Ambitle is the larger of two adjacent islands forming the Feni Islands, which are located near the SE end of an island chain north and east of New Ireland. This dominantly Pliocene-to-Pleistocene stratovolcano is characterized by a variety of alkalic rocks types. A 3-km-wide central caldera was constructed over Tertiary marine limestone deposits and is occupied by late-Pleistocene trachytic lava domes. A maar on the eastern side of the domes formed about 2300 years ago. Several thermal areas, consisting of hot and boiling springs, mud pools, and low-temperature fumaroles, are found on the western side of the caldera floor and near the western edge of the central lava dome. Shallow-water hydrothermal venting also occurs in a coral reef environment just off the western coast of the island. Babase Island, immediately to the NE of Ambitle, is composed of a Pleistocene stratovolcano and lava dome connected by a narrow isthmus.