Friday, February 20, 2004
Don’t assume avalanches are only the worry of snowmobile riders, extreme skiers and death defying snow sledders. Recently four avalanches crossed U.S. Highway 2 in under two hours in northwestern Montana and another avalanche flipped over several train cars east of Essex. Avalanches cause deaths, injuries, property damage and can interrupt communications lines and block travel routes.
If you live or recreate in Montana, you need to know the language of avalanches. It could mean the difference between life and death, or more often between having fun or having an all around bad day.
Avalanches are all about moving snow. The slope, weight and quality of the snow and weather all contribute to the potential for movement. These factors may combine at any time to trigger an avalanche by enabling gravity to overcome the natural cohesion, or “stickiness,” that holds snow in place.
Certain “bowls” and high mountain areas are notorious for avalanches—the slope, typical snowfalls and weather set up a potential avalanche and then gravity and weather changes do the rest.
Here are a few terms to help you begin speaking the colorful language of avalanches.
Where an avalanche pulls away from the snow above leaving a wall of snow perpendicular to the slope.
The snowpack is layered like a cake. Every time it snows, the temperature, wind and humidity all help to create a different snow layer. These unique layers make the snow weak and unstable.
This new snow looks like tiny Styrofoam balls falling from the sky. It creates a weak layer because this snow acts like a layer of ball bearings.
Wind Loaded Slopes:
Wind can drift or “load” snow onto the leeward or downwind terrain ten times faster than snow falls from clouds. This new load stresses the snow pack, changing conditions even as the sun shines.
Cracking and Collapsing:
When the snow pack collapses with a loud “whumph” as you cross it, or cracks in front of you, it signals the avalanche danger is severe. If this happened on a steeper slope it would likely trigger an avalanche.
This is frozen dew that forms crystals that look like feathers on the snow surface on cold, clear nights. Surface hoar is a persistent weak layer of snow responsible for many avalanches.
Faceted, angular snow crystals don’t bond well. They look and feel like sugar and it is difficult to squeeze them into a snowball. These grains form a weak snow layer.
The runout zone is where the avalanche loses speed and deposits debris.
Stress to the snowpack that exceeds its strength triggers an avalanche. Sometimes the weight of a person is all that it takes, other natural triggers could be more snow or wind loading.
To test your savvy with the language of avalanches go to the Gallatin National Forest Avalanche Center, http://www.mtavalanche.com/ Glacier Country Avalanche Center http://www.glacieravalanche.org/ or West Central Montana Avalanche Center http://www.fs.fed.us/r1/lolo/avalanche/advisory.htm Internet sites. The sites include up-to-date avalanche reports, weekend snow pack reports and weather outlooks.Now that you speak their language, make avalanches your business this winter by practicing avalanche awareness and safety in Montana's outdoors.