Tuesday, 31 January 2017

Pre Season Avalanche Avoidance Advice

1. Learn How to Interpret the Avalanche Forecast

The Avalanche Danger Scale uses five progressively increasing danger levels: Low, Moderate, Considerable,  High and Extreme. It indicates the likelihood of avalanches, how they might be triggered and recommended actions in the back country. However, the wording is very brief and does not include a meaningful indication of risk. Below is an explanation of each danger level, including the transitions between levels, signs of instability at each level and the implications of slope angle, aspect and elevation.
Understanding the SAIS forecast and acting on it could save your life
Travel is generally safe. The snow pack is well bonded and natural avalanches will not be seen except for small sluffs on extremely steep slopes. Human-triggered avalanches are unlikely except in isolated locations in extreme terrain. The danger will usually be from wind-driven snow in gullies and chutes or deposited across very steep open slopes near ridge lines. Ski or board one by one as smoothly as possible without falling if you suspect the formation of wind slab. Be aware of shaded, north to east aspects where the danger may be transitioning to Moderate. There are few fatalities at this danger level.

This is the most difficult danger level for back country skiers and boarders to assess snow stability. Many of the usual indicators such as cracks, settling, whumpfing and signs of recent avalanche are absent, especially at the lower end of the moderate level. Key indicators are any recent snowfall, and wind deposition. Snow pack tests may help assess stability.

Conditions are generally favorable for travel providing routes are chosen carefully. The snow  pack is only moderately bonded on some steep slopes. Areas of danger are usually restricted to certain types of terrain such as bowls and gullies. The altitude, aspect and type of terrain where danger can be expected are usually detailed in the Avalanche Forecast. Remote triggering is unlikely, so you only need to be concerned about the steepness of nearby terrain features.

Human-triggered avalanches are possible. Ski or board carefully, one by one, in suspect terrain and avoid high loading of the snow pack by spreading people out on the uphill track. Carefully evaluate the stability of very steep slopes (steeper than 35°) and aspects identified as potentially dangerous in the Avalanche Forecast.

Be especially careful if the higher elevation band in the forecast, or the danger on other aspects, is Considerable. There is a significant difference in instability between Moderate and Considerable. Don’t get sucked onto higher, steeper and more dangerous slopes. Although naturally triggered avalanches are not expected, ice climbers should watch out for the sun warming steep collection zones above their climbs. If deep-slab instability due to a persistent weak layer is mentioned in the Avalanche Forecast, you need to pay careful attention to the terrain. Avalanches from such a layer are not only likely to be large and extensive, they are completely unpredictable. Unless you have specific local knowledge, keep off large open slopes at this danger level if the forecast warns of a persistent weak layer.

29th March 2013 SAIS Graphic
Persistant Weak Layer March 2013

Click pics to enlarge

Large Slab Triggered off persistant weak layer 30th March 2013
Fatal Avlx x 1 Skier
Conditions have become much less favorable. The snow pack is only moderately or poorly bonded over a much larger area of the terrain. Human triggering is possible by a single skier on steep slopes and aspects mentioned in the Avalanche Forecast. Remote triggering of avalanches is possible, so the maximum steepness of the slope above you should be used when deciding if you want to continue.

Instability indicators mentioned in Moderate danger above will likely be present. Back country touring at this danger level requires good route finding skills, and experience in recognizing dangerous terrain and evaluating slope stability. Keep to slopes of less than 35°, especially slopes at the altitude and aspect indicated in the Avalanche Forecast. Remember that remote triggering is possible. Typically the scree fans at the bottom of gullies starts out at around 30° and the slope steepens as it gets higher. Keep off such slopes at this hazard level. The remarks about persistent weak layers in the previous section on Moderate danger level also apply to this danger level.

Reports such as the above showing circles or areas of "considerable" risk within a moderate NW to E is the sort of thing that it's easy to become complacment about as its a common feature of the Scottish winter. You might very obviously if you have any sense stay well clear of the West to South East apsects but wander into a high risk situation on descent on the NW to East aspects.  The majority of avalanche incidents in Europe occur in these moderate to considerable forecast days as they occur most frequently in the season and folk become complacent (the familiarity heuristic) and that's why route choice approaching a climb and thinking about descent options prior to leaving and during a trip as wind and weather change should become part of your thinking.

Conditions have become dangerous, most often as a result of significant amounts of new snow, snowfall accompanied by wind or the snow pack becoming isothermal and threatening wet-snow avalanches. The snow pack is poorly bonded over large areas and human triggering is likely on steep slopes (steeper than 30°). Remote triggering is likely and large natural avalanches are to be expected.

Stay on slopes that are flatter than 30° for any part of the slope and be aware of the potential for avalanches from slopes above. If you do decide to walk ski or board on less steep slopes, be very aware of the surrounding terrain to avoid inadvertently crossing the bottom of steeper slopes or cutting down a steep convex rollover.

Usually this level of hazard is only present for a few days at a time. The smart back country traveler will stay in simple terrain until conditions improve. If you are caught out on a multi-day trip you may have to dig in and wait for travel conditions to improve and the avalanche danger to lessen.

Glencoe 19th March 2013
These circles in the avalanche forecast. My take is to think of them as landmines blown by the wind, lurking in eddies from cross loading when the wind blows across as well as down or over a slope, the color of them is the sensitivity of the pressure plate to you the trigger. If there are enough of them the explosion will propagate setting of others, or if the surrounding slope is weak enough then it will slide with it. As you can see there are areas of High on slopes with a "considerable" risk.  A lethal combo of detonator in red -  and explosive on orange making for events that will take lives if you don't tread warily.

Extreme danger levels are rare in Scotland as usually this level is associated with buildings and roads or alpine villages under threat, and usually the result of unusually large amounts of new snow. The snow pack is weakly bonded and unstable. Numerous large avalanches are likely. The weight of the new snow can trigger avalanches on layers buried deep in the snow pack. Natural avalanches can release on slopes of less than 30° Back country touring is not recommended and often impossible. Avoid all avalanche terrain and keep well away from avalanche path run outs.

2.  Avoid Groupthink
In psychology "Groupthink" or "Risky Shift" behaviour is well known in groups and most of us will be aware that we have given in to it or even encouraged it. I strongly believe that in avalanche incidents in Scotland this groupthink or risky shift has become the biggest education issue and maybe why we see large group incidents or group events as occured in the Cairngorms when two seperate groups were avalanched last winter. Much has been made of the quick response from folk training in the corrie who helped.  And good on them. What I am about to say is not a reflection on these helper folks choices, as I am sure they stayed in safe terrain.  The  "however" bit though is that just by being there and numbers increase with lots of MRT's training, and groups under instruction, then a larger "Groupthink" takes place. Groups less experienced or not under instruction maybe feel safe, what McCammon labels  as Social Facilitation.  I would call this a  "risky shift". It's often this way in the climbing and skiing honey pots such as the Northern Corries where folk gather. Aonach Mor or ScRL in Glencoe are other places. Even if the waggon wheel of death shows Red on these slope aspects, they are still the places to be seen by the instructor masses who are now at the height of their annual gatherings with paying students. These are the places instructors are familiar with, and therefore where less experienced folk feel safer with an apparent safety in numbers. They maybe went there when they were on a course. Group thinking on a large scale perhaps.

Better minds than mine have already written about risky shift and here's an excellent article on it The Risky Shift Phenomenon and Avalanches. This kind of stuff has been getting applied to avalanche instructor training for a while by AAA.  Do current winter mountain training schemes  include enough if anything on this sort of thing?  I put this as a question, as I am certainly not in a postion to know, and maybe it is already covered. What I do know is that there is nothing that can change the pretty piss poor odds if buried and that pretty universally all of us involved in avalanche education are trying to jump forward and get to "no rescue".

No matter what we do, mountains and people are unpredictable. As a a keen off the piste skier I have to accept that luck is also in there as well, as on good snow days I am first in the que and having gone through the forecasts, stability tests you are only left with how the snow feels under you ski's and gut instincts. Sometimes it's a very subtle thing where in the morning it feels wrong, and by afternoon the snow "feels" safe.  I don't know how the feck that would stand up in court! I also know its taken 40 years and I still can't always be sure it all won't go tits up one day. I also know that it pays to voice your opinion when in a group, and make your own choice, not getting swept along by the group and it's most vocal leader. Beware Risky Shift!

"Destiny is a good thing to accept when it's going your way. When it isn't, don't call it destiny; call it injustice, treachery, or simple bad luck"   Catch 22 by Joseph Heller


For backcountry travel,side stash/off piste, or indeed anything out of ski area and uncontrolled, always carry the three essentials of transceiver, shovel and probe and do a pre depart group test and practice.

If you need an airbag you have fucked up but might survive. If you need your transceiver you have fucked up and probably won't!


1 comment:

  1. Hi Davy,

    Good blog post.

    I wonder if the new SAIS system of using dots to indicate "localized hazard" is perhaps somewhat misleading ? I can see merit, as it in theory it allows more detail to be added to the rose. However the dots can also be potential confusing....

    1) When looking at the rose you perhaps don't see the orange *considerable* risk being as being an obvious feature of days forecast.

    2) What is more important information to get across on the rose ? The "considerable" aspect ? Or the perhaps "localised risk" ?

    3) In retrospect there was nothing localised about the Avalanche on 30th March. Sadly one of the biggest avalanches I have ever seen on Meall A Bhuridh...

    Just a few thoughts about how people / punters like myself may interpret the forecasts & rose. No criticism of the SAIS in any way (the detail is always in the text)