Thursday, 16 February 2017

Fast and Light in Avalanche Terrain

Almost all of my ski mountaineering and ski touring has been done solo.

Weasel on the peak

I could have sought company over the past year, but I just enjoy the mountains so much more when it's just me and the natural environment. Having the odd chat when crossing paths is good, but I don't need to have someone around all the time.

This predilection does mean that I need to be somewhat conservative in the mountains, as often if something goes wrong, I'll have to rely on myself for quite some time before assistance can get to me. Or I'll just have to drag my own carcass back to the car and then home (been there and done that).

That extra awareness and responsibility applies particularly to the threat that avalanche terrain poses. In Australia we are fortunate that the conditions are mostly not as dangerous as in places like Canada or the Alps. The 'mostly' qualifier is definitely needed though - every so often we get a dump that brings significant wind-loading, and thanks to being lulled into a false belief that Oz snow never really slides, people get on to dangerous terrain and end up as one of the few but growing avalanche fatalities in the Australian BC.

I'm still learning much about how to manage avalanche risk, but I think I've developed a decent approach to mitigating it thus far.

My Approach

Firstly, I start with snowfall. I usually keep a diary of the seasonal snowfall for an area, particularly when going overseas - it's often quite helpful to start a conditions diary a month out from a trip, just to begin to build a picture of the snowpack.

When planning an objective, I ask myself a series of questions:
  • How much snow has fallen recently?
  • Which direction are the prevailing winds during the snowfall?
  • Are there any known weak layers?
  • Has there been rapid change (heavy snowfall / change in temperatures)?

From there, I make an estimate of which kinds of terrain are likely to be safe. If the snowpack seems likely to be highly unstable, that is going to be low angled, simple terrain where avalanches are very unlikely to run and the consequences of one being triggered are not as bad.

Other times, the wind direction during the storm may rule out some aspects, but allow other parts of the mountain to be relatively safe. Only when snow stability is known to be very good is it possible to consider skiing on aspects and angles that otherwise are unsafe. The fundamental point is to have some idea and estimation about snow stability before heading out the door.

In my head, I'll have three categories of terrain before heading out:
  • Likely safe - Usually low angled, windward aspects, little consequence terrain or more complex terrain only when snow stability is known to be high (eg. from previous days' observations).
  • Unknown - Could be safe, could be dangerous. Further information required before entering these areas.
  • Dangerous - Terrain that is recently wind-loaded, has a known weak layer, significant consequences if it does slide. These are parts of the mountain that are off limits for me unless local observations and tests alter my beliefs about conditions.

Once on the mountain, I think that the most important point is to start on Likely Safe terrain and begin to observe conditions. What I want to know is what the Unknown snow is up to - terrain that may be a great angle to ski, but could be subject to windslab or a weaker layer. The key point is to start with small, safer steps and gradually assess conditions before getting into more risky terrain.

There are helpful hints, observations and tests that I do along the way to start getting a more accurate, localised picture. From these observations, it might be the case that the terrain I called Unknown the night before is now most likely to be Dangerous, and I will dial back my objectives. Or what I see might make me feel more confident about snow stability, to the point where I can ski more serious terrain due to verified snow conditions.

The first thing to be on the lookout for are very obvious signs of snow instability. These include:
  • Recent avalanche activity - will help indicate the size, aspect and angle of other likely avalanche areas. Any sign of avalanche activity in the past couple of days is a very good indicator of snow instability.
  • Significant snowfall in past 24 hours - most avalanches occur within about a day of recent snowfall, especially if that loading has been rapid and heavy. Leeward aspects of the mountain are going to be the most dangerous. Significant snowfall is in the 30cm in 24hrs range.
  • Obvious signs of instability - whumpfing (the sound of deeper layers of snow collapsing underfoot), a drum-like sound as you move across firm snow and shooting cracks are all red flags in regards to snow stability.
  • Recent warming and rapid weather change - rapid warming of the snowpack can lead to increased avalanche conditions, such as through rainfall or a sudden spike in temperatures. Snow will always become less stable if it undergoes a rapid change, whether that be through rapid loading with more snow, or sudden and significant changes in temperatures.

Each of the above is a serious portent of avalanche activity - especially visible signs of avalanches and obvious signs of instability.

Other than these 'red flags', there are other ways in which to assess snow stability. The ones I use (in order of time required to conduct) are:

Pole poking - I push my pole in to get a feel for snow density and to feel what's under the surface. Inverting the pole can sometimes help in getting deeper. This test can be performed quickly and easily throughout the day to get a feel for the surface of the snowpack on multiple aspects and angles. This observational method is quick but can be limited to only the very top of the snowpack.

Block cutting - this takes a little longer - maybe 30 secs to a minute. I use my pole to isolate a shallow column in the snow, then give it a yank. If it slides easily (or worse, just slides off as you are isolating the block), then conditions are looking dodgy and it is time to back off and choose safer aspects or terrain. Again, this method doesn't reveal much about deeper layers within the snowpack.

Test slopes - Bruce Tremper (who writes the best books on avalanche awareness) describes these as gifts from the mountain that you should never hesitate to make use of. A good test slope has the angle and aspect that you are looking to ski, but is short and lacking in the nasty consequences of the bigger slopes you may later climb or ski. I usually just skin up and across them, jumping and weighting the slope as much as possible to try and get a response - especially near a convex part of the slope. If they do slide, 'enjoy' the ride and know that slopes of similar aspect and angle are almost sure to slide. An important proviso is to be aware of locally connected terrain, especially above the test slope.

Cornice bombs - are as close as most of us will come to chucking explosives on to a mountain face. Cornices are ready-made testing weights that can be released on to the snowpack to see how it responds. However, there are some risks; firstly, you must be sure that no one is below you when triggering cornices. Secondly, they are extremely dangerous to approach. Ideally, you will be roped up. If not, be extremely conservative by starting your approach a long way back, using your pole as a probe, and even sticking your uphill ski's tail under the snow to give you a bit more of an anchor. I prefer to poke with my pole from a distance, gouging out a roughly human weight block that will release and slide on down. Failure to trigger an avalanche is a good - but not indubitable - sign of snow stability.

Snow pits - my preferred test is the extended column, as it not only assesses snow stability, but also tests propagation within the snowpack. It may take a bit longer (due to being 90cm across and 30cm uphill), but testing an extended column gives a much better indication of the chance of a whole slope going at once. This is a great test to do to see where weaker layers are, and to get a sense of the latent energy stored within the accumulated snow. Can take about 10-20 minutes.

Ski cuts - having decided to ski a slope, ski cutting is a great way to test snow stability - of course, the hazard is that you are entering avalanche terrain to do the test. The idea is to ski quickly across a likely trigger zone (on top of a convex roll over, for example). If an avalanche is triggered, hopefully you will have enough speed to exit its path. It doesn't hurt to do a couple of these, increasing the force you apply to the snow each time. You also need to have a clear idea of where you will be able to escape, and be aware of triggering locally-connected terrain.

Snow pit on Bogong - good stability was evident on this day

Persistent Weak Layers and Late Spring

These are two areas where I do lack experience, and so won't dwell on too much. Basically, both of these factors can mean that the snowpack can avalanche in a big way (as in size two/three plus slides). For weak layers, that is particularly the case after recent loading. In spring, the way to mitigate danger is to get an alpine start and be off the steeps when it starts to warm up, and be very wary of rainfall and its effect on the snowpack. I'll be getting some experience in managing the latter of these hazards in Hakuba this April.

Avalanche Gear

It goes without saying - beacon, shovel and probe always go in my pack if there's a risk of avalanche...which means that they spend most of the Australian winter in the gear tub at home. The snow saw is a handy addition for digging pits, but I don't see it needing to come out every time, particularly if you have developed a detailed knowledge of the snowpack you are traveling on - guys like Tremper have argued that things like test slopes are probably more useful than snow pits if you can make use of them.

Airbag packs have taken off, no doubt in part due to clips like this appearing more frequently in the mainstream media:

This guy clearly fucks up, and is lucky not to get strained through trees in a barely-size two avalanche that has a forgiving run out zone. Could have been a lot worse, and he probably would have survived without the airbag pack.

For soloing, an airbag is kind of essential I think. If I get caught, I absolutely cannot end up buried, or else that will be lights out, and the beacon will only be helping with the body recovery. Besides conservative choices, I don't have the travel systems that people in groups do (eg. skiing one at a time, watching out for one another from safe spots). Hence the airbag becomes an important tool in mitigating some of the risk as a solo ski mountaineer.

I loved the idea of the lithium battery fan for an airbag backpack. What I was not so keen on was the weight - a bit over 3.6kg for an empty Black Diamond Saga 40.  Consequently, I've sold on the Saga, and have bought a couple of the new Removable Airbag System packs from Mammut.

The 'removable' aspect is great, because it allows me to move the one airbag I own between the two different packs - the Ultralight 20 and the Light 30.

I've got the Ultralight 20 for extremely light and fast spring missions. It is a very tight fit, but I can squeeze in everything I need for spring ski touring, with the whole shebang coming in at just over 4.5kg (which includes the airbag and carbon cylinder). If you know that you can ditch ancillary items like goggles or crampons, it could be more spacious, but right now it is pretty much as small as I can go for a daypack in the hills. Sans airbag, this pack is plenty big enough for ski mountaineering, and weighs in at just over 500g - making it quite suitable for days out without avalanche hazards as a stand alone pack.

Excitingly, it is a weight penalty of about a kilo to go from my normal spring touring pack to the airbag equipped UL. That is really cool for those of us who like the added safety whilst still traveling fast and light in the alpine.

Minimal features and minimal weight - Ultralight 20 (Mammut spike protector on the ice axe to prevent puncturing the airbag during deployment)

Notably thin profile means not a lot of storage

 Spring touring load just fits in

 Packing tip - make sure to use the space under the front of the airbag (can fit a puffy jacket there). Careful packing is needed to get everything in

The Light 30 is bigger and has more features than the UL, such as top lid and hip zippered pockets for small items, and the addition of some purpose-designed internal tool storage space for a shovel and probe. Rather than back panel access, it has a more traditional top zip to access the main compartment. As promised by the 30 liter designation, it has significantly more storage than the 20 liter version. It would be more than suitable for additional gear like ascent plates, a rope and extra clothing.

 Mammut Light 30 RAS backpack

Same load as above, much more room to use

Airbag unfolded - moving between packs and repacking is easy - especially if you watch the helpful videos on the Mammut website (Mammut airbags)

So it looks like the UL will be used when I can get away with a minimal load, whilst the Light will probably be more used in proper winter when I might need more layers / gear. The only penalties for taking the bigger pack are about 600g of extra weight and the fact that it will be a little harder to jam into the top of a multiday pack due to its more robust structure and size.

If I were being super critical, I'd wish that there was an in between sized pack - maybe a 25 or 28 liter version...but really, between these two packs I'll have my airbag pack needs thoroughly covered without creating a burdensome load on my back. Can't ask for much more than that.

Team Weasel

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