HR: 1340h
AN: V43D-1449    [Abstracts]
TI: Quantifying volcanic eruption fluxes with infrasound
AU: * Johnson, J B
EM: jeff.johnson@unh.edu
AF: University of New Hampshire, Department of Earth Sciences, Durham, NH 03824 United States
AB: Under suitable conditions the infrasound radiated during volcanic eruptions may serve as a valuable tool for quantifying eruptive outflux and / or eruption intensity. For example, synchronous video, acoustic, and seismic records of discrete explosions at Karymsky Volcano indicate a strong correlation between acoustic intensity and muzzle velocity, which is not clearly reflected in the seismic records. These observations can be explained by a volumetric acceleration of volcanic gases that directly perturbs the atmosphere (and produces acoustic waves). In contrast, the complex seismic response may be influenced by the specific location of fragmentation, magma vesicularity, complex volcanic structure, and character of the material choking the conduit. At Erebus Volcano, there also appears to be a strong relation between infrasound and eruption intensity. Short-duration bubble bursting explosions at Erebus are accompanied by very simple N-wave infrasound pulses of variable amplitude. Infrasonic waveforms may be used to estimate gas flux during these `near-instantaneous' degassing events. Flux values on the order of 10$^3$ kg suggest that bubble radii may reach 10$^1$ m or more, an impressive size which has been substantiated by visual observations. Although infrasound shows promise as a tool for quantifying eruption intensity, models must be developed to explain why certain large eruptions produce very small infrasound transients. Explosions from volcanic domes, such as Guagua Pichincha, Montserrat, and Santiaguito, have typically not produced very energetic infrasound, indicating that eruption mechanisms may be significantly variable. Slow accelerations and / or gas release from a dispersed source region may be responsible for the diminished acoustic efficiency of these events.
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting