If you’ve been to the Indonesian island of Java recently, you’ve likely been treated to a stunning view: electric blue rivers streaming out from underneath the Kawah Ijen volcano. It looks like lava, but it’s actually molten sulfur.
“I’ve never seen this much sulfur flowing at a volcano,” U.S. Geological Survey research geologist Cynthia Werner said.
Although seeing this much sulfur is a bit rare, it is common to see blue flames around volcanoes. Sulfur has a pretty low melting point at 239 degrees Fahrenheit. Kawah Ijen has the largest blue flame area, though.
In fact, Kawah Ijen is actually a major source of economic activity for locals. The volcano’s crater contains the world’s largest body of water filled with hydrochloric acid, which produces huge stalagmites of sulfur. Locals carry the raw sulfur down the mountain for about $10 a day.