[SVC42-01] Magma flow style based on deformed bubble structure of pumice
Keywords:bubble deformation, tube pumice, bubble texture
First, using the droplet deformation model of Jackson and Tucker (2003), we developed a model that can calculate the transient deformation of a single bubble in an arbitrary velocity field. Next, to evaluate the interaction between bubbles, we performed tensile experiments with a solidifying foam. By comparing the experimental results of bubble shape with the numerical simulations, we confirmed that the average shape of bubbles coincided with the theoretical deformation model of a single bubble. This result suggests that the average of bubbles in pumice can be compared with the numerical simulation of a bubble in a conduit flow.
Next, the bubble deformation model and the quasi-two-dimensional steady conduit flow model were combined to solve the bubble deformation in the conduit. The bubble shape at the fragmentation surface significantly depends on the velocity profile across the conduit. Flow with a constant viscosity had a parabolic velocity profile and produced highly elongated bubbles, which were deformed mainly by simple shear. On the other hand, viscous-heating with the temperature-dependent viscosity led to a plug-like velocity profile and produced less elongated bubbles, which were deformed primarily by pure shear.
Finally, we conducted a bubble structure analysis of pumice erupted at Taupo Volcano. It was found that the plinian eruption had a single peak in the bubble shape distribution, while the ignimbrite eruption had a broad distribution and contained highly elongated bubbles. The comparison of the natural bubble textures with the results of the combined simulation of conduit flow and bubble deformation suggested that the velocity profile of the plinian eruption was close to a plug-like shape. We propose the reason why the ignimbrite eruption produced a large amount of tube pumice that the widening of the conduit reduced the viscous heating effect, delayed the transition from parabolic flow to plug-like flow, and increased bubble deformation during the parabolic flow regime.
Acknowledgement: This paper integrates results of the studies collaborating with S. Takeda, K. Hirota, S. Sato, O. Kuwano, M. Kameda, A. Toramaru, D. Gravley, B. Kennedy, and F. Maeno.