Tree well
A tree well, also known as a spruce trap, is the space around a tree under its branches that does not get the same amount of snow as the surrounding open space. This creates a void or area of loose snow below the branches and around the trunk that is dangerous to any
who fall into them. If someone lands in such a well, often as a result of a fall, it can be too deep for them to climb up the surrounding loose snow before they are buried. Making the situation more dangerous, they often fall into the well head-first and as the result of an accident which could leave them injured or unconscious.Formation
A tree's branches shelter the area around its trunk from snowfall. If the snow is deep enough, there is a significant void or area of loose snow underneath the branches around the trunk. Such wells have been observed as deep as 20 ft (6 m).[1] Similar "wells" can also occur near rocks and along streams.
Tree wells occur outside of groomed trails and represent a significant risk to those who ski or snowboard off-piste, in backcountry areas, but can also be found on the boundaries between groomed and ungroomed areas. The risk of encountering one is greatest during and immediately following a heavy snowstorm.
Hazard
Victims become trapped in tree wells and are unable to free themselves. In two experiments conducted in North America, 90% of volunteers temporarily placed in tree wells were unable to rescue themselves.[1][failed verification] If the snow is deep enough, the surrounding snow banks can collapse over them, depriving them of air. "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", according to the Tree Well and Snow Immersion Suffocation (SIS) Information website.[1]
Frequently victims fall into wells head-first, complicating recovery efforts. Often they are injured in the process, suffering joint dislocation or concussion. When fatal, this type of incident is termed a non-avalanche related snow immersion death (NARSID).[1]
In the United States, on average several skiers or snowboarders die each year from non-avalanche related snow immersion.[2]
References
- ^ a b c d "Tree Well and Snow Immersion Suffocation (SIS)". Northwest Avalanche Institute. Retrieved 23 August 2018.
- ^ "Tree Well and Snow Immersion Suffocation (SIS) :: SIS By The Numbers". www.deepsnowsafety.org. Retrieved 18 March 2019.