beautiful toxic and acidic volcanic caldera lake with emerald green water in yugama, kusatsu, gunma prefecture, japan

acid acidic active adventure asia attraction beautiful blue caldera colorful crater dangerous emerald gases geology green gunma hiking hot japan kusatsu lake landmark landscape mineral mount mountain mountainous mountains mysterious nature onsen panorama panoramic rock scenic shirane sky spring sulfur sulfuric sulphur summer tourism toxic travel turquoise valley view volcanic volcano volcanology water yugama