2311 火山爆発のダイナミクス : 急減圧にともなう気泡を含む粘弾性体の破砕(S42-3 複雑流体の流動現象(3),S42 複雑流体の流動現象)  [in Japanese] 2311 Dynamics of Volcanic Eruption : Magma Fragmentation Mechanism  [in Japanese]

Fragmentation criterion is closely related to magma rheology. To reveal the relationship, we carried out laboratory experiments on magma fragmentation with analogous materials. Commercial syrup was used as an analogous material of magma. A pressure-vacuum chamber was used to apply rapid decompression on the materials. The initial pressure was varied from 2 MPa to 3 MPa. The gas-volume fraction of the syrup under pressure was fixed as 2% or 6%. The viscosity varied from 5×10^5 Pa・s to 5×10^7 Pa・s. The experimental results indicate that fragmentation process is classified with viscosity. The fragmentation is observed when the pressure drop reaches critical value within the order of relaxation time of syrup. In addition, this constraint on the decompression time is relaxed as the initial void fraction or initial pressure increases. This implies that the energy stored in the bubbles is a dominant parameter to characterize the fragmentation.