Backcountry Essentials: Faceted Snow
The culprit for the lion's share of avalanches
Sean Zimmerman-Wall is a full-time ski patrolman at Snowbird, an avalanche educator, and an Andean mountain guide. Check in on Tuesdays for resources and education that will help you have a safe and good season exploring terrain beyond the boundary line.
Early-season snowfall and a thin snowpack are some of our biggest enemies in the avalanche game. That’s because these conditions are prime for faceting, which creates persistent weak layers. So far this season, with October promises of an epic season still unfulfilled by January in many places, a faceted weak layer has been the culprit of a majority of the fatalities in North America and Europe.
The process of faceting is quite simple to understand and it happens in seemingly benign conditions. During cold, clear, and calm spells, the snow undergoes a process known as metamorphism. Those beautiful stellar snowflakes that fell from the sky immediately start to change the moment they hit the ground.
For faceting to occur, a temperature gradient must exist, or there must be a difference in temperature between the ground and the air. An early season snowpack is often thinner and therefore the temperature gradient is steeper. High vapor pressure moves from the ground up through the snowpack to the surface where a lower vapor pressure exists. That process weakens the snow crystals. It can take a few days or it can occur over the course of a week or more. In places like Colorado where the snowpack is usually thin and the temperatures are quite cold, this weak layer is a problem throughout the year.
A complete faceting of the snowpack is possible, and indeed that is what we have seen in a variety of places this season. Once a new load of snow is added and a slab forms over these facets, we have the perfect set up for avalanching. All it takes is a trigger. The deeper the facets, the more dangerous the avalanches become. A stout windslab or hardslab over facets is a deadly combo and most of the time these monsters break while you are right in the middle of them. Escape is not possible once the rug has been ripped out from under you.
The good news is that we can do a little detective work and get down in the snow to see where these dragons live. Tracking these weak layers and knowing how deep they are buried is the all-consuming goal of avalanche forecasters and they are good about relaying this information to the public in their daily bulletins.
Understanding the science behind faceting is important, but recognizing the hazard they pose is critical. Unfortunately, we have been dealt a royal flush of facets this season and all bets are off. The problem will be very slow to heal, especially with the meager snowfall across most of the continent. Safe options on lower angle slopes will provide hours of entertainment and you can practice getting out with your group and working together as a team. Perhaps the spring will bring us better conditions and more options, but for now, take it easy and enjoy simply being in the mountains.
|Last week’s backcountry tip: Wind Loading →|
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