Lascar is a stratovolcano in Chile within the Central Volcanic Zone of the Andes, a volcanic arc that spans Peru, Bolivia, Argentina and Chile. It is the most active volcano in the region, with records of eruptions going back to 1848. It is composed of two separate cones with several summit craters. The westernmost crater of the eastern cone is presently active. Volcanic activity is characterized by constant release of volcanic gas and occasional vulcanian eruptions.

Aguas Calientes Volcano or Cerro Aguas Calientes, also called Simba, is a cone-shaped stratovolcano located 5 kilometres (3 mi) east of the Lascar volcano and 10 kilometres (6.2 mi) north of Laguna Lejía, Chile. It is located within a 500 square kilometres (190 sq mi) area where the Cordón de Puntas Negras and the Cordón Chalviri volcanic chains intersect. The volcano is constructed from andesite and dacite containing hornblende and also anhydrite and its pyroclastics are all older than Lascar. It has a diameter of about 7 kilometres (4.3 mi). Some xenoliths of calc-alkaline material are found in Aguas Calientes lavas, and magma mixing has generated lavas containing andesite inclusions in dacites. One eruption of Aguas Calientes postdates the first centre of Lascar and was originally linked to the Lascar Piedras Grandes eruption, before sampling on the deposits of this eruption indicated a relationship with the Lascar volcano itself. Effusion of lava ceased after the cone was built. One summit lava flow may be of Holocene age, but no evidence of historical activity is found.