Off Piste Awareness Part 2— Avalanche red flags and signs of danger
Our recent trip to Mayrhofen and the surrounding resorts made me acutely aware of the dangers of off-piste riding. As we enjoyed some fresh lines in the sun after splitboarding up to Rastkogel 17 people were buried with 5 fatalities only a few miles away. We watched the constant stream of helicopters travelling above us as we made our way down the valley selecting the best pockets of snow for the most fun unaware of what was unfolding in the next valley.
My path to better understanding of off-piste guiding is still in its early stages, but the story of this seasons snow pack increased my awareness of how the early winter snow can have a long standing effect on the stability of the snowpack.
This season the Tirol region had the driest December since the late 1800’s, so the depth of the snowpack was minimal. We found south facing slopes had been battered by the sun and did not last long for riding so you gravitated to the more sheltered slopes that had some decent deposits of snow, but quite often they were wind loaded and sat on a layer of depth hoar.
So why is wind loaded snow on depth hoar a problem?
Wind generally breaks up the snow crystals, so the snow becomes very compact and dense when it eventually settles. That creates a heavy layer of snow. Ordinarily this would not be an issue unless that dense layer settles on a weaker layer of snow.
This season the snow pack started very thin. When you have a thin snow pack and colder temperatures you get the creation of something called depth hoar. In simple terms depth hoar is like frost. That frost becomes a weak layer, that has crystals shaped very much like cups or pyramids (faceted snow).
If you have those crystals sitting below a heavy snow layer, then when someone rides over that layer it can settle or slide creating an avalanche. This season on some of the terrain we also had a lot of bushes, so you had big pockets of air created by the bushes mixed with depth hoar and wind loaded snow. That is why extra caution had to be taken this season as the snow often settled as you rode over it.
We did encounter this settling effect on one of our tours. Three of us rode down to meet our guide, then Taddeo joined us, and suddenly the whole snowpack we were on dropped and we heard a whoomphing sound. It does freak you out. The weight of so few riders could have an effect like that on the snowpack.
The whoomph sound is an off piste red flag, and something not be to take lightly. For us it was a clear indicator to proceed with some caution as we moved to some lower angle more settled snow pack areas.
On reflection I could see how a larger group of riders could actually set off an avalanche in that type of terrain, with the sheer weight of the people.
As we moved into the latter part of the season the snowpack had settled considerably due to the regular warming trends that helps transform that depth hoar so it bonded with the upper layers of snow. That allows us to venture into those pockets of sheltered snow with more confidence.
Here is some more details on avalanche red flags, so you know a bit more about the hazards before you head out.
Assessment of Danger — 5 Avalanche Red Flags
1 — Recent avalanche activity
2 — Sudden warming trend or rise in temperature
3 — Significant new snowfall in the last 24hrs
4 — Cracking, blocking or whoomphing of snowpack
5 — Strong winds
You can read more on red flags via an article written by Matt Dickinson
As always, be safe out there and reading this article is no substitute for some proper off piste training. Check out the Salomon Mountain Academy for extra information on off piste safety.
Just remember this information is not a substitute for an avalanche class. Get educated before heading into the winter backcountry.