Acoustic emissions in the investigation of avalanches

This paper reports on the results of several years of investigations into the role of ultrasonic emissions in the deformation and failure process in snow. The origin of ultrasonic emissions in snow is discussed and the manner in which these emissions enter tnto the process of deformation is considered. The results of several laboratory experiments are presented. In the laboratory acoustic emission investigations were conducted in a frequency range from 30 KHZ to 300 KHZ. Snow samples were subjected to various load and deformation histories and the acoustic response recorded. Laboratory investigations were also conducted to study the pattern of acoustic activity as it relates to the failure properties of snow.In the field, a two-year investigation was conducted to determine if the acoustic patterns observed under laboratory conditions would also appear in natural snow slopes. This study indicated that although the acoustic activity is not as well defined in situ, certain patterned responses are detected which relate to developing stability and instability in the snow pack.