WATCH: Stunning electric-blue Lava erupts from volcano at night in Indonesia

In a spookily beautiful occurrence, Kawah Ijen volcano in Indonesia erupted electric-blue lava, that oozed down the mountain slope at night, attracting scores of tourists and nature photographers.

Olivier Grunewald, a Paris-based photographer, who has been recording the stunning Kawah Ijen volcano over several years said that the blue glow is not lava but light produced when the sulfuric gases from volcanic cracks come in contact with the oxygen-rich atmosphere, resulting in a blue flame. As the liquid sulphur burns while flowing down the slopes, it gives an impression of lava flowing. The best time to catch the blue flames is at night or after sunset, he said.

Indonesia also holds the world's largest acidic crater lake which is rich in hydrochloric acid. The gases from the volcano often react with the lake water and cause a reduction in pH of 0.5. Once it cools down, the gases leave sulphur deposits as residue near the lake.

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Here's how the burning blue volcano looks at night

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Volcano spews ash

Last month, Indonesia's most volatile volcano spewed ash and hot gas in a massive column as high as 6 kilometres (3.7 miles) into the sky. Mount Merapi's clouds of ash, accompanied by a rumbling sound heard kilometers away, blanketed several villages on the main island of Java.

Indonesia's Volcanology and Geological Hazard Mitigation Centre did not raise Merapi's alert status, which already was at the third-highest level since it began erupting last August. Villagers living on Merapi's fertile slopes are advised to stay 3 kilometres (1.8 miles) from the crater's mouth and should be aware of the peril of lava, the agency said.

The 2,968-metre (9,737-foot) mountain is the most active of 500 Indonesian volcanoes. It has rumbled and generated dark hot clouds since last year. Its last major eruption in 2010 killed 353 people. Indonesia, an archipelago of 270 million people, is prone to earthquakes and volcanic activity because it sits along the Pacific "Ring of Fire," a horseshoe-shaped series of fault lines around the ocean.

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