有珠山2000噴火初期活動の力学モデル(<特集>2000年有珠山噴火 (3))
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概要
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Mt. Usu began erupting Mar. 31, 2000. The activity of the eruption during the first two to three days has about a half day period. I construct a dynamical model which conforms the periodic nature and other observations. The physical process of this model is the formation of a low density layer by vesiculating the medium over the intruded magma, which causes Rayleigh-Taylor instability. The instability develops to form a conduit and results in the outflow (eruption) of the vesiculated material. The mechanical responses of the related materials (the magma and the surrounding medium, i.e., ground) are assumed to be that of viscous fluid. The model so constructed is a dynamical system consisting of a coupled first order non-linear differential equations with two unknowns, the radius of the conduit and the thickness of the vesiculated layer. The calculated outflow rate have the characteristics of the dumped oscillation, the period and dumping of which depend on the parameters such as the viscosities and a threshold pressure to keep opening the conduit. The oscillation is identified as that of the observed eruption activity with period of about 12hours. Adjusting parameters so as to have the same period as the observed, we obtain rather low viscosity of the ground of 10^9 Pas and horizontal dimension (radius) of the intruded magma of 20 m.
- 特定非営利活動法人日本火山学会の論文
- 2002-11-29