Citation

Iguchi M, Yakiwara H, Tameguri T, Hendrasto M, Hirabayashi J. J. Volcanol. Geoth. Res. 2008; 178(1): 1-9.

Copyright

(Copyright © 2008, Elsevier Publishing)

DOI

10.1016/j.jvolgeores.2007.10.010

PMID

unavailable

Abstract

A common sequence of phenomena associated with volcanic explosions is extracted based on seismic and ground deformation observations at 3 active volcanoes in Japan and Indonesia. Macroscopic inflation-related ground deformations are detected prior to individual explosions, while deflations are observed during eruptions. Precursory inflation occurs 5min to several hours before eruption at the Sakurajima volcano, but just 1-2min at Suwanosejima and 3-30min at the Semeru volcano. The sequence commences with minor contraction, which is detected by extensometers 1.5min before eruption at Sakurajima, as a dilatant first motion of the explosion earthquakes 0.2-0.3s before surface explosions at Suwanosejima, and as downward tilt 4-5s prior to eruption at the Semeru volcano. The sequence is detected for explosive eruptions with 0.1rad tilt change at Sakurajima, 90% at Suwanosejima and 75% at Semeru volcanoes. It is inferred that the minor contraction is caused by a volume and pressure decrease due to the release of gas from a pocket at the top of the conduit as the gas pressure exceeds the strength of the confining plug. The subsequent violent expansion may be triggered by sudden outgassing of the water-saturated magma induced by the decrease in confining pressure. 2007 Elsevier B.V. All rights reserved.