Our expedition leader Andi visited Ijen crater during a period of elevated activity in May 2012, when lots of sulfur from the fumaroles was burning at night with blue and reddish flames, creating abstract photos. 
The other photos are by our friends Jorge and Jessy who visited the volcano about 2 months later and give an impression of the volcano, known for its turquoise acid crater lake and the extensive sulfur mining. (Photo: Andi Rosadi)