The 83rd Colloquium of the French National Centre of Scientific Research (Topography and Ecology of Oceanic Deeps) held at Nice, 1958 May 5 - 14

Abstract

Volcanic activity which involves the vigorous flow of gases, such as strombolian eruptions and energetic fumarole activity, is commonly accompanied by noise or acoustic radiation caused by the interaction of the gas with the stationary solid boundaries of the vent as well as the turbulence of the gas in the jet itself. Analysis of sounds (both total power emitted and frequency spectra) produced during volcanic eruptions will provide detailed quantitative information concerning gas velocity history. Theoretical considerations suggest that acoustical power radiated during gaseous volcanic eruptions may be related to gas exit velocity by power laws of the form Pa V", where n ranges from 4 to 8 depending on the type of radiation involved.Noise from energetic fumaroles atop Volcan Acatenango, Guatemala, was recorded, analysed, and interpreted in terms of the nature of the radiation produced and the implied gas velocities. This gas vent noise is found to be dipole radiation (due to interaction of the gas jet and solid boundaries), with quadrupole radiation (aerodynamic sound), and monopole radiation (source noise due to changes in mass flux) playing an insignificant role. For the dipole case, total radiated power, PD is approximately:where po is gas density, A,, the vent area, a, the sound speed, V gas velocity, and K , an empirically-determined constant which our field data suggests is in the range lo-' to lo-'.Eruption acoustics appear to cbnstitute a means of quantitatively monitoring volcanic activity which, along with other techniques such as photography and seismology, can yield data bearing on eruption dynamics,

Poor scaling between elastic energy release and eruption intensity at Tungurahua Volcano, Ecuador

“…For example, a simple monopole-type acoustic radiator produces signal proportional to a volumetric acceleration [Lighthill, 1978], which could be negligible for a steadystate flux. A dipole-type acoustic radiator, proposed for gas jetting sources [Woulff and McGetchin, 1975], would also result in diminished acoustic radiation.…”

Application of the Monopole Source to Quantify Explosive Flux during Vulcanian Explosions at Sakurajima Volcano (Japan)

“…Although the monopole source is postulated as a suitable approximation for purely explosive transients, higher order dipole and quadrupole acoustic sources (Woulff and McGetchin, 1976;Johnson et al, 2008;Kim et al, 2012) and jet noise (Matoza et al, 2009;Taddeucci et al, 2014) have been proposed for a range of volcanic eruptive activities. Both jet noise and dipole type sources radiate sound less efficiently than a monopole source (for given eruption energetics) and are thought to radiate sound with an axisymmetric symmetry (Dowling, 1998).…”

Using infrasound to constrain ash plume rise

“…Fluctuations in air pressure recorded at a distance from a volcanic vent are directly related to acoustic power that, in turn, depends on mass outflux at the source (Caplan-Auerbach et al 2010;Woulff and McGetchin 1976). The relationship between acoustic power and eruptive flux, however, is complicated by uncertainties in the source dynamics.…”

“…volcanic vent radius), u is the velocity of the material at the source, and c is the speed of sound in air. The value of K m is of the order of 1, while K d and K q are approximately 10 −2 and 10 −5 , respectively (Woulff and McGetchin 1976). Following Caplan-Auerbach et al (2010) we favour a dipole source for the explosions at Mt.…”

“…The relationship between acoustic power and eruptive flux, however, is complicated by uncertainties in the source dynamics. Woulff and McGetchin (1976) introduced, within the framework of linear acoustic theory, relationships between velocity and power for three source types: monopole, dipole, and quadrupole. A monopole source is one in which variations in pressure are due entirely to the rate of change of mass flux, and can be envisioned as an isotropically expanding source.…”