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Investigation of thermo-hydrodynamic processes preceding the different eruption styles observed in a laboratory geyser

Ayuta Tsuge1, Mie Ichihara1

Abstract

Diverse eruption styles observed at geysers may be related to the plumbing geometry and thermo-hydrodynamic conditions. We expect insights into the eruptive cycle variability of volcanoes through understanding the physical controls of geyser eruptions. This study conducted a laboratory experiment simulating geyser eruptions with a simple setup comprising a vertical pipe and a flask. As reported in the previous studies, we had two eruption styles: major eruption, characterized by vigorous spouting and large discharged mass, and minor eruption with calm effusion and small discharged mass. Although the size of an eruption controlled the time to the next eruption, the size of the next eruption was not necessarily predictable. We explored the branching point of the major and minor eruptions. Both eruptions appeared to occur irregularly, but major eruptions were often followed by small eruptions. We observed and compared multiparametric time evolutions, including pressure, temperature, bubble generation in the flask, and bubble ascent in the pipe. We found that the bubble increase rate in the flask a few seconds before a major eruption was higher than that of a minor eruption by analyzing the video data. There were no apparent differences in most of the quiescence time (approximately 100--1200 seconds, depending on preceding eruptions) to that point. It is inferred that the thermodynamic condition and progressive process of the decompression boiling in the flask just before the eruption are the critical factors controlling the eruption styles. We need further investigation to clarify how this branching point is formed.