Terrain Tip No. 1: Apply a Margin of Safety

Terrain Tip No. 1: Apply a Margin of Safety

In the Terrain Tips introduction we quoted the old guide adage, “When unstable snow is the problem, terrain is the solution.” And we talked about what it looks like to use terrain to reduce the risk of getting caught in an avalanche.

In Terrain Tips No. 1, we discuss applying a margin of safety, or a buffer zone, between our proposed ski line and more hazardous terrain to allow a margin for error.

Photo No. 1 by Colin Zacharias. Whenever possible, place a protective piece of terrain—a ridge or a bench—between your route and more hazardous terrain.

In photo No. 1, the less hazardous slope lies skier’s right of the downslope ridge or moraine (looker’s left of the red line). The greatest hazard is exposure to avalanches from above. New snow, wind loading, sun exposure, or cornice fall can promote avalanches that could easily slide from the steep upper slopes and obliterate the moderate angled slopes below. Those who choose to stay on the skier’s right side of the ridge smartly place a protective piece of terrain (in this case a ridge) between them and the more exposed, hazardous terrain above. The less hazardous slopes still have shorter avalanche slopes and terrain traps, but these can be avoided using clear instructions and group management.

Photo No. 2 by Colin Zacharias. Build in a margin for error, or buffer zone, in case the adjacent slope remotely triggers and fractures deeper and farther across the slope.

In photo No. 2, the skiers noted a weak layer 20 to 25 centimeters deep and wisely choose to descend the slope one at a time. Of course, descending one at a time will not prevent avalanches nor reduce the chance of burying at least one skier. Terrain choices always supersede group management measures. Thus the most important decision the group makes is to choose the piece of terrain with less likelihood and fewer consequences.

The first skier uses his ski track as a fence line (“Ski right of my track!”) and leaves a buffer zone between the chosen descent route and the hazardous terrain farther skier’s left. This more hazardous slope is steeper, longer, and wider. This slope runs out into a low-angled bench that can accumulate avalanche debris. The start zone is more wind affected, has variable snowpack depth and layering, and has exposed rocks and small trees that indicate probable trigger points. This slope is more likely to be triggered and is more likely to result in a larger avalanche. Rather than punch in a line just skier’s right of the slope in question, the skiers choose to apply a larger margin of safety to today’s decision. In this case, they leave a buffer zone that allows for Murphy’s Law—what can go wrong will go wrong. (For example, the adjacent slope remotely triggers and fractures deeper and farther across the slope.) 

Photo No. 3 by Joe Royer. Choose a line that you think has a reduced chance of avalanching and fewer consequences, and build in a margin for error. If there is overhead exposure, put a protective piece of terrain, like a ridge, between you and the terrain above you. In this photo, skiers do both.

Photo No. 3 illustrates a masterful use of terrain in a shallow, rocky, continental snowpack—with a dangerous weak layer near the ground. Here is how the skiers here use terrain to lessen the risk:

 

1.     The skiers descend one at a time.

2.     The skiers leave just enough of a buffer zone on the upper slope to avoid the obvious trigger points (marked with an X) and avoid the cross wind-loaded unstable start zone.

3.     Below the first slope, instead of turning downslope and increasing exposure, they travel farther skier’s left and place a protective piece of terrain (a bench and small ridge) between their line and the unstable slope above.

4.     The descent line avoids travel through the lower slope and terrain traps, avoiding overhead hazard and increased consequences.

 

All three images are examples of how to apply a safety margin to our terrain choices. Never pass up the chance to place protective terrain, such as a bench or downslope ridge, between your line and a hazardous slope. And when you choose a line that you think has a reduced chance of avalanching and fewer consequences, don’t forget to build in that margin for error and place a buffer zone between what you think is likely safe and the more hazardous line.

 

Colin Zacharias is a consultant and educator in the avalanche and mountain guiding industries, and an IFMGA/ACMG mountain guide. He resides on Vancouver Island.

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