Tree Well and Snow Immersion Suffocation (SIS) is a real danger to skiers and boarders. This is particularly true in Washington and British Columbia due to the nature of our forest and snow pack. Skiers and boarders need to be aware of tree wells, recognize the danger they pose and know how to mitigate the risk. Unfortunately, snow immersion suffocation is probably one of the least appreciated risks skiers and boarders will encounter within ski area boundaries.
As the current trend in skiing and boarding takes riders deeper into the side and backcountry, the need for greater awareness of tree well immersion danger has never been greater. In an article published by Paul Baugher of the Northwest Avalanche Institute examining tree well immersion, he concluded, “The greatest single component of snow immersion risk is that it is substantially under appreciated.”
A tree well is a void in the snow that forms around the base of a tree. Evergreens common to Washington such as fir, cedar and hemlock often have large low canopies that function like an awning that can prevent snow from filling in around the base of the tree. As the snow pack increases through the season, the void under and around the base of the tree can continue to increase in depth and danger. Add fresh, loose, dry snow and you have a potentially deadly combination of conditions.
Most tree well immersions naturally happen after big snow events. That’s when most skiers and boarders leave the groomed runs and seek fresh powder in the trees. Unfortunately, that’s exactly the time the tree well danger is also the greatest. Coincidentally, most victims of tree well immersion are advanced or expert skiers or boarders.
Tree wells can literally swallow a skier if he or she is unfortunate enough to fall into it. The problems start when a skier falls near a tree with a deep well. If the skier falls or slides headfirst into the well, its easy to become trapped and unable to free oneself. At that point, loose snow falls in around the skier. Often the problem is compounded by snow being knocked off the tree itself. As the snow packs in around the skier it become denser and denser. The skier soon becomes immobilized and buried and is now quickly at risk of suffocation.
Real world experiments have been conducted on tree well immersion which underscore how dangerous the tree wells can be. Recent studies have demonstrated that 90% of people involved in tree well immersions cannot extricate themselves. In an experiment conducted at Crystal Mountain, Washington in 2006, volunteer ski patrol members were exposed to tree well immersion in a controlled environment in real world conditions on the mountain. They were observed attempting to extricate themselves from the tree well. The results were startling. Most of the test subjects could not extricate themselves. Most found that struggling only further compromised their situation by destroying any air pocket they may have initially established. Most of the subjects were not able to remove their skis or board. This experiment and others like it demonstrate how quickly skiers can become helplessly trapped in a tree well. Once that happens, the clock for survival is ticking.
There are things that a skier or boarder can do to protect themselves from tree well immersion. The first and foremost is to be cautious to avoid riding too close to trees. Its far better to avoid encountering a tree well than having to be rescued from one. Next, the single most important factor in tree well immersion survival is to practice skiing or riding with a partner. For this to be effective, partners need to stay close and be able to maintain visual contact with each other. Sadly, many immersion victims have died while their partners were waiting for them at the bottom of the lift.
Deepsnowsafety.org has some great tips for what to do if you fall into a tree well:
If your partner becomes trapped in a tree well, deepsnowsafety.org recommends these steps:
The bottom line for skiers and boarders is that awareness and appreciation of tree well immersion danger is critical. Statistics prove that you are much more likely to die in a tree well in bounds than an avalanche. However, the good news is that with awareness and vigilance, tree well danger can be managed.
Next time you are out skiing the trees on a powder day, keep your partner in sight, stay safe and have a great time.
For more information please go to www.deepsnowsafety.org