explosives are primarily used to prevent avalanches, especially at ski resorts where other methods are often impractical. Maintenance staff from the ski resort travel to potential avalanche areas with steep slopes. First, they measure the depth of the snow and its quality. They want to check for hard,loose,wet or icy snow layers. If an area is considered dangerous,small explosives are fired into the side of the steep terrain. The explosion loosens the top layer of snow,which tumbles harmlessly down the mountainside. But using explosives is costly and dangerous. Some researchers are currently experimenting with the cheaper and safer method of using ultrasonic sound waves that shock the snow into falling,averting an avalanche and saving lives.