Taapaca was originally considered to have been active for the last 1.5 million years during three volcanic phases. Later a fourth stage was identified, and some rocks were interpreted as pre-dating 1.5 million years ago. Eruptions at Taapaca have consisted of lava dome-forming eruptions and explosive activity with avalanches of blocks and ash, which form when lava domes collapse, as has been observed in historical time at the Soufriere Hills and Unzen volcanoes, although these events were much smaller than reconstructed episodes at Taapaca. Only one subplinian eruption has occurred on Taapaca, and tephra fallout deposits are not widespread. Eruptive activity has moved southward over the history of Taapaca, with activity centred at the top of the edifice.