ASSESS AVALANCHE RISK
Pay attention before and during your hike to make sure you’re on solid snow.
• Take a class. There’s no substitute for expert instruction (sign up for a course at AIARE.info).
• Check the avalanche forecast. Find your local report at avalanche.org. Note key factors, like certain areas, aspects, or elevations to avoid.
• Start early. Wet snow freezes at night, stabilizing it, but warmer afternoon temps can cause wet slides.
Factors to consider
1) Slope angle. Avalanches most often occur on slopes between 25 and 50 degrees, and dry avalanches, which are responsible for the majority of avalanche-related deaths, commonly at 37 to 38 degrees. Avoid hiking on or under those slopes.
2) Aspect. In the Northern Hemisphere, north-facing slopes receive less sun than south-facing slopes in winter. The snowpack on colder slopes is more likely to develop persistent weak layers, which inhibit stability. 3) Natural anchors. Snow on slopes with lots of visible trees and rocks is less likely to break loose as one piece. Only a few trees or rocks? Those signify a localized shallow spot, where the snowpack could be insufficiently anchored to the slope. Avoid these.
4) Slope shape. Snow stretched over undulating slopes, especially convex hillsides, is under more stress than straight or concave slopes, making avalanches more likely.
• “Whumpfing.” When a denser top layer of snow collapses onto a weaker layer beneath it, it creates a deep, reverberating “whumpf” sound.
• Shooting cracks. Stepping on unstable snow can cause it to crack and separate from the slope.
• Cornices. Wave-shaped heaps of snow at the apex of a ridge mean wind has deposited a heavy layer on the slopes beneath, making them likely to slide. Cornices can also snap off, triggering those slopes.
• Recent avalanche activity. Look for scraped hillsides with clumpy snow debris at the bottom. Clean, white blocks with sharp edges, and/or visible, giant snowballs mean the slide happened within days.
• Pinwheels. Rolling balls of snow portend wet slides.