Risk Assessment and preparation
Types of Avalanche
Risk Assessment and preparation.
The golden rule of back country or off piste skiing and snowboarding is to AVOID avalanches. Everyone should be properly equipped and trained to deal with an avalanche but nobody should ever have to ! The key to safety is Local Knowledge. The problem is that the best slopes to board and ski down are the most avalanche prone. If you are touring then you can plan your route to avoid dangerous slopes but if you are looking for steep powder runs then you are deliberately putting yourself in a dangerous position. Backcountry boarding and skiing is hazardous and you should be aware of the risks. Snowboarding and new ski technology has opened up the backcountry to people with limited alpine experience who treat it as a video game style competition and the avalanche accident rates have risen accordingly! You have as much right to be there as anyone else but everyone should be armed with a healthy fear of avalanches.
You should be aware of the local conditions before you go out. When did it last snow? Are there any slopes that always avalanche? Has it been warm or cold? How many snowfalls have there been this season? How windy has it been? Have there been many avalanches this season? All these questions give you an idea of the risk you are facing. There is no substitute for local experience and knowledge. You are most at risk just after a snowfall and the more snow that fell the greater the risk.
New snow added in 3 days compared with observed avalanches
Up to 10cm - rare avalanches, mostly loose snow
10 - 30 cm - very occasional slabs, frequent sloughs
30 - 50 cm - frequent slabs on slopes 35 degrees
50 - 80 cm - widespread slabs on slopes down to 25 degrees
2. Slope selection
If you are happy with the general snowpack conditions, you then need to consider the slope or terrain that you wish to use. All faces look fantastic covered in fresh powder but there are some important questions to be answered about each slope.
How steep is it? Below 25 degrees is not steep enough to slide, above 50 degrees is too steep to hold a lot of snow, anywhere between is prime avalanche territory
Is the slope concave or convex? Convex slopes do not support the weight of the snow high up very well and are more prone to avalanche
What is the slopes aspect? North facing slopes are less affected by the sun and colder just after it has snowed, south facing slopes consolidate more quickly and are safer a few days after the snowfall. This is especially true in the springtime where south slopes consolidate quickly and north facing ones can remain dangerous for days or weeks after a snow fall.
Is the snow wind affected? If the wind has been from behind the slope it will have deposited a lot of snow on the slope and given it a pillowed effect. There is now a great weight of snow to be supported and the risk is higher. If the wind was strong as well it may have formed a slab, where the snow has been blasted together in one huge lump. In this case the risk is high and if there is an avalanche it is sure to be a big one. If the wind was up the slope it will be scoured, and most of the loose snow will have been removed , this will be safer but the conditions not as good. A cross slope wind will give both conditions at different places on the slope. The ideal is for the snow to fall in still wind conditions but that happens only when there is a blue moon!
What time is it? How much sun has your slope received today. A slope can be safe at 10.30, dodgy by midday and downright dangerous by 1.30. The avalanche risk changes all the time, just because there are tracks does not mean it is safe!
What is the 'run out' like? If your slope fans out into a wide gentle area, an avalanche will slow down and spread out reducing your chances of being completely buried, if it runs into a gully or depression you may be buried under many metres of snow and digging you out could take hours
3. General tips.
If your assessment has revealed that the slope is too risky then you must walk away. It is tempting just to say 'sod it I'm going down' especially if the snow conditions are good, and you may escape incident this time. But that attitude will eventually get you killed. You can ride many more slopes in ten years safely, than skiing all the slopes all the time until you get killed.
Hopefully you have answered all these questions and decided it is ok to ride down. That, after all, is why you are there. These hints will further increase your security.
At the start of the day check all transceivers are on, switched to transmit and have good batteries. It is worth actually testing all the transceivers. Never take it off during the day.
Never board or ski alone, big groups are also dangerous because of the weight and difficulty of controlling everyone. 4 is the ideal size of party.
Loosen your backpack and pole straps. This can easily be dumped if the worst happens.
If you do end up in a dangerous situation, only one person should move at a time, the others should be watching him/her in case he/she is avalanched
Try to move from one safe spot to another, i.e. the top of the slope to below the big rocks halfway down and on the left side. If there is an avalanche that someone else starts you don't want it to get you as well
Use the edges of bowls and not down the middle
Ski/Board down ridges and spurs rather than bowls and gullies
Do not bunch up. This places extra stress on the snow pack and weakens it, plus leaves no one to do the rescue-ing
Do not board directly above someone else, you are putting them in danger
Do not traverse slopes. If this is unavoidable traverse as high up as possible. Never traverse above other people.
Watch and listen for cracks and movement in the snowpack, you may get a warning to be very careful!
Avoid boarding/skiing under cornices. They are evidence of wind loading and may fall off and cause an avalanche.
An avalanche needs something to start it. It is a myth that loud noises trigger avalanches. In 99% of cases it is the person that starts their own slide. This is normally caused by the person crossing a weak spot or 'trigger point'. This can be anywhere on a hollow slab or where the slope suddenly steepens. It can be along an obvious feature like the bottom of a row of trees or an old fracture line in the snow. It can also be undetectable like where the ground changed from scree to grass and the snow could not bond as well. You cannot know where the trigger point is but you can avoid the most obvious ones. This is the reason you never traverse above other people because your long cut in the snow may become the trigger point. Don't start something that you cannot stop!
This is a very brief summary of things you should know and think about. There are several books devoted to this subject. Avalanche safety for skiers, climbers and Snowboarders by T.Daffern is an excellent example. This book covers all these topics and more in greater detail and with more authority than I have here. Backcountry Snowboarding by C Van Tilburg also has a lot of information. There is no substitute for experience. Attending an Avalanche Awareness course is an excellent way to improve your skills. You can never eliminate the risks of backcountry boarding but you can do your best to reduce them to an acceptable level. There are accidents every year involving experienced climbers, boarders and skiers so never become complacent.
Despite all your efforts and using the above techniques you may still be involved in an avalanche, or you may come across someone in an avalanche who needs your help, now you need to have an avalanche transceiver, shovel and the skill to use them. I repeat, there is no substitute for experience. You should have practised search techniques until you can locate a buried victim in under five minutes.
This page is not about how to use a transceiver but about not having to use one.
If you are searching an avalanche site never forget the possibility of a subsequent avalanche. If possible post a look out to protect the searchers. If this happens quickly switch your transceiver back to transmit, try to move out of the path of the avalanche and hope there is somebody left to do the searching.
If you are in an avalanche or see one coming then there are a few things you can do. It may not be possible to do any of them but if you can, you should
Jettison your poles and backpack (already loosened ). You may want to keep your axe if the avalanche is small and there is a chance of holding your ground. Try to move out of the way or to the side of the avalanche path, prior planning will tell you which way to go. Once in the avalanche try to go down feet first to protect you from rocks and obstacles, If not using your arms to protect your head from debris try to do a double arm backstroke movement. This will stop you sinking too deeply into the snow. If the slide is cold and powdery try to cover your mouth and nose with your jacket or glove to reduce the risk of suffocation. Keep your mouth shut! Save most of your effort until you feel yourself slowing down, then try to fight your way towards the surface. Being on or near then surface will greatly increase your chances of a speedy rescue. You should also try to create an airspace around your head.
As you feel yourself stop make a supreme effort to push yourself up towards the surface. It might be the last thing you do, but it could make all the difference
Types of Avalanche
1. Soft Slab Avalanche
This is the most common type of winter avalanche and associated with the build up of fresh snow on lee slopes. The snow is moved by wind of 10-30 m.p.h. After a heavy snowfall it could occur on any slope. The slab is released as a single unit but breaks up as it flows over the ground. If there is enough fresh snow and the slope is steep enough then it may become a powder avalanche.
2. Dry Powder Avalanche
This type is most common in cold dry conditions and after a fresh snow fall. If it snowed heavily, at 2cm per hour or more, then it is especially risky. As little as 20 cm of fresh snow poses a threat. The snow starts to move as a soft slab and gathers speed and more snow. The snow will ride up on a cushion of air and become an airborne powder avalanche travelling in excess of 100 m.p.h. In front of the avalanche will be a blast wave. Inhalation of snow and suffocation is often a problem with this type of avalanche.
3. Hard Slab Avalanche
The hard slab represents one of the greatest dangers, not because of its frequency but because its solid appearance gives a false sense of security to those travelling over it. The combination of strong winds (more than 30 m.p.h.) and cold temperature favour its formation. If it remains cold then the danger may persist for some time. The slab can even be covered by further snow falls. The slab releases in one unit like a soft slab but breaks up into great chunks of snow and ice that have enormous destructive power. Watch out for sudden local subsidence, cracking or dull booming noises as clues that you may be on a hard slab.
4. Wet Avalanche
Common in spring and thaw conditions, water flowing through the snow or between the snow and ground has weakened its adhesion. These travel at relatively slow speeds but carrying a huge weight of snow and water. These are the easiest to predict due to the weather conditions for their formation. Cracks in the snow and large snowballs rolling down are visible clues