Avalanche Control in BrownshirtPosted: December 12, 2008
While the light didn’t cooperate during avalanche control on Wednesday, it certainly did yesterday as our control team headed towards Brownshirt for another round of explosives and ski cutting. Strong winds had continued from the previous day and on through the night, but since most of the fetch had already moved, we weren’t expecting to find significant wind loading. The wind did, however, make for beautiful ski conditions as all back side terrain was blanketed in a soft cover of snow that filled in the tracks from the day before and blue skies bathed the area in a warm light that made everyone feel like a hero.
Despite the fact that we had received big results from explosives in Whitehorn II on Wednesday, we weren’t expecting the same thing in Brownshirt yesterday. Our trips into D, E, and F Gullies in Whitehorn II were the first of the season, and the big results were due to the fact that the terrain had had a long time to build a snow pack, and the early November rain crust had remained intact. Brownshirt, on the other hand, has been getting worked almost from opening day, and we were confident that other than the shallow layer of new, wind-deposited snow on top, the snowpack had been disturbed enough through explosives and ski cutting to stick firmly in place on the slope.
Ski cutting is one of the most common forms of avalanche control used at Lake Louise, and involves patrollers descending a slope in a zig-zag pattern in order to penetrate any suspect layers and to slice one big area of snow into smaller pieces. When a slab avalanche begins, the fracture line propagates through the snowpack, both on a vertical and horizontal plane. If ski cuts have been put into an area of snow, this propagation is interrupted, and the chance and consequence of the avalanche is greatly reduced. Think of it as a fire break in a forest – by removing a swathe of trees, you can reduce the chance of an advancing forest fire progressing past it.
Ski cutting is only performed when deemed safe to do so, and if there is any concern about the stability of the snowpack, we’ll throw explosives onto the slope in advance of our progress. Even when we don’t expect avalanches, we must ensure the safety of the control team, and by throwing a bomb onto a slope, we perform a valuable slope test since the concussive force of the blast will either reveal weaknesses by avalanching or further settle the snowpack. We began our descent of Brownshirt main gully by throwing a charge below us, followed by a few ski cuts, and proceeded this way until all team members had reached the bottom of the run.
Now that the run is covered in ski cuts and blast craters, it won’t take much snow and wind to fill it all back in again. When that happens, the snow will fill in the tracks and holes, resulting in uneven and irregular layers, adding to the stability of the slope. For now, it’s still a little rocky, as the bases of our skis will attest!
The good light yesterday also allowed us to have a good view of the large results we got in Whitehorn II on Wednesday. Below are a few photos of the devastation: