Observations of underwater volcanic acoustics at Bárcena Volcano, San Benedicto Island, Mexico, and in Shelikof Strait, Alaska

Abstract

Magnetic tape recorders and sonobuoy equipment have made possible a practical approach to the study of underwater volcanic acoustics. Underwater audio energy originating from Bárcena Volcano on San Benedicto Island, Mexico, was studied from plane and ship between November, 1952, and May, 1955, and tape recorded on four different occasions. The recorded sounds are of two kinds: a rumble with a pitch of approximately 125 cycles, and a higher frequency hiss. These sounds, unlike any of known biological or other origin, are discussed and a frequency analysis of the rumble is given. In order to determine the source of audio energy produced from Bárenca a triangulation method was devised by making an effectively simultaneous time and frequency analysis of selected portions of the acoustic spectrum from pairs of strategically placed sonobuoys. This technique was successfully used from shipboard in November, 1953. An unsuccessful attempt was made in August, 1953, to determine if audio energy generated from the active volcano Mt. Trident, in the Katmai National Monument, could be received in Shelikof Strait. The attempt is described to illustrate the technique used.