If you want to ride safely over the Christmas holidays, you’ll need to do some work to get a handle on conditions and you’ll need to stay on top of things as the next cycle of stormy weather progresses.
At the moment, we have one or more weak surface hoar layers in the snowpack. These icy looking, glittery, feathery crystals are the winter version of dew (frozen of course, instead of liquid water) that forms during clear, cool, calm spells. The one that’s of greatest concern formed during the first couple weeks of December and was buried on or about Dec 10th in the northern regions and up to Dec 14th or so farther south. (I’ll refer to it as December 10th for simplicity’s sake.) Many areas are reporting more surface hoar layers in the storm snow above the December 10th layer. These formed during clear breaks between snowfalls and add to the complexity of the snowpack.
The Dec. 10th surface hoar is buried more deeply in the North and its depth tapers off as you go south. I suspect it exists in the North Rockies and if I’m right it’s probably 70cm or so below the surface. In the Cariboos and North Columbia, expect to find it 60-80cm down; 30-60 in the South Columbia/Purcells; and 10-20 in the Kootenay-Boundary. In the northern sections of the Sea to Sky, a December 19th surface hoar layer is about 20-25cm down.
In the north, surface hoar produced an avalanche cycle last week after about 40-50cms of storm snow fell on it. This resulted in numerous natural avalanches as well as human triggered slides. Some of these were quite large, up to size threes, which contain 10,000 tonnes of snow or more and are big enough to total a pickup truck. In the south and west, there were fewer natural slides and sizes were smaller but numerous human triggered slides were noted, including at least one very close call where someone was pretty much fully buried and had to be rescued by their partner. I suspect there were a lot more incidents and close calls that we have not heard about. In areas where avalanches did occur, I’m pretty sure not all slopes slid. In the west and the far south, where the layer is less than 30cm down, surface hoar has not yet produced any significant avalanche activity.
The December 10th and other surface hoar layers are currently in a state of balance. They have adjusted to existing overlying weight (load) but are not yet strong enough to support much more. This sets the stage for the next chapter of the winter.
The real question for me is not whether another avalanche cycle will occur, but when and where. The challenge lies in the weather. Meteorologists are quite certain that a series of storms are coming, in fact the first is on our doorstep. These are expected to be a series of small, short-lived systems interspersed with clear spells. This pattern could last as long as nine or 10 days if you believe the long-range forecast. However, there is significant uncertainty about the timing, track, and intensity of the incoming systems and, while none of these storms is expected to produce much precipitation, each successive event will incrementally add snow (that is, weight or “load”) on top of the surface hoar layer(s) that lie beneath. This will almost certainly overload one or more of the surface hoar layers and when that happens, natural and human triggered avalanches will occur. Because of the uncertainty in the weather forecast, it’s hard to tell when and where the next round of snow will hit and which of these smallish storms will add the final straw that breaks the camel’s back.
In areas where the problem is known or suspected to exist, managing the challenges this situation presents requires a three pronged approach: a) gathering information, b) applying rigorous safe travel procedures, and most importantly c) managing the human side of the equation.
The information you need is knowledge of where avalanches have run. If you can reliably confirm that a slope recently avalanched in its entirety, then it’s the surface hoar layers that were there are likely gone, and it’s probably good to go. By recently, I mean the fracture line is still visible and the debris is not covered up by new snow. If it’s an older slide, one of the newer surface hoar layers may have formed after and then been covered by new snow and you’ll need to treat this as if it had not slid (see below).
If a slope has not slid recently or you are unsure, it’s best to assume the surface hoar exists on that slope until proven otherwise. To determine if there’s surface hoar, you need some technical training and skills to identify the surface hoar and determine how deep the layer is (that is, you need to know how to dig a snow profile) or you need to depend on credible, reliable local sources to tell you whether it’s there and if it is, how deep it is. If you are unable to obtain this information, I advise avoiding avalanche terrain at all elevations: that is any slope with 30 degrees of incline or more, including open glades and meadows in the forest. If the layer is less than 30-40cm down and covered by soft powder snow, it may be reasonable to ride on it if your tolerance for risk is high and you rigorously apply the following safe travel procedures:
- Ride one at a time across, up, or down avalanche terrain.
- Have a spotter in a safe place watching you while you are on the slope.
- Spread out when crossing runout zones.
- Regroup only in safe areas.
- Avoid large, steep slopes.
- Eliminate exposure to large slopes above.
- Avoid exposure to terrain traps such as gullies/ravines; open water; trees, rocks, or cliffs below; and sudden transitions from steep to flat (e.g. roads, frozen lakes).
If the layer is overlaid by a firm or hard slab of dense snow (anything that’s not nice powder) avoid all avalanche terrain except slopes that have recently slid, as described above. Even if it’s powder, where surface hoar is more than 40cm deep I’d avoid all avalanche terrain.
The most important means of managing risk in these conditions is to control your natural urge to ride the beautiful powder on a steep slope. The mountains will be here all winter and for as long as any of us will be around. You can ride the big slopes will killer pow any time in the future when conditions are better, so resist the urge if you have any doubt whatsoever. Even when avalanche hazard is elevated, you can have a great time in the mountains if you reduce your “steep and deep” expectations, can find fun in riding smaller and less steep slopes, and are able to enjoy the mountains for their beauty instead of the adrenaline rush. In conditions like what we’ll experience in the coming week or two, patience and self-control are the hallmarks of the living.
If you want a longer and more in-depth read, check out this article from the winter of 2009-2010, which discusses surface hoar problems and their management in more detail: http://www.avalanche.ca/cac/library/researchandarticles/PWLpaper0910
I’m sure I’m preaching to the choir here, but I’ll say it again: be sure you have your transceiver, probe, and shovel. Consider a balloon pack. Make sure everyone in your party has the gear. Everyone should test and check all equipment before departure. Practice companion rescue techniques regularly.
I wish you all a wonderful and safe Christmas holiday.
December 23, 2011