What is a Terrain Margin?

So what is a terrain margin? It is a margin for error that allows you the ability to make a small mistake without going over the line and exposing yourself to injury or death. Translated into backcountry travel, a margin means not pushing your mental model of the avalanche problem’s size, likelihood and distribution right up to the edge where you think it will be. For example, if there is a layer of sensitive facets down 60-70cm on due north aspects you should also avoid large or consequential avalanche terrain on NE and NW aspects. If you suspect the avalanche problem is in specific places you not only need to avoid those specific place but add a “little extra” in the terrain you plan to avoid to accommodate a small error in the forecast, your observations, or your assessment of the terrain and where the avalanche problem lays within it either in the field or in the planning stages.

This can be challenging because a majority of the time everything will be fairly spot on. However if you get in the habit of always pushing the terrain right up to the avalanche problems' true margin, before long the forecast, your observations, or your assessment of the terrain is going to be slightly off and the consequences could be dire. Remember there is rarely a “do-over” if you do go over that line and the potential for a game-ender is real.

Employ good travel techniques

In your AIARE 1 you learned that travel techniques never come before terrain selection. This remains true but it's also important to see how the implementation of good travel techniques is a great way to increase your groups safety by increasing your margins. An example is spreading out or crossing a slope one at a time (while going up or down) while crossing or below pieces of avalanche terrain. Yes you need to feel good to even consider going into that terrain but spreading out decreases the exposure level of the group if you are wrong. Of note anytime you spread out or travel through terrain one-at-a-time you should have a predetermined regrouping point. This is because we have learned that we make better decisions as a group than alone and regrouping lets everyone come back together and discuss how they are feeling about the conditions and the terrain.

Margins and Uncertainty

There are no hard-and-fast rules with how much margin you need. Good familiarity with the terrain AND the snowpack OR generally more stable conditions and isolated avalanche problems mean you might not need as much of a margin. However, a more widespread avalanche problem, the potential for larger avalanches, or while traveling in new terrain or new partners mean you should give yourself an additional buffer with a larger margin.

Margins relate directly to uncertainty. The more unstable the conditions or the more uncertainty you have in the snowpack, the terrain, or your team the more you need to dial back the other parts of that you can control. For example if you have really unstable snow you need to go to areas were you know you can avoid the prescribed avalanche terrain with partners you are familiar with. Or if you would like to check out a new zone it is best to go with people you know during times of lower levels of avalanche hazard.

What it boils down to is the more uncertainty you have the more margin you should build in.