Montana is filled with people who love to back-country ski during the winter and well into the summer. Sometimes friends just head out for a day of skiing, or they might head to one of the back-country yurts scattered across the state for a solid week of skiing wild powder.
Although backcountry skiers and snow lovers across Montana have always been aware of the potential dangers of avalanches, questions about the ways in which our changing climate might affect avalanche frequency are on a lot of peoples' minds right now. We've just come off one of the most dangerous avalanche seasons in recent years. What do we know so far, and what major questions remain?
Here, we talk about the ways in which Montana's winter climate has changed in the last century, methods used by back-country skiiers to avoid avalanches, and possible trends for the avalanches in Montana's future.
If you know what to look for, avalanche chutes can be seen throughout the mountain ranges of Montana: these steep pathways are missing their trees because of the regular release of huge amounts of snow, which damage or kill trees within these corridors.
In this way, avalanches incluence patterns of forest cover and contribute to diversity in local plant species by providing new opportunities for seedlings to grow. Avalanche chutes also create natural fire breaks in mountain forests.
Avalanche corridors are also areas of high natural diversity - both in plant and animal species, and are a favorite feeding ground for wolverines, for example, which search for the carcasses of deer and elk caught in the path of winter avalanches.
Over the course of the past century, average winter temperatures in Montana have increased by more than 3 degrees Fahrenheit (see above graph from NOAA), which has led to more rain-on-snow events and long-term declines in snowpack. These warming trends are also a concern because of their potential for creating the "right" conditions for avalanches.
The size and frequency of avalanches are related to a number of factors, including increases in air temperatures and the 24 hour-period after a heavy snowfall: both of which can create unstable snow layers that are more likely to slide.
Another concern is that climate change could impact the types of avalanches as well as the frequency. For example, a warming climate in Montana has already meant more winter days above the freezing point, which can lead to a significantly wetter snowpack - possibly resulting in wet, as opposed to dry, avalanches.
With thin snowpacks and big ranges between daytime and nightime temperatures, snow crystals' structure can transform into what we all know as "sugar" snow -- the kind that doesn't bond well to other snow crystals. This can create a weak layer in the snowpack that lasts all season long, and can cause some slopes to slide two and three times as the weak layer persists.
Conditions like this meant that Montana saw prolonged periods of avalanche danger this year, and several fatalities. The Gallatin NF Avalanche Center, for example, issued five separate avalanche warnings this year, a new record.
Graph from National Oceanic and Atmospheric Administration Climate Services website
Fortunately, avalanche safety classes are available all over Montana each year, and are well attended by large numbers of our friends and neighbors who plan on heading into the back-country to recreate.
Basic safety gear for each person includes a portable shovel, a collapsible probe, and an avalanche beason (or transceiver). Instructors in avalanche safety classes highlight the risks, the time of year when avalanches are most likely (December to April), the risks associated with certain activities (like crossing hazardous terrain), and the safety precautions that everyone should take during these trips - such as digging a test pit (pictured above) to assess conditions in the area.
There are also a number of websites that report avalanche conditions throughout Montana daily for back-country skiiers and snowmobilers to check before heading out (see links at right).
Photo: Megan Birzell
While it is hard to tell the exact results that our changing climate will have on avalanches, one possibility includes an increase in the number of avalanches from current levels and the duration of high avalanche danger, followed by an eventual drop-off if snow-pack continues to decline over time.
For these reasons, avalanche safety classes and careful recreation in the back-country are more important than ever as researchers like Dan Fagre (see link at right) continue to study avalanche patterns in our state and share his findings with the general public and scientific community.
Photo: Scott Brennan