Avalanche, as are a constant threat on mountain highways. The rogers pass stretch of the trans Canada is at risk of being buried in snow from november to april every year. This is why the highway now has a sophisticated defense system. The best way. IT's important to control an avalanche when IT's small. So a slide is set off while it's still small before it builds up into a serious danger. A team of snow technicians monitors the snow pack. They sort of read the snow and try to predict when it's likely to slide. They studied data from the weather stations in the mountains. As the danger increases. They drop explosives on to test slopes to see if the snow can be made to slide. IT’s kind of tricky trying to decide just when the snow will slide. The weight of the snow together with the force of gravity is what starts an avalanche. The technicians don't wanna wait till it's too late, but if they're too early before conditions are just right, the snow won't release when the time is right. They close the road and remove all traffic from the past. Most closures last two to four hours, then the army comes in at men and artillery crew operates a mobile one hundred and five millimeter howitzer firing shells into the slopes. This sends out shock waves that trigger the avalanche as slides are set off one by one, the technicians direct the action, telling the troops where to aim the gun.