Two nested calderas cap the volcano, the outer one being about 12 by 15 km in size. Within it on the southeast side is a smaller caldera, about 2–3 km wide and 350 m deep. Numerous lava domes, cinder cones, maars, and lava flows are found both within the calderas and along the outer flanks of the shield.
Emi Koussi has been used as a close analog to the famous Martian volcano Elysium Mons. One of the most important morphological differences between volcanoes on Mars and Earth is the widespread furrowing of the surface due to flowing water on terrestrial volcanoes. The furrows are shallow valleys. Larger channels have a different origin. Major channels can be seen on volcanoes on both planets and indicate low points in caldera rims where lava spilled out of pre-collapse craters.