Copahue sits on a basement of sedimentary and volcanic rocks ranging in age from Eocene to Pliocene. The modern volcano sits in a volcanically active area, with a caldera from the Pliocene, measuring 20 km by 15 km, lying to the east of Copahue. The modern volcano became active roughly 1.2 million years ago (Ma). The modern caldera formed 0.6 to 0.4 Ma, and produced large pyroclastic flows, extending up to 37 km from the volcano.
The modern structure is an elongated shield volcano, with a maximum thickness of 22 km and a minimum of 8 km. There have been at least six eruptions within the Holocene, with the most recent on December 22, 2012. The easternmost (and most active) crater contains a crater lake with a pH ranging between 0.18 and 0.30.Although the lake emptied during the 2000 eruption, it has returned to its previous levels.
On 27 May 2013, it was reported that a red alert had been issued and the evacuation of around 2,000 people was to begin.
The volcano erupted again in October 2013, and July 4, 2014