HR: 0830h
AN: V51E-0319    [PDF]
TI: Experiments With Bubble Nucleation and Growth in Dacitic Melts at an Initial Pressure of 1 Kb and 875oC
AU: Gerke, T L
EM: erebus@choice.net
AF: Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 United States
AU: * Kilinc, A
AF: Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 United States
AB: Two sets of experiments with Mount St. Helen's dacitic pumice (SH-118) were conducted to understand the kinetics of bubble nucleation and growth in dacitic melts. Powdered samples of dacite were first equilibrated with excess water at an initial pressure of 1 Kb and 875oC for 48 hours. After 24 hours, in the first set of experiments the pressure was dropped 30 MPa and 300, 900, and 2700 seconds were allowed for bubble nucleation and growth. The pressure was dropped 50 MPa, in the second set of experiments and 900 and 2700 second were allowed for bubble nucleation and growth. Results of the 30 MPa pressure drop experiments for 300, 900, and 2700 seconds residence times were: total number of bubbles (nT) were 6.41E3, 5.23E3, and 3.37E3 mm-3; growth rates (G) were 5.03E-5, 1.56E-5, and 5.97E-6 mmsec-1; nucleation rates (J) were 21.1, 5.81, and 1.25 mm-3sec-1; and initial bubble densities (no) were 4.25E5, 3.73E5, and 2.09E5 mm-1. Results of the 50 MPa pressure drop experiments for 900 and 2700 seconds residence times were: nT were 2.10E3 and 4.10E3 mm-3; G were 3.01E-5 and 8.26E-6 mmsec-1; J were 2.34 and 1.52 mm-3sec-1; and no were 7.75E4 and 1.84E5 mm-1. These data indicate that as the pressure drop increases from 30 to 50 MPa at 900 sec G is increasing and no, J, and nT are decreasing suggesting that bubbles are growing faster and coalescing. On the other hand, when pressure drop increases from 30 to 50 MPa at 2700 sec G, J, and nT are increasing and no is decreasing slightly. This suggests that the bubbles faster but are not coalescing.
DE: 8414 Eruption mechanisms
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting