HR: 17:30h
AN: V24A-07 INVITED     [Abstracts]
TI: Exploring the thermodynamics of small ash plumes with thermal (FLIR) video
AU: * Patrick, M
EM: patrick@higp.hawaii.edu
AF: HIGP/SOEST, University of Hawaii Manoa, 1680 East West Road, Honolulu, HI 96822 United States
AB: Handheld thermal (FLIR) video cameras offer a unique perspective on explosive volcanism. During June-July, 2004, several hundred emerging strombolian ash plumes were imaged with a FLIR camera operating at 30 Hz on Stromboli volcano, Italy. Of these eruptions, 25-80 were suitable for varying levels of quantitative analyses. This study addresses two factors. First, the evolving morphology, motion and air entrainment rates were tracked and explored using the spatio-temporal component of the data. Plumes were observed to transition among several common forms in the first 30 seconds upon leaving the vent (jets, starting plumes, thermals), which reflected changing spreading rates and air entrainment coefficients. Based upon spreading rates, plume fronts exhibited air entrainment coefficients of approximately 0.10 in gas-thrust phases and approximately 0.20 in buoyant phases, while the steady plume air entrainment coefficients were approximately 0.10 throughout. In the second part of the study, the temperature and heat/mass contents were examined using the thermal information in the FLIR data. An essential prerequisite to measuring accurate plume temperature is plume opacity, which can be characterized by tracking apparent temperature and heat content trends. Bulk temperatures of the plume fronts began between 300 and 700 C at the crater rim, and dropped below 100 C within 130 m height. Whereas total heat content in a plume can be estimated with good precision (within a few percent) from this temperature information, translating heat content to ejecta mass is more troublesome (uncertainties of at least 60 percent). This complication is due to uncertainties in gas mass fraction which are inherent in strombolian scenarios and result from the incidental origin of strombolian particles.
DE: 8411 Thermodynamics (0766, 1011, 3611)
DE: 8419 Volcano monitoring (7280)
DE: 8428 Explosive volcanism
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005