In light of this recent tree well tragedy, I will be posting this in my "Sierra Lady About Town" blog on Howard's subscription weather letter which will be out this Thursday:
TREE WELL AND SNOW IMMERSION SUFFOCATION – SAFETY TIPS
In light of the 12/17/16 tree well fatality on Mammoth Mountain after a previous big storm which brought heavy, wet snow to the Sierra, I thought it important to supply some education on the dangers of tree well and snow immersion suffocation.
A tree well/ snow immersion suffocation accident can happen when a skier or snowboarder falls – usually headfirst – into a tree well or deep loose snow and becomes immobilized and trapped under the snow and suffocates. In an inverted position you can become trapped under the snow. Breathing becomes difficult as the loose snow packs in around you. Without immediate help from your partner, you may suffocate. Prevention of falling into a tree well or areas of deep snow is all-important because the odds of surviving deep snow immersion are low. 90% of people involved in Tree Well/ SIS hazard research experiments could NOT rescue themselves. If a partner is not there for immediate rescue, the skier or rider may die very quickly from suffocation - in many cases, he or she can die as quickly as someone can drown in water.
Most Tree Well/ SIS accidents have happened during or just after big snow storms or storm cycles. In general terms, the fresher the snow the higher the risk. As of 2011 research, an average of four Tree Well / SIS accidents happen each season in the United States.
Most all Tree Well/ SIS accidents happen in ungroomed terrain. A groomed run is a ski or snowboard run that has been driven on by a snow machine to compact and consolidate the snow.
More info here: https://www.deepsnowsafety.org/
There's a lot more info on this online...just Google it.