Abstract
We present simulations of the development of volcanic plumes during the 2011 eruptions of the Kirishima-Shinmoe-dake volcano, Japan, using a new three-dimensional (3D) numerical model that calculates eruption cloud dynamics and the wind-borne transport of volcanic ash. This model quantitatively reproduces the relationship between the eruption conditions (e.g., magma discharge rate) and field observations, such as plume height and ash fall area. The simulation results indicate that the efficiency of turbulent mixing between ejected material and ambient air was substantially enhanced by strong winds during the 2011 Shinmoe-dake eruptions, which caused a significant decrease in the maximum height of the plumes compared with those that develop in still environment. Our 3D simulations also suggest that the existing 1D plume model tends to overestimate the effect of wind on turbulent mixing efficiency, and hence, to underestimate plume height in a strong wind field for a given magma discharge rate.
Highlights
Explosive eruptions are characterized by the formation of buoyant plumes and widespread dispersal of volcanic ash
The simulation results indicate that the efficiency of turbulent mixing between ejected material and ambient air was substantially enhanced by strong winds during the 2011 Shinmoe-dake eruptions, which caused a significant decrease in the maximum height of the plumes compared with those that develop in still environment
These plume height simulations indicate that wind substantially enhances the efficiency of turbulent mixing between the eruption cloud and ambient air, leading to a decrease in plume height compared with plumes that form in still environments
Summary
Explosive eruptions are characterized by the formation of buoyant plumes and widespread dispersal of volcanic ash. As the ejected material entrains ambient air, expansion of this air during mixing with the hot pyroclasts drastically decreases the density of the mixture, so that it becomes less dense than the surrounding atmosphere This results in the development of a buoyant volcanic plume with a height that can exceed several kilometers. Eruption column dynamics are controlled mainly by the balance between thermal energy ejected from the vent and the work done during transportation of ejected material and entrained air through atmospheric stratification. This means that when magma properties (i.e., temperature, volatile content, and heat capacity) are fixed, plume height is dependent on the efficiency of turbulent mixing, the magma discharge rate and atmospheric conditions (Morton et al, 1956; Sparks, 1986; Carazzo et al, 2008); at given atmospheric conditions (e.g., temperature and moisture stratifications) the plume height increases as magma discharge rates increase and turbulent
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