Atmospheric internal waves generated by explosive volcanic eruptions
Published:January 01, 2014
Peter G. Baines, Selwyn Sacks, 2014. "Atmospheric internal waves generated by explosive volcanic eruptions", The Eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010, G. Wadge, R. E. A. Robertson, B. Voight
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Observations of microbarograph recordings on the island of Montserrat in the Caribbean have shown signals with periods of several minutes and amplitude of approximately 1 mb following explosive eruptions of the Soufrière Hills Volcano. These properties suggest that the explosions are causing the generation of atmospheric internal waves. Here an analysis of wave generation by sudden disturbances in a stratified atmosphere is developed, and the properties of these waves are described and compared with observations. Two types of forcing of the atmosphere by a volcanic explosion are considered: that due to the sudden addition of mass, and separately, of thermal energy. The pattern and distribution of these depend on the nature of the explosion, which has a timescale of the order of 1 min. The theoretical results resemble the effect of ‘throwing a stone’ into the atmosphere, producing transient waves that radiate radially away from the source. Near the source, these waves have frequency around 0.7–0.8N (where N is the buoyancy frequency) initially, and approach N with decreasing amplitude. The results of forcing due to added mass and thermal forcing are presented and compared for a variety of vertical forcing profiles, and these are compared with observations of surface pressure. The results suggest that forcing due to the injection of mass (mostly solid particles) is the principal factor in forcing the observed internal waves. The addition of thermal energy (heat) produces waves that have frequencies closer to N, and persist for much longer periods than those observed at the stations on Montserrat.
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The Eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010
The 1995 to present eruption of Soufrière Hills Volcano on Montserrat is one of the most important and best-studied eruptions of an explosive andesitic volcano. This volume presents scientific findings from the period between 2000 and 2010; it follows on from Memoir 21, which focused on the early years of activity between 1995 and 1999. In addition to descriptions and analysis of the growth, collapse and explosions associated with lava domes, there are papers on the deformation of the volcano caused by the deep magma, the petrology and geochemistry of the lavas and associated gases. Of particular note are: an overview of the insights into the deep structure of the volcano that resulted from a major international seismic tomography experiment; and an analysis of the quantitative risk assessment process that has run now for most of the eruption, the longest such continuous assessment in the world.