Robert Jacobson, age 11, of Indianapolis, Indiana, for his question:
Can sound really start an avalanche?
A resounding sonic boom can shatter windows because sound waves cause vibrations in particles of matter. Fluid liquids and elastic gases can give and yield with these pulsing vibrations. But brittle solids resist and sometimes crack. Under certain conditions experts claim that a sudden, sharp sound can break loose a mass of snow high on a mountain peak. From there it plunges down the steep slopes forming into a thundering avalanche.
Most avalanches, however, are caused by other factors. Masses of heavy snow are precariously balanced high on mountains. The downfall may be triggered by cracks caused by thaws, gale winds or heavy rains. The avalanche is triggered when a mass of loose snow begins to slide. As it falls, it shoves and topples down millions of tons of loose snow and rocks. It is claimed that the lofty snow is so delicately balanced that even the sound of a slamming door may trigger a mighty downfall. –