A water flow model of the active crater lake at Aso volcano,Japan: fluctuations of magmatic gas and groundwater fluxes from the underlying hydrothermal system |
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| Authors: | Akihiko Terada Takeshi Hashimoto Tsuneomi Kagiyama |
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| Institution: | (1) Aso Volcanological Laboratory, Kyoto University, 5280 Kawayo, Minami-Aso, Kumamoto 869-1404, Japan;(2) Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, North 10 West 8, Kita-ku, Sapporo 060-0810, Japan;(3) Present address: Volcanic Fluid Research Center, Tokyo Institute of Technology, 641-36 Kusatsu, Gunma 377-1711, Japan |
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| Abstract: | The first crater of Nakadake, peak of Aso volcano, Japan, contains a hot water lake that shows interesting variations in water
level and temperature. These variations were discovered by precise, continuous observations of the lake independent of precipitation.
We developed a numerical model of a hot crater lake and compared with observational data for the period from July 2006 to
January 2009. The numerical model revealed seasonal changes in mass flux (75–132 kg/s) and enthalpy (1,840–3,030 kJ/kg) for
the fluid supplied to the lake. The relation between the enthalpy and mass flux indicates that the bottom input fluid is a
mixture of high- and low-temperature fluids. Assuming a mixture of high-temperature steam at 800°C and liquid water at 100°C,
we evaluated the liquid and steam fluxes. The liquid water flux shows a seasonal increase lagging behind the rainy season
by 2 months, suggesting that the liquid water is predominantly groundwater. The fluctuation pattern in the flux of the high-temperature
steam shows a relation with the amplitude of volcanic tremor, suggesting that heating of the hydrothermal system drives the
tremor. Consequently, precise observations of a hot crater lake represent a potential method of monitoring volcanic hydrothermal
systems in the shallow parts of the volcanoes. |
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