HR: 1340h
AN: V53A-1537    [Abstracts]
TI: Experimental Constraints on Interactions and Coalescence of Poly-dispersive Bubbles in Magmas
AU: * Abrego, F
EM: fabrego@mail.utexas.edu
AF: University of Texas at Austin, Geol Science Dept 1 University Station C1140 , Austin, TX 78712-0254 United States
AU: Gardner, J E
EM: gardner@mail.utexas.edu
AF: University of Texas at Austin, Geol Science Dept 1 University Station C1100 , Austin, TX 78712-0254 United States
AB: The dynamics of bubble interactions and coalescence in magmas can directly influence volcanic eruptions by controlling whether permeability develops to allow magma to degas before erupting. This study investigates those processes through controlled decompressions of rhyolitic melt. Powdered rhyolite was hydrated at high temperature and pressure, generating one set of bubbles of various sizes prior to decompression. Then, a sudden drop in pressure caused a second, smaller set of bubbles to nucleate, which were allowed to equilibrate before further decompression at a constant rate to low pressure. Samples were quenched over a range of pressures and the resulting bubble sizes, shapes, number densities, and interactions are measured to infer the kinetics and dynamics of interactions. The largest bubbles coalesce first at higher pressures followed by a smaller set of bubbles at lower pressures. Only the beginnings of coalescence are present for those smaller bubbles, with short chains of two to three bubbles. A large population of bubbles less than 6 μm in size is seen in samples quenched at higher pressures, but is reduced in number at lower pressures. Those smaller bubbles often appear clustered around the largest ones possibly because of growth of the larger bubbles. Our preliminary results suggest that when bubbles are poly-dispersive in size, connectivity develops in stages, with the larger bubbles connecting first. The fewer number of small bubbles at low pressure may indicate that gas within them diffuses out, because of the lower pressure in the larger tubes of bubbles.
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005