Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima,Suwanosejima and Semeru volcanoes |
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Authors: | Masato Iguchi Hiroshi Yakiwara Takeshi Tameguri Muhamad Hendrasto Jun-ichi Hirabayashi |
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Institution: | 1. Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, Kagoshima 891-1419, Japan;2. Nansei-Toko Observatory for Earthquakes and Volcanoes, Faculty of Science, Kagoshima University, Kagoshima 892-0871 Japan;3. Center for Volcanology and Geological Hazard Mitigation, Geological Agency, Bandung 40122, Indonesia;4. Volcanic Fluid Research Center, Tokyo Institute of Technology, Kusatsu, Gunma 377-1711, Japan |
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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 5 min to several hours before eruption at the Sakurajima volcano, but just 1–2 min at Suwanosejima and 3–30 min at the Semeru volcano. The sequence commences with minor contraction, which is detected by extensometers 1.5 min before eruption at Sakurajima, as a dilatant first motion of the explosion earthquakes 0.2–0.3 s before surface explosions at Suwanosejima, and as downward tilt 4–5 s prior to eruption at the Semeru volcano. The sequence is detected for explosive eruptions with > 0.1 μrad 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. |
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Keywords: | volcano Sakurajima Suwanosejima Semeru explosive eruption explosion earthquake ground deformation |
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