The oldest rocks at Irruputuncu are lavas that have been dated by potassium-argon dating to 10.8 ± 0.6 mya. The oldest component clearly belonging to the volcano is the El Pozo ignimbrite that was erupted 258.2 ± 48.8 ka, forming a multi-layered ignimbrite that was probably generated by the injection of new, hot magma into older, cooler magma. A lava dome on the upper flank on the western side of the volcano is 0.14 ± 0.04 mya old. The block and ash flow between 55.9 ka and 140 ka old, but has not been precisely dated. The Crater lavas are 55.9 ± 26.8 ka old. The block and ash flow on the southwestern flank was formed 1570 ± 900 years BP.