The road that winds through the mountain valley was closed. Skiers were banned from the area. The sound of artillery fire echoed from the mountains. It seemed out of place in this picturesque scene of snow-covered peaks surrounding the valley. A moment of quiet followed the blast. Suddenly the snow broke loose with a menacing roar. Tumbling down the mountainside, the snow buried everything in its path. You can see in Figure 1 the enormous mass of accumulated snow that had hung above the valley. After the avalanche, the valley was quiet again. It is safe for skiers and hikers to return to the area.

Figure 1  In an avalanche, a mass of loose snow, soil, or rock suddenly gives way and slides down the side of a mountain.

This is the work of researchers at the Avalanche Control Section in Glacier National Park, Canada. These scientists monitor the snow as it builds up layer by layer on the park's upper peaks. They can predict when an avalanche is about to happen. With well-timed artillery shots, they make the avalanche happen at a time when the released energy cannot harm anyone.