Tuesday, 13 January 2015

It's all about TERRAIN

When it all comes together all the thinking and planning means you get a lifetime of fun and a pension
A few thoughts on slope assessment. At a basic level its all about TERRAIN. Firstly you need to look ahead, consult the avalanche forecast and plan ahead making decisions to avoid avalanche terrain. During travel look around you and observe what's happening under your feet and listen to the snow.  Look for red flags such as avalanche activity, wind drifted snow, recent snowfall, whumping and cracking and also be wary during rapid rises in temperature as wet snow slides and cornice collapse can trigger huge slides such as occur in Observatory Gully and Lagangarbh Corrie to name but two. Based on the avy forecast (it's a forecast and not cast in stone that its right!) and importantly what you observe, stop and do snow stabilty tests. ECT or shovel shear and compression.  This is to confirm what you should spatially be aware of.  Stopping and doing these tests is also an opportunity to talk and air views (and concerns) and make the critical decisions of whether your about to bet with your life or that of others.  Before making a drop in also consider these factors:

Angle. Most avalanches are triggered on slopes roughly between 32 and 45 degrees. Below 32 degrees victim triggered slab avalanches are less common and above this angle slopes purge more frequently. The "Sweet Spot" where most avalanches are triggered is about 40ish degrees with over 90% of victim triggered slides occurring in a 7 degree range bracketing that sweet spot. You can conclude from this that angle is a really important part of slope assessment and subtle changes of angle on a given slope can have major consequences, therefore route choice and awareness of slope angle is really important. Modern phone apps make judging the angle much easier.  Rule of thumb for me personally is that as the avalanche forecast risk for a given altitude and aspect goes up - then the angle and altitude of what you ski comes down. More recent research has shown convexity/concavity to be less important than angle.

Anchors. What is the snowpack connected to. Have you been following the weather and SAIS forecast. Are there weak layers within the snowpack. Tree's and rocks can hold a slope as your friend or can be weak spots as your enemy where sun heat or hoar frost has gathered. Subtle angle changes create trigger points at these places. Tree's are also natures cheese grater if you get taken into them. Also ask yourself what the slope you are on is linked into from the underlying snowpack. Unstable snowpack can often propagate a collapse into nearby slopes and draw an avalanche into lower angled terrain.

Aspect. Which compass direction does the slope you want to ski or travel face. Like angle, subtle changes in aspect can take you from a safe slope onto a loaded one. Carry a compass and learn about "slope aspect" as both a navigation and safe travel tool.  The SAIS forecast gives you the necessary hazard warning for compass direction but you need to apply it on the ground accurately. Again some phone apps can help with this and even give you the area forecast   BCA Snow Safety & Mammut Snow Safety

Altitude. You can see by looking at the SAIS forecast that the hazard risk is most often greater with altitude, even in Scotland. The rate of snow deposition is higher with height, and the wind is also stronger increasing side loading of slopes. On dodgy days stay lower as well as skiing lower angled slopes.
Folk need to know how to apply the forecast to trip planning by learning to understand it
Apply safe travel methods when skinning up and keep spaced and avoid terrain traps when choosing your skin line.  A slide coming from above will have the full width, breadth and depth bearing down on you. Unless its a clear runout your pretty well fecked as any stream bed or features will trap you and allow the snow to build up deeply over you. Choose your line well and with some thought.

Complexity. As mentioned above. Be aware of subtle changes in angle and aspect and that localised instabilities are hidden and like a landmine can link one triggered mine to a chain reaction and a small slide gathering surrounding instabilities into a major avalanche event. Learn to read mapping for subtleties of terrain features and how snow may be affected, and think safety by pre imagining what could go wrong. If it's a complex route then its often unsafe as there are too many unknowns. Learn to know what you don't know! (The Dunning Kreuger Effect)

Commitment. Always have a plan "B" so that if conditions change or are not what you expected you have another safer option.  Commitment to a slope can mean no bale out options, i.e having no where to go.  If you look at the pro's on youtube they choose their line so they can bale out onto a spine and have good runouts and that's where the next "C" comes into play - consequences.

Consequences. If its an amber light's on in your head so your in a go/no go process, then add consequence into the thought mix.  Are there crags, hollows, stream beds, tree's or any other terrain features that could shred you or trap you if there is an avalanche. Transceiver, shovel, probe and/or airbag will not stop you getting your limbs ripped apart from tree's, your head humped like mince, or with an inflated airbag under a few hundred tons of snow. Airbags are good with a save rate of between 10 and 13  more people per hundred victims - but only if the runout is good. More up to date North American stats also show that many more people die from two of the triple "H" than was thought. Hypoxia and Hypercapnia kill quickly and any browse of excellent news sites like piste hors will tell you that even folk dug out very quickly with advanced life support don't often survive. (Triple "H" syndrome is Hypoxia, Hypercapnia re breathing your own carbon dioxide, and Hypothermia. Hypothermia can have a protective effect in rapid cold water immersion, but in an avalanche cooling is slow especially as modern clothing retains heat so well. In fact its not so much the lack of oxygen as the hypercapnia that makes survival so poor in a an avalanche, and this with hypoxia is also related to snow density). 15m as often shown in survival graphs is quite optimistic. You need to search faster and dig faster which means practise more!

When dropping in stay next to each others tracks, go one at a time well spaced and from a safe area to safe area. What's a safe area?  Good question as sometimes there are none, but basically its somewhere out of any slide path that you can identify. Consider that if its a big slide it could encroach on your safety island so pick your spot with care.

Be prepared to carry out a rescue. You are on your own as organised rescue will be too late. Talk this over before dropping in.  You should all have done an avy course and so will have the gear, done the pre checks and discussed a plan - won't you?  If you have not done an an avy course then consider why the feck are you even doing this!

Fail to plan and think it through and it's never pretty. A ski tourer who was avalanched.

1 comment:

  1. Really powerful article Davy - much appreciated by many.