Using red flags to avoid avalanches can save lives

By Joe Stock
Special to the Turnagain Times

Avalanches are sly and mean. They have a reputation for sneaking up and clocking you on the head. Avoiding these lowly avalanches requires trickery. The most effective trick in the book is to look for red flags. Red flags are clues to when the snow is unstable—ready to avalanche—and indicate when the avalanche danger is present or increasing. They are also known as bull's eye clues in the Alaska Avalanche School-written book Snow Sense. When decisions become difficult, even avalanche professionals resort to red flags.

If you observe red flags, a general rule is to stay off avalanche terrain. Avalanche terrain is snow-covered slopes, tipped to 30-45 degrees (purchase an inclinometer for $7 to $28 to learn slope angles). Road cuts along the Seward Highway are avalanche terrain. Much of Turnagain Pass is avalanche terrain. The Crow Pass trail is avalanche terrain. Alyeska ski resort is almost all avalanche terrain, but patrollers control the avalanches with artillery. Unless it's covered with dense forest, a 30-45 degree slope is avalanche terrain.

Below are the five red flags for unstable snow.

Recent Avalanches

This is nature's way of screaming “DANGER!” If you see a recent avalanche then you know the snowpack is unstable. Recent means within the past 36 hours in maritime climates such as the Turnagain area, or the past 48 hours in continental climates such as Hatcher Pass. The question to ask is: “Do the conditions that created the avalanche still exist? In other words, are the weak layer and the trigger still present? “

Wind

Wind forms avalanche slabs (a slab is a stronger layer of snow over a weaker layer of snow). If the wind is blowing, or has blown recently, then it has probably built avalanche slabs. Blowing snow can load slopes ten times faster than precipitating snow. A red flag guideline is wind strong enough to move snow (about 15 miles per hour), for several hours or more, onto aspects where you will travel. If you have fine-tuned avalanche eyeballs, then you can see these wind-deposited slabs—where the snow has been scoured and where it has deposited.

Heavy Precipitation

The seasonal snowpack doesn't like rapid change. The more it snows, and the faster it snows, the more unstable the snow becomes. Red flags for precipitation are snowfall rates greater than one inch per hour or 12 inches in 12 hours. Another recipe for immediate avalanching is rain or wet snow falling on cold, dry snow.

Whoomphing

You are happily breaking trail when your heart rate jumps to 200 and you soil your Gore-Tex pants. That's from whoomphing—when the weak layer within the snowpack collapses, putting out a creepy “whoomph!” sound. Put that whoomph on a 38-degree slope and you have an avalanche. Sometimes these whoomphs will produce visible cracks on the surface of the snow. If you hear a whoomph then stay off avalanche terrain and on low angle slopes. You can have plenty of fun skiing, snowboarding and sledding on slopes less than 25-degrees. When I hear a whoomph, I stop right there and bust out my shovel and dig to the layer that made the whoomph. Digging only takes three minutes and then I know the weak layer.

Rapid Temperature Rise

Once again, snowpack doesn't like rapid change, especially over 32 degrees Fahrenheit. The red flag trend to watch out for is rising temperatures during a storm, which causes an upside-down layer cake, with heavier layers on top. Another red flag value is prolonged warm periods above 32 degrees Fahrenheit, like in spring when the snowpack becomes saturated and avalanches scour to the ground. Also, an avalanche slab is forming if the powder you're skiing in the morning becomes wet and heavy during the day.

Learn More About Red Flags

Take an avalanche class from the Alaska Avalanche School: www.alaskaavalanche.com. Purchase an inclinometer and carry it in your pocket when in the mountains, as do avalanche professionals.

Joe Stock works as an avalanche instructor for the Alaska Avalanche School and as a mountain guide, writer and photographer. Visit his site at www.stockalpine.com.