Colorado's Fatal Avalanche Incidents (2009-2015)
A data-driven exploration of fatal incidents
Before I left to go skiing, my mom would always tell me to be careful driving on the snowy roads. No matter how many cliffs I dropped, how steep my lines and how fast I skied, she said, the most dangerous thing I would do that day would be drive the two-lane highway leading up to the mountains. But, looking back on a decade of skiing the backcountry of Southwest Colorado's San Juan Mountains, I don't know anyone who's been killed in a car accident. I do know two young people who have been killed by avalanches. My parents know five more--young friends from the vast mountaineering, climbing and skiing communities they are a part of, taken too soon doing something they loved, that they lived for.
In the creation of this piece, I hope to use data collected by the Colorado Avalanche Information Center to draw conclusions about the unique dangers that come from skiing in the San Juans and beyond.1
The dataset used in the following analysis comes from the Colorado Avalanche Information Center accident reports. All accidents included in this report occurred within the last six seasons (2010-2011, 2011-2012, 2012-2013, 2013-2014, 2014-15). The dataset includes 42 avalanche fatalities, all of which occurred during some form of backcountry travel (skiing, climbing, snowmobiling). To that end, I have excluded one 2010 incident, in which a snow slide from a roof top buried and killed two individuals.
Also of note is the fact that there are two incidents resulting in multiple fatalities: the 2010 Sheep Creek Avalanche and 2013 Star Mountain Avalanche.2 For the purposes of this analysis, these accidents count as a single fatality, unless otherwise noted, leaving 37 fatal avalanche incidents.
This map includes information about each of the 37 backcountry avalanche fatalities in Colorado over the past six years.
Three main clusters of avalanche incidents are apparent: the I70 Zone along Interstate 70 including the Vail area and Berthoud Pass (16 fatalities, including five during the Sheep Creek accident), the Aspen Zone reaching down to Crested Butte (ten fatalities, including two during the Star Mountain incident), and the San Juan Zone including the Northern, Southern, and Eastern San Juan Mountains (10 fatalities). Therefore, 86% of fatalities occurred in one of these three "zones."
A cluster along I70 would be inline with heavy backcountry traffic coming from the Front Range. This zone also includes three sidecountry fatalities and two inbounds fatalities. The Aspen Zone includes four sidecountry fatalities, as well as one in bounds, at the Aspen ski areas. The San Juan Zone includes six fatalities near Telluride of Silverton and one sidecountry fatality.
Fatal Incidents 2009-2015
Fatalities by Avalanche Danger Level3
Fatalities/ Number of Forecasts
A 2014 study by Greene et. al. shows us that Colorado stands apart from other forecast areas in North America and around the world in that the the most fatalities occur when the forecast danger level is Moderate, as evidenced by Figure 1. This tells us, of course, that fatal avalanches often occur when danger level is Moderate, and we should not consider a Moderate danger level a green light for backcountry access.
At the same time, Moderate danger levels were forecasted nearly 52% of the time, so this might help to explain the high number of fatalities. Figure 2 normalizes the avalanche fatality distribution by showing the number of people killed divided by the number of forecasts. Through this analysis, we can see that as the danger level goes up, so do the chances for a fatal accident. (Note: The Extreme danger level has been left off of the normalized graph because, due to the extremely low number of times this forecast has been given, it becomes an outlier)
This graph tells us that fatal avalanches occur across a very wide range of slopes. In this dataset, there were no fatalities on slopes below 35°, but 57% of fatal incidents occurred on slopes of 40° or less.
Avalanche Slope Aspect
Fatal avalanches mainly occur from NW to SE aspects due to the prevailing direction of storms. Interestingly, fatal avalanches are spread relatively evenly across these five aspects. This suggests the dangers of relying on traditional forms of avalanche and atmospheric knowledge when it comes to Colorado's mountains. Due to the diversity of terrain within the Colorado mountains and the localized weather patterns they create, there exists a strong chance for a wide range of slopes to become wind-loaded and adversely affected.
of avalanche fatalities in the last six years occurred in-bounds or in sidecountry accessed from a ski area.
With more sidecountry access opening up at areas across the state, discussion has taken place over the proper ways to enforce beacon usage and make apparent the dangers of entering these unpatrolled areas. Even the term "sidecountry" has been critiqued, with writers pointing out that the term is misleading because sidecountry really is no different than backcountry in terms of the dangers it poses.4 In short, it is vitally important to treat any gate accessed skiing in the same way one would the backcountry, which means using and knowing how to use beacons, shovels and probes and employing consideration of avalanche reports and on-hill inspection.
The vast majority of those killed in Colorado avalanches have been backcountry tourers, with in-bounds and sidecountry accidents also contributing to ski fatalities. The advent of split-boards, allowing snowboarders to access the backcountry, has also lead to a rise in snowboarder fatalities.