Focusing on a hydrological phenomenon of groundwater outflow Gout from lakes, relations between calculated Gout and hydrological conditions of the lakes were reviewed and interpreted for some caldera lakes and a crater lake, where their water budgets, groundwater outflow Gout and groundwater inflow Gin had been quantified. Although the water budget periods were then adopted at a wide range of several days to several years, hydrological features of the volcanoes were clarified by comprehensively grasping relations between calculated Gout and lake level or lake volume. The net groundwater input (Gin – Gout) was numerically obtained by estimating the hydrological budget of each lake, and then the Gin or Gout value was obtained by the following three ways: 1) by calculating a Gin value as a baseflow in a completely ice-covered period when both evaporation and precipitation at lake water surface can be ignored, 2) by solving the simultaneous equations for hydrological and chemical budgets, and 3) by simulating a lake water level based on a Gin value from the surrounding catchment calculated by a tank model. The calculated Gout values exhibited the high correlation (R2 = 0.988, p ＜0.01) with the lake volume, suggesting that Gout occurs as a confined groundwater flow. It is also found out that, reflecting the permeability of the volcano, the lake has a different adjustment ability to water level.

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