HR: 0800h
AN: T11A-0350    [Abstracts]
TI: Fragmentation Wave in Viscoelastic Medium Containing Bubbles and Crystals
AU: * Ichihara, M
EM: ichihara@eri.u-tokyo.ac.jp
AF: ERI, University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Nakamura, K
EM: kazuki@cneas.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
AU: Takayama, K
EM: takayama@ifs.tohoku.ac.jp
AF: TUBERO, Tohoku University, Katahira, Aoba-ku, Sendai, 980-8577, Japan
AB: We conducted fragmentation experiment using viscoelastic silicone compound with various pressure, vesicularity, crystallinity and permeability to understand the magma fragmentation in an explosive volcanic eruption. We used a vertical shock tube to generate rapid decompression. The specimen was pressurized with nitrogen very slowly so that the pores are filled with the high-pressure gas. Then the membranes separating the high- pressure part from the atmospheric pressure part are artificially ruptured, and the specimen is rapidly decompressed. The fragmentation behavior of the specimen is photographed by a high-speed video camera. The fragmentation wave velocity is measured from the video images. After each experiment, the fragments are taken out of the chamber on top of the shock tube carefully and the structures are observed. We obtained the following results from the observation of the fragmentation speed. The fragmentation speed is in the range of 20-40 m/s. Its dependence on the void fraction is not clear in the present experimental conditions with void fraction ranging from 0.33 to 0.44. It tends to be decreased by existence of crystals and increase of permeability. The larger it is, the larger is the acceleration of the fragments. We have noticed significant cavitation in the viscoelastic compound after rapid decompression. The bubbles are generated homogeneously within the compound. The cavitation occurred regardless of the initial gas-saturation condition of the compound. It was not observed with slow decompression, though the decompression amplitude is the same. The bubble nucleation depending on the decompression rate might be significant also in the volcanic processes with rapid decompression and magma fragmentation.
DE: 5104 Fracture and flow
DE: 8010 Fractures and faults
DE: 8428 Explosive volcanism
DE: 8434 Magma migration and fragmentation
SC: Tectonophysics [T]
MN: 2007 Fall Meeting