Quetrupillán is a high composite stratovolcano with a wide caldera and a shrinking glacier cover. 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. The small volume of the main Quetrupillán edifice and the widespread vents may reflect the interaction between the volcano and the Liquiñe-Ofqui fault, which generated fault-controlled secondary vents.