This is a large (45 km east-west) twin volcano the older and higher Ayelu centre lying west of Aabida. Ayelu is built of thick rhyolitic flows with the eastern flank covered by ignimbrites that were emitted from Aabida. Aabida is a strato volcano with a 5x4 km summit caldera within which is a trachytic dome. Ignimbrite, emanation of which led to formation of the caldera, covers a wide area and extends for up to 40 km from the summit. The ignimbrite is of a greenish colour, pantelleritic in composition and has surface 'blisters' similar to those described from Fantale (No. 36). Rock analyses and petrographic descriptions of Ayelu rocks will be found in Hieke (1950 and 1953).