No abstract

Volcano Stromboli, Italy, has been in a nearly continuous state of activity since the earliest records were made by Aristotle. Well‐collimated jets of incandescent gases loaded with basaltic vitric lapilli characterize these eruptions, for which the term strombolian activity has been coined. We report results of a photographic study of two eruptions, one relatively large and one small, using principally high‐speed movies taken with a Hulcher 102 (70‐mm) camera at a rate of 10 frames/s and exposure time of 1/72 s. Ninety‐six frames, containing about 13,000 streaks, were analyzed with a computer interfaced digital film reader yielding detailed data on the bulk and time‐dependent properties of these two eruptions. We believe that these two eruptions bracket typical conditions at Stromboli; hence the results can be taken as representative of strombolian activity at the type locality. Geometric ambiguities, data acquisition, and reduction problems are discussed. Results for the two eruptions were as follows: duration of eruptions, 8 and 5 s; number of particles ejected, 2594 and 152; average (and maximum) particle size, 2.2 (31.8) and 2.5 (13.5) cm; average (maximum and minimum) particle velocity, 26.2 (2.5–72) and 15.3 (4.5–38) m/s; median angular dispersion from the jet axis, 8° and variable (10°–45°); mass of particles ejected, 100 and 7.6 kg; total kinetic energy of particles, 16.2 and 2.5×1010 ergs; calculated possible range of gas density, 0.05–0.30 mg/cm3 for both eruptions; maximum gas velocity, 112 and 94 m/s; calculated mass of gas ejected, 240 and 120 kg; and gas to lava mass ratio, 2.4 and 15.8. Particle velocity and calculated gas velocity decayed from their initial maximum values, but well‐marked oscillations with a period of about 1.6 s were superimposed. One model explaining these fluctuations is organ pipe resonance implying a tube length of 300–400 m. We estimate the flow to be subsonic, with a Mach number of 0.2–0.3. The range of estimated gas density is consistent with mixtures of CO2 and H2O.

Northeast crater is a pyroclastic cone near the summit of Mount Etna, built to its present volume (1 X 108 m s) by nearly constant strombolian activity since its birth in 1911. Detailed analysis of one typical photograph of a June 1969 eruption indicates that particles exit with a median velocity of about 51 m/s at angles distributed nearly uniformly between 70 ø and vertical. Ejecta consists of ash to 1-m bombs. Physical properties of ejecta include median bomb density, 1.53 g/cmS; particle size of ash found locally on the cone, 150 •t; median size of bombs constituting the cone, 15 cm; sphericity of bombs, 0.78; and surface roughness of bombs, approximately 0.05. Ballistic analysis using these data and including effects of atmospheric drag shows that cinder cone morphology can be predicted by a quantitative model that is in excellent agreement with observed cone features. Cone shape or profile, rim location, limit of continuous ejecta, the ballistic limit (maximum range of ejected fragments), and the size and location of talus slopes are uniquely determined by fragment exit conditions and ballistics. The model suggests that cinder cones grow through four distinct stages: (1) simple cone, with ma.ntle bedding and a low rounded rim, (2) onset of an exterior talus slope, (3) destruction of the original rounded rim by backward migration of the talus, and (4) outward growth of the talus slope beyond the ballistic limit. In the lunar exterior ballistic environment, cinder cones (if they erupted at conditions qualitatively similar to Etna's Northeast crater) should form tuff rings with low, barely discernible rims. Small dark halo craters and dark mantling deposits observed on the moon (such as those near the Apollo 17 site) may be lunar equivalents of normal terrestrial cinder cones. Clusters of such lunar cones might form continuous blankets rather than groups of discrete cones as they do on the earth. Martian cones, formed under the same conditions, would be more like lunar cones than terrestrial ones. This paper presents results of a study of the mode of growth of cinder cones. It focuses on structure, physical properties of ejecta, ballistics, and growth of Northeast crater, a young pyroclastic cone that originated in 1911 near the summit of Mount Etna, Sicily. We describe the cone and the physical properties of the ejecta and relate these properties to the ballistics of the ejecta revealed by an analysis of a photograph taken of Northeast crater in a typical state of eruption in June 1969. From the eruption photography we obtain statistics on ejection velocity and ejection angle for the ejected particles. We use these data to discuss two problems: (1) the mode of growth of Northeast crater and of cinder cones in general and (2) the structure and surface morphology of cinder cones such as Northeast crater on the surface of Mars and the moon, if they were formed under similar eruption conditions. Both problems are approached by exploring the distribution of ejecta and the growth of cones by repeated similar erupti...

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,

SirrnmaryVolcanic 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 P a 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 p o is gas density, A D the vent area, a. the sound speed, V gas velocity, and KD an empirically-determined constant which our field data suggests is in the range lo-* to lo-'.Eruption acoustics appear to constitute a means of quantitatively monitoring volcanic activity which, along with other techniques such as photography and seismology, can yield data bearing on eruption dynamics.