Avalanche danger rated ‘considerable’ in Tahoe back country
Winter’s ultimate force was unleashed in the high Sierra on Friday when an avalanche thundered down from the rim of the mountain bowl at Alpine Meadows. One skier was killed, another seriously injured.
On Sunday across the Tahoe back country, the Sierra Avalanche Center rated the danger as “considerable.”
Yet at the ski areas, there seemed scarcely a thought over Friday’s catastrophe. The snow had settled and firmed, skies were blue and cold, and groomed runs provided a fresh corduroy surface for colossal crowds for the threeday weekend.
It can be odd how time and place change reality in nature.
After 2 to 3 feet (or more) of fresh powder, such as Thursday night, avalanche conditions are common. One winter, I was provided an inside look at this world. After a heavy snowfall at Squaw Valley, a team of skipatrol avalanche experts rode the lifts in the middle of the night up to the ridges. The experts were equipped with lighting and small explosive charges.
On sight, the patrol would identify areas of dangerous snow buildup. They then would toss the explosive into the slab, which would release the snow in a small avalanche. Danger averted. The groomers then followed.
By morning, when the ski areas opened, most are not aware what has transpired the night before to get the runs ready. That is what made Friday’s event confounding. These things aren’t supposed to happen at ski areas.
The danger occurs when a fresh, deep layer of snow, often 2 to 3 feet, piles high atop a frozen, icetopped slab. On a steep slope, like in alpine bowl, there is nothing to hold that surface layer of powder in place atop the ice slab. It can give way, rumble downhill and turn into an avalanche.
On slopes that range 25 to 40 degrees, when fresh snow atop an ice slab starts to shift, it makes a giant “whumph” sound. Winter is about to unleash a hurricane of snow down the slope.
Info: Sierra Avalanche Center, www.SierraAvalancheCenter.org; Mount Shasta, Avalanche and Climbing Information, www.ShastaAvalanche.org; National Avalanche Center, www.avalanche.org.