The rocky elements in the heart of a volcano are always red, while the natural color of lava is black. The red color is linked to the modification of the oxidation state of the iron the elements contain. Located near the activity center, the projections fall very hot and incompletely degassed on the soil. Their oxidation then continues in contact with the air for a certain time over their entire accumulation zone and well beyond the action zone of the volcano chimney's smokes.