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Know the Snow: Habits in avalanche terrain

Posted: March 16, 2012 - 12:07am
To measure the safe distance from a slope we measure the angle between us and the area where avalanches start on the slope. We call this angle the alpha angle. The alpha angle around the world is between 18 degrees and 21 degrees.    Graphic courtesy of Ron Simenhois
Graphic courtesy of Ron Simenhois
To measure the safe distance from a slope we measure the angle between us and the area where avalanches start on the slope. We call this angle the alpha angle. The alpha angle around the world is between 18 degrees and 21 degrees.

Early in my career I was working as an avalanche forecaster for a ski area in New Zealand. One stormy morning, we headed to an area called South Face to do avalanche control. We assumed that we would encounter unstable snowpack and trigger several avalanches.

To our surprise, our efforts were unsuccessful. None of the control teams triggered a single avalanche throughout the morning. Things were about to change, when we reached the last spot on the control route. There were five of us, standing in the same area, waiting for a bomb to go off. As soon as the bomb exploded, a fracture line developed above us and an avalanche started to slide taking the other four patrollers with it. No one got hurt and after a few minutes of searching for lost equipment, accompanied with colorful words, we headed back to base equipped with another life lesson and a good story to tell. Could we have done better? Yes! We were all bunched up in one questionable spot on the slope. We chose to ignore one important rule: Never expose more than one person at the time.

We were not alone; the vast majority of avalanche victims choose or unknowingly ignore safe travel practices. In his book, “Staying Alive in Avalanche Terrain,” Bruce Tremper notes that in about nine out of 10 avalanche accidents, the avalanche was triggered by the victim or by someone in the victim’s party. This staggering statistic means that killer avalanches rarely happen by chance; we trigger them. Since we trigger the vast majority of the avalanches that catch us by choosing where and how we travel on snow, we can improve our odds by developing a few simple behavioral habits when we play in the mountains.

There are a number of safe behavior habits out there. Most of the habits I have developed throughout the years aim to minimize exposure and heighten consequence awareness. When I travel in a group, I like to cross, ski or be in an avalanche path only one person at the time. I don’t like to load a slope with more than I have to. I also like to minimize the number of people that are exposed to a single avalanche path to one time. This is my number one rule. Following the one-at-the-time rule can almost eliminate all cases of multi-victim avalanches. That means that if a buddy gets the snowmachine stuck high marking, for instance, she needs to sort herself out by herself. Getting on the slope to help a friend can overload the slope and expose more than one person to an avalanche. Also, in case an avalanche accident does occur, I like to make sure that at least one person is always in a safe spot. After all, someone has to do the rescue and call for help.

When I climb a slope, I like to climb on a rib between avalanche paths. If I have to cross avalanche paths on my way, I try to cross them in a slight downhill direction to maintain speed and decrease exposure time crossing avalanche paths.

On flat areas with slopes above, I try to stay as far as I can from the slope. Whenever I can, I try to travel in the trees. If there are no trees in the areas, I try to travel far enough from the slope above that if an avalanche comes down from above, it will stop before it hits me. How far is far enough? To measure the safe distance from a slope we use an inclinometer and measure the angle between us and the area where avalanches start on the slope. We call this angle the “alpha angle”. The further we are from the slope, the smaller the alpha angle. Over the years people measured the alpha angle in different places around the world. They have found that the alpha angle slightly varies from one mountain range to another. Depending on the shape of the slope and the type of the snowpack, it can be somewhere between 18 degrees and 21 degrees.

If I travel on a flat area within the reach of a potential avalanche from a slope above me, I try to give myself the best chance of getting away from a potential avalanche by traveling on the edge above a slope below me. By doing so, I can pick up speed quickly and increase my chances of skiing away from the avalanche path. Many of my avalanche savvy snowmachine friends do the same when they sit and watch their friends play on the slope. They keep their snowmachines idle and facing away from the slope, ready to get away from the slope as soon as they see an avalanche coming their way.

• Ron Simenhois is an avalanche forecaster who lives in North Douglas. You may contact him at simenhois.ron@gmail.com.

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