New Snow at the LakePosted: January 15, 2010
Had I left work to return home to Banff at the usual time last night, I would not have been around to see the snow start falling shortly after 8:00pm last night, and would have been more surprised to arrive back in Lake Louise this morning to discover almost 10cm of snow had fallen overnight. With little wind to accompany it, the hill is now coated in a nice new fluffy layer of snow. Things will pick up a bit in the avalanche control world at Lake Louise, especially if we get wind in the next few days. Following my last post about Elevator Shaft, crews did have a chance to get a good start on the control work needed to be able to open that area.
Due to the size of the area, many explosive shots are needed to cover everything. To get a head start on things, control teams began with an avalauncher shoot, allowing the deployment of many rounds in a short period. Starting in the Shaft itself, the gun was then aimed to the areas above and on skier’s right and left of the main pitch. After the last shot was fired over towards Wolverine Ridge to cover the exit from Purple Bowl, crews took apart the gun, then returned to the explosives magazine to prepare some hand charges for the afternoon hike up to Elevator Shaft. Another nine shots were deployed by hand, but like the launcher rounds, produced few noteworthy results.
To help the projectile find its intended target, the avalauncher gun is aimed in three ways. First, the gun is rotated on the platform so it’s pointing in the right compass direction. The gunner then consults a laminated photo that indicates the other two components: pressure and barrel elevation. These determine the arc of the shot, and are based on experience and assume calm weather, meaning the gunner must make adjustments for wind speed and direction if needed. On the occasions a shot misses its target, adjustments can be made for a second attempt.
The rounds used for the avalauncher are similar to hand charges, but have plastic nose cones and tail fin assemblies added at each end. The nose cone is a simple piece of plastic shaped to make the round aerodynamic, but the tail fin assembly is a much more complicated beast, as it has the firing mechanism and a two-stage safety system in addition to the fins themselves. The safeties work in progression – removal of the first allows the removal of the second. Ignition also happens in stages, with the firing pin igniting a grain of gun powder, which then lights the blasting cap, leading finally to ignition of the round.
The safety system is simple to use, and is effective in making the rounds safe to handle and fire. The firing pin is held in place by a magnet until impact with the ground dislodges it and starts the ignition sequence. Blocking the firing pin is the two-stage safety. The first stage is a pin that is removed by hand once the round is placed in the barrel of the avalauncher. This frees the second stage to be removed, and while also a pin, it gets removed in a different way. It’s attached to a base plate, which looks like the top of a tin can at the rear of the fins. When the round is fired from the barrel, the rushing wind pulls the base plate away from the round, and the second safety pin with it. The firing pin now has clear access to the blasting cap, though this doesn’t happen until the round is well clear of the gun and platform, accomplishing the job it’s supposed to in keeping staff as safe as possible. If you ever have the chance to watch an avalauncher shoot, you can see the round exit the barrel, and then the base plate falling to the ground thirty or forty metres uphill of the gun.