U.S. DEPARTMENT OF THE INTERIORBUREAU OF LAND MANAGEMENT
As soon as the snow starts piling up each year, outdoor enthusiasts begin gearing up for skiing, snowboarding, snowshoeing, snowmobiling, and other winter activities in the backcountry. However, what seems like the perfect conditions for a day on the slopes can also present avalanche hazards, and even the most experienced adventurers can get caught in an avalanche. With this in mind, the BLM-Alaska Campbell Creek Science Center in Anchorage hosted an avalanche education program on January 16 as part of the center’s Fireside Chat Series. About 25 community members and high school students braved the winter weather to munch on complimentary cookies and hot drinks as John Fitzgerald, an avalanche forecaster with the Chugach National Forest Avalanche Information Center, described how avalanches form, how to avoid them, and how the Avalanche Information Center develops each day’s avalanche forecast.
There are two kinds of avalanches: loose snow avalanches and slab avalanches. Loose snow avalanches generally occur in steeper terrain, where fresh snow has recently fallen in low-density layers, or where older snow has been softened by strong solar radiation. Slab avalanches occur in snow that has been deposited or re-deposited by wind. These slabs appear to be a block of snow cut out by fractures. Slab avalanches account for around 90 percent of avalanche-related fatalities in backcountry users.
Soft slab avalanche set off by a snowboarder near Turnagain Pass, Alaska. Even small avalanches such as this can be deadly. Photo by Joe Kurtak
Avalanche forecasting involves both watching the weather and heading out into the field to record observations. Forecasters cut a slab in the snow in the backcountry to examine the snow layers and test how much force causes weak layers in the snow to collapse. Each morning starting at around 4:00 am, forecasters like John gather to examine both weather observations and backcountry field observations from the previous day to estimate each day’s chance that an avalanche will occur somewhere in the area. Advisories are posted each day on the Chugach National Forest Avalanche Information Center’s website (http://www.cnfaic.org/index.php) so that people considering heading outside can see whether avalanche hazards are especially high. As John outlined in his presentation, it’s also important for everyone to be able to recognize the signs that an avalanche could occur in an area. These signs include: 1) evidence of a recent avalanche, 2) signs of unstable snow, such as cracking or collapsed snowpack, whumpfing sounds, or hollow, drum-like sounds on hard snow, 3) heavy snowfall or rain in the past 24 hours, 4) wind-blown snow, 5) quickly warming temperatures or large increases in temperatures, and 6) persistent weak layers. During the presentation, John showed photographs the snow slabs that he and other forecasters cut and explained what signs to look for while in the backcountry that could indicate an avalanche hazard. He also took some time to answer questions from attendees.