Backcountry skiing and snowboarding is becoming increasingly popular, especially in areas such as Whistler/Blackcomb that enable lift access to backcountry terrain. Although the backcountry skiing and snowboarding can be a very rewarding experience, it is replete with hazard. Many recreationalists fail to consider the danger they are putting themselves in. In addition to the hazard posed by the terrain itself, there is the fact that there is no ski patrol. You are responsible for yourself in the event of an accident, and injuries can have very serious consequences.

    In addition to being unpatrolled, the backcountry is uncontrolled. Ski patrol works within resort boundaries to ensure that avalanche hazard is minimized. They intentionally trigger avalanches using explosives and ski cuts. There are avalanche professionals working to ensure that all the runs listed as 'open' are safe. If there is any perceived avalanche danger, the runs are closed and skiing privileges are revoked for trespassing. In the backcountry, there is no ski patrol working to minimize risk from danger, and there are no closures.  It is up to the backcountry user to make their own decisions regarding the safety of a given slope. 

    This is no easy task. It takes years of experience to be able to assess avalanche danger, because it results from a confluence of factors that have different effects on different terrain. Examples of such factors are elevation, temperature, slope, aspect, terrain shape, snow type, and weather throughout the season, among others. All of these factors influence each other, and many of them are constantly changing. In addition, the terrain variation is often occluded by snow drifts, meaning that 'weak' layers (Fig. 1) could be buried deeply - securely 'bridged' by 'safer' snow (Tremper 40) - in some places and very shallow in others, waiting for a trigger. This means that avalanche prediction is an elegant science that borders on art. Even seasoned professionals make incorrect judgments from time to time, sometimes with tragic results.

    It is worth emphasizing that avalanches are very dangerous, killing more people annually in the United States than either earthquakes or hurricanes (Tremper 9) - despite the fact that only a tiny minority of the United States' population is exposed to avalanche risk. Furthermore, avalanches do not simply 'strike;' they are not a random, unlucky occurrence. The vast majority of fatal avalanches are triggered by the victim or someone in their party (Tremper 11), and there are nearly always warning signs that the victims ignore, either due to ignorance or obstinance. Many people are under the impression that it is possible to escape from an avalanche by simply moving out of the way or skiing off of  one. This is almost never possible; avalanches simply accelerate too fast, and can move in excess of 100 km/h  (Tremper 13). There is also a pervasive myth that, if you are trapped in an avalanche, you can simply spit to tell which way is up, and then dig in that direction to free yourself. This too is inaccurate. You cannot dig yourself out of an avalanche (Tremper 14). The violent turbulence of a slide causes the snowpack to consolidate into something resembling cement when it stops moving. If you are trapped in an avalanche, you may not even be able to wiggle your fingers. Additionally, a significant amount of avalanche victims die from blunt trauma during the slide itself; due to the nature of mountainous terrain, avalanches often slide through trees or boulder fields, or over cliffs. Though an increasing percentage of backcountry users carry emergency equipment - e.g. avalanche beacons, collapsible shovels and probes, and occasionally backpacks with airbags that 'float' you to the surface of a slide - designed to facilitate the rescue of a buried friend, this equipment may not be effective at all, especially as it takes a considerable amount of constant practice to learn how to use. The best way to avoid dying in an avalanche is to avoid encountering an avalanche. This sounds laughably obvious, but it is something that many people, confident that their equipment will protect them, fail to consider.



    Avalanche danger is directly related to the snowpack. A given snowpack will consist of many layers that have varying strengths (Fig. 1). The strength of a layer depends upon many factors such as the temperature gradient of the snowpack, the type of snow that formed that layer, and weather events that followed or preceded a snowfall. Learning how to read the snowpack and monitor it over the course of a season is not an easy task, especially because the strength of a layer does not remain static once it is buried. It is not necessary to include further detail for the purposes of this analysis, but anyone interested in learning more about snowpack dynamics should consult my list of further readings.

Fig. 1

    Avalanches occur when too much stress is exerted on a weak layer in the snowpack. The weak layer collapses, allowing the snowpack above to slide on the layer below, known as the bed surface.  Stress can be placed on a snowpack in several ways. The weight of additional snow can trigger the release of a buried weak layer; cornices can collapse under their own weight and land on the slope below; or, unfortunately for backcountry travellers, the weight of a human is often enough to cause a weak layer to collapse. Though there are many different types of avalanches, slab avalanches (Fig. 2) are responsible for nearly all the avalanche deaths in North America (Tremper 20).

Fig. 2

    The preceding explanation is a very simplistic overview of avalanche dynamics. Though there are tests one can perform to determine the strength of a snowpack, it is impossible for anyone to predict when or if a slope will release with complete certainty. Incorrectly diagnosing the snowpack can prove fatal. If this is the case, then what business does the average recreationalist have being in the backcountry? Although it looks inviting - fresh snow, no crowds, interesting terrain - it is unforgiving terrain. Yet, every year droves of people make their way into the backcountry. Some are more experienced than others. While there are, shockingly, people who venture into the backcountry with no foreknowledge of the hazards they can expect to find, others are more sensible. However, as mentioned, being able to accurately determine the 'safety' of a slope is a skill that takes many years of practice to master. Therefore, a large percentage of backcountry users simply rely on the backcountry hazard ratings posted by Ski Patrol.

    This rating system provides a general guideline for slope stability. It ranges from low danger - which means that it is almost certainly safe to ski any slope - to extreme danger - which means that avalanches, either human-triggered or natural, are certain. The guide makes reference to the fact that pockets of instability can persist and advise "normal caution" even in low-rated conditions, but it is inescapably vague. Most recreational backcountry users would be unable to identify where those pockets of instability might exist; all terrain is equally safe or hazardous in their eyes. However, the characteristics and strength of the snowpack varies considerably with terrain. This rating system is unable to account for this variation.

    Many avalanche forecasters are attempting to mitigate this problem. Bruce Tremper, director of the Utah Avalanche Forecast Center, recognizes the inadequacies of the hazard rating system, and has begun putting more detail in his forecast regarding slope, elevation, and aspect. However, he asserts that providing too much detail can be confusing. He continues to search for the perfect avalanche forecast format, which he says must "both be obvious enough for avalanche neophites to understand, yet give enough useful detail for the hard-core skiers to make routefinding decisions."

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    The purpose of this analysis is to improve upon the standard hazard rating model by producing a terrain-specific, image-based avalanche forecast format. A picture is worth a thousand words; I assert that this format thus has the potential to fulfill Tremper's criteria of being obvious enough for neophytes to understand while still providing sufficient detail to make routefinding decisions. Furthermore, I will undertake the additional step of producing a least-cost path analysis, wherein 'cost' is equated with 'hazard'. That is, I will show the least hazardous route through avalanche terrain based upon the combination of my selected criteria. Additionally, I will account for the fact that mountain slopes are anisotropic surfaces: it requires more energy to travel up a slope than to travel down it. This will enable even those neophytes Tremper mentions to make somewhat more informed route-finding decisions than they would otherwise be able.

    For the purposes of my analysis, I will consider only static - that is, largely unchanging - criteria. It is important to recognize that avalanche hazard is largely dependent upon the interaction between constantly fluctuating weather conditions and terrain characteristics such as elevation, slope, aspect, and shape. It is currently not feasible to consider such mutable criteria as temperature, snowfall, or snow type, because such data must be as current as possible. Seasonal averages would be insufficient to determine hazard on a given day.  Furthermore, my analysis ignores elevation, because my area of focus is located entirely in the alpine. While I intend to include slope shape in my analysis, it is not worth considering small-scale variations such as whether a slope is concave or convex. Convex slopes tend to be dangerous because the 'rollover' increases the stress applied to the snowpack (Fig. 3). Convex slopes, on the other hand, tend to be less dangerous because their shape enables compressive support (Fig. 3), like a keystone in an upside-down arch. However, this effect is mitigated  on medium-to-large scale slopes (Tremper 83). Furthermore, even small concave slopes tend to accumulate wind-deposited snow, which increases avalanche danger on them.

    Given these considerations, the static criteria I have elected to use for my analysis are slope, aspect as affected by insolation, aspect as affected by windloading given the prevailing wind direction, and general terrain variation - that is, the location of ridgelines and terrain traps. This reflects Tremper's analysis that "variations in snow stability tend to correlate most closely with aspect, elevation and slope steepness."

Fig. 3		Fig. 4

  

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     I chose to analyze the Spearhead Route (Figs. 5, 6) because it is one of the most popular backcountry traverses in North America. It is large area of backcountry terrain immediately adjacent to Whistler, British Columbia (Fig. 7), easily accessible from both Whistler and Blackcomb ski resorts. I elected to perform a multicriteria evaluation (MCE) of the terrain in order to provide terrain-specific hazard ratings. I then calculated the least hazardous path through the terrain. Due to the static nature of the criteria I selected, the relative level of hazard encountered along the route will not vary much due to weather conditions. Therefore, my analysis has the potential to be a useful tool for backcountry recreationalists.

PLEASE NOTE: All maps on this site, with the sole exception of the Google map below, are in reference to NAD 83 and use a BC Albers projection.

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