Mechanism of Phreatic Eruptions at Aso Volcano Inferred from
Near-Field Broadband Seismic Observations,
Kaneshima, S., H. Kawakatsu, H. Matsubayashi, Y. Sudo, T. Tutui, T. Ohminato,
H. Ito, K. Uhira, H. Yamasato, J. Oikawa, M. Takeo, T. Iidaka
Science, 273. 642-645, 1996.
Abstract
Broadband seismometers
deployed at Aso volcano, Japan,
have detected
a hydrothermal reservoir
1 to 1.5 kilometers beneath the crater
that is
continually resonating with periods as long as 15 s.
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 (~20 s) pulsations of the reservoir
during the 100-200 s 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.