Homogeneous nucleation of nano size H2O bubbles and their growth to micro size in rhyolite melts

Volcanism accompanies transfer of volatiles such as H 2 O and CO 2 from the Earth interior to the atmosphere. The underlying process for transfer of the volatiles is magma degassing. As magma rises toward the Earth surface, the volatiles in silicate melts become supersaturated due to decompression of magma so that nucleation of volatile-bearing bubbles and subsequent growth of the bubble occur. In this study, bubble nucleation rate of water in rhyolite melts above 1000 K, which determines the style of the eruption of the magma, is calculated by using molecular cluster model. Calculation results indicate that the homogeneous nucleation of water in the rhyolite melts is possible when the supersaturation pressure exceeds 110 MPa and the number density of bubbles formed increases as increase in the degree of the supesaturation. Growth of bubble formed from the critical cluster was also calculated and the results were compared with observed bubble sizes. When the bubble number density is greater than 10 15 /m 3 , depletion of the concentration of volatiles hinders further growth of bubbles.