Rock BlastingPosted: October 2, 2009
Throughout the winter ski season at Lake Louise, it’s part of the daily routine for members of the Snow Safety team to prepare explosives and head up onto the mountain. It’s much rarer to see that in September, with this week being an exception.
Rock blasting is just that – using explosives to blow up rocks. This has been done a few times in the past at Lake Louise, mostly to improve the safety of the World Cup downhill course. Specialists would come to the ski area in an attempt to flatten rocks that had a history of compromising the safety of the course and damaging equipment. Early in the course-building process, snow cats travel in the softer snow to pack down a base. Sharp rocks can cause mayhem with the underside of a cat, causing delays that are costly in both repairs and time, which can be a scarce commodity in the weeks leading up to the races. Receiving the most attention were the areas in and below Sunset Gully, just below the start of the men’s course.
Surface blasting requires a wholly different certification than the one required for winter avalanche control. The protocols are much different, and the explosives used are made specifically for the task. Previously, certified surface blasters were contracted to come in and spend a day or two getting rid of pesky rocks. Last summer, an instructor came for the week and conducted a course for snow safety and operations staff from Lake Louise and Sunshine Village. The Lake Louise avalanche forecaster became certified to lead a surface blasting program, allowing us to proceed without the need of outside supervision.
This year, the run to receive the bulk of the rock removal was Saddleback, from the Notch to Rodney’s Ridge. This cat track is always difficult to build in the winter, as the ground is very uneven and does not provide an obvious way to traverse below Whitehorn 1. Boulders litter the slope, and the worn top edges of all of them are a silent testament to years of scraped skis and worn cat blades.
With the proper permits in hand from Parks Canada, a team of two went to the sites the day before blasting was to start in order to identify and prepare the rocks for their big day. Once identified, the crew began to drill the holes into which the explosives would be inserted. To do this, they had to lug around a generator and large rock drill to each location, then drill up to six or seven holes in each rock, depending on the size. Drilling the holes in advance saves time and allows the blasting to proceed more quickly.
The following day, four Snow Safety staff assembled the explosives and went back to the site to start blasting. The explosive charges are placed into the drilled holes, and the way they’re detonated depend on whether there’s one or more than one. For a single shot, the explosive is detonated by the same 2.5 minute fuse used on avalanche control rounds. The team member pulls the igniter, then has two and a half minutes to retreat to a safe distance, usually at least 100 metres.
For multiple shots, it is most effective to have all of them go off at the same time, which would be impossible if each had their own fuse. In this case detcord (detonation cord) is used to connect each shot. Detcord is an explosive cord that comes on spools and can be strung out and cut to whatever lengths are needed for the job. Each explosive has its own line, and they’re all taped to a single line that will have an igniter placed on the lone end. As before, the blaster pulls the ignitor, then retreats to await the blast. Once the fuse reaches the end of the det cord, it’s all over – detcord explodes at an incredible 8000 metres per second along its length. This speed allows for the simultaneous blasting of multiple charges, regardless of their distance from the ignitoin point.
The short video below shows two explosions, both using detcord. If you look carefully, you can see the cord explode along with the charges in the rocks. It travels much too fast to be able to tell which end it started at, though.
Once the explosion is over and it’s safe to approach, the site is inspected. Ideally the rock will have been shorn right at ground level. If there’s still some above ground level, more explosives are used. If a hole is left, the broken pieces of rock are used to fill it back in. Like any ground disturbance that occurs on the mountain, we must make the area look as undisturbed as possible.
In a mountain range known (and named) for its rocks, one might ask “Where do you start?” That’s a good question, and recognizing that it’s a long job that will likely take a few years, you have to start somewhere, and upper-mountain green runs like Saddleback, which can sometimes be hazardous to man and machine early season, top the list.