HR: 0800h
AN: V31D-0654    [Abstracts]
TI: Investigating the dynamics of Vulcanian explosions using scaled laboratory experiments
AU: * Clarke, A B
EM: amanda.clarke@asu.edu
AF: Arizona State University, Department of Geological Sciences , Tempe, AZ 85287 United States
AU: Phillips, J C
EM: j.c.phillips@bris.ac.uk
AF: University of Bristol, Department of Earth Sciences, Bristol, BS8 4HG United Kingdom
AU: Chojnicki, K N
EM: kirsten.chojnicki@asu.edu
AF: Arizona State University, Department of Geological Sciences , Tempe, AZ 85287 United States
AB: Laboratory experiments were conducted to investigate the dynamics of Vulcanian eruptions. A reservoir containing a mixture of water and methanol plus solid particles was pressurized and suddenly released via a rapid-release valve into a 2 ft by 2 ft by 4 ft plexiglass tank containing fresh water. Water and methanol created a light interstitial fluid to simulate buoyant volcanic gases in erupted mixtures. The duration of the subsequent experiments was not pre-determined, but instead was limited by the potential energy associated with the pressurized fluid, rather than by the volume of available fluid. Suspending liquid density was varied between 960 and 1000 kg m^-3 by changing methanol concentrations from 5 to 20%. Particle size (4 & 45 microns) and concentration (1 to 5 vol%) were varied in order to change particle settling characteristics and control bulk mixture density. Variations in reservoir pressure and vent size allowed exploration of the controlling source parameters, buoyancy flux (B_o) and momentum flux (M_o). The velocity-height relationship of each experiment was documented by high-speed video, permitting classification of the laboratory flows, which ranged from long continuously accelerating jets, to starting plumes, to low-energy thermals, to collapsing fountains generating density currents. Field-documented Vulcanian explosions exhibit this same wide range of behavior (Self et al. 1979, Nature 277; Sparks & Wilson 1982, Geophys. J. R. astr. Soc. 69; Druitt et al. 2002, Geol. Soc. London, 21), demonstrating that flows obtained in the laboratory are relevant to natural systems. A generalized framework of results was defined as follows. Increasing M_o/B_o for small particles (4 microns; settling time > experiment duration) pushes the system from low-energy thermals toward high-energy, continuously accelerating jets; increasing M_o/B_o for large particles (>45 microns; settling time < experiment duration) pushes the system from a low collapsing fountain to a high collapsing fountain; and increasing particle size for collapsing fountains decreases runout distance of gravity currents and increases production of current-generated rising plumes.
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005