Avalanches represent the number one cause of snowmobile-related fatalities in the western United States, said Rich Gummersall, off-highway vehicle education coordinator with the state agency, who urged individuals to use caution when driving snowmobiles and other off-road vehicles in these high-risk areas.
"Most large avalanche paths are obvious -- an open slope, bowl or gully above timberline that leads to a swath through the trees," Gummersall said. "But small avalanche paths in the trees can be just as dangerous."
Avalanches are more common when snow conditions become unstable, although nature often broadcasts some clear danger signals, he added. Fresh avalanches are the best clue and can include signs of snow that cracks, collapses or makes hollow sounds. Snow that becomes wet from thaw or rain is also dangerous.
In each case, avalanches need some type of trigger, whether it's caused by human contact, the presence of animals or weather, he said.
Another factor is the angle of the snow pack. Generally, "slab" avalanches occur on hillsides with 25 to 60 degree angles, although 90 percent of all avalanches start on slopes with angles between 30 and 45 degrees.
When in doubt, it's best for people to carry a slope meter with their gear. Travelers should also check for snow deposition patterns and the effects of anchors such as rocks or trees that might prevent avalanches on some slopes.
"Bent or damaged trees are good clues that show where avalanches have run in the past," Gummersall said.
The avalanche danger increases with major snowstorms and periods of thaw, he added. About 2,300 avalanches are reported to the Avalanche Center in an average winter, and more than 80 percent of them happen during or just after large snowstorms. Ranked by order, the most avalanche-prone months are February, March and January with April the most frequent time in which thawing conditions trigger avalanches.
However, Gummersall emphasized that conditions in the backcountry can change daily, even hourly, and avalanche centers provide recent snowpack stability information. For more information, go online to www.avalanche.org.
"You cannot entirely eliminate risk if you travel in avalanche terrain, but you can minimize risk by using good technique, such as climb, descend or cross avalanche areas one at a time," he said.
It's safest for people to cross a slope at the very top or bottom if possible and climb or descend the edge of a slope versus the center. When in doubt, people should turn back or alter their route if they detect signs of unstable snow.
Gummersall stressed that people crossing potentially unstable terrain should do so one at a time versus driving as a group.
At the same time, anyone driving a snowmobile or off-road vehicle in the backcountry should always carry a pack that includes three days of emergency supplies along with a probe, shovel and avalanche beacon. That gear can often mean the difference between life and death, said Gummersall, who added that people should be comfortable using this rescue gear.
Statistically, 90 percent of avalanche victims survive if they are recovered within 15 minutes. At the same time, 25 to 30 percent of these victims die from trauma incurred during the slide.
"Surviving avalanches can depend on luck; therefore, it is always better to avoid them in the first place," he added. "Only one of three victims buried without a (locator) beacon survives."
If caught in an avalanche, people should first try to escape to the side or grab a tree or rock. It's best to "swim" with the avalanche to try to stay on top while avoiding trees.
"When the avalanche slows down, reach the surface or make an air pocket," Gummersall said.
Avalanche danger - Learn more
The Idaho Department of Parks and Recreation holds a snowmobile-based avalanche awareness and companion rescue clinic starting at 6:30 p.m. Feb. 24 at 350 North Pine-Featherville Road. A field class follows at 9 a.m. Feb. 25 at the Trinity warming hut. The free program familiarizes participants with recognizing avalanche hazards as well as techniques for outdoor enthusiasts to safely travel in this type of terrain. To register, call Rich Gummersall at 208-514-2414 or go online to www.parksandrecreation.idaho.gov.