Lascar is located in the main volcanic arc, on the western margin of the Altiplano. The andesitic-dacitic Aguas Calientes is located east of Lascar; it may have formed a lava flow close to the summit during the Holocene. Aguas Calientes is older than Lascar, and it might share a magma chamber. Miocene-Quaternary volcanic centres in the neighbourhood include Cerro Negro in the north, Acamarachi northeast, Tumisa southwest, and the Cordon de Puntas Negras in the south, which Lascar is sometimes considered to be part of. Tumisa, to the south of Lascar, was active between 2.5 and 0.4 million years ago, is composed of dacite and surrounded by pyroclastic flow deposits. East of Lascar lies the La Pacana caldera.