Avalanches are a rapid flow of snow down a slope, from either natural triggers or human activity. Typically occurring in mountainous terrain, an avalanche can mix air and water with the descending snow. Powerful avalanches have the capability to entrain ice, rocks, trees, and other material on the slope. Avalanches are primarily composed of flowing snow, and are distinct from mudslides and rock slides. In mountainous terrain avalanches are among the most serious objective hazards to life and property, with their destructive capability resulting from their potential to carry an enormous mass of snow rapidly over large distances.Thus alpine lovers learn how to read nature’s clues to assess the likelihood of an avalanche. In fact, avalanches are measured in terms of the risk of an impending avalanche.
How to Assess the Risk of an Avalanche?
Assessing avalanche risk is no simple matter. It involves a complex judgment process based on expert forecasts, personal experience and up-to-the minute weather changes. Among the numerous variables that go into assessing a terrain for avalanches are slope steepness, wind speed, wind direction, current temperatures, humidity, weather pattern history, snowfall, snowpack stability, exposure to sun, timeframe and route choice. Moreover, these variables can change weekly or even hourly, and differences in snowpack stability can exist in close proximity.
Utilizing Alpine Experts to Measure Risk
To measure the risk of an avalanche, avalanche bulletins are issued by alpine experts worldwide to provide information on snowpack conditions, weather conditions, concerns for the day, travel advice and avalanche activity. Also known as avalanche advisories or avalanche forecasts, these bulletins include danger ratings based on a five-level international avalanche danger scale that is used all over the world. The five danger levels are low, moderate, considerable, high and extreme. Each level includes travel advice as well as a description of avalanche probability, distribution and trigger.
For example, at the low level, natural and human-triggered avalanches are unlikely and travel is deemed generally safe. At the considerable level, natural and human-triggered avalanches are possible. Travel caution is advised in these areas. At the far end of the scale, at the extreme danger level, widespread avalanches are certain, and travel in this terrain is to be avoided.
The danger scale, however, provides only an overall guide and must be supplemented by real-time evaluation of conditions found on the ground. At least four factors should be assessed in order to measure the risk of an avalanche. The first is slope angles (steepness). Most avalanches occur on intermediate slopes of 35 to 45 degrees, the very slopes frequented by skiers and snowboarders. However even mild slopes can pose a danger if they are connected to steeper terrain above.
The second is tender spots or stress-concentrated areas, which include sudden increases in slope angle, windy areas, rollovers and thin spots.
Slope anchors include branches, logs or rocks protruding from the snow that help hold snowpacks in place, making them less likely to slide than those sitting on smooth surfaces.
Finally, shady, north-facing slopes produce more avalanches in the winter, while south, sun-facing slopes produce wet avalanches in the spring. Areas receiving moderate amounts of sunlight are the most stable.
Werner Munter’s 3×3 Filter and Reduction Method
In Europe, alternative ways to measure an avalanche were created by Werner Munter. Munter’s Elementary Reduction Method is geared to facilitate making a quick decision and entails avoiding certain slope angles based on the the avalanche forecast. For example, a moderate danger level means no travel on slopes steeper than 40 degrees, and a considerable danger level means no travel on slopes steeper than 35 degrees, and so on.
Munter is best known for his 3×3 Filter and Reduction Method, which calculates whether a forecasted danger level can be reasonably reduced by evaluating it from three vantage points: regional, local, and slope. The actual formula is: Danger/Reduction = Risk.
Finally, alpine recreationists can use the Red/Green Light method to assess the likelihood of an avalanche hazard. This process takes into consideration the interrelationship between four key factors: terrain, weather, snowpack and human. Each factor is thought of as a red, green or yellow light, according to the following hazard level symbols: G for green light means go; Y for yellow light means caution, potential danger; R for red light means stop, danger. Experts recommend that an extra level of caution be added for the unknown.
How many people have died in avalanches in the USA?
The number of people who have died from avalanches in the United States has been rising steadily. An average of 25 people have died annually in avalanches over the past 10 years, up from close to zero in the early 1950s.
How Many People Died in Avalanches in 2009-2010?
In the 2009-2010 season alone, there were a total of 36 avalanche fatalities in the USA. Of those who died, 17 were snowmobilers, 10 were skiers, six were snowshoers/climbers, three were snowboarders, and one was an inbound skier.
How Many People Died in Avalanches in 2008-2009?
In 2008-2009, 27 people died from avalanches in the United States. Among the victims were 16 snowmobilers, four skiers, three inbound skiers, one snowboarder, one snowshoer/climber, as well as two other deaths.
How Many People Died in Avalanches in 2007-2008?
The 2007-2008 season saw 36 USA avalanche deaths.
How Many People Died in Avalanches in 2006-2007?
In the US there were 20 fatalities in the 2006-2007 season.
In the United States, the greatest number of deaths due to avalanches occur in the wintertime, and in particular during the months of January, February, and March, when the largest snowfalls occur in the mountain areas, and when avalanches tend to run. The springtime months of May and June record another significant surge in avalanche fatalities due to hidden but dangerous melting spring snows. Climbers make up the bulk of avalanche victims during the summertime. Of the people who die in avalanches, about 88% are found fully buried, while the rest are either partially buried or not buried.
Eighty percent of all avalanche accidents in the USA take place in five states – Colorado, Alaska, Montana, Utah, and Wyoming. Colorado alone accounts for about one-third of all avalanche deaths, and since the 1950s more people have been killed in avalanches in Colorado than in all other natural hazards.
Who is More Likely to Die, Male Or Female?
Of those who die in avalanche incidents, 89% are male, middle-class, educated, and between the ages of 20-29. Notably, almost all the victims are highly skilled in their respective crafts. Specifically, snowmobilers, backcountry skiers, and snowboarders – in that order – comprise the majority of avalanche fatalities, with climbers, snowshoers, skiers, hikers, residents, ski patrollers, workers, and motorists filling out the list.
Snowmobilers alone comprise twice the number of avalanche fatalities compared to other activities. This may be due to a snowmobile activity called “high marking,” wherein the snowmobile is pointed straight up a steep slope and driven hard towards the top (in essence, the snowmobile climbs the mountain). Following a heavy snowfall, high marking can easily trigger an avalanche.
Why Has There Been More Avalanche Deaths in Recent Years?
The increase in avalanche deaths over the years has been attributed to a boom in ‘out-of-bounds’ or ‘backcountry’ recreation, where no avalanche control takes place. As the number of winter sports enthusiasts has grown, more people have headed for the backcountry slopes, enabled by advances in snow gear and equipment that facilitate their entry into avalanche terrain. While ski and other resorts provide defined recreation areas that are bound off by ropes and signs, those who venture beyond enter terrain that is not patrolled or groomed. In these out-of-bound areas, alpine visitors are on their own and proceed at their own risk. Yet while backcountry avalanche deaths have soared, less than one percent of avalanche deaths over the past 30 years in the United States have taken place within bounded areas.
Although snow avalanches occur naturally, brought on by Mother Nature as gravity pulls upon snow on an incline, 90% of avalanche slides are triggered by human beings – either by the victim or by someone from the victim’s group. Thus while avalanche victims tend to be experienced in their sport, they seem to lack important, life-saving knowledge regarding how to watch out for avalanches. Conversely, lending support to the purported benefits of avalanche prevention initiatives, there has been a reported decrease in deaths among groups who participate in avalanche control programs.