A Morning on Avalanche ControlPosted: December 10, 2008
As those who have been here over the past few days know, Lake Louise is enjoying great skiing conditions, thanks to the recent storm and the relative lack of wind accompanying it. No wind means that the snow gets evenly distributed over the terrain, and remains soft and fluffy.
The wind picked up yesterday, however, and kept up through the night and into today with gusts at reaching 50-60km an hour. With lots of snow available to be blown around (called fetch), things can change dramatically in a short time, depending on how hard and from which direction the wind is blowing. This recent wind came from the south-west, and since this is where pretty much all of our wind comes from, the wind-loading that occurred as a result followed fairly predictable patterns.
The avalanche forecaster usually arrives at the Snow Safety office by6:30am, and begins the process of gathering weather information from a number of sources in order to produce a plan of attack for the day’s avalanche control. From our automated weather stations, we can see a detailed record of what happened since the resort closed the previous day. The stations record snowfall, wind speed and direction, temperatures, and moisture content of the snow, among other things. With this knowledge, the control teams head out the door and up the mountain, having a good idea in their heads of what they’ll see when they get there, but still careful to travel cautiously, since while a weather station can give a good general picture of the weather, complicated and varying terrain have their way of affecting the weather around them, and one should always be ready to experience the unexpected.
My control team headed out the door with the plan to control the front side of Summit, then Whitehorn I, and then over into Whitehorn II. On the front side of Summit, there aren’t a lot of places of concern, but the few that are there still need the same attention we pay to everywhere else. For Whitehorn I, we travelled down the fence line on skier’s right, since that is where the cornice usually forms, and a large part of avalanche control is making sure cornices don’t have the chance to grow too large. The newly-deposited snow was between 15-25cm in isolated spots, and only somewhat showed signs of slab. Our ski cuts produced few results, and the sow appeared to be bonding well to the underlying layer.
After these runs were opened, we moved on to Whitehorn II – D, E, and F Gullies in particular. We had a bunch of explosive charges, and planned to place them on both sides just below the tops of the gullies, where they roll over into their steepest pitches. These ‘convexities’ in the slope are the usual suspects when it comes to avalanche trigger points, and are most likely to produce results when explosives are used. In D Gully, it was hard to tell exactly what kind of result we got since the light was poor, but we could still see the powder cloud that signifies the advancing edge of avalanching snow. Into E Gully, we used a similar placement for the charges, and the photo below shows the bombs as they’re thrown onto the slope below:
One shot landed and stuck in the snow, right where it was meant to be. The other shot landed on hard snow and started to slide down the slope, stopping in the narrowest part of the choke, 150m below where it was supposed to be. The choke didn’t have much snow, so we weren’t expecting the shot to produce any significant results. After a wait of 2.5 minutes (length of the fuse), the bomb that had slid downhill went off. It started an avalanche in its immediate area, but as the snow started to slide away, the snow above became unsupported from below and began to go as well, piece by piece, until eventually the snow in which the other charge was sitting began to slide as well. Our hearts sank as we realised that the second shot might be moved away from where it would have the most impact, but just as quickly as the slide began the shot went off, increasing the size of the already moving avalanche. We watched with amazement as almost the entire gully was completely cleared of snow, and a few boulders as well. The poor light didn’t permit any photos of the avalanche, but if you’re up skiing Boomerang or Brownshirt in the next few days, look up into Whitehorn II – you can’t miss it!