Using Infrasound to Detect and Characterize Avalanches

Infrasound arrays and geophones have been deployed at three sites in Utah’s Little Cottonwood Canyon are used to “listen” to both naturally occurring and human triggered slides along many of the area’s avalanche paths. Each station consists of four infrasound sensors (in a 50-m aperture array) and two seismic sensors and are recording continuous data since December 2017 in an effort to locate and examine the nature of the slides occurring as far away as three kilometers. Avalanches produce a unique frequency spectrum peaked at about 5 Hz in the infrasound band and with slight differences that may reflect slide dynamics including size, velocity, duration, and snow composition. Seismic detections seem to be most responsive to avalanches occurring in very close proximity (less than 500 m) from the arrays and seem to provide less utility for comprehensive detection. Cross correlation analysis of the infrasound signal, using precise GPS locations of sensors, permits us to determine which direction the signal is coming from, and based on knowledge of active slide paths, allows us to extrapolate which avalanche path released. Paired with the SNOTEL data of the area and alerts provided by the Utah Department of Transportation, who trigger avalanches to mitigate hazards, we have explored the characteristics of avalanches throughout the duration of the recent (February) storm cycles. Avalanches play a large role in the recreation and transportation communities of the area and better understanding of avalanche signatures during large storm events will permit more effective risk management