain guide based at Castle Hill Village and in Salt Lake City, Utah. She mostly guides ski touring and teaches avalanche education to recreational tourers. The weekly ski columnist for the Christchurch Press for the past 3 years, Anna is also an assessor for the NZMGA and AMGA (American Mountain Guides) and is the Training Officer for the NZMGA.