Objective
An experimental set up has been devised to mimic Strombolian volcanic eruptions, where a series of large bubbles breaking at the surface of the lava columns produces the characteristic explosions. Acoustic measurements have shown that most of the noise is produced by the vibration of the bubble prior to bursting, and that the bursting is much less energetic by comparison.
The equipment consists of a long vertical cylindrical tube (2 m high and 0.14 m in diameter) filled with oils of different viscosities. Large overpressurized bubbles of controlled size are introduced at the bottom of the tube. A microphone and sonometer record the noise of the bubble as it rises, and its position in recorded simultaneously by high speed photography.
It was found that the bubble undergoes oscillations of shape and volume. The uppermost surface of the liquid was also found to develop an instability when the bubble was at a distance of once or twice the tube diameter from the surface. The frequency of the instability was not dependent on the viscosity of the liquid, and ranged from 5 to 9 Hertz.