As snow accumulates it forms layers of different density and strength. When weak layers below the surface can no longer support the snow above, an avalanche results. Seems simple enough, but with the addition of factors such as temperature, slope angle, wind and time, winter travel becomes much more interesting and dangerous. Then there is the human variable--the fact is that most avalanches are triggered by their victims. And this: avalanches are most likely to occur on slopes with an angle of 35 to 45 degrees, which also happens to be the slope angle most interesting to skiers, snowboarders and climbers. Determining whether a slope is safe to ski down or climb up requires three things: knowledge, action and attitude.
KnowledgeWhen it comes to avalanche safety, you simply can't know too much. Many excellent books about avalanche safety are readily available and the comfort of your easy chair is a fine place to begin researching avalanche safety.
Once you've done your homework, it's time to go to school--avalanche school. Avalanche classes are a vital link between book learning and the real world of winter. Your time with an avalanche instructor will supply first-hand knowledge on how to properly evaluate snowpack, terrain and weather. It's also a time to learn how to use the tools of the winter backcountry game. These include avalanche transceivers that help quickly locate buried party members, and shovels (one per person) that allow you to dig out your companion.
ActionEventually, you act on your new knowledge. In reading and classes, for instance, you will have learned about digging snow pits to evaluate a snowpack. As you dig into the snow you are glimpsing the history of snowfall, wind and temperature, much like reading growth rings of trees. Careful observation of the snow will reveal how well the layers are bonded to one another, the existence of an ice layer than can act like Teflon, or the formation of large slabs of snow that may slide as a single unit.
Once you have evaluated a snow slope as best you can, you still face a pesky decision: Do I ski this slope or not? If your gut says "not today," listen to it. Sit down, pull out your thermos of hot chocolate, and think about how great this slope will be when the snowpack is consolidated.
On a 1997 ski traverse of the Wapta Icefields in Canada, I came up against this moment of truth and failed the test. Four of us had skied to the summit of Mt. Gordon, a wonderful ski peak along the way. For several days we watched avalanches on surrounding peaks, a sure sign of instability if there ever was one. Standing on the summit of Gordon, we considered our options. Ski back down the way we had come, or sample a short but steep adjacent slope that appeared to hold a thick stash of powder.
Mark and Tim listened to their inner voice, and quickly chose to take the safer option. But Jeff and I turned the skis toward the enticing slope without digging a snow pit. Jeff was in the lead and took the first run, disappearing from my view as the slope dropped away. Below, Tim and Mark watched as Jeff cut a turn and released a slab of snow some 50 yards across. Jeff somehow stayed on his skis and escaped to one side, avoiding possible burial. I saw only Tim and Mark's reaction and heard their exclamations. I realized in that moment that I had allowed my enthusiasm to get the best of me.
How could I have lost my normally cautious mountain demeanor so easily? How will I explain this to my wife when she asks how the trip went? As it turns out, the lower angle slope made for great skiing. How much are the extra few degrees of slope angle worth? Not enough. I should have listened more carefully to the inner voice. Next time...