The Kawah Ijen in Java, Indonesia is an incredible composite volcano that burns a beautiful bright blue. While it is a wonder to witness, it is a toxic mix of sulfuric gases and not lava that creates the vivid color. Great Big Story explained how this brilliant combustion occurs and what happens when the sulfur cools down.
Once the gas is cool, a bright yellow sulphur forms, which is mined and sold. Miners use steel bars to break off portions of the sulfur and carry up to 200 pounds back down the volcano. The emitted gas is toxic if inhaled, making this strenuous work incredibly dangerous.