火山爆発時の噴煙の運動について (I)

概要

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Shapes of volcanic smoke by eruptions are various and irregular, but are governed by the relation in which maximum radius of smoke can be expressed as a linear function of height. For examples of Sakurajima eruptions, r=bz+r_i where b is a constant relating to the growth of smoke of which approximate value is 0.4. On examples of Sakurajima, vertical velocities of smokes show the complicated variation with height, as Figs. 6 and 7. Assuming that smoke is erupted instantaneously and constituted with ash and mixed air, variations of apparent density, temperature and vertical velocity with height may be derived theoretically from equations of mass, momentum, etc. Theoretical apparent density becomes smaller than that of surrounding air at some height, and in this case buoyancy is generated. This effect of buoyancy results on the momentary increas of velocity. Such a result of the numerical solution of vertical velocity shows good agreement with the observed facts of Sakurajima.
1969-12-01