Aucanquilcha is a massive stratovolcano located in the Antofagasta Region of northern Chile, just west of the border with Bolivia and within the Alto Loa National Reserve.

Part of the Central Volcanic Zone of the Andes, the stratovolcano has the form of a ridge with a maximum height of 6,176 metres (20,262 ft).

During the ice ages, both the principal Aucanquilcha complex and the other volcanoes of the cluster were subject to glaciation, resulting in the formation of moraines and cirques.

[5] The volcanic cluster of which Aucanquilcha is a part contains about 19–20 volcanoes and has generated about 340 cubic kilometres (82 cu mi) of andesite and dacite over eleven million years.

Covering a surface area of 700 square kilometres (270 sq mi), the cluster is surrounded on its northern, western and eastern sides by salt flats and alluvial deposits.

Its volcanoes are arranged in north-south and northwestern alignments, which may indicate a rupture of the crust above shallow magma reservoirs.

The flow was channeled between Miño Volcano and Cerro Cumbre Negra (an eroded lava massif) towards the dry Rio Loa valley, favouring the preservation of the slide deposit.

[8] Another landslide occurred during the Redondo stage on the eastern side of the main volcano into the Salar de Carcote.

[3] The rocks from the main Aucanquilcha volcano are uniformly dacitic and show little evidence of temporal variation in their composition.

[7] Eruption rates increased 6 million years ago, coinciding with magmas becoming more uniform in composition and the onset of strong hydrothermal alteration.

It is possible that solidification of magmas below the volcano insulated the feeding channels from heat loss and caused the temperatures in the system to increase.

Activity waned again 2 million years ago, with magma and included crystals being drawn from depths of 3 to 23 kilometres (1.9 to 14.3 mi) and forming the Aucanquilcha volcano proper.

It is constructed from two northern composite cones, Alconcha and Volcan Tuco (also known as Cerro Garage, dated 10.96–10.51 mya), and five lava domes on the northeastern side of the cluster.

Alconcha has a large breach on the southern side of its crater that is likely the product of a flank collapse but the avalanche deposit may be buried beneath younger material.

The Ujina ignimbrite was erupted 9.4 mya from an unknown vent and has a volume of 2 cubic kilometres (0.48 cu mi) of dacite.

[7] The Gordo group, which erupted 6–4 mya following a probable 2-million-year hiatus, is located in the southern and western parts of the cluster.

Cerro Gordo itself (5.49 mya) has a crater that is breached westwards, exposing about twelve radial dykes but with no trace of a debris avalanche.

It forms a 4 kilometres (2.5 mi) wide stratocone with a lava-filled crater, and layers of scoria and agglutinated lavas dip from it.

The Las Bolitas lava field (5.23–5.13 mya) is associated with the Gordo group but the vent locations are unknown.

Cerro Polan's (3.5–3 mya) eastern side is deeply dissected, and the exposed materials are heavily altered in the deeper sections.

Hydrothermal alteration has affected some lavas and pyroclastics from Tres Monos, and the western side has lateral and terminal moraines.

[7] After the four main phases, some scoria cones of basaltic composition, including Poruñita and Luna de Tierra, formed between Aucanquilcha and Ollagüe.

The Azufrera stage lavas are blocky dacites with large clasts and flow fronts up to 20 metres (66 ft) high.

Four lava flows derived from the main vent, all less than one kilometre long and 40–60 metres (130–200 ft) thicker than previous stages.

This stage generated Aucanquilcha's only pyroclastic flow during a lava dome collapse as occurred on Merapi in Indonesia.

[19] The volcanic cluster was modestly glaciated during the Quaternary, as evidenced by glacial striations and moraines at elevations above 4,500 metres (14,800 ft),[7] and shows evidence of glaciers both on the main volcano and its subsidiaries.

At least three moraine stages have been mapped on that edifice, and on its southern side is found a modest cirque with glacially polished lavas on the floor.

Another small cirque with a moraine has been found in the northeastern side of the Cerro Cumbre Negra summit next to an Azufrera stage lava flow.

[28] There is still a relic network of roads leading up to 5,900 metres (19,400 ft)[5] as well as ruins of the Amincha and El Ángulo stations.

[31] A small group of men, caretakers of the mine, has lived at an altitude of 5,900 metres (19,500 ft) in a galvanized iron hut.