Llullaillaco (Spanish pronunciation: [ʎuʎajˈʎako]) is a dormant stratovolcano on the border between Argentina (Salta Province) and Chile (Antofagasta Region).

About 150,000 years ago, the volcano's southeastern flank collapsed, generating a debris avalanche that reached as far as 25 km from the summit.

[6] There are numerous abandoned mines in the region,[18] and the active lithium production plant "Proyecto Mariana" at Salar de Llullaillaco.

[31] The height of the mountain and the clear air in the region make Llullaillaco visible from Cerro Paranal, 190 km away as measured through Google Maps.

[66] This landslide has been subdivided into four facies and features landforms like levees up to 50 m high,[67] longitudinal ridges and a run-up mark on Cerro Rosado.

[68] The surface of the slide is covered by lava bombs less than 1 m long, blocks exceeding 2 m width, cobbles, and gravel-like rocks.

The formation of magma results from the release of water and other volatile material from the subducting plate, which is then injected into the above-lying mantle wedge.

[82] The region is dominated by large volcanic cones (often more than 6000 m high) in the Altiplano and Western Cordillera,[79] and extensive salt flats in low-altitude areas.

[21] Cerro Rosado is 17 km east of Llullaillaco;[2] iit is a 5383 m high volcano which erupted dacitic lava flows on its northeastern and southern flanks during the Pliocene-Quaternary.

25 million years ago, the "Quechua event" triggered the uplift of the Puna-Altiplano, a highland covering a surface area of 500000 km2 and reaching an altitude of 3700 m. In the late Miocene-Pliocene a phase of strong ignimbrite volcanism occurred.

[106] Phenocrysts are mostly hornblende or pyroxene with lesser quantities of biotite and quartz; apatite, iron-titanium oxides, opaque minerals, sphene, sulfides and zircon are rare.

[106] Processes in the chamber such as magma mixing and plagioclase crystallization[111] yielded melts with homogeneous composition and low volatile concentrations that upon eruption formed viscous lava flows.

[119][26] Mean annual precipitation reaches 20–50 millimetres (0.79–1.97 in),[53] decreasing from west to east,[114] and is episodic to the point that it is difficult to give average values.

[32] The snow and icefields on Llullaillaco reach thicknesses of 7–10 metres (23–33 ft)[148] and supply water to the Salar de Punta Negra.

At this altitude, Adesmia spinosissima, Fabiana bryoides, Mulinum crassifolium, and Parastrephia quadrangularis are found in addition to the previously mentioned plants.

Above this altitude, plant cover decreases again, probably due to low temperatures,[54][160] and disappears above 5000 m elevation;[145] most of the volcano lies above this line.

[174] Species-poor fungal and bacterial communities have been found in the soils (more precisely: tephra[175]) of Llullaillaco,[176] with the fungus Naganishia friedmanii being the most common species.

[178] They have to survive environmental conditions[179] among the most extreme on the planet,[180] with aridity, strong UV radiation, daily freeze-thaw cycles and a lack of nutrients.

[193] Half-destroyed walls[189] form a building complex, which was built on terraces[194] and partly buried by loose debris from the mountain above.

[203] The paths on Llullaillaco are not simple footpaths but equipped with retaining walls, delimited edges[204] and above "Portezuelo del Inca" with staircases.

[36] In the case of Llullaillaco, they may have been sites of pilgrimage[194] used by the local Atacama people during Inca rule,[208] no evidence of pre-Inca activity has been found.

[188] Because of the findings, the summit area of the volcano in 2001 was classified as a Lugar Histórico Nacional by the government of Argentina,[215] and in 24 June 2014 the entire Llullaillaco complex was declared a World Heritage Site by UNESCO.

[216] A number of myths are associated with Llullaillaco,[30] and the mountain is still important to the inhabitants of Socaire[217] east of the Salar de Atacama,[218] from where it is visible.

[225][231] Other archaeological objects found along with the mummies included: Bags made out of leather, headdresses with feathers, pottery (cooking instruments like jars, plates, pots and vases), statues representing both people (male and female) and animals made out of gold, silver or Spondylus (oyster) shells, shoes and textiles,[11][187] wooden and woolen vessels.

The cones and associated lava flows are heavily eroded by[34] glaciation and hydrothermal alteration[89] and buried by more recent volcanic rocks, but still make up about 70% of the surface of the volcano especially in its western sector.

[34] At the 5561 m high Azufrera Esperanto mountain 5 km north of Llullaillaco little original volcanic substance is preserved and where erosion has exposed deeply altered white rock.

[82] Pyroclastic flow deposits with a composition similar to Llullaillaco II are found on the southern slope of the volcano and may have formed before the lava eruptions began.

[60] An explosive eruption of Llullaillaco II produced a 3 km long deposit of lava blocks and pyroclastic pumice,[240][35] with fallout reaching Cerro Rosado.

[42] It is possible that some lava flows interacted with glaciers, causing them to melt,[152] and volcanic rocks overran glacial[241] and periglacial landforms.

[2] Three eruptions were recorded during the 19th century,[244] which were however not directly observed[245] and are unconfirmed:[246] Activity was probably limited to the emission of steam and ash, given the presence of the archaeological sites.