You've heard of "red hot" and "white hot" to describe searing temperatures. But what about "blue hot"?

Despite the dangers, photographer Olivier Grunewald captured the scene, along with a group of men who toil on the volcano at night, battling noxious gases to mine sulfur from the crater and carry it out by hand.

Miners carry between 176 and 220 pounds of sulfur chunks per trip and sell the pieces for around 2.5 cents per pound. Yahoo reports they average two loads every 24 hours, thereby doubling their salaries amid sulfurous flames that can reach 16 feet high.

The volcano is the subject of a new documentary -- produced by Grunewald and Régis Etienne, the president of Geneva's Society of Volcanology -- released earlier this month. (See the trailer, in French, below) SUBSCRIBE AND FOLLOW Get the top stories emailed every day. Newsletters may offer personalized content or advertisements. Privacy Policy Newsletter Please enter a valid email address Thank you for signing up! You should receive an email to confirm your subscription shortly. There was a problem processing your signup; please try again later Twitter

Facebook

Instagram

Flipboard

PHOTOS of Kawah Ijen's blue lava: