Aguas Calientes, Stratovolcano in Antofagasta Region, Chile

Aguas Calientes is a cone-shaped stratovolcano in Chile's Antofagasta Region, about 5 km east of Lascar volcano. It is built from andesite and dacite lavas containing hornblende and anhydrite, with a diameter of roughly 7 km. Its upper slopes reach about 45° due to viscous, short lava flows, while the lower flanks are covered by fine debris and Lascar ash.

The first recorded ascent was made on 27 October 1971 by Sergio Kunstmann, Pedro Rosende and José Carrasco of the Club Andino de Chile, a few days after the same team carried out an archaeological ascent of Acamarachi. Like other high summits of the Puna de Atacama, the peak may have been visited by the Incas. No historical eruption is known; the youngest summit lava flow may be Holocene.

The name Aguas Calientes refers to the small thermal springs on the shores of the Salar de Aguas Calientes II, a 134 km² salt flat southeast of the volcano inside Los Flamencos National Reserve. A second, smaller salt flat, Aguas Calientes I, lies east of the massif between the Pujsa and Tara salt flats and also has thermal outcrops. Like most high summits of the Puna de Atacama, the peak may have been visited by the Incas.

Access to the volcano requires specialized high-altitude equipment and time for acclimatization before attempting the ascent. Visitors must register at the nearest CONAF office before climbing to ensure safety and track access.

The crater lake at 5,870 m is one of the highest lakes in the world, with a surface of about 2,500 square metres. Its water is acidic, and winds from Lascar carry sulfuric acid and water vapour to it. Researchers found only a few bacterial taxa and many DNA sequences that match no known phylogenetic group, and the lake has been studied as a possible analogue to Mars.