The stability of Colorado’s current snowpack is comparable to a house of cards, as demonstrated by the number of Avalanche Warnings, Watches and Special Avalanche Advisories issued by the Colorado Avalanche Information Center (CAIC). Here is a highlight from a recent CAIC forecast.
Structurally, the snowpack across the Northern Mountains is pretty simple. Facets formed during the drought from Thanksgiving onwards make up most of the lower part of the snowpack. On top of this incredibly weak base is one to three feet of snow of varying hardness from the post-Christmas storms. This simple snowpack structure - a widespread weak layer under a thick, cohesive slab - makes for dangerous avalanche conditions. The one consolation is dangerous conditions make for easy travel advice. You should avoid most slopes steeper than 30 degrees. Upper-elevation drifted slopes are the most dangerous, but you can still trigger slides in steep, sheltered areas below treeline.
This forecast highlights the seasonal weather pattern and unstable snowpack structure that led to the current avalanche hazard and how we should behave as winter travelers.
Facets describe the shape of the snow crystals that exist in the lower layers of the snowpack. Each new snow storm forms layers that change over time. The snow that fell during Thanksgiving week was initially a deep and cohesive layer, characterized by round snow crystals that bonded to each other fairly well. The skiing in Vail around Thanksgiving was excellent and on Vail Pass I experienced some of the deepest and best early skiing conditions in years. However, due to the long period without snow and typical cold and clear nights, the snow crystals changed from rounds to facets, or square and angular snow crystals that don’t bond well to each other. Facets create a persistent weak layer in the snowpack and can produce an avalanche on slopes above 30 degrees. On a subsequent ski tour up Spraddle Creek, two weeks after Thanksgiving, I was surprised by how much of the snowpack had melted on southern aspects and had become entirely facets and unsupportable on other aspects. The skiing was terrible!
This brings us to the current avalanche problem, weak faceted layers at the bottom of the snowpack with several feet of cohesive newer snow at the top. The lower layers are weak and cannot support the additional load of the newer snow. The snowpack is at a tipping point and only requires the slightest of triggers to slide. A trigger could be a person on skis, snowshoes, snowmobile, more new snow, or even wind loading between storms. This is highlighted by the number of recently reported human triggered avalanches. Many of these avalanches have been dramatic in size and triggered remotely from far away by backcountry travelers. The avalanche triggered on Peak 1 on January 4, above Frisco is a good example of this phenomena.
Unfortunately, six avalanche fatalities have already occurred in the Western US this winter. While detailed information is not available for all of these accidents, in at least three of them the failure in the snowpack occurred in the weak faceted layer. And in at least one, the avalanche was triggered remotely by a party on a 26-degree slope and steeper slopes slid above them.
While these seem like scary times in the winter backcountry, you can still travel safely in terrain that is less than 30 degrees without steep slopes above. I’ve had some wonderful days ski touring over the holidays in terrain that I know well, staying disciplined, and not venturing onto slopes steeper than 30 degrees. Popular GPS map apps have slope angle shading that helps identify slope angle and avalanche terrain. You can also choose to stay within the boundaries of the ski resorts where the avalanche hazard is controlled and mitigated daily by ski patrol. Keep in mind, however, any terrain accessed by backcountry gates from the ski resorts, such as East Vail, the Minturn Mile, and the Bald Spot, are all backcountry areas and should be treated as such, regardless of the amount of skier traffic they receive. Avalanche hazard is cyclical and depends on a variety of factors, all which can be monitored and avoided as the winter season progresses. Typically, in the spring as the snowpack deepens and temperatures increase, faceted layers are buried and more rounded snow crystals dominate. The avalanche hazard can be more predictable and subsides sooner after new storms.
If you decide to venture into the winter backcountry, being educated about the terrain and avalanche hazard is lifesaving. Take an avalanche education class, travel with proper equipment and experienced partners, and always check CAIC’s website and heed their Warnings, Watches and Special Advisories.
Markian Feduschak is the President of Walking Mountains and a self-described snow geek and passionate skier. Markian is also a board member of the Friends of the Colorado Avalanche Information Center, a nonprofit organization that supports the Colorado Avalanche Information Center.