Permalink : http://hdl.handle.net/2115/32756

JaLCDOI : 10.14943/gbhu.71.1

From the volcano-energetics point of view, it is very important to evaluate the velocity, direction and distribution of ejected volcanic blocks. However, in most cases, it is hard to measure directly such quantities during the eruption. Therefore, the volcanic blocks landed on and around the crater have been investigated to reproduce dynamic aspects of eruption after the eruption. In the present paper, ballistic curves of the volcanic blocks are numerically analyzed for various combination of parameters, such as direction of the explosion principal axis of ejection, velocity and direction of the wind, air resistance to the block and dependence of direction of the initial velocity of ejection. The calculations are made on the basis of a generalized ballistic equation of ejected blocks, in which the wind velocity and the air resistance to the block are treated as vector quantities. Calculated results lead to the following characteristic conclusions: (1)The winds above 20m/s along the direction of ejection plays the major role in the ballistic curves, while the lower wind velocity is less effective. (2) Spatial distribution of the landed blocks is mainly affected by the direction of the explosion principal axis. The distribution of the volcanic blocks which was spread to the specific direction is described by inclination of the explosion principal axis. (3) The spatial distribution of the small size blocks depends remarkably on the air resistance.