衛星赤外画像による雲仙溶岩ドーム成長域・噴気域の同時熱観測 : リモートセンシングによるガス放出・蓄積状況の推定

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To investigate possibilities for 'forecasting' the potential for explosive eruptions at active lava domes a method using time-series analysis of satellite shortwave infrared images was studied. The rational behind this is that the potential 'explosiveness' of an active lava dome seems likely to have a close relationship to the state of gas accumulation in the volcanic edifice, which can be inferred from the correlation between the discharge rates of magma and gas, i.e. the gas/magma discharge rate ratio. To assess this we used ten night-time Landsat 5 Thematic Mapper images of Unzen Volcano, taken between October 1991 and January 1993 during Phase 1 of the volcanoes 1991-1995 eruption. Our hypothesis is that the surface thermal state of the endogenous and exogenous dome growth areas is at least partly controlled by the magma discharge rate, whilst the thermal state of the fumarolically active areas is similarly controlled by the discharge rate of magmatic gas. If this hypothesis is correct then we can indirectly infer the gas/magma discharge rate ratio from analysis of the thermal anomalies detected on the satellite infrared images. In the Unzen time-series, the size of the thermally radiant areas in the dome growth and fumarolic areas were significantly positively correlated (r^2=0.56, n=10). This suggests a mechanism for effective gas release existed at the volcano over the time-period studied, with the rates of magma and gas discharge varying in proportion. Through this mechanism gas was efficiently vented from the edifice and major gas accumulation prevented, thus helping to minimise the number of large explosive events that occurred during the Unzen eruption.
2002-11-29

衛星赤外画像による雲仙溶岩ドーム成長域・噴気域の同時熱観測 : リモートセンシングによるガス放出・蓄積状況の推定

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