Fig. 3

A long-term variation of the gas concentration molar ratios from 2003 to 2015. a CO₂/SO₂ molar ratio, b H₂O/SO₂ molar ratio, c SO₂/H2_S molar ratio, d SO₂/Cl molar ratio, e H₂/SO₂ molar ratio and f Apparent equilibrium temperature. Circles and squares are the lake gas and the fumarolic gas compositions, respectively, and diamonds are the representative compositions during the eruptive period (Table 1, see text for details). Shadowed areas indicate the low lake volume periods