With GLS trips to Mammoth and Cross-country skiing locally in these winter months, one of the questions sometimes asked is about the danger of avalanches.† The thought of being overtaken by sheets of ice traveling at 100mph, dashing one against rocks and trees and leaving you entombed beneath a ton of snow could give anyone nightmares.† However, our chances of that being reality are quite remote.† Actually, from 1950 to 1975 about 6 people died in avalanches per year.† Now that number has increased to 28 per year, due to an increase in backcountry winter sports.†
Knowing a few facts can help us make good choices that reduce risk.† 80 Percent of valances occur within a day of new snow.† Avalanches usually occur on slopes between 30 and 45 degrees.† Avalanches more likely run on northeast-facing slopes.† (South-facing slopes get more winter sun.)† Books are written about the specific physical and mechanical properties of individual snow crystals.† One easy to picture scenario goes like this: Imagine an existing snowpack that covers the irregularities of the terrain like boulders and bushes.† It may have been sunny for a few days and the top of the snow pack has melted and recrystallized several times forming a thin, icy layer.† Then we get a light fluffy new snow coming down.† The wind starts to blow, breaking those crystals into needles that pack together to form a dense upper slab.† When the weight of the upper layer is greater than the weak fluffy layer below or when a skier steps out on it, the slab begins to move.
Picture a sheet of glass on ball bearings on a slope.
Layers within the snowpack can determine the stability of a slope
We have fewer problems than Colorado because where the temperatures are warmer, the snow is less likely to feature this weak layer.† The text says that if you are ever in an avalanche try to grab on to something even if only for a few seconds.† Let go of your equipment, take a deep breath and make swimming motions.† As the snow settles, create an air space for yourself.† After the motion stops, the snow will harden and it will be too late to dig much.† Avalanche victims found within 15 min. have a 90 percent chance of survival.† Nobody buried under more than seven feet of snow in a North American avalanche has been rescued-even with a transceiver device.†
To tell you the truth I usually cross-country ski on almost flat or rolling hilltops.† And most of the time we have to say prayers and do snow-dances just to see the white stuff in our local mountains.
†For additional information check out NOVA Online, 'Avalanche!', a look at the making of a documentary film on a natural disaster http://www.pbs.org/wgbh/nova/avalanche}