Licancabur formed in three units, all of which have lava flows; the last one also includes pyroclastic deposits. The bulk of the cone was formed by the second unit. The second unit's eruption was preceded by the injection of basic magma into the magma chamber. The oldest flows crop out on the western and northern sides of the volcano and are partially covered by more-recent flows from Licancabur and flows from Sairecabur. Flows from both appear to be pre-glacial. The older lavas have compositions similar to shoshonite and old Sairecabur lavas, and tend to be more basic than recent lavas. Weak explosive activity left pyroclastic deposits on the volcano. Licancabur formed primarily after the late glacial period, between 12,000 and 10,000 years ago. Flank lava flows are its youngest feature. The neighbouring Juriques dates to the Pleistocene.