Mechanism of Phreatic Eruptions at Aso Volcano Inferred from Near-Field Broadband Seismic Observations
Broadband seismometers deployed at Aso volcano in Japan have detected a hydrothermal reservoir 1 to 1.5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds. When phreatic eruptions are observed, broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit: gradual pressurization and long-period (approximately20 seconds) pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge, followed by gradual deflation of the reservoir concurrent with the discharging flow. The hydrothermal reservoir, where water and heat from the deeper magma chamber probably interact, appears to help control the surface activity at Aso volcano.
Kaneshima
S
S. Kaneshima, Department of Earth and Planetary Physics, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. H. Kawakatsu, H. Matsubayashi, J. Oikawa, M. Takeo, T. Iidaka, Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 113 Japan. Y. Sudo and T. Tsutsui, Aso Volcanological Laboratory, Faculty of Science, Kyoto University, Aso, Kumamoto 869-14, Japan. T. Ohminato and H. Ito, Geological Survey of Japan, Tsukuba, Ibaraki 305, Japan. K. Uhira, Japan Meteorological Agency, Chiyoda-ku, Tokyo 110, Japan. H. Yamasato, Meteorological Research Institute, Tsukuba, Ibaraki 305, Japan.
Kawakatsu
H
Matsubayashi
H
Sudo
Y
Tsutsui
T
Ohminato
T
Ito
H
Uhira
K
Yamasato
H
Oikawa
J
Takeo
M
Iidaka
T