BUBBLE GROWTH IN RHYOLITIC MELT

Abstract

We report experimental data of bubble growth in natural rhyolitic melt with 1.4-2.0 wt% initial total H2O at 0.1 MPa and 500-600°C. Growth of many bubbles is monitored in every experiment. Bubble growth rate increases with temperature and initial total H2O. At a given temperature and initial total H2O, bubble growth rate also increases slightly with bubble size. The average growth rate for bubbles growing in an infinite rhyolitic melt at a bubble radius of 25 μm is ~0.038 μm/s at 600°C and 2.0 wt% H2Ot,i, ~0.0064 μm/s at 550°C and 2.0 wt% H2Ot,i, ~0.00034 μm/s at 500°C and 2.0 wt% H2Ot,i, and ~0.007 μm/s at 600°C and 1.45 wt% H2Ot,i. Our data show that bubble growth is controlled by both viscous flow and diffusion, with viscous flow playing a dominant role at the initial stage. We used the numerical bubble growth model of Proussevitch and Sahagian [J. Geophys. Res. 103 (1998) 18223-18251] to calculate bubble growth rate. Using recently assessed solubility, diffusivity, and viscosity models, the bubble growth model can reproduce our experimental data to within a factor of about 2. Adjusting the viscosity model by a factor of up to 5 (within the stated 2σ uncertainty of a factor of 8.3) generates almost perfect fits to our data. (Adjusting other parameters within uncertainty does not help significantly.) Other recent bubble growth data, except those at 0.1 MPa and 375-460°C with 5.0 wt% initial H2O, are also consistent with the calculation. This is the first experimental verification of a bubble growth model in a silicate melt. We suggest that the verified model can be applied with confidence to quantify bubble growth during volcanic eruptions.