Burning elements is something we should all remember from our teenage years in chemistry class. When potassium is placed in the flame of a Bunsen burner, it burns and produces a lilac color. Burning calcium produces a yellowish-red flame, and copper burns green-blue. Sulfur? Yep, you’ve guessed it: when ignited, in this case by the searing heat of the lava itself, it burns an iridescent blue.

The burning process reveals much about the energy of the chemical reaction that is occurring. A red coloration indicates a low quantity of energy is being released; green hues are representative of moderately energetic reactions. Blue flames are releasing the most energy, meaning that the blue flames of Kawah Ijen are incredibly energetic. The sulphurous pockets, released under high pressure, ignite at temperatures of 600°C (1,112°F), producing flames that reach up to 5 meters (16 feet) high, as the Nerdist reports.

If you do go to Indonesia to check out the technicolor displays of deep-red liquid sulfur, bright blue igniting sulfur, and the eerie walls of cooled, yellow sulfur, do keep something in mind. Sulfur gases are, apart from being horrifically pungent, incredibly damaging to the respiratory system. Aside from being an aesthetic wonder to marvel at, this volcano can kill you without the lava even touching you. Best take a gas mask with your DSLR camera, then!