Llullaillaco is a stratovolcano at the border of Argentina (Salta Province) and Chile. It lies in the Puna de Atacama, a region of very high volcanic peaks on a high plateau within the Atacama Desert, one of the driest places in the world. It is the second highest volcano in the world, and it is also the seventh highest mountain of the Andes. Llullaillaco follows the typical Puna de Atacama volcano pattern: it is surrounded by large debris fields, and is perpetually capped by small snow patches, though there are no true glaciers due to the extreme aridity.The snow line in this region is the highest in the world at around 6,500 metres (21,300 ft), which is around 1,000 metres (3,300 ft) higher than in the Himalayas and 2,000 metres (6,600 ft) higher than in the Andes of Colombia and Ecuador.
There are several climbing routes which do not require specialized climbing techniques, although the altitude imposes great difficulty and is by itself a very dangerous factor. Crampons and an ice axe are needed as most paths cross ice patches.However, the area on the Chilean side of the mountain is known to have some land mines that were installed during the Argentina-Chile conflict period of 1978–1982,thus rendering it extremely dangerous.
During 1983–85 American archaeologist Dr Johan Reinhard directed three surveys of archaeological sites on the summit and slopes of the mountain.In 1999 on Llullaillaco's summit, an Argentine-Peruvian expedition co-directed by Johan Reinhard and Argentine archaeologist Constanza Ceruti found the perfectly preserved bodies of three Inca children, sacrificed approximately 500 years earlier.This is the highest Inca burial so far discovered in Tawantinsuyu, and is the world's highest archaeological site.
Two major geological stages can be highlighted in the history of the volcano: Llullaillaco I, the ancestral primary volcano, dates back to the Pleistocene. Two very eroded cones with associated lava flows, up to 20 km in length, distributed mainly to the West, evidence these stages.