 The volcano contains in total two nested calderas, the larger of which is wide, and a field of lava domes, maars and pyroclastic cones that occupy a surface of .These subsidiary vents include the scoria cone Huililco, the Volcanes de Llancahue and the Volcanoes de Reyehueico.Fissure vents of Pleistocene-Holocene age occur on the southern side of the volcano.