Inversions & Elevator Shaft

I’ve just returned from a post-holiday week off, and found a few questions lurking in the comment section of the Lowdown.  Since they were both pertinent to what’s happening now at Lake Louise, I thought I’d address them here in a post.

The first question regarded the temperature inversion we experienced for a few days around Christmas, and its effect on the snowpack.

Warmer temperatures do indeed affect the snowpack, and while our recent inversion saw temps go above freezing, that’s not always the case. In other words, an inversion alone doesn’t necessarily have implications with regards to snowpack stability. What’s more important is the above-freezing temperatures.

The degree to which warmer temps affect the snowpack depends on both how warm it gets, and how long it stays above freezing. For the most part, we only experienced warming in the top cm or so of the snow, resulting in a softer skiing surface but not penetrating deep enough to really affect the stability. In general, an increase in snowpack temperature is bad for the short-term stability, and good for the long-term, but it needs to affect more than just the surface of the snowpack.

At the other end of the scale, snow becomes least supportive and stable when it becomes isothermal, which means that the entire snowpack, from top to bottom, is the same temperature. This is usually a springtime occurence, as the sun shines more directly on the snowpack and for longer. Towards the end of the ski season, it is common to find that the maximum heat of the day happens around 6:00 or 7:00pm, long after skiers and staff have left for the day. It can be difficult for the snowpack to recover after a long day baking in the sun, particularly if the overnight temperatures do not spend much time below freezing. If the mercury does go below 0C, the surface of the snowpack will begin to freeze, and the longer it stays cold, the deeper that freezing will go, adding to stability. If another hot sunny day follows, then avalanche control crews must continually monitor snowpack temperature on all slopes, as stability can change very quickly, and slopes that were good skiing on one run become unsupportive and dangerous the next.

One could also ask that if melting is limited to the snow surface, can it still alter the stability of the slope’s snowpack. The answer is it can, since any sort of melt/freeze cycle results in a few conditions that can add to avalanche hazard. First of all, a melt/freeze crust is a poor bonding surface, and means that any snow crystals added on top, whether through natural precipitation or wind-loading, don’t have good snow underneath with which to bond. The harder surface also provides a smoother running surface for avalanches, and snow will always be more likely to slide on a hard, smooth surface than on a rough, softer one.

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The second question asked what avalanche control work has been done so far this season to get Elevator Shaft open.

The simple answer to that question is that because Elevator Shaft is not lift-serviced terrain, it lies pretty far down the priority list for avalanche control. Big avalanche slopes require intensive work to make ready for skiers, and crews will perform lap after lap after lap to ensure all parts of the slope have been controlled. In a place like Whitehorn II where patrollers can be on the slope literally seconds after getting off a lift, that kind of work is much easier to do than in a place like Elevator Shaft, where crews must hike for 20 or 30 minutes just to get to the top of the slope.

Ease-of-access also means fewer people ski the slope, so naturally more attention will be given to slopes that more people want to ski. Easy-to-access avalanche terrain abounds at Lake Louise, especially now that places like Whitehorn II and ER 6 & 7 open regularly. All of these places require the same intensive control work, and the more frequently avalanche control teams can get in there to do their work, the sooner these places can open.

Having said that, there were some explosive rounds placed on the slope during a shoot with the Marmot avalauncher gun earlier in the season, and that represents all of the control work done in that area so far this year.  With the busy holidays over, control teams expect to resume work there as early as this week, provided of course that Mother Nature cooperates!

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