Quaternary volcanism gave rise to the cones on the slopes of Emi Koussi, and the three maars are the most recent vents in the combined caldera, while long lava flows have been interpreted to be the youngest volcanism at Emi Koussi. The most recent volcanic vents show little erosion. Early in the Pleistocene, erosion took place on the flanks of Emi Koussi, and carbonates were deposited in Era Kohor until recent times.