 The oldest activity is an ignimbrite erupted 0.65 ± 0.18 mya, called the Tuzgle ignimbrite. On the rim of the caldera left by this eruption is a lava dome complex named the Old Complex Unit. 0.3 ± 0.1 mya ago effusive activity commenced with the Pre-platform and Platform units that were then followed by a tectonic event that dissected these units. Afterwards, the Post-platform and Young Flow Units were erupted. The youngest unit is latitic and was dated 0.1 ± (0.1-0.3) mya ago. This unit may be Holocene or Pleistocene – Holocene in age. It is possible that the continuing activity of the Chorrillos fault zone is compressing the magma chamber and feeder dyke of Tuzgle, thus impeding eruptive activity. The well-preserved summit crater and youthful-looking lava flows have been assigned Holocene ages.
