Travellers flock to the Indonesian island of Java to see the magnificent Kawah Ijen volcano – but what they don’t expect to find is the stunning turquoise-hued caldera lake at the volcano’s summit. To add to the drama, bright, citrine-coloured stones and billows of white gasses surround the 1km-wide aquamarine lake in a spectacular show.

游客蜂拥着去印尼爪哇岛是为了亲眼目睹壮观的卡瓦伊真火山——但他们从未想过能够在火山顶上看到这蓝绿交加的火山口湖。更令人叹为观止的是，柠檬黄色的明亮石头和翻腾不息的白雾环绕笼罩着这一千米宽的海蓝宝石般的火山口湖。

One element is responsible for the entire, striking scene: sulphur. The magma chamber below the volcano pours sulphuric gases into the lake. Combined with a high concentration of dissolved metals, the gases turn the water a brilliant shade of blue. They also render the Ijen crater-lake the world’s largest highly acidic lake with a pH of 0.5.

这震撼人心的景观都要归功于一种化学物质：硫磺。火山下的岩浆房向湖中排放硫磺气体。大量被腐蚀了的金属与硫磺气体反应，使得湖水变成深蓝色。事实上，pH值达0.5的伊真火山口湖是世界上酸性最高的湖泊。

“Hydrogen chloride released from Ijen volcano mixed with the lake and turned it into an acidic monstrosity that it is today,” writes Quora user Vinay Sisodia. “What makes this place even more stunning, especially at night, is shots of sulphuric gases that combust into glints of bright blue upon contact with air.”

Quora用户维奈•西索迪亚这样解释道，“伊真火山还会释放氯化氢，氯化氢混入湖水，造就了今天奇特的酸性湖泊。而这个地方更具震撼力的是，尤其在夜间，几束硫磺气体在与空气接触的过程中会迸发出闪烁的蓝色光芒。”

Intrepid travellers can join three-hour hikes to the bank of the crater to experience the lake in person.

喜欢冒险的游客可以参加三小时游火山口湖岸的远足活动，更好地亲身体验火山湖的壮观。