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Volcanic sounds: Investigation and analysis

1963; American Geophysical Union; Volume: 68; Issue: 3 Linguagem: Inglês

10.1029/jz068i003p00919

2156-2202

Adrian F. Richards,

Seismic Waves and Analysis

Volcanic sounds were tape-recorded on ten occasions during the decade 1950–1960. Analyses of the recordings show that underwater sounds from Barcena volcano in the north-eastern Pacific, in November 1952, possessed frequencies in a strong harmonic progression with an apparent fundamental frequency of about 50 cps, little energy above 550 cps, and a pulse duration of 1 to 2 sec. Airborne sounds of explosions in Mihara Yama, O Shima volcano, Japan, in January 1954 had an apparent fundamental frequency of 16 to 17 cps, a strong harmonic progression, and a pulse duration of 0.5 to 1 sec. Less violent explosive activity of the same volcano in September 1950 produced essentially broad-band acoustic energy, with sound durations of 1 to 2 sec. Recorded airborne sounds of Izalco volcano, El Salvador, in 1956, were similar to those from O Shima in 1950, but had longer pulses. Capelinhos volcano, Azores, in 1958 generated the following airborne sounds: crater explosions had maximum energy below 50 cps and little energy above several hundred cycles; eruptions of liquid lava from the crater produced broad-band sonic energy; and almost all energy of pressure waves or flashing arcs was below 50 cps. It is suggested that the quality of recorded sounds is related to the types of volcanic activity defined by Lacroix and in this paper: Hawaiian eruptions tend to be acoustically quiet; strombolian activity is characterized by broad-band sounds that may show a fundamental frequency and harmonics of small intensity; and vulcanian eruptions are denoted by a marked fundamental frequency and strong harmonics of relatively large intensity. Pelean activity has not been recorded. Recording instrumentation and analytical procedure in which sound pressure level-frequency and frequency-time methods were used are briefly discussed as an aid to those wishing to make similar investigations.