Study on the Magma-External Water Interaction

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In order to investigate the mechanism of a phreatomagmatic explosion and to predict the distribution of disaster accompanied by the explosion, we have made an effort to accomplish the following research points.(1) Development of the instruments for measuring the pressures of blast and pyroclastic surge produced by the volcanic explosion, (2) observation of the explosion and measurement of the explosion energy at Aso Volcano using the instruments we developed, (3) establishment of the scaling rule which relate the explosion energy to geological and disaster distributions accompanied by the volcanic explosions, (4) and making a scenario which interpret the magma-external water interactions.The system for the observation we developed consists mainly of piezo-pressure sensors, thermo-couple, degital-oscilloscope and a personal-computer. We began to observe the volcanic explosions at Aso Volcano using this system. To fulfilll the research point (3), we have made a field explosion experiment, and found that the cube-root scaling law established between the explosion energy and geological and disaster distributions ; we can predict the distributions if we know one parameter which relate directly to the volcanic explosion such as the explosion energy and crater diameter. For the research point (4), we presented a new scenario (for the case magma-aquifier interaction) which interpret the phreatomagmatic explosion occured in shallow underground. In this case we pointed out that the liquification of aquifier is essential for the interaction ; extremely rapid generation of vapor.