Book excerpt: This report describes the phenomena that snow avalanches produce sounds in the 0.5 to 5.0 Hertz range. It also documents testing of an infrasound detection system to detect snow avalanches in the southwest mountains of Colorado. Two infrasound sensors were installed so the direction of the sound could be determined by comparing the phasing and arrival times. Avalanche detection was sometime obscured because of the high mountains nearby diverting the sound and causing clear-air turbulence. Linking sound events with avalanche events was hampered by the fact that the time of actual avalanches could only be determined within a 12-hour period.