10:45 AM - 12:15 PM
[SVC29-P03] Numerical study on growth and coalescence of bubbles in magma
Keywords:bubble coalescence, viscous fluid, outgassing
Bubble coalescence plays a crucial role in the outgassing of magmas controlling transition from explosive to non-explosive eruptions. Bubble coalescence also affects magma rheology and fragmentation criteria through changing the bubble size distribution (BSD). The BSD is a fundamental observable recorded in the pyroclasts, which allows us to infer the physical conditions inside the volcanoes. Understanding bubble coalescence in magma is thus important for modelling gas dynamics during eruption and for interpreting the vesicle texture of the pyroclasts.
We numerically calculate the evolution of the BSD by bubble coalescence, considering the four processes of two bubbles for coalescence: shear, buoyancy, viscosity-limited growth, diffusion-limited growth. We use the collision frequency functions for the four process, which are derived from the trajectory analysis using the equations of motion for bubbles in Maruishi & Toramaru (2022). For diffusion-limited growth, the BSD shows a power law with a slope of -0.5. The width of the BSD increases logarithmically and converges to about 2 orders of magnitude. For the other driving forces, the BSD shows a power law with a slope of -2. The width of the BSD increases exponentially or more rapidly and diverges.
These variations in BSD evolution result from the differences in the interactions between the bubbles. For diffusion-limited growth, larger bubbles growth and coalesce slowly because larger bubbles growth slowly due to lower diffusion flux of volatiles. For the other processes, bubbles grow and coalesce faster as they become larger. Our results are useful for interpreting the BSD in the pyroclasts. We could estimate which process is dominant and the timescale of bubble coalescence from the width and slope of the BSD.
This study was supported by JSPS KAKENHI Grant No. 21J11749, Grant-in-Aid for JSPS Research Fellow.
We numerically calculate the evolution of the BSD by bubble coalescence, considering the four processes of two bubbles for coalescence: shear, buoyancy, viscosity-limited growth, diffusion-limited growth. We use the collision frequency functions for the four process, which are derived from the trajectory analysis using the equations of motion for bubbles in Maruishi & Toramaru (2022). For diffusion-limited growth, the BSD shows a power law with a slope of -0.5. The width of the BSD increases logarithmically and converges to about 2 orders of magnitude. For the other driving forces, the BSD shows a power law with a slope of -2. The width of the BSD increases exponentially or more rapidly and diverges.
These variations in BSD evolution result from the differences in the interactions between the bubbles. For diffusion-limited growth, larger bubbles growth and coalesce slowly because larger bubbles growth slowly due to lower diffusion flux of volatiles. For the other processes, bubbles grow and coalesce faster as they become larger. Our results are useful for interpreting the BSD in the pyroclasts. We could estimate which process is dominant and the timescale of bubble coalescence from the width and slope of the BSD.
This study was supported by JSPS KAKENHI Grant No. 21J11749, Grant-in-Aid for JSPS Research Fellow.