Ski Museum series: Spring backcountry avalanches
Colorado Ski & Snowboard Museum
The following is part of a series of articles compiled by the Colorado Ski & Snowboard Museum and Hall of Fame that will take a closer look at the sport of alpine ski touring. The museum is located atop the Vail Village parking structure and features a treasure trove of ski history and heritage.
Backcountry enthusiasts agree that spring skiing and snowboarding can be some of the best of the season. Good snow coverage, warmer weather and more predictable snow stability, at times, can lead to unmatched conditions.
But, while spring touring can make for a great day in the backcountry, it can also present avalanche hazards that are not encountered during the colder parts of winter. Cornices have matured and tend to be at their biggest this time of year. As snowpack and weather transition into a warmer and wetter spring pattern, there are a number of new avalanche variables to pay attention to.
One of those variables that can influence the stability of the snowpack during spring conditions is terrain and aspect. Due to the impact of solar radiation, wet snow avalanches typically occur earlier in the day on south-facing slopes. As the day progresses, this type of instability then moves to east, west and potentially, north-facing slopes.
Using different aspects to your advantage is a great way to enjoy spring skiing and riding conditions, while also avoiding increased instability. However, a change of aspect is not always a guaranteed way to avoid unstable conditions as there are numerous factors that influence snowpack stability during the spring.
Another significant factor influencing spring avalanches is temperature. As temperatures climb above freezing, surface layers of the snowpack begin to melt. If temperatures drop back below freezing, then this process is slowed, allowing the snowpack to adjust to these changes.
However, if temperatures stay above freezing for an extended period of time, then a large influx of free moving water can be introduced into the snowpack. This can create widespread instability and dangerous avalanche conditions. The first prolonged period of above freezing temperatures, both day and night, is a common time for spring avalanches to occur.
Also, with temperatures above freezing for an extended period, the snowpack can become isothermal as the temperature of the entire snowpack reaches 32 degrees Fahrenheit. When the snowpack becomes isothermal, the structural integrity begins to break down, making wet snow avalanches likely. Typically, during spring skiing, it’s best to get an early start when the snowpack is frozen and stable, while making it a point to be off the slopes by the heat of the day.
Snowpack structure also plays a significant role in springtime avalanche danger. A major contributing factor, particularly to wet slab avalanches, is the presence of buried persistent weak layers. These weak layers can produce dangerous avalanche conditions months after forming and getting buried. Depth hoarfrost, which is faceted snow near the ground, is the most notorious weak layer for producing large wet slab avalanches.
However, springtime avalanches can still occur without buried persistent weak layers. A common avalanche during warm spring weather tends to be a wet loose avalanche or sluff. This form of avalanche is typically less dangerous than wet slabs, although wet loose avalanches can contain large volumes of snow, capable of carrying, and sometimes burying, a skier or rider.
Wet loose avalanches generally start at a single point, but fan out as they move downhill. In steep terrain, they can travel long distances and pick up significant volume and speed. Wet loose avalanches typically occur during prolonged periods of warm and dry weather, which is generally the opposite of mid-winter avalanches, that tend to occur after periods of heavy snowfall.
Classic spring instabilities are relatively easy to identify and manage. If you’re shedding layers because you’re warm, then the snowpack probably feels the same way. If you see snow pin-wheeling down steep features, or if the snow is so moist you can easily make a snowball, then the snow is definitely warming up and it’s time to think about packing it in for the day.
If you’re planning some backcountry skiing or riding this spring, then take advantage of the melt-freeze cycles when you can. For those heading out on spring traverses, plan your day so you cross exposed solar aspects before they heat up and avoid overhead hazards such as cornices.
In short, spring avalanche danger can sometimes change from low to high in a matter of hours or even minutes so remember, timing is everything. Reading the avalanche advisory and staying current on snowpack structure and temperature fluctuations is the best way to stay on top of, rather than being buried below the snow during the spring riding season.
The upcoming transformation of the Colorado Ski & Snowboard Museum will provide more space and modernized technology for the museum to tell stories like this. Please stop by the museum on Sunday afternoon anytime between 4 p.m. and 6 p.m. to learn more about the upcoming transformation and how you can get involved.