Volcanoes are terrifying, dramatic features of the natural world. But images of them are pretty familiar to anyone with a taste for photography, geology or Hollywood movies.
Until, that is, they burn blue.
These incredible pictures were taken by photographer Olivier Grunewald of Indonesia's Kawah Ijen Volcano, which naturally burns blue due to large amounts of pure sulfur inside the rocks.
The result at the summit is a molten mass of 239 degrees F rock, which is highly toxic, but which local miners brave daily in order to carry down huge amounts of sulphur by hand.
The volcano and its brave resident miners are the topic of a documentary by Grunewald and Régis Etienne, the president of Geneva's Society of Volcanology. The movie was released earlier this year but the trailer can be watched above.
