We had an exceptional start to the ski season this year. Early snow and lots of it prevented the pattern of anemic snowfalls interspersed with cold spells that made the base of last winter’s snowpack so sketchy for most of the winter. Even better, the high altitude rain I trekked through back in November soaked into the early feet of snow and as a result, in most places around here the base of the pack has been welded to the ground.
But as my avalanche education continues, I learn over and over that the one constant in this area is change. In the last month various regions across mountain Montana have gotten complex and variable enough weather that various instabilities can now be found, things that must be taken seriously.
The above slide was triggered by skiers outside Bridger Bowl on Sunday. A hard windslab ran on the demon of continental snowpacks, buried facets. Two weeks ago, some folks just outside Snowbowl in Missoula got lucky when new, dense snow failed on a steep slope, and this past Saturday a snowmobiler was buried and died in the northern Swans not far from here.
Many different reasons to be careful.
At Avy class last night, Stan Bones discussed his investigation of this last incident. They found the same two weak layers we found on Sunday, though with the Swan getting much more precip than the area we skied, the layers were bigger and the layers between and on top of them substantially larger. The uppermost layer appeared to be a very thin melt-freeze and/or faceted layer. I got it to fail at a CT11 Q2 on Sunday, but it did not propagate at all during an extended column. For us the lower layer was a 2 cm very hard ice crust. It didn’t fail during the aforementioned tests, and getting it to move during a shovel shear required a lot of force. Based on this, we felt safe skiing moderately anchored slopes to 30 degrees, as we did on Sunday.
The fatal swan avalanche had the uppermost layer as the weak layer at the crown, but according to Stan the majority of the bed surface was on the lower ice layer, which in the Swans is apparently 4 inches thick. It seemed that the FS had yet to speak directly with the party involved in the slide, and they don’t yet know where and how the slide was triggered. Somehow enough stress was applied to get things sliding on the thick ice crust, which produced a large avalanche with a lot of destructive force.
A good part of class last night was devoted to discussing this incident, which was illustrative in numerous ways. First in the details and the way Stan presents them. He’s not the most nuanced pedagoge in the world, but is a knowledgable and passionate snow scientist, capable of discussing the many variables while paying due to all the complexities and unknowables. The second thing of note was observing a dynamic which I’ve seen, to at least a certain extent, at every such event I’ve attended: the desire of people in the audience to rationalize away the danger.
Folks want to hear of at least one clear and egregious lapse in judgment on the part of the triggering party. In this particular case that was, to a certain extent, possible. Going into avalanche terrain with a heavy, powerful machine the day after an enormous amount of heavy snow fell, and doing so in the most vulnerable area around, is not the best choice. At the same time, reading back through all the incident reports found on the three aforementioned avalanche center websites will reveal, over and over, that many incidents contain quite a bit of gray area. It may be easy to spot the mistake or lapse in judgment but it is also easy to see how those errors were made. Making hypothetical decisions in a room drinking coffee is one thing, doing so well out in thick of things is another.
Moreso than in any other area of outdoor adventure, decision making while backcountry skiing is complex. No other natural variable is so multifaceted, variable, and deadly. No other outdoor activity is as fun, foot for foot, as powder skiing (none). The two are a problematic combination.