From sound waves to bubbling within a magma reservoir: Comparison between eruptions at Etna (2001, Italy) and Kilauea (Hawaii)
Published:January 01, 2008
S. Vergniolle, 2008. "From sound waves to bubbling within a magma reservoir: Comparison between eruptions at Etna (2001, Italy) and Kilauea (Hawaii)", Fluid Motions in Volcanic Conduits: A Source of Seismic and Acoustic Signals, S. J. Lane, J. S. Gilbert
Download citation file:
The 2001 eruption of Etna, prior to the flank eruption, has shown an alternation between episodes rich in gas, composed with a series of Strombolian explosions sometimes leading to a fire fountain, and repose periods. The regular alternation results from the coalescence of a foam trapped in the reservoir and periodically rebuilt prior to each episode. The degassing of a magma reservoir depends on bubble diameter, gas volume fraction, surface area and height of the reservoir. These four parameters are deduced from the measured gas flux, the timescale over which the gas flux decreases and the foam dynamics. The dimensionless foam thickness, 0.76 for a purely Strombolian episode, increases to 0.89 for an episode leading to a fire fountain, indicating a more efficient foam coalescence. At Etna, the bubble diameter, gas volume fraction, surface area and height of the reservoir are estimated at 0.50–0.59 mm, 0.25–0.39%, >0.20 km2 and 97–220 m, respectively. At Kilauea, the excellent agreement between the prediction of the foam model, 0.94–1.2 km2 and that resulting from deformations, 1 km2, reinforces the validity of the foam model qualitatively and quantitatively. The thickness of the degassing reservoir, 16–12 m in 1959, is now 1.3–1.1 km.
Figures & Tables
Fluid Motions in Volcanic Conduits: A Source of Seismic and Acoustic Signals
Volcanoes become active when fluids are in motion, and erupt when these fluids escape into the atmosphere. Volcanic fluids are a mixture of solid, liquid and gas. These mixtures result in a complex range of flow behaviour, especially during interaction with conduit geometry. These processes are not directly observable and must be inferred from interpretations of field observation and measurement. One of the outcomes of this complexity is the generation of pressure and force transients as high-density phases accelerate and decelerate during unsteady flow. These transients are one means of flexing the conduit wall, a process that manifests itself as ground motion and is detectable as volcano seismic signals. On eruption, volcanic fluids interact with the atmosphere and generate acoustic and thermal signals. In this Special Publication we present a series of papers based on field, numerical and experimental approaches that seek to establish links between geophysical signals and fluid motion in volcanic conduits.