INNSBRUCK, Austria — How long can you survive when buried under snow in an avalanche? The answer, according to studies conducted by snow scientists, is that it depends. Shorter duration, obviously, is better — but not an assurance of life.
The first avalanche survival curve was assembled in Europe in 1992. More studies have been done in recent years, with the latest being presented last year at the International Snow Science Workshop in Innsbruck, Austria.
That study, led by Giacomo Strapazzon, examines reports of avalanche burials compiled during seven winters in Austria and Switzerland. To qualify, both the head and chest of the victim had to be buried.
According to its findings, survival is relatively high at 87 to 91 percent — if the person is unburied within 7 to 10 minutes. Rates of survival drop to 25 to 28 percent for longer periods of about 35 minutes.
The death rate is 18 times higher when a person is buried 36 to 60 minutes. Beyond an hour, a person is 29 times more likely to die than is a person buried for 15 minutes or less.
Not all avalanche burials are equal, though. If a person ends up with a pocket of air, the odds improve. The more deeply a person is buried also matters.
An earlier study, released in conjunction with a snow science workshop in Banff in 2014, similarly defines 35 minutes as the outer limit of the curtain call. Beyond that, there’s little chance of survival.
A 2011 study led by Dr. Pascal Haegeli, now of Simon Fraser University in British Columbia, dives deeper, but with a comparison of avalanches in Europe and North America over the course of six winters. Again, the victims had to have had their heads and chests covered. But as in the other studies, the odds of survival are reasonably good if the person is uncovered quickly.
However, asphyxiation is only one way to die in an avalanche. Of the 143 deaths in Canada that were examined, nearly 19 percent were due to trauma.
How about the difference between mountain ranges? Haegeli and his colleagues compared three major ranges of Western Northern America (avalanche deaths occurring in the East are rare): 1) The coastal maritime ranges, such as where Mt. Bachelor and Whistler are found; 2) the transitional areas, Cariboos, Monashees and Selkirks; and 3) the interior or continental Rocky Mountains.
Survival curves for the transitional and maritime snow climates had “considerably” lower survival in comparable periods of immersion, they found. Denser snow and thus avalanche debris could result in fewer oxygen pockets, they theorized. In addition, “denser debris would apply greater compressive forces, thus preventing chest movement.”
But again, while quick extrication is paramount, avalanches are altogether nasty things. Airbags and beacons definitely improve your odds, but they fall well short of guaranteeing survival.
For example, 33 percent of all Canadian avalanche fatalities suffered major trauma. Only half of the trauma-related deaths involved people who had been completely buried. In addition, 44 percent of those who had a trauma-related death had severe trauma, which likely resulted in death shortly after those victims were buried in snow.
Allen Best compiles Mountain Town News, an Arvada, Colorado-based e-magazine that provides in-depth analysis of economic, environmental and social trends in resort-based mountain communities of the West.