Volcano Aso is a depression caldera. In caldera the large quantities of ground wter flow to downward with slope. Then water quality of ground water change be caused by flow movement. Corresponding to change of water table elevation of ground water, we collected the sampling water each apuifer, and water analysis was done.
The following became clear after the investigation on the besis of the results. (1) Change of water temperature and electrical conductivity of groumd water show us difference of aquifers. (2) Variations of. composition in water samples, be caused by flow movement, are characteristic on anions and in general samples has qualitative character in volcanic basin.